Citation
Thermodynamic investigations upon carbenium ions derived from pyridyldiphenylmethanols--free and complexed

Material Information

Title:
Thermodynamic investigations upon carbenium ions derived from pyridyldiphenylmethanols--free and complexed
Creator:
Horvath, James Charles, 1942-
Publication Date:
Copyright Date:
1978
Language:
English
Physical Description:
x, 145 leaves : ill. ; 28 cm.

Subjects

Subjects / Keywords:
Absorption spectra ( jstor )
Alcohols ( jstor )
Electronics ( jstor )
Ethers ( jstor )
Ions ( jstor )
Phenyls ( jstor )
Pyridines ( jstor )
Spectral bands ( jstor )
Spectral index ( jstor )
Titration ( jstor )
Carbonium ions ( lcsh )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
Pyridyldiphenylmethanol ( lcsh )
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis--University of Florida.
Bibliography:
Bibliography: leaves 140-144.
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by James Charles Horvath.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
Copyright [name of dissertation author]. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Resource Identifier:
026309388 ( AlephBibNum )
04049300 ( OCLC )
AAX3695 ( NOTIS )

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11:"t.:~;- 0.m lI 1' 1'T T C'. I .l 1.1- r F..H ., ;,_ TO r)1' LL
[\0 '--In LIPHO IA;L':.n --1.0 'E' (.0.!. G








L.',
Jemes~.. E.:a.le lin -


\ DISERIST ION 11-7 P T..1) 10 111[ (,;:.LD'J.:11
COLTR IL OF THE. 0171753.11 OF FLOH ED.1
T:1 ..11.EIAL 1 L1EILU.C.T OF TriE 1-LOUTIN-' .'.TS
THE Dr: RCE 0! -01 2 OF I 1LOSOi'. ?


L..11..'S!Ti Or -ICTLJ


1 ') 2.




































This is dedicated to rhe Spilric of: Paan;~.I--antus, fr1 hef (:5s

;MessedL.( \-I th:: a courn~vy and! che des.ire to; Scl;: the. Phillos'J'...0'ls




3.<. Ec 0 c i-.c he 'a ern fc nt1, e-re ,he ise















r'.C t:IO..1E DII : G 10TS


trb~~ o hswr.Th~iS authorI~L i. i::C.edirg:iI; j-...rtuna~.ti ar.6I




rar,' therefEore~ extend. his; hearT~folt appreTLc~iaion. anT thaul~.S t..

thL;Ioigtaa es nci: :y ooehsbe mtta





















1AULE~ OF CONT'ENTiS


....1.






. . .




. .. .1,5


....lS




. . 3




. . 35




....SS


. . .


. . 4


r'ill\l:i 'i .-SLES . . . .






















i~-r:-a;n jl:.3r: to thiis ERsear-ch













I. . . . .




il.ll~';~, klt1. . .. .









'T/U',LC OF~ CON)11IT.;;-S cont inued~C


Page~












.1.36

.140

i. ].5


1. Sp'ci~fii- Gravityt of A~queous H1C10,I Dar~tl;nined Is :
Function of Ujt ;; HClG .

2. Degree of Protonationn of ai Pyriclyl icothenarl (,pyT.O3il)
in .aqueous"~ PC10,

3.Exi orime~nts Conducted upon th~e CnaconidD: I00 S;,e~ii
Found Lat Exhtibt Rearra~ngement .in 70,- HC10 .



DI:OGRAPH'IICAL SKETCH .
















LIST OF TA'~l.LS:


1.Spe~cial Co!mm-ciall Obtained Rea~conts - and
Supplier 42

1.El~ectronic Spectral. nDta for the Variouls Carbenium
lon Species, in ;O0 1 CIC, aIt 25" . . . 77

III. Values of HR in Aqueous HCIO. at 25' . . 87

10 Specific Grav~ity of AIqueouls HC10.. So:lutions :Ir '5'' 1

'.Thermodyllnamijc Stability DTa~= la~r-olti..l! irn'n~ the~ "Dnco"
T'itratirr; of ilthe Va~io~us Py\r~iil.learba::e-ull~ (an; Speckf~S,
in :iCI0, H,O at 25" 5

14
VI F ninr Chremical Shifts (2) for, C'arbonS-n 101~ I'Lclonsors
in Accotone s;d 1~ N 10 and for1 Carbe;Jnjiu 101? in 70%~
H!C10 a t 250 ..... 11.0




















.1. :-.:,1;-- rid~ diphon leneth nals ( .*.H.OR . .



02 ( -p ri y h n lm te' ip-,.N. .~ . '








.? Ii .r % i;b.T.2 ipec cn of~:1: t; e ar n ium 1o Je iv ro-

HC ,., 0 2 9; T





ii. V.*cl.le sLpe?:~ctr of r.he. cochaniumr io:! dei-veld fromi

phonl-4- l~ccopeavmethnalin 0% lC10 2~.ij.



P. .iti bi . !.~r~wi:; u of r.!l carbeni umn ior-, decti'.t e fr-om


:I-;l1lra,ihi.;:'aeithanzl, in 70; HC104~. 06 7...
ma.



10 1.~ ib.lon; curve'( for! che tr ac:r~~ ion of 4 -pIr id.:l-;-:ne~r t hyl-
ph :7-'.-fo ro h ny cab nim ion . . 43

!.1 Dlut;ionr ecir.:e fr che titratio3n OF [Pd(iI)(4-pyL)-
(L:,)C19)? '-, where b-'s-,L =- !-p:,r iiyl ;- mathyllph;enyl-


12 iluto ccuc**e foC"Er che tieracion of.ITf PHll)(-'s-pyl.)C1,]




13. litle i 7 -.A c r e i m ion formati on) . . 116

S1. C2.vbe niumr ;on ii rela:0~i.'t to c:-:cer nal cJFC1,? im.. I:G' of same 119









lErS'F OF '-'iGUrElS -- c-.nt in~lte


15. i!uicnnct t 20 vs. carbsniuri ion d relat~ive- to external
CFCl13 13 8

16. G (n e. i a d -p ri .c rbn u n )v Io
rcooirJinat~d 2--py',idyl,?arbaninct ..ons) . . .121.

1;. AG'~(unt.ou':dinatedc 4-pyrid',1carbenium1 ions) .s. AOZ(bis-
coriple::edd 4-py~ridylcalrbon".uin ion~s) !II1


v ili
















--ci.llaC o Disetai on?;S~~CU~ Presented to tilL Gra~duate i:ouu.:llj
..4 (the- Un~ve:-si.r y of F'nllorid in. at7:iarl. Fulfillment: of rho- irequitorn;ents
Incr the D~-Egree of necror of Philly..phyl










J\flCS CRARL.ES HOP.':,RiAT

IMarch, 19?72



C'=dru: Ca;rl Scouface
'~ ~ ~ ~ C --0;Deorrren: histr,




The yne'.-e-se-; f aseris o 2-adLndI' I-pyraiyl-R-ho 3- a-









:.0 .- called:I~ "rrcei;o"-alcohol comple::-:e, or tooe ide~nricral 11_:lohls ,re




c:o:ri~responding: 2-pr;d:.-1. alcohol complc teS could iot. be p~repare'd p-r'--

;coi:~ ,~ .T r:' reult of 5Cturic difficulties. The-r e t ri C yt-L-yPC al .. snkli






1-4




; ~ ~ ~ ~ ~ ~ ~ I~s :-*!<101.a.:ueinsadfeeeeg .lcc-arameter 4 :-orrotatron

















..t-e;l.: Fir. inllternaily: consisrent ~lect~ronic .specital inter~r..r-

!...> onl.: ilave been obtai,:id :.'ichi~ indicate: that thle stab-ilizing in-

I'u-n.:n everltedL by. the mletal contter on a1 givel ero:ple.::r:;i carbenium

100:- is; r;:-lected by) tl.0 frequency~) changes- ofT the~ (:arbell~lni ion ab-

..-rlption han;ds detectble upon coord';~inatio of the~ ion. Sccondly,;

rep:rop~ri;,ce, linearl Intcrd~ependent Ere~e ene~rgy ccrre~laions ha-.re

8-11->.:8 rleia ;r thei dievelopmr nt of arZgumeni- e whtchl indicated that al1-

th01 cml~uin(f:or the~ CaISes+ conideredL~C herelil) sntabliZesc

.2 achniu io rea~i.'dLE'theCro-reponingprsoElnatedl Ion,

;~~rcir:.r.icr.. tion t o.r i fa~ct di:tabilize7 a py~ridlylearln;!rbeu Ion relative

to~ thei- *.mpl'ot.03Ld !ic led"fn !Ip:cics..















1N1PODUCETON


Th~e Cafic.~.i:.*: Jon




T h; i pr.;1~p icuousI na t re of ,hce term "carboniu ion tmsf

the?::C h:. Ci3 ~meI~atue lassifiCathe~ has bee2n aIpplied to~ a~ll

=..Ies, of~ multiv.alen~c carbOcaCions chrong.:Iout. the chiemiical lirer,:; ure.-



: ;,
(C1..Tnhe fore throjughoutt this work the terr; echedu~nllt joo shall be




vesnc clucal exet. pc~iFically, the~ c.3ionsj Considered he~rei; n

ar< thsevb'rbaredeP~e1 romp rily 'diiphl!..ny Lmethanols upon di5ss~o-

Mr:..;..au uf tlnei -o l~cohcl in Fuitable, stro~n: .ty cider ;ic :d a.








Proci lnilnary. Consljidle ratiocns






(-, ..!]. iy~karbitrol.*: has been reilorted by J. P. \.'iboUI- et al. (3). Theree




o: chas ::e py,(ir irinecarbinols to tr~iyiheny~~lcar:,inot (t r: ipheny i methanol)

ulnd therefo~'re inv~estigated their halochr-oulic properties in 1001? suliu-ic

.-ibd solution. They d~isco:ered~ h:e~.:ever that such! solutlions exhibited

?0 -color ::hacsoe:? te. TIhut;, there p,ridinocurbiuch we r~fe not ionized

-in strvnp acid in ;a inshion akin to thant of tripheny.lczrblinal. That is

there '.;ss little, if any., conversion of the pyridinanchinalinos to the

corr:Fpo~imtritlyl-typie carbouium ion.

iMonel thle d.lss this disclosure pro'.oked further speculation ;Is cil

wiZhe~Th or noti su1ch ierciar-.- aromatiC alcohols could be fonv.erted to

thle cor-r;;pond~inS corhen~ium ion. Indeed it scened ;_o be~ the case thrat

iithe princ=ipe) difference in the beh7\vior of these pyr~idinr alcohols, nr

recc..pe:ed
o; positi:ve charge development whiich w~ould sup~erv~ene upon their disso-

Lution:: in :;tronigl;; acidic nedia. TIhus., the concentr'ation of pocLiv~et

c;;-rC produced~ rh;-ouglh base site protronation (orf thle pyridina ring

attago~n! atom..) *;nid: bel sufficient to prev.ent~ carbenium i,7n formaciion

on .wgi re cthe conlcomicant de~velopment of lik~e cha3r E repuiSiOUS.. ?hTFer--

-- .:e~e~rle reasonablr:e tniat if these basic Sites cOuL:; be cher~iicallly

::.,n.::G 1.. c~rle,- 'o pr'eventr proco~nallon upon ricretm,:nt lwilbi strong acid,




."iotreov~r,, Er wans recognized chati >.chL iin'..-estigatlions upon mrono-

,,-,cid:lIdlriphe-:aykarbbi inls w:ere ver. ;: ru.* Ic\relevan to thlis coln:;iider,7t onl.






















trcoalr l be com--:rIted to a3' reason~i abl7 3".4.1 cl ltrbn. rv= .:. sinceil~ this !~














a:!~cr.;i!:*.ri~ycdi. Th:- *4cerIvin it're measurabb- nionrl ro ine concji~entrated:


.;ul~feriIc acic; -.1 t ion t~.i s, til- c.ppearedi ~ l rha cra.' a ~ ~cnior it a-s c hr.;i.e-




Flan these c pao to--r-icate~t m:-nobusic. lcoos rounldl!i beo Lenpoe for stabli~n ir


(rr.e. cig. : lm, ll'~n-: so o- lani. pciies ,ri.!i: Shey re ci n p--educed !r ;n.. it

ac, 1;id;? ~I-: ..' ; c;ll.vi 1:i.:.1- ;ore p t un o th p.;sr~~i.r ibilt of inh-rib.L H:3 pyrid -.r








clians--c.1~~ cm~the-r ']emanc~ly' by' luichIrld.30n (!i:i0-11) andl nier hrcle

rdl.irrcl Io C1Cow:aiently.)



GrounLdWork~ to thiiS Reseal~rc




?n 19r;G BhIl.attcharyyas and Stoufocr (7) began v~ock in rhiis a-riea of

re~search. IP. ac~cord with standardl synthetic methonds theyP prepared

va~rzco.;s usa~nopylridy:ldip~nlohelnylmehnl (Figu~re 1) a!s wecll as b~i'2-pyrlid: ])-

wh~c;liet;nyletal s (Figure 2). Preliminary invcstigations uipon the~ free

alcohols Treveanled, as expected, that the m~onopyridyll der-ivativ.es wJere

collverTed~ r.o che~ correpondi ng, triryl-type carbenium! lon ulpon treatment


2-pyrdyl)(3-pyridyl;) (

P. =-H, -CH ,' -0CH3, -fl(Cl3 2~

F'ig. 1. IHonopy~ridyld iphenylmethanols (plyLOH)


-pridy


(


11 1,
)!rr










Fi g. 2. D ( 2 -py'r i 1y ) ph onI:.- i ne tha nols (p Li)









;ver, l.*2ro notL ioniziJ hy thick: solvsen to7 an~y' ?-!preci niiable r-~,Ee. ThiiS

ap-lccd vlit; the~ 1-esul' s of .-li'aut et al. (3). Nuchl of :Ie ;initial

verl~b~~.caS clhrefore directed tow~rds s thle ucilization of the m~onopyridyll-

aiolcohls borth as cairben~ium ionr precursor s nd a7S hote3rt r canatictjr dojnor

spc-ies. inl co;;junrction ?:iLh chis, B~hactacharyya anrd .SC'-iferi s;ucces-

fully- prcpared ai numbe~hr of palladiuni(11) complex~es of the~se mo~nopyridy~l-

alcohols by; em~ploying them as neutral donor lignodsi;. The macarials

obtainedj ver= !.-el !.-c~haracceri7ed as the ne~utral dichlo robis alcohol)

coinpler:-.e of palladium(ii II). These comple:-~:e were of che general f'or-

mula Fd(I!p 11)(yLH2C:1 2, where- p'LOH represents the "'ionlizable" pyridinet

a~lcohol. Thcse compounds wezre diam~agnetic ;Ind square p~lannr as expctedl

for 4-cooardinite comiplexes of palladilum(11). (See, for instance, the

discussion concerniin g thie com~ple:es of palladlium(IT:) bl Htanley (5:17-19).)

Subsequlent: inl.estigationti 7s by tho.-:e rrorkecrs upon thie carbenium ions

de~ri.ed from these palladlium co~mple:-es revealed chac dilution of the

ionizing mediuml i.e., the 96E: H2 04 solucion) wiith '...ater affordedl the-

raisolation of the intact neutral compllex:. This experimental fijnd

indicated chat the py~ridine-merlc~l coordinace bondS wa~s reaslnably: stable

in ec~ongly acidic; media. In this ~asy a tangible basis fo7r e::camining

the stabli-ties of suich coordilnated carbenium ions v.:as established.

Thle results of Bhal~r.tacharyy'!a and StouCFar ser.vcd to demornjtrate

thes che monopyridyldiphen:.lmechanols vecrJ suicablee o-donor- lisands as

w:ell as- carbe~niulu ion pricursors. To Ccontinue~ iich1 this w:ork,

:i~char:dsonn (6) pr-epare- d a series of palladiuim(TII comp;le:-es of the~ bic-

(.7-py'ridlrl'phand~mechano~l Gls ich1 hard beetn synthesir.ed prevsioulsly by?

FR;atachacyyn.s:,; and Stouler. Thtse compr~le::esi wer;e of the Igei~nerl ormnula7








i*J.i;(y.,0HLT, ndl wcre presumably 4-ioordlianto- about the~ metal

CLontes. \..ith the~ alcoho01l unrtioning as5 a hriden!tate liFgand.Itha h

.anicIipated that 3s a conSequencle of bIndin:: the nitrogen donor sltos

LLrdu ;'1 ocOrdlination to thle me~tal that theseC COlnr.CUndsj could be ynn--

;',-r~cd to the" comple:-cdd carbcenium ion(s). It was~ discovereJ, hlow~eve,

rii-i'. 'y emprloying ,-ustomary c::perimentall methodin s this ionizattonr ws

notachevale.there was no ob'.tous ex:planation to, iarccunt for this

reul.Perhaps~ ic vacs the case that the dissolultion of these c~omplexes

10. strong,~ acid cas aIccompanied by' simrultaneouls riipture of thle metal-

nit:orow coo-dir~tco bonds. Since there exists a conlside~rable degree

of ?teric st-r.-i:1 in these 2-pyridy~l complexe~s as a consequence of

wazial.;1 cl-rodly~ beL~een the neanl center and the carbinaol carbonl,

thii coordinate bond rupture uponr acid treatment was not unlik~ely.

r~i.cha~rds!on carried on 1-:ith inverst~igations on thre stability' of car-

Leiumrl; ionis derivecd f roml the ;-F'-pridyl l iphonylmethanols.l He recorded

ther e~lectroni: c spctrumm of ther fr-ec alcohols and of their pa!ladiu~m~fl)

Icnmplexsc i~n near triflu~oroacetic acid (TFA). Th(:se solutions wcrLe

hiLghly color~edl hereby indicating carbeniuim ion formation with TPA as

solvent. The ;isible region of the spectrum of these colored solutions

r(elCated~ theL !presence of two intense, broad absorption bands which werl.

shown to be chlaracteristic of che carbonium ions. A~n examinatton of

t h-.- visblel1 spe~ctrum of t riphenyl:li.~echylr.nrbenium ion piroduces d by d is-

solving trli pher-y~llinethanl3 in trifluororacetic acid showed rhi: moreL

srong~u absorpI.ILionl bands. Indeed vwhen tno electronic speecrum of solu~-

tion:; cl ch~~~ose mterlials in nonioniz~in:: media (e.g.,, le1Lhl~unO Or gla-

ci.i1 :leeri~c aci.1) uns~r e:-:sminLed in thec visible reg~ionn these~- strocng

];l-or~rlitl l~aiin handsC we oulnd to~ b.: absrentl. Ic was3 also ob~serv.edl during








th::ae~ F-c-:cal C::?'il.ei'.tton 51hat the position! S o~f theLse atbsorpt;ion

i?:17ds for. a Gi.'ea calbeniu m io~n spe;CceS jhiitedl ulpon going~ fre:r theC

o nl:.:ple::edJ protonOarted carbe~nian 10r n to:C the corrS!? ?liPondin meaF~l--

.:..pe.:e cabeiu in.Thlis sugiescadd thaut therre *-.>sa d iiced rela-

:ions-hiin betweenir tie s;tability of the carb~en tum Lon and thle at te~nda:nt

!;lc-rsion in~ !electronic c environment as~sociated writh py~ridinel n~itrogen

pr7t,:,n~tion vs. pySridine nitrogen roordination.

Simnllar band. positica shifts :iere also detectable as the i13ry-

aubsti~tjtc. t (R~) o-n th:e phenyl: rings in ChIE alcohols was vlaied: oichin

thec series I; = -H, to R = -CH3, to I: = -00135. In Lhi; in:tance the

l1:1.:i shifts were acttributed to~ resonance elctroni: interactions between

the; i.-;I'sublt~ituen and~ the carbeniumn~ io-n center. Ir. was also fouind LIITt

':,; stability of: the ion v;as considerably: increased whien I: = -0CH3'

Th~is i.EflectEd a j.ubstantial capa3city of para-0CH,? to participatee in

fEnvocable con~jugationall inte-raction with the nl-system of~ the trityl:-



Rlichardsonr u~ltimatec~ly atteimpted to eta;cblish a i-elatcionsip betwJeen

c:othenlJIn io~n devetlopmente in these j-pyridyl di-phengahcchano1 s~s tems and;

nAvTsurable pro3ton (1H) n'uclear magnetic resonance (iimr) chiemical: shifts.

Tou do th1is the 11l nm:; spectra of~ TIFAi nclutions of these alcohols and

theirj; poliadium(,II) complexexi s wer-e recorded. Thntfigrrt e

phenyl protorn andi pyrid!'1 proon absorptions the TF~ eoluition spcl-.ra

::ere comparlnr d w~ich the solution spectra of1 che unioni-ted compoulnds.

.11.:U co faciictte the2 resolution and idiencification of: rhe va3rious

;Oracon signa~ls, thesec umne specctra uerC s:uojected t colpua CIP.L1 simu~latE~d

coal:-!.ses. Thl-e.e in;.escigatiions ho;ever, p~rovecd to b~e un~successfulu








_in Thdi~ i.60 PrvoUCO abrSOrpiOnS Oi t[60 ur81001300l CCnpo-ulnd5 COUld not he

;:orcl-ated:~ Inumb!iguoulyrUc~. uith the proton abson-'ption~s o; th~e co~rrspond-

ing c rb..miuJ~r. ionsz.



,'\s a lognical ~x~tension1 of the v~ork~ upon the pyridylmethPl~1ol os .deintz

(8) preparjrd a .series of structuralll related ailcolo~ls by FubscicatingS

a th~i3atol cing lo~r th~e pyridine~ ring. Thelse materials w:re 2-, and

S-thlissolyldiphlenylrmeth~n;els (Figure 3). Thez similarity of these

;lco.*ols to the: pyridyll alcohols is apparent. In accord uiichi ptevious

workr thie neutracl p111adlium(II) bis-complexes of these alcohols were~

..Y:-pared The+-- lll C1 nopoud re of the generlra;l formurl.e PH(!iT) (TrhOH)2 2'..

vii.hl X representing~ a coordinated halide lon, either chloride (prin-

cTivally) or bestle.:12 Uentz_ had considered thant thle replaemenit- of













2 I r / i~




R = -11, -Cli -0CH3; R' -H, -C11 ; i" = -H~, -CHj

a)2-'Thia;*oly.ldip~holnylmethanolo ; b) 5-Thiia zolyld i phonylme tha nol
(2-ThOH) (5-THlOl)

Fi. .Th inz;olyl d ipho~Iny'lme~t ha.neis








iLy:'icdin-c: vtt~l ch1.120l woldUlr add~ a degro~u O un~;querncc. to th,_ antic-



t-.: iX-t~idinr anrd th~inole hcteratino.3 arer isoelectronic and con~taln

es~;**t;; ll~y ;dentical niitrogen mrOJs t~he::. should e::hibicr like donoi

riharacterii s i'cs. Hrow~evet, because thianzole also conculins a Cthiopho~nl l

type~r selfur~ a-om1, the th~iazole-subsettuteJ alcoh:ols Should bei pr~cursors

to carbenium ionrs wit~h sromew~ha differeltt stability, thlani chose got

.mD th anlog:-:pyrdin alohos.Turnbo and c~~oiokers- (9)j had

indeedl de~nonistrrate that the Chien:.1 maluiety 'could enhan~e the stability

of n.chl ca~rbentual ions relatives to the corresponding phe~r.:,l-sub.;t; ~itued

I rbeni-um I(on. They' did this b!- duermining ther equ!ilibhrium constants

([) fo~r thr. reaction



R: +f 2 1121 R:-OH + li 0{



in! reage~t seil'uri_ acid for a series of~ struLccurally, eqIuivalenlt

thicrnvl :-.nd phe~nyl cirbinols. The Keq values w~ere e::p~erimentally

:Meas~3ured by' mployping'il the spectrophotometric method of Deno aind co-

::ok~rs(1).An ordrering o~ the equilibrium data whlich wrere obtained

Ic:rieiele that a1 SIt-en thien,l-su~bstciilcut carbeniuim ion. is miore stable

:Iran thle re~lated phenyl: c~arboniurr ion. Thus, these data alsoi estab-

.11shed thiat the ,ulfulr atomi in the thian:,l nucleus wars not: protonated~

5-, thei sullfurie acid as this development of additio~nal positive chlarge

wucldli h.avec indulced a not dal.tabiliz~ati o~n of~ these thionv1,. carbenium

o:,.Theu, it \:s reazsonable~ to e:-.p~e that thle thiiazollyld iphenyl-

m!ethanalls couldlc be sources otf triar':1 carkcniumn ions more sta'ole- than

L ,:.e wh~~ic unu~ giot f romn the p:,r igid:iphe~nylmelthanals. F urthermll;ore,








~ich irlriza~tionl of~ :he~ ;)hzclly1 oicohols c..IJtld be nverst ign';;tedb thle

!:.:!e teil~chnique L::i.;l for .Lstudying thei thiicall ionL; sriincl thc p:,cidine

.a~~rlevat, had~ beii ; sol...* to be ioni.-mblh e in conrcentrted .riufortc acid.

II; Tac: the~ -st.;-bii Lty of ther thinzolll icas couldl be quan~rtitutrively:

;-;-:lue.l~, provided~l thle acid sol\'nt; iOnliZed ther parent alcohols tj an

extent~ IrF one hun..rod percent (100%;). In other urdsts, Ef the degree of

c.c-r.vot-mionr oF zcicool to carboniium ions r.-as mearsurable ini terms of th~e

capac~ity of the" riid so:lvout to p~rodu~e ioniizatio n s a functioni of

e:cifi concentration,~ thrrn any, equiilibriumn pertinecnt to alclioh-i ol-io inter-

(.';!ver::ton[ wIould pTeSUmably be moniterable. Undoubted~l y it: had3 been

Irlth criteria sul:h as these in miind, thiat Deno anll rcework~..as (10) w!ere

ab~le ;o define rin acidity, function regardingg the ion~ization oft 3rcyl!-

Inatthanol. e in con~centrated sulfuric acid -- water. The results of Tu.rnbo7

r-nr! cQ.ol-orkers (51) proveJ the suitabDilityI of appl:ing De~no's "ac2iditl,

ililaction"I technique~ towardSS follou~ing alcohol cairbcnium ion equilibria

in~ =he rhanyll! systems. Therefore it seemed reasonable to emrploy: this

mejth~od for quanrttitativ studies uipon thilazol:.lralcohol carbenium ion

equl~iijbria, pcrovidedd the alcohiols could be completely. ionirzed at a k~ne::n

solvent conlcentration..

I!cntz made a very, important contribution whenn he demonstrated that:

manyu of thle thiiazcly1 alcohols wleree converted comp-letely to carbeniiuml

tnin reag~cen pcrchloric acidl (701 HCI(,/). T~h-is vas accomplishied by

I';amriining the v.isible absorption spectrumn of these alcoholl s as pferchloric

Jlid solucians~- ar varriouls ncid coicentrations. Th'iis sim~pler investiga:-

tion: Icov aledl thart for relati~el ly hig~h rocd concentatinsin the carbcntuim

100 dri ved fIIi~C rom mny~: of these alcohols eXllhibted a BeR'L1s law\ dePlen-

nclrle; buit, a:rc thse aIcid solutions weTCSre sytC.uatiically diluted by, the










de :-nr~mnc rr;: r1o !l'Tner mai;ntained. F'romr those obsrr vac;tious it urn;

iion-.-Leded: thatl inl thle high~ acid conce-ntrationn reg-ionl~s carbenium ion

faciall;o? was iEffeCtua~lls 1002, aind thie result of addjing;- small quantities

of':~; c~ sta ws to dilute the conc-encration of thle absorbiny speici (i.e.,

he ertmim io). owvceIr, as nore v~ater was~ added. the equilibrium

dr-scr~i -ed byr equation (1), (ubhich represents t~he re:onv!.ersion of thiazoly1l

carberilim ion coj thijazoly1 alcoholl, began to be sh~ifted signifi~cantly

to th~e rightI as urittenl. A plac of carbeniu~m ion absorb~ance is. eight

ipeicce:t (ue 2:) HC104 served to reflect thos-e observartions. This plot

ove,r aI region of high acid conce~ntrations ~ielded a straight linec for

.x enmp::ltetely ionized thiazolyl ailcohol. This vas thc Hieer-'s lawi portion

of th~e plac. Piut, ac an acid concen~r3CiOn ;,artisular cO the 3lCOhol.

LIade Lr inveSt~igat'io~n, a mark~ed chirnge in slope vas observeld. That is,

th p'lot began! to dev~iate considerably From an extrapolated Beer's law

ln.It Iwas at this a~cidity, region where th~e concentration of thle

aboarbing species (th e carbeniuml ion) va3s being diminished not onlyr byi

being!:, dlalted, bult also~c as a cojnseque:nce of being~ reronvlerte~d toI lthe

vnonabsorbing neultral alcohol precursor. Thus, absorban~ce tall off i-.as

Iagnfiedjic cons~ideirably' as che: ionizring sol.'ent wJas made progressively



Thus:, by applying .*Ippropriate neidity function data (nade ava;il--

ab~le b;y Dene anld couJOckers (1.1) for aqL~-ueou perchloric aciid) k'ence ..'as

nM~i:: to m~easui~rc speatop~hootometrically eq-uilibr~ium constaints for' the

gene~ration ofE ;carhnium ions resulrincg f~omm thie dlissolution of free alnd

complexed:c c thli3;olytd1ipheCny~i~lteh~nos in re~AJgent pech~loric aci'.. Thlis

Iuseilzatoion thereFare allowed- a qua~nicticatie order-ing: of the stabiltitts









of iclrhe~niumi ionls deriv.able from these hecceracyclii basic co-:pounJs.

The~. .Tn~r,-d inl stabiliry wh~ich~ wer~e eStalblisheCd by' thlis~ ctudy., ant the

ptine~iilnt ge~neralZ17tionn Ihic~h these trends se~rvedl to \?alrrat, are

;Iunt~wd up1 accordingly:y

(ii) Cari-er,13mn ions derive~d from 5-thinoly~l alcohols are more

rnrble tha:n those got from1 tie corre~spondiin 2-thiiazoly1 rlcoh~olc. 'This
.1uctran~s th!e inherent destabilizing effect that cag euso a


on~ :-sai~rbenium ion deve~~~lopment. Since the sites of positive charge~ aret

threet bornds separated in the 5-th-iazoly1 ions, vs. twon bonds separately

in :the 2-thiazoly1l ions, and models of these species indiicate a likely

"throllgh-space charg-e interacrcion for ths 2-thinizr,; y1 ionr.S. thii trend

i~n stali~lity is cr-tainly e:-:pected.

(ii)! For a particular alecho~l, R~-groupp substitution in tol par

rrsition onl the pheny~l rings, for the series R: -11, -C11 -OCH results

'.n ..n increase in caribtniumn ion stability. Th~is rcflects c~onjugational

!.acailzation of positive charge devrelopment kner..' for Chis particular

series of "R" gl.oUp!s as PT'rn sulbStituelnts in trir.y1-cy~pe carbieniumr

ions. (See, for instance, the results reported in the papers by Taft

andii Mc~eever (12), MIcIinley et al. (13), andl Dcon and cow~ork~ers (10).)

(iii) For a parcicular alcohol R'-, or R"-group substitution onl

the chiazole ring (see Figure 3). and for R' = -H, -CH3~, and for R" =

-!', --Cii3, results in an increased in carbrenium 10n stab~ility' as "R"31 js

Inceaedinmas.Tiis c:-:hibits tiho greater' ab~iity: of -CH3 compa:red

\.Lh -'l to induhcciv~el relenase electron dens~tt.

(i)Cache:.ium~ ions ;ierivcd from thle palladliiu Lomnplexes, Pdt(ll)-

(TI01)2 re Isee stable than those? got fromn the correspondling free

o'echc~s. 151, at least, illustrrates thle effect of bindiing the basic








oit.-s i:: the: 'i;.-ends through ioordinatei bo~ndl format1ion w~;it an essel--

rE:I;Lty Ilcutral. L;p-.izs. Inis obviously minjinizes pjoitive~ char;: e

de -;lofPmen: upon: treatment ulrth strolng ncid since l.igaind p~roconation



(v) T thC in~stances investigated, Car~boniumi ions deri.ed fr'om

t.P..* comp~lexes Ed(11)(Th0Hl) 2Br2, are mor~e stable the-ir those g~ot from

the; corresplonding chloride ligandlr comple::es. 'ThIis suggests thast a

biackbonding mlchlanism is operati.e through which the metal conlter

donatee:~ n-electronl density. into emapt]. i-or-bitals olf appropriate syn-

IPete;, un the coo3rdinated carbenium ion species.i Thuis, bromide, which

1.4 i:excctd to be a better r;-donor thann chloride, should in turn coni-

tirt'btte a nilt ascailizing~ ;f~fect on thie ioni via J~onat~rio of r;-electronl

de;nLst,- ;iint suita~ble empc:. metal orbital~s.

Tw:o final jInVeStig~tioJns of 1r!Consequence were careled out.Th

equl Ibrium constant for the con~velrsion of tripheny lmeithainol to tri--

phoen].karben.liumi ioin in perchloric acid wa~s measur-ed TJhe va~lue ob-

tained~ was5 found to be in good agreemenuc vith the var-lue which had bieen

riiported for thiis ionization by Deno and crocorkers (11). This served

in:Chfier t7 verify thle reliability. of the thecrmodyl:,namic dalta goc for the

:neaeration or th~iazoly1 car-benium ions. An~d lastly, th~e ioniza~tion oL:

4-pyidydi~-coy1)ethnalin perchloric acid was; examined. The 4-

pylridy:,ldi';, --toly:l~ carbenium ion ..;asc found to be! more stable t~an the

2.-chia-olyt icarb-nton iojns but less stable tha~n the 5-thii~anl.ly carbenium

ionls. This result wlas siSnif~ica~nt in that it allowed a comparison o

cnlse~ h:terirings: to b~e madc, as if thiy w:ere position isomers, withi

cer.pecrt t~o their rabtlity to stabili-e trityl-typ~e carbrenium ions. Mtore

i--orlantly, r.nis resulE demor~nstra~tedl the appropr~~i~ncone.s of thn








~..pe: roplhotor.:e-tr; c technique of Dceno andl couorkersc (10) fo r study~ing;

pyri,*liph-nylathl crbeniumm ions. Thelrrefr.. c7Crbontuin ions derived

'.No~a thE: pylridinet alcoho;ls prev.iously5 inlvest;igaced. by1 Dbac3taclh~nry]?L a.nd

:;1.o.;Fer (7), .-c:r by Richardlson (6j), could no)w be studiedl quantitacively.

and1 broa3denI colnsidierably- the scope of this w:or-4.



The rescclth replorted. in this dissertation deals principality with

lov'.etigations,_ upon free and complexe~d carbonina~ ions derived from

pyriytdihan')r~thanls. theser pyridiLne alcohols and thec complexes

thatei~of weai ptrepred such as to be espec~ially- suitable for thermidy:-

n.amic stab~ility studies.

T'he cleOholec considdered are spcificallyr 2-, andl !-p:r idLj:Ipher3P~I-

4-iillerophenyl.Lmr thanols (Figure cl). The 4-fluorop~honl~r ring ha~s been

incrpor;.ed .Into the molecular framew~ork of the pyridy~lmethanols to

provided a 1F nr~~ probe uniqu~ely sensitive to the development of

pos~itive cha~rge upon car-benium ion formation. Considerations f~or thie

zpelication of- 9' nmir techniques towanrds stability SLuldiES on these

ions~ were prompnted by the unsuccessful 1H nmr inrvest2tiaions whichh for

siml~ar purrposes, had31 been attumpted by Richardson (b). The single

filuorine nucleu; is parTticulrly31 suitable for use as a? riag~nostic nmr

tag~ in these .sy~tems-.. Thle principal. reasons are: the follow~ing. Fr

v~ich bult one suchi resonnting nucleus in the species murder inveslgtioaton

the~ speercumii obtained is not compile andr is thiereforei smana~ble to

.ar-lightforwc/ard interpretation. Secondly, fluorine in thle 4-positton

or. ? phenyll~ ring is k~nown to be highly sensitive to changes in elcos~con

de~lsity in the ;I-sySIclm oF thle r~ing. Seec, For instances, the :aPers by

T1:t It al1. (1.,15), D~ervac and 'iarcha~nd (16), aind Pows,, T-suno, .nrd Taft























11 .




P. = -H, -CH3, -0013


p~henyl:lme:thano1 (2-pyLOH) pl en:.lnylmehao! (j-!, T.cH)


Fig. 4. Pyridylphen 1-4-fluorophphnylmethar-ols



(17), ;;hilch r5por;. that changes in i;electron deni~~t:; in an am~;Iintii:
19
cyst~em u:ayi be precisely correlat~ed with J-fluc~roph~nyl 'F nme chemical.

shits.These results therefore indicate chat the fluccine nucleus

mcus parteipate in n-bonding interactions wiith the aromatce ring ro
19
r:h-ichl it is attached. Thus, 'F nimr chemical shift data obtinend for

a "A-PUG-flucrohanyl"_ fliiorine would reflct anyy changes in a-alectron

Jenrsity~ throuighout a conjugated systemn in which this phenyl rin;: was

i icor poratred A.:xd so, of primary significance is the celaetionship which-

e::is'-s btwacui the ma3gnitude of the f~loor~ine chremical shiftr for a

?srricular pyr idy.Idiphen;earbenium ion, and thle ther-llodyinrmic stabi~li~ty

ofl t~hat 5n. Tlhe VF nmr studies bl, Filler (13) and Sc~huser (LrO) ald

thetti <.owlorketrs uponi tris- (p-flucrophenylI)c:adenilim ion in different

ui:;zingE solvelnLs de~monstra~ted the suitabiility of thi; c:-.perimelntal1









a-;:thraio .y ineednl eemnn ~~ o: =thi: cation-car'oind.

>>.Ribria frm 19 chemical shif~t data.

This1; won.l also focuse.S upon thle use- of thle D)eno spectro~photom~etric

terat~ica techniques for quantitativel mneasurement of the stalbiities of

c:r.: ni.. a ions deirived from frees and: comp~lexedl pyridylphonyll~---Flooro-

-.!I?'L'~honlnethanal Th!e r.hermody.namic data so obltained 7Zre thcn comparedl

~:ji- ,correspond~ing 19 nmer chemical shift datal via correlat~ion anailysis

et!ods Tis da3ta r.TConcent; is car-ried out for rhe purpose of estab-

Ji.Th;in:. incor~dpeaknt~n relationships extisting, betwieln the stabi~lityi

iinformation1 got trorr. coch of these tCpe~s of physical measu~-remnt.

In1 ]:Lrroptol wit~h :.re'Jiousr work the n~eutal'l his(;llrcohol) palladlilm(I)~

co.Tplexs, FJ(iI)Z(pyLOH)2 C12, were prepa~red and studlied by~ the physical

r.i.ethod~s descr".bed above. Hio:.'ever, since these materials contain tuo

rlais of "ioniizable"" alcohol per mollo E c~omplex, th~e degrse of po~sitive~

chsrge der-clopmenr upon carbeniumm ion generation is questionable.. This

difficulty had been encountered by Ue~nts (S) in his invest~tigation upon

the~ th~ia.ioly1 comsplexed carbeniumn ions. In~ an! attempt to resolve this

problem comrplexcs of' thec t;'pe Pd(II)(pyLOH) (LN~)C12 were prepared. In

tritan nliw msterials, LN represents a neutral, nonionizable liga~nd which

con~idins coordina~ted upon carbenium ion genca.rtion., The~rm~odynamic

studlies on~ those ne*.< complex~es fieldd information which directly~ relatES~

th: aunture of a singly~ charged coordinated carbpnium lo: to the stabi-

Li..:.rEn influence of the meral Lenter. Thel~rmodnam)nic: tiua nre prresented

:lesin chirch are "t resrpct to the Folloulng eqci;lobrin::



I O H+p.[11 +t n









s'tLPp L +2lC .1L,.dpyLOH +.. H.,O0t








E ;ationi (1') pena~tuils to the 3queou~s titention of an. uncoordinated

pacdyiipougascylcarbenium ion. This equat~ion is Lr~itten to

E:phasize thatr the pT.r~idin- e ring remains protona~ted thr~OUghoutrl Che

reollersion of carbenium ion to alcohol.. This transform3Clon is

.asanciated! with a positi..e charge change of 2+ co 1+. Equation (:)

corespndsto the~ tierimetric conversion of a single' charged: co--



'Th.:. .. ro,:iss is arssociated witrh a charge change of 1+ to 0. Equat~ion

(4) Is ai comp~rosite statement of ::h-at actually;' may:; be at leaSt twJo

stC.'u~ise prrocesses; initially (perhaps) the reconversion of a sPecies

conl::::.ining~ twc- coordinated carb~enium ions to a spe~cies with but one

ex-.dinated~e iors, follouied by5 complete r~conversion to thle ne~utral

pallardius bis~-alcohol comiple::. Thiis process may thierefore be associaltedl

:;lc cuo full uniltS of positive charge change, viz., 2+ to 0. Con-

sjierations t~oc purposes of critically, evalu~atingf the thermody~namric

-.la:_.r obtainedl from investigations uIpon these equilib~ria are accounlted.

Thec apposite conclusiions which followJ have been? presented and are ca~re-

;IullyI d;iscusJe~d .















EXPERiC- :IEN]TAL


Synthesis of Ligands



The py'r i il dipheny~lmetha~nots which havre been employed as hoctero-

ricolmtic donnors (and as carbeniumi ion precursors) In this research,

werre prepared by~ -andard Grignardl synth~etic meth~ods. This Rfgenerl Ly

J~crelved, cha addiition of an ether solution of thle approriaitce '- or /r-

py.-d!yl. Iktone t~o an either solution of the, riequired; GriguardT acylm!ag-ne-

.,iL.*.*hli~de, follouied by acid hydroly~sis of the s.oh-like incomriediatie

to~ viold th!e deSired alcohol. Since thte necessary k~et:Ones wrcle also

nodre in this .Iaboratory, the sy~nthetic methods Eaor their preparationl

h:1-' been kneludled. A list of~ the special, commerrc-cially: obtained

coage:nts employed in these procedures, wJith names of~ su~ppliers, is

prov\.ided in Ta~ble i.

Thie samie apparatus and assem7bly wa~s used in the1- ?reparation of

ruch: of thef ligands (a~lcoh;ols) and k-etones. All glassware conne~ctions

we;re with standardr taper ground joint fittinigs unless othlerwiise specified..

Al~l glasswa~lre u~ns scrupulously rcenned and dried prio- to assemly.l

rLi Iground joints ere~r carefullly lubriented by thle appllication oT a

'.*ecyL, 5.2311 i]ua~ntity' of I.o Cor~ning silicone grease. RoLnLion~ 05 the

co,nicted joints utLthin o~ne anothe-r assured th~e decposition of a unilornrl

fa~noflurian.Thc assem~bled a~pparatu(s consisted of~ a 3-nLcked,,





10





in the' centc~!:r;: nec. he scirring shalt vias fitted w;ith a 'leflon sri~r



.-tirroer l~ub~ricant, "Stir-Lube," Arce Class; Co., V'inelandl, Ile. Ter--ey.

Stirring speed v,-:s regu~lated wjith ;I rheastat conlcrolled electric stirring

n~octor. The side necks or the flask \were fit.teel respectively w~ith a

2501 ml pressure equalizing a-ddition funnot and a1 one-lite~r rspacity.

Dealr cy'pe~ condenser charged w.ith dry: ice during preparacivle runs. Tihe

condenser wa.-s atcaiched to the flask with a ball joinL connection iibich

fac~ilitated reaccionl vessel manripulation erequired to maintain? con-

trol~lrd atmos~phcere conditions thr~oughoutl~ thF s::-tem. Timmediarely

follkring assembrly the .system was~ purged w.ith a steady strean- of dry

attragen gas. T'he nicrogien en-vironm~ent was maintained until the

hydlrolyt~il step was rea~ched. All1 syniches- s uere p~erformPed Ising: ar-

hyldrorus dliethyl e-ther a:s solvlent. Ilagcnesinm metal turninss used for

Gr-ignolrd reagent prepairation wereL co~nvenien ntly sctivatled (Iinless de-

scribed othFerwise)j by placirng the required quant'ity of turnings into

the dry reaction Elask and stirring them rigorously for a period of 24

- 36~ hours at ambient teLmperature. This procedure redluedi the mecal

to a finely dtivide~d gray-bl ack pouidei'r which usua-lly reacted readily w~ith

the appropriate aryl halidle co yield the desired Criynard (20).

Grignard formation was initia-ted by gentle carming of~ the reaction

nature. If this reaction became too vilgorous, cooling thec flask; vithi

a ~coll*. water bath slowed the reanction to an equable rae. The~ sub-

seqruent addi~tiorn of reage~nts to the C~rig~uard (in situ) waes done atC

rcacedcc temperature by cooling the recaction flock~ writh an inlsulatedl








1sta--odaiin3a m--Lae o c~lortww.and*Ir ice. he ti:agera-ture

rof !-he b.-th~ \In. rcegulatel by th;e add!Cicio of djry -ice as reeded.



5-Win,,,crphonyl~ L-2;pyr id v ik~e one. Flooo honl~ylmag;nesium~ bromide was5

Irl.pr~rcG; esscanlilly by the me~tholi outliined by~ Mc~~acy a~nd co:worke~s;

2).A solutionn of 63 mnl (95 g, 0.545 mol) 4-broonror., i~-obenzene in

"00 ral echeltr cas acdded dropwise to 13 g (0.53 mol) oE acciva:ted manen-

Tium. The ixturee waas sowlyr stirred, and the reacItion proceedced iilooth~-

1:. as evidenced by the gentle ebulli~tion of et-her and th~e formatiion of'

a L-.roln~i- sh ;ledge. Following the complete! addition of clhe ether~ -

rYl hal~i-de solution thie mixture wJas brought to ~ent~le rellu:-: by

ar;rinig ~the ;caction flask wiithi a "Glas-Col" heating~ mo'nele. Grignard'

lormatinio:S was prsumed to be complette follouing rcfiln:- for a per1iod of

10! 12 ?our:s.

The remain:;er of the procedure paralleled the method of de Jonge

at al. (22). Th-e. iluorobenzene Grignard solution (abo:e) :-.s r.coled

to -35'. Ai solutionn of 26 g (0.25 mol) 2-cyanopyritidin (pi~coli~no-

nlirrilc) in 200 mnl ether wa3s thien added dropurise to the. Grian.:rd:. T

inniedirrely resulted in the- Sepalrationl of a tan-colored~ solid~. The

react_ion mixtulre wasI stirred continuously during thle addit on of the

2-ryan~opyridine to percent luiiping of the can solid. A~ceci all of thie

-coyardnoydne hlad btee addedl theL coin, bath was remo*./red, and stirring

::-,I continued UDEcl1 he rC3C~inon mixturl-e warmedl to a7mbient tem~perature.

Th=l~ the .; rind c~onte~nts n~elCc theni cooled to -SCOo, an1d thle Iketmirnil E

,dd *.Lonl compound u~ns hyjdrols', ed b~y thle careful add-ition of 50! ml cee

wae.'Ihic; Uns followed by the addltition atL O" of 100) mt concentrated

11. I so!luiorn res~u~lting inl the formation o~f a yello:-: (upperCL) either 1-.1yOr








anid a rcJ-i-l~r Unmm lovr) eqcueous nezidlayr The~~ '[' t helir 1~c~r wais

drawn? off and discardid, and the 33qeouIs layer~ wa~s trea'ited~ arerfuilly

Ii.th~ concentlratedl H.!.! solution until a pHi of (1 7 res o~bti~nedl. Th~is

rcn:ulced! in the: separat-ion of copious quanlsticies of a yellowis7

pr!-cipitate.. Tntls ma:terial :-as washeded w~richl doionj-et d rJater and thren

shak~~en w~ith- suff~icient freJsh~ ether until all che so~lid was rediersolved.

Th'le other phase wasr evaporated to yie~ld !i0 g (835.) of the~ ketone, a

light tan solid which melted ;7c 79 810. Th'le kec~oue was1 purif~ied by

vaciuum sublimaticn to ;ield a whlite crystalline solid mec-lting aIt 83 -






4-et':phne-2pyid to e- (gco lyl-.r- pyr idylke Eitone). Ar hexane

sol~t~ioni of n-butyllithium (63 ml, 1.I6 11) was placed in thet reaction

flaskr and dilutted. cich 250 mll ethe-r. This solution wasl; cooled to

-40"', and~ an iceI-cold solution of 10 ml (1.7 g. 0.11 mol) 2-~romiopyJridine

inl 100 ml other was added dropJise wiith stirring. During the addition

of the broma~pyridine the reaction mixture became an orange 01u~rr

wJhichr changed gradually to a yellouJ-green slurry. Following t-he

complete addition of the bromopyridine, stirring was continued until

the reactioni mit~iure armed to -300. The reaction m~ixctuire wa then

re~cooled to -;50, and a3 solution of 13 g (0).11 mol) p-tolunitrile

(p,-nethy'l~bensonit rile) in~ 1007 ml echrer w~as added dropw~ise~ with stirring.

Thiis resultred in thea foLrmation of a ylellov 3lurry.- Follow~ing~ the

addition~ of: the alir.rile stirring: was continued until the reactionr

mtl:.tuire~ warmeid to ambient temperatures~. Thei reaction mixture was now!

rec-ooled to -400 and hydro~llyed by th~e dropulise additional of 200 ml1

2 -100.The either w:as distiJlled off, anrd thle rec~tion mi:-:tuire was








:;?-et~ to, 1000 anrd stirrLed for I hiour aIt thiis temperature! zo fa~clitatel

'.Mi ~ ~il niede(poiio.Th qeousl rcactionl n:ixcure cws coole~-d in

Lei ;:nd neultralized byj the careful adli~tio~n of 6; 1-( ::H3 wresting in

the~ sepa;ration of a tan solid. The~ aqucons~ ri:-iture ?Ias then shaken

I.ith; suff:icint. icesh ether to disso~l.e thle soli.d. Ther aq~ueous residcle

was~ dijscar~cd, endr the ether rwar evaporated to y~ield; 12 g; (61.1) of thet

cr-ede !etone. This material wa~s vacuum distilled (0.010 mn, hp 1270)

and collected as a light yellow~ oil which crystallizedr on cooling as

yelouih nedls. he needles were dissolved ill the minimum amount: of

a hot nixt~ure of n-pentane -- dichloromethane (3:1) =rod recrystallized

aIr. dry 'ie teaperature as wlhite needles smelting atL 42: 430



Phoyl---yidygtheone (4 L-beneaspyr~idine). This~ Ietone waBs pretpared1

~..0 cord ,:lth the method emnployed for chie synthesis of ;-fluoro;-

?htny l-2-pyridyl~ e~cone (p. 20O). Th~e Crig~nird vJac preparlid byl the

addition of 50 r01 (74 g, 0.47 mol) bromobenze~ne dissolveld ii 75 mnl

o.the~r to 101 g (0.12 mol) of activated magnesium which w!a co.ered with

50 ul oth~er. Fo.low~inS the addition of the~ brom~obenzene solucion

ihe rea-tion mi:ruce w~as refluxe:d with stirring for 2 hours.

A\ mi:-:r.ure: of 21 g (0.20 mol) :-cyanopyridine (isonicat inanitrile)

in 200 ni; cther vas reflu:!ed until th~e nitrile dissolvedl. This

solution wJas th~en added dropwise to the cooledl Crignardl (-'001). Thiis

rcI~e..lte Ln thei imnmedi~ate~ formation of a tan solid, -,nd the reaction

miaiture- rl;s stiered vigorously to prevent lumpint. Tlhe kethlnins

intermeldiatec was cooled to -55" and bylJrol~yzei by; the addlitton of 50 mt

icr-cold1~ saturatedl aqrucous :1Hl '1. his was follouod~i by cthe addition

oi 100? u1 c~onedl HCL at Go0, resulting in the~ formai-ion of muc~h rist.-








:;lorcd sollid. Tefrhradto fai LDvL6E 11 Is

.:lvd hi3 :Md.The echrlr player '.:3.-. sepalratel andi discarded.l

.'.B:0~s!ment of cher pH1 of the~ aqueousI Phaset bII thle endLul addi.tinn of

lcamecl 111.3 resul~ted in the separation of~ copious qluantit ee: of 2. yelloui

mecpiat. his; material eas5 dissolved in ,he m~iinimum amount of

E-a-h oter. vaporation of the ether yielded 34! g (935) of '.he herono.

a \Jll. definei: cr stalline yellow! solid, which mel+!id at 6Y - 70"



4 -l-lechylh tnyl -i- p:;r id v1~e t ~,on (p- t ol;:1-4-piy rid:,1lke t one) Thiis material

~'..<. F-preprecd in~ the samne manner as 4-f rluoroph~en*;1l-2-pyrridylkeito~ne (p,. 20).

Th->~ Cril.air-l !.0- preparedd by: the a~ditiion of 1.7 ml (.24o T, 01-> mtl)j

il-blrriomoteluene dissolv.ed in 100O ml other to 3.7 g (0.15~ mol) activatedd

uI.egoesiumn covered withi 50 ml ether. Following th-e comnplete addlition

lit th2 acvi haslide .solution th-e reaction mixture wass reflu.-.edl for-

Shouris andc then cooled to -100. This resulted ini the separation of

.- brown;; precipi=3te so the G~ri;nord vars not cooled further. Ai

filtered solution of 10 g (0.10 mol) A-cyanopyridine in 100 ml Pther

was adde-d drop*.oise with stirring resulting In the forma~tion of~ a large

am~ount OE tan .=ol~id. Harming of~ this mixture: to ambient temperature

dild ~ot. caust e ;th solid to d-issolve~. The ether pha~se wa~s denun otf

b:.' aspiration through a coarse frit filtering stick~ to remove u~nreacted

4-cynopridne.The reaction mi::ture was r-ecooled to 00 chile

tilrring, and h:,d:rol.:,sis w~as eff~ected by, che dropwise addition of

-r0 mir ice-colld sa~turatrd aqueous ..Bqd~r. This was followed~c by~ the

Edition); of 60 m~i 2 l (1 C!, andl the mi.:;tu~e wJas allowied to stand until

the un~retctd magne-lsium hadl dissol.iedl completely. floco acid ear.. zdded

rai need~ced to insure tha~t the pH of thei aqueous phas?' a: s less t~hzn 1.








'r'i'? -cr;ueous1 pheI~.e was1 now1 un~IChe Lt:icF- w~ith! Z00-ml portions of

it te.Ii "he
was~ r!.j:!-;cc to ilH- 7 hy thei careful addition of 6 N ITH3 Thi:: resulted

I rin. .ch sepalration of a considerable amount of w~hite precipitate. This

motorialn wasy shakenii uith sufficient other tol effct dissolution. E~vapo-

cntion ot thle echar yielJed 14 g (71c'.) of choe yellou~jic ketone <.*hich~

malcted at 86h 890




4-Nehoxghen1-4ovrdv~kton. (his material had been prepared

previously by' Brtr~hattahara and Stouf~er (7) in accord wich thec methond

of Iafoge (3.f'or the sakec of complaceness its preparatiion is gi~von

belowr. )

A solution of 51. ml (741 g, 0.;0 miol) e-bron.0annsole (1-bromo-4-

meth-lo:-;:ybe:nzone) dissolved in 160 ml~ etheir eeas added tlropw~ise over a

period of 1 hour at ambient temperature to 9.6 g (0.40I mol) of acLiva7ted

magesim. he renct~ion mixture wags stirreJl Vigorously throughout an~d

rcEfluxedc for 1 h~our following thle addition of che b~romnoanisol~e. The'

Ccigunard :Jas thecn cooled in an ice bach, and to this wa3s added dropuijse

P. cn.lution of 21 g (0.10 mol) $-cyanopyridine in 400 mrl othe~r. h

rraeacion mi:-:~cu w~as stirrid constantly throughout. FollowJing thei

rajJition of the~ 4-cyanopyridinee the- reaction mixture \:s re~fluxe~d fort

; hour and then cooled in an ice bachl to 00. Ily'drolysis reAs effCctd

by; thle ncarful addition of 50 ml ice-cold~t saturated aque;ous ITH,C1. The

unhier- andc aqu~oos la3yers4 were Chen supported, andl the aqrueous player

ve~:: turice r':-:Crcted~ wilth l100-ml jlorci.ons of Frtesh either. Thec mother

extra:.CtS were combllinedJ writh che or~iinall other Invcr. The~ otrlc fractlion

w~v exraced hrce -.*th 00- I or~tion1 s of 3 M H C1. 'theC aquLouIS








frti\:iions warr-? jiooiC'd and i:<3tracd rliricce uich 100)-mi nortiions of

Eac ohe .1 A CL cc er actions :-:ere nour disrcarcded. ndl clhe aqueorus

--~1.o cl' n \:.ls noted. for I hour to -ruire conp~lete. !-timnint: dcmclposti-

ti 11. '}he equous fraict-ion was1 cooletd and cnrefullyy neuitralirlie vith

ie-col 3 jI 20il re~sulcin\g in th~e separaition of a yellow; precipitace.

':hi<: IvlerialL wa~ filtered:, w~ashedl '.-th fresh Jolo.-nized water, and;

or dted.The crude ke~tone un~s then dissolved in 100 m~l hot chloro-

fo'.This resolution was treated while hot uijth anhy'drous :-1350 and

f-:.; ered~. Th'e volume of the chl.oroform filtrate wa.s tripled by, the

addtl~tion of freshi either and cooled for 1 hour. Ther re-precilpita~ted

soir; was filtered, un.she~d with ice-cold other, and air dried co

I.:jd iS ng (71.':) of the vellouiish k:eto~ne which melted at 123 12:10




-bri,'lheny-4-loorpheylmehan l. Mnesiumi tu~rnings (8.1 ::,

U1..' -i ?o) wer~e p!Jced into the dry~- reaction flask, and a :-mail crystal

of iod~in;? was added. Tihe flask: was care-fully heiated with a heating

:.l.tle? until hai iodine just vaporized whlereupon heating wass discon-

ti;ed s the iodine reco~ndensed the~ masg:nsiu~m rurni~ng vere' stirred

briefly to ensure the deposition of a reaLsonably~ hom~ogoneous lawyer

of Zodine onto th-e surface of th~e metal. A solution of 32 ml (51 g,

0.29 rmt~) 4r-bromofl :orobensone in 200 ml either wJas added- dropsise to

c'he acciv.atedl mag~nesium. Tihe reactionr mixture was5 stirred contin~uously~

a:-: it Was; WarmT~ed t~o reflu:-:. Ref~lu :-: s continued for 2 hour: following

the~ addizion of the 3ryl halide. andl the reaction mi::Lure wa~s thon

ruooled to -60'. A~ solution of 11 ; (0.060 moll) phleny-2-pyriid;1.l~eton

(2.-ben~oyrlpyrriidine dissolve~d in =O00 ml either wasnr added. drop:Jise to

thl? stirred3 Cr~ig~rard. T'he cooling bach wa.s removed periodically to








:rnloliir~il thc frer~~ingn out of materianr from the reaction mni-xture.

.'.~-4 the Entwi' ;oliition was s;:ded the reaction mixrture became recd-vioslet

ir. colo. 1-ath.?inG the addlician of thie ketonle solutions the coojln

I?.irl. was run-ajed, and the Lonte-nts of thle flock u:ere stirredl unrtil

a t:.:araureof -10" wias attained. During this time t.1xe reac;:jon

nM:rure becramre lark brownm in color. Tihe addition product rrns hy~droliz-ed

at -100 ,,y thle careful addition of 25 ml ice water resulting in the

forma~tionl of a lemron-yellowi ether la::er and a pink. aqueous layer.

T'h: sqeoucls Ilayer -ta~s discarded, and the ether layer Iias extracted

;i.:-ice with 200 -- n1 portions of 3 M4 HC1. The extracted ether lawyer

wass discardati,, ,and th~e aquCenus phase was adjusted to pH- 7 8 by; the

careful addition of 6 11 NH This resulted in the snparation of a

ye:'lolo-ol3~rang polid. The solid aqueous mixtur e was shake~n with

suiificien flein other to dissol.et all the solid. The aqu-ous portion

was! ithen; dlisCa-rded, and th~e ether solution w~as combtined uirth 3A\

is llecular silv.sc uIntil incipient crystallizaionio was observecd. The

s .e~Ve.Is weret removed, nnd the either evaporated completely to yield 13 g

(~77.1 of the crude yel~lou-orange carbinol. Thisr solid Was dissolved

-in 2.00 i.,1 h~ot methansl and treated wJith 6 g of wood ch~arcoal.. This

mixture was refl~u:ed 30 minutes and~ filtered. The hot, yellow mnet.hanal

colu;tion uns5 allowed; to stand until cry;stallization of a yellowJ -olid

occurred.. 'The carbinol exhibited a melting rannge of 79 - S2o

Anal: Caed fr CH ,00?: C, 77.40; H, 5.05; Ni, 5.02.

Foun3: C. 77.51; 11, 5.10; ii. 5.16.



1-Prid-4-othlahnd4-fuorphev~mthaol Th rgnr n










0.7 ml 4-rumlslu Lorc~her nan. T'he reaction mixlture uns the~n cooled

;:o --~i'i, rand! j solu tion of 10 & l<.0.051 mlol) 4'-mct~hy~llphonyl~-2-p:yr iidyl-

!,..or:-d~issrlolve in 250; mil echefr vas 3dded dropuiise to ;the slciered

I:r i -na rd. Thlis re-sulted in the format9eion1 of a bu tte~rsco tch-coloreC

0 pesin.Follo:inQ ther addition of th~e k~etone the cooking hath wlass

r;.-i'ved,~ andi~ the reaction obyture waJs stirred until a temperaturee of

JO'" <-s reac~edl. The reacrcion ai:-:cure wans recooled to -103 and hydco-

lyze;d by' thc diropw~ise addition of 200) ml ice-cold saturalted aqueous

il1 01. hils r:esulted initially~ in the formation of a wh~-ite slurry'

-whichl sl.ouly~ became a yellowish emu~lsion. The emiuls;ion wass broken

h-. iiltei~ring hrough glass wool followed by; squeezing thrCough course

fite ppe.'thie yellov~ ether laycr wias the? e::tra~cted t~hr~ice ut~ch

100; --.n1 portions of 6 11 HC,1. The ether phanse wajs discardildl and the

,-nil!ous o~rtiolns were.9 comibine~d and trea~tedc carefully wjith 6 11 rH3

anel pl 7wa ataind.This resulted inr the separ-ation of a sticI:yr

welois ol.The oil wasc e:-:tracted w~ith the m~inimnum~ volume of fresh

otherr, and tlhe aquJeous residue wass discarde~d. Evaporation of th-e

ether agajin resulted in separation of the oil. Characterization

oif the oil (12 g, 32E) re--raled it to be the desired carbinol. The

oil v3s va3c~uumi: istilled (0.010 am, bp range 160 17'00); bu: the

collected distillate ~reained as a li~lhe yellow oil after cooling.

7-.rl.:Caled forr C19Hl1.0F:F C, 77.75; H(, 5.56; N!, 4.77.

Found: t., 77.37; H, 5.56; :., 4.60.




2-Pyidvl4-rieth:-;vhen-4-fuorohanmethnel. .- solution of

J.4 n1 (9.1! g, 0.0?50 nol) E-br;'moanisole in 25 ml other rwas aidcdd








ri.-crp!ist e utith L;Zirring to 1.3 g: (0.05j mol) activanted m-~agnosium cove~rred

u';LDi :5 I21 L.ther.I Th: rcoaction mi::tu~re wa~s hcaredl to ncicle~ reflu:s,

Ind' :he formnatiln of Crignolrd was ev.idecnced by the de~vlo, ment of: a

gr:,~l-brown, translu~cency. Following rcelux fo~r a period of 2 houirs

ICrig-n.:rdl foClrnt.ionI appea~red to be complete. The reaction mi::ture

untI: now~ cooled to -50 wiith an ice salt bath, and to thrirs a solution

of 'J.0 8 (0.030 v~ol) 4-fluorophenyl-2-pyridylketone dissolved ini 120 ml

ethe;r was- addced dropwaise with continuous stirring. During~ th-is addition

o~f ketonef a ye~ll~ow solid settled oun. FollowJing the additionn of keEone

the coolj.in bath~ u~s removed, and scirrin was continued as the reaction

.!.E::rilre~ souly :onned to amrbient temperature. Thiis resulted in the

formation o: a lighlt ten-coloredl suspension writh traces o~f reddish1-

pulrple mace~rial dispersed throughout. The reaction mi:turet was sub-

5.-quetntly heated to reflux- for a period of 1 hour and then cool.ed!.

The~ bul;: of the cthereal solution was removed fromn the reaction flask

by aspirations! thirough a coarse fric fijltering stick. Temtra

w.hichr 1remainedl i~n th~e flask wa~s w~shed three times wJith 50 -- ml

piortions of fresh! E~ther. The ether washes were removed by' aspiration

andil combined with t~he original other laye~r. Upon scending a1 white

::..m.:1solid unltorihl separated from the either. The residual reaction

ali.:stu~re as niow hydrolyz~ed at 00" by the careful addition or' 50 n1

~saurated aquleous lll,8r, followedt by 150 mil 1 H IIC1. Th'i~s resulted

1In the sepanration of a re~llou oil. Thie aqucous phlse was~ adjusted to

pi! ? !y the ca~reful addition of 3 1 013. Thlis pr~oduced a mnilky; tlis-

rpcer::ion or Ibe 011. Thl aqu~couls ph3Se? was. thien shlajkn writhi fresh L-th~r

u!,til the dlisperston cleared, and the aqulcous layer was driawn off

and. discarded. Thei~ asPiratedi otheLr P3rLionsl- (at)uVe) WrGCE f;ICLterd








through a~ rledium fl-it to separate thle white e-emisolid matria_~rl. Thle

otherL filtratf w:as discarded,. and thle u!hite Imaterial me~ nysd?oLyzed

on1 thi frit by, thle additionr of a1 lev l do1~lenized uniter.Th p

LJrced m~ore of~ theC yellowi 01.1. Thle o~il waLs dissolved .in freshi other,

andlr th" oil -- Pther~ solutions wereC combined.. Eva;POracion! of the

ethcr I.ielded 6.2 g (67..:) of the~ oily carbinal. Repeaitedl attempts to

crystalltzec thiq ma~terial usce unsuccessfully. Anr accurate 3sss For th?

molecular icn of the cairbinol was determined maiss spectrally. Called

fo~r C F NlbO F. 309.116:. Found: 309.1170 (mean of Four determnina-

cicus;: deviation, 12 ppm).




4 9yr id ylp hen:. l-4 flu orop~h_~n~~~len lmethnol A? solution of 12 mnl (1S gi,

0.10 mol) 4-broniofluorobenzene in 50 ml ether was added dropwise to

2.4 g (0.10 i.01) eiher-covcred activa~ted magnesium. Stirring rwas conr-

tinuous during the additional of the aryl ha.ide, and1 Crignard formac-ion

ensued upon igentle wa~rmig9 of the recction flaskz as evidenced by) the

d-velopmelnt of a grey-brorwn dispersion and the ebullit-ion of ethe~r.

After chet aryl halide had been adlded thle reaction mixture ais sti;rred

alni ~refluxed for a period of hours. Subsequently:, the reactionl

mixture wass cooled to -50, and a fltered solution of 11 g (0.60O mol)

pho~nyl-4l-pr idylketone dissolv~ed~ in the minimum amount of othc-r (ca.

2003 mi) wais added dropuiise. This resulted in the innediate formation

of a ,,ink: oli;d. V'.gorous stirring was miaintairned to insure uniforms

mnL;ixin,. Stirring wans stopped followinG che addlition of kectone, alnd

thle mi::tlure stood at a-mbi"en temrperacture for a period o; 1.1 IOUr~S.

The b~ ulk of thle ethe~r phase was nowJ drawnm off by; aspiration through








.1 evenser~r 'rit filterilng stick rrnd discarrdrd. Ther resjidual so~lli was

wrashed~ tw~ice r:ITh frcsh 50 mil portions of other, and the waslhes arce

d'.s'rded Th slid was~i su~bsequentl re~cooled to -So .nd hy~droly.:cd

with~l stLirrius~ by: Lhi' dropulise addition of 100 ml rsaturatdcc ice-c~l~d

aqlul(lc Inell.Er. Thlis was3 followed by, thle addcition of I 1 H 1101 until? a

pHi at 5 - 6 vac attainied. The aqueous mrix~ture als nowj tralnfEcrred

ico n large separa~tory, funnel and shaken with 4I00 nL ether. Tihe aqueous

(lev~ler) layer w~as tan in color, and the ether- (up~per) Jayer was; yellow.

A rcall qluantiry: of semisolid yellow material resided at the interface

of: thle liquid layers. The aquieous layer wJas drawn off, and the11 semi-

sol~id war combined with the other la;.er and together~ shak~enl vich four

separately 150 -- al portions of 2 M lC1.. This resurced in the- dissolu-

tiorn of m~ost of' the solid and a translucent ether layer. Evaporation

of :.he_ either viulded a smiall. amo7unt of brouni nateriall wh-ichl was

dilscardecd. All1 o: the aqlueous porcions w~ere then pooled resulting

in th0 dlevelopment of an e~paque dispe~rsion. Treatment of thle aqueous

to o::r with 6 0I NH, produced initially~ a clear-ing of the opaquieneSs,

and1~ as thei pli wias raiseJ to 4 5 muichi white solid separat-ed. The

solid w~as isolatedl by filtration an~d the f~iltrace again treated with

d'6 I 181 to bring the pH to 7. Thiis ~rsulted in the capar-ation of

m~orc '.hlite solid whichc h was also filtered off:. All of thet aqIuous

filtrat-e wa~s discarded, and thie combined solid sam-plce w~Ee air driedl

to y.ield 15 ,, (92?,) of product which el:-:hibitedlr deComiPOSition to~ a

bronis oi at185- 100.To convert Iny hydrochlolride salt Lo free

c:.rbhinall thE ancire .amount of~ white soilidl was slurr-ied uitch 100 rml 1 I

'!l5. After' standing1- for- 1 hour theslic wasl~t ~n separatedd by auctionn

Filtra~tion, u~nshedr wtith 200 mil of dolocnized usetr and aiir driodl. Thle










102.-- 1940 \JTliwirhu appreciable disCo1loration.

/.-..l.a: Cile for C HNF:C 7.0;3 50; ,5.2

Found: 77.13; Hi. 5.09; 1:, 5.00.

.'.!1 accura~te miass fore the molecular ion of the carbinot was3 determined;

Ira:Mr. -cpctral~ly. Caled for L18 14:0F-F 279.10 58. Fournd-: '77.1052

(menc~l o: five'~ determi~atio~ns; deviation, +2 ppm).



I,4._.-;ii-Enidy- mthyl. phenl- i- f luo rophenylrm c hano 1.. The preparations of

this arbrino1 ;::s carried out by; the method used fojr the preparation

of $-;:,ridylpheF;nlnyl-l4-fluorophenktaa (abovJe). The qulantities of

rezctorials employedJ uere- 9.C g (0.12 miol) magnesium; 14 ml. (21 g.

C.12 noul) 4-bromoiluoro 'canzenec dissolved in 50 al ether; and a

lil;tered Solution of 7.4 g, (0.038 mol)i 4-meths 1pho;nyl-l-4-pyrid::lket ne



Follo-:ing iyr:,olysis the aqueous phiase was adjusted to pH 1 wilth

1.0 i;Ii.1 re ulti~ng in the separation of 5 10 ml of a bro'.- oil. This

nil waRs d~raw~n rrff; the wor::-upof the oil it. givcn below~. Taii

equlEous chase was; twJice shaken with 400 ml portions of fresh ethe~r.

::achl Shakingf result1ed in the separation of a small Sua7nt~ity of yelloiwish

semisolid material. T'his material and the ether estracts wrere dis-

c~~tded. The aqueous phiase w'as neurralized by, the careful addition of

(r -1h93.This resulted in the sepatration of a yellow~ish1 solid which

:r iso:lated b... st:ction filcracion. Chiaracterization of the solid

(4.-'s .) rewacledl that i; waJs the~ crudef car-binol. The browni oil (abo'.e)

rns sti~rred with 300O al 1 I HC11 resulting : inl tmec form:Ec~ion of a browin








cruely1 cml-o.nh mllsion wass extcraictet thrice with 100: ill.

p~ortionis of -ther. Thiis re~movedl rho t~rans~lucnc y from the aquelc::s la.'e~r

w~hichl was now? lightL yellowJ solution. A~ll thle organnic r;ashes wrere

discarded, and thec alquous layer wa3s neuerarlizel b h carefi~ul

addition of 6 Ni NH3. This resulred irn ene separation of a yecllourish

soiled which w;as fil.cored, washied with deionized water, and aiir dried

co yield 1.2 3 of solidly whichh melted at 169 1720. This material,

comblined with the previously isolated solid, afforded a yield of 504.

Anal.~: Caled for C19 16NUF:: C, 77.75; H1, 5.56; 1i, 4.77.

Found: C, 77.60; H, 5.5.5; 11, 4.82.

A~n accurate nam~ for thle molecular ion of hthe carbinal uas determined

miass sp~ectr3lly. Caled for C19H1610FP: 293.1215. Found: 793.1216

(mean of thiree decorninations; deviation, +0.3 ppm).



4 -Py;r i dyl-j-me thoxy;phen],1- 4- f uo roph enyl me ethanol The Cr ignard was

pre par~le e::a t ly a s ia s t hat f or 4-pyr i dylph eny1 -4I- fluoroph eny l-

methanol (p. 29) using 1.3 g (0.53 mol) magnesium; and 60 ml (9.0 g,

0.51 mol) 4-bromofluorobenzene dissolved in 30 ml ether. To this at

-5o cas added in 100 ml increments a1 solution of 5.5 g (0.25 mol)

!A-methoFv.yphenyl-4-pyr ilylketon~e dissolvedl in 600 mil echer. A\s th

k~etone solution contacted the reaction mixture~ a yellowl solid forrmed

andl sePar3ted. Fol0loingS the addition of kitone the stirred reaction

minuclre was5 re~lluxed for 930 m~inttes and was then set aside ,?d not

dlirturbed f~r a period of 12 hours. Tihe reactionl mi:-:ture was; nov: 3

yellov! cream:, dlispersion, and little of the othlerent1 3iquiid phase

could be draw;n off by suctioni through the glass rllter~ing stick

Then-fo'c~re, the rea;-ction m~ixture wa~s cooled to -5" and~ hydrol:.zed by







thle drop'w;. le :addxtion of 50 ml o:f !,acu~ratedl ice-cold eq~uerous :;H,Lir,

followed by the a~ddition of 10i, ml 1 ii HC1. This resulted in the dis-

pe"rsion of' a brow~n oily material in thle arqueous:- pharse. Thei ether layer

kwas ce:-.5tactd four' titles with 125 131 portions of 1 i( H1C1 and the-n di -

crlrde~d. The: aqu~eous p~ortio~ns wlere pooled ryielding~ a ye'llow-green~:;

I'pC;que mixture. Thiis rmi:-.ture was aIdjustFed to pH~ 7 by' the c~arefull adldi-

tioan of 6 8I 1H3, andJ upon stand-ing for ? -- 3 hours a quanLity, of light

tain solid separated. The1 solid was filtered, air dried, anid dissolvedd

in ? refluxing mixture of 100 ml 4:1 ethylacetat e ;cetone. ~f ter

standing 72 hours, this solution w~as reduced to ;: volume of ca. 30 ml

by: evaporation which resulted in the separation of a white cr::stalline~

solid. The cr::cL'als weire; filtered, washed e.ithi c fewJ ml of ice-cold

othier, an: ait dried to vield 4I.0 g (4125) of thle carboinol melting at

181i 1830

Anal: Cled or H O,F: C, 73.77; H, 5.21; N:, 4.53.
Calcd1 to Cg16 L
Found : C, 73.75; H, 5.2!6; N, 4.51.

An accurate mass for the molecular ion of che carbino1 was determined

mass spectrPlly. Caled for Cl9H16N\OF: 309.1164. Foun~d. 309.1167

(n2ean of six determnrntions; deviation, '1 ppm).



The Pur;Ei ca tion. o f D iohenyl-4-Pv-pyidll :met ha ne. The commecrcially obtained

alkant (mp 120 1250) was found to be contaminated by trace 3aountis

ofE t he corre-fspond ing d iphe~nyl-4-pyrridyl cab inol ( fromr wh ich t he a lka ne

wa~s probably pr~epared). This was deimonstraced by~ treating a sample- of

the "3lkanne" vich 703l HCIO4 which produced color cha3racteristic of

Jlcohll ioniza~cion. A~ i.isible spectrumri of this acidl solution gav.e

barndl Iositions~ identical to those got for a! simnilar (k:non~) solution of

dl~T~ipheny-4 prid ylca;rbi nol.








.:rl~-1 ~ Mass colun (20O cmi :- 2 cm i.ti.) was fitted \ith a st;opeoc; .

abaceJ, wh~ich was~ innei-rted a oclu of 2:lass wool covl-ered withl a 1 cm

clik ur~ ot.Thc ver~tic~lly' Su'ported column was tilled ca. half

fu~l\?tl withtaent he:-.ane. anid thle stopeock~ was opened sli>.;htly. to

parrail c hch dropw,;ise our.flowJ of solv.ent. A? hexane sluirry of f~re:;hly

.Ictil.'rted 80 - 200 mnesh alumina (Brockman Activity~ I) was poured into

the .clulmn, and as theC al~uminai settled on the~ sandl I:;a the columnl wa~s

c ::.:afclly; agitated; to insure uniform adsorbent deposition. A. 0.5 cm

rchick sanid mi?: w;as added to the top of the aluminas Inayr in the packed

column, .nd the level of sch:ent wass adjusted to coincide with the

::op o; the sand mat. A~ saturated solution of the alkane w~as prepared

by stirring 2 g o~f thle allkanie into 6~ ml benzene. Tihis~ solution w~as

filerfled antd carefully placed on the column. Gravity~ clutio~n was

curler d out, bly the d~rolpuise percolationr of the following so.1,e.lens:

1) 250 el1 1:1, hexiine benzene; 2)j 5) 500 mi. portion:- of either.

''ch of the ether; ractions 2 4 as elrapora~ted separnately yielding ca.7

cqul.l qualn5titie of a white solid. A~ small portion of each of these

samples of solid wa~s tr-eated uith 703; HC10 In each instance thle

rresulting solution wans virtually:. colorless. Thiese samples oi solid

rrsre combinedc and dlissolved in the mninimnum amount of hot mechaniot.

Crystallizacionn aordedl a yield of' 1.0 g of wel~l developed white needles

1-:hich mlelted at 125 1260. A. solution of these needles inl 705; HC(104

:--as; transparentn ini the visible region of the spctrum.








Sancha~ss oi Com Lexes



The~ Preparatioti n of chet "btis"l Ilcohol Complle::es of Pa~ll.3dii lowT,(i)








dial, chlocide pio:Jder (0.16 g, 9.3 s: 10- n ol) \:as placed in a 250-r1

ro:nd botrola flocksi together with 0.10 g (2.41 x: 1-3 mol) dry~ lichiumi

chl~oride~ and 100~ ml acetone~. Tihe: mixture w~as scirred magnetica7lly and-

:ently refiuned until all solids had dissolved (ca. 211 hours). The

sIo'.utioni rlich resulted~ was deep red-brow.n in color. To chia solution

0.i1 g (1.8 x; 10!-3 mol) of solid 4;-pyridylphoinl- l-4-fluorop~ell henynlmha1

va~s a~d~ed; trumdiately thle red-brownl color changed to yellow~-ora3nge

Thei: yellow-crange solution wa.Zs refluxed for 2-; hours while stitring.

.'.nertonc riss then remlov'ed by discillacion until a solution volume of

11. 20o mnl was zttar~ined Th-e rea~crion mixt~ure uns filcered through a

n:ciumi frit, transfElrred to a small beaker, and created withl 5' ml of

da~ionized water. A; yellow, sryscalline precipitate de~velopedl during

standing for I hour-. Th-e precipiacae wa.s isolated by suction filtration

;norugh a rreidjuum frit, wa3shed on th~e filter with thr~e 10 mi portions

o: fresh dcjoniz~ed water, and oen dried on th~e filter at 1300. The

solid was th~en washed fromn the filcer- vith 50 azl fres!h acetone yield-

i.:r .7 yello--.' solutionL. ThiS soluICion rJas flooded rwiith Suff~ticiet

n,--!plt-lntn to produce perma~ne~nc cloudiness and wa3s th~en allowed co

st :ndl un~il cr.Lul~- a f~ormcacion occurred. i. yield of 0,.15 g (202r) of

901.1 dcfined -.ellow needles was obtained. Th-e products e:xhibited

c! c;:rninl:-: at >260" and decompo::ed to a blac: o-il at 2950










Founlld: (:, 58.73; H, $.03; t!, 3.70.






naladumJ.).TheC material was3 pre~pared in exact~ly the same fashion

;Is frl: the preiparat~ioni of the bis(:-pyridy~lphenylyl couple~:: (abov)

using C.53 g (i.8 >: 10 mol) 45- py ridyl- 4-m~e t hylphenyl- i- f~luor~opheyjl-

methnol A yield of 0.17 g (22%) of w~ell defined yellowi needles wass

o7btane!,d. 'Tne Iproduct exhibited darkening: at >2?.0') and drcomposed

tLo a black oit alt >2600

Anl:Caledi for CqH? 2 #,i,!?PdlClp: C, 59).74; H, ?1.22; N. 3.67.

Foundl: C, 60.26; H1, 4.3'3; N,? 3.;9.



D~I'hlcb.li~~i (4- y il-.rr-m-t ho:-:ph e ndl-4 flu o cophcnyluee t hranol )-

valeda~i).Th:is matcrial wlass prepared i~n exactly t~he same fashion

as forl the~ preparation of the bis(4-pridylphlenyl) complex (abov~e)

usoing 0.56 g (1.R x 10-3 mol) ;-pyrid:;l:1--me thoxyphenyl - fluoro-

ph'e nlme1 12t i nol1. A\ yie~ld o~ 0.16, g (20'i) of wecl~l dceir:erd ye'llowG needles

was~ obtainedl. TheC prodLct e:-:hibited dajr(ening: at >24i00 andu ecomposed

ro a black oil at 2500

Anal.: Calc d fo~r C 1122 '2dC 2 ,5 .3 ;H .5;0 .2
38 J,10rPC2 C,5.a ,40; n .2
Found: C, 57.90; Ii, 4.21; Ni, 3.383.



IL'.iOch'lorb.:(2 -Lpyri'Jyl- 'I-~e t hyl phony 4- flolo r-ohenylmert hnn l)prulla~d ium(iiT ) .

I'1hi~s materin1 uns~ not: amenabler to theC the~nrmodnamic investisations

wh;ich wcrc calrriedt out. in thiis work. (Sce Results7 and Discussioon, p.

9/). Ho..lcs:or, for the sake of: comp~leteness,; its pre~paration is given..







Tr is, chr only uel~l dzEined. "2-pyridy13 co~mplex r!ichi w:3 :is~ol.;te~d.



thtizci meth~od which ha~d beecn de~stgned for the~ prteparation of the "sanlt-

1ie c-. omplex (Z ~, PdCllT ), where ZI is a suitable cocion, and L is

the PYr'idyn~inetInl r .

Palladiumi chloride powJder (0.28 g, 1.6 x: 10- mol) WaIs placed in

a 250-ml round botcom flask~ E3agther with 0.072 g (1.7 x 10- n ol)

dry lithium chloride, 0.417 g (1.6 :: 10- mol) 2-pyri1Jy-l-r4-nethylphenyl-

4-fl]uorophenylmet~r hanal, and 50 mnl acetone. This mi:-:ture wias stirred

maignet~ically~ as i~t rlas refluxedj for a period of 2 hours resulting in the

dissolution of all1 solids and the formatio-n of a deep ried-bro:.n solution.

The ace~-toner ia~s the~n ret~moved~r b:. dlistillation~ yieldingS some red gAmmyII~

mtil.The psuntmy semisolidi was redissojlvedd by. cth addition of 10 ml

fresh acetone- reprodui~cing the red-brownm solution. A heaping micro-

spaltulia of te c anr:ethy13rlammonium chiloride w3s d issolved; in a mixtiure of

2 n1 acecone~ and 1 ml methianol. This coloritess salt solution wa~s addedd

ito the red-bro~ni solu~tion (above~) producing n~o apparent change. The

addition of 2 ml dichloromechane induced the separacion of a reddish

oil~y material which cl~ung to the inner walls5 of the r'lask.. After standing~

overnight the oily material had failed to cry:stallize and was redissolvedd

by t~e~ further addiction of 20 ml frresh ace~tone. This solution w~as heated;

following 30 milnut~es reflux; a sal~mon-colo~red crystalline solid seFparated~

wi;th che solution phase nowi being yellu.orw-orange in co~lor. Ai second

micro;.patula of tere rme thylammuonium ch~loride v~as added, and the react ion

mi.-:ture wars retuirnedl to reflu:- for a period of 2 hours. A~frer cooling,

the~ salmonl-olored solidl- wasZ separa~ced by filtration. (Thtlis solid cass

lt:c:_ sh~own to be totrame thylammonium tetrac~hloropell a~te(II).) The








5.*iLl:.=u--orange~ arctone Filtcrate :-ls rloodedl u~tth dEjOnlZize water re~sult-

ing~ j;in te fcapara~tion of a y.Ellow~ crystallline sol.id. Trhis so.'.id w.aS

filteredc byY su~ccrirn through a1 medium Fr:it, was~hedl with deion~ized wtecr.

;:d a~i~r dried to, ield 0.52 g (:3.1) of a ma7te~rial c~haracterized as the~

"bis'' Larlcool comp;le:-: (Pdt2,Cl2). This mate~rial decompo~sedr to a black

:011 above- 1950"

And.: Cale for C H 940,FPd~C1,: C, 59.71,; Hi, 4.22; N, 3.67.

Found: C, 59.56; Hi, 4.39; N, 3.70.



10. Thei Prepairation of the "Nono" A'lcohlol Complexess of Pa7lladium~(r 1),



also p1. 33,).





-!
-filuoropheng~ln ~n.~ etha=nol1. i~n a dry environment 0.01 o (5.6 x: 10 mol)

pal~adiumn Iichlor-ide powder was trasnsferr-ed to a 2503-rail round~c botcc~n

fl.20.: together with 0.16~ G (5.8 xi 10- mol) driedl tetra-n-bulaxls~oinoniu

chlloride and 100 Inl acetone. This mix:cure was stirred magn~etically as

it_ was re~flux~e d foir 72 hours to dissolv/e all solids,producing a de~ep

re.:d-bow~n solution. .To this solution wase added 0.1: g (5./ x 10- mal)

puLrifie d diphonyl-J-pyridylmIethrane (p. 33). A~s the alkane dissolved

the(- color1 of the~ solutionl chan~rred fron redl-brown to red-or7nre. Ti

.-oilutionn was5 rflu:.e~d for 2 hours andr cooled. To this wa~s adlded: 0.16 g

13" 0 mcl) :,-pyridylphreny.I-4-fluorophenynylmethanol ; as thle alcohiot

dli:,t;lved~lthe color- o: thie solution changdct f~rom red-oran,0,o Ln ye.l.nu:-

orng. his solutton wans rcfln:-:cd for 1 honur afte1 c:htch neetone vast

c:-aved~ by, disrillatiion until rr rolucton~ volume of eni. 30I ml was~ attatcd.







it.; rc:<;ture: was3~ n3?.: di(tincell yel-llowI with i)cip)ient preciipitaci~n o~f a

.elowsold :-.:ing egn.Suf f icienti do~ioni.-:cd \]ater1 (ca. 10 mnl)

~..us1 .R.'ded until pe~rmianent loudinesz crar produ-ed. Ture mni:-ture usz~

a~l~nloure to rscind 4S houlrs to promote icrys.tal. gr.owh, and ivas th-n f~ilte~red

by:, succion, throughfi a taredr frit (irradium). The collected :ellowi solid

G...a washedJ wirh ileioni.:ed ::ater and dried or, thie frit: at 1300 f~or a



weedles;]- wasi Obtainei. This m~acer-i3l darkened abowt 2450 and d2com:poseC

1o .2 brlack 011 above' 2700

Anl:Caled for C3'6 29 20jFddC1 C, 61.605; H, (1.16; Nd, 3.99.

Folur.d: c~, 61.3:; H, 3.93; N1. 3.83.



Th. P egara"-'~ tion of Pd~I(II)(py:LOH:I:)(L-)Cl. urhere pyLZOHI is :-Pv:.rid~vl-:-

a.-.h'-Loeny-4-luropenymecano. his complex; was prepared ini e::actlyl.

rhe sameC fash ion ras tha c for ths 4-pyrld yl pheny l-t:.-fluorophen;. liet hanol

rnomplex> (abovr). The Same~ quantities of~ mazerials w~ere emrplo:.ed t3geth~er

\;ithi 0.17 r= (5.i .: 10 001) -:- p:; r jIdyl-:-me thyl~pho n:.l- -4- flunrophenyl -

mehaol A yield~ of 0.35 g (872) o~ well defined vellou. needles wa;s

obtaned.Thi material decom~posed~ to a brow~n-bilack oil abovel 2450

Anl:Caled for C ,H N..0OFPdC1.. C, 62.0; H, :1.3 16- 731.0

Foun:C, 62.20; H~. $.32; I. 3.77.



I'e reprio ofP(I)pyO)L-;C1>. were p:LOH is 4-Pvrid-:1-4-

virh::ge*1 f~Eluompbendm t h an"ol~. This complex; u.ns prep~ared~ in

*F-..i.: tly\ the~ sahe fashion as cha~t for the 4r-pyridylphonly l---a-frluo cophinyl-

noona~l:ll compler::: (a-bove). Tlher sna-.ne quanntites; of ma-terials were emnplo:.d








c;rcher~: l Ilith: 0.18 g (5.7 x 10 la i0) 4- py cid yl-(I-metho ~l:.y phcnyl, -4-

"buopenlmehaol A iC.!d of0.3 OgJ)I (SA\)j Of~ -:ell1 dcEined~c ?llow:

neelesi-~ wasI obtained. This material. darkenied aiovi 180j" and decomposcJ

'-o .-, brown oft ab~lov~e 21C00

An:1: C-led for C ~~Sil 0 OF'dCl : C, 60).71; ~, (4.27; NI, 3.83.

:'oundl: C. 60.94, 11, 4.416; 1:, 3.83.



Tecro by-lt ylalnmmoni um Tr ich lo ro- (4~- 'ridl phenv1-4 -flioor oph en:v mec hrnol) -

palaat(H.This "salt-like" cormplex; was preparedl reparately. in order

to estaiblish tle- L"act that it w:as a stable, isolable intermnediate.~ (See

esuls:1- and! Discurssion, p. 5S.)

In a dr! e:C;ironment 0.12 gi (4.3 x 10- mol) tet ra-n-b~ucylla~n oiulm

chlorjde, C.075 C (:.2 x 10- mo~l) palladiumi chloride pouider, and 100 ::sl

.acatone \:Lre pla.ced together in a 150-ml round bottom flask-. Thiis

ni:;rure was stirred magsnetically as -it wa~s reflux:ed for a period of 241

hours. The reaction mixture now consisted of a deep red-brownm solution

j;hase containing traces of undissolved white and redl-brom solidso. 'The

solution phaso was~ carefully. deconced into a clean flask, andl to chiis

wans added 0.12 g (41.2 x. 10 mnol) :I-pyr;id lphenyll-4-fluorophenylmechano1...

A~s the nicoh:ol dissolvecd the solution changed color fromt red-brown to

o~rage. Thiis mtxvture was stirred magnetically at ambi~nt temperature

for- a periJ;d oE 1 hour a~nd cas hchen hea~tedr to refl~u;.. Acetone uns re--

rmov,d by. distillaJtion durring reflux~ until a solution vol]ume of co7. 30 at1

..uaataied o Cme hot red-ocanger neetonec solution wa-s aIdded 30 mnl

other., and1: tl~is .L:(lutio~n was allowed to cool wlithou~t stirring. To thel

clo-leJ soluio n n-pecntanet 1.as added~ in small p~ortions until permanent

el.ulnes as ttind.Upon stirring for a period of a2 fewJ hoursr n








c:..*a11 Iowni.ic) y of ye~lloul-ocange: crystals; deire,~loe and se:ttlLd to thle

bo:ttom7 O t:f the 1:i: iark. Th solution phasc, w:hichi ;:s now; SligZhtl.y yello~:.*

.::as f:ro:trid Oa'an 4ithl n-pentanle to reinduce cloudinei'ss. Aite_ standingg

i:er.:ir,: tt th:e mirtuire vafs grav.ity filtered through ai fluted filter, andc

:L..'1el 15 IIirtua)}y coores iltratee was discardeJ.. The crys~tals uIhich

LateL Co~llcted~ were1' sir dried. examined under a Lli.croscope,, and~ loun-d

ra o be thin:, tran~sparent gold-orange she~et-like neecdles. This material

unrlited at 1.500 to: a red-brown~ oil. A\ yield of 0.29 ; (94.1, as based

on ?.ialluium)n wa.s obtained.

And..-C~aled for C34H50 20iFddC13 C, 55.60, H, 6.86; I1, 3.81.

FouLnd : C, 55.35; H, 6.7;; it, 3.;77






Elemental Analyses


Carbo hydrogen. and nitrogen elemental analyses oliasan


ccctmple;-r:C were! performed eithe-r by PCR Incorporated, P. O. Bo:-: ji66,

Gainesv~.ille, FL', ;2601, or by A~tlantic Mficrolab, In-corpoorated, P. O.

C.:-:i J3C300, Atla-n, a GA~, 30308. Noa special handling1 techniqlues werec

reqluired3 for either the ligan~ds or the complexes..






Rentents and Colvents




The! s~pecal. co;;rmacrcirally obtained re~agents :hlich vcre- employed

j n~~ thi: research aIre listed in Table i (p. 412). These materials wlere

useJ;~ x::thouic fulrther purification ulnless oth~erwise specified. TheL








Tal
Spcial. Commeircially~ Obta~ined Reagents - andl Su~pplie-rs



Kceagent Supp~lier



E-bromoanisole (1-bromo-:- Aldrich Chemical Co., Inc.,
n e th c:-:yrb en ze n) M.iIilreauk~ee, HdI, 53233

4il-bromlo fliuo ro ben sene Alr d ri ch

2-bromopyridine Aldrich

2-cyanopyridine (picalino- Aldrich
ulitrile)

4 cano pyr id inc (is o n ic t ino ic
nitrile)

li pheny~l- pyIr id y larb inal K: & I Laboratoriees, Inc.,
Plainviej, li', 11933

d iphcnyll-4~-p:.r idylml~e t h ne Aldrl-i ch

phenv1-2-pyridylketonec ALdrich~
(2-bconzoylpyridine)!

tetra-n-butylammoniniu chloride Eastman E:ndak Co.,
Rochester, NY, 14650

P-tolunitrile (e-methy:,be~.nco- Aldrich
nitrile)







adldi~tional reagents and solvents which w~ere employed we~re readily

availablee, reagent gradef quarlity, ma3terials, andi :core used vrichout

further purif:lenti~on








Enstrumennta A'naly.ticlr3 Nethods




Pro~tonir Iincrtic: RcsonanceSpcora. Thle 11r nmr spectran e-ar~e obltaine~d

ui::I;;:. n Varian A~ssociates :Iodel A'l-r:0.1 nmr rspec~r-omo~ter opelraciingn at 60)

Pll2. The- spectra-~ vcre: taken as saturarted carbonr tetrcchloridee solutions

us:ing~ tetLCilmeth:, lSilane (T:S) as internal stanldard. Th~e spctra vesre

e:..:.mined principall:, with respect to integrated peak intensity ratios

lot thbe purposes of ascertaining sample homogeneity and molecular

composition.



MaeSpcra rlns spec-tra w~ere obtained using an A~LI 03-30 rolaES

r!:elctron:= ec ter eqipped with~ a DS-30l data isysem. Solid and oil samples

;vote introduc.-;d into th~e ioniza~tio n chamber via direct insert-ionl probe

at 200" ;id run: atr an ionizing volcage: of 70 eV.




I-f-ra-redi Snectra3. The IR: spectras veire obtained using .a Perk~in-El ner

Model 337-R gratir.3 infrared spec-itrophlotomieter scanning the reg-~ion

iu000 -- 400 em-1. Solid samples were i~timately Ground witih ovefn dried

reagent potassium bromide and run as pressed semimicro discs. Oily

namplets weire ruln as follou~s: A neat potassium bromide dtisc w~as pressed

anid su~pprted horizontally. The oil wras wrarmedr until it became fluid,

andi a drop ofT the oil wans added tol the surface OE theF salt disc. Ti

tecl-hnique~ deporsited the oil as a uniform thlin film on the diszc. Thie

rjplctrum~ wa'S rc~orded L1s soon as the oil cooled sulfficiently to become

.' .sco1's.

The1: I: spcctra vere uIsed to i7rov.ide evidenlCe of ligand homogl;~enity:

~:r~thv stal~ishi the abs-en-e ;of a carbonyl. stretchin= vibrati;on (keto~ne),








thec presnce of a hy~dro?:yl baond alcoholol, andl to confirmn thle preconce

of bothI litgands in the "'mled" mo1,ne-alcohol complexsc (pp. 33-60).



15r
F~luorine ;Iugnet'ic iResonanle Spcyetra. Thle 'F rir.r sp-ctra unroT obtainedl

ur-inI; a Varian A~rssciate~s Mlodel SL-100-15 nalr spectromieter~ operartin:7

at 94.1 MIHz in neither continues wanve or Fouri-er transf-oirn pulse node.

Folurier trarnsform capabilities were provided with a !ico~lct TrT-.100

computer systemn equipped w~ith a 16 K capacity. memor::. .111 spectra ccere

recorded using extern~al H20 as a lock.- signal. FIluorine rlso~nanes were

recorded rclativie to 10.5 CFC13 in acetone and to neat triflulnconcetici

acid as ex:tern'l. reference standards. Operation at a sw:EeeP width of

5000 11/ affoidlde an uincertainty. of +15 Hz_ (-10.16 ppm) in the position:

of observed 19F: signals.

L~igand spctra were recorded as 0.05 M acetone solution was 0.05 ::

10i: HC104 soilutions, andi as saturated 70%: HC104 solutions. Spctra of

comp'lexes wJere recorded as saturated acerone solutions and as saturated

70%/ HlCIO solutions. All solutions were filtered through a coarse ;rit

dirctly into the nmr sample tube just prior to recording of spectra.

11C010 solution. spe~ctra of thie colmpleess welre run in large capacity,

nme tubes employing Fourier transform techniques exclusivelyy to facilitate

signal dletection For thesce .ery~ dilute samples. All1 samples wJere air

cooled in the sample holder during the recording of spectra In order

to, maintain ambient temperatures.



Vi~siblel Spelctra aIndl Malr Ab~sorIpt ivi ty, 2oreficient_ De~tiermination. \'.i s ble

spectra wer'ce obtained using a Ceckmar. Model DR-C grating spsctrophotoml-

citor eqluipped withi a Snogent Modecl SR: recorder. Malar1 absorp tiv.rity











;;c;ies dair-I.cd front eachit of the ft-Ce andJ compcjle:-:0 '1ohledisov

in 7 HC0,.Samples; of appropriate si.ze (1.0 to 10 ) ere .leig;hid

:..l theec significilnt figures using a Cahn Model 1501 Grami E~.lectrobab. l anice

ecibra1.- Ced inl ;lth 1mg range. Gily samples haJd tou be we~i led by~ dif-

'eec.This a;, s dlone byr Laring a: small. finely, dlrawnr ins: wh~ltakr

;tac toonl c:arefully toulching the glass wlhisker to the~ oil until 3 vtery

:;,nall hit of the oil adhered to che whisker. The vei~he olf the oil

?-as obtrainced from the combined wiight of che oi~l and whii-sker. Thre

..-el~ghed rsap.:css were stirred in ca. 9 mii OE the 3cid to complete dis-

adcurlion and chen maide to 10.0 i01 uich fresh acid. These acid s;olutions

-elr, scarnned va'. che new~3 acid as blank- spjanning th~e re;=ionl 760 320

!11n to ascor.:-.inl the position of .1 for che~ various car'oenium ion

species. F~ach- ionic species exhibited cuo main anbsorptioni hands withi

the more in~tenrse band appearing at louel-r e~nergy. If the absorption

mi~:C:jlia weure "off~-cale", the: acid solutions w~ere diluted w~ich the-

necessary cluancicy of fresh acid to produce "onl-scale" readingse wicn-in

rceptable sensitiv.icyl limsitation~s of the spectrophotomatert readout,

vir., >10.1 T (<1.0 absorbance units).



\~'is.sble~ Spectre. 3nd the "Deno" Titration Technique. The e~quilibriumn

conoant :p..) d~tum pertaining r to hi ther~mody-namic atability of each:

ji the~ carbe~nturu -pecie~s which h-a'.et been considered in thit uork Gvas

e:- l:pe n~rimunta.11 obtane~dl as follows: a 701, HC10, solution of the alcohol

(lipr,,d) or co~mlle:-: under inv.escigaci~n wJAs pr)ePaCedL and diluted (ii

neice.-ssry); utlth Eresh acid until an "an-scale" (vi ., 15 255 T)

.;pei~l.ctrohotomete.r readiin3 vaJs ob)crined uithl theC ins~trumetI1; set at .~1max








T..r thatr paz~rticule ionic species. It .is not necessa~ry ton fi:- the

r..ic-ccurrati[ ion f tlis roLuCLon. (See RHesults: anc Discusionil p. 92 .)

A~ !,.:rehteir miinedi Ilunt ity' o thiis solution (ca. 5 g) wais wJeighed~ to f i ne

;Ctnifica~nt fiigurou intlo ther special cenvette (doscr-bibe belowi). (Ey,

Lcaptlo:. inl; the asne sampllle. size for each titration, dat3 tPP~;~reatment wa

g~rcaly~ simplified.) In o;-der to obtain exactly the .same weight f~or

echC~ samille, iery minute quantities of the parent acid solution could

be transf-er red t or from (as necessary) the conte3nts of thle cuve~tte

u:lch thec tip of a f~inely drawnm Slzss rod. The acid solution in the

special ruve~tte Was thnn transferred to the cell compartm-nt of the

spe"~ctropho-tomate-l~r and "'read" at .) relatives? to a sample of the neat~
DOX

acid usedr as blank. The cell comp~artment was thermo3tattedd at 20 250

by' the circulation: of tap 'ater. The. special euvette w~as removed

from the cell compartment, and the parent acid solution of the- carbenium

jon was diluted by the addition of a measured in~cr-ement (ca. 0.02 -

(1.08 g) of deionized water from the special b~urette (described below).

Follow~in:: each addition of water the acid solution w~as carefuilly.~ mi:-:e4

iin the cuvette-; the cuvett? w~as returned to the spectromeiter, and thle

ablsorban~ce rercad. This procedure was repeated until the absorbance

of the acid solution had fallen off considerably (<0.20 absorbance

units) the~reby, indicating a reconv.ersion oE c~arbeniuim ion to alcohol

(ror hcomple:-:ed alcoohol) precursor in e::cess of 50i;. Data creatme~nt Is

~onsidcered -in Results and Di.;cus:;ion (pp. 83-103).

The:c specific gravity (a) of the reagent 702 11010L wans determ~ined

before pedrrmiiing the ticcacionsl by, weighing aIccurately; (5 sig. fjig.)

;! measureddl vc~lume of the acid In a 10) ml volumetrii c flrisk whlichi had

bacci volumetrtically caibralted (to 4 siG. fig.) w~ith 3 \righedl sa-nple









ofditile .arr.Prior to ca~libration theI neck of the flclk w;a:

Walred andt drdW~~~r LO n fine bore of sufflcCni HL1. Inrge li~ner diamec,t-r O

paiirati insertion of a Paseuir pipe~cc for liquid transferral. 150l flasl.

usI~ cheT- cal.ibratedj by mnarking the drawjn necck. at ;i volume dict-:r-ed by.

rl!:he wihedl samp~le of later contained in the flask. Specific_ gravijcy

ata;i- for Jncer a,'. amb~inen conditions were use~d to calculate the volume

jf the flask at the callbration mark.




Spreal udGE 1. 1.00 ro pat~h lengrth quartz cell ficted with a quartz/

P'-itc: graded seal stem was obtained from P:,cociill Ilanufaccuring C~o.,

Inc. Wetwoo 1.1.0765, he seem I.:?.3 shortened .-o that the ce~ll

iitect~ conlven-iently into thie sample compartment of the speecro:neecr.

A~ ;tandard caper size 13 ground glass neck un~s added to the top of the

stemo to fac:ilit'ate the direct: dropuise addition of w~ater- co the- acidl

so~lucioon of the carbe~nium ion contained in the body of the cell duringI

ticracion. A, side arm of ca. A al1 capacity. was5 Fuied to the stem at an-

angler- at ca~. /5" co the cell. TIhus the Ehoroughi mixing of wsater with

the( acii -3olution! during tieracion was readily accomplished by rocking

the 1:ell after each addition of water through an angle of 900. This

pa~rticulari~ cell de~-singn also elimoina~ted any] problems associated with

samplec less upon removo.al of the cell stoupper prio7r to each addition of

tirrant (urntedi since none of the liqulid~ sam~ple was in contact w~ith the

s~topper- througihout the~ titration.



SpeialBuett. 5.0)0 1!11 capacity semlimicrou burette~ equipped ..=ith sn

aultomaticr refiling reserv.oir 3nd sidle arm uns~ Eictedl vichn 3 5 cm lengch

at srgial ubig a th drp cp. 12 em 'lenthl Of' 6 ilm (O.d.)








n,-.pill.Try tuI.bin!; was~ dlrat~n rc a \ry! fine bolre pipater tip at onerc en(d.

be~ opstl:Iite~ cndl o the capillalry- was insertedl sngly~ into th: open

co~:<. o the scbllE l~d tubing. A Sma~ll screw~ clamp w:as affi:-.d to the

nue~ica tuing L.ich the stopcock opened on rho~ bucatte, t~he? snow

-.l.ing .lax adjusted until drops of unifonn size werle discharged~ at a1

convenie:.t rate f'rom the drip tip of the caprillalry. It wras found that

.:uring~ a c~itr~i"eeric run1 (ca. r:0 minutes) drops of water could be col-

lette:1l fromr ilhts bur-ette assembly which Jiffered in vigrh t by not nolre

t:;er ~10.0002 4 for drops aeraging 0.0190 to 0.0230 g, providjed the

cip of the capillary was weeted prior to drop size calibration. This

obviated the~ nertd to weigh the sample in the cell follow-ing: each addition

of water; thate i, it wa~s nccessary only, to count the number of drops

coLlc~ted in o-rdler to de~termine the coal quantity of aIdded waRter at

any) givenl time during the titration.















RESULTS ;;;D 3Is;CUSSIION


S;nthetic Consideration



On te Pnartionof igady.The :Jyidicnc alcohc1 carbonium ion

pr,.cursors employed as ligands in this wor~k Iere found to ber con-

vcljniEnl:' preparable by. the Grianard re3Sent sy~nthetic routes, outlined

to r~e e::permenz l setion. It \as discovelred,, hou~ever, thac con-

::.-;:ently bertter :,ields oif produ~c't wjere obtained whlen the Crignard

IrP:-gent wa5 prepared f-oml 1-bromioflloorobenzene follo;:ed by the addition

.oj th~e rpp~ropriate pyr-idy1 k~etone. That is, in attempts to prepare rhoe

:dcnc;.eal~ aLcholl fr~om a :- fluorophenylpyr~;idylke tonel andi the req4uired

pho~nyl-type~i Grligia~rd, mu~ch poor~er :ields~ aire goL. These results suggest

tht~ll ;-,-bmmoi~lacr~. obenzene Grign--rd ...as readlil:. Preipared in g~oodl yield as

.: reactive intermediace and uns a su~fficiencly potent carbanionic roagent

:0- attrack th7e "3rbonyl carbon of the k~etone. The Jifficultie; encountered~

in the~ alternate synthetic route leading to accepublle quanititis of

I'.oduce are attributed3 co the preparationi in poor- y~i;d.d of th~e ne~cesrsary

"r aardin~rm-eiat. Tis ':3s partiCularly; obvioulS in the c.ase for

..aliih -'l-methy;l phen:,l Gr-ignard or~ ~-l-m eto.-:iphcnyl Crignorcd erer thle

r-qu~-- .aheio.Thius, kctones-: prospo~red forom these Gr~ignords contid



pe.;.'1,.:n of Iconslque-nce since the~ deireji~d m~terial (the~ Icione) u~ns








Ier:ityl sepjrat~d fr~om the- urcncntd StaL=rlin m:aterinls. Hlowevlr, the

$separation71 of .7a~lcOho from parent ke~tonle was very difficult, and it w:as

::ecl.ssaryn therefore to convetrt. Ietone~ proculrsor to alcohol1 as comp~letely

~sIno pssibe in orde-r to isolate the desired alcohol as a hoitone-free

Proanct. Thius, the preparative route for~ thie alcoho(ls emlpoloying 4-brolmo-

thuorobenzone Crtginard was; the beettr method.

Trhe filter stick- filtration technique emrployed prior to hy~drolysis

in the .synthertic procedures for the preparation of alcohlols facilitated

ther rem7ova~ oF u~nrec3ted ketone from the reaction mixture. This techniques

utilized the fa~ct char th~e ketone Grignard addition compound was

splarinllyy so~luble in the ether solvent wrhereas the ketone itself was:

:nodecrateily to readily. soluble~. Thesrefore prior to hy:drolysis unrieactedl

Mtonec which was dlissolved in the ether player could be drawn off by

c..letionn through the filter stich~. Repeated washings of the reaction

rmjxture writh fresh either, followed b:, filter~ stick filtration, afforded

a-ssentially completed remo:al of~ unrcected k~c~one.



On t~he Choice of Palladrium(H)~. The most obvious reason for the incorpo-

ration of pallad~ium(TI) as the concral me~tal species into the com~ple:-.s

consideed in this research is to permit a direct and irmnrndiate extension

Ipon the re1tclte work~ of previous inves'Ltigan(( trs. RiichaLdson (h) and

W~E;cH (8;) bCothl pointed out the sulitalbiLity' of palladi~um(TI) to such

inversil;atios ouling to its lowJ ox~idation state and hig~h penultim~ate

n-.0.1.it~: n-,occpsncy. These factors wJoulld he exprected to contribute

toc wordn .3mbii jecion of a coorTdinated carbcnium ion vira back. donation

of mneta: rl 4J Lcctl-rol density into the n-framworkO~ of theC Calrbon'tuml lon

;Irividled thec ligandl donorr atom~ and echnibnjum lon carbon atom wcre bothl









r-::.rbrjci- of thc Ligand ;i-sl,--em. The- rclative inertnll-Ls of p1~allaicmm(H)

onIn>)!.r-);.L; a~lco~ segPest's tha~t such rompl-:-mcs wou~lld beJ 3imenable to theset;

typ.!,h ofi stu~dies. Finally. th- diamagnetic nature of i-coordinate

rnl:7diosln(I.I steamirin;: fro its squarE planar compnllex; gemet try, makes

it con~venlient fo ilr- nmeinescigations onr the stability. of a coordinatedl

Lclrbanium ioni sine no paraimagnetic contributions to measured chemical

shires :uouldI be observecd.




un Llth Selection and P'preparatio of Complexes. The renulcs of previous

irn.escgtigaton of bis palladium(II), complex;es of ioni7able py~ridyli and

til;7.0171ll alc~ohir s dcmone~r.i-ated the sulrAb!itbli of coordinated1 ca~rbeniumi

ions deirlved from thnse comUplCexe for ther~modynamic stablilityr Studies

upon such: ion;;. Therefore, the bis palladium(II) compilxces were prepared

in or-der to~ enlairge the scope of earlier work through .-:imilar studies

upo:n~ cartEniuc ionsa derived f~romi the fluorine-tagged p:ridylmethnols.

Th)e palladi~um(lII comple:-:es contaiinin but one ionizable ligandt

msolecule Ier complex \,ere prepared so that a one-to-one rela~tionshipp

rould be established between a coordinated carbeniu~m ion snd the stabl-

lizir~g effects exerted by the metal-containing moitot. Indeed, the

die.elopmentii of such a synrthcic method uould in itself be a novel

cont~ribution tol th~at area of preparative coordrination chemistry embody:-

ing palludium(I;I) as the central metal species. Th~is follows in that

th-re are k~noIi many) "mri::cd" neutral complexe~s of pallndium(IT) of the

c.*e d(I)&LL2]. Where ~i ad Y1 are anrionic groulps, and L1 and L2

;Irer neutrlfj donor ligandl-:. Ini none of~ tle~se. comple:-:es, hIoweVer?, are

t; : L. ligands py:,ridine h~oniologs; rather they~ are uIsujlly' donors uihich

c::..ibit particularly; strong T;-ncid chairactor. Esampi,.cs of those li~gands











C`K2, CO,, n.1 varliiouis alkenes. ~ctually,, vork; hiar: been reportted con:-

'-rnLugl tle' precparaio~in of .such mixed comlple:x-:e where?-in py.ridine J~onors

;h=vet been .incoliporated into thle coordination sphere as ne~utrali liga:nds,

bult thFe bu:;lk of th~is wJork has focused upon~ thec use of placinua~n(II) as

thre crntral mouc~l species.

:!.n 1936 Manni and~ Purd~ie (=l4) reported the preparation of mixed

com:~ploexe orf palladium(IT.) hav.ing the general formulJ [Pd(II)(Du3P)(iam)

0121,] where Eu IP is t~ri-n-ktyu ,lphosphine, and am is either aniline,

p-touidi~ne, or pyridine. Th~se~ complexes wrere obcainedl via the initial

preparationi of the binu~clealr chloride-bridged tcans bis(Eu3P) complex

1.Pd,(Rul,P),Ci,'. fo:llowded by cles.aoae of the chlloride bride a-s with the

requl..:.!-ed .malar rac7io7 o the~ amine of choice. However, an e:-.arnina-cion

CL thle ilifrmai.tinr citeti in the e:-:perimental section of this .Ictii:

icTivaar'ld tha.)t acounlts are given only for the- p--reparation of the comple:-:s

ab~ich incolprpratedd aniline and Il-toluicline as thle nitro~gen donors.

Investigti ions~ir 1~ by Chatt and Venanzi (25) in 195,7 uponi similar comple:-:cs

or p-illadium(11) again serve'Ld to demonstraLe that the neutral chloride~-

brid23d, binuc~lear compounds could be converted to the corresp~onding~

lonlonulcla comnplexsc via rupture of the bridging bonds of the halide

10amr~ w.ith~ triphenl;pr-phohine The~ parent bridgeJ matlrerials hand beetn

prepr- abcl l e with d~i-n-pe~ncylaminei or pipecridine as thle ni~trogen do~nor

ligandls In tranr; positions; but these workers rep'orted thatc chley were

niot sble to obtain thet colote~d bridg-ed compounds using pyricine or

pycdin-cotaitnglignd iOhviouly, thl~erefore nCUCtra mo~noune.10ac~

complexes with p~yridline in thle ,oordlinatton sphiere hand no: boo~n inul~-acuJ

diulincl these inverLstig:ti ions. In 1?09 Cha3tr andl fin os (i~i) rcport.?l








Go!I :;ui~ccssful cl reparaion: of neuccal, Fsquar1e planasr. mi::-:ed, monolnuclear:

emplexcL:: s of' (,lcluT(ldium( I) wic-h hald pyridine included vrich~n the

coodintin shee o th ntal Aain the synrlthetCic Trolte1 to theset

.nri:~i red monnudent materialss relieii upon the cle~~avag of bridgighad

ir. birluclrear precursors uhe~rein the brid iang pce eeete

ihlosride ions 02 Ip-colue~nesulfinace ions. In 19J75 Hjoschi and cou~arlters

(27)j succeeded in preparing some neutral, square planar,mo~i:e, mononiuclear

Complllexes~ o7f palladiiumi(LI) wlith coo~rdinated pyridinle. TIhey also employed

a chlonride-b-brigdg binuclear- precursor [Pd L.C1 ] wrherein Ehe~ neutral

L groups were arcrmatic ison-icriles. Trea~tment of~ the bridge~d crompcund

with the r.Equir~d molar racio of p:,ridir-~ne affrded the isorlaiiOD, in

goodl Sield, oi choe corresponding trans rmononu~clecr cojmpex. TIhe results

Of bohi~ of these sctudie= (virz., Chatt and Mlingos, and Bosch~i and co-

_-.nckers)-~ chc~frefor indicated thac a g-neral rouce toua~rds th~e synrche~sis

:>1 mied m~onnuclerr complye:-:es of palladium(11) which inclu~ded~ pyridlne-

rl'pe li.gan~ds required initiall) the pr~eparacion of~ a suitable hlalide-

bridgied bluu~cleir complex, follo-.eed by the rupture of the bridging

bonds; wich th~e selected pYridine dornor(s).

So, in order co obtain the desired py~rid ine-containing, lixe~d

rannonucleare~ comp~ie:-:es in th-is research, it wjas first a~ttemnpted toi

preparre theic binuclear chloride-bridged dimeric materials [P~d2L2C1,)

r.!ih the L groups, .as the pyridine aeth~anols. This me~thod depended upon

thle direct combinacton of the mononuclear his-alcohol co:nple:-:0s [PdL2C12]

withthecomle:: anon PdCj~on a 1:1 mole basis wiith respeer to

palla.diumn. Thle briTdgel dimer, howeve.rr, could not he ob~tained b~y this

metho. Th.cofre, he chloride~ bridg~ed comnple:-: [P'dL2,] thr-

pl:.. .llp~~[hosphi (P'lr3P liganj-s in:0rporalced as thle neuitra-l 1. groups w-:s








Ipr pa~red anci7ording to thle meth~od cue~lincd by5 Chaltt and6 Venan~zT (25).



..dymejnls Tiis bridged m~aLIPri:l, Ghich U.TC ; redl-tloron Srlol,

'wasl slurrijedl in rs".luxing acetone andi treated viich :I-npridrl-4-fl uoro-

phonyllm,thann d (I4-pyLOH) on a 1:1 role basis richl respect to pallad-ium.

An: Irelux!: vasl continued (ca. 3 hours) thle bridgied matcerial dissolved

an:d a7 yellowI~ solutions~ resulted:. Wha~n thlis solution wJas satu~raed with

:-pentc;: ne a pale yellow cryntalline~ solid settled out. Chraracteri zatiion

of ;hils sol..td ~inJcated thlat the desired mixed mononclears co~mple:-

[i(~i~I)(PhfI?) (L-pyiLUH)Cl2] had been obtained. This result suggestedl

that the prob~lem~ ~F: preparing the onocnuclear mived com~plexecs ;ontaining

thec py~rid;ine a~lco~ol~s had been solvecd. However, ?Iben thii ma7terial was

treated vith1 702 HC10,I for the pur-pose of crryi-ng,. out s~tabilityr ini-

vIesti:;3;ions 'Ipo; che "lcoor3 nCidinated" crbnium ion it was discove-red tha~t

t;:e co~or';inate bond between -the ionized pyridine alcoolrl and the palladi~um

noctal center vas5 qulickly ruptured (ca. 5 minutes or less). It: unis pre-

sav~dl that thlis bond breaking :was .3 consequence of the e~ffctive trans

la3bilizi~ng ef fect exerted by the st rong rr-acid l igandl, criphocnylph~osph i.ne.

Thi3 result thecrefore dlictated the ne~cessity to prepare thle mixed mono-

Iouclear comple~.<.s with a neutral, nonionizable counter ligandl, which

could not e:-.hibit. particularly strong Tin-cidl behavior in these: comple:-.es.

Theri selection of 4-pyrid-ld iplhenyln~ethane as an appropriate? counter-

1;:1.:no ;;as clearly a gooJl ihoi~ce T'his is attribuctble co che structural

clmparabl:~; lity of the 3lkane co the py'ridine 3lcoholsr. and to the antic-

il'tel s'imilarity in che~mical behav.ior of the alkanne to pyridijne ic-

.sel. Tus, thle problem art hand was cdo development oE 3 synt~hetic

srncL-dure thlrojug~ whichl a uolecule of thet alcohol as well. as a moleiiicul








ior the1G;:~; alkano cld be s'.Sicomoltlicall, ntrod~ucco into theI; icordination

::periie rsi the mIEtal inl the monncuuclear comple:-:. Thec fo~llowiJng con-

-izraio::ver prtnet:1) Thie i~nab;ility to prepare~ the chlioride-

bridge-~c.1 brin~uh!lar c:omplexrs containing p~yridinc donors i;n cralns positions

I U,,(pyr~ LCHI JC~ (v.idey Eupra) ruled out thie u.Ge~ of such ai material As;

a preursor Theridging~ bonds in this dimer: would prosuu~abl: ha~ve

beenI GLuscoprblej Ito attack b:. th~e "second"d py~ridine~ donor thereby~h

,iclding~ t!e mi:-:cd py;ridine mononuzlear comTPlex. 2) In i.iewi of thei

anlticipatied simrla-rity in donor character orf thei p::ridine alkane to t~hl

pyr-cidine slcohiols there- appeared col be no methlod b:; which these t!:

u:,ridi;ne ligaind:; ciuld be added directly to the palladiun metal on~cer

inl the required~ stoichiometric ratio.

The a .ntheisc- finds of Goodfellowa Goggin, and Duddell (28) provided

easo~nable prospe-cts for the preparation7 of theC desired comple.7-:cs. These

wo~~1~rkers reiconi:- edr C1ht there are many comple:-: anions of th~e type

[FC(11)L)l ] L- 24,C, 0, N.H3, orz py~ridini; preferences for thec

preparati~t on of thliS cmpTle:-: anion w..ith threse respectl~iv ligands a-re

ci-ted in thiis ar.ticle) which are well knol.m. Th~e; disco.'~red that such~

LLomplex anions wJEre also, preparablle withi L as PR SIT2, or AsR. (P.

i'lkyl o~r ary~l), and that a similar series of comple:-:Les (et:-cluding,

pyrildins) wIas prep~arable as well wlithi palladium(10j. This was the first

gencral a~ccount~ given For the; successfully p.reparation of such~ typCS art'

complex; onions of pall;.Jium(IT). Thle usual synthetic route wjhichi those

-.corskrs employed unls cha~-~tracterizJ~ by re~lu.:ring the ch~loridc-brid,3!ed,

h~inuclear ma~terial l;M2L2C1,],. 11 equals Pt(IlT) or Pd(II), w:ithi the re-

quli~ced st~oichionetrictyj qua~ntity. of etr7-_n-propylammmoniumi chloride~ in an

inerit orq~nlc solvent~ such as dichiloorometane. 'The comple:-: anion wrhil:h








;;s Cilon:cJ u~pon rulpture of thle chloiride bridges~ vas. apparently stablilized

in scluionil by, the lnrge ter ra~lkylaramonium coun~terjiJ: n The comle:-:.u.

eniocn wout found to be isolab le as the Lct r;:lkdamm~i~ronium salt vlia trout-

r!L.?; Iof the d~i;!;h0lorometane reaction m~ixt~re wJith R::ocess; the~r wh~ich

resu:~l~ted inl cry.s:~ca~]Li-ation of the decsiredl product. The salient aspect

or this: preparrtivet nethiod is that it permitted the controlled in~clursion

of, . particullar neutral ligrand into the coordination sphere of the: metal

;Ccur.. HolverC, as previous-ly indicated, this particular nothod was n~ot

d;irct.ly,~ appicaible to the situation in~volvring the py~ridine donors

cineaP thei necessJalry bridged precursors wiith trannsT py'ridine donors had

..at bee-n preparab~le. r;-?verthelesns, fuirrthr c~onside~rati~n- s parallelingE

this sy'nthetic: zpproach vrere certainly varrantedi in that this technique

sc~erle to reinfor~rce- thle possibility of being able to investigate stabil-

Iry relationships between the metal center and a singly chlarged co-

ordinratedi pyridline enrbeniumn ion pro.ide~d [P1(II)LC13l complex: anions

of the pyrlidine alcohols could be prepared.

CoodfEcllow, Goe~in, and Duddell had also reported the preparation

of the anionic complexes [PdiI(11)(C2H)CI.] and [Pd(II)(CO3)Cl ] by

r-eac~ting the binu~clear anion [Pd,C1 ]- v~ih th~e reqluired molar qua~ntity

of thle neutral ligand in the presec~e of teten-n-butylannonium ion

Ils..nSg c is- 1 -d ichloroachl'lene as solveln t. A gain treatment of' the

reaction mi:-:ture with ece;css other induced cho separation of the decsired

prod;ui L 3S a C::.talline Sclid. InE;-rodci SpGCirOSCOpic: inVOLStEtigtOnS

bty Adam~..L; and I:ove~rke~rs (29) also served to indicate the potential use-

Fullneiss of che b:inuclear .Inion [P~d2Cg)~j as a prccursolr to mnononuclea~r

comiplexas of p.;lladium(IT) of theic type [Pd(TIT)LC13l by deml Ion s treating








thalt I100 fo~rcel Lcommn~ t fOr the: terninal metar;l-halide stretcrhin

vibratinE. I 1..1:-: yeaer than tlhe for th~e brid;;ing metal-halide v'ibra-

c;.on. TIus, i~t :-.'ould h~e e:-:pced that the dil~erie .Inion [Pd?

r.oluldr oc atta~ck~ed at the br-idging positions by incomingi 10c;;nds.

'. ~ppea red, rhere fo re to be reasonable to t rea t pollych'lo copnllo-

r~Jcate(11 anions utt~h the~ pyridine alcohols i~n an appropriate solvancrt inl

the1; presnce~ of tetr3.alkyl3ammoni~um7 cautions \:ith the anticipacion~ of sus-

t;ining the stabil:ity' of the [Pd(II)(pyLOH)L3 cmpe aios.I

conjunction w~ith this, palladiu.m chloride powdet r wass stirred .:n re-

thri.ng acetone~- 'ith tetranethyllammonium~l chloridei (t;AC1) on a 1:2

nole bsis. red-orange solution initially resulted as the solids

be,2.au to diissolve~;, but as r~eflux w~as continued thle color of the solution

cijsa~ppeare ,d coa sjlmon-colored solid sEparated. This solid w~as slur-

r;.ed w:i thl -p:.rid ylphenl-4-f~-~luoroph;nylmechanalo in recflu.-:: ng solveint bu t

me additional change occurred. iNe-ecrtheless, the incipient formation

of th;e -red-oralnge solution. indicated the presence of n solution-stable

chloroanicon of pnlladiumn(II). Further invesiJtigaios indicated thait

the solution-stable species was [Pd2CL,]- and that the sa!.mon-col~ored

aolid was :Ch acetone-insoluble salt ((tPA)2PdC1 1. Thus, the nature

o~f rhie palladium.(II) poly~chlooanion r!ns dependent upon the concentra--

tion orf the armeannium salt. Studies by: Henry and Marks ('30) upoln

glacial acetic acid solu~tions of palladliumr(II) in the presence of

\airious alka:li me~tal chlorides ser.;ed to ind~icate th31t with readily

I..luble chlor-ides suchl as LiC1, (PdC1,l]~ us thre co7mmonly1 encoun~tere

pallmdium(ZII anion, w~hereas !ith node~rately soUlubl chlor~ides suchi

;as NaC1, the biinuc-lear species [Fd,Cl6]~- oas got. Thereforere it

p.1r;.corecd thant regulation ofr thei tetrrualk'l arnmoniumn chlo-ride concenrnrainn





5i.


JE~iTorde! e.! mthr? d by' abtich ch~e nature o: thie palladiu~n([ll p~olyhl~oro-

.7nion could b!e controlled. The combilnation of pallediumn chloride

powrdelr w~ithl t!LA1 (~1:1 in reflu:-:ing nct~one did inl fact yield comp~le~te

disso~; lution of all solids and a rjtable~ redl-orasnge~ solution. Treatment:

o-f thlI.is =:lutionl wi~th a typical 4-pyrijdyl~et hanlol(:1ihreec

to palladium)) aga:in resulted inl the Sllparationl of a .salmon-c~olored

prcecipitate [(EA~) PdC1 ]j and a yellow solution. !orlkup of che yellow

:olutio~n yielded Lhe bis-alcohol complex [Pd(II) (pyLOHl)2CL2) Thius,

th~e ttt-\ caution did niot appear to b~e capable of stabilizing the desired

un~ionlic mono-alcoholl conple:-: r1gardless of the2 nature of: the polychloro-

pd)l.aldate!(II) pr~cur sor.

Palledium chlcride powder was then combined with~ tetra-p~-bucyl-

o::n~sniu;r. chloride (1:1) in refluxing: ccetone again resulting in th-e

Ees~olution of all: solids and a stable red-oranige solution. Trecatment

of thi.s s-olution wilth a typical -;-pyridine mechanol (1:1 with respectl

to~ pa:lldium) indulced an immediate color change in the solution from

rcod-orange to yc110wd-orange withi the separation of no solids. Wlorkup

of th~is solution (see Experime~ntal p.. 40) revealed that th:e desired

anionic complex [PJ1(II)(;-pyLOH))C13] had been obtainel. Further

studies shiowed ch~at this anionic complex vias re~adily coniverted to the

des~ired mixed~, neutral. mononuclea~r comnpleX by! treatuepnt (1:1) With

the i-pyiidy1 alkaine in acerone solution~ (see Experimental pp. 38-40).

(!!o!: Du~ring the! course of this researchi all syn~ithetic procedures

ilnvolving pa~lladiiium(II) wtre run using~ nectone as so~lvent. Theret are~

ma~ny stealcord methlods for the preparationl of comple:-:cs of pallrd~ium(iT)

c!-ploy~ing alcohol (usuall:. motha~nel or etharnol) as solvent, but inl th~is

.:0crk it was discoveteld thace in the presence of alcohol palladiumn(IT)








was- ifreuientl:, redu~cced co pulladium~ blach:. ;:o sim:il.ar difficult: :; as

enriountered~ withr ::cetorne.)




onr _the Suitability of 4-PypTigypi'hynv~_nvmethane_~ as a Courntedlic:and in the

b~i:nd C1:rypleggs. As reportedt previously (see Experimen;rtal p. 33) the

can~cc.I:. ally obtained alka:ne wacs found to be cont~aminat~ed with trace

quantiities of the corresponding :-pyridll alcohol. To b~e sure that

-,he a'.lkne w:a3 not convetrted no the alcohol (carbeniumi ion) 'ia oxidra-

clonl In 709 HC10,. a solution of the purified nlkane in the acid was

arirred at ambienc temperature in the open environmental of the laboratory.

After stirring for a period of 2 hours this solution waJs scanned in the

visible region of the spectrum and wa~s found to be transparent. There-

fore~ no complicationss we~re e:-:pected to arise d!r-ing the:rmodynamic

scudies upon~i comp~le:es which contained the alk-ane since all such nea-

suremcents we~re made within a 2 hour time span.

The similarity in donor behavior of the nlkane to che :-pyridyl

nic~chols was demonstrated byl the preparation of the- unionic ~omp~le:;es

("'dLC1.] tin sit~u) writh either the alkane or the alcohol. followed by

convrs\fion to the mixed comnple:-:. Thus, the mix~ed conplex~es w~ere

preparable independent of the order of addition of the respective py;~r-

idiine3 donors.

Finally, a small sample of mi:-:ed complex; (any) w.as tr-itura-ted in

70..' I1lC10, for a period of en. i, hou~r. The acid was; removedl b, filtra-

LIon an;I thc lesidue sas wa~shel with d~eioni,-ed water and dried. A~n IR:

.nan o; thle resridueli reveltaled it to be of the same~ consLituenlcy a the

,rilinal nt::ed compkxc. T'his indicated thiat both p:,ri.dine lianlnds re~-

m.iinedi coordinatedI during thecrmedy;nani e sr:~nility i~n..e.tillntion;s nd




C0


at;;n demor~rtralted theC suitabi~l~ity of 4-pyrid!yldi phcn::]lmethane~ as an

orpopra'e cuntrlgan. \'hn thle complex [Pd(II)(P@P)(4-pyLOF~l)C2!c.,

hi' be~en created inl a similar fashion (i.e., trituraterd in 701, HC10 I)

;: wrs fouin: thart thle pyridline ligand (carbeniumn ion) was di:srharged

EIr.L1 the~ corrplex (p. 54().



L~TConerin3 Carbenium lon Salts. Various synthetic roulte-s are available

for the~ preparation oF stable salts of trityl-type! carbonium ions (seec~

the: inrtanlLe, the methods given in theC papers by Sharp and Sheppard

(31l), by Da~ubenl te al. (32), or by 01ah et al. (33)). It may certainly

prove" t" be? in.teresting a~nd profitable to investigate the stabilit5 of

th~e fre;- and: complei:e:d carbenium ions uhich hav~e been dealt with in this

.:ork; as d'L;_isree salt-like species in aprotic, nonreactiv.e solvecnts.

Culrren: t rconside!rrations hlowever, hlave e::clusively, involved the use of

703 HC1C', my an ionizing medium in order to provide a direct exl;tenlsion

to pravi~our; 1.*ock upon trityl-type carbeniulm ions derivecd from the

pyrijd ylld~ipharke:l t hanols.





Thermodynamic Investigationso~l~ and M~easureme-nts



Eilctronnic SCpectra aldnd Carbenumon Constitution aInd Strulctulre. Con-

SideC~rablE. work has been d~one oni the electronic spectra of trityl-type

carboniu:. io~ns In the 200 -- 750 rem (50.0 13.3 kK~) spectral region.

T;hu~ mal:j:?ity of this wor-k, however, has bcon focused uponi the transit-ions

o*l~:Biit~ed by these iclns in a ratheLr limlited portion of th~is re~ion~,

li.. 7100 r;50 nmn (3's.3 -- 19.2 fK), because~ thel- electronic haonds fo~undl








he::.. arer r.hose rchich) are ch.~a ccracescic solrely cl the crrenchnumi lon.

':::1 higher InerCgy transicion~c (50.0 33.3 kK:) exh~ibitedl by thes~1e io~nl

are :Iomally; present inl :hie spectriir of the procurso~r molecules (i.e.,

terci:ary alcrhols) :and are characreristie of thle electronic aborptionrs

of ch:e isolatee; conjugatedl sy'stcas which are bound to the carbinol

Iar,~bon in thie un!ionizedl alcohol. Previous s elci-troni.c absorption studies

cln th-ese tlypes- of ions (e.g., Richairdson (6) and Went7 (3)) including

siraillr studies pe-rfor~med during the course of thlis work~ have d~em~on-

st-rated that the hiigher energy (ultravioletr) spectral. region of these

,lcohicnl remaains virtulally: unchanged for a given alcohol independent

of then nature of cheo solvent. Thus, the signif~icant el ctronic chan es

ibich o~ccur In these sys.items upon carbenium ion generation are noc

lirectly reflcted by these higher energy transitions. Thie dramatic

;:lrangls Whiich do take place in the e~lcjtroni~ic spec-trum of these niCohols

une-al 10ai formation acre illustrated b, the dev.elopenzrt of tw~o intense

(cca. 10 105 lcic mol- cm )~, broad absorption bands ordinarily.

a~pperingL between 300 and 550 am. This spectral region is transparent

for the alcohols dissolved in a nonionizing solvent, e.g., zcetone,

sl~Cohol, or 1 I! HC10 The extreme intensities of these b;1ndS are ex:-

Iec~ted fo-r st-.xongly allowed n a charge transfer type transitions.

As pointedi out by Dunn (34) based upon considerations of the classiicl

theo!.etical workl~ of alllik:en (35) on electronic spectrscopy, the

latensity, o~f a1 rbar~ge transfer ban~d is i:--pectably largec since thle

chalraeic Lensfc` r pheno~meoln occurs overi at least one~ int-nrtom~ic dlia-

t.ance in thle abacohing~ scpecies. Tihus, the radius vector (r) of che

Leonr-itionr is relatively: large. Since the magniturde of th~e transition

L.:.nLn initegr;l1 is dlircCtly pro~portlional to r, and in ciorn directly






62

'!rI:p'L tonll 1 to\ r.hie oscillator strengthl (F) of thle transition, f mnst

.~iL1 beC ]large. Hlenice, the intensity~ of thle tranSitton i; C.onSiderabic.l e

ithe :eneral positions of these trityl-ion chanrge trlns;fer band~s have

be:r. :atiorlalized by; considering thar 3lclohol io~nization is accompaniedt

oy rh; c~onversioni of the system fromr a quasi ev'en-alternalnt benzene

):j dl~ro icar l to hrn addl-alternant, fully conjugated beniene hIYdrocarbhon.

.4ccord~inb to various workers (see, for instance, Deno et al. (36))

bascd -In simple L.CA0 10 calculations this tr~ansformait on introdu~ces a

ZerTO enerrgy. (nonrbonding) 'rsymmetry orbital into the molecular orbital

schemec of the previou;ly unionized alcohol intermediate between the

highest ;ncergy filled ;-a-orbitals and the lowest energy unrfilledl w*

orbtas.T;hls, the e~ncrgy of the longest vavelengthi (lovlest energy)j

electronic transition observed for these ionic species should be on the

o~rder of half the energy of the longest wavelength transition e:-hibited

tl- bLenzicle, the model compound. Since the wavele engt of this transitionn

fo~r benzer.lo is 2'56 rnm it is expected that the longest wa~velength electron-

ic tr~ans~it~on of thie trityl-type ions would appear i~n the vicinity of

5t? am. As pointed out by Richardlson (6:153) the rather inexact nature

o~ this Intratmenat is revealed by thie fact that the longest uaveclength

electronicr aIbsorption exhibited by triph~~;roinylcrboiu ion is 431 nm

(in 961 11~S,l0. which~ is at considerable shorter wlavelength than that

I`r'edictedl fromt the borone model.

An eclectic account of previous investigations uipon the electronic

untu~ire of a1;crgenenium iolns revea3ls that extensive conisideratio ns have

been madlc, b~ut that~ these considc creation are not uitfhouit cerain petr-

p.-!e-:ingi aapecrt.. In 19J32 Schoopfle and Rylnn (37) reported t~hat the two

: distance tr i pheiny~lchlorome thalnl and me thyld ipholnyl;ch loruemothane.c y ield








e:,:,an!ciallyy thc samne visible spectrum wIhen, di.ssilved ini dlchl~oro~ethylone~~

rin thre rcue-ncl or scannie chlo~ride. This prompytedl Newmn. ~ and Deno (38)

-ro conclude thlat hir~s was evildence iidicating that in trinrykachrenium

'Lons no, core thenr two (and perhaps julst one) of the~ ary1 rings could

sin-itoneously participate in resonance interactions vichl the carbonium

i:!i center (the exc:cyclic caribon atom). Compr~letely s:;nch:ronous resonance

srtabiization of a triairylc7rbaniumn ion involv'ing all1 of the aryl rings

,~uld of course require an all-planar molecular ion configuration of D~~

syr~nlr). Lewis et al. (39) had already, reported as a consequence OE:

;.tl:ies onl cryatal violet ion (tris-(d inethy.l-g-aminophonyl)l) -methyl ion),

thaL thle tl~l-p~lannr configuration of the ion i~s not possible owin= to

3rteric interactions between the orthel hydrogen atc..:s on the phenlyl rings.

These workers had speculaed On the existence of tiwo isomiers of thle ion

having str-uctures akin to a syrmmetric and an asymm~ietric propeller wherein

the~ p~henyl. rings wetre the blades of the propeller. ~The pr-esence of two

intensr bande in th~e electronic spectrum of crystal violet io? suipported

as~- proposal tha~t each of th-e tw~o isomeric forms; of :Ihe ion wras a distinc=

chrsomophotic systemr. Additional evidence cited by New\man and Doeno which

suggested the structural unique~ness of tricyl-type ions wias the following.
Tt i-a-tolylcarberhnium ion was reported to be as stable as tri-g-tolyil-


ca~rb~niium ion ;nd to exhiibit esscencislly the some electronic spectrum.

Shis w~as an une!;pected result o::ing to th~e considerably greater degrree

of; irhibi~tion towalds ring~ resonance stabilization of the ion anticipated

for ithe tri-o-toty1l ton as a conseq.uenice of stceric: interactionl b~tween

the~ o-methl J grouips. A~lso, sran't HoEff i-factor dtat on solutions of tri-

p-Jlimaichylam;inophejtny~clcabinal in 11:001. H,SO, indlicated th~at eve-n in this

selongly. acidic med~iuml one of the p-amninoo grolups; uns n~ot protonated.







;'its su:ppostedl EhatI only one of the rings wa~s involved substanltially in

resonan:c:: sabiiSzil::ion w~ith thc caution center. Othecr I~nvestigations;

ie; Not.--nn ,Indl kno on the electronic -,pectr? ol' valriolus carb;-ntum ions

revented~~e tlat. the observed haind positions wIere sensitive to rchanges in

!Ihocryl ring sulbstitution. .rttempts to rationailize these han~d shifen~

p~remIi~sed! m~aily on resonance considerations wJere inconcluisive. Further

streets :o rationalize the observed differences in band intensicy and

position, inl the Ele~tctrnic~ spectra of various series of relati:d aryl-

r.crbenium~ ions by Denor, Jaruzelski,, and Schr~iesheimi (40), mret wIith

1:mtedsuces.These wJorkers discovered a systemaitic spectral trend

ch~aracterized! by an i~ncrease in ma- as well as in band intensity re-

sulting frrom Iingl: arb sub~stitution of any of the giroulps, -N~(Ch3)2' 2'r,

-OCls, or -Cl, into0 the para pos~ition on one of che~ phenyl rings in

t r iheny tea r;'co unn i on. T he crend appeared to coincided with e:pecta-

tions continge~nt upron simple ex~tension of the 7-el;ectron donatingl, con-

jugnLed rsystrem of thle substituted cacion relative to the triphlenyl ion.,

Hul.'et-er. Succe~ssiva para substitution o: these groups on subsequent

phenyl rings in a given ion resulted in discontinuous shifits in una and

in mlolor zbsorptivity. In 1954, Brannch! and H~albar (G1) studied the

elec:ronic spectra of v3r1ious ara~r-aminotrip henylcorbino~s in 96:1; H2SO I.

The~y reported ;hat each~ of the carbinals which was converted to its

rcorrespon~ding carbocnium ion upon dissolution in the acid exhibited two

inltense: handsr1 in thle v~isible- region of the spectrumn whiich hadi not bee~n

foundrt to be present in the spectrumn of th~e parent echrinarl. It is

intercut~;ing to note, however. thant those woirkers reportedi no sulch ban-J.

Icor tri~.-l-d imechllamlrlinophnylcarbinol iLn th~e acidt and co~ncluided in thiis

in.;ta;nce that carbocniumll ion formatcion had not occirried (c[. the resurlts








?; Nocrm~an and~ Den. (abole)j wi~th re~pect to their inlvestigations on thiis

n-ri: I1uj~ larT cabinzl). Er3.nch and~ I'albal rleco isolatedi a trend ;in hand

postio shftr frm teirdat. hey rationalizedl thalt inicreases in

rr-;Lnance~: stab-liiati'on ofE a given carbe~niumr ion rcsultecd in aln ineCCCas

in l.hc fre~quenlcI. oE thef han~d associated wJith tha~t partiiular: c.irboniulm

Lan Chronophere... TIhe Simle~lst e3xample3 of their consid~riltion is iLlus-

t-.ated by comi~puting the relative positions of ma or the ionic species

(ql)CHt an: (C6H5)3C+ wherein "nax(di'phenyl ion) < ma(triphen:;l

ion.). Crunch -nd Ilalba had attributed thij abso-rptionl to the (CgH5)2C+

chrlomopher~e. Tnuls, these worker; concluded thzat resonanci stabilization

of th~e (C6 :5 ?C chromspholre in the trit!1 ion bly the presence of thec

"t~hird" phenyl rin~g resulted in a blue shift of C ranch~ andi Walba
m~nx

aliso cont~e;~nde that trity1 carbenium ions e~::hibiced twn .isible~ region

absorp~cion bandlis (instead 3f b~ut one) because of two rer ieiumi ion cnn-

tin~in:: chro~mophores believ.edl to e.-.ist in the sterically~ hinideredc parent

ion. This was in basric agrezmnen v..'ith similar considerations made

preioulyby ewi a al (3).P.elated scudies in this Larea by E.anrs

a~nd co-forkersn (42) provided e~vidence: pointing to thei existence of a

relationship between bandl intensity and resonancre interactions in tri-

arycabenumion. hose~ inv.estidators reporrted thait Parai Substitution

oF a1 glv;n group on a phenyl ring in triphe~ny lcarbeniumn ion rESHltCd in

a notable increase in c. for the main absorption band nE chat parcicular

ion:, w~hereas- the corre~sponding; ortho substitution of the samle group

resulted in a marked decrease in a for the snrme bnnd.

Studieis by Deh1 et al. (413), and byr Decin at al. (36) serl.ed to in-

'.aoidate a number of thec earlier .irzuments concerning thle interpretation

or Li,- electronic spectra of tr-ity1l carbeniu~m ionrs. ~ehl et al.1








cun:lr ldcd frol:m pir,r investigations on \arious denICt3erae triphenyt-

c~:.choo.'.um io:ns tha~t the~ three phony.l rings in thle eitio~nic aggr-~aega

:Ire :quivalent. Th~is result sueggsted thate analyses of th~e electronic

spe:irarc of such~ io~ns would require the' contribution of any, trity'l caT--

henumioni chrom~oihorec to thle ion as a whOle, therefore denyinz the

po.ssibili3cy of simultaneous e:-:istence of two (oL m~or) chiroa.ophores in

th1-e mole~1cularr framework- of the ion. Deno et al. performed simple LCAD)

.-20 Cal1cula1tions on ary,l cations and found that the results of tle:;e

c~le:laionsj~,, prd~icted identicall una positions for thie principal e-lec-

trocnic abso;\rpt~ion ~Ehibited by~ related mono-, di-, and tria-ryl cations.

Thuiis, inh~!.ibiitton of r-esonance~ in a s;terically; hindered czrbeniumi ion

.;old =.L)1 eav umxrdlculat ed) unchanged. A~lso, these calculations

in-li~ca:od tha~t th? initensity, of the principal absorption for such ions

-ls isl.arIant to phenyl rinig rotation (due to steric interaction). Hene,

thes-e authors LoIciluded that electronics abtsorptions e.hibited bty suchi

ions could not be used as a measure of sceric inhibition zo resonance

inlteraction ex;isting within thle ion. In y~et a later article, D~on (44)

has again~ pointed to the irresolute naiture of the situation n in comme~nting

tha:t much of the work on the electronic spectra of ~rylcarbenium iolls

still requires rcavision. Olah et al. (45), as well have concluded that

there :is a great deal. of uncertainty; in the literature citations con-

c21rniing the visibtle and ultraviolect spectra of carbconium ions. Interest-

ingly; enough1, hoGwever, in order. to cationalize some ofl their results

thetse workers employed the\- notion that in a sterically:, cr-owded triary-l-

L~ ;crranium ion only twio of the acyl.l substicuoutss are p~art of thle absorbting=

-0.omrophlore, whllieC the third funccians ais a cross-conjugatntini; eketroni

d a;nor or necceptor moiLety. So, once Jagii thle possibility of the exristcn~ce









ofl mu:liple C::ch..ro.phore~s in critl.l-type echireniumR lons is connaidered.l

l'nue.. as laite -?sc 1956, ma1ny of the nroblemsl resultinn~ from uinEsatisfaccor

inte~rpr'tat-;ion of t-he electronic ;pecctra of carbroinium ions remaninedi.

To a largely degree, recent inv.escigaticns inl ;his area rely headriy

uponl nolelarC13 oriital treatments of Lhie electronic ;tructure of 3ryl-

.n-.achlani io~ns. Streiti-riCSer (-'+:226j-230:) has shos;nr that in thle iL:O

3pprel:-:imai on the lowest eniergl, t'ransit'ion e::hibited b~y triphonyl-

curl:0nium Lon can be considered co be associated with the pacssge of

al ~lecsron 1:romn the highest occupied: bonding 010 to the viacant nontbond-

iiig ;0 in the odd-alternant hydrocarbon created upon~ cation ge~neration.

In a first appro:-:imation thle energy level diagram associatedl :-.ith this

cransiciann is~ the fiame 3:s for the benr:~:l cation. Varlou!, mlore? sophisti-

cicare tl treatiments (46:360-?36) ho::..ever, reflect the comiple:-: andl imibro-

2,110til natu-re of: this approach to the problem bl: calculating rather~

gronsslly difEcrcen charge densities for the w-framesock carbon atomis in

cthe- ground state of the trit:.1 ion.

By em~ploying~ :1 and resonance theory \-laack: and Doran (;17) actempted

:3 correlate the effects of neth:.l group ;ubstitut~ion in add-al~ternanit

an~ions vich; thle resultant band shifts of the main absorption hands

found in the electr-onic spectra of these ions. They noted that this

'!ipe of~ substitutionn (i.e., miethsl or alky~l) on an ev.en-alternant hydcro-

carbon h3ad - in the absence of ste~ric: aff~ects - aluays~ inducci a recd

hife in the dcctronic coningatio~n bands, whercrns fiimilar- su~bstitution

c.n :I r.onalr on;:nt h:drocarbon ha~d indluced cither a rced or blue shiftt

dr-p.:ndl!! ng upon the3 sit~e of sulbsticution. The-y reported specctral

changel~cs fr~ thle odld-alternanc anion, to be scimlar to thiosie for the

nonalte1 rnant31s and e:-:porien~ce qualicacive success in applying ch!e








rr!sults of their cailculations ton the prod~ict~ion of thle speictral behavior

;II odd--clternant. ion~s. A\ p-articulsr hig~hi.ligh of th~is cEffort ulns the'

pIrct~ciction thou c:-;1Llky1 su~bstitution on an odtd-~l~tcrnant cation would

result~t in a blur shiftt of v c;bichl is in ;Igreement \:ith re:Porcte d can.

A ratherl comprehoulsive MO1 treatment by G~rinter and Ha3son (:8) vteld:ed

.1 rjame~try-bab~ sed nerg:. levtel diagram for struccurally ;omparsabl ary~l-

ncrthyl ions. Ani ex~amination of this energy, level diagraim rev'ealed th.7t

C:'r longe~st waveleng.th, loweFst frequency transitions for a related bi;s-

andr tri~.magnethyl~: ion pair should be~ approx~imately idelntical (cf. thie

conclusionrs reached by D~eno et al. (3))!. iowJever, stemmiLng from ru:ore

acute considerationsns these authors shot-:er that the g~rounld state

Ih!arge stabl~iilzaion of a giv~ern triaryl ion was greater than: that for

1.he corresIPodndin biSaryl ion (recall the conclusions o' Cranchi and

U~llb8 i(Il), p)p. 64-65). Thus, the highest occupied bondinG MO's for

the~- trisary1 ioln weJre somewhat lower in onergy than the related~ r.O's

a: the- hisaryl; icn, and therefore, the longest rave'length transition

of. the tcisaryl i.on was of slightly greater energy than ther correspond-

ing tralnrition for the bisoryl ion. The dual nature of th; visible

region~ absorption envelope of the crisaryl ions uns also considered by

Grinter and Ma3sonr. Their ex:planation ran as fol.lois. In the point

grroup "Cn (following from the anticipated propeller shap7e of those

ions) cho! highest bonding ;O's of the trisaryl ions are "five-foldl

drgenerate," wdithl the 3tcendant1 sy;nmcaries e, e, aind. ;2. Tlhe M11Osof

thle fIrst excited state(s) are lil:ewaise live-fold degCe~nerte, and are

o~r :!L. ?I at, and a symmetries. .-;gain, p~rovided tha;t the~ ion is

pro-pe!llerc shapedl, transitions to the 'A27 and 'E eci;sted termls are

,::Lieved and sh!oulld be polarized para~llel and perpendiiular respectively,









co r he pr ine @,il thre'ie-fo.ld s:,mm~etry. ex:is of the ion. Ti perdt

b~e ini bas~ic ag~reemehnt uJith simlilac- consideraciions whtich~ had7 bee~n madre bv~

.!:;.ls anld ieldsenlc~p (:9) on the~ pheno~menon of po~larization upon the

transitionsr.- in theC electronic specti'ui m of crystal v.iolet anid ma~la-chite

greer.. Thuis, Crinter and Ma~son concludedr that two~ lowr tnergy: transitions

ofr high incenisiL:; nre e:Ipectei (andi are found) for such ions. (It is

herec appropriate to point out that resultS of nevec~ studies on the elc~-

tr~cnic abso~rptiin spectra and magnietic cir~cular dichroisn (MCD) of tr-i-

p:~.niew'uricar'eniu irons have suggested rreinemients of cectain. of the con-

siLeraitions ~ae byv Gri~nter and ;Iason.. No et al. (50) found~ three HCD

bands in thc nea3r UV:, visible spictrum of t~ripheny,lcarbenium ion. TIhis

risul~t irdijca~Ted thu existence of chrree electronics transitions in this

tpect~ral region for trityl-tlype carbinium ions w~herass only tw~o such

bnds er,e propo~sd to exiist by~ Grinte~r andi Mason. Dkkr n ila-

vani 100;. (51) in fact have~ stated that n10 theory dloes pre~dict three nearcby

sing~lec + ainglE;t transitions for a trioryl' ion of D3 Symma'etry.. Two

of these three transitions are to excited states of a syrmmetry and are

polarized in the w,y-plane of the ion. (This plane is defined for an

aLSsuefd! coplanar arrangement of the aryl rings and the~ execyclic carbon

;co.7. Th~us, the ar-yl rings are perpendicuLar to the principal symi~metciy

ex:is of the molecular ion, the 2-axris.) The third tr-ansiion, howlee-..

Miciih is- to a r~cotE Of 32 .cym~meCtry and z-polarized, uouldl not bre observed

:if the cation w~ereL comp~letely~ planar. Since the cation is propeller-

:sh y-ed a nd not planar, this transition is observer~d (act slightly higher

t~~ilcquency Lhanl the higher ene~rgy intense~ band), blut it is considerablly

won'.;!:r~ than either of thle highly' allowJedl cirnsitions co the ae staces.

:e L.; 11lso note~..orthy th~aE ttLieS jinVEictignoers ere not able to re;solve-:








thec 1.:;o a ,'.re tra~nsitions vMich :Ire (observe( r.o ovelaT=p rathler- .evere-

ly, (.an ici: ,lre at 23.2 ?nd 2!4.6 kK~ respectively ~ith1 a reportrJ c of

35.1-r o, ach ba~nd (4r5)). Th'iis Siggests an inhereni: relationship

bert?-...en theC eleict~ornic staltes inl the ionl from whlich~ thesej two~ b~ndl s

or;igin toc. Cornsequences of this implication concerning the chromno-

pha~r~ic n.Tr.ure- oE trincyrlcarbeniiurn ionj lie in thle forthlcoming text,

.ide infra.

It is nowa interesting and profitable to c:-:amine the u~nve functions

for :ihe iool~icular orbitals which wJere considered by Crinte2r and Mansoni

to correspond to the energy levels which arise upon generation of a tris-

nrylmnethylcarbe'tius-1l~ ion. The forms of these wave functions are:






= (9 -l I ,)/ 2 {6
11 ry ary1





and




II' aryl ary' -2.rl,// 7



whelre 4 0 is the~ wave function of the? 2p state of the e::oeve~lic cirbon

atoml. Thle JI unctionls represent: the highest occuipied bonding states

of the ion, a!nd their forms indicate that the bondinS contriburion of

tthc "lth~i:rl" arryl i'n (1aryp) is of princ-ipal significance in I! ,.

([jote: The Ibasic form-s of th~esi ar~e functions are virtua:lly identical

rio thle corriespondingi wa.ve- functions usedt inl the onlcullations by Dcekklers

uniCooma-va 1.yt(51.)Since tile deg~eneracy of thle ?IT functions









h3'1 ::een1 remove~J co an a~ppreciable degree by virtue olf thle n~onpl;e:rrit:.

O~lL~ th oui (AS); nord by configuration interactiron offects (46:227), (.51),

it fol.lowJs that only~ one! o: the Irlon w~avele~ngth, loui energy tralnsitionss

t:-:ou!ld r;flect ri~nif~iccnt electronic contribrutions to carbeniate ion~

stability (or instability:, as the ,ase~ may be.) by; the~ so-cs!lled thirdr"

rling whliich is ~ciuoted abovec as nryl" in equa3tios..s {5) and! (;). This

cconsidererr tion is giver~n aditional substance fromi the resullts of various

investigarltions Earker and coworke~irs (52) studlied theL electronic spectral

of derlvatives of~ malachitet green produced by. substitultionl in the "'non-

aniilirno"' phen:,l ring. They showed that the longest wanvelength absorptio~n

Wi::ld reco~rdedi fo~r e~ach deriva3tivec reflected primarily a flowi of ele~ccrns

from the~ two para-II, N-dimethyll subs~tituted rings towa-rds the exYocyclic

caronatm.Thi~s is in keeping :with ;10 calculations wihich~ havre esca3b-

li:;hcd that thlis carbon atom bears the principal degree of positive

charge in the ground slate of the ion (53), (an expected result). There--

iore, rep~lacemen of thie para-N!, ;-dimethy~l groups lithh poorer electron

~releasingl .ubstit~uents resulted in a blue shiift of v heewokr
max

also demonstrate the existence of a linear relationship betrien the

appropuriatei Hlamm~ett constant for thie phenyl ring subscituen~t and the

magn~ii~tud of sh.ift: in VI inducedc by thiat particullar substituent.Ths
ma.-:

Scypet or i:ross-conjugaticaI s~eems to exist be~cween? th!e phienyl ring and

the~ rercinder- of che conijugated sl.scem vith respect~ to thle energy. o;

ci.- lonS=.st wavelength h transition.1 TIhe resulcs of: scudies b]. H~opkijnson

and~ Up~.tc (SA,) concerning; substituent effects upon the~ electronic ab-

Carlpt;3on.of phr-nolphlthaleini monoposlicie ions (Figure 5') allowed- these

umo'::I:Ls to conclude tha3t umv of thle second longest elcoconic transition

:.:tlhiiced by these ionsi refl;ecc roriimarily~ a shire inl electronic dlansi;t:








Frn.:.T ilhe "lthird"~ cing~ towa3rds th~e exorcyclic arb~ion atomn. ZIn phennl-

:-hthakl~in this "third" ring is the ring: to w!hichl thec or ho-canrbo.-.ylic

rid groupu is attached. Hlopkinson; and Uyat~t alsoi compared~ the elec-

i -ocnic absorpril~ion spec tra of phienolphthlenlin an~d phfnnlalulphonph~thal~ein

and~ observed~ a considerable blu~e shift of the second ban:d for the

''*-lphlo" containing phtlhal~ein. This was expected owing to the~ apprccia-

blei electron ;i~thdrav~ing power of the sulphonto acidl grou.p. These results

wer~e rorro~boratec d via extended RMOlc calculation s to resolve the electronic

offects rwhichI 3Lise from para.-s-ubstitulti on~ of n-elecctron donstine groups

oni two~c of the phonyl rings in trIiphenylcarbeniuml iun. Furthermore, the

render.:LC of tneCe c~alculations were found to be in agreement with the

rtnit~. s of thi. HNO c~al~culations which had been carried out by M;ason andJ

*Driever~r.S (-s).Dasalciilacions also verified that suchi substitution

oi 7-1Jrchrrron Jonatin2. groups ser.'ed to re~move still further the de-

::tneraec:, of thle twio highest occupied MlO's in trisryl-ty~pe carbeniium

ion1s (see r. 70) G'ith the higher energy oc~cupied rIO acquiring a greater.










r, ' R ; -COO)H
r 'w I R' =-CH 3, -C1., -Br, etc.

,IrR / = -Cli3, -CI, -Br, etc.


Fi. .Phonol~phthaleinl mnopnositivec Ions~c








:I--!.-lctron cj:ILrbution: from~ the rin~s wlhichl bear thei m~ore IpotenC c100-

::IIr a ce~leasng subsrituents. C;-n equentlyltl the conIclusions rachIled

\::;r 1i~lch ita:~tive.l1; associate t~he two3 priocipal1 electronic a~bsorpLions

of ieibry.icrhantori ions vitic the rOi's from wJhich thlese trransitions

orrigln,:e (,p. 7;;) have been upheld. Inl addition, Hlop:inson and Ilyett

:-~so isolated from: their spectral da3ta a linear viari.-tionl betweenl

Ha.mmettE c-meca s~ubstituent constants and sh~ift magnitudess of the higher

enrgr1y elecr~ionic band produced upon the subscitu.tio n of groups ortho

to thle ringY hydroxy:.l groups in phe~nol~phthalcein. Thus, whereas the

results obtained by Barker and cowo_rkers (52) indicated a cr-oss-con-

in~patio~n eEfect to, exist upoln the frequency of the lower energy band

.ud.. ch~e "rchird"l ar:.l ring, Hlop~~nson and WJyat= showed a similar effect

upon chr frequincy; of the higher energy. band by' the tooV ringS in a

Igivetn triaryl-'pe carbenium ion which are the plrimar (as compure~d

to the remanining ring~) ii-electron donating Inoieties.



Finally, it is still not clear whether the higSh in~tensity elec-tronlic

rbsoirption bands ex;hibited by triary-lcarbeniumm ions maay. or may not be

considered rigorously as charge transfer transitionis! This concern is

no~t cruicial to th-e considerations madle in this work; but for comnplete-

ne;Ss a7 favJ remarkS shall be tendered. Initially:,, inl th~is discussion of

electronic sp~ectra, it: was1 assumed rather tacitl. that thiese electronic

Lands are charge transfer in nature (pp. 61-62). H~ow;evr, these ab-

Lc~lrptions do not moor with~ certain of the criteria? (:5) which have bee-n

.-iplioedi for clrssifyin g electronic transitions as chargee transfer."

Coach (56:6~5-56) For instances, has poaiinted out that? tooe facrors tendling

to indicate charrge transfer interactionsl; inl nonouryl tropyliumr ions









:;prov. d Lby Couch to c::hiibiL in:tramolccular charge transfEr)r are elthcr

not: pre~Sent, or' are; opp~OSite, in m~ononeyr)lcarbenturr. ions~. F~ur thermcre ,

Iela3toe studCie by' Coluch (57:113-122) hav'e suggcstedl thart triarylcar-

ben:ineu~ ..ons :-1. wJell do not eXhlibit~ bona fidle charnr e transfer in~terctionE.

Dau~ben and Wilson (58) hatre at las: dtenolistraited the e:-isconlce OE au-

thieitic charge transfer interactions for sy.stems containinzz trioryl-

calrbonlrum ions. Th'ley accomrplishe~d this via the~ preparation of varice~s

pl'cene.~-; eing!lacrbeniumrr ion complexes whereini thre coordinated carbeniun

ion! wer foundi to I(unction as a particularly potent Ti-acceptor. TIhe

elctr.ollic spectrum of any of these complexes ga~ve a very intense band!

at re~l;?tiel:. 11-.w energy (Iizl. 1;.1 kK' for coordinated triphc) che~nylrbeniu

don) wlhichl wa;s not present in the spectruma of either comp~onentc. Th~ee

resullts -ingly that th- existence of a1 "true" charge transfer initer-

actilon in a sysrtem requ~ir-es an apprciable shift of electron de~nsity

from~ a sp~crifi~c lorcationl in th~e ground state of the parent moltlcule

(:;on, etc.) to a neu (and removed) location in tle c:-:cited state..

Perhaps then, it is in fact not extremely unrealistic to treat thle

principal electronic absorptions of arylcarb~enium lons as charge trans-

fetr. Raimsey (5S) has alluded to this assumption by suggesting that a

chacrge! transfer cransir.ion in a triarylborane can be assocriatedl with

thei promotion of; an aryl ring n-electron into thre empty available r

orbittal on tli~ho boron atom. Similarly, since the results of various

urudies on the electronic specccra of orylcarbeniumn ions ..ave asscriated

thc m~ainl aborprtionl bands ::ith transfer of aryl ring :-electron

Julneity to th~e exacy'clic carb~on. thosEC transition s may~, ac .least broadly,

ie incategoried ;Is charge transfer. Argume~tnts conitrary~ to this claissi-

fkatiion can be~ rlegiste~rred hated uponi degree OE charge riransfer.. For








1Ci


.ia~~ll,;C I:u rcerbonium; ions; has demconstrated that: thec de-ree of e'norge

reloclco ; tion~Lcl int~o th~e scryl rings in thlese ice is substantial. Thus,

c-lccrronte Tgrocnd srtate charge deloca~lization in these ions appears

Lc bl con1siderablle. E::t,7nded RMOI cal~ulation1s (514), how;e.er, havre

in~dicatred~ an appreciable difference in carban atom cha~rge densiLies

;b~~ecren rhe ground and first e;:cite~d states in arylcarbenium? ions.

Let~ it suffrice, therefore, to say that this aspect otf arylca-rbenium ion

ejlectronic- spectrl investigations remains largely a moot issue.



An examination of the electronic spectra and attendant data collected

durcing this workk is now in or-der. E:-:amples of~ electronic spctrLZa ob

Lined for ca~rbenium ions derived from a related secies of compounds,

namelyp;LUHPJ(H)(yLOH)( )012,and P'd(II)(py~LOH)c12(uer pL

equa~ls :- pyr idy~l-:-methylphen:,l-l4-f luorophefnylmetha nr:l, and Lr equals~

d iphcnyl-:- pyr idgmefthane) have;t been presented in Figures 6 -- 3, p. 16.

As these spectra are represencaci?-e of all electronic spectra recorded

iar the iarbanion: ion species considered herein, no other electronic-

spoetra are prcrsented. Pertinent electronic spectral data are gi.en

ini Teble II, pp. 77-78).

Thec carbenium ion electronic ;pectra obtainecd in thih work are

foundl to t;- veLrj. sinflar to the relatedl spectra (in the same sprectr3l region)

whichsi hav.e beenl :-eparcecd bl, previous inv.estigators (R:ichardson (6) and

k'ets 8)) A examination of these :;pectrai reveals Ehe p~rescoce of tw;o

br~oadl, intienlse absorption bands- 1loscatd within the 33.3 -- 18.2 klK rainge.

Thelone e00 nerrgy band found in thie Fpectruml of a given cairbonniuia ion is

alway~;s thec more~ intense. The r- values replorted in Table II indlicate















??







33.3J 28.j 25.0 22.2 20.0 18.2 17.;

Fi; 6.Visible spect~rum of the carbcnium ion derived from 4--pyridyl-:-
Il-lch,lpheny,?-l-E-luorophenylmechno in 703 11010 17 ,~ 20.2,
29!.7.ma













I. I











.. ..---- --. -- ------ --- -- r 1-- -;-4--:
?3.3 23.*\ 25.0 2.2. 20.0 18.2 17.;

F l. 7. Visible spectrum of the carbon-ium ion derivecd frcon PdGI)~(pyL.OH)2
iLIC12, Mohre p;LOHI is :-pyridyt-4;-mothy).'phonyl-:-fluorophnl
:.l _~~ncInhanal, in 702 HC10 17,ax, 10.6, 27~.7.













OO

CU



OC

* F -

U) *r 4


iJ
enl


e.,
O
lJ



,,"A
C

'


S C-
.i

j jo


CF

C..



C











CT
a









































G-.-

II










o*


=



i i





















*ii


-r




:
IJ























ri


--I F r-


C





T~ L











II
I. 11
"- E.**


.--I










-- O

C-

r-


CL
tr O



co








-- -d O


CLO
UC -,.
i,- C
C ,-


















C1





-a
...


r(






O
v--









-r-
c



O







C
O









MO



UO






uc
u cr






aE
Orr
o




to








'U e---



H' O
U


rJ
O '
OU




I U







I n

r-

"O 3

O

I: :


I C

r 0






C5 '


~ c



:O






I ~

-: E








: O















O




V
F -

E
a




I-
0
U (


M 0

H O
O

0 H O








rJ sJ rC


("t. --, O











n






N CI1 rn




rCo 01CO








CC so rc


... N
.--too














r- CO l1



N2 C
r-- n
u .
Nt l
em a

"C i
O *-4 ~
...1 H a


r- M




C) I I I


0
O I I I
'ri


314
O -I c

O






0 U

!j -



CO




N P

I N N












O < Cs









~ N C








m m r"


















em r

>. > c











.2I I: I
w. <7r :-7
I I I

la
i I I


.
wr
O







C



O
-e-4

"S







O





CJ

C


e-1



O
C-I

E




ra

0

o

0








-e-







U)

CIJ


C

S.






Ln



i 3



t-'
0


-
*C

*M



O


*H
r





-1










L,

0

!
r

r
u

0

>






O







C~
-e-


u-1
r.









.-I




O


-e1


r- 4

,

E

L





.c-








t;.i di:ecti*:. Th~is balnd is thle so-calledr "'::" cloctroutei b~nd so

ci..:-m~iie! byi Lewis and CaVlvin (60) 11n an elegant ...ach: on th~e color of

organic compoun~ds. Similarly. the~ highc;- energy, less initensc (in this~

casc) ba-nd, is I:isbledl the "y" 'cand (60)r. C-rtain r-elev~ant ctrends are

e~~rstali;hedi by. cLbe spectral position shiifts of LheSe~ malin ablSOrptioni

brond ; s :ich oc cu r upon proceed ing frIomn R = phenyli to R~ = ', -wrot-hoi:-:yphenyl

(*,ee Tablel II) ior a related series Of carbenianil ions; and Ecomt the

roo~~parison of the spectrum of a free alcohol carben~ium ion to that of

th- correspondingly comiplr~exe carbenium ion. A~n inspection of the

rl.snec~tive 'J values (fable II) reveals these trends to be the
max



(1) For Iarbienium ions de-rived fromt a family of preicurr ers (eg.,

the Z-pyridy:l alcohols, the I-pyridyl alcohols. ctc.), in proceeding

fromj r, phelnvl to R = ;-mett ho:.:lrphiendr v~ of: the x-band decrearses ca.

(;.-' L\.5 :.K f~or the free alcohol ions and ca. 0).9 1.0 1kK for the

co-rple;;edi alco~hol ion~s. A~nd for the 4-pyr-idy1 ions the :i-ban~d \ma for

a given free alcohol ion is lower than that for the corresponding

cumplexede ion, cich the d~ifferencc e in related :<-band frequencies dimijn-

ish~ing in going from r, = p~henyl to R: = 4~-metho:-:yphenyl Thus, whereas

the~ x-bandl v' is at 20.7 kK~~ (free alcohol ion) and 21.3 IhK (b~is-

comple::cd ion) respectivelyl for R = phenyLb it Is at 20.2 1-K (f~ree

,! b ohol ion ) a nd 20.3 kK~ (com~ple:.ed ion) f or 0 = 4--m~eth1:-:]'pheny1.

(ii) Mak~ing the~ same comparisons as in (i) (a'oove) On the relative

3 -5,.10 vaxvlues coveals that proceeding from R! = pheny~l to R: = 4I-

ns--hr.::yphony?)l results in a concomiitant increase in vma. of ca. 0.7 LEt;

b.!t this~ doe~S not include the Fr-ee 4-pyt~idy1 ions 1-.ehere an increase in

:---hand um of only. c3. 0.3 kK1 is e~ncountered. And. in thiis case thle








e-anaf or a! given 45-pyridy1 ionl is found to ber higher usuallyy

LI.7 1.0l l.K) thian thle v,-band v of the correspondling comiple;:.d ion.

He~re,: however, no a parent trenid exijsts in the manl~icules of ob~served

differalceo :in~ :-ban;ird Vmax: values for a replaced free ion -- co:.l),:;, ..-d ;on



(iii) A co-parison or' the X;- andl v-band vI values of ai from-
ma

2-py~ridly] ion anrd corresponding 4r-pyridy1 ion shouis that for ai givenr R

group-. 1 alway~js lowetr for bothi the x: andl _, asorptions. (o
!185:

Thil:s pa~~rticlar: trend was ailso e:-:hibited by, a related series of 2-chi-

are:ly. vs. 5-tht~azolyl carbenium Ions (8). That is, the x and y ab-

sorroc.ions. e:-hibitedd by, a 2-thiazolyl ion vrere always' found to be at

.aerathan the samen absorption~ for the co~rrspondin~g 5-chiaizoly1~



Fojr rcnvenien~CE and simiplic-ityl these spectral. trendrs are suremari::e2

.in the immetdiatlel y rsucceeding s~tatem~ents. The~ effctr of proceeding fron

ri = phe~nyl to K = j -meth~o:::;phetny1 is ref le cted by a barthochronic (recd)

shift of the x-h~and and an hypsochromic (blue) shift: ofl the y-band.

A-rd, the effect of coordination thle calrbeniumn ion always results in an

by~psclchromic ::-band shift and a bath~ochromic v-bandl shift. It can

n'ow~ be sh~oun that these results are quallitaltively in accordt vithh con-

siderations madle previously~ concernling the electronic spectf8 Of ary1-

carbhcnium ions. For instance, if the energy, of the :-bandl transition

csxhibitedl by) pyridylearbenium ions is dlependlent primarily u~pon a flo:,

o r elecr.cous~ Lnouards the c:-:ocyclic endocn atone from the ary:l grouip(s)

whtlch are IE pred~o'ninant electron releasing capab;ilit, it is exp;cted,

aInd~ found, chlL heN OnfrgyJ Of Itiis transition is reduiiced upon replacing

;I phon~lyl u!~lh I: 4-methy~:. phonyl,1 or C = j-m,7thoxyphocny1. The









sub meant cr~~ ~os3-conjurigationnl eiffEct of this E: subat:itution ort the1

Lni.Cgy orC rhle :,-ha~nd cransiti;on is illustraired byj the~ colrospondicgg

-band1i blue sl:ifL inl thie spectra of a re~laed series; oE ions. MoreT

ivourl':sltnt to thlis work.~, howeve.rT, are the ban~a shi;fts uihic~ takce p1lae

as : cnsqueceof complle:-.acion of a given carbenium i~on. It follolss

rhat. if the transition L-nergy of eiche~r or both of che bandss (x~, andl

ot, y) in ihs spectruml of a p:,ridgeal.-rbenium ion is ass~ociated, at

leaJst rou a degree., wiith a flowJ of electrons frcom thle pyridine rinl; to

cha. t,::ocyclic carbon aitom, any~ change- in the electronic narura of the

;I:.ridine~i rilng makling it a more effective electron releasing moietl'

bo:CH:r result~ in! :: loverir-3 in o~nergy of thar (t-hose) :.lcrtron~ir bandlr(s).

;Ieithermrlel~r3 it is reasonable co e:-:pect that the coordinasted pytridine

ring uiould in fact~ be a better donor than the pyridine ring in the

uncomlexed?:~ ion as in 70.' HC104 the ring nitrogen is certainly protonated

in the free ion, vide infra~. Clearly then, any diff~erence in these

situ.ations should reside in the fact that in the coordinated pyridline

cIase~ electrons flow frorm an oscensibly neutral rine couiards che e:ocyclic

carblon; wherea~s- La the uncoordinated pyridine carbenium, ion electrons

ami required to flow, fromn a ring which already: bears a positive charge

(t~he proton) resultinrg in a comparabls unfavorable energetic trans-

focrmition. IIoui, since co~ordination of a given pyridylcarbenium ion

results in a blue shift of the :X-band, and a relat~ively substa-ntiaL red

shlift of the y-band, it appears Lo be the case t-hat the yr-bnnd transi-

tioni onergy is, to an appreciable degree, paronymously related to the

pyridine ring, and therefore dependent upon its electronic nature.

'Ihee ariumnents, of cour'se, serve to indicate thoc che p::ridine ring








adi~ 11, (7 0 resented prevriously (p. 70). So ro ual~t~itatt

n!.::napoke~a it it: reasonable tehat the~ ae-loctron energy level of' :. ,

.:o;uld be LoweJIred wiSth the py:ridine ring protonated relaive~ 1.o thle energy

leve! of ,'i wijth this ring coordinated, as in the protonaited situacion

thel pyrid~ine cing vould be expectedly more electrollcg.tivr . Hcnce, if:

I:h energy level of !11 is not altered as nu~ch as that of 9TI FO co achi

of tiitse to~o prossibi..ities, the yJ-band should (nnd does) shiftt red for

ch= -:lor~linatedJ csbeniium ion relative2 to the "Eree" ioni. It is also

sugge.<:;:ed that Clthese assessments are correct owing co the~ olagnitud~e of

chifr in encrgyr obs-erved for the y-band upon pr idylcarbenimar i ion co-

or~dinar;io. An inspection of the v data (Trable II, pp. 77-78) folr th~e

4'-pyridyL ions re.eal.s that coordination indu~ces a ced shifr. inl the

ene~rgy of the y-blnd proportional to as mulch as 2.1 kK: for th~e pnl11adium-

comp.:lexes of thie R~ U 4-methrlphenv1l ion vs. thie corresponding ":ree~" ion.

St~mlarly, for this ion, che :-.-hand is blue shifted only 0,& kK~. (T'h is

t~trend is also realized byr the remainder of the data found in T'able II.

F'urthecrmore, related data reported previously by R~ichardson (6) and

b; \!e~ntz (8) suIpport this trend.) Consequently, thle electronic ~~energy

Lchangs which arre. produced in the ion via coordination appear to be

reclated- principa~lly to the attendant changes inl the transition encrgy

of the y:-band. This engenders the speculation thalt relative energetic

contributions provJidedl by coordinated metal specie-s toua7rds stabilizing

''comple,?::,ble" ca7rbe-nium ions would be reflected in a1 comparison of the

respective~ !'-band; transition energies for a given comnplexed ion. Psr--

hopls futulre- cock.1 will furnish th~is possibility~ with substances










i'::raton iehe. he~ rsuitablity of the Den~o tier~tiion :lethod1 (10,!1)

fo~r thr decormination of clhe tr~l;~mody-nnmic stabilitie~s, n the carbaniiem

\--sinves:ti:a~ted in thiis study ha~s been aptly demnonstrated by Ileari (8).

Thei, interested I-reder is referred to this wo~rk for ra sj:elce discusionic i

ofT the~ necessary and pertiinent c::pe~imental considerations. Prago~ltt

pe~rchloril: add,3 702I HC10 has~ pro;ed to be a most appr-opriate ioniza-

Ition medium~ for those titrimetric tstbility determlinationr. It is

a pe:te~n: uincanl alcid as reflected by its thermiodynamic ionizatio:n

conant(KlC10) reported to be 3800 (61). In fact, as pointed out by

G1:cllespie (62), HClod~ H20j systems can be more acidic than reagent

i2 "'!, and onlly r-rtnin, no;,aqueous supreracid syStems affrd^~. hiS;her

senitytha aqeou HC0 .Indeedl. HiC10 HL0 is found io be uniquely

be~rtwen n~eat H2?SOl and sulperacid s)-s~cms uch~C as- HSO3F Shq (..e

by. rOlad (G3) to prepare oan:. relati..ely unstab~le carbeniLum ions) as a

U~acful solvent for r~he generation of critlyl-type carbenium ions.

I;eedman (64:1535) hias commcented that carbenium ion investigations in

conentate 1250~ can be complicated by side reactions such as .aulfona-

iion o~r o:;id~tion which in turn can destroy either the parent carbino1

or thle crbenium ion. Problems such as these are without a doubt respon-

sible for mruch of che confusion found present in earlier studies on

carbcnium ions. The superacid st.stem HrSO31 SbFS as vocll, recently has

beezn shown to ;:enerate carbeni~um ions as a consequence of 0.-<;tltion by

S.C;.Toir SUj3 (6i5). Thus, pre'.iously Jeised methods~ and mechasnismr s of

c~rik ai:m .ion generation in chis sol;ent mnay require ex~consiv~e modif~ica-

rions. F-urcha~'mrmor the use of superjcids for chie preparation of these

twees- of cacrboniumm ions wouldl d cercainly require modifi~cations o: the








1:.-no., tit*a: innl authodl to tarke into account tles fact s~hac: superarcid media

,*c ongocu. hrlefE~ore, at the minimums, thle del~inition ofE newI acidity'

runlct~ion param~eters w~ould be requisite, as w~ell as dr-astic alterations

..;I the mlechaniz s of the 3qaqus~ titration techniques.

A\ considerlati onr of thle equilibria which pertain upon catrbeniumi

i,,n generat3ion is i~n order. A~n examination of the literature in, this

.vresr~ rrveals th~at on occasion vanriouls authors are ront to wri'-e H as

r;h ;idj species responsible for the conL -sion of carbinal to car'oenium

is.Alb~i. ~conv~en~ient this practice is certainly not rigorous, and

canl ilequentl!ly be miisleading. In the present situation where pcrchloric

racil has be~-en employed as the ionizing medium it is necessary t~o choose

betwoonr HC:.10, or I LO~ AS the principal proton source Lowards thle ion

p~rrecuir:; ir carbinl;s, assuming,, of course, tbut other complex or unusual

addi rpatecis do n;ot o:--ist in this sy.stem in appreciarble concentration.

Sincc colncntllrrated .ol~utions of such mineral acidls as H12SO RNO:3, or

!!C1; are not c~apabic of -arbonium ion generation in instances where

IIC1. -H20isit fllos tat C10is the acid species responsible

for caIrbtrliulm ion formation in those systems in whiich chose other

acids produce little or no carbenium ion. A~s a result of nor studies

on CliCLO H20, Redlich anld Hood (66) reported that reagnent 70-i72

ll100 (ca. 11.8 H~) is approximately 75': ionized. Hence, sufficient

mJ1-leclar 1100O, is present in 70;: HClO 112 for car-bonium ion genera-

tioni :in systems uhi~ch contain as solute limited quanrtities of ion

pIroculrscr pyridylmethanlal. And here, concincntrate soluitionis of 113O

do noti ;o.wor't rcmht~not to carbeirum ion- to any~ app-reciable ex~tcnt,

e:-:c~rp for thle relantivelyr mdore stable cations suc~h aIs those which contain

stronlyl; e1'Clectro relonsing phony~l ring subrstituents .ruchi as 4-meiLhoxy;














(C.@3CO 2 :!C10 (CH) + H O + 2 G10, (S)



-rnd, eveln through ring nicrogen pr~oonatioln of the freec alcohol ions

tends to comrplic~te the- accendan t equilibria, thec oy~rilylm~erhanols

sholcc:i be ioniied similarly. (Also, see: the discussion w.hichl ensues

(p. OD;) in references to thes stability dalta cont-ainedJ in Table U'.)



TIhe-r eqluation for cho Deno acidity function (HR) may' be urritten as~



~~L ~[R:-OH] Ij



!.'etre t-he values of HC for a3 parcioula~r acid meedium aire a meal.SUre~ of

ther capaibility, of that medium at various concentration s to, ionize a

givena alohorl (R-0Hj generatingi thie corresponding carbonium~i ion (P +).

Pin~ce thiis eqluacion is of the frm-i, y~ = b + ax, it followvs thac if a

seriesr of v~alue:. Ealr HF ere k~no.-m, and if the respective conicntrations

of 11-0:- and R+ for a relaitedl alcohol carbrniumn ion pair can be e.-.

perimencall y determined at the different t 8 ', pl 4 may bce obtainFed

ar, a qulan~ic~ti ive measure of the charmodynami e stabtlity of a gi\en

eacenumio. f cor.vse, it, is required the~refore ~hat, thie acid mriediumn

het capable Or measurarbly ionizing E~le alCohol Over-r ;7 rYine Of aCid

c~oncenl-r ations; and it is also inherentl ~reguil~re chacir in order for

the- HP~ relationship to hold, teli slope (mi) of thle curve~' got b plottingl

1!1 -.s. the log term be eqlual to~ 1.00. iGentz (8l) showed3 chat: botch of








c::-5.i conitlijons ',ec-: net in HC104 i 11 ~0 fo t he py ridyslmct han acls



A 11sti of 1:1 \'alluesfr aqueenlUPI S HIC0I andc the correspon;ding: lt :`/

;rcid ar:e given in Tab~le III, ps. 87. A plot of -iL, vs. uc : acid

(Figiure !r, p. 38) yielded a smooth cur.e of app~roximntely conistant

fsllope wchci was easily exitrap31 7rlae (Is shown in Figur-e 9) to~ 70.0'-

H~CLO3 ;: order to obtain IlR~ values for acid concentrations greater than

6-00'.Employmeint of the fact that Eeer's laur (A = ecb) directly

relates the absor;,r anc (A) of an absorbing species to its toolar con-

centrastion (c). al110ws values for [R-OHl]/[R t] in equation {9) to be

i.t:1ine!l: by mes.=urin~g the a-bsorbance (to 10.001 absortance units) of the

carbe~niuum ioln at v=Irio7us II10,1 concentrations. The absorbanlce (con-

c.ealtration) o; P.-OF1 vas then taken as the Jifferrre between~ the beer's

1-syJ absorbance of the carbenium ion (see Dilution Curv~e, p. 93) and

the; Lctuanl absorba~nce of the ion at a given acid conicentration. Th7i s

method of daita treatment is v~alid since R-0H- doe3s not ab-sorb at .4
maxs
or the cacbenium ion. Consequiently,, it is justifiable: to assume that

chln the~r actual absorbane of the carbeniium ion matched the expected

a~bsor-bance asu p~redicted from Bleer's law~, thre alcohol un~s jcnized to an

extient of ca. 100E. 1Iaturally then, as the~ ionizing acid was sy~stena~t-

:icnlly~ diluted (actually, at the onset of thle titration molecularr il1010

i:. also converted to 11 0 C10,) by the addition of measured increlnents

ofT r:ter, Lhe :Ibs:orbance rall off was~ linear (Eeer's law: dependent) as

a)n,; as the~ alcohol remained essenti:Illly 100r2 ionlized. However, as soon

,Ir the carbouiumn ion became titrimnetrically reconverted to alcohol. prc?-

cliusol r S a reSuljt of further addition of waJter, absorbance fall OlF

wn-. no longer linPor: and indeed, it wa~s greater tha.n thant predicted












Iable III
i'auctof lbinLqucusHC1, t 25'







3.79 30.0

;.61 35.0

5.5'1 40.0

5.95 4 .

:1.38 4

6.S2 46.0

7.31 4.

7.86 50.0

8.'5 52.0

9.05 54.0

9.6S 56.0

10.37 58.0

11.14 60.0!


~Deno ec al. (11)








O
'' o


a





OJ



AJ













e-1


OV i
-0 C


1



\


c, o o
b d d C A b o

r--7 TCI T I-- r? ty
rd e-1 r-


I
I


I
r








110.1, ;:l:0 :-tI-trapoa ccd Leer's !ne strigh~lt line. An e:l:nminaition of: the



[1I'.: ior rachl carbeniumlur ion: so tit';tratd, aI colZlection of al~Slbsorbnce

d:;:::1 uln obtained as~ a function of' ch-anging~ wt T: HC10~,.

Data treatmiilt w~as crried outL ulsing the methods em~ployed by: 1.'ntz

(C) ;:-.'LD1 come mlin-Pr modiftications.. Th~SE mtthod3 ma,' be deCribedi~ c COn-

veniently~ in conljunctioti n with a sltewise c:-:3mination~ of the pertinent

.?rit.8metic rrelatrionships~ required for datai treatment. Initia'lly. an

un.-,hFed samlple of ion precursor p)yridylme~thanol (Free or comple:-:ed)

.5 dissolvedG inl sufficient reagent HC10) (determined as 70.8i7, see-

:,cjou) to~ produce anr a~ccptable~ on-scale (viz., 15-25r. T) spectrophotom-

car eadig at.'_ for the absorbing species (the carbenium ion).Th

LhTr1 Snlution sample is now w.eighed and the absorhalnce recorded. TIhen,

r,-: .mlri ed i;ncrrements of de~ionized wal~ter are aldded to th~e carb~eniumln ion

;olution anid, after thorou h mi:-in, the absorbance of the sample is

a~re:.J.. I'ne~ we r of the acid solvetnt resulting from dilution is calcu-

IJted f'rom:



vt (g), of acid
1.'t r: acid =(0
ut g) o samle +st (g) of 1120 added



where wt of icid = original we :; acid (70.87:,) x~ original total sarniple

vt. TIiius. che ue r. of the acid can be determined follovwing each dilution

by. simpl rnotin# ch~e cumulclati. e qu:anticy of water which hasl been; added

to rlhat sL~ag in the: titration. Trhe- :olume~ of thle sample follouting

tach a~dditton of :-ater is the~n dee~Trmine from:








.R-.m:01c- '.-olum _1all -- _11}
'corre~sponndin r (g/ml) oE the samnple



r.-ho:*<- ,, -- -pcif~i c gSravity of thle ac~id sol~vent. A'ndl therecfore, it is

cho.iousc~~llynceSsary to hdlve val3ues of ii for aqu~eous HC10,. (Ilevltz had

abaninal~ Crrs information from a plot of p, (rt sig. fig.) vs. wit 2; (4

al;.. fii.) EC.r Solutions of aqucous HlC10, (se~e Table TV, p. 91).)

H:,weverc~, s;.nce the volume of an aqueous HC10O, solution doe~s not increase

1..nerily3 5 ''pon Jilution with water (i-e., the v'olumes of water and parent

Mcj. ci slution. are; not additive), \*!entz: found .it neccerssary to) "blow up"71

;lhic plot in the,- Iegion of each Gwt : docum point in order to obtain

:.ro orespndngvale orp.This procedures~ I.ns fou~ndl to be? etrFemelly

cod~icus s:;ingl ro ther difficulcy foundl in obtaining :r s-ig. fig. neccacyc:

(to incure.: re.iabilitt y of related data to 3 sir. fig.) for a conside~rable

Ia~~ron ofr :-E .!. data from such a graphical reeadout. This; prtliCular

p:.Cl'l.I:.m was, convau:iently. alleviated by~ taking a "]east squaress" clrve

rit of E-rickwetd:t's data (67), (Table TV', p. 91) to golcd a "p~rinted

out" seem~s of values for a spanning the range 0.00 we 2 HC10~ to 75.00

ut it10d). Th details of this least squares treatment are "iLven ini

the Appendlix.) Thus, ha~ving e:-:perimentally determined p of the original

riiogc~nc acid, the corresponding, ut of the original acid w~as obtaiined

frl-r. this p --ult i: Labulation. 'The usFe of eqluation; (10} then yi~cetle

uit 'i data, for subsequent diliitions, in turn for which rorre~spondinlg 0

values wrlere a;ailable from the~ 0 -- ut T; tabulationi. Finally., it is

ne:(c:SSaryV to determine the dilultion Eranction (D.F.) fo~r c7chl diluti;on.

TInis is obtailned from:




Full Text

PAGE 1

THERMODYNAMIC INVESTIGATIONS UPON CARB ill I i FROM PYRIDYLDIPHENYLMETHANOLS — FREE AND COMPLEXED By James Charles Rorvath A DISSERTATION PRESENTED TO THE CRADLE COUNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS ' THE DEGREE OF DOCTOR OF PHILOSOPHY [VERSI'D OJ FLORIDA 1978

PAGE 2

This is dedicated to the Spirit of Bombastus, for lie was blessed with the courage ami the desire to seek the Philosopher's Stone. In so doing he was magnificently rewarded, for instead i •round the tru th . This is also dedicated to my Mother and to one Sufferin trd frora Iowa. For without their inspiration this work would beei . np I eted .

PAGE 3

ACKNOWLEDGMENTS It is not possible to acknowledge by name all who hove contributed to this work. This author is exceedingly fortunateand proud to have had the benefit of so much assistance and friendship and therefore extends his heartfelt appreciation and thanks to those; knowing that, at least in this way, no one has been omitted. in

PAGE 4

TABLE OF CON continu Page 'ENDIX 13 3 1. Specific Gravity of Aqueous HC10, Determined as a Function of Wt 7, KC1C, . 133 2. Degree of Proton&tion of a Pyridylmethanol (pyLOH) in Aqueous HC10, 134 3. Experiments Conducted upon the Carbeniur Ion Species to.md to Exhibit Rearrangement in 70% HC1Q, . . . 136 MKUOGRAFHY . 140 BIOGRAPHICAL SKETCH 145

PAGE 5

TABLE OF CONTENTS Page ACKNOWLEDGMENTS . LIS1 OF TABLES LIST OF FIGURES . ABSTRACT INTRODUCTION The Carbeniunt Ion Preliminary Considerations Groundwork to this Research 1 XPERIMENTAI Synthesis of Ligands Synthesis of Complexes I I . Elemental Analyses Reagents and Solvents I strumental Analytical Methods RESU3 TS AND DISCUSSION Synthetic Gonsiderat ions Thermodynamic Investigations and Measurements INCLUSION x ix vi vii J. 1 2 4 18 18 35 35 38 41 41 43 49 49 60 128 IV

PAGE 6

LIST OF TABLES Table Page I. Special, Commercially Obtained Reasents and Suppliers 42 IIElectronic Spectral Data for the Various Carbenium Ion Species., in 70% HCIC^ at 25° 77 III. Values of H_. in Aqueous HC10. at 25° .... 87 IV. Specific Gravity of Aqueous KC10 A Solutions at 25 c ' . . 91 V. Thermodynamic Stability Data Resulting from the "Deno" Titration of the Various Pyrldylcarbenium Ion ?pec:'es, in HC10. ELO at 25° . 95 19 VI. F nm.r Cher, ical Shifts (6) for Carbeniura Ion Precursors in Acetone and 1 K HCIO^, and for Carbenium Tonin 70% HC10. at 25° 110 4 VI

PAGE 7

./ ST 0] FIGU ', ' I .'.' "• Monopyridyldiphenylmethanols (pyLOH) Bis (2-pyridyl)phenylmethanols (py^LOH) Thiazolyldiphenylmethaiiols .... Pyr Ldylphenyl-4-f luorophenylmethanols Phenolphthalein monopositive ions Visible spectrum of the carbenium Jon derived f pyridyl-4-methylphenyl— 4— f 1 uorophenylmethanol, HCIOa. v , 20.2, 29.7 '+ max rom «tn 70% 4 4 8 15 72 76 7. Visible spectrum of the carbenium ion derived from Pd(II)
PAGE 8

LIST OF FIGU U5S contimied ire Page 15. Hammett -0-^+ vs . carbenium ion 6 relative to external CFCI3 . . 118 16. AG° (uncoordinated 4-pyridylcarbenium ions) vs. AG (uncoordinated 2-pyridylcarbenium ions) . . . . . .121 17. &G° (uncoordinated 4-pyridylcarbenium ions) vs. AG°(biscomplexed 4-pyridylcarbenium ions) . . . . . . .121 vm

PAGE 9

Abst act of Dissertation Presented to the Graduate Council University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy THERMODYNAMIC INVESTIGATIONS UPON CARBENIUM IONS DERIVED FROM PYRIDYLDIPHENYLMETHANOLS FREE AMD COMPLETED By JAMES CHARLES HORVATH March, 1978 Chairman: R. Carl Stoufer Major Department: Chemistry The syntheses of a series of 2and 4-pyridyl-R-phenyl-4~ fluorophenylmethanols arc reported; R may be 4-H, 4-CH , or 4-OCH,, within each series of alcohols. Palladium(II) complexes of the 4pyridyl alcohols have been prepared also wherein either a single alcohol is Included in the coordination sphere of the metal to yield the so called "mono"-alcohol complexes, or two identical alcohols are included to yield the so called "bis"-alcohol complexes. The corresponding 2-pyridyl alcohol complexes could not be prepared presumably as a result of steric difficulties. These trityl-type alcohols (and their complexes) arc precursors to stable arylcarbenium Lor obtained via dissolution in HC10,-H„0, the Ionizing medium, -a I 19 r -\\s "Deno" It , acidity function titration technique, i nmr chemical shift measurements, and free energy parameter correlate have afforded a quantitative evaluation of the stability the • rious carbenium ion species. These invest; is have also '

PAGE 10

ihed Information which elucidates the Llizing i . ?ct concoordinated met a] conl tii Lng moiety to a coinpj :d carbeai urn ion. Two particularly noteworthy outgrowths have resulted from these st idies. First, internally consistent electronic .spectre! interpreons have been obtained which indicate that the stabilizing influence exerted by the metal center on a given complexed carbenium ion is reflected by the frequency changes of the carbenium ion absorption brncls detectable upon coordination of the ion. Secondly, opriate, linearly interdependent free energy correlations have given rise to the development of arguments which indicate that although complexation (for the cases considered herein) stabilizes a carbenium ion relative to the corresponding protonated ion, coordination does in fact destabilize a pyridylcarbenium ion relative to tl irotonated free ion species.

PAGE 11

INTRODUCTION The Carl; e. iun; Ton The imperspicuous nature of the term "carbonium ion" stems from the fact that this nomenclature classification has been applied to all types of multivalent carbocations throughout; the chemical literature. This problem has been pointed out by McManus and Pittman (i) and more recently by Olah (2). These authors have stated that the term "carbenLum ion" is a more systematic reference towards trivalent carbocations (i.e. , R-C ) which contain a sextet of valence electrons This follows in that these trivalent carbocations are. valence isoelectronic with such ions as o -ionium and sulfenium. Here the suffix "-eniura" distinguishes these ions from their "-onium" counterparts. Furthermore, this nomenclature directly establishes a relationship to the species which results from car bene (:CH„) protonation, namely the carbenium ion -1(Ol-j. Therefore throughout this work the term carbenium ion shall be •J employed as an explicit reference to a trivalent carbocation xoith a valence electron sextet. Specifically the cations considered herein are those which are det Lv>-:: from pyridy 1 dipheny.l.methanols upon dissolution of these alcohols in suitable, strongly acidic media.

PAGE 12

pL ~ eliminary Co i is id e r ; 1 1 urns The preparation of various bis(pyridyl)phenylcarbinoJ : trisCpyi Ldyl)carbinols has been reported by J. P. Wibaut e_t al. (3). These .:• recognized the direct structural and electronic similarity of these pyridinecarbinols to triphenylcarbinol (triphenylmethanol) and therefore investigated their halochromic properties in 100% sulfuric acid solution. They discovered however, that such solutions exhibited no color whatsoever. Thus, these pyridinecarbinols were not ionized in strong acid in a fashion akin to that of triphenylcarbinol. That is there was little, if any, conversion of the pyridinecarbinols to the corresponding trityl-type carbeniutn ion. None the less this disclosure provoked further speculation as to whether or not such tertiary aromatic alcohols could be converted to the corresponding carbenium ion. Indeed it seemed to be the. case that the principal difference in the behavior of these pyridine alcohols, as compared with their benzene homologues, was attributable to the degr of positive charge development which would supervene upon their dissolution in strongly acidic media. Thus, the concentration of positive charge produced through base site protonation (of the pyridine ring nit • : atoms) would be sufficient to prevent carbenium ion formation to the concomitant development of like charge repulsions. Therefore Lt seemed reasonable that if these basic sites could be chemically l ordei to prevent protonation upon treatment with strong acid, it v then b feasible to generate the carbenium ion. Moreover, it was recognized that such investigations upon monoLdyldj ' snylcarbinols were very much relevant to this consideration-

PAGE 13

: i.i, Ls. It was expected that this type of simp] py Ldine alcohol could be converted to a reasonably stable carbenium ion since this transformation would be accompanied by the development of less posj L\ char, this possibility was substantiated through the work <> ,: Smith : Holley (4) wherein they report,.! tbu two structural isomers of lyldiphenylmethanol ware measurably ionized in concentrated sulfuric acid solution. Thus, it appeared that carbenium ions derived from these, particular monobasic alcohols could be employed for stability investigations up na such ionic species as they are produced in suitable acidic media; and with respect to the possibility of inhibiting pyridine ail rogen protonation upon carbeniua ion generation, the binding of these tic nitrogens through coordinate bond formation to an essentially neutral metal center seemed to be an appropriate method of general ,,.. Lity. Ih ci Eore investigations upon carbenium ions stabilized.., by this attendant limitation of positive chai / »uild-up would be peri. Also, since pyridine is a ligand which is known to exhibil n-acid behavior (5:1.17), the potential fc ;asuring the enhancement of a stability as c: consequence of coordinated atom (ion) "back-donation" established. That is, if the species bound to the pyridine nitrog 'jessed occupied valence orbitals of appropriate symmetry and energy to interact with the ir-system of the carbenium ion by creating ir-charac-nitrogen bond, theion could also be so stabilized. , if the coordinate bond(s) was sufficiently stable as to remain Intact upon conversion of such complex compounds to the corresponds carbenium ion(s), these considerations would be experimentally accessible. (The consequences of oand tt-1 i Intel ctions between a coordinated carbenium ion and a prosped al center hove, been

PAGE 14

disci r elegantly by Richardson (6:10-11) and arc hei re) : to iiveni . t ly . ) G roundwork to this Research In 1966 Bhattacharyya and Stoufer (7) began work in this area of research. In accord with standard synthetic methods they prepared various iiionopyridyldipbenylmethanols (Figure 1) as well as bis (2-pyridyl ) [methanols (Figure 2). Preliminary investigations upon the free alcohols revealed, as expected, that the monopyridyl derivatives were converted to che corresponding trityl-type carbenium ion upon treatment r (2-pyridyl) (3-pyridyl) (4-pyridyl) R = -H, -CH , -0CH 3 , -N(CH 3 ) 2 Fig. 1. Monopyridyldiphenylmethanols (pyLOH) ^fo B = -II, -CH-, -0CH-, -N(CH 3 ) 2 Fig. 2. Bis (2-pyridyl) phenylmethanols (py 2 L0H)

PAGE 15

w ith reagent sulfuric acid (96% l^SO^) . The bis(pyridyl)alcohols, h< ever, were not ionized by this solvent to any appreciable degree. r lhis agreed with the results of Wibaut et al. (3). Much of the initial work was therefore directed towards the utilization of the monopyridylalcohols both as carbenium ion precursors and as heterourcr.-.t io donor species. In conjunction with this, Bhattacharyya and Stoufer successfully prepared a number of palladiura(II) complexes of these monopyridylalcohols by employing them as neutral donor ligands. The materials obtained were well-characterized as the neutral dichlorobis (alcohol) complexes of palladium(II) . These complexes were of the general formula Fd(II) (pyLOH) 2 Cl 2 , where pyLOH represents the "ionizable" pyridine alcohol. These compounds were diamagnetic and square planar as expected for 4-coordinate complexes of palladium (I I) ; (See, for instance, the discussion concerning the complexes of palladiura(II) by Hartley (5:17-19).) Subsequent investigations by the.-;e workers upon the carbenium ions derived from these palladium complexes revealed that dilution of the ionizing medium (i.e. , the 96% R^SO solution) with water afforded the reisolation of the intact neutral complex. This experimental find indicated that the pyridine-metal coordinate bond was reasonably stable in strongly acidic media. In this way a tangible basis for examining the stabilities of such coordinated carbenium ions was established. The results of Bhattacharyya and Stoufer served to demonstrate that the monopyridyldiphenylmethanols were suitable o-donor ligands as well as carbenium ion precursors. To continue with this work, Richardson (6) prepared a series of palladium (II) complexes of the bis(2-pyridyl)phanylmethanols which had been synthesized previously b> f tacharyya and Stoufer. These complexes were of the general formula

PAGE 16

J.OiOcl., , and were presumably 4-cootdinate about the me! th the alcohol functioning as a bidentate ligand. It had been ted that ss a consequence of binding the nitrogen donor sites '1 coordination to the metal that these compounds could be cor verted fu the complexed carbeniutn ion(s). It was discovered, however, rir.i by employing customary experimental methods this ionization was not achievable. There was no obvious explanation to account for this result. Perhaps it was the case that the dissolution of these complexes in strong acid was accompanied by simultaneous rupture of the metalnitrogen coordinate bonds. Since there exists a considerable degree or steric strain in these 2-pyridyl complexes as a consequence of spatial crowding between the metal center and the carbinol carbon, this coordinate bond rupture upon acid treatment was not unlikely. Richardson carried on with investigations on the stability of carbeniinn ions derived from the 4-pyridyldiphenylmethanols . He recorded the electronic spectrum of the free alcohols and of their palladium (II) complexes in neat trif luoroacetic acid (TEA). These solutions were highly colored thereby indicating carbenium ion formation with TFA as solvent. The visible region of the spectrum of these colored solutions revealed the presence of two intense, broad absorption bands which were mv to be characteristic of the carbenium ions. An examination of the visible spectrum of triphenylmethylcarbenium ion produced by dissolving triphenylmethanol in trif luoroacetic acid showed the same :ong absorption bands. Indeed when the electronic spectrum of soluof these materials in nonionizing media (e.g., methanol or glacial acel ic acid) was examined in the visible region, these strong i bands were found to be absent. Ct was also observed durin

PAGE 17

these spectral examinations that Lhc positions of these absorption bancls for a gi if en carbenium ion species shifted upon going fro th omplexed protonated carbeniun ion to the corresponding metalcomplexed carbenium ion. This suggested that there was a direct relationship between the stability of the carbenium ion and the attendant teration in electronic environment associated with pyridine nitrogen protonation vs . pyridine nitrogen coordination. Similar band position shifts were also detectable as the p_arabstituent (R) on the phenyl rings in the alcohols was varied within the series R = -H, to R = -CH„, to R = -OCH.-. In Lhis instance the bind shifts were attributed to resonance electronic, interactions between the R-substituent and the carbenium ion center. It was also found that the stability of the ion was considerably increased when R = -OCH., . This reflected a substantial capacity of paraOCFU to participate in favorable conjugational interaction with the ir-system of the trityitype ion. Richardson ultimately attempted to establish a relationship between carbenium ion development in these 4-pyridyldiphenylr.iethanol systems and measurable proton ( H) nuclear magnetic resonance (nmr) chemical shifts. To do this the H nmr spectra of TFA solutions of these alcohols and their palladium (II) complexes were recorded. Then to fingerprint the phenyl proton and pyridyl proton absorptions the TFA solution spectra -.-ere compared with the solution spectra of the unionised compounds. Also to facilitate the resolution and identification of the various proton signals, these nmr spectra were subjected to computer simulated analyses. These investigations however, proved to be unsuccessful

PAGE 18

'. the proton absorptions of the unionized compounds could not be c< rrelated unambiguously with the proton absorptions of the corresponded rhenium ions. As a logical extension of the work, upon the pyridylmethanols Wentz ( ) prepared a series of structurally related alcohols by substituting a thiazole ring for the pyridine ring. These materials were 2-, and 5-thiazolyldiphenylmethanols (Figure 3). The similarity of these alcohols to the pyridyl alcohols is apparent. In accord with previous k the neutral palladium(II) bis-complexes of these alcohols were pared. These compounds were of the general formula Pd(II) (Th0H) o X o , with X representing a coordinated halide ion, either chloride (principally) or bromide. Wentz had considered that the replacement, of R = -H, -CH , -OCH ; R' -H, -CH.,; R" = -H, -CH i) 2-Thiazolyldiphenylmethanol ; b) 5-Thiazolyldiphenylmethanol (2-ThOH) (5-ThOH) Fig. 3. Thiazolyldiphenylmethanols

PAGE 19

Ldin with thiazole would add a degree of uniqueness to the anticed chemica] behavior of such heterocyclic bases. That is, since the .••;:' Ldine and thiazole heterorings arc isoelectronic and contain essentially Identical nitrogen atoms they should exhibit like donor char act eristics. However, because thiazole also contains a thiophene type sulfur atom, the thiazole-substituted alcohols should be precursors to carbenium ions with somewhat different stability than those got from the analogous pyridine alcohols. Turnbo and coworkers (9) had indeed demonstrated that the thienyl moiety could enhance the stability of such carbenium ions relative to the corresponding phenyl-substituted carbenium ion. They did this by determining the equilibrium constants (K ) for the ieaction eq R -t 2 H 2 $ R-OH + H + {1} in reagent sulfuric acid for a series of structurally equivalent thienyl and phenyl carbinols. The K values were experimentally measured by employing the spectrophotometric method of Deno and coworkers (10) . An ordering of the equilibrium data which were obtained revealed that a given thienyl-substituted carbenium ion is more stable than the related phenyl carbenium ion. Thus, these data also estabihed that the sulfur atom in the thienyl nucleus was not protonatod by the sulfuric acid as this development of additional positive charge would have induced a net destabilization of these thienyl carbenium Thus, it was reasonable to expect that the thiazolyldiphenylmethanols would be sources of triaryl carbenium ions more stable than e which were got from the pyridyldiphenylmethanols. Furthermore,

PAGE 20

LO i mization of the thiazolyl alcohols cou] I b lie Lted by L'.ie I chniq used for .studying the thienyl ions since the pyridine alcohols . shown to be ionizable in concentrated sulfuric acid. • the stability of the thiazolyl ions could be quantitatively evaluated provided the acid solvent ionized the parent alcohols to an extent of one hundred percent (100") • In other words, if the degree of conversion of alcohol to carbenium ions was measurable in terras of the i pacity of the acid solvent to produce ionization as a function of aci-i concentration, th^n any equilibrium pertinent to alcohol-ion interconversion would presumably be monitorable. Undoubtedly it had been with criteria such as these in mind, that Deno and coworkers (10) were able i" define an acidity function regarding the ionization of arylmethanols in concentrated sulfuric acid — water. The results of Turnbo Iters C9) proved the suitability of applying Deno's "acidity Ei " technique towards following alcohol — cjrbenium ion equilibria in the thienyl systems. Therefore it seemed reasonable to employ this method for quantitative studies upon thxazolylalcohol — carbenium ion equilibria, provided the alcohols could be completely ionized at a known solvent concentration. Uentz made a very important contribution when he demonstrated that ly of the thiazolyl alcohols were converted completely to carbenium ion in reagent perchloric acid (70% HC10 , ) . This was accomplished by Lning the visible absorption spectrum of these alcohols as perchloric acid solutions at various acid concentrations. This simple investiga. Lon revealed that for relatively high acid concentrations the carb. Lved from many of these alcohols exhibited a Beer's law depenicej but, as these acid solutions were systematically diluted by the

PAGE 21

1] i o Lsured increments of deionized water, this Beer's law ience was qo longer maintained. From these observations it was concluded that in the high acid concentration regions carbenium ion con Loil was effectually 100%, and the result of adding small quantities of water was to dilute the concentration of the absorbing species (i.e., the carbenium ion). However, as more water was added, the equilibrium described by equation {1}, (which represents the reconversion of thiazolyl carbenium ion to thiazolyl alcohol), began to be shifted significantly tc the right as written. A plot of carbenium ion absorbance vs . weight percent (wt %) HC10, served to reflect these observations. This plot over a region of high acid concentrations yielded a straight line for a completely ionized thiazolyl alcohol. This was the Beer's law portion, of the plot. But, at an acid concentration particular to the alcohol under investigation, a marked change in slope was observed. That is, the plot began to deviate considerably from an extrapolated Beer's law line. It was at this acidity region where the concentration of the absorbing species (the carbenium ion) was being diminished not only by being diluted, but also as a consequence of being reconverted to the nonabsorbing neutral alcohol precursor. Thus, absorbance fall off was magnified considerably as the ionizing solvent was made progressively more dilute. Thus, by applying appropriate acidity function data (made available by Deno and coworkers (11) for aqueous perchloric acid) Wentz ;.;as il Le to measure spectrophotometrically equilibrium constants for the •oration of carbenium ions resulting from the dissolution of free and plexed thiazolyldiphenylmethanols in reagent perchloric acid. This itij .Lion therefore allowed a quantitative ordering of the stabilities

PAGE 22

12 ',' carbenium ions derivable from these heterocyclic basic compounds. ends in stability which were established by this study, and the pertii if generalizations which these trends served to wsrranL, are aed up accordingly: (i) Carbenium ions derived from 5-thiazolyl alcohols are more stable than those got from the corresponding 2-thiazolyl alcohols. This illustrates th.e inherent destabilizing effect that charge repulsion has on carbenium ion development. Since the sites of positive charge are three bonds separated in the 5-thiazoiyl ions, vs. two bonds separated in the 2-thiazolyl ions, and models of these species indicate a likely "through-space" charge interaction for the 2-thiazolyl ions, this trend in stability is certainly expected. (ii) for a particular alcohol, R-group substitution in the para position on the phenyl rings, for the series R = -H, -C1I~, -OCH_, results in an increase in carbenium ion stability. This reflects conjugational stabilization of positive charge development known for this particular scries of "R" groups as para substituents in trityl-type carbenium ions. (See, for instance, the results reported in the papers by Taft nail McKeever (12), McKinley et al_. (13), and Deno and coworkers (10).) (iii) For a particular alcohol R'-, or R"-group substitution on the thiazole ring (see Figure 3), and for R' = -H, -CBL, and for R" = , --CH , results in an increase in carbenium ion stability as "R" is reased in mass. This exhibits the greater ability of -CH, compared with -H to inductively release electron density. (iv) Carbenium ions derived from the palladium complexes, Pd(IL)(ThOH) 9 X~, are more stable than those got from the corresponding free ohols. This, at least, illustrates the effect of bindin basic

PAGE 23

13 sites Ln the Ligands through coordinate bond formation with an essenI ' illy neutral species. This obviously minimizes positive charge development up;-n treatment with strong acid since ligand protonation now prevented. (v) In the instances investigated, carbenium ions derived from ; complexes Pd(II) (ThOH)JBr„, are more stable than those got from the corresponding chloride ligand complexes. This suggests that a backbonding mechanism is operative through which the metal center donates ir-electrcii density into empty TT-orbitals of appropriate symtnetry on the coordinated carbenium ion species. Thus, bromide, which is expected to be a better ir-donor than chloride, should in turn contribute a net stabilizing effect on the ion via donation of it-electron density into suitable empty metal orbitals. Two final investigations of consequence were carried out. The equilibrium constant for the conversion of triphenylmethanol to tri~ phenylcarbenium iun in perchloric acid was measured. The value obtained was found to be in good agreement with the value which had been reported for this ionization by Deno and coworkers (11) . This served further to verify the reliability of the thermodynamic data got for the generation of thiazolyl carbenium ions. And lastly, the ionization of U-pyridyJ di (p-tolyl)methanol in perchloric acid was examined. The 4pyridyldi'S-tolyl)carbe-Liiuin ion was found to be more stable than the 2-thiazoly3 carbciiun ions but less stable than the 5-Lhiazolyl carbenium Ions. This result was significant in that it allowed a comparison of :e hoterorings to be made, as if they were position isomers, with t to their ability to stabilize trityl-type carbenium ions. More ortantly, tnis resulc demonstrated the appropriateness of the

PAGE 24

14 ctrophot» Lc technique of Deno and coworkers (10) for studying I hyJ carbenium ions. Therefore carbenium ions derived a the pyridine alcohols previously investigated by Bhattacharyya and Stoufer (7), and by Richardson (6), could now be studied quantitatively and broaden considerably the scope of this work. The research reported in this dissertation deals principally with investigations upon free and complexed carbenium ions derived from pyridyidiphenyJ-iaethanals . These pyridine alcohols and the complexes thereof were prepared such as to be especially suitable for thermodynamic stability studies. The alcohols considered are specifically 2-, and 4-pyridylphenyl4fiunropheny .(.methanols (Figure 4) . The 4-f luorophenyl ring has been incorporated into the molecular framework of the pyridylmethanols to 19 provide a F nmr probe uniquely sensitive to the development of positive charge upon carbenium ion formation. Considerations for the 19 application of F nmr techniques towards stability studies on these ions were prompted by the unsuccessful H nmr investigations which, for similar purposes, had been attempted by Richardson (6). The single fluorine nucleus is particularly suitable for use as a diagnostic nmr tag in these systems. The principal reasons are the following. First, h but one such resonating nucleus in the species under investigation, the spectrum obtained is not complex and is therefore amenable to straightforward interpretation. Secondly, fluorine in the 4-positLon on a pheny] ring is known to be highly sensitive to changes in electron density in the Tr-system of the ring. See, for instance, the papers by L. (14,15), Dewar and Marchand (16), and Pews, Tsuno, and Taft

PAGE 25

15 r-
PAGE 26

16 al Lon by independently determining K. j_ tor this cation-carbinol 19 Libi Luni from F chemical shift data. This wort also focuses upon the use of the Deuo spectrophotometry ration technique for quantitative measurements of the stabilities of carbenium nons derived from free and couiplexed pyridylphenyi-4-rTuoro. annuls. The thermodynamic data so obtained are then compared 19 with corresponding F nmr chemical shift data via correlation analysis hods. This data treatment is carried out for the purpose of establishing interdependent relationships existing between the stability Information got from each of these types of physical measurement. In keeping with previous work the neutral bis(alcohol) pal ladiura(TT) complexes, Pd(II) (pyLOH)„Cl„, were prepared and studied by the physical methods described above. However, since these materials contain two moles of "ionizable" alcohol per mole of complex, the degree of positive charge development upon carbenium ion generation is questionable. This difficulty had been encountered by Wentz (8) in his investigations upon the thiazolyl complexed carbenium ions. In an attempt to resolve this problem complexes of the type Pd (II) (pyLOH) (T.„)C1„ were prepared. In tht ie new materials, L represents a neutral, nonionizable ligand which remains coordinated upon carbenium ion generation. Thermodynamic studies on these new complexes yield information which directly relates the nature of a singly charged coordinated carbenium ion to the stabilizing influence of the metal center. Thermodynamic data are presented In which are in respect to the following equilibria: H + pyI 4 + 2 HO t H + pyLOH + HgO* {2}

PAGE 27

1 / Cl^PdpyL* + 2 H 2 t C1 2 L PdpyLOH + H 3 + {3} CiUPdCpyL)^ + 4 H 2 t Cl ? Pd(pyLOH) 2 + 2 H 3 + {4} Equation {2} pertains to the aqueous titration of an uncoordinated pyridyldiphenyltnethyl carbenium ion. This equation is written to emphasize that the pyridine ring remains protonated throughout the reconversion of carbenium ion to alcohol. This transformation is associated with a positive charge change of 2+ to 1+. Equation {3} corresponds to the titrimetric reconversion of a singly charged coordinated carbeniuai ion to the neutral palladium complex precursor. This process is associated with a charge change of 1+ to 0. Equation {4} is a composite statement of what actually may be at least two stepwise processes; initially (perhaps) the reconversion of a species containing two coordinated carbenium ions to a species with but one coordinated ion, followed by complete reconversion to the neutral palladium bis-alcohol complex. This process may therefore be associated with two full units of positive charge change, viz^. , 2+ to 0. Considerations for purposes of critically evaluating the thermodynamic daLa obtained from investigations upon these equilibria are accounted. The apposite conclusions which follow have been presented and are carefully discussed.

PAGE 28

EXPERIMENTAL Synthesis of Ligands The pyr id} Idiphenylmethanols which have been employed as heteroaromatic donors (and as carbenium ion precursors) in this research, were prepared by standard Grignard synthetic methods. This generally involved the addition of an ether solution of the appropriate 2or 4pyridyl ketone to an ether solution of the required Grignard arylmagneiiura halide, follov;ed by acid hydrolysis of the salt-like intermediate to yield the desired alcohol. Since the necessary ketones were also e in this laboratory, the synthetic methods for their preparation have been included. A list of the special, commercially obtained its employed in these procedures, with names of suppliers, is provided ia Table I. The same apparatus and assembly was used in the preparation of h of the ligands (alcohols) and ketones. All glassware connections e with standard taper ground joint fittings unless otherwise specified. All glassware was scrupulously cleaned and dried prior to assembly, ground joints were carefully lubricated by the application of a lall quantity of; Dow Corning silicone grease. Rotation of the connected joints within one another assured the deposition of a unifV i of lubricant. The assembled apparatus consisted of a 3-necked, 18

PAGE 29

19 one-liter round bottom flask equipped with a ground gla ! stirring shaft in th.? center neck. The stirring shaft was fitted with a Teflon stir naddLe, and the shaft, was lubricated with the minimum amount of 8117 stirrer lubricant, "Stir-Lube," Ace Glass Co., Vineland, New .Jersey. Stirring speed was regulated with a rheostat controlled electric stirring motor. The side necks of the flask were fitted respectively with a 250 ml pressure equalizing addition funnel and a one-liter capacity, Dewar type condenser charged with dry ice during preparacive runs. The condenser was attached to the flask with a ball joint connection which facilitated reaction vessel manipulation required to maintain controlled atmosphere conditions throughout the system, Immediately following asseml i.y the system was purged with a steady stream of dry nitrogen gas. The nitrogen environment was maintained until the hydrolytic step was reached. All syntheses were performed using anhydrous diethyl ether as solvent. Magnesium metal turnings used for Grignard reagent preparation were conveniently activated (unless described otherwise) by placing the required quantity of turnings into the dry reaction flask and stirring them vigorously for a period of 24 — 36 hours at ambient temperature. This procedure reduced the metal to a finely divided gray-black powder which usually reacted readily with the appropriate aryl halide to yield the desired Grignard (20) . Grignard formation was initiated by gentle warming of the reaction mixture. If this reaction became too vigorous, cooling the flask with a cold water bath slowed the reaction to an equable rate. The subsequent addition of reagents to the Grignard (in situ) was done at reduced temperature by cooling the reaction flask with an insulated

PAGE 30

20 bath containing a mixture of chloroform and dry ice. The temperature of the bath was regulated by the. addition of dry ice as Deeded. < hen yl -2--pyridy lketone . Fluorophenylmagnesium bromide was prepared essencially by the method outlined by McCarty and coworkers (21). A solution of 63 ml (95 g, 0.54 mol) 4-bromof luorobenzene in 200 ml ether was added dropwise to 13 g (0.53 moi) of activated uiagnesium. The mixture was slowly stirred, and the reaction proceeded smoothly as evidenced by the gentle ebullition of ether and the formation of a brownish sludge. Following the complete addition of the ether — aryl halide solution the mixture was brought to gentle reflux by i irming the reaction flask with a "Glas-Col" heating mantle. Grignard formation was presumed to be complete following reflux for a period of 10 • 12 hours. The remainder of the procedure paralleled the method of de Jonge e^ al . (22). The f luorobenzene Grignard solution (above) was cooled to -35°. A solution of 26 g (0.25 mol) 2-cyanopyridine (picolinooltrile) in 200 ml ether was then added dropwise to the Grignard. This immediately resulted in the separation of a tan-colored solid. The reaction mixture was stirred continuously during the addition of the 2-cyanopyridine to prevent lumping of the tan solid. After all of the ?.--cyanopyridine had been added the cooling bath was removed, and stirring continued until the reaction mixture warmed to ambient temperature. ; and contents were then cooled to -30°, and the ket inline dition compound was hydrolyzed by the careful addition of 50 ml ice water. This . followed by the addit t 0° of 100 ml. concentrated I so] i Lng in the formation of a yellow (upper) ether layer

PAGE 31

21 and a red brown (lower) aqueous — acid layer. The ether layer was drawn off and discarded, and the aqueous layer was treated carefully with concentrated Nil solution until a pH of 6 — 7 was obtained. This resulted in the separation of copious quantities of a yellowish precipitate. This material was washed with deionized water and then shaken with sufficient fresh ether until ail the solid was red if. solved. The other phase was evaporated to yield 40 g (80%) of the ketone, a light tan solid which melted at 79 — 81°. The kecone was purified by vacuum sublimation to yield a white crystalline solid melting at 83 — 84°. 4--Methylphenyl -2-pyridylketone (p_-tolyl-4-pyridylketone) . A hexane solution of ri-butyilithium (63 ml, 1.6 M) was placed in the reaction flask and diluted with 250 ml ether. This solution was cooled to -40°, and an ice-cold solution of 10 ml (17 g, 0.11 mol) 2-bromopyridine in 100 ml ether was added dropwise with stirring. During the addition of the bromopyridine the reaction mixture became an orange slurry which changed gradually to a yellow-green slurry. Following the complete addition of the bromopyridine, stirring was continued until the reaction mixture warmed to -30°. The reaction mixture was then recooled to -45°, and a solution of 13 g (0.11 mol) p_-tolunitrile (p-nethylbenzonitrile) in 100 ml ether was added dropwise with stirring. This resulted in the formation cf a yellow slurry. Following the addition of the nitrile stirring was continued unti] the reaction mixture warmed to ambient temperature. The reaction mixture was now recooled to -40° and hydrolyzed by the dropwise addition of 200 ml 2 M HC1. The ether was distilled off, and the reaction mixture was

PAGE 32

to 100° and stirred for 1 hour at this temperature to facilitate decomposition. The aqueous reaction mixture was cooled in Lee and neutralized by the careful addition of 6 H Nil., resulting in the separation of a tan solid. The aqueous mixture was then shaken with sufficient fresh ether to dissolve the solid. The aqueous residue was discarded , and the ether was evaporated to yield 12 g (61%) of the cru'.ie ketone. This material was vacuum distilled (0.010 nun, bp 127°) auc! collected as a light yellow oil which crystallized on. cooling as yellowish needles. The needles were, dissolved in the minimum amount of a hot mixture of n-pentane — dichlorome thane (3:1) cud recrystallized at dry ice temperature as white needles melting at 42 — 43°. Phenyl-4-pyridylketone (4-benzoylpyridine) . This ketone was prepared in accord with the method employed for the synthesis of 4-fluorophenyl-2-pyridylketone (p. 20). The Grignard was prepared by the addition of 50 ml (74 g, 0.47 raol) bromobenzene dissolved in 75 ml ether to 10 g (0.-'-2 mol) of activated magnesium which was covered with 50 ml ether. Following the addition of the bromobenzene solution the reaction mixture was refluxed with stirring for 2 hours. A mixture of 21 g (0.20 mol) 4-cyanopyridine (isonicotinonitrile) in 2C0 mi ether was refluxed until the nitrile dissolved. This solution was then added dropwise to the cooled Grignard (-40°). This :ulted in the immediate formation of a tan solid, and the reaction i i if was stirred vigorously to prevent lumping. The ketimine intermediate was cooJed to -55° and hydrolyzed by the addition of 50 ml I ] saturated aqueous NH.C1. This was followed by the addition of 100 ml coned HC1 at 0°, resulting in the formal" ion of much rust-

PAGE 33

23 tlored solid. The further addition of acid (100 ml 6 M HC1) dis' red this solid. The ether layer was separated and discarded. Adjustment of the pH of the aqueous phase by the careful addition of coned NH-j resulted in the separation of copious quantities of a yellovz precipitate. This material was dissolved in the minimum amount of fresh ether. Evaporation of the ether yielded 34 g (93%) of the ketone, a well defined crystalline yellow solid y which melted at 68 — 70". 4 --Me thy lphenyl-4-pyridylke tone (p_-tolyl-4-pyridylketone) . This material wn^ prepared in the same manner as 4-f luorophenyl-2-pyridylketone (p. 20) The Grignard was prepared by the addition of 17 ml (24 g, 0.14 mol) p_-bromo toluene dissolved in 100 ml ether to 3.7 g (0.15 mol) activated magnesium covered with 50 ml ether. Following the complete addition of the aryl halide solution the reaction mixture was refluxed for 2 hours ana then cooled to -10°. This resulted in the separation of a brown precipitate so the Grignard was not cooled further. A filtered solution of 10 g (0.10 mol) 4-cyanopyridine in 100 ml ether was added dropwise with stirring resulting in the formation of a large amount of tan solid. Warming of this mixture to ambient temperature did not cause the solid to dissolve. The ether phase was drawn off by aspiration through a coarse frit filtering stick to remove unreacted 4-cyanopyridine. The reaction mixture was recooled to 0° while "ring, and hydrolysis was effected by the dropwise addition of 50 ml ice-cold saturated aqueous Nil, Br. This was followed by the addition of 60 ml 2 H HC1, and the mixture was allowed to stand until unreacted magnesium had dissolved completely. More acid was added needed to insure that the pH of the aqueous phase was less than 1.

PAGE 34

24 , sous phase was now washed twice with 200-ml portions of I' ct'u.er. The ether washes were discarded, and the aqueous phase was adji Lo pH 7 by the careful addition of 6 H NH . This resulted in I h sparation of a considerable amount of white precipitate. This trial was shaken with sufficient ether to effect dissolution. Evaporation of the ether yielded 14 g (71%) of the yellowish ketone which melted at 86 89°. 4-Hefchoxyphenyl-4-p yridylketon e. (This material had been prepared previously by Bbattacharyya and Stoufer (7) in accord with the method of LaForge (23). For the sake of completeness its preparation is given below.) A solution of 51 ml (74 g, 0.40 mol) p-bromoanisole (l-bromo-4methoxybenzene) dissolved in 160 ml ether was added dropwise over a period of 1 hour at ambient temperature to 9.6 g (0.40 mol) of activated magnesium. The reaction mixture was stirred vigorously throughout and refluxed for 1 hour following the addition of the broraoanisole. The Grignard was then cooled in an ice bath, and to this was added dropwise a solution of 21 g (0.20 mol) 4-cyanopyridine in A 00 ml ether. The reaction mixture was stirred constantly throughout. Following the addition of the 4-cyanopyridine, the reaction mixture was refluxed for J hour and then cooled in an ice bath to 0°. Hydrolysis was effected !>, the careful addition of 50 ml ice-cold saturated aqueous NH.C.1. The r and aqueous layers were then separated, and the aqueous layer Lee extracted with 100-ml portions of fresh ether. The ether is were combined with the original ether layer. The ether fraction extracted thrice with 200-ml portions of 3 M RC1. The aqueous

PAGE 35

25 Era< tioi s were pooled and extracted thrice with 100~ml portions of h Jther. All ether fractions were now discarded, and rhe aqueous fraction was ooiled for 1 hour to ensure complete katimine decomposition. The aqueous fraction was cooled and carefully neutralized with Lce-cold 3 M NaOH resulting in the separation of a yellow precipitate. This material was filtered, washed with fresh deionized water, and air dried. The crude ketone was then dissolved in 100 ml hot chloroform. This solution was treated while hot with anhydrous MgSO, and filtered . The volume of the chloroform filtrate was tripled by the addition of fresh ether and cooled for 1 hour. The reprecipitated solid was filtered, washed with ice-cold ether, and air dried to yield 28 g (71%) of the yellowish ketone which melted at 123 124°. ?--lyr idylphe nyl-4-f luorophenylmethanol . Magnesium turnings (8.1 g, 0.33 mol) were placed into the dry reaction flask, and a small crystal of iodine was added. The flask was carefully heated with a heating mantle until the iodine just vaporized whereupon heating was discontinued. As the iodine recondensed the magnesium turnings were stirred briefly to ensure the deposition of a reasonably homogeneous layer of Iodine onto the surface of the metal. A solution of 32 mi (51 g, 0.29 mol) 4-brcmof luorobenzene in 200 ml ether was added dropwise to the activated magnesium. The reaction mixture was stirred continuously as it was warmed co reflux. Reflux was continued for 2 hours following the addition of the aryl halide, and the reaction mixture was then cooled to ••60", A solution of 11 g (0.060 mol) phenyl-2-pyridylketone (2-benzoylpyridine) dissolved in 300 ml ether was added dropwise to .' Grignard. The cooling bath was removed periodically to

PAGE 36

26 5e the freezing out ot" materials from the reaction mixture. As t tone solution was added the reaction mixture became red-violet in color. Following the addition of the ketone solution the cool ; removed, and the contents of the flask were stirred until a temperature of -10° was attained. During this time the reaction mixture became dark brown in color. The addition product was hydrolyzed at -10° by the careful addition of 25 ml ice water resulting in the formation of a lemon-yellow ether layer and a pink aqueous layer. The aqueous layer v.as discarded, and the ether layer was extracted th ice with 200 — ml portions of 3 M HC1. The extracted ether layerwas discarded, and the aqueous phase was adjusted to pH 7 — 8 by the careful addition of 6 M NH„. This resulted in the separation of a yellow-orange solid. The solid — aqueous mixture was shaken with ficient fresh ether to dissolve all the solid. The aqueous portion was then discarded, and the ether solution was combined with 3A ilecular sieves until incipient crystallization was observed. The sieves ware removed, and the ether evaporated completely to yield 13 g (77%) of the crude yellow-orange carbinol. This solid was dissolved in 200 ml hot methanol and treated with 6 g of wood charcoal. This cure was refluxed 30 minutes and filtered. The hot, yellow methanol solution was allowed to stand until crystallization of a yellow solid occurred. The carbinol exhibited a melting range of 79 — 82°. Anal.: Calcd for C. Q H,,N0F: C, 77.40; II, 5.05; N, 5.0?. J.O X.H Found: C. 77.51; H, 5.10; N, 5.16. 2-E rid 1-4-methylph nyl -4-f luorophenylmetha nol. The Grignard was ictly as that for 2-pyridylphenyl-4-fluoropheny] nol

PAGE 37

27 (above) employing 8,2 g (0.33 mol) magnesium turnings and 31 ml (<^9 g, nol) 4-bromof luorobenzene . The reaction mixture was then cooled -50°,
PAGE 38

28 h stirring to 1.3 g (0.053 mol) activated magnesium covered b 25 ml ether. The reaction mixture was heated to gentle rei'iux, 1 the formation of Grignard was evidenced by the development of a grej -brown translucency. Following reflux for a period of 2 hours gnard formation appeared to be complete. The reaction mixture was now cooled to -5° with an ice — salt bath, and to this a solution of 6.0 g (0.030 mol) 4-f luorophenyl-2-pyridylketone dissolved in 120 ml ether was added dropwise with continuous stirring. During this addition of ketone a yellow solid settled out. Following the addition of ketone the cooling bath was removed, and stirring was continued as the reaction • ; . : :cure slowly warmed to ambient temperature. This resulted in the formation of a light tan-colored suspension with traces of reddishpurple material dispersed throughout. The reaction mixture was subsequently heated to reflux for a period of 1 hour and then cooled. rhe hulk of the ethereal solution was removed from the reaction flask by aspiration, through a coarse frit filtering stick. The material which remained in the flask was washed three times with 50 — ml portions of fresh ether. The ether washes were removed by aspiration I combined with the original ether layer. Upon standing a white semisolid material separated from the ether. The residual reaction are was now hydrolyzed at 0° by the careful addition of 50 ml irated aqueous NH.Br, followed by 150 ml 1 M HC1. This resulted in the separation of a yellow oil. The aqueous phase was adjusted to pH 7 by the careful addition of 3 M NH„. This produced a milky dislion of the oil. The aqueous phase was then shaken with fresh ether until the dispersion cleared, and the aqueous layer was drawn off discarded. The aspirated ether portions (above) were filtered

PAGE 39

?-•) through a medium frit to separate the white semisolid material. ] ether filtrate was discarded, and the white materia] was hydrolyzi on the frit by the addition of a few ml deionized water. This produced more of the yellow oil. The Oil was dissolved :in fresh ether, and the oil — ether solutions were combined. Evaporation of the ether yielded 6.2 g (67%) of the oily carbinol. Repeated attempts to crystallize this material were unsuccessful. An accurate mass for the molecular ion of the carbinol was determined mass spectrally. Calcd for C^K^NO^F: 309.1164. Found: 309.1170 (mean of four determina19 16 I tions; deviation, ±2 ppm) . 4-Pyridylphen 3^1-4-f lu orophen ylmethanol . A solution of 12 ml (18 g, 0.10 raol) 4-bromof luorobenzene in 50 ml ether was added dropwise to 2.4 g (0.10 mol) ether-covered activated magnesium. Stirring was continuous during the addition of the aryl halide, and Grignard formation ensued upon gentle warming of the reaction flask as evidenced by the development of a grey-brown dispersion and the ebullition of ether. After the aryl halide had been added the reaction mixture was stirred and refluxed for a period of 2 hours. Subsequently, the reaction mixture was cooled to -5°, and a filtered solution of 11 g (0.60 mol) phenyl-4-pyridylketone dissolved in the minimum amount of ether (ca. 200 ml) was added dropwise. This resulted in the immediate formation of a pink solid. Vigorous stirring was maintained to insure uniform mixing. Stirring was stopped following the addition of ketone, and the mixture stood at ambient temperature for a period of 12 hours. The bulk of the ether phase was now drawn off by aspiration through

PAGE 40

30 a coarse (Trie filtering stick and discarded. The residual solid \ I twice with fre.>h 50 ml portions of ether, and the war re carded. The solid was subsequently recooled to -5° and hydrolyzed with stirring hy the dropwise addition of ICO ml saturated ice-cold sous Nil, Br. This was followed by the addition cf 1 M HC1 until a pH of 5 — 6 was attained. The aqueous mixture was now transferred .'. large separatory funnel and shaken with 400 ml ether. The aqueous (lower) layer was tan in color, and the ether (upper) layer was yellow. A small quantity of semisolid yellow material resided at the interface of the liquid layers. The aqueous layer was drawn off, and the semisolid was combined with the ether layer and together shaken with four separate 150 — ml portions of 2 M HC1. This resulted in the dissolution of most of the solid and a translucent ether layer. Evaporation of the ether yielded a small amount of brown material which was discarded. All of the aqueous portions were then pooled resulting in the development of an opaque dispersion. Treatment of the aqueous layer with 6 M NHproduced initially a clearing of the opaqueness, and as the pH was raised to 4 — 5 much white solid separated. The solid was isolated by filtration and the filtrate again treated with 6 M Nil., to bring the pH to 7. This resulted in the separation of o white solid which was also filtered off. All of the aqueous filtrate was discarded, and the combined solid samples were air dried to yield 15 g (92%) of product which exhibited decomposition to a 1 iwnish oil at. 185 — 190°. To convert any hydrochloride salt to free rbinol the entire amount of white solid was slurried with 100 ml 1 M After stan ling ("or 1 hour the solid was separated by suction filtration, i I with 200 ml of deionized water and air dried. The

PAGE 41

; ;i Lated material was a finely divided white solid which incited at L92 — 194° without appreciable discoloration. m1.: Calcd for C lg H ,NOF: C, 77.40; H, 5.05; N, 5.02. Found: C, 77.13; H, 5.09; N, 5.00. An accurate mass for the molecular ion of the carbinol was determined 18 spectrally. Calcd for G' I'NOF: 279.1058. Found: 279.1052 ' lo 14 (mean of five determinations; deviation, ±2 ppm) . 4-Pyx Ldyl-4-methylp henyl-4-f luorophenylmetha nol . The preparation of this carbinol was carried out by the method used for the preparation of 4-pyridylphenyl-4-f luorophenylmethanol (above). The quantities of materials employed were: 2.9 g (0.12 mol) magnesium; 14 ml (21 g, 0.12 moi) 4-bromof luorobenzene dissolved in 50 ml ethar; and a filtered solution of 7.4 g (0.038 mol) 4-methylphenyl-4-pyridylketone dissolved in 125 ml ether. Following hydrolysis the aqueous phase x^/as adjusted to pH 1 with 1 M HC1 resulting in the separation of 5—10 ml of a brown oil. This oil was drawn off; the workup of the oil is given below. The acidic aqueous phase was twice shaken with 400 — ml portions of fresh ether. Each shaking resulted in the separation of a small quantity of yellowish semisolid material. This material and the ether extracts were discarded. The aqueous phase was neutralized by the careful addition of 6 M NH~. This resulted in the separation of a yellowish solid which was isolated by suction filtration. Characterization of the solid (4.4 g) revealed that it was the crude carbinol. The brown oil (above) was stirred with 300 ml 1 M HC1 resulting in tne formation of a brown

PAGE 42

creamy emulsion. The emulsion was extracted thrice with 100 — ml portions of ether. This removed the translucency from t. leous 1 which was now a light yellow solution. All the organic washes were discarded, and the aqueous layer was neutralized by the careful addition of 6 M NH>. This resulted in the separation of a yellowish solid which was filtered, washed with deionized water, and air dried to yield 1.2 g of solid which melted at 169 172°. This material, combined with the previously isolated solid, afforded a yield of 50%. Anal. : Calcd for C ig H 16 N0F: C, 77.75; II, 5.56; N, 4.77. Found: C, 77.60; II, 5.55; N, 4.82. An accurate mats for the molecular ion of the carbinol was determined mass spectrally. Calcd for C in H n ,.N0F: 293.1215. Found: 29^.1216 19 16 (mean of three determinations; deviation, ±0.3 ppm) . 4-Py ridyl-4-methoxyphenyl-4-fluorophenylmethano l. The Grignard was prepared exactly as was that for 4-pyridylphenyl-4-f luorophenylmethano.1 (p. 29) using 1.3 g (0.53 mol) magnesium; and 60 ml (9.0 g, 0.51 mol) 4-bromofluorobenzene dissolved in 30 ml ether. To this at -5° was added in 100 — ml increments a solution of 5.5 g (0.25 mol) 4-methoxyphenyl-4-pyridylketone dissolved in 600 ml echer. As the ketone solution contacted the reaction mixture a yellow solid formed and separated. Following the addition of ketone the stirred reaction mixture was refluxed for 90 minutes and was then set aside and not disturbed for a period of 12 hours. The reaction mixture was noi; a yellow creamy dispersion, and little of the ethereal liquid phase could be drawn off by suction through the glass filtering stick. Therefore, the reaction mixture was cooled to -5° and hylrolvzed by

PAGE 43

33 the dropwise addition of 50 ml of saturated ice-cold aqueous NH.Br, 4 followed by the addition of 100 ml 1 M HC1. This resulted in the dispersion of a brown oily material in the aqueous phase. The ether layer was extracted four times with 125 — ml portions of 1 MHC1 and then discarded. The aqueous portions were pooled yielding a yellow-green opaque mixture. This mixture was adjusted to pH 7 by the careful addition of 6 M NH~, and upon standing for 2 — 3 hours a quantity of light tan solid separated. The solid was filtered, air dried, and dissolved in a refluxing mixture of 100 ml 4:1 ethylacetate — acetone. After standing 72 hours, this solution was reduced to a volume of ea . 30 ml by evaporation which resulted in the separation of a white crystalline solid. The crystals were filtered, washed with a few ml of ice-cold ether, and ait dried to yield 4.0 g (41%) of the carbinol melting at 181 183°. Anal.: Calcd for C 19 H 16 N0 2 F: c > 7 3-77; H, 5.21; N, 4.53. Found: C, 73.75; H, 5.26; N, 4.51. An accurate mass for the molecular ion of the carbinol was determined mass spectrally. Calcd for C. n H_ ..NOF : 309.1164. Found: 309.1167 (mean of six determinations; deviation, ±1 ppm) . The Purification of Diphenyl-4-p y ridylmethane . The commercially obtained alkane (mp 120 — 125°) was found to be contaminated by trace amounts of the corresponding diphenyl-4-pyridylcarbinol (from which the alkane was probably prepared). This was demonstrated by treating a sample of the "alkane" with 70% HC10, which produced color characteristic of alcohol ionization. A visible spectrum of this acid solution gave band positions identical to those got for a similar (known) solution of d j phenyl-4-pyr idylcarbinol .

PAGE 44

34 I is column (20 cm x 2 cm i.d.) was fitted with a r;Lopcock which was inserted a plug of glass wool covered wit'.i a I cm it . The vertically supported column was tilled ca. half full with reagent hexane, and the stopcock was opened slightly to the dropwise outflow of solvent. A hexane slurry of freshly activated 80 — 200 mesh alumina (Brockman Activity I) was poured into the column, and as the alumina settled on the sand mat the column was . Fully agitated to insure uniform adsorbent deposition. A 0.5 cm thick sand mat was added to the top of the alumina layer in the packed column, and the level of solvent was adjusted to coincide with the top of the sand mat. A saturated solution of the alkane was prepared by stirring 2 g of the alkane into 6 ml benzene. This solution was filtered and carefully placed on the column. Gravity elution was carried out: by the dropwise percolation of the following solvents: 1) 250 ml 1:1 hexane — benzene; 2) — 5) 500 — ml portions of ether. Each of the ether fractions 2—4 was evaporated separately yielding ca . equal quantities of a white solid. A small portion of each of these samples of solid was treated with 70% HC10, . In each instance the resulting solution was virtually colorless. These samples of solid were combined and dissolved in the minimum amount of hot methanol. Crystallization afforded a yield of 1.0 g of well developed white needles which melted at 125 — 126°. A solution of these, needles in 70% 1IC10, ; transparent in the visible region of the spectrum.

PAGE 45

35 S ynth cs [ s of Complexe s I. The Preparation of the "bis" Alcohol Complexes of Palladium (If) , [Pd260° and decomposed to a black oil at 295°.

PAGE 46

36 . C Led Eor C 36 H 2g N 2 2 F 9 PdCl 2 : C, 53.75; H, 3.83; N, 3.81. Found: C, 58.73; H, 4.03; N, 3.70. 0ichlor'jbis(4--pyrio yl-4-niethylphenyl-4-fluoro pheny lmethanol)palladium(II) . The material was prepared in exactly the same fashion as for the preparation of the bis(4-pyridylphenyl) complex (above) _3 using C.53 g (1.8 x 10 mol) 4-pyridyl-4-methylphenyl-4-f luorophenylthanol. A yield of 0.17 g (22%) of well defined yellow needles was obtained. The product exhibited darkening at >240° and decomposed to a black oil at >260°. Anal.: Calcd for C-JBLgN^FjPdClj: C, 59.74; H, 4.22; N, 3.67. Found: C, 60.26; H, 4.33; N, 3.49. Dichlorobis(4-pyridyl-4-methoxyphenyl-4-f luorophenylmethanol)palladium(II) . This material was prepared in exactly the same fashion as for the preparation of the bis (4-pyridylphenyl) complex (above) _3 using 0.56 g (1.8 x 10 " mol) 4-pyridyl-4-methoxyphenyl-4-f luorophenylmethanol. A yield of 0.16 g (20%) of well defined yellow needles was obtained. The product exhibited darkening at >240° and decomposed to a black oil at 250° . aal. : Calcd for C^U^O^PdCl^ C, 57.34; H, 4.05; N, 3.52. Found: C, 57.90; II, 4.21; N, 3.38. ' 'J -h lor obis (_2-pyridyl-4-methylp henyl-4-f lu oro phenylmethanol) p alladium (I I) [This material was not amenable to the thermodynamic investigations ich were carried out in this work. (See Results and Discussion, p. 97). However, for the sake of completeness, its preparation is given.

PAGE 47

It is the only well defined "2-pyridyl" complex which was isolated.] In actuality this material was obtained as a side product of the synthetic method which had been designed for the preparation of the "saltlike" complex (Z , PdLCl~) , where Z is a suitable cation, and L is the pyridylnethanol. _3 Palladium chloride powder (0.28 g, 1.6 x 10 " mol) was placed in _3 a 250-ml round bottom flask together with 0.0/2 g (1.7 x 10 mol) _3 dry lithium chloride, 0.47 g (1.6 x 10 mol) 2-pyridyl-4-methylphenyl4-f luorophenylmethanol, and 50 ml acetone. This mixture was stirred magnetically as it was refluxed for a period of 2 hours resulting in the dissolution of all solids and the formation of a deep red-brown solution. The acetone was then removed by distillation yielding some red gummy material. The gummy semisolid was redissolved by the addition of 10 ml fresh acetone reproducing the red-brown solution. A heaping microspatula of tetramethylammonium chloride was dissolved in a mixture of 2 ml acetone and 1 ml methanol. This colorless salt solution was added to the red-brown solution (above) producing no apparent change. The addition of 2 ml dichloromethane induced the separation of a reddish oily material which clung to the inner walls of the flask. After standing overnight the oily material had failed to crystallize and was redissolved by the further addition of 20 ml fresh acetone. This solution was heated; following 30 minutes reflux a salmon-colored crystalline solid separated with the solution phase now being yellow-orange in color. A second microspatula of tetramethylammonium chloride was added, and the reaction mixture was returned to reflux for a period of 2 hours. After cooling, the salmon-colored solid was separated by filtration. (This solid was later: shown to be tetramethylammonium tetrachloropalladate(II) . ) The

PAGE 48

38 Llow-orange acetone filtrate was flooded with deionized water resultLi in the separation of a yellow crystalline solid. This solid was red by suci Lou through a medium frit, washed with deionized water. and air dried to yield 0.52 g (43%) of a material characterized as the ''bis" alcohol complex (Pdl^Cl^ . This material decomposed to a black Oil above 195°. tl. : Calcd for C^H^l^O^PdCl^ C, 59.74; H, 4.22; N, 3.67. Found: C, 59.56; H, 4.39; N, 3.70. II. The Preparation of the "Mono" Alcohol Complexes of Palladium ('Q) , 1 Pd (II) (pyLOI-I) OkJCl,] , where L„ T is Diphenyl-4-pyridylrae thane. (See also p. 33) . The Preparation of Pd(I I) (pyLOH) (L N )C1?, where pyiOH is 4-Pyridyl phenyl4-fluorophenylme thanol . In a dry environment 0.01 g (5.6 x 10~ mol) palladium chloride powder was transferred to a 250-m.l round bott cm flask together with 0.16 g (5.8 x 10 + mol) dried tetca-n-butylamuioniunv chloride and 100 ml acetone. This mixture was stirred magnetically as it was refluxed for 72 hours to dissolve all solids, producing a deep n 1 -brown solution. To this solution was added 0.14 g (5.7 x 10~ mol) purified diphenyl-4-pyridylmethane (p. 33). As the alkane dissolved the color of the solution changed from red-brown to red-orange. This solution was refluxed for 2 hours and cooled. To this was added 0.16 g (5.7 x 10 mol) 4-pyridylphenyl-4-f luorophenylmethanol; as the alcohol isolved, the color of the solution changed from red-orange to yelloworange. This solution was refluxed for 1 hour after which acetone was -.1 by distillation until a solution volume of ca. 30 ml was attained,

PAGE 49

mixture was now distinctly yellow with incipient; precipitation of a yellow solid having begun. Sufficient deionized water (ca. .10 ml) was added until permanent cloudiness was produced. Tne mixture, was allowed to stand 48 hours to promote crystal growth, and was then filtered by suction through a tared frit (medium). The collected yellow solid was washed with deionized water and dried on the frit at 130° for a period of 1 hour. A yield of 0.35 g (89%) of well defined yellow needles was obtained. This material darkened above 245° and decomposed to a black oil above 270°. Anal. : Calcd for C 36 H 29 N 2 OFPdCl 2 : C, 61.60; H, 4.16; N, 3.99. Found: C, 61.34; H, 3.93; N, 3.83. Th e_ Prepara tion of Pd(II) (pyLOH) (L>;)C1?, w here py LOH is 4-Pyri dy3 -41 ..•.'hylphanyl--4~ f luorophenylmeth anol . This complex was prepared in exactly the same fashion as that for the 4-pyridylphenyl-4-f luorophenylmethanol complex (above) . The same quantities of materials were employed together with 0.17 g (5.7 x 10~ * mol) 4-pyridyl-4-methylphenyl-4-f luorophenylmethanol. A yield of 0.35 g (87%) of well defined yellow needles was obtained. This material decomposed to a brown-black oil above 245°. Anal. : Calcd for C 37 H 31 N 2 OFPdCl 2 : C, 62.07; H, 4.36; N, 3.91. Found: C, 62.20; H, 4.32; N, 3.77. ghg ..g. r c .P rtr;ition o £ Pd(II) (pyL 0H)(L Y )Cl ? , where pyLOH is 4-Pyri dvl-4'.::xyph enyi-4-f luoropheny l methan ol. This complex was prepared in exactly the same fashion as that for the 4-pyridylphenyl-4-fluorophenylmethanol complex (above). The same quantities of materials were employed

PAGE 50

40 together with Q.io g (5.7 x 10~ mol) 4-pyridyl-4-methoxyphenyl-4phenylmethanol . A yield of 0.35 g (S4%) ol M defined yellow is obtained. This material darkened above 180° and deco^po . to a brown oil above 210°. Anal. : Calcd for C 37 H 31 N 2 2 FPdCl 2 : C, 60.71; F, 4.27; N, 3.83. Found: C, 60.94; H, 4.46; N, 3.83. Tetra-ji-butylammonium Tr ichloro(4-pyridylphenyl-4-f luorophenylmethanol) palladate(II) . This "salt-like" complex was prepared separately in order to establish the fact that it was a stable, isolable intermediate. (See Results and Discussion, p. 58.) -4 Jn a dry environment 0.12 g (4.3 x 10 mol) tetra-n-butylarcmonium _4 chloride, 0.075 g (4.2 x 10 mol) palladium chloride powder, and 100 ml acetone were placed together in a 250-ml round bottom flask. This mixture was stirred magnetically as it was refluxed for a period of 24 hours. The reaction mixture now consisted of a deep red-brown solution ;e containing traces of undissolved white and red-brown solids. The solution phase was carefully decanted into a clean flask, and to this -4 was added 0.12 g (4.2 x 10 mol) 4-py;:idylphenyl-4-f luorophenylmethanol. As the alcohol dissolved the solution changed color from red-brown to orange. This mixture was stirred magnetically at ambient temperature for a period of 1 hour and was then heated to reflux. Acetone was reived by distillation during reflux until a solution volume of ca. 30 ml is attained. To the hot red-orange acetone solution was added 30 ml ether, and this solution was allowed to cool without stirring. To the cooled solution n-pentane was added in small portions until permanent Liu ;s was attained. Upon stirring for a period of a few hours a

PAGE 51

41 all quantity of yellow-orange crystals developed and settled to the bottom of the flask. The solution phase, which was now slightly yellow, is treated again with n-pentiine to reinduce cloudiness. After standing o might the mixture was gravity filtered through a fluted filter , and the virtually colorless filtrate was discarded. The crystals which were collected were air dried, examined under a microscope, and found to he thin, transparent gold-orange sheet-like needles. This material melted at 150° to a red-brown oil. A yield of 0.29 g (94%, as based on palladium) was obtained. Anal. : Calcd for C .H^Q^OFPdCl.,: C, 55.60; H, 6.86; N, 3.81. Found: C, 55.35; H, 6.87; N, 3.77. Elemental Analyses Carbon, hydrogen, and nitrogen elemental analyses for ligands and complexes were performed either by PCR Incorporated, P. 0. Box 466, Gainesville, FL, 32601, or by Atlantic Microlab, Incorporated, P. 0. Box 34306, Atlanta, GA, 30308. No special handling techniques were required for either the ligands or the complexes. Reagents and Solvents The special, commercially obtained reagents which were employed i i this research are listed in Table I (p. 42). These materials were used without further purification unless otherwise specified. The

PAGE 52

Table I Special, Commercially Obtained Reagents and Suppliers Reagent Supplier p_-bromoanisole (l-bromo-4ne thoxybenzene) 4-bromof luorobenzene 2-bromopyridine 2-cyanopyndine (picolinonitrile) 4-cyanopyridine (isonicotinonitrile) diphenyl-4-pyridyIcarbinol dipbenyl-4-pyridylniethane phenyl-2-pyridyl ketone (2-benzoylpyridine) tetra-n-butylammonium cbloride p_-tolunitrile (_p_-methylbenzonitrile) Aldrich Chemical Co., Inc, Milwaukee, WI, 53233 Aldrich Aldrich Aldrich Aldrich K & K Laboratories, Inc., Plainview, NY, 11303 Aldrich Aldrich Eastman Kodak Co., Rochester, NY, 14650 Aldrich additional reagents and solvents which were employed were readily available, reagent grade quality materials, and were used without further purification.

PAGE 53

43 Instrumental Analytical Me th Proton Magnet ic Resonance Spectra . The "I) nmr spectra were obtained using a Varian Associates Model A-60A nmr spectrometer operating at 60 MHz. The spectra were taken as saturated carbon tetrachloride solutions using tetramethylsilane (TMS) as internal standard. The spectra were examined principally with respect to integrated peak intensity ratios for the purposes of ascertaining sample homogeneity and molecular composition. Mass Spectra . Mass spectra were obtained using an AEi MS-30 mass spectrometer equipped with a DS-30 data system. Solid and oil samples were introduced into the ionization chamber via direct insertion probe at 200° and run at an ionizing voltage of 70 eV. Infra red Spectra . The IR spectra were obtained using a Perkin-Elmer Model 337-B grating infrared spectrophotometer scanning the region 4000 — 400 cm . Solid samples were intimately ground with oven dried reagent potassium bromide and run as pressed semimicro discs. Oily samples were run as follows: A neat potassium bromide disc was pressed and supported horizontally. The oil was warmed until it became fluid, and a drop of the oil was added to the surface of the salt disc. This technique deposited the oil as a uniform thin film on the disc. The tctrura was recorded as soon as the oil cooled sufficiently to become v Lscous. The IR spectra were used to provide evidence of ligand homogeneity by establishing the absence of a carbonyl stretching vibration (ketone),

PAGE 54

44 the presence of a hydroxyl band (alcohol), and to confirm the presence of both ligands in the "mixed" mono-alcohol complexes (pp. 38-40). 19 Fluorine Magnetic Res ona nce Spectra . The F rurcr spectra were obtained using a Varian Associates Model XL-100-15 nmr spectrometer operat i at 94.1 MHz in either continuous wave or Fourier transform pulse mode. Fourier transform capabilities were provided with a Nicolet TT-100 computer system equipped with a 16 K capacity memory. All spectra were recorded using external H„0 as a lock signal. Fluorine resonances were recorded relative to 10% CFClo in acetone and to neat trif luoroacetic acid as external reference standards. Operation at a sweep width of 5000 llz afforded an uncertainty of ±15 Hz (±0.16 ppm) in the position 19 of observed F signals. Ligsnd spectra were recorded as 0.05 M acetone solutions, as 0.05 M 10% HC10, solutions, and as saturated 70% HC10, solutions. Spectra of complexes were recorded as saturated acetone solutions and as saturated 70% HC10, solutions. All solutions were filtered through a coarse frit directly into the nmr sample tube just prior to recording of spectra. HC10, solution spectra of the complexes were run in large capacity nmr tubes employing Fourier transform techniques exclusively to facilitate signal detection for these very dilute samples. All samples were air cooled in the sample holder during the recording of spectra in order to maintain ambient temperature. Visible Spe ctra and Molar Absorp ti vity Co efficien t IX 1 1 cr mfna t ion . Vis Lble spectra were obtained using a Beckman Model DBing spectrophotometer equipped with a Sargent Model SR recorder. Molar absorptivity

PAGE 55

coefficients (e, Table II, p. 77) were, determined for carbenium ion species derived from each of the free and complexod alcohols dissolved in 70% HC.1.0, . Samples of appropriate size (10 to 10 " g) were weighed to three significant figures using a Cahn Model 1501 Gram Electrobalance calibrated in the 1 mg range. Oily samples had to be weighed by difference. This was done by taring a small finely drawn glass whisker aad then carefully touching the glass whisker to the oil until a very small bit of the. oil adhered to the whisker. The weight of the oil was obtained from the combined weight of the oil and whisker. The weighed samples were stirred in ca. 9 ml of the acid to complete dissolution and then made to 10.0 ml with fresh acid. These acid solutions were scanned vs . the neat acid as blank spanning the region 760 — 320 run to ascertain the position of A for the various carbenium ion max species. Each ionic species exhibited two main absorption bands with the more intense band appearing at lower energy. If the absorption maxima were "off-scale", the acid solutions were diluted with the necessary quantity of fresh acid to produce "on-scale" readings within acceptable sensitivity limitations of the spectrophotometer readout, viz ., >10% T (<1.0 absorbance units). Visible Spectra and the "Deno" Titration Technique . The equilibrium constant (Kg-p datum pertaining to the. thermodynamic stability of each of the carbenium species which have been considered in this work was experimentally obtained as follows: a 70% HC10, solution of the alcohol (ligand) or complex under investigation was prepared and diluted (if necessary) with fresh acid until an "on-scale" (viz . , 15 — 25% T) jctrophotometer reading was obtained with the instrument set at *

PAGE 56

46 for Chat particular ionic species. It is not necessary to fix the concentration of this solution. (See Results and Discussion, p. 92.) I iter mined quantity of this solution (ca . 5 g) was weighed to £ i significant figures into the special cuvette (described below). (By employing the same sample size for each titration, data treatment was greatly simplified.) In order to obtain exactly the same weight for ouch sample, very minute quantities of the parent acid solution could be transferred to or from (as necessary) the contents of the cuvette with the tip of a finely drawn glass rod. The acid solution in the special cuvette was then transferred to the cell compartment of the spectrophotometer and "read" at X relative to a samole of the neat max acid used as blank. The cell compartment was thermostatted at 20 — 25° by the circulation of tap water. The special cuvette was removed from the cell compartment, and the parent acid solution of Lhe carbenium ion was diluted by the addition of a measured increment (ca. 0.02 — 0.0S g) of deionized water from the special burette (described below). Following each addition of water the acid solution was carefully mixed in trhe cuvette; the cuvette was returned to the spectrometer, and the absorbance reread. This procedure was repeated until the absorbance of the acid solution had fallen off considerably (<0.20 absorbance units) thereby indicating a reconversion of carbenium ion to alcohol (or complexed alcohol) precursor in excess of 50%. Data treatment is considered in Results and Discussion (pp. 83-103). The specific gravity (p) of the reagent 70% HC10, was determined before performing the titrations by weighing accurately (5 sig. fig.) a measured volume of. the acid in a 10 ml volumetric flask which had > volumetrically calibrated (to 4 sig. fig.) with a weighed sample

PAGE 57

47 of distilled water. Prior to calibration the neck of the flask w heated and drawn to a fine bore of sufficiently large inner diameter to permit insertion of a Pasteur pipette for liquid transferral. The flask was then calibrated by marking the drawn neck at a volume dictated by the weighed sample of water contained in the flask. Specific gravity data for water at ambient conditions were used to calculate the volume of the flask at the calibration mark. Spec ial Cuvette . A 1.00 cm path length quartz cell fitted with a quartz/ Pyrex graded seal stem was obtained from Pyrocell Manufacturing Co., Inc., WestwoodNJ, 07675, The stem was shortened so that the cell fitted conveniently into the sample compartment of the spectrometer. A standard taper size 13 ground glass neck was added to the top of the stem to facilitate the direct dropwise addition of water to the acid solution of the carbenium ion contained in the body of the cell during titration. A si.de arm of ca. 4 ml capacity was fused to the stem at an angle of ca. 75° to the cell. Thus the thorough mixing of water with the acid solution during titration was readily accomplished by rocking the cell after each addition of water through an angle of 90°. This particular cell design also eliminated any problems associated with sample less upon removal of the cell stopper prior to each addition of titrant (water) since none of the liquid sample was in contact with the stopper throughout the titration. la l Burett e. A 5.00 ml capacity semimicro burette equipped with an automatic refilling reservoir and side arm was fitted with a 5 cm length irgical tubing at the drip tip. A 12 cm length of 6 mm (o.d.)

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48 ;ry tubing was drawn to ry fine bore pipette tip at one end. opposite end of the capillary was inserted snugly into the open of the surgica] tubing. A small screw clamp was affixed to fcl gical tubing. With the stopcock opened on the burette, the screw clamp was adjusted until drops of uniform size were discharged at a nonvenient rate from the drip tip of the capillary. It was found that nig a titrimetric run (ca. 30 minutes) drops of water could be collected from this burette assembly which differed in weight by not more than ±0.0002 g for drops averaging 0.0190 to 0.0230 g, provided the tip of the capillary was wetted prior to drop size calibration. This obviated the need to weigh the sample in the cell following each addition of water; i.hat is, it was necessary only to count the number of drops collected in order to determine the total quantity of added water at any given time during the titration.

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RESULTS AND DISCUSSION Synthetic Consideratio n On the Pr eparation of Ligands . The pyridine alcohol carbenium ion precursors employed as ligands in this work were found to be conveniently preparable by the Grignard reagent synthetic routes, outlined in the experimental section. It was discovered, however, that consistently better yields of product were obtained when the Grignard reagent was prepared from 4-bromof luorobenzene followed by the addition of the appropriate pyridyl ketone. That is, in attempts to prepare the identical alcohol from a 4-f luorophenylpyridylketone and the required phenyl-type Grignard, much poorer yields were got. These results suggest that 4-bromof luorobenzene Grignard was readily prepared in good yield as a reactive intermediate and was a sufficiently potent carbanionic reagent Co attack the carbonyl carbon of the ketone. The difficulties encountered in the alternate synthetic route leading to acceptable quantities of product are attributed to the preparation in poor yield of the necessary Lgnard intermediate. This was particularly obvious in the case for Lch 4-rae thy 1 phenyl Grignard or 4-methoxyphenyl Grignard were the . [uired carbanion. Thus, ketones prepared from these Grignards could usually be obtained only in poor yield. None the less this was not a »f consequence since the desired material (the ketone) was 49

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r >0 Ly separated from the unreacted starting materials. However, the jparation of alcohol from parent ketone was very difficult, and it was necessary therefore to convert ketone precursor to alcohol as completely possible in order to isolate the desired alcohol as a ketone-free product. Thus, the preparative route for the alcohols employing 4-broraoorobenzene Orignard was the better method. The filter stick filtration technique employed prior to hydrolysis in the synthetic procedures for the preparation of alcohols facilitated the removal of unreacted ketone from the reaction mixture. This technique utilized the fact that the ketone — Grignard addition compound was sparingly soluble in the ether solvent whereas the ketone itself was sioderately to readily soluble. Therefore prior to hydrolysis unreacted ketone which was dissolved in the ether layer could be drawn off by ion through the filter stick. Repeated washings of the reaction mixture with fresh ether, followed by filter stick filtration, afforded essentially complete removal of unreacted ketone. On the C hoice of Palladium(ll) . The most obvious reason for the incorporation of palladium(TI) as the central metal species into the complexes considered in this research is to permit a direct and immediate extension upon the related work of previous investigators. Richardson (6) and Ventz (8) both pointed out the suitability of palladi.um(II) to such investigations owing to its low oxidation state and high penultimate rbita] ocrupancy. These factors would be expected to contribute L
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51 members of the llgand -n-system. The relative inertness of palladium (II) complexes also suggests that such complexes would be amenable to these types of studies. Finally, the diamagnetic nature of 4 -coordinate palladium(II) stemming from its square planar complex geometry, makes it convenient for nmr investigations on the stability of a coordinated carbenium ion since no paramagnetic contribution to measured chemical shifts would be observed. On t he Selection and P reparation of Complexe s. The results of previous investigations of bis palladium(II) complexes of ionizable pyridyl and thiazolyl alcohols demonstrated the suitability of coordinated carbenium ions derived from these complexes for thermodynamic stability studies upon such ions. Therefore, the bis palladium(II) complexes were prepared in order to enlarge the scope of earlier work through similar studies upon carbenium ions derived from the fluorine-tagged pyridylmethanols . The palladium(II) complexes containing but one ionizable ligand molecule per complex were prepared so that a one-to-one relationship could be established between a coordinated carbenium ion and the stabilizing effects exerted by the metal-containing moiety. Indeed, the development of such a synthetic method would in itself be a novel contribution to that area of preparative coordination chemistry embodying palladium(II) as the central metal species. This follows in that there are known many "mixed" neutral complexes of palladium(II) of the type [Pd(II)XYL L„] , where X and Y are anionic groups, and L.. and L,. -.iro neutral donor ligands. In none of these complexes, however, are L ligands pyridine homologs; rather they are usually donors which exhibit particularly strong 77-acid character. Exampjes of those ligands

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52 eh are usually found in these complexes are PR„ (R = alky! or aryl) , •SR,,, CO, and various alkenes. Actually, work ha? been repotted conn Lug the preparation of such mixed complexes wherein pyridine donors have been ini Led into the coordination sphere as neutral ligands, but the bulk of this work has focused upon the use of platinum (I I) a;s central metal species. In 1936 Mann and Purdie (24) reported the preparation of mixed complexes of palladium(II) having the general formula [Pd (II) (P.u„P) (am)Cio] > where Bu^P is tri-n-butylphosphine, and am is either aniline, p_-toluidine, or pyridine. These complexes were obtained via the initial preparation of the bi.nuclear chloride-bridged trans bis(Bu,P) complex (Pd„(Bu,P)-Cl, ] , followed by cleavage of the chloride bridges with the required molar ratio of the amine of choice. However, an examination or the information cited in the experimental section of this article revealed that accounts are given only for the preparation of the complexes which incorporated aniline and p_-toluidine as the nitrogen donors. Investigations by Chatt and Venanzi (2b) in 1957 upon similar complexes of p'illadium(II) again served to demonstrate that the neutral chloridebridged, binuclear compounds could be converted to the corresponding mononuclear complexes via rupture of the bridging bonds of the halide j.oxin with tripheuylphosphine. The parent bridged materials had heen preparable with di-n-pentylamine or piperidine as the nitrogen donor ligands Ln trans positions; but these workers reported that they were able to obtain the related bridged compounds using pyridine or pyridine-containing ligands. Obviously, therefore, neutral mononuclear Le 5 with pyridine in the coordination sphere had not been iso] I during these investigations. In 1969 Chart and Hingos (26) repor

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the successful preparation of neutral, square planar, mixed, mononuclear pli xes of palladium (11) which had pyridine included within the coordination sphere of the metal. Again the synthetic route to these :ed mononuclear materials relied upon the cleavage of bridging bonds in binuclear precursors wherein the bridging species were either chloride ions or £-toluonesulf inate ions. In 1975 Boschi and coworkers (27) succeeded in preparing some neutral, square planar, mixed, mononuclear complexes of palladium (II) with coordinated pyridine. They also employed a chloride-bridged binuclear precursor [PdJL^Cl, ] wherein the neutral L groups were aromatic isonitriles. Treatment of the bridged compound with the required molar ratio of pyridine afforded the isolation, in good yield, of the corresponding trans mononuclear complex. The results of both of these studies (viz. , Chatt and Mingos, and Boschi and coworkers) therefore indicated that a general route towards the synthesis of mixed mononuclear complexes of palladium(II) which included pyridLnefcype ligands required initially the preparation of a suitable halidebridged binuclear complex, followed by the rupture of the bridging bonds with the selected pyridine donor(s). So, in order to obtain the desired pyridine-containing, mixed mononuclear complexes in this research, it was first attempted to prepare the binuclear chloride-bridged dimeric materials [Pd^L^Cl,] with the L groups as the pyridine methanols. This method depended upon the direct combination of the mononuclear bis-alcohol complexes [PdL„Cl„] 2with the complex anion [PdCl, j" on a 1:1 mole basis with respect to palladium. The bridged dimer, however, could not be obtained by this method. Therefore, the chloride bridged complex [FdyLJZl.] with triaylphosphine (Ph,,P) ligands incorporated as the neutral L groups was

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54 tared accoi lii , to the method outlined by Chatt and Venanzi (25). The Ph.^P was employed because of its structural similarity to the pyrj.d) sthanols. Thi? bridged material, which was a red-brown solid, slurried in refluxing acetone and treated with 4-pyridyl-4-f luorolylmethanol (4-pyLOH) on a 1:1 r.ole basis with respect to palladium. '••; reflux was continued (ca. 3 hours) the bridged material dissolved and a yellow solution resulted. When this solution was saturated with pentane a pale yellow crystalline solid settled out. Characterization of rhis solid indicated that the desired mixed mononuclear complex tPd(II)(Ph 3 P)(4-pyLOH)Cl 2 ] had been obtained. This result suggested that the problem of preparing the mononuclear mixed complexes containing the pyridine alcohols had been solved. However, when this material was treated with 70.'" HCIO^ for the purpose of carrying out stability investigations upon the "coordinated" carbenium ion it was discovered that the coordinate bond between the ionized pyridine alcohol and the palladium metal center was quickly ruptured ( ca . 5 minutes or less) . It was presumed that this bond breaking was a consequence of the effective tran s labilizing effect exerted by the strong ir-acid ligand, triphenylphosphine. This result therefore dictated the necessity to prepare the mixed mononuclear complexes with a neutral, nonionizable counter ligand, which would not exhibit particularly strong Tr-acid behavior in these complexes. The selection of 4-pyridyldiphenylnethane as an appropriate counter 1 Lgand was clearly a good choice. This is attributable to the structural parability of the alkane to the pyridine alcohols, and to the anticI ed similarity in chemical behavior of the alkane to pyridine itLi . Thus, the problem at hand was the development of a synthetic procedure through which a molecule of the alcohol as well as a molecule

PAGE 65

JJ of the alkane could be. systematically introduced into the coordination of the metal in the mononuclear complex. The following considerations were pertinent: 1) The inability to prepare the chloridebridged binuclear complexes containing pyridine donors in trans positions I Pd« (py'LGH)„Cl, ] (vide supra ) ruled out the use of such a material as a precursor. The bridging bonds in this dimer would presumably have been susceptible to attack by the "second" pyridine donor thereby yielding the mixed pyridine mononuclear complex. 2) In view of the anticipated similarity in donor character of the pyridine alkane to the pyridine alcohols there appeared to be no method by ;^hich these two pyridine Uganda could be added directly to the palladium metal center in the required stoichiometric ratio. The synthetic finds of Goodfellow, Goggin, and Duddell (28) provided reasonable prospects for the preparation of the desired complexes. These workers recognized that there are many complex anions of the type [Ft (II)LC1 3 ]~ (L C 2 E A> C0 » N0 > ^v or pyridine; references for the preparation of this complex anion with these respective ligands are cited in this article) w 7 hich are well known. They discovered that such complex anions were also preparable with L as PR.,, SR„ , or AsB.~ (R = alkyl or aryl), and that a similar series of complexes (excluding pyridine) was preparable as well with palladium(II) . This was the first general account given for the successful preparation of such types of ilex anions of palladium(II) . The usual synthetic route which these workers employed was characterized by refluxing the chloride-bridged, binuclear material [M ? L^C1, ] , II equals Pt(II) or Pd(II), with the required stoichiometric quantity of tetra-n-propylammonium chloride in an rt organic solvent such as dichloromethane. The complex anion which

PAGE 66

56 was formed upon rupture of the chloride bridges was apparently Lized in solution by the large tecraalkylammonium counterion. The complex anion was found to be isolable as the tetraalkylaronionium salt via treatment of the d.Lohloromethane reaction mixture, with excess ether which resulted in crystallization of the desired product. The salient aspect this preparative method is that it permitted the controlled inclusion of a particular neutral ligand into the coordination sphere of the metal acorn. However, as previously indicated, this particular method was not directly applicable to the situation involving the pyridine donors since the necessary bridged precursors with trans pyridine donors had not been prep arable. Nevertheless, further considerations paralleling this synthetic approach were certainly warranted in that, this technique served to reinforce the possibility of being able to investigate stability relationships between the metal center and a singly charged coordinated pyridine carbenium ion provided [Pd(II)LClo] complex anions of the pyridine alcohols could be prepared. Goodfellow, Goggin, and Duddell had also reported the preparation of the anionic complexes [Pd(II) (C 2 H,)C1 3 ]~, and [Pd(II) (C0)C1_]"*, by 2reacting the binuclear anion [Pd ? Cl.] with the required molar quantity of the neutral ligand in the presence of tetra-n-butylammonium ion i tng cisl,2-dichloroethylene as solvent. Again treatment of the reaction mixture with excess ether induced the separation of the desired product as a crystalline solid. Infrared spectroscopic investigations bj Adams and coworkers (29) also served to indicate the potential use2fulness ofthe binuclear anion [Pd ? Cl,] as a precursor to mononuclear 1 aces of palladium (II) of the type [Pd(II)LCl_] by demonstrating

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57 that the force constant for the terminal metal-halide stretching vibration was greater than that for the bridging metal-halide vibra2tion. Thus, in would be expected that the dimeric anion [Pd Cl,l /. b would be attacked at the bridging positions by incoming ligands. It appeared, Therefore, to be reasonable to treat polychloropalladate(II) anions with the pyridine alcohols in an appropriate solvent in the presence of t etr a alky 1 ammonium cations with the anticipation of sustaining the stability of the [Pd(II) (pyLOH)Cl.,] complex anions. In conjunction with this, palladium chloride powder was stirred in refluxing acetone with tetramethylammonium chloride (tMACl) on a 1:2 mole basis. A red-orange solution initially resulted as the solids began to dissolve, but as reflux was continued the color of the solution disappeared and a salmon-colored solid separated. This solid was slurried with ^-pyridylphenyt-4-f luorophenylmethanol in refluxing solvent but no additional change occurred. Nevertheless, the incipient formation of the red-orange solution indicated the presence of a solution-stable chloroanion of p3lladium(II) . Further investigations indicated that 2the solution-stable species was [Pd Cl,V and that the salmon-colored i. b solid was the acetone-insoluble salt [ (tMA) „PdCl, ] . Thus, the nature o F the palladium(II) polychloroanion was dependent upon the concentration of the ammonium salt. Studies by Henry and Marks (30) upon glacial acetic acid solutions of palladium(II) in the presence of various alkali metal chlorides served to indicate that with readily 2_ soluble chlorides such as LiCl, [PdCl,] was the commonly encountered palladium(II) anion, whereas with moderately soluble chlorides such 2as NaCl, the binuclear species [Pd„Cl,] was got. Therefore, it •eared that regulation of the tetraalkylammonium chloride concentration

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53 orded a method by which the nature of the palladium (I I) polychloroaion could be controlled. The combination of palladium chloride der with tMACl (1:1) in refluxing acetone did in fact yield complete dissolution of all solids and a stable red -orange solution. Treatment of this solution with a typical 4-pyridylmethauol (1:1 with respect to palladium) again resulted in the separation of a salmon-colored precipitate [ (i.MA) 9 PdCl, ] and a yellow solution. Workup of the yellow solution yielded the bis-alcohol complex [Pd(II) (pyLOH)„Cl„] . Thus, the tMA cation did not appear to be capable of stabilizing the desired anionic mono-alcohol complex regardless of the nature of the polychloroJ.adate(II) precursor. Palladium chloride powder was then combined with tetra-n-butyllium chloride (.1:1) in refluxing acetone again resulting in the d Lssolution of all solids and a stable red-orange solution. Treatment of this solution with a typical 4-pyridine methanol (1:1 with respect to palladium) induced an immediate color change in the solution from red-orange to yellow-orange with the separation of no solids. Workup of this solution (see Experimental p. 40) revealed that the desired anionic complex [Pd (II) (4-pyL0H)Cl_ ] had been obtained. Further studies showed that this anionic complex was readily converted to the Lred mixed, neutral, mononuclear complex by treatment (1:1) with the 4-pyridyl alkane in acetone solution (see Experimental pp. 38-40). (Note: During the course of this research all synthetic procedures Involving palladium (II) were run using acetone as solvent. There are lard methods for the preparation of complexes of palladium(II) l.oying alcohol (usually methanol or ethanol) as solvent, but in this ' it was discovered! that in the presence of alcohol palladium (II)

PAGE 69

59 .; frequently reduced to palladium black. No similar difficulty was encountered with acetone.) he Suitabilit y of 4 -Pyridyld iph enylm e thane as a Counte clif; and in the Mixed Complexes . As reported previously (see Experimental p. 33) the commercially obtained alkane was found to be contaminated with trace quantities of the corresponding 4-pyridyl alcohol. To be sure that the alkane was not converted to the alcohol (carbenium ion) via oxidation in 70% HC10, . a solution of the purified alkane in the acid was srirred at ambient temperature in the open environment of the laboratory. After stirring for a period of 2 hours this solution was scanned in the visible region of the spectrum and was found to be transparent. Therefore no complications were expected to arise during thermodynamic studies upon complexes which contained the alkane since all such meas cments were made within a 2 hour time span. The similarity in donor behavior of the alkane to the 4-pyridyl alcohols was demonstrated by the preparation of the anionic complexes p.VLCl^] (in situ) with either the alkane or the alcohol, followed by conversion to the mixed complex. Thus, the mixed complexes were preparable independent of the order of addition of the respective pyridine donors. Finally, a small sample of mixed complex (any) was triturated in 70% HCIO^, for a period of ca. 1 hour. The acid was removed by filtraI ic n and the lisidue was washed with deionized water and dried. An IR scan of the residue revealed it to be of the same constituency as the original mixed complex. This indicated that both pyridine ligands rened coord in.-' ted during thermodynamic stability investigations and

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GO ;ain ' t rated the suitability of 4-pyridyldiphenylmethane as an iropriate counterligand. Mien the complex [Pd(II) (Ph^P) (4-pyL0H)Cl ? ] had been treated in a similar fashion (i.e. , triturated in 70% HC10.) i ; was found that the pyridine ligand (carbenium ion) was discharged from the complex (p. 54). Conc ernin g Car b enium Ion Salts . Various synthetic routes are available for the preparation of stable salts of trityl-type carbenium ions (see, for instance, the methods given in the papers by Sharp and Sheppard (31), by Daube.n et al. (32), or by Olah et a^. (33)). It may certainly prove to be interesting and profitable to investigate the stability of the free and complexed carbenium ions which have been dealt with in this work as discrete salt-like species in aprotic, nonreactive solvents. Current considerations however, have exclusively involved the use of 70^ HCIO, as an ionizing medium in order to provide a direct extension to previous work upon trityl-type carbenium ions derived from the I dyldiphenylmethanol s . Th ermodynamic Investigations and Measurem ents I ; ct ronic Spect ra and Carbenium Ton Constitution and Structure . Considerable work has been done on the electronic spectra of trityl-type carbenium ions in the 200 — 750 r.m (50.0 — 13.3 kK) spectral region. The majority of this work, however, ha.; been focusod upon the transitions ' by these ions in a rather limited portion of this region, ^00 — 550 nm (i'i.3 — 18.2 kK) , because the electronic bands found

PAGE 71

61 h re ire those which are characteristic solely cl the carbenium ion. higher energy transitions (50.0 — 33.3 kK) exhibited by these ion;-, nre normally present in the spectrum of the precursor molecules ( i.e . , tertiary alcohols) and are characteristic of the electronic absorptions of the isolated conjugated systems which are bound to the carbinol carbon in the unionized alcohol. Previous electronic absorption studies on these types of ions (e.g., Richardson (6) and Wentz (8)) including similar studies performed during the course of this work have demonstrated that the higher energy (ultraviolet) spectral region of these alcohols remains virtually unchanged for a given alcohol independent of the nature of the solvent. Thus, the significant electronic changes which occur in these systems upon carbenium ion generation are not directly reflected by these higher energy transitions. The dramatic changes which do take place in the electronic spectrum of these alcohols upon ion formation are illustrated by the development of two intense /_, 5 _] _i (r ca. 10 — 10 liter mol " cm ), broad absorption bands ordinarily' max — appearing between 300 and 550 rim. This spectral region is transparent for the alcohols dissolved in a nonionizing solvent, e.g., acetone, alcohol, or 1 M HC10,. The extreme intensities of these bands are expected for strongly allowed n +tr charge transfer type transitions. As pointed out by Dunn (34) based upon considerations of the classical theoretical work of Mulliken (35) on electronic spectroscopy, the .intensity of a charge transfer band is expectably large since the charge transfer phenomenon occurs over at least one interatomic distance in the absorbing species. Thus, the radius vector (r) of the transition is relatively large. Since the magnitude of the transit ton tent integral is directly proportional to r, and in turn directly

PAGE 72

62 p oportional Lo the oscillator strength (f) of the transition, f must also be large. Hence, the intensity of the transition is considerable. rhe general positions of these trityl-ion charge transfer bands have .. rationalized by considering that alcohol ionization is accompanied bj the conversion of the system from a quasi even-alternant benzene hydrocarbon to an odd-alternant, fully conjugated benzene hydrocarbon. According to various workers (see, for instance, Deno et al. (36)) based on simple LCAO MO calculations this transformation introduces a zero energy (nonbonding) iT-symmetry orbital into the molecular orbital scheme of the previously unionized alcohol intermediate between the highest energy filled vr-orbitals and the lowest energy unfilled ir*crbitals. Thus, the energy of the longest wavelength (lowest energy) electronic transition observed for these ionic species should be on the order of half the energy of the longest wavelength transition exhibited by benzene, the model compound. Since the wavelength of this transition for benzene is 256 nm it is expected that the longest wavelength electronic transition of the trityl-type ions would appear in the vicinity of 512 run. As pointed out by Richardson (6:153) the rather inexact nature of this treatment is revealed by the fact that the longest wavelength electronic absorption exhibited by triphenylcarbenium ion is 431 nm (in 96% H-SO^) which is at considerably shorter wavelength than that predicted from the benzene model. An eclectic account of previous investigations upon the electronic nature of arylcarbenium ions reveals that extensive considerations have been made, but that these considerations are not without certain per:ing aspects. In 1932 Schoepfle and Ryan (37) reported that the two aces, triphenylchloromethane and methyldiphenylchloromethaue, yield

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iV3 e ientially the same visible spectrum when dissolved in dichloroethylene in the presence of stannic chloride. This prompted Newman and Deno (38) to conclude that this was evidence indicating that in triarylcarbenium ions no more than two (and perhaps just one) of the aryl rings could simultaneously participate in resonance interactions with the carbenium ion center (the exocyclic carbon atom). Completely synchronous resonance stabilization of a triarylcarbenium ion involving all of the aryl rings would of course require an all-planar molecular ion configuration of D_ symmetry. Lewis e_t al. (39) had already reported as a consequence of studies on crystal violet ion (tr is(dimethyl-p_-aminophenyl) -methyl ion), that the all-planar configuration of the ion is not possible owing to sterie interactions between the ortho hydrogen atoms on the phenyl rings. These workers had speculated on the existence of two isomers of the ion. having structures akin to a symmetric and an asymmetric propeller wherein the phenyl rings were the blades of the propeller. The presence of two intense bands in the electronic spectrum of crystal violet ion supported the proposal that each of the two isomeric forms of the ion was a distinct chromophoric system. Additional evidence cited by Newman and Deno which suggested the structural uniqueness of trityl-type ions was the following. Tri-o-toiylcarbenium ion was reported to be as stable as tri-p_-tolylcarbenium ion and to exhibit essentially the same electronic spectrum. Tliis x^as an unexpected result owing to the considerably greater degree of inhibition towards ring resonance stabilization of the ion anticipated for the tri-o-tolyl ion as a consequence of sterie interaction between the o_-raethyl groups. Also, van ' t Hoff i-f actor data on solutions of trip-dimethylaminophenylcarbinol in 100% H„S0, indicated that even in this Jngly acidic medium one of the p_-amino groups was not protonated.

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64 This suggested that only one of the rings was involved substantially in tonance stabilization with the cation center. Other investigations by Newman rid Deno on the electronic spectra of various carbenium ions revealed that the observed band positions were sensitive to changes in phenyl ring substitution. Attempts to rationalize these band shifts >.rc;.iiscd mainly on resonance considerations were inconclusive. Further attempts to rationalize the observed differences in band intensity and position in the electronic spectra of various series of related arylcarberiium ions by Deno, Jaruzelski, and Schriesheim (40), met with limited success. These workers discovered a systematic spectral trend characterized by an increase in A as well as in band intensity remax 3 suiting from singular substitution of any of the groups, -N(CH«) , -NH , -0CH_ or -CI, into the para position on one of the phenyl rings in triphenylcarbenium ion. The trend appeared to coincide with expectations contingent upon simple extension of the 7T-electron donating, conjugated system of the substituted cation relative to the triphenyl ion. Ho'/ever. successive para substitution of these groups on subsequent phenyl rings in a given ion resulted in discontinuous shifts in v and r J & b max in molar absorptivity. In 1954, Branch and Walba (41) studied the electronic spectra of various para-aminotriphenylcarbinols in 96% H„S0, . They reported that each of the carbinols which was converted to its corresponding carbenium ion upon dissolution in the acid exhibited two intense bands in the visible region of the spectrum which had not been found to be present in the spectrum of the parent carbinol. It is interesting to note, however, that these workers reported no such bai for tr '-p-d imetrhylaminophenylcarbinol in the acid and concluded in this '.nice that carbenium ion formation had not occurred (cf. the results

PAGE 75

6 r > of Newman and Deno (above) with respect to their investigations on tl ilar carbinol) . Branch and Walba also isolated a trend in band position shifts from their data. They rationalized that increases in re sonance stabilization of a given carbenium ion resulted in an increase in the frequency of the band associated with that particular carbenium ion chromophore. The simplest example of their consideration is illustrated by comparing the relative positions of v for the ionic species max + + — — (C,H C )„CH and (C,H.-) C wherein v (diphenyl ion) < v (triphenyl 6 ;> 2 6 5 3 max J max r J ion). Branch and Walba had attributed this absorption to the (C,H C )„C o J / chromophore. Thus, these workers concluded that resonance stabilization of the (C,H,.)„C chromophore in the trityl ion by the presence of the "third" phenyl ring resulted in a blue shift of v . Branch and Walba max also contended that trityl carbenium ions exhibited two visible region absorption bands (instead of but one) because of two carbenium ion containing chromophores believed to exist in the sterically hindered parent ion. This was in basic agreement with similar considerations made previously by Levis e_t al_. (39) . Related studies in this area by Evans and coworkers (42) provided evidence pointing to the existence of a relationship between band intensity and resonance interactions in triarylcarbenxum ions. These investigators reported that para substitution of a given group on a phenyl ring in triphenylcarbenium ion resulted in a actable increase in e for the main absorption band of that particular don, whereas the corresponding ortho substitution of the same group resulted in a marked decrease in e for the same band. Studies by Dehl e_t^ al. (43), and by Deno et al. (36) served to invalidate a number of the earlier arguments concerning the interpretation o F the electronic spectra of trityl carbenium ions. Dehl et al.

PAGE 76

66 oncluded from pmr investigations on various douterated triphenyl'.'im ions that the three phenyl rings in the cat ionic aggregate were equivalent. This result suggested that analyses of the electronic >ctra of such ions would require the attribution of any trityl carbenium ion chromophore to the ion as a whole, therefore denying the possibility of simultaneous existence of two (or more) chromophores in the molecular framework of the ion. Deno e_t al. performed simple LCAO MO calculations on aryl cations and found that the results of these halations predicted identical v positions for the principal elecmax r r tronic absorption exhibited by related mono-, di-, and triaryl cations. Thus, inhibition of resonance in a sterically hindered carbenium ion would still leave v (calculated) unchanged. Also, these calculations max indicated that the intensity of the principal absorption for such ions is invariant to phenyl ring rotation (due to steric interaction). Hence, these authors concluded that electronic absorptions exhibited by such ions could not be used as a measure, of steric inhibition to resonance interaction existing within the ion. In yet a later article, Deno (44) has again pointed to the irresolute nature of the situation in commenting that much of the work on the electronic spectra of arylcarbenium ions still requires revision. Olah et a_l. (45), as veil have concluded that there is a great deal of uncertainty in the literature citations concerning the visible and ultraviolet spectra of carbenium ions. InterestLy enough, however, in order to rationalize some of their results these workers employed the notion that in a sterically crowded triarylrbenium ion only two of the aryl substituents are part of the absorbing omophore, while the third functions as a cross-conjugating electron lor or acceptor moiety. So, once again the possiblity of the existence

PAGE 77

67 oi mult Lple chromophores in trityl-type carbenium ions is considered, Thus, as late as 19&6, many of the problems resulting from unsatisfactory arpretation of the electronic spectra of carbenium ions remained. To a large degree, recent investigations in this area rely heavily upon molecular orbital treatments of the electronic structure of arylcarbenium ions. Streitwieser (46:226-230) has shown that in the HMO approximation the lowest energy transition exhibited by triphenylcarbenium ion can be considered to be associated with the passage of an electron from the highest occupied bonding MO to the vacant nonbonding NO in the odd-alternant hydrocarbon created upon cation generation. To a first approximation the energy level diagram associated with this transition is the same as for the benzyl cation, Various, more sophisticated MO treatments (46:360-362) however, reflect the complex and imbroglio tic nature of this approach to the problem by calculating rather grossly different charge densities for the ir-f ramework carbon atoms in the ground state of the trityl ion. By employing MO and resonance theory Waack and Doran (47) attempted to correlate the effects of methyl group substitution in odd-alternant anions with the resultant band shifts of the main absorption bands found in the electronic spectra of these ions. They noted that this type of substitution ( i.e. , methyl or alkyl) on an even-alternant hydrocarbon had in the absence of steric affects always induced a red shift in the electronic conjugation bands, whereas similar substitution on a nonalternant hydrocarbon had induced either a red or blue shift depending upon the site of substitution. They reported spectral mges for the odd-alternant anions to be similar to those for the ilternants and experienced qualitative success in applying the

PAGE 78

results of their calculations to the prediction of the spectral behavior odd-alternant ions. A particu] highlight of this effort was the prediction thai: a-alkyl substitution on an odd-alternant cation would result in a blue shift of v> which is in agreement with reported data. ; N rattier comprehensive MO treatment by GrinLer and Mason (48) yielded a symmetry-based energy level diagram for structurally comparable arylmethyl ions. An examination of this energy level diagram revealed thot the longest wavelength, lowest frequency transitions for a related bisand trisarylmethyl ion pair should be approximately identical ( cf . the conclusions reached by Deno et_ al. (36)). However, stemming from more acute considerations, these authors showed that the ground state charge stabilization of a given triaryl ion was greater than that for the corresponding bisaryl ion (recall the conclusions of Branch and Walba (41), pp. 64-65). Thus, the highest occupied bonding MO's for trisaryl ion were somewhat lower in energy than the related MO's o": the bisaryl icn, and therefore, the longest wavelength transition oi the trisaryl ion was of slightly greater energy than the corresponding transition for the bisaryl ion. The dual nature of the visible region absorption envelope of the trisaryl ions was also considered by Grinter and Mason. Their explanation ran as follows. In the point group "C. ," (following from the anticipated propeller shape of these ions) the highest bonding MO's of the trisaryl ions are "five-fold degenerate, " with the attendant symmetries e, e, and a„. The MO's of the first excited state (s) are likewise five-fold degenerate, and are of a,, a,, a„, and e symmetries. Again, provided that the ion is propeller shaped, transitions to the 'A™ and 'E excited terms are allovzed and should be polarized parallel and perpendicular respective

PAGE 79

69 co the principal Lhrce-fold symmetry axis of tlie ion. This appeared to be in basic agreement with similar considerations which hod been made by Lewis and Bigeleisen (49) on the phenomenon of polarization upon the transitions in the electronic spectrum of crystal violet and malachite green. Thus, Grinter and Mason concluded that two low energy transitions of high intensity are expected (and are found) for such ions. (It is here appropriate to point out that results of newer studies on the electronic absorption spectra and magnetic circular dichroism (MCD) of triphenylcarbenium ions have suggested refinements of certain of the considerations made by Grinter and Mason. Mo et^ al_. (50) found three MCD bands in the near UV, visible spectrum of triphenylcarbenium ion. This result indicated the existence of three electronic transitions in this spectral region for trityl-type carbenium ions whereas only two such bands were proposed to exist by Grinter and Mason. Dekkers and Kielmanvau Luyt (51) in fact have stated that MO theory does predict three nearby singlet * singlet transitions for a triaryl ion of D„ symmetry. Two of these three transitions are to excited states of e symmetry and are polarized in the x,y-plane of the ion. (This plane is defined for an assumed coplanar arrangement of the aryl rings and the exocyclic carbon atom. Thus, the aryl rings are perpendicular to the principal symmetry axis of the molecular ion, the z-axis.) The third transition, however, which is to a state of a„ symmetry and z-polarized, would not be observed if the cation were completely planar. Since the cation is propellershaped and not planar, this transition is observed (at slightly higher •quency than the higher energy intense band), but it is considerably weaker etian either of the highly allowed transitions to the e states. Ls also noteworthy that these investigators were not able to resolve

PAGE 80

70 state transitions which are observed to overlap rather tverely (maxima arc at 23.2 and 24.6 kK respectively with a reported c of 38,700 for each band (45)). This suggests an inherent relationship Lween the electronic states in the ion from which those two bands originate. Consequences of this implication concerning the chromophoric nature of triairylcarbeniuni ions lie in the forthcoming text, vide infra. It is now interesting and profitable to examine the wave functions for the molecular orbitals which were considered by Grinter and Mason to correspond to the energy levels which arise upon generation of a trisarylmethylcarbenium ion. The forms of these wave functions are: i>>. = a<> + bOJi , + i> ., + ij> lH ) {5} 1 'c r aryl r aryl aryl r II aryl r aryl and $__, (iji . + i> . , 2 1lf )//6 {7} II aryl aryl v aryl where (j> is the wave function of the 2p state of the exocyclic carbon atom. The ij^ T functions represent the highest occupied bonding states of the ion, and their forms indicate that the bonding contribution of the "third" aryl ring (iji ,,) is of principal significance in ty TT i« ite: The basic forms of these wave functions are virtually identical to the corresponding wave functions used in the calculations by Dekkers I lan-van Luyt (51).) Since the degeneracy of the ty__ functions

PAGE 81

71 , >en removed to an appreciable degree by virtue of the nonplanarity of the ion (48) and by configuration interaction effects (46:227), (51), it follows that only one of the long wavelength, low energy transitions should reflect significant electronic contributions to carbenium ion stability (or instability, as the case may be) by the so-called "third" ring which is denoted above as aryl" in equations {5} and {7}. This consideration is given additional substance from the results of various investigations. Barker and coworkers (52) studied the electronic spectra of derivatives of malachite green produced by substitution in the "nonanilino" phenyl ring. They showed that the longest wavelength absorption band recorded for each derivative reflected primarily a flow of electrons from the two p ar aN , N-d ime thy 1 substituted rings towards the exocyclic carbon atom. This is in keeping with MO calculations which have established that this carbon atom bears the principal degree of positive charge in the ground state of the ion (53) , (an expected result) . Therefore, replacement of the paraN , N-dimethyl groups with poorer electron releasing substituents resulted in a blue shift of v . These workers max also demonstrated the existence of a linear relationship between the appropriate Kammett constant for the phenyl ring substituent and the magnitude of shift in v induced by that particular substituent. Thus, max J * a type of cross-conjugation seems to exist between the phenyl ring and the remainder of the conjugated system with respect to the energy of I longest wavelength transition. The results of studies by Hopkinson and Wyatt (54) concerning substituent effects upon the electronic abrptionsof phenolphthnlein monopositive ions (Figure 5) allowed these workers to conclude that v of the second longest electronic transition max & exhibited by these ions reflected primarily a shift in electron density

PAGE 82

72 . ',. "third" ring towards the exocyclic carbon atom. In phenolhalein this "third" ring is the ring to which the orthocarboxylic acid group is attached. Hopkinson and Wyatt also compared the elecronic absorption spectra of phenolphthalein and phenolsulphonphthalein and observed a considerable blue shift of the second baud for the "sulpho" containing phthalein. This was expected owing to the appreciable electron withdrawing power of the sulphonic acid group. These results were corroborated via extended HMO calculations to resolve the electronic effects which arise from para -substitution of u-electron donating groups oq two of the phenyl rings in triphenylcarbenium ion. Furthermore, the results of these calculations were found to be in agreement with the results of the HMO calculations which had been carried out by Mason and Grinter (48). These calculations also verified that such substitution of "-electron donating groups served to remove still further the degeneracy of the two highest occupied MO's in triaryl-type carbenium ions (see. p. 70) with the higher energy occupied MO acquiring a greater iW R = -C00H R' = -CH,, -CI, -Br, etc, R" -CH-, -CI, -Br, etc, Fig. 5. Phenolphthalein monopositive ions

PAGE 83

73 Lectron contribution from the rings which bear the more potent electron releasing substituents. Consequently, the conclusions reached which qualitatively associate the two principal electronic absorptions of triarylcarbenium ions with the MO's from which these transitions originate (p. 70) have been upheld. In addition, Hopkinson and Wyatt also isolated from their spectral data a linear variation between Hammett c-meta substituent constants and shift magnitudes of the higher energy electronic band produced upon the. substitution of groups ortho to the ring hydroxyl groups in phenolphthalein. Thus, whereas the results obtained by Barker and coworkers (52) indicated a cross-conjugation effect to exist upon the frequency of the lower energy band and the "third" aryl ring, Hopkinson and Wyatt showed a similar effect upon the frequency of the higher energy band by the two rings in a given triaryl-type carbenium ion which are the primary (as compared to the remaining ring) ir-electron donating moieties. Finally, it is still not clear whether the high intensity electronic absorption bands exhibited by triarylcarbenium ions may or may not be considered rigorously as charge transfer transitions! This concern is not crucial to the considerations made in this work; but for completeness a few remarks shall be tendered. Initially, in this discussion of electronic spectra, it was assumed rather tacitly that these electronic bands are charge transfer in nature (pp. 61-62). However, these abI tions do not meet with certain of the criteria (55) which have been employed for classifying electronic transitions as "charge transfer." 1 h (56:65-66) for instance, has pointed out that the factors tending to indicate charge transfer interactions in monoaryl tropylium ions

PAGE 84

74 (prov« d by Couch to exhibit intramolecular charge transfer) are either not present, or are opposite, in mononrylcarbenium ion5;. Furthermore, related studies by Couch (57:113-122) have suggested that triarylcarbenium ions as well do not exhibit bona fide charge transfer interactions. Dauben and Wilson (58) have at last demonstrated the existence of authentic charge transfer interactions for systems containing triarylcarbenium ions. They accomplished this via the preparation oi" various pyrene-triarylcarbenium ion complexes wherein the coordinated carbenium ion was found to function as a particularly potent ii-aeceptor. The ctronie spectrum of any of these complexes gave a very intense band at. relatively low energy (viz. 14.1 kK for coordinated triphenylcarbenium icn) which was not present in the spectrum of either component. These results imply that the existence of a "true" charge transfer interaction in a system requires an appreciable shift of electron density from a specific location in the ground state of the parent molecule (ion, etc.) to a new (and removed) location in the excited state. Perhaps then, it is in fact not extremely unrealistic to treat the principal electronic absorptions of arylcarbenium ions as charge transfer. Ramsey (55) has alluded to this assumption by suggesting that a charge transfer cransition in a triarylborane can be associated with the promotion of an aryl ring ir-electron into the empty available p_ orbital on the boron atom. Similarly, since the results of various studies on the electronic spectra of arylcarbenium ions have associated the main absorption bands with transfer of aryl ring 77-electron density to the exocyclic carbon, those transitions may, at least broadly, I ;ed as charge transfer. Arguments contrary to this class LLon can be registered based upon degree of charge transfer. For

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75 19 tance, work by Olah et al. (59) on the pnir and "" F nmr spectra of I fluorocarbenium ions has demonstrated that the degree of charge derealization into the aryl rings in these ions is substantial. Thus, alectronic ground state charge derealization in these ions appears tc be considerable. Extended HMO calculations (54), however, have indicated an appreciable difference in carbon atom charge densities between the ground and first excited states in arylcarbenium ions. Let it suffice, therefore, to say that, this aspect of arylcarbenium ion electronic spectral investigations remains largely a moot issue. An examination of the electronic spectra and attendant data collected during this work is now in order. Examples of electronic spectra obtained for carbenium ions derived from a related series of compounds, name!} pyLOH, Pd (II) (pyLOH) (L N )C1 2> and Pd(II) (pyL011) 2 Gl 2 (where pyLOH equals 4-pyridyl-4-methylphenyl-4-f luorophenylmethanol, and L equals diphenyl-4-pyridylmethane) , have been presented in Figures 6 — 8, p. 76. As these spectra are representative of all electronic spectra recorded for the carbenium ion species considered herein, no other electronic spectra are presented. Pertinent electronic spectral data are given in Table II, pp. 77-78). The carbenium ion electronic spectra obtained in this work are found to be very similar to the related spectra (in the same spectral region) which have been reported by previous investigators (Richardson (6) and Wentz (8)). An examination of these spectra reveals the presence of two broad, intense absorption bands located within the 33.3 — 18.2 kK range. The lower energy band found in the spectrum of a given carbenium ion is ys the more intense. The e values reported in Table II indicate

PAGE 86

76 A . 5 o.o 4 20.0 18.2 17.4 1.0 _, 25.0 22.2 v (kK) Visible spectrum of the carbenium ion derived from 4-pyridyl-4mef.hylphenyl-4-f luorophenylmethanol, in 70% HCIOa. v ,20.2, 29.7. maX A 0.5 „ o.o X 33. Fig. 7. * i i 28.6 25.0 22.2 20.0 18.2 17.4 V (kK) Visible spectrum of the carbenium ion derived from Pd (II) (pyLOH) (Inr)Cl2j where pyLOH is 4-pyridyl-4-methylphcnyl-4-f luorophenylmethanol, in 70% HCIO4. v" max , 20.6, 27.6. A 0.5 ) 20.0 18.2 17.4 T" 25.0 22.2 V (kK) Fig. 8. Visible spectrum of the carbenium ion derived from Pd (II) (pyLOH^ Cloj where pyLOH is 4-pyridyl-4-methylphenyl-4-f luorophenylthanol, in 70% HCIOa. "S , 20.6, 27.7. ^ max

PAGE 87

. . LO c--i 4-J cd st O i-H y o --• •H m CD H o a) P. p o H H a) M X> M P td CD CO 1 — -! ,X3 0) cd P H O •H p TO > .c 4-J V! o U-l ctf O H sd P u o cu p.
PAGE 88

•d ci T3 P3 01 u X H X) m o O t-i .H o u c_> W C >-. o o CJ -H s

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79 . directly. This band is the so-called ":•:" electronic band so classified by Lewis and Calvin (60) in an elegant work on the color of garlic compounds. Similarly, the higher energy, less intense (in this cast-) band, is labeled the "y" band (60). Certain relevant trends are established by the spectral position shifts of these main absorption bands which occur upon proceeding from R = phenyl to R = 4-raethoxyphenyl (see Table II) for a related series of carbenium ions; and from the comparison of the spectrum of a free alcohol carbenium icn to that of the corresponding complexed carbenium ion. An inspection of the resnective v values (Table II) reveals these trends to be the max following: (i) For carbenium ions derived from a family of precursors (e.g., the 2-pyiidyl alcohols, the 4-pyridyl alcohols, etc.), in proceeding from R = phenyl to R = 4-methoxyphenyl v of the x-band decreases ca. * Jr J max 0.4 — 0.5 kK for the free alcohol ions and ca. 0.9 — 1.0 kK for the complexed alcohol ions. And for the 4-pyridyl ions the x-band v for r rj max a given free alcohol ion is lower than that for the corresponding complexed ion, with the difference in related x-band frequencies diminishing in going from R = phenyl to R = 4-methoxyphenyl. Thus, whereas the x-band v is at 20.7 kK (free alcohol ion) and 21.3 kK (bismax complexed ion) respectively for R = phenyl, it is at 20.2 kK (free alcohol ion) and 20.3 kK (complexed ion) for R = 4-methoxyphenyl. (ii) Making the same comparisons as in (i) (above) on the relative y— band v values reveals that proceeding from R = phenyl to R = 4hoxyphenyl results in a concomitant increase in v of ca. 0.7 kK: J r J max — but this does not include the free 4-pyridyl ions where an increase in y-band v cf only ca. 0.3 kK is encountered. And, in this case the max —

PAGE 90

80 for a given 4-pyridyl ion is found to be higher (usually 1.0 l-.K) than the y-band v of the corresponding completed ion. max * ° ' however, no apparent trend exists in the magnitudes of observed difference in yband v r values for a related free ion — ci :ed ion TT13.X J pa ir. (iii) A comparison of the xand y-band v values of a fro*max 2-pyridyl ion and corresponding 4-pyridyl ion shows that for a given R group v r is always lower for both the x and y absorptions. (Note: This particular trend was also exhibited by a related series of 2-thiazolyl \^s. 5-thiazolyl earbenium ions (8). That is, the x and y absorotions exhibited by a 2-thiazolyl ion were always found to be at lower v than the same absorptions for the corresponding 5-thiazolyl max ion. ) For convenience and simplicity these spectral trends are summarized in the immediately succeeding statements. The effecu of proceeding from R phenyl to R = 4-methoxyphenyl is reflected by a bathochroraic (red) shift of the x-band and an hypsochromic (blue) shift of the y-band. And, the effect of coordinating the earbenium ion always results in an hypsochromic x-band shift and a bathochromic y-band shift. It can now be shown that these results are qualitatively in accord with considerations made previously concerning the electronic spectra of arylcarbenium ions. For instance, if the energy of the x-band transition exhibited by pyridylcarbenium ions is dependent primarily upon a flo of electrons towards the exocyclic carbon atom from the aryl group(s) h are of predominant electron releasing capability, it is expected, and found, that the energy of this transition is reduced upon replacing R = phenyl with R 4-me'Lhylphenyl, or R = 4-methoxyphenyl. The

PAGE 91

81 subsequent cross-conjugationa] effect of this R substitution on the energy of the y-band transition is illustrated by the corresponding band blue shift in the spectra of a related series of ions. More important to this work, however, are the band shifts which take place as a consequence of complexation of a given carbenium ion. It follows that if the transition energy of either or both of the bands (x, and or, y) in the spectrum of a pyridylcarbenium ion is associated, at least to a degree, with a flow of electrons from the pyridine ring to the exocyclic carbon atom, any change in the electronic nature of the pyridine ring making it a more effective electron releasing moiety should result in a lowering in energy of that (those) electronic band(s). Furthermore, it: is reasonable to expect that the coordinated pyridine ring would in fact be a better donor than the pyridine ring in the uncomplexed ion as in 70% HC10, the ring nitrogen is certainly protonated in the free ion, vide infra. Clearly then, any difference in these situations should reside in the fact that in the. coordinated pyridine c?se. electrons flow from an ostensibly neutral ring towards the exocyclic carbon; whereas in the uncoordinated pyridine carbenium ion electrons are required to flow from a ring which already bears a positive charge (the proton) resulting in a comparably unfavorable energetic transformation. Now, since coordination of a given pyridylcarbenium ion results In a blue shift of the x-band, and a relatively substantial red shift of the y-band, it appears to be the case that the y-band transition energy is, to an appreciable degree, paronymously related to the pyridine ring, and therefore dependent upon its electronic nature. These arguments, of course, serve to indicate that the pyridine ring is the so-called aryl" which appeared in the wave equation, i> = {5},

PAGE 92

I i|)__, [7K presented previously (p. 70). So, from a qualitative tint it is reasonable that the ir-electron energy level of ;J'fT , would be lowered with the pyridine ring protonated relative to the energy level of ^ T -n with this ring coordinated, as in the protonated situation pyridine ring would be expectcdly more electronegative. Hence, if energy level of \\> is not altered as much as that of 'J'-r-rt for each of tuese. two possibilities, the y-band should (and does) shift red for the coordinated carbenium ion relative to the "free" ion. It is also suggested that these assessments are correct owing to the magnitude of shift in energy observed for the y-band upon pyridylcarbenium ion coordination. An inspection of the v data (Table II, pp. 77-78) for the 4-pyrldyl ions reveals that coordination induces a red shift in the energy of the y-band proportional to as much as 2.1 kK for the palladium plexes of the R = 4-methylphenyl ion y_£. the corresponding "free" ion. Similarly, for this ion, the x-band is blue shifted only 0.4 kK. (This trend is also realized by the remainder of the data found in Table II. Furthermore, related data reported previously by Richardson (6) and by Wentz (8) support this trend.) Consequently, the electronic energy changes which are produced in the ion via coordination appear to be related principally to the attendant changes in the transition energy of the y-band. This engenders the speculation that relative energetic contributions provided by coordinated metal species towards stabilizing "complexable" carbenium ions would be reflected in a comparison of the respective y-band transition energies for a given complexed ion. Perre work will furnish this possibility with substance.

PAGE 93

ili ty in HCIO^ — H?Q as Determined by the "Peno' [ ion Method . The suitability of the Deno titration method (10,11) for the determination of the thermodynamic stabilities of the carbenium qs investigated in this study has been aptly demonstrated by Wentz (8), The. interested reader is referred to this work for a salient discussion of the necessary and pertinent experimental considerations. Reagent perchloric acid> 70% HC10, , has proved to be a most appropriate ionization medium for these titrimetric stability determinations. It is a potent mineral acid as reflected by its thermodynamic ionization constant (K ) reported to be. 3800 (61). In fact, as pointed out by Gillespie (62) , HC10, — H,,0 systems can be more acidic than reagent H_S0., and only certain, nonaqueous superacid systems afford higher acidity than aqueous HC10, . Indeed, HC10, — HO is found to be uniquely between neat H„S0^, and superacid systems such as HSO^F — SbF (used by Olah (63) to prepare many relatively unstable carbenium ions) as a useful solvent for the generation of trityl-type carbenium ions. Freedman (64:1535) has commented that carbenium ion investigations in concentrated IUSO^ can be complicated by side reactions such as sulfonation or oxidation which in turn can destroy either the parent carbinol or the carbenium ion. Problems such as these are without a doubt responsible for much on the confusion found present in earlier studies on carbenium ions. The superacid system HSO^F — SbF,. as well, recently has been shown to generate carbenium ions as a consequence of oxidation by SbF or S0„ (65). Thus, previously devised methods and mechanisms of carbenium ion generation in this solvent may require extensive modifications. Furthermore, the use of superacids for the preparation of these •s of carbenium ions would certainly require modifications of the

PAGE 94

R4 mo lit':ni ion method to take into account the fact that superacid media ar« nonaqueous. Therefore, at the minimum, the definition of new acidity nction parameters would be requisite, as well as drastic alterations he mechanics of the aqueous titration technique. A consideration of the equilibria which pertain upon carbenium ion generation is in order. An examination of the literature in this area reveals that on occasion various authors are wont to write H as the acid species responsible for the com yion of carbinol to carbenium ion. Albeit convenient, this practice is certainly not rigorous, and can frequently be misleading. In the present situation where perchloric acid has been employed as the ionizing medium it is necessary to choose between HC10, or H-0 as the principal proton source towards the ion precursor carbinols, assuming, of course, that other complex or unusual acid species do not exist in this system in appreciable concentration. Since concentrated solutions of such mineral acids as H~S0, , HN0~, or Ik 3 HC3 , are not capable of carbenium ion generation in instances where HC10. HO is, it follows that HC10. is the acid species responsible for carbenium ion formation in those systems in which these other acids produce little or no carbenium ion. As a result of nmr studies on KC10 4 H 2 0, Redlich and Hood (66) reported that reagent 70-72% IIC10, (ca. 11.8 M) is approximately 75% ionized. Hence, sufficient molecular UC30, is present in 70% HC10, — H„0 for carbenium ion generation in systems which contain as solute limited quantities of ion + arson pyridylmethanol. And here, concentrated solutions of 1U0 do not convert carbinol to carbenium ion to any appreciable extent, exi ! for the relatively more stable cations such as those which contain ly electron releasing phenyl ring substituents such as 4-methoxy

PAGE 95

85 ups. Thus, the ionization of triphenylcarbinol in HC10, — H ? may 1<^ written appropriately as: (C 6 H 5 ) 3 COH * 2 I1C10 4 * (C 6 H 5 )C + + H.^o" 1 " + 2 CloT {8} And, even though ring nitrogen protonation of the free alcohol ions tends to complicate the attendant equilibria, the pyridylmethanols should be ionised similarly. (Also, see the discussion which ensues (p. 98) in reference to the stability data contained in Table V.) The equation for the Deno acidity function (H ) may be written as \ ' P'V + ^"W ») i here the values of IL for a particular acid medium are a measure of the capability of that medium at various concentrations to ionize a given alcohol (R-OH) generating the corresponding carbenium ion (R ). Since this equation is of the form, y = b + mx, it follows that if a series of values for H are known, and if the respective concentrations K. of R-OH and R for a related alcohol — carbenium ion pair can be experimentally determined at the different H^'s, pRp-f ma y ^ e obtained as a quantitative measure of the thermodynamic stability of a given carbenium ion. Of course, it. is required therefore that the acid medium be capable of measurably ionizing the alcohol over a range of acid centrations; and it is also inherently required that in order for the H relationship to hold, the slope (m) of the curve got by plotting H D vs. the log term be equal to 1.00. Wentz (8) showed that both of

PAGE 96

86 Lons were met in HC10, HO for the pyridylmethanols '. ar< considered in this work. A list of R values for aqueous HCIO^ and the corresponding wt % Ld are given in 'Cable ITT, p. 87. A plot of -H vs. wt % acid (Figure 9, p. 88) yielded a smooth curve of approximately constant slope which was easily extrapolated (as shown in Figure 9) to 70.0% HC10, ir: order to obtain 1L values for acid concentrations greater than 60.0%. Employment of the fact that Beer's law (A = ecb) directly relates the absorbance (A) of an absorbing species to its molar concentration (c) , allows values for [R-0H]/[R ] in equation {9} to be obtained by measuring the absorbance (to ±0.001 absorbance units) of the carbon iuin ion at various HC10, concentrations. The absorbance (concentration) of R-OH was then taken as the difference between the Beer's law absorbance of the carbenium ion (see Dilution Curves, p. 93) and the actual absorbance of the ion at a given acid concentration. This method of data treatment is valid since R-0H does not absorb at X max of the carbenium ion. Consequently, it is justifiable to assume that i the actual absorbance of the carbenium ion matched the expected absorbance as predicted from Beer's law, the alcohol was ionized to an extent of ca. 100%. Naturally then, as the ionizing acid was systematically diluted (actually, at the onset of the titration molecular HC10. is also converted to II_0 , CIO.) by the addition of measured increments of water, the absorbance fall off was linear (Beer's law dependent) as as the alcohol remained essentially 100% ionized. However, as soon as the carbenium ion became titrimetrically reconverted to alcohol precursor as a result of further addition of water, absorbance fall no longer linear; and indeed, it was greater than that predicted

PAGE 97

37 Table III Values of H in Aqueous HC10. at 25' -\ Wt % HC10 4 a 3.79 30.0 4.61 35.0 5.54 40.0 5.95 42.0 6.38 44.0 6.82 46.0 7.31 48.0 7.86 50.0 8.45 52.0 9 . 05 54 . 9.68 56.0 10.37 58.0 11.14 60.0 a Deno et al. (11)

PAGE 98

r-1 3^ a

PAGE 99

89 from octrapolated Beer's law straight line. An examinatiun of the dilution curves (Figures 10-12, p. 93) illustrates this straightforwardly, Thus, for each carbenium ion so titrated, a collection of absorbance data was obtained as a function of changing wt % HC10, . Tata treatment was carried out using the methods employed by Wentz (8) with some minor modifications. These methods may be described conveniently in conjunction with a stepwise examination of the pertinent arithmetic relationships required for data treatment. Initially, an unweighed .sample of ion precursor pyridylmethanol (free or complexed) is dissolved in sufficient reagent HC10, (determined as 70.87%, see below) co produce an acceptable on-scale (viz., 15-25% T) spectrophotometer reading at X for the absorbing species (the carbenium ion). The max total solution sample is now weighed and the absorbance recorded. Then, measured increments of deionized water are added to the carbenium ion solution and, after thorough mixing, the absorbance of the sample is reread. The wt % of the acid solvent resulting from dilution is calculated from: Wt % acid = t ^ f W V g) +° f T)\ * H n -AA-A {10 > wt (g) of sample + st (g) of H„0 added where wt of acid == original wt % acid (70.87%) x original total sample wt. Thus, the wt % of the. acid can be determined following each dilution by simply noting the cumulative quantity of water which has been added to chat stage in the titration. The volume of the sample following h addition of water is then determined from:

PAGE 100

90 pie volume (ml) cumulative sample wt (g) corresponding p (g/ral) of the sample >ecific gravity of the acid solvent. And therefore, it is obviously necessary to have values of p for aqueous RCXO,. (Wentz had obtain.,., l this information from a plot of p (4 sig. fig.) vs. wt % (4 . fig.) for solutions of aqueous HC10, (see Table IV, p. 91).) However, since the volume of an aqueous HC10, solution does not increase linearly upon dilution with water ( i.e. , the volumes of water and parent acid solution are not additive), Wentz: found it necessary to "blow up" this plot in the region of each wt % datum point in order to obtain corresponding value for p. This procedure was found to be extremely tedious owing to the difficulty found in obtaining 4 sig. fig. accuracy (to insure reliability of related data to 3 sig. fig.) for a considerable amount of wt X data from such a graphical readout. This particular problem was conveniently alleviated by taking a "least squares" curve fit of Brickwedde's data (67), (Table TV, p. 91) to yield a "printed out" series of values for p spanning the range 0.00 wt % HC10, to 75.00 4 wt % HCIO,. (The details of this least squares treatment are given in the Appendix.) Thus, having experimentally determined p of the original reagent acid, the corresponding wt % of the original acid was obtained from this p — wt % tabulation. The use of equation {10} then yielded wt % da La for subsequent dilutions, in turn for which corresponding p values were available from the p — wt % tabulation. Finally, it is : iry to determine the dilution fraction (D.F.) for each dilution. This is obtained from:

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9.1 Table IV Specific Gravity of Aqueous HCIO, Solutions at 25' Specific Gravity (g/'ml) a 0.997 1.026 1.056 1.088 1.123 1.160 1.200 1.244 1.291 1.343 1.400 1.462 1.527 1.596 1.664 Brickwedde (67) wt %

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n „ origina] sample volume (ml) cumulative sample volume (ml) ' Ln, inspection of equation {9} reveals that the required values for the log term are ratios of concentrations (of alcohol to corresponding carbenium ion), and not absolute concentration values. Thus, it is not necessary to determine the concentration of the absorbing species at any time during the titration. It is only necessary to measure absorbances throughout the titration at the various, known dilution fractions, which are proportional to changes in the concentration of the absorbing species. Hence, a plot of absorbance (A) vs . dilution fraction (D.F.) yieJ.dc a plot which reflects the decrease in concentration of carbenium ion as a consequence of dilution as well as of reconversion to alcohol precursor. And, the only requirement which must be met in ord >r for this treatment to hold is that the alcohol be ionized completely at the onset of the titration. An examination of the dilution ves for free and complexed carbenium ions derived from the same alcohol precursors (Figures 10-12, p. 93) clarifies these considerations. In each cr.se the beginning of the titration ( i.e. , in the vicinity of D.F. = 1.00) corresponds to a linear fall off of absorbance with dilui. Thus, at this juncture of the titration the alcohol precursor ^p.'cies is essentially completely ionized; and, to repeat, the effect of the addition of titrant (water) is to titrate molecular HC10. while 4 only diluting the carbenium ion. When the equilibrium reconversion of ion to alcohol (described by equation {1], p. 9) becon-s mearable the titration curve begins to slope down and away from the lated Beer's law straight line as seen in the dilution curves.

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,; "CJ 0.40 0.80 0.725 D.F. Pig. 10. Dilution curve for the titration of 4-pyridyl-4-methylphenyl4-f luorophenylcarbenium ion 0.6 (i.40 0.725 D.F. Fig. 11. 0.60 0.40,+ Dilution curve for the titration of [Pd (II) (4-pyL) (L n )C12j , where 4-pyL = 4-pyridyl-4-methylphenyl-4-f luorophenylcarbenium ion 0.90 0.80 0.725 D.F. Fig. 12. 2+ Dilution curve for the titration of [Pd(1 1) (4-pyL) 2CI2]' where 4-pyL = 4-pyridyl -4-methylphenyl-4-f luorophenylcarbenium ion

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' isr straight line shown (which practically bisects the plot horizon corresponds to the so-called "1/2" Beer's law line. This cond line ha i b sen urawn by considering that if at the onset of the • i :ration the concentration of the absorbing species (the carbenium ion only) were divided by two, its absorbance would also be. divided by two. Thus, this "1/2" Beer's law line may be constructed from a series of points got by halving the absorbance values which served to establish the initial (upper) Beer's law line. Consequently, the intersection of this second Beer's law line with the dilution curve for a given carbeTiium ion marks the D.F. location at which [R-OH] is expected to equal [R ] during the titration of that ionic species. The point of this graphical treatment resides in the fact that the log term in equation (9} is equal to zero for equal values of [R-OH] and [R ] . Hence, vertical extrapolation from this intersection point to the abscissa of the plot yields the D.F. at which the corresponding value of EL equals pKi of that carbenium ion. Of course, H is obtained after relating D.F. to the appropriate wt % HC10,, (note: here, simple arithmetic interpolation is usually necessary to obtain the required values for wt % HClO, since the data points used to plot the dilution curve seldom include the exact D.F. values at which [R-OH] = [R ]), which in turn is related to H (see Figure 9, p. 88). K The thermodynamic stability data resulting from these titrimetric mts upon the pyridylcarbenium ions investigated in this study are pr I in Table V, pp. 95-96. The following considerations which are in respect to this data are relevant. The reliability of the data was corroborated through a titrimetric cnient of pK R + for triphenylcarbenium ion. The value obtained

PAGE 105

a

PAGE 106

96 V1 0) -) d 0J 4J X w .-I cd H g >-< ft d o c OJ X >-i td ON VO vc vO ON CM O vo vo <3~cjcr> vO O r-« CO in cm rH y o J n I -J13 ft OJ QJ : rH U ft ^-. O (J 13 c oj X ft I II Pi >, a . X 4_) CD E I ~cr I CM CO ft

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97 ile V) is in good agreement with pK . measured for this ion in 60Z KC10. by Bono and coworkers (11) using the titration technique. ; \ requirement which obviously must be met by the complexed carbenium Ions to insure that the corresponding stability data be meaningful is that the coordinate bond between the palladium metal center and the pyridine ring remains intact throughout titration. Undoubtedly, the pro tonic solvent will compete strongly for the basic ring nitrogen site(s) as evidenced by the fact that the pyridine ring is protonated for the "^ree" alcohol ions in 70% HC10, (shown below). The simplest demonstration of the stability of the coordinate bond during titrimetric (and 1 Q J ""'F nmr chemical shift) measurements stems from the fact, that the electronic spectrum of a given complexed 4-pyridylcarbenium ion in HC10, — HO remains unchanged for a period of at least a few hours. In fact, the electronic spectrum of the bis complex of 4-pyridyl-4-methylphenyl4-f luorophenylcarbenium ion in HC10, — H„0 was found to remain intact 4 2 for 12 hours as evidenced by the fact that during this tine no appreciable change in band intensity could be observed; and, more importantly absolutely no shifts of the xand y-absorption bands had taken place. Furthermore, the solution color of the complexed ion did not deteriorate to the solution color of the corresponding "free" ion. Additional investigations on the intact nature of complexed carbenium ion electronic i rum in HC.10, — il o upon the lone 2-pyridylmethanol complex isolated (see Experimental, p. 36) revealed that as soon as this compound was dissolved in the acid the intensities of the xand y-absorptions began to increase steadily; and also, the xand y-absorptions began to shift diately towards the respective positions of these absorptions characteristic of the uncoordinated, "free" 2-pyridylcarbenium ion.

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98 lylcarbenium ion i ' ,: waa insufficiently stable to be studied using HCIO^ -• HO as an ioniz sdiuraA comparison of the stability data for a related free ion— complexed ion series also :ves to establish that the metal — nitrogen bond(s) remain(s) intact during thermodynamic measurements, and that coordination certainly bilizes a given carbenium ion relative to the corresponding free ion. An examination of the respective AG° values (Table V) indicates that the degree of stabilization afforded by coordination is greatest for the 4-pyridylphenylcarbenium ion. Although the thermodynamic titration data for the unsubstituted phenyl carbenium ions is somewhat suspect owing to rearrangement of these ions in HC10, — H^O (discussed, pp. 10319 106) j F nrar chemical shift measurements in conjunction with relevant fr« e energy relationships substantiate the reliability of the reported stability data, v ide infra . The stabilizing influence of coordination upon a given carbenium ion is also seen on inspection of the dilution curves fur a free ion — completed ion related series (see Figures 10-12, p. 93). Here, the Beer's law dependence of the plot reflects the relative stability of a given carbenium ion. That is, a relative comparison of the D.F. values corresponding to that point in the titration at which each dilution curve no longer adheres to Beer's law, allows an ordering of the stability of all carbenium ions investigated by the titration method. This particular D.F. for the free 4-pyridyl-4-r>ethylphenyl-4-fluorophenylcarbenium ion is ca. 0.9?., whereos the corresponding s for the complexes of this ion are ca . 0.87, thereby showing i it the coordinated ions are more stable. a stability constant values (K) found in Table V correspond to iquilibria which are est l1 ' d upon the titrimetric reconversion

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99 of a particular pyridylcarbeniura ion to its free or complexed precursor. equations for these equilibria have been presented previously (p. 16) but for expedient purposes they are repeated in the order in which they are discussed. The equilibrium titration of a free alcohol ion is represented by: H + pyL + + 2 H 2 t H + pyLOH + H,0 + {2} This statement is consistent with the fact that the unionized alcohol is protonated. This is certainly expected for pyridine in such strongly acidic media as 45-70% HC10, (these values correspond to the acid concentration ranges spanned during the titration of the more stable carbenium ions). Moreover, Wentz (8) demonstrated that equation {2} was the correct equilibrium statement for describing the titrimetric reconversion of an uncoordinated thiazolylcarbenium ion to its alcoholic precursor. This was accomplished by titrating the N-methyl iodide salt of a particular 2 > 4-dimethyl-5-thiazolylcarbenium ion yielding a K value which was identical to that which he had obtained for the titration of the original alcohol ion. Clearly then, in each instance the thiazole ring nitrogen must have borne a unit positive charge throughout titration. Also, by assuming that the pyridylmethanol pyridine ring is of -9 similar basicity as pyridine itself (K, pyridine = 2.3 x 10 ) , it n be shown from simple acid-base equilibria that a given pyridylmethanol dissolved in 1 H H.,0 at an initial alcohol concentration of 03 "., is protonated to an extent in excess of 99.99%! (This calculai ion is given in the Appendix.) Since, for the HC10, — H„0 — pyridylloI systems considered, the combined concentration of IIC10. — H_0 k 3

PAGE 110

is al gn ater than 1 M, and the concentration of a pyridylsmall comparatively, the pyridine nitrogen is protonated . 100%) for a free alcohol carbenium ion. A direct effect of ring ;en protonation on carbenium ion stability is indicated from a parison of the data in Table V for a structural!}' related pair of e '.'. and 4-pyridylcarbenium ions. That is, a 2-pyiidyl ion is seen to be considerably less stable than its 4-pyrLdyl congener. The only significant difference, between such a related pair of cations should reside in the disproportionate degree of positive charge separation in the 2-pyridyl vs. the 4-pyridyl ion. Hence, it appears that the destabilizing consequence of like-charge repulsion on the stability of a given 2-pyridyicarbenium ion is relatively substantial in that the positive charge en the 2-pyridyl nitrogen is in much closer proximity to the carbenium ion center than in the corresponding 4-pyridyl ion situation. The equilibrium titrations of the coordinated carbenium ions may be represented by: Cl„(L >7 )rd(TI)pyL + +2H.0 ± Cl o (L KT )Pd(II)pyL0H + H„0 + {3} and Cl 2 Pd(Il)(pyL)2 + + 4 H 2 t Cl 2 Pd(II)(pyLOH) 2 + 2 1I 3 + {4} Statement {3} designates the reconversion of a singly charged coordinated ion to its complexed "mono" alcohol precursor. The stability ited with this t ran:format! on therefore afford a reflection

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I >' the stabilj ' effect exerted by the metal on a single pyridylcarl.un Lon. Statement {4} corresponds to the reconversion of a "bis" benium ion complex to its alcoholic precursor and is premised npon complete ionization of both of the coordinated alcohols in 70% HClO, h ( .e. , prior to titration). The £ data (Table II, pp. 77-73) indicate that both coordinated alcohols are ionized for the bis complexes in the 19 acid. The F nmr chemical shift data ( vide infra ) also corroborate this consideration stemming from the fact that the absorption position 19 oi the F nmr signal for a mono complexed ion is identical to that found for the corresponding bis complexed ion. If both the coordinated alcohols in the bis complex Xv r ere not ionized, either a time averaged signal would be expected or two signals would be observed in the spectrum corresponding respectively to an ionized and an unionized ligand raole19 cu.'e. That is, the F nmr spectrum should reflect the presence of either two rapidly equilibrating, or two distinctly different, fluorine nuclei. Furthermore, as previously indicated, the dilution curves resulting from the titrations of the bis complexed ions all exhibit appreciable Beer's law dependency at the onset of the titration. If the bis complexes had not been ionized completely upon dissolution in 70% HC10, , an immediate lv detectable equilibrium would have been estab•had upon addition of the initial quantities of tit rant (water) , and no Beer's lav. 7 dependence would have been illustrated by the Beer's law Lot at the beginning of the titration. This consideration alone does no 1 preclude the unique possibility of having ionized only one of th irdinated alcohols in a bis complex in 70% 11C10, . However, the e data, which indicate multiple ionization of the bis complexes in the acid, vide rathor forcing evidence substantiating the assertion that both

PAGE 112

lated alcohols are converted to carbeniura ion in 70% HC10. . 4 I, ' bis complexes dissociate in the acid, no Lncreas in absorption Intensity is detectable. Thus, both coordinated alcohols isl have br-ea ionized. Of course:, this contention could be definitively established by titrating a weighed sample of a bis complex vs. the corresponding mono complex, for which twice the quantity of water would b< required to reconvert the bis complexed ions to the neutral precursor i £ both coordinated alcohols had been ionized initially. It is also pointed out that the values for the thermodynamic data Ln Table V correspond to the reverse of the titration equilibria (equations (2), (3), and {4}) as written. Hence, an examination of these data in relation to the relative ease of carbenium ion foi'mation affords a measure of the stability (as opposed to instability) of that ion. In writing these equilibria it was tempting to consider the equal Lons which obtain upon carbenium ion generation; viz., for a free alcohol ion: H + py^0H + 2 HC10 4 -> H + pyL + + H + + CIO" {13} That is, this statement illustrates the net chemical change which occurs upon dissolving a protonated pyridylmethanol in 70% HC10. and obviously corresponds to carbenium ion formation. (It is not germane to consider oton source required for the initial protonat.ion of the pyridine ' ,;.) It must be emphasized, however, that the carbenium ion stability i from the aqueous titrations which are correctly Lbed by equations {2}, {3}, and {4}: and it is for this reason I this distinction has been mail

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103 Finally, a comparison of the stability data for the mono complexes to the data lor the corresponding bis complexes proves worthwhile. Those data suggest thai related mono — bis complexed carbeniurn ions are of practically identical thermodynamic stability. In the absence of. charge effects this would have been an expected result. However, based upon the consequence of like-charge repulsions on the stabilities of related free 2-pyridyL vs_. 4-pyridylcarbenium ions, it seems reasonable that a given bis complexed ion would be somewhat less stable than the correspondin; mono complexed ion. Apparently s therefore, the degree of charge separation in the bis complex ''di''-carbenium ion is sufficiently great that there is r.o residual ion destabilizing effect exerted mutually upon one another by the two coordinated ions in the complex. This stability similarity is also reflected by a virtual superimposability of the dilution curves for a related pair of these complexed carbeniurn ions. Thus, the stabilizing influence exerted by the metal center on the stability of such 4-pyridyl complexed ions appears to be independent of none vs . bis coordination. Although, it may be the case that destabilization arising through charge repulsions in the bis ions is counterbalanced by enhanced stabilization through solvation in the highly polar HC10, — H„0 solvent system. This possibility is suggested as a consequence of the considerably greater solubility of the bis vs. the mono c omul exes in HC10, — K,0. Additional studies are required to test 4
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104 ' ' ual and unanticipated results. For instance, it was disred Chat the dilution curves for the HC10 , — H o titrations of these carbenium ions could not be treated by the "1/2" Beer's law line extrapolation technique in order to get the corresponding stability constant data! That is, the second portion of the dilution curves (cf., Figures 10-12) obtained for any of these particular ions never fell off suffii i ntly to intersect with the "1/2" Beer's law line. In other words, the intensities of the principal electronic absorptions of these ionic species were found to grow steadily on standing (until the intensities had magnified by a factor of ca. 1.5 of original). In relation to this 19 unanticipated result was the fact that the '" F nmr signal initially exhibited by HC10. — HO solutions of these ions was found to disappear with tinie (ca.. within 1-2 hours to 2k hours depending upon the original concentration of the carbenium ion under investigation). The nmr result suggested therefore that the parafluorine phenyl ring substituent was discharged kinetically. Shutske's results (68) verified this contention. Shutske studied the reduction of various £ luorospiro(isobenzofuranpiperidine)s in 97% formic acid and discovered that on standing fluorine was lost as a phenyl ring substituent in the parent compound. This result prompted Shutske to repeat the investigations of Dayal e_t_ a]_. (69) on the reduction of 4-fluorophenyldiphenylmethanol in 97% formic acid — sodium formate solution. Shutske recognized the similarity of this estigation to the fluorospiro study with respect to the anticipated ction of the parafluorine substituent. Dayal _et a 1 . had reported isolation of only 4-fluo vldiphenylmothone as the reduction ." uct. Shutske, however, found that although this alkane was the u Lpa] reduction product, 4-hydroxydiphenylmethane was also obtain

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10! In a yield of 13%. Consequently, the loss of the parafluorine substituent from the unsubstituted phenyl pyridylmet ha 'in 1IC10, — H_0 paralleled Shutske's results. And. in retrospect, this result indicates : it the ability of a 4-fluorophenyl group to participate in conjugational interaction with the exocyclic carheniura ion carbon via it— electron release Ls more substantial than is that of unsubstituted phenyl. This is, in fact, borne out by the results of various studies on the thermodynamic stabilities of trityl-type carbenium ions which also contain 4-fluorophenyl rings (18,19,70,71), etc. Hence, the degree of positive charge which migrates by resonance into the 4-fluorophenyl ring in these particular carbenium ions is significantly greater than for either of the ion systems containing 4-methylphenyl, or 4-methoxyphenyl substituted rings. Thus, in these latter cases the fluorine nucleus was not lost during studies on carbenium ions in HC10. — HO. The "Deno" titration stability data (Table V) for the unsubstituted phenyl pyridylcarbenium ions were obtained in the following fashion. The initial portion of the dilution was plotted as usual ( viz . absorbance vs . D.F.) to yield the Beer's law dependent region followed by the normal smooth curve deviation from the extrapolated Beer's law straight line. It can be seen by inspection of the dilution curves (Figures 1012) that the plot is then again linear over a substantial region of the titration until a smooth curve upswing of the plot is reached which thereby establishes that the titration is virtually complete. That is, i e curves are very similar to those got from ordinary acid — base titrations, with the difference that the nertinent carbenium ion equii ria persist over a rather substantial concentration range of tb Lzing medium (ca. 10 wt 7. HC10 , ) , resulting in a titration curve

PAGE 116

Lth consid tbly less drastic chang i Ln ' than are customarily >ited by acid — base titration curves. So, since the dilution curves carbenium ions (i.e. , the ions which rearrange in HC10. — H, 0) I <.t curve upswing prior to intersection with the "1/2" Beer's law , the so-called second straight line portion of the curve (thai portion between curve dox^nswing and curve upswing) was extrapolated i Intersect with the "J/2" Beer's law line. This simple technique Llitated the isolation of the D.F. value for which [R-OH] = [R + ] , and thereby allowed the determination of K . for the unsubstituted phenyl carbenium ion in question. The reliability of tiie data obtained by this method was tested by precalculating appropriate v;t %*s HC10, required to yield D.F. samp Les whose carbenium ion absorbance would tentatively lie on the extrapolated dilution curve in the region oi interest. The D.F. samples tested in this fashion gave absorbances which coincided very well with absorbances predicted from the extranted plot. Hence, the stability data so obtained are considered 19 to be very satisfactory. It will also be shown that F nmr chemical shift data, in conjunction with attendant free energy relationships, serve to establish that these data are acceptable, vide infra. (Not-: Certain experiments were performed in attempts to determine the nature of the species which resulted upon fluorine atom ejection. A brief account of this work is provided in the Appendix.) Furthermore, it [ally of interest to study the stability of such fluorophen pyridyL nium ions as a function oF the rate of discharge of the Luorine substituent. Indeed, these experiments should be relatively straightforward to monitor via F nmr, and could provide additional illation concerning the carl ion stabilizing influence as exerted is coordinated metals.

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L07 19 F Chemical Shii I Carbenium Ion Si ! lv. To i , the results 19 oi previous L' nmr investigations have. demonstrated that a parasubStituted fluorine nucleus on an aryl ring is a highly sensitive probe in regard to the stability of carbenium ions which are conjugated with the fluorine nucleus. Hence, further discussion respecting thy appropriate nature of this nmr technique shall not be presented, excepting, 19 of course, as it pertains to the F nmr data obtained during the course of this vrork. 19 The use of F nmr chemical shifts as a criterion for the stability of coordinated carbenium ions is, in itself, a novelty. Past studies 19 which have employed F nmr measurements for the purposes of elucidating the stability and structure of coordination compounds have normally incorporated fluorine into the system as a ligand itself, i.e ., fluoride ion (see, for instance, the nmr studies by Dixon and McFarland (72), and references to related work cited therein). Also, fluorine in this capacity has been used for nmr investigations as a substituent on a ligand moiety bound directly to the metal center such as in the controversial studies by Parshall (73,74). This author proportioned the 19 measured F chemical shift of 3and 4-f luorophenyl groups coordinated to platinum(II) to the trans-directing abilities of ligands in the complex located trans to the f luorophenyl groups. In any event, it is believed that the current work embodies the first attempts to correlate 19 F chemical shifts with the thermodynamic stabilities of metal-complexed trityl— type carbenium ions. 19 The ' F nmr spectra which were recorded for the free and complexed pyrldylmethanol — carbenium ions are uncomplicated and highly similar.

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I ' absorption pattern was characterized by the presence of a tuplel fluorine signal which is predicted for H— F coupling in these systems by the relationship: Number of peaks (2 I-n, + 1) (2 l„n + 1) • • • (2 I n + 1) i i 2 2 n n {14} •re T I 1/2 for hydrogen, and n, = n« = 2 for the two pairs of hydrogens situated ortho and raeta respectively, to the single fluorine nucleus present in each species investigated. (The basic form of this equation is given in (75).) The center peak of the 9-fold absorption expectedly the most intense. The only difference of consequence resulting from a comparison of all the spectra lies in the relative positions of the signals for each species. For simplicity, the center 19 of the 9-fold resonance pattern is taken as the F absorption position. Hence, the position of the fluorine signal, recorded relative to an appropriate reference standard, provides an indication of the stability of the carbenium ion under investigation relative to the degree of ir-electron delocalization present within the structural framework of each, carbenium ion species. The reference standards employed were external CFC1_ and external trif luoroacetic acid (TFA) . The use of two standards afforded a double check on the reliability of the obtained shift data. External referencing procedures were, used for all carbenium ion spectra owing principally to the extremely reactive nature of the and of the HC10, — li ? solvent. Consequently, the absorption position 'i standard might have been appreciably affected by interi Ions with solute, or solvent. Nonreactive, nonpolar materials, obLy could not be si i i tctorily employed as internal references

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because of th< ; miscibility with HC10, -II 0. Referencing against i tie same externa] standards also facilitated the comparison of chemical shift data obtained for the unionized ligands and complexes in acetone to the related data for the corresponding carbenium ions in HC.10, — H. ; 0. Bulk suseeptib.u i ty contributions by the solvent to carbenium ion chemical shifts were expected to be unimportant in that each, ion spectrum was recorded in 70% HC10, . Hence, solvent chemical shift susceptibility contributions were leveled for each nmr measurement. 19 The shift data resulting from these F nmr investigations are 1 19 given in Table VI, pp. 110-111. Since H — F coupling is of no 19 particular concern to this work, examples of the F spectra are not given.) The following statements in relation to the relevant trends established by these data are in order. A comparison of 6 values for the alcohols in acetone, 1 K HC10, and 70% HC10, , systematically shows the effect of proceeding from an aprotic solvent, to a protonating solvent, to a solvent capable of carbenium ion generation. Consequently, 3 small downfield shift of the resonance for a given alcohol is detected upon protonation (i.e . , acetone vs . 1 M HC10, as solvent) ; whereas trans formation to carbenium ion is accompanied by a relatively substantial 19 downfield shift in the F signal. This same trend is exhibited by the complexes but, of course, no 1 M HC10, spectrum was recorded for these materials as they are not soluble at this acid concentration. Hence, as expected, conversion to carbenium ion results in appreciable resonance dc Li calization of positive charge throughout the conjugated molecular framework. In proceeding from R = -phenyl to R = -4-methoxyphenyl for any related series of carbenium ions an appreciable upfield shift of ] signal is observed. This reflects the substantial capacity of

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I -J-

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1 1 u cd a « CD 4-1 > r/1 CD i — ! /-% « o! rH i u IT. CJ co U o H C_> o < o H u SI co !-( u CJ M a* 3 o •H d
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112 phenyl substituent relative to hydrogen, • • • and in turn relative to a parafluorine substituent, to remove po charge from ocyclic carbon via conjugational interaction. A comparison of 6 for the 2-pyridyl vs. the corresponding 4-pyridy l.carbenium ions shows the destabilizing effect of like-charge repulsions on carbenium ion stability to be more significant in the 2-pyridylcarbenium ions. Hence, 19. the F signal for a given 2-pyridylcarbenium ion is downfield relative to its more stable 4-pyridylcarbenium ion congener. This is in keeping with the thermodynamic data which have been considered previously. The consequence of coordination on a given F resonance is reflected by a substantial increase in 6 found in proceeding from a free to the corresponding complexed ion(s). This trend also parallels related thermodynamic data obtained from the titrimetric investigations and again indicates that complexation stabilizes unsubstituted phenylcarbenium ions to the greatest extent. 19 For the data reported, it can be seen that the " F signals for a related monoand bis-complexed carbenium ion pair are virtually 19 Ldentical. Since two F resonances were not initially detectable for the bis complex ions, it is clear that both coordinated alcohols are converted to carbenium ion in 70% HC10,; and again, a related monob Ls-complexed carbenium ion pair are predicted to be of essentially equal thermodynamic stability. Here, it is conveniently pointed out 19 that when Lhe 70% HC10, F nmr samples of the mono and bis complexes (of R = -4-methylphenyl, for example) were allowed to stand, eventually two lignj Ls Lop d, 0i of the signals coincided with the original m d carb< i sorption, whereas the newly developed signal with the free carbeniu i Lon resonance. These data verify tl

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i L3 n i :t nature of the coordinate, bone! between palladium and the pyridii ring in 70% ILC10 as the second signal was not detectable within I fi st few hours of sample preparation. Furthermore., for the monoed ion, the intensity of the free ion signal was not equal (approximately) in magnitude to that of the complexed ion until the iple had stood ca. 24 hours. Again, this demonstrates the stability of the coordinate bond. 19 The '" F nmr shift data reported for the carbenium ions derived from the free and complexed unsubstituted phenyl pyridylmethanols are considered to be reliable for the following reasons. Principally, the 19 detection of a F signal in these systems for a freshly prepared sample essentially guaranteed that the nmr measurement was made on the species .19 of interest. This follows since the originally detectable F signal disappears only after rearrangement of these carbenium ions takes place. Free energy correlations (considered i.n the forthcoming section) also served to corroborate the credibility of the nmr data; and, as well, instated the use of appropriate F chemical shifts for the determination of the thermodynamic stability of 2-pyridylphenyl-4-f luorophenylcarbenium ion (recall that the stability of this carbenium ion species was not ti trimetrically measurable). As this particular carbenium ion was allowed to stand, several poorly resolved signals 1 9 loped in the F spectrum. An attempt was made to fingerprint 19 these absorptions _via. comparison with the F nmr spectrum of 1:5 48% 70% HC10, . The F signal for HF in 96% H o S0. reportedly exists I -116.9 ppm relative to external TFA (76), hut no similar absorption wa ' detectable in the HF — HCIO^ spectrum. Presumably, the HF reacted the glass nmr tube to produce silicon fluorides or fluorosilicates.

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: r side products were expected for the remaining unsubstituted Lcarbeniura ion samples where HF was also the initially anticipated taining rearrangement product. A comparison of all unitituted phenylcarbenium ion nmr spectra, hov/ever, yielded little correspondence of resonance positions for the signals which developed upi i rearrangement. (For the concerned reader: the 2-pyridylphenyl4-f luoropheny Icarbenium ion spectrum degenerated upon standing into two ill-resolved signals at ^a. 52.3 and 63.9 ppm relative to external TFA; and the HF — HCiO, spectrum exhibited four principal absorptions, at 52.6 (very broad), 63.1, 64.3, and 66.6 ppm, respectively, relative to external TFA. And, the intensity of the signal at 64.3 ppm grew rapidly during scanning of the sample.) One final set of nmr experiments was performed in an attempt to 19 relate ca rhenium ion — carbinol precursor equilibria to associated F chemical shift data. The wt % HCIO, datum for 50% ionization of a given rhenium ion species was obtained from the appropriate dilution curve 19 — D.F. plot. A " F spectrum of a carbenium ion system in this wt A HCIO, was expected to exhibit either two principal signals corresponding to loci and alcohol, respectively, or one signal arising from rapid solution equilibration of ion and alcohol (see p. 101). To carry out this investigation a solution of 4-pyridyl-4-methoxyphenyl-4-fluorophenylhanol was prepared using 53.8% HCIO^ . This is the so-called 50% acid for this carbenium ion precursor. The nmr spectrum of this solution, how sver, exhibited only a single resonance which correi q I with the posil Lon for the " F signal of this ion in 70% HCIO,. i, no additional resonance was detect ,[>! for this system until

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115 the acid was diluted to _ca. 46%. At this acid concentration a second mance finally developed which corresponded to the signal exhibited by the protonated pyridylmethanol precursor. These signals became of approximately equal intensity at _cji. 44.5% acid, and at _ca. 43% acid t:ie carbenium ion resonance disappeared entirely, This result is unusual for the following reasons. First, the dilution curve — D.F. data for this carbenium ion indicate that the carbenium ion — protonated alcohol equilibrium is measurably significant over a minimum range of 8-10% acid (this is, in fact, the case for each of the titratable carbenium ion species, see p. 105), whereas the nmr result suggests that this equilibrium is measurable only over a rather limited range of ca. 3%. Secondly, the nmr result indicates that this particular carbenium ion is essentially 50% reconverted to protonated alcohol precursor at 44-45% HC10, which is much less than the 53.8% value predicted from the titrimetric investigation. Hence, the nmr measurement suggests that a considerably less concentrated ionizing medium is capable of producing substantial conversion of protonated pyridylmethanol to carbenium ion, and, as yet, this result is unexplainable. It should be noted, however, that there is a significant difference in concentration required for carbenium ion nmr investigations compared co concentrations necessary for carbenium ion electronic spectral investigations. That is, in order to obtain acceptable nmr spectra for materials of relatively high molecular weight which are dilute in the absorbing nucleus (viss . , one fluorine atom per pyridylmethanol of M.W. ca. 280-? 300 amu), it is necessary to maintain solute concentrations at 10 II, 19 or 1 Lgher, in order to obtain detectable "F resonances, even with currently available Fourier transform techniques. In fact, the

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] 1 6 phenyl subsl I tuted carbenium ion was visually detectable in HC10, by virtue of the characteristic solution color of the ion, even though no nmr resonance could be obtained. Thus, concentration u Lrer.ients for nmr studies are considerably greater than for electronic spectral measurements on pyridylcarbenium ions. Hence, the two experimental methods cannot be cross-checked quantitatively owing to the grossly different concentration ranges necessary for each measurement. (Note: The same nmr dilution experiment was performed on the bis complex o£ 4-pyridyl-4-methoxyphenyt4-fluorophenylmethanol (carbenium ion}. However, this investigation proved futile as dilution induced the precipitation of the complex.) Although additional studies are required to resolve the problems encountered in the so-called nmr dilution experiments, a potentially fruitful study is suggested concerning the carbenium ions which eject fluorine in HC.10. — H„0. That is, presume it is possible to fix a known 4 2 concentration ratio of a given unsubstituted phenylpyridylmethanol and corresponding carbenium ion via appropriate manipulation of HC10, concentration. This should establish two simultaneous equilibria: a) al-,o\ interconversion with carbenium ion; and, b) carbenium ion interconversion with the species resulting after fluorine atom loss. This 19 investigation would obviously be monitorable by F nmr, and perhaps new information concerning the stability of such types of carbenium ions would be afforded from kinetic, as well as from thermodynamic tndpoints. iree Energy (LFE) Correla tions and Car benium T on Stability. A bei of analytical free energy correlations have been successfully

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117 Lied to the thermodynamic data obtained for the pyridylcarbenii [ ins considered in this work. These correlations are presented graphically (where appropriate) in this section and discussed principally in terms of the relative stabilities of the various carbenium ion species. A significant outgrowth of these considerations is the indication that coordination, which has been shown to stabilize a given carbenium ion relative to the protonated ion, destabilizes the ion relative to the unprotonated , uncoordinated ion (vide infra) . This implies, rather obviously, that the localized removal of "sigma" electron density occurring upon coordination to the palladium containing moiety cannot be separated from a concomitant reduction of ir-electron density in the pyridine ring. Consequently, it appears that complexation (for the cases considered herein) does in face destabilize the pyridylcarbenium ions. Various studies (see, for instance, (12), (19), (77), (78), and (79)) have demonstrated the suitable application of the famous Hammett equation (80), log K = log K° + pa, towards the correlation of thermodynamic parameters for arylcarbenium ions. Therefore it. was reasonable to analyze the thermodynamic data obtained for the pyridylcarbenium ions by similar methods. The plots which are presented in Figures 13, 14, and 15, p. 118, established the following relationships to be linearly dependent: (i) Hammett "exalted" Za + constants vs. AG° of carbenium ion p-r — formation. (The. a + values employed were 0.00 for para-H; -0.07 for paraF; -0.31 for para-CH-; and -0.78 for paraOCH (31). Curves 1, 2, and 3, are for protonated 2-pyridyl, protonated 4-pyridyl, and bis palladium(II) complexed 4-pyridylcarbenium ions respectively.)

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0.8_ 0.6 , 0.40.2. -| — 10.00 for 1

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119 19 (ii) Carbenium ion F nmr chemical shifts recorded relative to i :ternal CFCI3 vs . related values of LG° . (Curves 4, 5, and 6, correp id to the same carbenium ion sequence as in (i) above. The point on carve 4 designated by the * is extrapolated to the abscissa to yield AG" for the formation of unsubstituted phenyl-2-pyridylcarbeniun ion.) 19 (iii) Hammett "exalted" Zo < constants vs. carbenium ion " F P+ — nmr chemical shifts relative to external CFClo(Curves 7, 8, and 9, correspond to the same carbenium ion sequence as in (i) above.) The ensuing discussion is in respect to these relationships. The appropriate application of Hammett a + constants (rather than the usual a constants) in free energy correlation analyses for arylcarbenium ions upon variation of electron donating, para -phenyl substituents has been established principally through the work of Deno and Evans (78), and Broxvni and Okaraoto (82). Therefore it was expected that these parameters were found to correlate exceptionally well with the pyr idylcarbenium ion stability data. Admittedly, it is seen that in each case the curves have been drawn employing only three data points. None the less, the degree of linearity obtained for all correlations considered is astonishingly good. And, although in certain instances nonlinear free energy cox-relations may prove to be interesting and important, a linear correlation is the required sine qua non for the immediate and direct prediction of interrelated but otherwise "unknown" thermodynamic information. Indeed, it is on this basis that the stability constant data reported for 2-pyriuylpheny] -4-f luorophenylcarbenium ion (Table V, pp. 95-96) have been obtained and deemed reliable. That is, plots 2 and 3 in Figure 13 served to establish the linear interdependency of T,a + and for carbenium ion formation for the various 4-pyridyl species.

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Similarly, plots 7, 8, and 9, have demonstrated the linear relationship of Eo .j and 6 for each carbenium ion speci> estigated. Hence, a-s shown, Che construction of plot 4 in Figure 14 using the nmr and data tor the 2-pyridyl-4-methylphenyl, and 2-pyridyl-4-methox> phenyl protonated carbenium ions, allowed the determination of AG° for the corresponding unsubstituted phenyl ion. (Note: For these analyses the data recorded relative to external CFC1.-. were used exclusively owing to the greater significant figure accuracy obtained for carbenium ton chemical shifts measured relative to this standard. Viz., as indicated by che dnta contained in Table VI, pp. 110-111, the positions of the sample and reference signals wi th external TFA as standard were r?latively close. Consequently, only two significant figure reliability could be obtainsd for the nmr data measured relative to external TFA. I'rcheless, to check these LFE analyses, similar plots were drawn using the TFA. referenced nmr data, and these plots also were linear.) Two additional LFE plots of interest are illustrated in Figures 16 and 17, p. 121. The linearity of these plots suggests a proportionate change in carbenium ion stability throughout the related 4-pyridyl vs . 2-pyridyl (Figure 16), and 4-pyridyl vs. bis-complexed 4-pyridyl (Figure 17), series of ions. The slope (= 0.829) of the line in Figure 16 reflects the lower stability of a given 2-pyridylcarbeniura ion compared to its 4-pyridyl congener. Extrapolation of this curve to the intercept, however, yields an inexplicable result from which it is implied that for relatively stable pyridylcarbenium ions (i.e. , A0 C very small, or .tive) the 2-pyridyl ions are ultimately the more stable. Consequently, it appears that extrapolation of this curve to a considerable extent I the data points is not warranted. The slope (= 1.04) of Figure 17

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123 50.00 15.00 ^ 10 . 00 _. v.C.° (fecal) v mol ' 5.000.00 0.00 10.00 ub ^kcax/mol) 20.00 24.00 Fig. 16. AC° (uncoordinated 4-pyridylcarbenium ions) vs. AG° (uncoordinated 2-pyridylcarbenium ions) . .kcal, ^mol } 20.001 15.00H 10.005.00o.oo0.00 slope = 1.04 intercept = 1.60 10.00 AG° (kcal/mol) 20.00 24.00 Fig. 17. AG° (uncoordinated 4-pyridylcarbenium ions) vs. AG° (bis-complexed 'r-pyr idyl carbenium ions).

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122 roborates the c< ion previously a I upon that comp] : on stabilizes th Least stable 4-pyridylcarbeniura ion to the greatest extent. In ti> ; <; case the intercept value implies that a coordinated pyridylcarbenium ion is inherently more stable than the corresponding protonated icn. This is a reasonable result. Of course, identical analyses of new, related data are required before more exacting conclusions can be. drawn. (Note: Several other linear plots are constructive using the accumulated thermodynamic data owing to the established linear iuterdependencies (as shown) of AG°, a + , and 5. These plots can be synthesized as necessary for supplementary correlation studies.) An examination of the slopes of the curves of Figures 13, 14, and 15 (1/p -9.42 for curve 1; 1/p = -7.82 for curve 2; and i/p = -7.43 tor curve 3; these slopes are reported as 1/p for the comparisons which % to be made) affords a simple method for comparing the stabilities of i he pyridylcarbenium ions to related systems of arylcarbenium ions vhich have been investigated previously via similar techniques. That is, as pointed out by Freedman (64:1548), a plot of AC° vs. Y.c + for a series of structurally and substitutional^ related arylcarbenium ions yields a straight line whose slope reflects the degree of electronic demand at the carbenium ion center. And, in these cases, a negative e indicates that the presence of electron releasing substituents capable of interacting conjugationally with the carbenium ion positive. charge facilitates the development of that charge. Thus, carbenium ion stabilit Ls enhanced by substituents such as para-methyl and parai i :y relative to p_ara-II, etc. Also, the magnitude of the slope is tive measure of the stability of the particular family of ions consideration. For example, p for plots of AG + vs. T.o + is on

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the order of -2.5 for a .series of malachite green carbenium ions, -4.5 for a series of tritylcarbenium ions (64:1749), and -8 for para-substituted diphenylmethylcarbenium ions (64:1550). Therefore the stabilities of the pyridylcarbenium ions are again shown to be in the order: Coordinated 4-pyridyl > protonated 4-pyridyl > protonaLed 2-pyridyl; and furthermore, these, results imply that the 4-pyridyl ions are but minimally more stable than diphenylmethylcarbenium ions, whereas the 2-pyridyl ions are appreciably less stable. Finally, the use of certain, appropriate arguments permit a reasonable comparison of the stability of the protonated and complexed 4-pyridylcarbenium ions to the stability of such ions premised upon a nonbound pyridine nitrogen. That is, although it is not possible, obviously, to investigate an unprotonated free ligand pyridylcarbenium ion in strongly acidic media, it is necessary to speculate on the stability of this ion in order to estimate the net stabilizing effect exerted by the metal containing moiety on the coordinated ion. This is done in the following fashion. The contribution to the stability of a triaryltype carbenium ion by an unprotonated pyridine ring may be approximated using the literature pKj, + values for malachite green (MG) carbenium ion (pK^-f. = 7 07) and 4-pyridine malachite green (4-pyMG) carbenium ion (pK^j. 5.66). These data have been taken from the compilation of Nemcova et al . (83). (Note: Here T>K, + corresponds to the equilibrium reconversion of carbenium ion to precursor alcohol: R + 2 H„0 J R-OH + ELO ; and 4-pyMG is simply MG with the unsubstituted phenyl ring replaced with a 4-pyridyl ring.) An examination of these pKp+ values indicates that exchange of a phenyl ring for a 4-pyridyl ring induces a net carbenium ion destabilization of 1.41 pK units (1.92 kcal) in

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124 Les of ions. This destabilization may he quantitatively to strictly triphenyl-type carbenium ions (i.e. , those without Lno Bubstituents) by comparing the slopes (p's) of the plots of log K vt>. £0 + for the MG series of ions (p = -1.4) to that for the triphenyl ions (p -3.5), (84:101-102). That is, as pointed out by Hine, phenyl ring substitution in the triphenyl ions induces a considerably greater change in carbenium ion stability than does the identical titution in the MG series of ions. Hence, the larger negative slope oi this plot for the triphenyl ions reflects the greater sensitivity of the stability of these ions to electronic effects. This consideration it. illustrated through a simple analysis of the pK data given below. These data are in respect to the general equilibrium described above. (i) pKd+ of triphenylcarbenium ion = -6.63; and pK_}_ of para t'ltrotriphenylcarbenium ion = -9.15 (10). (i l) pk p + of MG carbenium ion = 7.07; and pK~o+ of paranltroMG c u-benium ion = 6.00 (64:1534). Thus, as expected, the destabilizing effect exerted by a paranitro substituent is much greater in the triphenyl scries of carbenium ions (-2.52 pK units) than in the MG series of carbenium ions (-1.07 pK units). And, the ratio of these destaging contributions, 2.52/1.07 = 2.36, is certainly comparable to that predicted from the slope ratio, 3.5/1.4 = 2.5. Now, in that pyridine exhibits tendencies towards electrophilic aromatic substitution Lch nre similar to nitrophenyl rings, and since both of these systems illize trityl-type carbenium ions, it is reasonable to predict p] unprotonated 4-pyridyldiphenylcarbenium ion to be on the order of -6.82 2.5(1.41) = -10.34 = ?K,+. (Mote: For this approximation -6.82 . iue for plvp+ of triphenylcarbenium ion. This is the average of

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125 the pK_ + values cited in Table V, pp. 95-96,. for this ionic species in 70" HC10,.) A comparison of this value (-10,34) to the pK + values which have been determined for the protonated (pKp+ = -13.47) and biscomplexed (pKj.+ 12.21) 4-pyridylphenyl-4-f luorophenylcarbenium ion, strongly suggests that the unprotonated ion is appreciably more stable Chan either the protonated (obviously) or the palladium complexed ion. Moreover, the para-f luoro substituent would contribute additional stabilization to this ion such that the actual pK^ + would be slightly greater (less negative) than the speculative value of -10.34. This further substantiates the validity of the hypothetical stability comparison. Suitable use of the log K vs_. Za + plots given by Hine (84:101) in conjunction with the results of Barker et_ al. (52) affords another simple corroboration of this consideration. That is, examination of the plot for the MG series of ions (Hine) reveals that for MG with pK^+ = 7.07, Zcr . = -3.4; and for 4-pyMG with pK^ = 5.66, Za + = -2.5. Thus, with a + = -1.7 for para-N(CH„)„, a hypothetical value of a = 0.9 is predicted for a 4-pyridyl ring, thereby demonstrating the electron withdrawing capacity of a pyridine ring taken as an arylcarbenium ion substituent. This value is comparable Lo a =0.78 for a nitro group as a para-phenyl substituent; and the ratio 0.9/0.78 = 1.2 is in good agreement with the ratio 1.41/1.07 =1.3 which is obtained from the respective energetic destabilizations of a 4-pyridyl ring and a 4-nitrophenyl ring in MG carbenium ion. Similarly, the linear correlation of (kK) with Hammett a substituent constants discovered bv Barker and coworkers for a series of phenyl substituted MG carbenium ions

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.ion of a of C2. 1.0 1,1 for the 4— pyridyl ring in relation is made b;y using the value of 15.4 kK real: A for 4-pyIIG (83). Furthermore, use of the second max plot presented by Hine of log K vs . L"o for triphenylcarbenium ions, and the provisional value of ca. -10.3 for pK + of unprotonated ''t-^yridylphenylcarbenium ion, allows a value of o of ca. 1 to be obtained for the 4-pyridyl ring. Thus , the hypothetical a values which are predicted for a 4-pyridyl ring treated as a substituent in arylcarbenium ions are found to be in very good agreement. Therefore, on this basis, it is reasonable to conclude that an unprotonated pyridine ring is of approximately the same electron v/ithdrax^ing capacity as a nitropneuyl ring, but, as suggested previously, is not as electron withdrawing as the palladium coruplexed pyridine ring. A last extension of these considerations can be made employing trie results of Atkinson e_t al. (85). These workers satisfactorily demonstrated the existence of a linear correlation between the frequencies (v, kK) of the longest wavelength electronic absorptions and Taft o"-' c polar substituent constants for a family of diphenylmethylcarbenium + ions (
PAGE 137

127 [n fact s this treatment may indeed be more logical than the. a evaluation ag to the polar character produced in the pyridine rin^ by protonation (and, apparently, by coordination as well). Inasmuch as the electronic spectral investigations have indicated that the absorption at ,\ reflects principally electronic interactions between the carbenium max ion cent ex and the phenyl rings, it is necessary to consider the frequencies at A for the protonated and bis-palladium complexed unsubstituted 4-pyridyldiphenylcarbenium ion. The frequencies are 21.0 kK and 21.4 kK, respectively, for these ions in 96% H,.S0, (7). (Note: The electronic spectra of these ions are not changed in 70% HC10, .) Using the v — a* correlation plot (85) hypothetical values of a* of _c£. 1.0 for protonated pyridine, and a* of ca. 0.85 for palladium-complexed pyridine are obtained. These a* values indicate rather substantial electron withdrawing capacities for these pyridine moieties. Again, based upon the comparable stabilities expected for 4-nitrotriphauylearbenium ion and unprotonated 4-pyridyldiphenylmethylcarbenium ion, a speculative value of a* can be estimated for the unprotonated pyridyl ring. That is, since v at X for the nitro ion is 22.0 kK, which max correlates with a* of ca. 0.6, a value of a* of ca . 0.6—0.7 is predicted for the unprotonated pyridyl ring. Of course, this speculation rests on the assumption that these two ring systems influence the frequency at X to approximately equal extents. This contention is max supported by the fact that these rin. ; systems have been shown to be of comparable electron withdrawing capacity. Therefore, as indicated previously, the palladium(II) containing moiety employed in this work as the coordinating agent, appears to contribute an overall thermodynamic destabilization to trityl-type pyridyl carbenium ions.

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IN CONCLUSION The. experimental bases which have been established for the investigation of heteroaromatic carbenium ions (6, 7, and 8), have been reinforced and expand ed by this work. The achievements which are felt to be o£ principal significance are. the following: (i) The preparation of the mixed "mono" alcohol complexes (denoted in Che text as [Pd(II) (pyLOH) (L )C1„]) appears to be the first successful application of a synthetic method generally suitable for the selective incorporation of strong ir-acid ligands into the coordination sphere c^ palladium(II) , to include pyridine-type donors. Consequently, it is now expected that pyridine containing arylcarbenium ion precursors can be introduced as ligands ad l ibitum into palladium(II) , as well ascertain other, metal centers. Therefore, many additional, related studies on complexed carbenium ions have been made feasible by the development of this synthetic technique. (ii) The thermodynamic stabilities determined for the various caibeniuni ion species considered herein provide strong evidence to indicate that charge repulsion effects tend to destabilize the 2-pyridyl ions to a considerable degree. On the other hand, the very similar L ties found for related "mono" and "bis" complexed carbenium ions indicate bhat charge repulsion effects in the doubly ionized "bis" ion terns are no longer sufficient to destabilize these ions. So, it is 128

PAGE 139

ntially of value to prepare several "bis" carbeniura ion complexes Ltl the Interesting prospect of determining the sensitivity of the Stability of a particular completed carbenium ion to intra-species charge repulsion effects. Moreover, carbenium ion stabilization provided by various metal-containing coordination centers can be considered in respect to this possibility. That is, effects on carbenium ion stability resulting from variation of the central metal species, variation of the oxidation state of the metal species, variation of the counter ligands, etc.;, can now be investigated with similar intent. (iii) Again, the results obtained from the "Deno" titration stability measurements, established to be reliable by appropriate LFE analyses, have shown that this titrimetric technique is a suitable method by which to evaluate the thermodynamic stabilities of protonated and complexed pyridylcarbenium ions. Furthermore, successful electronic spectral interpretations have provided experimental and theoretical substance towards correlating arylcarbenium ion electronic absorptions with the aromatic ring systems which comprise the carbenium ion entity. Consequently, it has been made possible to assess tentatively the contribution to coordinated carbenium ion stability exerted by various metal containing moieties in terms of the relative degree of influence upon the frequency of the so-called y-band electronic absorption as measured for the different metal centers. 19 (iv) The applicability of F nmr chemical shift measurements as a criterion of the stability of pyridylcarbenium ions has been established. That is to say, a fluorine nucleus para substituted on a phenyl ring been shown to be a suitably sensitive probe for the purpose of quantitatively estimating the stabilities of these types of carbenium

PAGE 140

13(1 u is. A possibly fruitful extension of this work might well be provided l 9 by emeuts with the fluorine nucleus incorporated as a phenyl substituent in the carbenium ion molecular framework. By a comparison of the results of these nmr investigations with the nmr dsf:t at hand, a separation of avs. 7i-eleetronic effects within the py .' idyl carbenium ions is potentially achievable. (v) The LFE correlations which have been applied to the. thermo19 dynamic stability data, F nmr data, and the appropriate Hammetc-type substituent constants, have proved to be exceedingly good even though only three data points were used for each analysis. Obviously, the preparation and investigation of additional pyr idyl carbenium ion species by varying para phenyl ring substituents, affords a simple means of extension of the current work. The stability predictions made in reference to unprotonated 4-pyridyldiphenylcarbenium ion could be pursued experimentally via the syntheses of salts of the various pyridylcarbeniura is, followed, of course, by appropriate measurements to determine the stability of these ions. The preparation of stable salts of the coordinated carbenium ions could well be stimulating and provocative owing to the stringently anhydrous, nonbasic, conditions required in order to sustain the existence of such materials. Consequently, it. could prove difficult to develop a preparative route during which the metal containing moiety would remain coordinated during the conversion of oho! to carbenium ion salt. To recapitulate then, the experimental studies on the various ,ienium ion species which have been carried out during this work have i very successful. It is therefore proposed that the scope of lamic investigations upon free and complexed heteroaromatic

PAGE 141

benium ions can now be broadened considerably by extending these to include related systems of arylcarbenium ions.

PAGE 142

APPENDIX

PAGE 143

1_. Specific Gravit y of Aqueous HC IO^ Determined as a Func t ion of Hi HCIO4 . By employing the. specific gravity (n) — wt % HC10, data in ible TV. p. 91, a computer fitted "least squares" estimate of p as a function of wt % HC10, was obtained. This was carried out by assuming the functional relation y(p) = f(x) (x = wt %) to be of the form: 2 3 4 a + a,x + a„x + a„x + a,x {15} for y vs . x which yields a smooth curve plot over the entire range of experimental (x,y) values. Then, the values of the coefficients (a's) for this polynomial are obtained from a least squares estimates analysis by minimizing the sum of the squares of the deviations which result im: 2 2 (deviation) = [y(calcd from {15}) y(exptl)] {16} sucamad over all the experimental points. With the a's calculated, equation {15} is: y = 0.996357669170ex 00 -h (0. 606617134345ex 02)x (0..171560538090ex 04)x 2 + (0. 164401851371ex 05)x 3 (0.98l691970813ex 08)x 4 {17} from v,hidi a complete series of p values as a function of wt % HC10, 4 is obtained. (Note: it was found that the x and x terms may be n '.Lected with no loss in data precision to 4 significant figures.) le data were processed at intervals of 0.010 wt % spanning the range ]33

PAGE 144

134 p = 0.996357 at wt Z HC10, = 0.000 (i.e. , pure water at ?.5' J ), top = 1. '37627 at wt % HC10, = 75.000. The p values were rounded to A significant figures or tne required D.F. calculations. The program employed was: WAHG Series 700 V 1. General Library, Program 1063A/ST3 "N order regression analysis". A general description of the method is provided by Kuo (86) . 2. Degree of Protonation of a Pyridylmethauol (pyLOH) in Aqueou s HCIOa In reference to the assumption that a pyridylmethanol is of approximately the same basicity as pyridine (p. 99), straightforward acid-base equilibrium calculations may be employed showing that the degree of pyridine ring protonation is virtually 100%: (i) In connection with this assumption the following equilibria can be written: pyLOH + I1 2 t H + pyL0H + 0H~ {18} and H + pyL0H + H 2 t pyLOH + H 3 + {19} -9 (ii) Using {19} and K, ~ 2 . 3 x 10 ' for pyridine, the equilibrium constant for {19} can be evaluated: v = [pyLOH] [H-tO + ] [OH ] _ K | . [H+pyLOIf] [0H-] K^

PAGE 145

K * : 9 ! """'' ~ / -, in" 6 2#3 x 10 _9 • 4.3 x 10 (iii) Now, with the conditions specified as [H.,0 ] = 1 and [pyLOH]. . 0.01 (p. 99), it follows that for pyLOH + H 3 t H pyLOH + H 2 {20} 1 1 _ o o -m 5 \Z0j K f , 4.3 x 10 D 1. 19 1 and. if [H + pyLOH] x, v [H + py L0H] x 5 K {20] [pyLOH] [H 3 0+] (0.01 x) (1 x) /J X 1U ai d (0.0.1 x)(l x) 0.01 x since 1 > > 0.01 > x and for _JL__ „ 10 5 = 10* 0.01 x XU 10-7 x is on the order of ca. 0.0099999! Hence, within the limits of the calculation, a given pyridylmethanol at ca. 0.01 M (initially) is protonated to an extent of 100% in 1 M [HO J.

PAGE 146

3-_ ' : .' ,; . Conducted upon the Carbenium Ion Species Foj to Exhibit ;ement in 70% HC10& . As indicated by previous inwhich have employed acidic media to generate arylcarbeniun CO I lining parafluorophenyl substitueats, the fluorine atom may eventually be displaced resulting in the formation of either an alcohol (68) or a quinone (79). Consequently, loss of the para fluorine substituent from the pyridylphenyl--4-f luorophenylcarbenium ions in the HCl^ — H„0 was not unusual since in these carbenium ion systems the. para-f luoro substituent; is the predominant electrondonating entity involved in conjugational interaction with the carbenium ion center. Therefore positive charge build-up at the para position in the fluorine-containing ring ultimately results in nucleoptiilic displacement (presumably by H-O solvent molecules) of the fluorine substituent. In recording the electronic spectra of these pyridylphenyl-4f luorophenylcarbenium ion species it was observed that the intensity of the main absorption bands (the x and y bands) grew steadily upon standing until the intensities had approximately doubled. Moreover, it was observed that the positions of these bands remained essentially unchanged during rearrangement of the uncoordinated ions, whereas the mono-complexed [Pd(II) (L )Cl„pyL] carbenium ion exhibited an x-band shift to 494 nm after standing a period of 12 days. (Recall that A for this carbenium ion as the protonated species is 482 nm, and for this particular complexed ion is 477 nm) . Thus, it is seen max "new" A (494 nm) is appreciably longer even than A for max ' max ee (protonated) ion (482 nm) . Also, the bis-complex of this ion Lbited a shift in A from 470 nm to 482 nm after standing a period

PAGE 147

! 17 of 6 days; this species, however, exhibited no further red shift of x-band absorption ar. did the corresponding mono-complexed ion (above). These results are as yet not explicable. In an attempt to estimate the relative stability of the rearranged product, assuming it to be a new arylcarbenium ion, this species was titrated via the usual method. This was carried out by preparing a fresh sample of 4~pyridylphenyl-4-f luorophenylcarbenium ion in 70% HClO^j and titrating immediately. The sample was then allowed to stand ca . 24 hours during which time the intensity of the x-band absorption had essentially doubled. This result indicated that although the original carbenium ion had been substantially reconverted to protonated alcohol precursor by titration, the protonated precursor was still capable of rearranging to the new species thereby implying that the new species was a more stable carbenium ion. After the intensity of the x— band had become constant, indicating that rearrangement was complete (under these conditions), the titration was repeated. This second titration required approximately three times as much titrant (water) in order to effect the same absorption fall-of? as compared to the Initial titration. So, again, this species appeared to be a more stable carbenium ion than the original pyridylphenyl-4-f luorophanyl ion from which it was derived. Finally, a sample of 4~pyridylphenyl-4-f luorophenylmethanol (ca. 100 rag) was dissolved in 70% HC.10, (ca. 10 ml of acid) to completely invert it to carbenium ion. Rearrangement was again monitored spectroscopically, and after it was apparent that no further changes in the tronic spectrum of the sample were occurring, the acid was neutralized by the careful addition of reagent Nil-. This resulted in the

PAGE 148

138 of a mixture of a white crystalline solid and a rather gummy Low solid. The mixture of solids was transferred to a filter and wi : ; CO] Lous quantities of deionized water. The white solid was readily removed by the washing, and the yellowish material remained on i:he filter. The contents on the filter were, air dried to yield ca . 1!) mg of a yellow-orange amorphous solid. This material exhibited decomposition to a brown-black oil above 140° and an ill analysis revealed that this material was different than the original alcohol. A visible spectrum of this material in 70% HC10, was identical to that 19 previously obtained for the so-called rearrangement product. The. " F nmr spectrum of this material in 70% HC10, was also recorded. Following 3000 scans with the Fourier transform synthesizer two weak signals (^'. 37.7 ppm and 68.9 ppra upfield with respect to external TFA) were detected. These signals did not; correspond to any of the nmr signals which had been recorded relative to external TFA during previous carbenium ion nmr analyses; and the very low intensities of these signals indicat€:d the. absence of any appreciable concentration of fluorine in the sample. Mass spectral cracking analyses of this material revealed the presence of molecular ion fragments of nominal mass as high as 520.5 ami'.; and, at relatively low probe temperatures (200° or less) a 259 amu peak was consistently observed. Interestingly, the 259 peak corresponds to the mass of the quinone species which would result from combined effects in the parent alcohol, of quinone formation at the original fluorine site and hydroxy! loss at the exocyclic carbon. Care— analyses of these spectra, however, suggested the presence of as many as four new compounds with the distinct possibility of one or more of these materials existing as a polymer. Rather obviously

PAGE 149

139 refore, the nature of the material (s) produced upon fluorine atom displacement from the pyridylphenyl-4-f luorophenylcarbenium ions in I LO, H_0 remains to be ascertained,

PAGE 150

BIBL10CRAPHY 1. S. P. McManuS and C. U. Pittiaan, Jr., in "Organic Reactive Intermediates," S. P. McManus, Ed., Academic Press, New York and London.. 1973, pp 200-201. 2. G. A. Olah, J. Am. Chem. Soc, 94_, 808 (L972). '3. J, P. Wibaut, A. P. de Jonge, H. G. P. van der Voort, and P. Ph. H. L. Otto, Rec. Trav. Chim. , 70, 1054 (J951). 4. H. A. Smith and C. W. Holley, J. Am. Chem. Soc, 80, 3714 (1958). 5. F. ft. Hartley, "The Chemistry of Platinum and Palladium," Applied Science Publishers, Ltd.. Ripple Road, Barking, Essex, England, 1973. 6. T. W. Richardson, Doctoral Dissertation, University of Florida, 1971. 7. B. C. Bhat tacharyya and R. C. Stoufer, unpublished t-esults. 8. P. W. Went?., Doctoral Dissertation, University of Florida, 1972. 9. R. G. Turnbo, D. L. Sullivan, and R. Pettit, J. Am. Chem. Soc, 86, 5630 (1964). JO. N. C. De.no, J. J. Jaruzelski, and A. Schriosheiin, J. Am. Chem. Soc, 77, 3044 (1955). LI. K. C. Dene, J. E. Berkheimer, W. L. Evans, and H. J. Peterson, .]. Am. Chem. Soc, 81, 2344 (1959). 12. R. ''• Taft and L. D. McKeever, J. Am. Chem. Soc, 87, 2489 (1965). 1.3. S. V. McKinley, J. W. Rakshys, Jr., A. E. Young, and II. K. Freedman, J. Am. Choir,. Soc, 93, 4715 (1971). R. W. ijiL, F. Prosser, L. Goodman, and G. T. Davis, J. Chem. B, 380 (1963). 13. R. W. Taft, E. Price, 1. R. Fox, I. C. I. ewj K. K. Andersen, and G. T. Davis, J. Am. Chem. Soc, 85, 3146 (1963). M. J. S. Dewar and A. P. Harchand, J. Am. Chem. Soc, ^38, 3318 (1966) . 140

PAGE 151

141 17. R. G. Pews, Y. Tsuno, and R. "., T . Taft, J. Am. Chem. Soc, 89 . 2391 (196 7). 18. R. Fi.Jler.. C-S . Wang, M. A. McKinney, and F. N. Wilier, J. Am. Chem. Soc, 89, 1026 (1967). 19. I. I. Schuster, A. K. Colter, and R. J. Kurland, J. Am. Chem. Soc, 90, 4679 (1968). 20. A. Mendel, J. Organomet. Chen-., 6, 97 (1966). 21. F. J. McCarty, C. H. Tilford, and M. G. Van Campen, Jr., J. Am. Chem. Soc, J79, 472 (1957). 22. A. P. de. Jonge, H. J. den Ke.rtog, and J. P. Wibaut, Rec. Trav. Chim. , 70, 989 (1951). 23. F. B. LaForge, J. Am. Chem. Soc, 50, 2484 (1928). 24. F. G. Mann and D. Purdie, J. Chem. Soc, 873 (1936). 25. J, Chatt and L. M. Venafczi, J. Chem. Soc, 2351 (1957). 26. J. Chatt and D. M. P. Mingos, J. Chem. Soc A, 1770 (1969). 27. T. Boschi, B. Crociani, M. Nicolini, and U. Belluco, Inorg. Chim. Acta, 12, 39 (1975). 23. R. J. Goodfellow, P. L. Goggin, and D. A. Duddell, J. Chem. Soc A, 504 (1968). 29. D. M. Adams, P. J, Chandler, and R. G. Churchill, J. Chem. Soc A, 1272 (1967). 30. P. M. Henry and 0. W. Marks, Inorg. Chem., 10, 373 (1971). 31. D. W. A. Sharp and N. Sheppard, J. Chem. Soc, 674 (1957). 32 H. J. Dauben, Jr., L. R. Honnen, and K. M. Harmon, J. Org. Chem., 25, 1442 (1960) . 33. G. A. Olah, J. J. Svoboda, and J. A. Olah, Synthesis, 544 (1972). 34. T. M. Dunn, in "Modern Coordination Chemistry," J. Lewis and R. G. Wllkins, Eds., Interscience. Publishers, Inc., New York, 1967, p 281. 35. R. S. Mulliken, J. Chem. Phys . , ]_, 14 (1939). ;'>. N. C. Deno, P. T. Groves, and G. Saines, J. Am. Chem. Soc, 81 , 5790 (1939). 17. C. S. Schoepfle and J. D. Ryan, J. Am. Chem. Soc. 54_, 3687 (1932)

PAGE 152

L42 M. S. Ie nan and N". C. Deno, J. Am. Chem. Soc. , 73, 3644 (1951). 39. G. N. Lewis, T. T. Magel, and D. Lipkin, J. Am. Chem. Soc, 64, L774 (1942). N. C. Deno, J. J. Jaruzelski, and A. Schriesheim, J. Org. Chem. 19, 155 (1954). 41. G. Branch and II. Walba, J. Am. Chem. Soc, _7_6, 1564 (1954). 42. A. G. Evans, J. A. G. Jones, and G. 0. Osborne, J. Chem. Soc, 3803 (1954). 43. R. Dehl, W. R. Vaughan, and R. S. Berry, J. Org. Chem., _24, 1616 (1959) . 44. N. C. Deno, Progr. Phys. Org. Chem., 2, 178 (1964). 45. G. A. Olah, C. U. Pittman, Jr., R. Waack, and M. Doran, J. Am. Chem. Soc, 88, 1488 (1966). * 46. A. Stre I.Lwleccr , Jr., "Molecular Orbital Theory for Organic Chemists," John Wiley and Pons, Inc., New York, London, and Sydney, 1961. 47. R. Waack and M. A. Doran, J. Phys. Chem., 68, 1148 (1964). 48. R. Grinr.er and S. F. Mason, Trans. Faraday Soc, 60, 264 (1964). 49. G. N. Lewis and J. Bigaleisen, J. Am. Chem. Soc, 6_5, 2101 (1943) 50. Y. K. Mo, R. E. Linder, G. Earth, E. Bunnenberg, and C. Djerassi, J. Am. Chem. Soc, 96, 3309 (1974). 51. H. P. J. M. Dekkers and Ms. E. C. M. Kielman-Van Luyt, Molec Phys., 31, 1001 (1976). 52. C. C. Barker, M. [I. Bride, G. Hallas, and A. Stamp, J. Chem. Soc , 1285 (1961). 53. H. C. Longuet--Ui-gins, J. Chem. Ph\s., 18, 265 (1950). 54. A. C. Fopkinson and P. A. H. Wyatt, J. Chem. Soc B, 530 (1970). 55. B. G. Ramsey, J. Phys. Chem., 70, 611 (1966). 56. M. W. Jov.ch, M.S. Thesis, University of Florida, 1966. 57. M. V.'. Couch, Doctoral Dissertation, University of Florida, 1969. 58. II. J. Dauben, Jr. and J. D. Wilson, Chem. Cotumuns., 1629 (1.968). 59. G. A. Olah, C. A. Cupas, and M. B. Comisarow, J. Am. Chen. Soc, > (J 966).

PAGE 153

60. G. N. Lewi : and M. Calvin, Chera. Revs., 25, 273 (J93 ; ;). 61. A. K. Ci Lngton, M. J. Tait, and W. F. K. Wynne-Jones , Proc. Roy. Soc. A, 286 , 235 (1965). 62. R. J. Gillespie, Endeavour, 32, 3 (1973). 63. C. A. Olah, Chem. Britain, 8, 231 (1972). 64. H. H. Preedman, in "Carboniura Ions," Vol. IV, G. A. Olah and P. v. R. Schleyer, Eds., Wiley Interscience, New York, London, Sydney, and Toronto, 1973. 65. M. Herlem, Pare Appl. Chera., 49, 107 (1977). 66. 0. Redlich and G. C. Hood, Disc. Faraday Soc, 24, 87 (1957). 67. L. H. Brickwedde, J. Res, Nat. Bur. Stand., 42. 309 (1949). 68. G. M. Shutske, J. Org. Chera., 42, 374 (1977). 69. S. K. Dayal, S. Ehrenson, and R. W. Taft, J, Am. Chera, Soc, 94, 9113 (1972). 70. R. Cigen and C. G. Ekstrom, Acta Chem. Scand., 17,2083 (1963). 71. E. D. Jenson and R. W. Taft, J. Am. Chem. Soc, 86, 116 (1964). 72 K. R. Dixon and J. J. MaFarland, Chem. Communs., 1274 (1972). 73. G. W. Parshall, J. Am. Chem. Soc, 86, 5367 (1964). 74. C. W. Parshall, J. Am. Chem. Soc, 88, 704 (1966). 75. D. J. Pasto and C. R. Johnson, "Organic Structure Determination," Prentice-Hall, Inc., Englewood Cliffs, N.J., 1969, p 182. 76. K. Baum and H. M. Nelson, J. Am. Chem. Soc, 88, 4459 (1966). 77. N. C. Deno and A. Schriesheim, J. Am. Chem. Soc, 11 ', 3051 (1955). 78. M. C. Deno and W. L. Evans, J. Am. Chem. Soc, _79, 5804 (1957). 79. S. V. Kulkarni, R. Schure, and R. Filler, J. Am. Chem. Soc, 95, 1839 (1973). 80. L. P. Hammett, J. Am. Chem. Soc, _59, 96 (1937). 81. J. Shorter, "Correlation Analysis in Organic Chemistry," Clarendon Press, Oxford, 1973, p 14. 82. H. C. Brown and Y. Okamoto, J. Am. Chem. Soc, 80, 4979 (1958).

PAGE 154

83. t. Nemc >va, M. Malat, and R. Zahradnik, Collect. Czech. Ch Conununs., 34, 2880 (1969). Lne, "Physical Organic C'aemistry," Second edition, McGraw-Hill, ED ; York, 1962. 85. A. Atkinson, A. C. Kopkinson, and E. Lee-Ruff, J. Chj.m. Soc. , PerkinTrans.il, 1854 (1972). 86. S. S. Kuo, "Numerical Methods and Computers," Addison-Kc-sley Publishing Co., Reading, Mass., 1966, Chapter 11.

PAGE 155

BIOGRAPHICAL SKETCH James CharJ.es Horvath was born June 29, 1942, in Toledo, Ohio. He was very fortunate to recognize that learning is a wonderful experience which life forever offers. Who knows what may lie ahead' I 5

PAGE 156

I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. uituULR. Carl Stoufer, Chairman Associate Professor of Chenistry £yH 1 certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. ^LJflJL^k lierle A. Battiste Professor of Chemistry I certi thai E li * . this study and that in my opinion onforms to acceptabJ • dards oi irl; pi ation and Is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. JJud^d^jJj amA Richard D. Dresdner Professor of Chemistry

PAGE 157

I certify that I ha\e read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate,, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. George E. fltysch'.cewitsch Professor of Chemistry I certify that I have read this study and that in ray opinion i : conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. &*S Jack R. Smi Professor of Electrical Engineering This dissertation was submitted to the Graduate Faculty of the Department oi Chemistry in the College of Arts and Sciences and to the GraduateCouncil, and was • ;. i ted as partial fulJ Lllmenl hie re its for the degree of Doctor of Philosophy. M 1978 Dean, Graduate School

PAGE 158

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TIT
U kf IODYK -\IIIC INVEST I CATIONS UPON
FROM P Y RID ELDIPHEN YLi-IE T MANO L S -
OAReEh.UM
- FREE AND
TONS DERIVED
COMPELLED
Ey
James Charles Horvath
A DISSERTATION PRESENTED TO TIIE GRADUATE
COUNCIL OF THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR
THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OK FLORIDA
.19/S

This is dedicated to the Spirit of Bombadlas, for lie vas
blessed with toe courage and the desire to seek the Philosopher's
3Lone. In so doing he vas magnificently rewarded, tor instead
he found t:he truth.
This is also dedicated to my Mother and to one Suffering
bastard from leva. For vrithout their inspiration this work would
not Slave been completed.

ACKNOWLEDGEMENTS
It is not possible to acknowledge by name all who have con¬
tributed to this work. This author is exceedingly fortunate and
proud to have Lad the benefit of so much assistance and friendship
and therefore extends his heartfelt appreciation and thanks to
those; knowing that, at least in this way, no one has been omitted.
iii

TABLE OF CONTENTS - continued
Pagfi
APPENDIX . 13 3
1. Specific Gravity of Aqueous HCIO^ Determined as a
Function of lit % HC.10^ . 133
2. Degree of Protonation of a Pyridy]methanol (pyLOH)
in Aqueous HCIO^ 134
3. Experiments Conducted upon the Cnrbeniun Ion Species
Found to Exhibit Rearrangement in 70% HCIO^ . . . 136
3ISLiOGRAPHY . • 140
BIOGRAPHICAL SKETCH 145

TABLE OF CONTENTS
ACKNOWLEDGMENT S
LIST OF TABLES
LIST OF FIGURES
ABSTRACT
INTRODUCTION
The Carbenium Ion .......
Preliminary Considerations .....
Groundwork to this Research . . . . .
EXPERIMENTAL
Synthesis of Ligands ......
Synthesis cf Complexes ......
I.
II
Elemental Analyses .......
Reagents and Solvents ......
Instrumental Analytical Methods
RESULTS AND DISCUSSION
Synthetic Considerations . . . . .
Tnc.rundyurcnie Investigations and Measurements
IK CONCLUSION
Page
iii
vi
v#.
1
1
2
4
18
18
35
35
38
41
41
43
49
49
60
128
v

L[ST OF TABLES
Table Fage
I. Special, Commercially Obtained Reagents - - and
Suppliers 42
II- Electronic Spectral Data for the Various Carbenium
Ion Species, in 70% HCIC^ at 25° 77
III Values of TL, In Aqueous HC10. at 25° .... - 87
R n 4
IV.Specific Gravity of Aqueous HCIO, Solutions at 25° . , 91
V.Thermodynamic Stability Data Resulting from the "Deno"
Titration of the Various Pyridylcarbeuium Ton Species,
in HCIO, - Ho0 at 25° 95
19
VI.F nmr Chemical Shifts (6) for Carbenium Ion Precursors
in Acetone and 1 M HCIO^, and for Carbenium Ions in 70%
HCIO. at 25° 110
4
vi

LIST Oí ¿ICUX.ES
Vi nurc
y .
10.
11.
12.
13.
14.
Monopyrid/ldiphenylmethanols (pyLOH) ....
tíxs(2-pyridyl)phenylmethaaols (py^LOK)
Thlazolyldipbenylmethanols ......
fyridylphenyl-4-fluorophenylmethanols ....
Phenolphthalein monopositive ions .....
Visible spectrum of the carbenium ion derived from 4-
P3/rid3'].-4-methylphfenyl--4-f 1 iiorophenylmeths.no 1 . in 70%
Pape
4
4
8
15
72
HC10
4- 20.2, 29.7
â– max
76
i ...
Visible spectrum of the carbenium ion derived from
Fd ( IT) (pyLOH) (L«^) Cl? , where pyLOII is 4-pyridyl -4--methy
phenyl-4-fluoroohenvlmethanol, in 70% IIC10/ . v’ , 20-6,
27.6 . . : : max. .
76
Visible spectrura of the carbenium ion derived from
Pd (TI) (pyLOH) 2CI9 , where pyLOH is 4- py r id y 1- 4 -me t hy 1 p.' 1 e ny I -
4-fluoronhenyImethanol, in 70% HCIOa. V , 20.6, 27.7.
4 max
Values of IL in aqueous HC.10. at
R 4
25'
Dilution curve for the titration of 4-pyridyl-4-methyl-
phenyl--4-£luorophenylcarbeniura ion . ... .
Dilution curve for the titration of [Pd(II)(4-pyL)-
(LyjCly] -', where 4-pyL = 4-pyridyl-4-methylphenvl-
4-fluorophenylearbeniem ion .......
Dilution curve for the titration of [Pd ( II) (4-pyL) 2^2]
where 4-pyL - 4-pyridyl-4-meth}'lphenyl-4-f luorophenyl-
carbenium ion ..........
2+
Hammett T.u . vs. AG° (carbenium ion formation)
p-r —
Carbenium ion ó relative to external CFCln vs. AGC of same
88
93
93
93
118
118
Vll

LIST OF FIGURES
oa©tinned
Finn
r tí
Page
15.
Hammett vrs. carbenium ion d relative
c?ci3 . â–  a
to external
. 118
16.
AG° (ancgor'1 ina t o d 4-pyridylcarbeniura ions)
coordinated 2--pyridylcarbeniun ions)
vs. AG°
(un-
. .121
i;.
AG°(uncoordinated 4-pyridylcarbenium ions)
coraplexed 4-pyridylcarbeniuin ions)
vs. AG°
(bis-
. 3 21
viii

Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy
THERMODYNAMIC INVESTIGATIONS UPON CARDENIUM IONS
DERIVED FROM PYRIDYLDIPHENTLMETHANOLS - FREE AND COMPLEXED
By
JAMES CHARLES HORVATH
March, 1978
Chairman: R. Carl Stoufer
Major Department: Chemistry
The syntheses of a series of 2- and 4-pyridyi-R-phenyl-i-
f1uorophenyImethanois are reported; R may be 4-H, 4-CH^, or 4-OCIM,
within each series of alcohols. Palladium(ll) complexes of the 4-
pyr.idyl alcohols have been prepared also wherein either a single
alcohol, is included in the coordination sphere of the metal to yield
the. so called "mono"-alcohol complexes, or two identical alcohols are
included to yield the so called "bis"-alcohol complexes. The
corresponding 2-pyridyl alcohol complexes could not be prepared pre¬
sumably as a result of steric difficulties. These trity 1-type alcohols
(and their complexes) arc precursors to stable arylcarben.i urn Lons
obtained via dissolution in HC10.-H„0, the ionizing medium.
4 L
] 9
The "bono" H , acidity function titration technique, F mnr
chemical nit iff measurements, and free energy parameter correlation
analyses, have afforded a quantitative evaluation of the stabilLties
of the various earbenium ion species. These investigations have also
ix

(urn ¡shed yaformariou which elucidate.*? the stabilizing effect con¬
tri outed by the coordinate'! metal contad r.ing moiety to a given
co'uplexed csrbeciam ion.
Two particularly noteworthy outgrowths have resulted from these
:;lndies. First, internally consistent electronic spectral interpre¬
tations have been obtained which indicate that the stabilizing in-
1Juence exerted by the metal center on a given complexes! carbenium
ion is reflected by the frequency changes of the carbenium ion ab¬
sorption bands detectable upon coordination of the ion. Secondly,
appropriate, linearly interdependent free energy correlations have
given else to the development of arguments which indicate that al¬
though coiaplexation (for the cases considered herein) stabilizes
a carbenium ion relative to the corresponding protonated ion,
coordination does in fact destabilize a pyridyLcarbeniurn ion relative
to the unprotonatod free ion .species.
y

INTRODUCTION
The Carrot inn: Ion
The igperspicuous nature of the term "carbonium ion1, stems from
the fact that this nomenclature classification has been applied to all
types of multivalent carbocations throughout the chemical literature.
This problem has been pointed out by McManus and Pittman (1) and more
recentLy by Olah (2). These authors have stated that the term "carben-
i.um ion" is a more systematic reference towards griva.'lent carbocations
(I.e. , R^C') which contain a sextet of valence electrons This follows
in that these trivalent carbocations are valence isoelccIronic with
such ions as o-cenium and sulfenium, Here the. suff ix "-enium" distin¬
guishes these ions from their "-onium" counterparts. Furthermore, this
nomenclature directly establishes a relationship to the species which
results fcom carhene protouation, namely the carbenium ion
(Cui>). Therefore throughout this work the term carbenium ion shall be
employed as an. explicit reference to a trivalent carbocation with a
valence election sextet. Specifically the cations considered herein
are those which are derived from pyridy!dipheny.Lmethanols upon disso¬
lution of these alcohols in suitable, strongly acidic, media.
1

Preliminary ConsideraLions
The preparation of various bis (pyridyj )phenylearb ¡.rol s and tris-
(pytliyl)carbinol» has been reported by J. P. Wibaut ejt al. (3). These
workers recognized the direct structural and electronic similarity
or these pyridinecarbinols to triphenylcarbinol (triphcnylmethanol)
and therefore investigated their halochromic properties in 100% sulfuric
acid solution. They discovered however, that such solutions exhibited
no color whatsoever. Thus, these pyridinecarbinols were not ionized
in strong acid in a fashion akin to that of triphenyicarhinol. That is
there was little, if any, conversion of the pyridinecarbinols to the
corresponding trityl-type carbenium ion.
None the less this disclosure provoked further speculation as to
whether or not such tertiary aromatic alcohols could be converted to
the correspond Lug carbenium ion. Indeed it seemed to be the case that
the principal, difference in the behavior of these pyridine alcohols, as
compared with their benzene homologues, was attributable to the degree
of positive charge development which would supervene upon their disso¬
lution in strongly acidic media. Thus, the concentration of positive
charge produced through base site protonation (of the pyridine ring
nitrogen atoms) would be sufficient to prevent carbenium ion formation
owing no the concomitant development of like charge repulsions. There-
•. ore it seemed reasonable that if these basic sites could be chemically
bound in order to prevent protonati.cn upon treatment with strong acid,
if would then lie feasible to generate the oar ben tun ion.
Moreover, it was recognized that such investigations upon mono-
P, riclyldiphcnylcarbinols were very
much relevant to Chis consideration.

type of aimplar pyridine? alcohol
That rs, it was expected that this
could be converted to a reasonably stable carbónica ion since this
transformation would be accompanied by the development of less positive
charge. This possibility was substantiated through the work of Smith
jad Holley (4) wherein they reported r hat two structural isomers of
monopyridyIdipaeryImetHanoi ware measurably ionized in concentrated
sulfuric acid solution. Thus, it appeared that carbeitium ions derived
iron these particular monobasic alcohols could be employed for stability
investigations upon such ionic species as they are produced in suitable
acidic media; and with respect to the possibility of inhibiting pyridine
nitrogen profanation upon carbenium ion generation, the binding of these
basic nitrogens through coordinate bond formation to an essentially
neutral metal center seemed to be an appropriate method of general
applicability. Therefore investigations upon carbanicm ions stabilized ,
by this attendant limitation of positive charge beilei-up would be per-
'aitted. Also, since pyridine is a ligand which is known to exhibit
r,-acid behavior (5:117), the potential lor measuring the enhancement of
ion stability as c consequence of coordinated atom (ion) "back—donation''
was established. That is, if the species bound to the pyridine nitrogen
possessed occupied valence orbitals of appropriate symmetry and energy
r.o interact with the ir-system of the carbenium ion by creating ir-charac-
tet in che metad-nitrogen bond, the ion could also be so stabilized.
Thu.;, if the coordinate boud(s) was sufficiently stable us to remain
.intact upon conversion of such complex compounds to the corresponding
cavbenxum ion(s), these considerations would be experimentally acces¬
sible. (The consequences of a- and n-bondiag interactions between a
coordinated carbeuium ion and a prospective metal center have been

cl i scussed eaftuw elegantly by Richardson (6:10-11) and are here
refarro# to conveniently.)
Groundwork to this Research
In 1966 Bhattacharyya and Stoufer (7) began work in this area of
research. In accord with standard synthetic methods they prepared
various monopyridyldipbenylmethanols (Figure 1) as well as bis(2-pyridyl)-
Phcnylme than o1s (Figure 2). Preliminary investigations upon the free
alcohols revealed, as expected, that the monopyridyl derivatives were
converted to the corresponding trityl-type carbenium ion upon treatment
(3-pyridyl) (4-pyridyl)
-och3, -n(cii3)2
Fig. 1. Monopyridyldiphenylmethanols (pyLOH)

with reagent, sulfuric acid (96% l^SO^) . The bis(pyridyl)alcohols, how¬
ever, were not ionized by this solvent to any appreciable degree. This
agreed with the results of Ifibaut et_ ;rL. (3) . Much of the initial
work was therefore directed towards the utilization of the monopyridyl-
alcohols both as carbenium ion precursors and as heteroarcmatic donor
species. In conjunction with this, Bhattacharyya and Stoufer success¬
fully prepared a nuDiber of palladium(II) complexes of these monopyridyl-
alcohols by employing them as neutral donor ligands. The materials
obtained were well-characterized as the neutral dichlorobis(alcohol)
complexes of palladium(II). These complexes were of the general for¬
mula Fd(II)(pyLOH)2CI2, where pyLOH represents the "ionizable" pyridine
alcohol. These compounds were diamagnetic and square planar as expected
for 4-coordinate complexes of palladium(II). (See, for instance, the
discussion concerning the complexes of palladiura(II) by Hartley (5:17-19).)
Subsequent investigations by these workers upon the carbenium ions
derived from these palladium complexes revealed that dilution of the
ionizing medium (i.e., the 96% solution) with water afforded the
reisolation of the intact neutral complex. This experimental find
indicated that the pyridine-metal coordinate bond was reasonably stable
in strongly acidic media. In this way a tangible basis for examining
the stabilities of such coordinated carbenium ions was established.
The results of Bhattacharyya and Stoufer served to demonstrate
that the monopyridyldiphenylmethanols were suitable o-donor ligands as
well as carbenium ion precursors. To continue with this work,
Richardson (6) prepared a series of palladium(II) complexes of the bis-
(2-pyridyl)phenvlmethanols which had been synthesized previously by
Bhattacharyya and Stoufer. These complexes were of the general formula

5
t\l f í I) (py?LOH)Cl¿, anil were presumably 4-coordinate about the metal
centei. with the alcohol functioning as a biclentate ligand. It had been
anticipated that as a consequence of binding the nitrogen donor sites
through coordination to the metal that these compounds could be con¬
verted to the complexed carbenium ion(s). It was discovered, however,
Uia". by employing customary experimental methods this ionization was
not achievable.. There was no obvious explanation to account for this
result. Perhaps it was the case that the dissolution of these complexes
in strong acid was accompanied by simultaneous rupture of the metal-
nitrogen coordinate bonds. Since there exists a considerable degree
of steiic strain in these 2-pyridyl complexes as a consequence of
spatial crowding between the metal center and the carbinol carbon,
this coordinate bond rupture upon acid treatment was not unlikely.
Richardson carried on with investigations on the stability of car-
benium ions derived from the 4-pyridyldiphcnylmethanols. He recorded
the electronic spectrum of the free alcohols and of their palladium(II)
complexes in neat trifluoroacetic acid (TFA). These solutions were
highly colored thereby indicating carbenium ion formation with TFA as
solvent. The visible region of the spectrum of these colored solutions
revealed the presence of two intense, broad absorption bands which were
shown to be characteristic of the carbenium ions. An examination of
the visible spectrum of triphenylmethylcarbenium ion produced by dis¬
solving triphenylmethanol in trifluoroacetic acid showed the same
srrong absorption bands. Indeed when the electronic spectrum of solu¬
tions of these materials in nonionizing media (e.g., methanol or gla¬
cial acetic acid) was examined in the visible region, these strong
absorption bands were found to be absent. It was also observed during

y
these spectral examinations that the positions of these absorption
bands for a gi-'en carbenium ion species shifted upon going from the
uncomplcxed protonated carbenium ion to the corresponding metal-
oomplexed carbenium ion. This suggested that there was a direct rela¬
tionship between tiie stability of the carbenium ion and the attendant
alteration in electronic environment associated with pyridine nitrogen
protonation v_s. pyridine nitrogen coordination.
Similar band position shifts were also detectable as the para-
substituent (R) on the phenyl rings in the alcohols was varied within
the series R = -H, to R = -CH^, to R = -OCH^* in this instance the
band shifts were attributed to resonance electronic, interactions between
the R-substituent. and the carbenium ion center. It was also found that
the stability of the ion was considerably increased when R = -OCH^.
This reflected a substantial capacity of para-OCTL, to participate in
favorable coujugatiunal interaction with the ir-system of the trityl-
type ion.
Richardson ultimately attempted to establish a relationship between
carbenium ion development in these 4-pyridyld.iphenylmethanol systems and
measurable proton (^H) nuclear magnetic resonance (nmr) chemical shifts.
1
To do this the ‘‘ll nmr spectra of TFA solutions of these alcohols and
their palladium(II) complexes were recorded. Then to fingerprint the
phenyl proton and pyridyl proton absorptions the TFA solution spectra
were compared with the solution spectra of the unionised compounds.
Also to facilitate the resolution and identification of the various
uroton signals, these nmr spectra were subjected to computer simulated
analyses. These investigations however, proved to be unsuccessful

8
in that the prutón absorptions of the unionized compounds could not be
corre].a ted unambiguously with the proton absorptions of the correspond¬
ing curbenium ions.
As a logical extension of the work upon the pyridylmethauo'J s Wentz
(8) prepared a series of structurally related alcohols by substituting
a thiazole ring for the pyridine ring. These materials ware 2-, and
5-thiazoly.ldiphenylmethanols (Figure 3) . The similarity of these
alcohols to the pyridyl alcohols is apparent. In accord with previous
work the neutral pnlladium(II) bis-complexes of these alcohols were
r.-reonred. Thes^ Bbmoounds were of the general formula Pd(IT)(ThOiDoX»,
wiw.h X representing a coordinated halide ion, either chloride (prin¬
cipally) or bromide. Wentz had considered that the replacement of
a) 2-Thiazolyldipheny.lmethanol; b)
(2-ThOH)
5-Thiazolyldiphenylmethanol
(5-ThOll)
Fig. 3. Thiazolyldiphenylmethano.ls

9
pyridine with chLazóte would add a degree of uniqueness to the antic¬
ipated chemical behavior of such heterocyclic bases. That is, since
the pyridine and Lhiazole heterorings are isoelectronic and contain
essentially identical nitrogen atoms they should exhibit like donor
characteristics. However, because thiazole also contains a thiophene
type sulfur atom, the thiazole-substituted alcohols should be precursors
to carbenium ions with somewhat different stability than those got
from the analogous pyridine alcohols. Tumbo and coworkers (9) had
indeed demonstrated that the thienyl moiety could enhance the stability
oi such carbenium ions relative to the corresponding phenyl-substituted
carbenium ion. They did this by determining the equilibrium constants
(K ) for the reaction
eq'
R+ 4 2 II20 t R-OH 4 H30+ {1}
in reagent sulfuric acid for a series of structurally equivalent
thienyl and phenyl carbinols. The K values were experimentally
measured by employing the spectrophotometric method of Deno and co¬
workers (10). An ordering of the equilibrium data which were obtained
revealed that a given thienyl-substituted carbenium ion is more stable
than the related phenyl carbenium ion. Thus, these data also estab¬
lished that the sulfur atom in the thienyl nucleus was not protonatod
by the. sulfuric acid as this development of additional positive charge
would have induced a net destabilization of these thienyl carbenium
ions. Thus, it was reasonable to expect that the thiazolyldiplienyl-
met'nanols would be sources of triarvl carbenium ions more stable than
those which were got from the pyridyldiphenylmethanols. Furthermore,

JO
the .ionization of the thiazolyl alcohols conld be investigated by the
some techniques used for studying the thienyl ions since the pyridine
aleonoLs had befiii shown to be ionizable in concentrated sulfuric acid.
In fact the stability of the thiazolyl iens could be quantitatively
evaluated provided the acid solvent ionized the parent alcohols to an
extent of one hundred percent (100%). In other words, If the degree of
conversion of alcohol to carbenium ions was measurable in terms of the
capacity of the acid solvent to produce ionization as a function of
acid concentration, then any equilibrium pertinent to alcohol-ion inter¬
conversion would presumably be monitorable. Undoubtedly it had been
with criteria such as these in mind, that Deno and coworkers (10) were
able to define an acidity function regarding the ionization of aryl-
methanols in concentrated sulfuric acid — water. The results of Turnbo
and coworkers (9) proved the suitability of applying Deno's "acidity
function" technique towards following alcohol — carbenium ion equilibria
iv, the thienyl systems. Therefore it seemed reasonable to employ this
method for quantitative studies upon thiazolylalcohol — carbenium ion
equilibria, provided the alcohols could be completely ionized at a known
solvent concentration.
Wentz made a very important contribution when he demonstrated that
many of the thiazolyl alcohols were converted completely to carbenium
ion in reagent perchloric acid (70% HCIO^). This was accomplished by'
examining the visible absorption spectrum of these alcohols as perchloric
cjcjd solutions at various acid concentrations. This simple investiga¬
tion revealed that for relatively high acid concentrations the carbenium
ions derived from many of these alcohols exhibited a Beer's law depen¬
dence; hut, as these acid solutions were systematically diLuted by the

11
addition of measured increments of deionized water, this Beer's lav;
dependence was no longer maintained. From these observations it was
concluded that in the high acid concentration regions carbenium ion
farmalion was effectually 100%, and the result of adding small quantities
of water was to dilute the concentration of the absorbing species (i.el,
the carbenium ion). However, as more water was added, the equilibrium
described by equation {1}, (which represents the reconversion of thiazolyl
carbenium ion to thiazolyl alcohol), began to be shifted significantly
tc the right as written. A plot of carbenium ion absorbance vs_. weight
percent (wt %) HCIO^ served to reflect these observations. This plot
over a region of high acid concentrations yielded a straight line for
a completely ionized thiazolyl alcohol. This was the Beer's law portion
of the plot. But, at an acid concentration particular to the alcohol
under investigation, a marked change in slope was observed. That is,
the plot began to deviate considerably from an extrapolated Beer's law
line. It was at this acidity region where the concentration of the
absorbing species (the carbenium ion) was being diminished not only by
being diluted, but also as a consequence of being reconverted to the
nonabsorbing neutral alcohol precursor. Thus, absorbance fall off was
magnified considerably as the ionizing solvent was made progressively
more dilute.
Thus, by applying appropriate acidity function data (made avail¬
able by Deno and coworkers (11) for aqueous perchloric acid) Wentz was
able to measure spectrophotometrically equilibrium constants for the
generation of carbenium ions resulting from the dissolution of free and
complexed thiazolyldiphenylmethanols in reagent perchloric acid. This
investigation therefore allowed a quantitative ordering of the stabilities

12
oí' xw rhenium ions derivable from these heterocyclic basic compounds.
The trends in stability which were established by this study, and the
pertinent generalizations which these trends served to warrant, are
summed up accordingly:
(i.) Carbenium ions derived from 5-thiazolyl alcohols are more
stable than those got from the corresponding 2-thiazolyl alcohols. This
illustrates the inherent destabilizing effect that charge repulsion has
on carbenium ion development. Since the sites of positive charge are
three bonds separated in the 5-thiazolyl ions, vs. two bonds separated
in the 2-thiazolyl ions, and models of these species indicate a likely
''through-space" charge interaction for the 2-thiazolyl ions, this trend
in stability is certainly expected.
(ii) For a particular alcohol, R-group substitution in the para
position on the phenyl rings, for the series R = -H, -CH^, -OCH^, results
in an increase in carbenium ion stability. This reflects conjugational
stabilization of positive charge development known for this particular
scries of "Ri groups as para substituents in trityl-type carbenium
ions. (See, for instance, the results reported in the papers by Taft
and McKeever (12), McKinley et al_. (13), and Deno and coworkers (10).)
(iii) For a particular alcohol R'-, or R"-group substitution on
the thiazole ring (see Figure 3), and for R' = -H, -CH^, and for R" =
-I', ~CH^, results in an increase in carbenium ion stability as "R" is
Increased in mass. This exhibits the greater ability of -CH^ compared
with -H to inductively release electron density.
(i.v) Carbenium ions derived from the palladium complexes, Pd(IL)-
(ThOH)jX , arc more stable than those got from the corresponding free
alcohols. This, at least, illustrates the effect of binding the basic

13
sites in t.he ligands through coordinate bond formation with an essen¬
tially neutral species. This obviously minimizes positive charge,
development upon treatment with strong acid since ligand protonation
is no;/ preven! ed .
(v) In the instances investigated, carbenium ions decived from
the complexes Fd(IX)(ThOH), are more stable than those got from
the corresponding chloride ligand complexes. This suggests that a
backbonding mechanism is operative through which the metal center
donates ir-electron density into empty r-orbitals of appropriate sym¬
metry on the coordinated carbenium ion species. Thus, bromide, which
is expected to be a better ir-donor than chloride, should in turn con¬
tribute a net stabilizing effect on the ion via donation of ir-electron
density into suitable empty metal orbitals.
Two final investigations of consequence were carried out. The
equilibrium constant for the conversion of triphenylmethanol to tri-
phenylcarbenium ion in perchloric acid was measured. The value ob¬
tained was found to be in good agreement with the value which had been
reported for this ionization by Deno and coworkers (11). This served
further to verify the reliability of the thermodynamic data got for the
generation of thiazolyl carbenium ions. And lastly, the ionization of
4-pyridyJdi(j>-tolyl) methanol in perchloric acid was examined. The 4-
pyridyldi(p-tolyl)carbenium ion was found to be more stable than the
2-thiazolyl carbenium ions but less stable than the 5-thiazolyl carbenium
ions. This result was significant in that it allowed a comparison of
these heterorings to be made, as if they were position Isomers, with
respect to their ability to stabilize trityl-type carbenium ions. More
importantly, this result demonstrated the appropriateness of the

14
spectrophotojíitítc|hc technique of Deno and coworkers (10) for studying
pytidyldjphenylmethyi curbcnium ions. Therefore cachen Luía ions derived
from the pyridine alcohols previously investigated by Bhattachn.ryya and
Scoufer (7), and by Richardson (6), could now be studied quantitatively
and broaden considerably the scope of this work.
The research reported in this dissertation deals principally with
investigations upon free and complexed carbenium ions derived from
pyridytdiphenylmethanols. These pyridine alcohols and the complexes
thereof were prepared such as to be especially suitable for thermody¬
namic stability studies.
The alcohols considered are specifically 2-, and 4-pyridylphenyl-
4-fiuorophenyimethanols (Figure 4). The 4-fluorophenyl ring has been
incorporated into the molecular framework of the pyridyImethanols to
19
provide a F nmr probe uniquely sensitive to the development of
positive charge upon carbenium ion formation. Considerations for the
19
application of F nmr techniques towards stability sludies on these
ions were prompted by the unsuccessful nmr investigations which, for
similar purposes, had been attempted by Richardson (6). The single
fluorine nucleus is particularly suitable for use as a diagnostic nmr
tag in these systems. The principal reasons are the following. First,
â– ith but one such resonating nucleus in the species under investigation,
the spectrum obtained is not complex and is therefore amenable to
straightforward interpretation. Secondly, fluorine in the 4-posit Lon
on a phenyl ring is known to be highly sensitive to changes in electron
density in the ir-system of the ring. See, for instance, the papers by
Taft et al. (14,15), Dewar and Marchand (16), and Pews, Tsuno, and Taft

15
R = -H, -CH3, -OCH3
a) 2-Pyridylphenyl-4-fluoro—
phenylmethanol (2-pyLOH)
b) 4-Pyridylphenyl-4-f luoro-
ph enylmethano1 (4-pyhOH)
Fig. 4. Pyridylphenyl-4-fluorophenylmcthanols
(17), which report that changes in r-electron density in an aromatic
19
system may be precisely correlated with 4-fluorophenyl F nmr chemical
shifts. These results therefore indicate that the fluorine nucleus
must participate in r-bonding interactions with the aromatic ring to
19
which it is attached. Thus, F nmr chemical shift data obtained for
a "4-fluorophenyl" fluorine would reflect any changes in -¡T-electron
density throughout a conjugated system in which this phenyl ring was
incorporated. And so, of primary significance is the relationship which
exists between the magnitude of the fluorine chemical shift for a
particular pyridyldiphenylcarbenium ion, and the thermodynamic stability
1 9
of that ion. The F nmr studies by Filler (18) and Schuster (19) and
their coworkers upon tris-(p-fÃœuorophenyl)carbenium ion in different
ionizing solvents demonstrated the suitability of this experimental

16
consideration by independently determining tor this cation-carbincl
19
aquelibrium from if chemical shift data.
This work also focuses upon the use of the Deno spectrcphotometric
uitraticn technique for quantitative measurements of the stabilities of
earbanium ions derived from free and complexed pyrldylphenyl-4-fluoro-
phenylmethanols. The thermodynamic data so obtained are then compared
19
with corresponding F nmr chemical shift data via correlation analysis
methods. This data treatment is carried out for the purpose of estab¬
lishing interdependent relationships existing between the stability
information got from each of these types of physical measurement.
In keeping with previous work the neutral bis(alcohol) palladium(TT)
complexes, Fd (II) (pyLOH) 2^2 ’ were PrePare>d and studied by the physical
methods described above. However, since these materials contain two
moles of "ioriizable" alcohol per mole of complex, the degree of positive
charge development upon carbenium ion generation is questionable. This
difficult}’’ had been encountered by Wentz (8) in his investigations upon
the thiazolyl complexed carbenium ions. In an attempt to resolve this
problem complexes of the type Pd(II)(pyLOH)(L^)Cl^ were prepared. In
tóese new materials, represents a neutral, nonionizable ligand which
remains coordinated upon carbenium ion generation. Thermod}namic
studies on these new complexes yield information which directly relates
the nature of a singly charged coordinated carbenium ion to the stabi¬
lising influence of the metal center. Thermodynamic data are presented
herein vhLch are in respect to the following equilibria:
H+pyL4 + 2 H20 t H+pyL0Il + H^O4'
(2)

+ 2 H20
17
Oi^PdpyL'
t C12L PdpyLOH + H30+
{3}
Cl2Pd(pylÍ.2+ + 4 H20 t Cl2Pd(pyLOH)2 + 2 H30+
{4}
Equation {2} pertains to the aqueous titration, of an uncoordinated
pyridyidiphenylmetnyl carbenium ion. This equation is written to
emphasize that the pyridine ring remains protonated throughout the
reconversion of carbenium ion to alcohol. This transformation is
associated with a positive charge change of 2+ to 1+. Equation {3}
corresponds to the titrimetric reconversion of a singly charged co¬
ordinated carneaium ion to the neutral palladium complex precursor.
This process is associated with a charge change of 1+ to 0. Equation
{4} is a composite statement of what actually may be at least two
stepwise processes; initially (perhaps) the reconversion of a species
containing two coordinated carbenium ions to a species with but one
coordinated ion, followed by complete reconversion to the neutral
palladium bis-alcohol complex. This process may therefore be associated
with two full units of positive charge change, viz., 2+ to 0. Con¬
siderations for purposes of critically evaluating the thermodynamic
data obtained from investigations upon these equilibria are accounted.
The apposite conclusions which follow have been presented and are care¬
fully discussed.

EXPERIMENTAL
Synthesis of Ligands
The pyr I d) Idiphenylmethanols which have been employed as hetero¬
aromatic donors (and as carbenium ion precursors) in this research,
were prepared by standard Grignard synthetic methods. This generally
involved the addition of an ether solution of the appropriate 2- or 4-
pyridyl ketone to an ether solution of the required Grignard arylmagne-
slnm halide, follov7ed by acid hydrolysis of the salt-like intermediate
to yield the desired alcohol. Since the necessary ketones were also
made in this laboratory, the synthetic methods for their preparation
have Leen included. A list of the special, commercially obtained
reagents employed in these procedures, with names of suppliers, is
provided in Table I.
The same apparatus and assembly was used in the preparation of
each of the ligands (alcohols) and ketones. All glassware connections
were with standard taper ground joint fittings unless otherwise specified.
All glassware was scrupulously cleaned and dried prior to assembly.
All ground joints were carefully lubricated by the application of a
very small quantity of Dow Corning silicone grease. Rotnliou of the
connected joints within one another assured the deposition of a uniform
film of lubricant. The assembled apparatus consisted of 3 3-necked,
18

19
one-liter round bottom fln.sk equipped with a ground glass stirring shaft
in the center neck. The stirring shaft was fitted with a Teflon stir
paddle, and the shaft was lubricated with the minimum amount of 8117
stirrer lubricant, "Stir-Lube," Ace Glass Co., Vineland, New .Jersey.
Stirring speed was regulated with a rheostat controlled electric stirring
motor. The side necks of the flask were fitted respectively with a
250 ml pressure equalizing addition funnel and a one-liter capacity,
Dewar type condenser charged viith dry ice during preparacive runs. The
condenser was attached to the flask with a ball joint connection which
facilitated reaction vessel manipulation required to maintain con¬
trolled atmosphere conditions throughout the system. Immediately
following assembly the system was purged with a steady stream of dry
nitrogen gas. The nitrogen environment was maintained until the
hydrolytic step was reached. All syntheses were performed using an¬
hydrous diethyl ether as solvent. Magnesium metal turnings used for
Grignard reagent preparation were conveniently activated (unless de¬
scribed otherwise) by placing the required quantity of turnings into
the dry reaction flask and stirring them vigorously for a period of 24
— 36 hours at ambient temperature. This procedure reduced the metal
to a finely divided gray-black powder which usually reacted readily with
the appropriate aryl halide to yield the desired Grignard (20).
Grignard formation was initiated by gentle warming of the reaction
mixture. If this reaction became too vigorous, cooling the flask with
a cold vmter bath slowed the reaction to an equable rate. The sub¬
sequent addition of reagents to the Grignard (in situ) was done at
reduced temperature by cooling the reaction flask with an insulated

20
baLh containing a mixture of chloroform and dry ice. The temperature
of the bath was regulated by the addition of dry ice as needed.
4-vlnorophenyl-2-pyridylketone. Fluorophenylmagnesium bromide was
prepared essentially by the method outlined by McCarty and coworkers
(21). A solution of 63 ml (95 g, 0.54 mol) 4-bromofiuorobenzene in
200 ral ether was added dropwise to 13 g (0.53 mol) of activated magne¬
sium. The mixture was slowly stirred, and the reaction proceeded smooth¬
ly as evidenced by the gentle ebullition of ether and the formation of
a brownish sludge. Following the complete addition of the ether —
aryl halide solution the mixture was brought to gentle reflux by
warming the reaction flask with a "Glas-Col" heating mantle. Grignard
formation was presumed to be complete following reflux for a period of
J Q - 12 hours.
The remainder of the procedure paralleled the method of de Jonge
et_ al_. (22). The fIuorobenzene Grignard solution (above) was cooled
to -35°. A solution of 26 g (0.25 mol) 2-cyanopyridine (picolino-
nitrile) in 200 ml ether was then added dropwise to the Grignard. This
immediately resulted in the separation of a tan-colored solid. The
reaction mixture was stirred continuously during the addition of the
2-cyanopyridine to prevent lumping of the tan solid After all of the
2-cyanopyridine had been added the coding bath was removed, and stirring
was continued until the reaction mixture, warmed to ambient temperature.
The ilask and contents were then cooled to -80°, and the ketLmine
addition compound was hydrolyzed by the careful addition of 50 ml ice
water. This was followed by the addition at U° of 100 mL concentrated
bd solution resulting in the formation of a yellow (upper) ether layer

21
and a ted- brown (lower) aqueous — acid layer. The ether layer was
drawn off and discarded, and the aqueous layer was treated carefully
with concentrated NII^ solution until a pH of 6 — 7 was obtained. This
resulted in the separation of copious quantities of a yellowish
precipitate. Inis material was washed with deionized water and then
shaken with sufficient fresh ether until all the solid was redissolved.
The other phase was evaporated to yield 40 g (80%) of the ketone, a
light tan solid which melted at 79 — 81°. The ketone was purified by
vacuum sublimation to yield a white crystalline solid melting at 83 —
84°.
4--Methylphenyl-2-pyridylketone (jd-tolyl-4-pyridy Ike tone). A hexane
solution of n-butyilithium (63 ml, 1.6 M) was placed in the reaction
flask and diluted with 250 ml ether. This solution was cooled to
-40°, and an ice-cold solution of 10 ml (17 g, 0.11 mol) 2-bromopyridine
in 100 ml ether was added dropwise with stirring. During the addition
of the bromopyridine the reaction mixture became an orange slurry
which changed gradually to a yellow-green slurry. Following the
complete addition of the bromopyridine, stirring was continued until
the reaction mixture warmed to -30°. The reaction mixture was then
recooled to -45°, and a solution of 13 g (0.11 mol) p-tolunitrile
(pymethylbenzonitrile) in 100 ml ether was added dropwise with stirring.
This resulted in the formation of a yellow slurry. Following the
addition of the nitrile stirring was continued until the reaction
mixture warmed to ambient temperature. The reaction mixture was now
recooied to -40° and hydrolyzed by the dropwise addition of 200 ml
2 M HC1. The ether was distilled off, and the reaction mixture was

n
wv-.red to lUO5 and stirred for 1 hour at this temperature to facilitate
ketiriue decomposition. The aqueous reaction mixture, was cooled in
Lee and neutralized by the careful addition of 6 M NH^ resulting in
the separation of a tan solid. The aqueous mixture, was then shaken
yi ¡til sufficient f resh ether to dissolve the solid. The aqueous residue
was discarded., and the ether was evaporated to yield 12 g (61%) of the
crude ketone. This material was vacuum distilled (0.010 mm, hp 127°)
and collected as a light yellow oil which crystallized on cooling as
yellowish needles. The needles were, dissolved in the minimum amount of
a hot mixture of _n-pentane — dichloromethane (3:1) and recrystallized
at dry ice temperature as white needles melting at 42 — 43°.
?hf;nyl-4-pyridylketone (4-benzoylpyridine). This ketone was prepared
in accord with the method employed for the synthesis of 4-fluoro-
phenyl-2-pyridylketone (p. 20). The Grignard was prepared by the
addition of 50 ml (74 g, 0.47 mol) bromobenzene dissolved in 75 ml
ether to 10 g (0.42 mol) of activated magnesium which was covered with
50 ml ether. Following the addition of the bromobenzene solution
the reaction mixture was refluxed with stirring for 2 hours.
A mixture of 21 g (0.20 mol) 4-cyanopyridine (isonicotinonitrile)
in 200 mi ether was refluxed until the nitrile dissolved. This
solution was then added dropwise to the cooled Grignard (-40°). This
resulted in the immediate formation of a tan solid, and the reaction
mixture was stirred vigorously to prevent lumping. The ketimine
intermediate was cooied to -55° and hydrolyzed by the addition of 50 ml
ice-cold saturated aqueous NH^Cl. This was followed by the addition
or 100 mi coned HC1 at 0°, resulting in the formation of much rust-

colored solid. The further addition of acid (LOG icl| 6 M HCl) dis¬
solved this solid. The ether layer was separated and discarded.
Adjusureent of the pH of the aqueous phase by the careful addition of
coned HKg resulted in the separation of copious quantities of a, yellow
precipitate. This material was dissolved in the minimum amount of
fresh ether. Evaporation of the ether yielded 34 g (93%) of the ketone,
a well defined crystalline yellow solid, which melted at 68 — 70°.
4-Methylphenyl-4-pyrldylketone (jo-tolyl-4-pyridylketone). This material
was prepared in the same manner as 4-fluorophenyl-2-pyridylketone (p. 20).
The Grxgnard ’was prepared by the addition of 17 ml (24 g, 0.1-4 mol)
p-bromotoluene dissolved in 100 ml ether to 3.7 g (0.15 mol) activated
magnesium covered with 50 ml ether. Following the complete addition
of the aryl halide solution the reaction mixture x^as refluxed for
2 hours and then cooled to -10°. This resulted in the separation of
a brown precipitate so the Grignard was not cooled further. A
filtered solution of 10 g (0.10 mol) 4-cyanopyridine in 100 ml ether
was added dropwi.se xíith stirring resulting in the formation of a large
amount of tan solid. Warming of this mixture to ambient temperature
did not cause the. solid to dissolve. The ether phase was draxm off
by aspiration through a coarse frit filtering stick to remove unreacted
4-cyanopyridine. The reaction mixture was recooled to 0° xjhile
stirring, and hydrolysis was effected by the dropwise addition of
50 ml ice-cold saturated aqueous NH^Br. This xvas follox^ed by the
addition of 60 ml 2 M HCl, and the mixture was allox-zed to stand until
the unreacted magnesium had dissolved completely. More acid was added
as needed to insure that the pH of the aqueous phase XvTas less than 1.

the aqueous phase was now washed twice with 200-ml portions of
fresh ether. The ether washes were, discarded, and the aqueous phase
was adjusted to pH 7 by the. careful addition of 6 H NH^. This resulted
in the separation of a considerable amount of white precipitate. This
•raterial was shaken with sufficient ether to effect dissolution. Lvapo-
ration of the ether yielded 14 g (71%) of the yellowish ketone which
melted at 86 — 89°.
4-Hethoxypheny1-4-pyridyIketone. (This material had been prepared
previously by Bhattacharyya and Stoufer (7) in accord with the method
of I.aFcrge (23). For the sake of completeness its preparation is given
below.)
A solution of 51 ml (74 g, 0.40 mol) jD-bromoanisole (l-bromo-4-
metboxybenzene) dissolved in 160 ml ether was added dropwise over a
period of 1 hour at ambient temperature to 9.6 g (0.40 mol) of activated
magnesium. The reaction mixture was stirred vigorously throughout and
refluxed for 1 hour following the addition of the broraoanisole. The
Grignard was then cooled in an ice bath, and to this was added dropwise
a solution of 21 g (0.20 mol) 4-cyanopyridine in 400 ml ether. The
reaction mixture was stirred constantly throughout. Following the
addition of the 4-cyanopyridine, the reaction mixture was refluxed for
] hour and then cooled in an ice bath to 0°. Hydrolysis was effected
by the careful addition of 50 ml ice-cold saturated aqueous NH^C.l. The
ether and aqueous layers were then separated, and the aqueous layer
was twice, extracted with 100-ml portions of fresh ether. The ether
extracts were combined with the original ether layer. The ether fraction
was extracted thrice with 200-ml portions of 3 M HC1. The aqueous

fractions were pooled and extracted thrice with I00_ral portions of
fresh ether. Ail ether fractions were now discarded, and the aqueous
fraction was boiled for 1 hour to ensure complete ketimine decomposi¬
tion. The aqueous fraction was cooled and carefully neutralized with
ice-cold 3 M NaOR resulting in the separation of a yellow precipitate.
This material was filtered, washed with fresh deionized water, and
a?.r dried. The crude ketone was then dissolved in .100 ml hot chloro¬
form. This solution was treated while hot with anhydrous MgSO^ and
filtered. The. volume of the chloroform filtrate was tripled by the
addition of fresh ether and cooled for 1 hour. The reprecipitated
solid was filtered, washed with ice-cold ether, and air dried to
yield 28 g (71%) of the yellowish ketone which melted at 123 — 124°.
2-Pyridylphenyl-4-fluorophenylmathanol. Magnesium turnings (8.1 g,
0.33 mol) were placed into the dry reaction flask, and a small crystal
of iodine was added. The flask was carefully heated with a heating
mantle until the iodine just vaporized whereupon heating was discon¬
tinued. As the iodine recondensed the magnesium turnings were stirred
briefly to ensure the deposition of a reasonably homogeneous layer
of iodine onto the surface of the metal. A solution of 32 mi (51 g,
0.29 mol) 4-bromofluorobenzene in 200 ml ether was added dropwise to
the activated magnesium. The reaction mixture was stirred continuously
as it was warmed to reflux. Reflux was continued for 2 hours following
the addition of the aryl halide, and the reaction mixture was then
cooled to --60°. A solution of 11 g (0.060 mol) phenyl-2-pyridylketone
(2~benzoyipyridine) dissolved in 300 ml ether was added dropwise to
the stirred Grignard. The cooling bath was removed periodically to

26
minimize the freezing out of materials from the reaction mixture.
As the kc-tonc solution was added the reaction mixture became red-violet
in color. Following the addition of the ketone solution the cooling
hath was removed, and the contents of the flask were stirred until
a temperature of -10" v/as attained. During this time the. reaction
mixture became dark brown in color. The addition product was hydrolyzed
at -10° by the careful addition of 25 ml ice water resulting in the
formation of a lemon-yellow ether layer and a pink aqueous layer.
The aqueous layer was discarded, and the ether layer was extracted
thrice with 200 — tal portions of 3 M HC1. The extracted ether layer
was discarded, and the aqueous phase was adjusted to pH 7 — 8 by the
careful addition of 6 H NH^. This resulted in the separation, of a
ye.llow-orange solid. The solid — aqueous mixture was shaken with
sufficient fresh ether to dissolve all the solid. The aqueous portion
was then discarded, and the ether solution was combined with 3A
molecular sieves until incipient crystallization was observed. The
sieves were removed, and the ether evaporated completely to yield 13 g
(77%) of the crude yellow-orange carbinol. This solid was dissolved
in 200 ml hot methanol and treated with 6 g of wood charcoal. This
mixture was refluxed 30 minutes and filtered. The hot, yellow methanol
solution was allowed to stand until crystallization of a yellow solid
occurred. The carbinol exhibited a melting range of 79 __ 82°.
Anal.: Caled for C1oHwN0F: C, 77.40; H, 5.05; N, 5.02.
Found: C. 7 7.51; II, 5.10; N, 5.16.
2-Pyridyl-4-methylphenyl-4-fluorophenylmethanol. The Grignard was
prepared exactly as was that for 2-pyridylphenyl-4-fluorophenylmethanol

27
(above) employing 8.1 g (0.33 mol) magnesium turnings and VI ml (99 g,
0.28 mol) 4-hromofluorobenzene. The reaction mixture was then cooled
to -50°, and a solution of 10 g (0.051 mol) 4-methylphenyl-2-pyridyl-
ketone dissolved in 250 ml ether was added dropwise to the stirred
Orignard. This resulted in the formation of a butterscotch-colored
dispersion. Following the addition of the ketone the cooling bath vías
removed, and the reaction mixture was stirred until a temperature of
10° was reached. The reaction mixture was recooled to -10° and hydro¬
lysed by the dropwise addition of 200 ml ice-cold saturated aqueous
This resulted initially in the formation of a white slurry
which slowly became a yellowish emulsion. The eiouiijion was broken
by filtering through glass wool followed by squeezing through coarse
filter paper. The yellow ether layer was then extracted thrice with
100 — ml portions of 6 M HC1. The ether phase was discarded, and the
aqueous portions were combined and treated carefully with 6 M NH^
until pH 7 v;as attained. This resulted in the separation of a sticky
yellowish oil. The oil was extracted with the minimum volume of fresh
ether, and the aqueous residue was discarded. Evaporation of the
ether again resulted in separation of the oil. Characterization
of che oil (12 g, 82%) revealed it to be the desired carbinol. The
oil vías vacuum distilled (0.010 mm, bp range 160 — 170°); but the
collected distillate remained as a light yellow oil after cooling.
Anal.: Caled for C H..,.N0F: C, 77.75; H, 5.56; N, 4.77.
io
Found: C, 77.87; H, 5.56; N, 4.60.
2~Pyridyl-4--methoxyphenyl-4-fluorophe.nylmethano.l. A solution of
6.4 ml (9.4 g, 0.050 mol) p-bromoanisole in 25 ml ether was added

28
d1Wpwi.se v. Lth stirring Lo 1.3 g (0.053 mol; activated magnesium covered
w> tti 25 ml ether. The: reaction mixture was heated to gentle rciiux,
and the formation of Grignard was evidenced by the development of a
giej»-brown translucency. Following reflux for a period of 2 hours
Grignurd formation appeared to be complete. The reaction mixture
was now cooled to -5° with an ice —• salt bath, and to this a solution
of 6.0 g (0.030 mol) 4-fluorophenyl-2-pyridylketone dissolved in 120 ml
ether was added dropwise with continuous stirring. During this addition
of ketone a yellow solid settled out. Following the addition of ketone
the cooling bath was removed, and stirring was continued as the reaction
mixture slowly wanned to ambient temperature. This resulted in the
formation of a light tan-colored suspension with traces of reddish-
purple material dispersed throughout. The reaction mixture was sub¬
sequently heated to reflux for a period of 1 hour and then cooled.
The hulk of the ethereal solution was removed from the reaction flask
by aspiration, through a coarse frit filtering stick. The material
which remained in the flask was washed three times with 50 — ml
portions of fresh either. The ether washes were removed by aspiration
arid combined with the original ether layer. Upon standing a white
semisolid material separated from the ether. The residual reaction
mixture was now hydrolyzed at 0° by the careful addition of 50 ml
saturated aqueous NH^Br, followed by 150 ml i M HC1. This resulted
in the separation of a yellow oil. The aqueous phase was adjusted to
pH 7 by the careful addition of 3 M NH^. This produced a milky dis¬
persion of the oil. The aqueous phase was then shaken with fresh ether
until the dispersion cleared, and the aqueous layer was drawn off
and discarded. The aspirated ether portions (above) were filtered

through a medium frit to separate the V7hite pemisolid material. The
ether filtrate was discarded, and the white material was hydrolyzed
on the frit by the addition of a few ini deionized water. This pro¬
duced more of the yellow oil. The oil was dissolved :in fresh ether,
and the oil — ether solutions were combined. Evaporation of the
ether yielded 6.2 g (67%) of the oily carbinol. Repeated attempts to
crystallize this material were unsuccessful. An accurate mass for the
molecular ion of the carbinol was determined mass spectrally. Caled
for CiriK_rN0oF: 309.1164. Found: 309.1170 (mean of four determina-
19 16 2
tions; deviation, ±2 ppm).
4-Pyridylphenyl-4-fluorophenylmetnanol. A solution of 12 ml (18 g,
0.10 mol) 4-bromofluorobenzene in 50 ml ether was added dropwise to
2.4 g (0.10 moi) ether-covered activated magnesium. Stirring was con¬
tinuous during the addition of the aryl halide, and Grignard formation
ensued upon gentle warming of the reaction flask as evidenced by the
development of a grey-brown dispersion and the ebullition of ether.
After the aryl halide had been added the reaction mixture was stirred
and refluxed for a period of 2 hours. Subsequently, the reaction
mixture was cooled to -5°, and a filtered solution of 11 g (0.60 mol)
phenyl-4-pyridylketone dissolved in the minimum amount of ether (ca.
200 ml) was added dropwise. This resulted in the immediate formation
of a pink solid. Vigorous stirring was maintained to insure uniform
mixing. Stirring was stopped following the addition of ketone, and
the mixture stood at ambient temperature for a period of 12 hours.
The bulk of the ether phase was now drawn off by aspiration through

a coarse frit filtering stick and discarded. The. residual solid was
washed twice with fresh 50 — ml portions of ether, and the washes were
discarded. The solid was subsequently recooled to -5° and hydrolyzed
with stirring by the dropwise addition of ICO ml saturated ice-cold
aqueous Nll^Br. This was followed by the addition of 1 M IIC1 until a
pH of 5 — 6 was attained. The aqueous mixture was now transferred
to a large separatory funnel and shaken with 400 ml ether. The aqueous
(lower) layer was tan in color, and the ether (upper) layer was yellow.
A small quantity of semisolid yellow material resided at the interface
of the liquid layers. The aqueous layer was drawn off, and the semi¬
solid was combined with the ether layer and together shaken with four
separate 150 -- ml portions of 2 M HC1. This resulted in the dissolu¬
tion of most of the solid and a translucent ether layer. Evaporation
of the ether yielded a small amount of brown material which was
discarded. All of the aqueous portions were then pooled resulting
j.n the development of an opaque dispersion. Treatment of the aqueous
layer with 6 M NH0 produced initially a clearing of the opaqueness,
and as the pli was raised to 4 — 5 much white solid separated. The
solid was isolated by filtration and the filtrate again treated with
6 M Nil^ to bring the pH to 7. This resulted in the separation of
more white solid which was also filtered off. All of the aqueous
filtrate was discarded, and the combined solid samples ware air dried
to yield 15 g (92%) of product which exhibited decomposition to a
brownish oil at 185 — 190°. To convert any hydrochloride salt to free
carbinol the entire amount of white solid was slurried with 100 ml 1 M
NH^. After standing for 1 hour the solid was separated by suction
filtration, washed with 200 ml of deionized water and air dried. The

31
isolated material was a finely divided white solid which melted at
J92 -- 194° without appreciable discoloration.
Anal.: Caled for C.loH,/N0F: C, 77.40; H, 3.05; N, 5.02.
Found: 0, 77.13; H, 5.09; N, 5.00.
An accurate mass for the molecular ion of the carbinol was determined
mass spectrally. Caled for C^gH^.NOF: 279.1058. Found: 279.1052
(mean of five determinations; deviation, ±2 ppm).
4-Pyrldyi-4-methylphenyl-4-fluorophenylmethanol. The preparation of
this carbinol was carried out by the method used for the preparation
of 4-pyridylphenyl-4-fluorophenylmethanol (above). The quantities of
materials employed were: 2.9 g (0.12 mol) magnesium; 14 ml (21 g,
0.12 mol) 4-bromofluorobenzene dissolved in 50 ml ether; and a
filtered solution of 7.4 g (0.038 mol) 4-methylphenyl-4~pyridylketone
dissolved in 125 ml ether.
Following hydrolysis the aqueous phase was adjusted to pH 1 with
i M HC1 resulting in the separation of 5—10 ml of a brown oil. This
oil was drawn off; the work-up of the oil is given below. The acidic
aqueous phase was twice shaken with 400 — ml portions of fresh ether.
Each shaking resulted in the separation of a small quantity of yellowish
semisolid material. This material and the ether extracts were dis¬
carded. The aqueous phase was neutralized by the careful addition of
6 M llflg. This resulted in the separation of a yellowish solid which
was isolated by suction filtration. Characterization of the solid
(4.4 g) revealed that it was the crude carbinol. The brown oil (above)
was stirred with 300 ml 1 M HC1 resulting in the formation of a brown

creamy emulsion. The emuLsion was extracted thrice with 100 — ml
portions of ether. This removed the translucency from the aqueous laye
which was now a light yellow solution. All the organic washes were
discarded, and the aqueous layer was neutralized by the careful
addition of 6 M NH^. This resulted in the separation of a yellowish
solid which was filtered, washed with deionized water, and air dried
to yield 1.2 g of solid which melted at 169 — 172°. This material,
combined with the previously isolated solid, afforded a yield of 50%.
Anal..: Caled for C H^NÃœF: C, 77.75; II, 5.56; N, 4.77.
Found: C, 77.60; H, 5.55; N, 4.82.
An accurate mass for the molecular iou of the carbinol was determined
mass spectrally. Caled for rN0F: 293.1215. Found: 293.1216
(mean of three determinations; deviation, ±0.3 ppm).
4-?yridyl-4-mRthoxyphenyl-4-fluorophenylmethanol. The Grignard was
prepared exactly as was that for 4-pyridylphenyl-4-fluorophenyl-
methanol (p. 29) using 1.3 g (0.53 mol) magnesium; and 60 ml (9.0 g,
0.51 mol) 4-bromofluorobenzene dissolved in 30 ml ether. To this at
-5° was added in 100 — ml increments a solution of 5.5 g (0.25 mol)
4-methoxyphenyl-4-pyridylketone dissolved in 600 ml ether. As the
ketone solution contacted the reaction mixture a yellow solid formed
and separated. Following the addition of ketone the stirred reaction
mixture was refluxed for 90 minutes arid was then set aside and not
disturbed for a period of 12 hours. The reaction mixture was now a
yellow creamy dispersion, and little of the ethereal liquid phase
could be drawn off by suction through the glass filtering stick.
Therefore, the reaction mixture was cooled to -5° and hydrolyzed by

33
Lne dropwise addition of 50 ml of saturated ice-cold aqueous NH^Br,
followed by the addition of 100 ml 1 M HC1. This resulted in the dis¬
persion of a brown oily material in the aqueous phase. The ether layer
was extracted four times with 125 — ml portions of 1 M HC1 and then dis¬
carded. The aqueous portions were pooled yielding a yellow-green
opaque mixture. This mixture was adjusted to pH 7 by the careful addi¬
tion of 6 M NH^, and upon standing for 2 — 3 hours a quantity of light
tan solid separated. The solid was filtered, air dried, and dissolved
in a refluxing mixture of 100 ml 4:1 ethylacetate — acetone. After
standing 72 hours, this solution was reduced to a volume of ca. 30 ml.
by evaporation which resulted in the separation of a white crystalline
solid. The crystals were filtered, washed with a few ml of ice-cold
ether, and air dried to yield 4.0 g (41%) of the carbinol melting at
181 - 183°.
Anal.: Caled for C19H16N02F: c> 73-77; H, 5.21; N, 4.53.
Found: C, 73.75; H, 5.26; N, 4.51.
An accurate mass for the molecular ion of the carbinol was determined
mass spectrally. Caled for CiriH1¿.N0F: 309.1164. Found: 309.1167
19 lo
(mean of six determinations; deviation, ±1 ppm).
The Purification of Diphenyl-4-pyridylmethana. The commercially obtained
alkane (mp 120 — 125°) was found to be contaminated by trace amounts
of the corresponding diphenyl-4-pyridylcarbinol (from which the alkane
was probably prepared). This was demonstrated by treating a sample of
the "alkane" with 70% RC10^ which produced color characteristic of
alcohol ionization. A visible spectrum of this acid solution gave
baud positions identical to those got for a similar (known) solution of
diphenyl-4-pyridylcarbinol.

A glass column (20 cm x 2 cm i.ci.) was fitted with a stopcock
above which was inserted a plug of glass wool covered with a 1 cm
thick, sand mat. The vertically supported column was tilled ca. half
full with reagent hexane, and the stopcock was opened slightly to
permit the dropwise outflow of solvent. A hexane slurry of freshly
activated 80 — 200 mesh alumina (Brockman Activity I) was poured into
the column, and as the alumina settled on the sand mat the column was
carefully agitated to insure uniform adsorbent deposition. A 0.5 cm
thick sand mat was added to the top of the alumina layer in the packed
column, and the level of solvent was adjusted to coincide with the
top of the sand mat. A saturated solution of the alkane was prepared
by stirring 2 g of the alkane into 6 ml benzene. This solution was
filtered and carefully placed on the column. Gravity elution was
carried out: by the dropwise percolation of the following solvents:
1) 250 ml 1:1 hexane — benzene; 2) — 5) 500 — ml portions of ether.
Each of the ether fractions 2—4 was evaporated separately yielding ca.
equal quantities of a white solid. A small portion of each of these
samples of solid was treated with 70% HCIO^. In each instance the
resulting solution was virtually colorless. These samples of solid
were combined and dissolved in the minimum amount of hot methanol.
Crystallization afforded a yield of 1.0 g of we.11 developed white needle
which melted at 125 — 126°. A solution of these needles in 70% IICIO^
was transparent in the visible region of the spectrum.

35
Synthesis of Complexes
1. The Preparation of the "bis" Alcohol Complexes of Pallad.turn(IT),
LPd(II)(pyLOH)2Cl2].
Pichlorobis (4-pyridylphenyl~4~f luorophenylmethanol)palladium(ll) . Palla¬
dium chloride powder (0.16 g, 9.3 x 10 * mol) was placed in a 250-ml
_3
round bottom flask together with 0.10 g (2.4 x 10 mol) dry lithium
chloride and 100 ml acetone. The mixture was stirred magnetically and
gently refluxed until all solids had dissolved (ca. 24 hours). The
solution which resulted was deep red-brown in color. To this solution
_3
0.51 g (1.8 x 10 mol) of solid 4-pyridylphenyl-4-fluorophenylmethanol
was added; immediately the red-brown color changed to yellow-orange.
The yellow-orange solution was refluxed for 24 hours while stirring.
Acetone was then removed by distillation until a solution volume of
ca. 20 ml was attained. The reaction mixture was filtered through a
medium frit, transferred to a small beaker, and treated with 5 ml of
deionized water. A yellow crystalline precipitate developed during
standing for 1 hour. The precipitate was isolated by suction filtration
through a medium frit, washed on the filter with three 10 — ml portions
of fresh deionized water, and oven dried on the filter at 130°. The
solid was then washed from the filter with 50 ml fresh acetone yield¬
ing a yellow solution. This solution was flooded with sufficient
n-pentane to produce permanent cloudiness and was then allowed to
stand unr.il crystal formation occurred. A yield of 0.15 g (20%) of
well defined yellow needles was obtained. The product exhibited
darkening at >260° and decomposed to a black oil at 295°.

36
Ana ICaled for f’3(3H28N202F7?dC1 2C> 5S-75> H> 3-83’ N> 3.81.
Found: C, 58.73; H, 4.03; N, 3.70.
í)iehlorobis (4-py ridyl-4-niethylphenyl-4-fluorophenyImethar.ol) -
palladium(II). The material was prepared in exactly the same fashion
as for the preparation of the bis(4-pyridylphenyl) complex (above)
_3
using 0.53 g (1.8 >: 10 mol) 4-pyridyl-4-methylphenyl-4-fluorophenyl-
methanoi. A yield of 0.17 g (22%) of well defined yellow needles was
obtained. The product exhibited darkening at >240° and decomposed
to a black oil at >260°.
Anal. : Caled for C^H^h^O^PdCl,,: C, 59.74; H, 4.22; N, 3.67.
Found: C, 60.26; II, 4.33; N, 3.49.
lVLchlorobis(4-pyridyl-4-methoxyphenyl-4-fluorophenyInethanol)-
palladium(II). This material was prepared in exactly the same fashion
as for the preparation of the bis(4-pyridylphenyl) complex (above)
_3
using 0.56 g (1.8 x 10 ‘ mol) 4-pyridyl-4-xuethoxyphenyl-4-fluoro-
phenylmethanol. A yield of 0.16 g (20%) of well defined yellow needles
was obtained. The product exhibited darkening at >240° and decomposed
to a black oil at 250°.
Anal. : Caled for C^H-^I^O^PdC^: C, 57.34; H, 4.05; N, 3.52.
Found: C, 57.90; II, 4.21; N, 3.38.
T?ir] ilorobis(2-pyridyl-4-methylpheny1-4-fluorophenyImethanol)palladium(II).
[This material was not amenable to the thermodynamic investigations
which were carried out in this work. (See Results and Discussion, p.
97). However, for the sake of completeness, its preparation is given.

37
It is the only well defined "2-pyridyl" complex which was isolated.]
In ucl.uaLity this malerial was obtained as a side product of the. syn¬
thetic method which had been designed for the preparation of the "salt-
like" complex (Z*", PdLCl^), where Z* is a suitable cation, and L is
the pyridyinethanol.
_3
Palladium chloride powder (0.28 g, 1.6 x 10 mol) was placed in
-3
a 250-ml round bottom flask together with 0.072 g (1.7 x 10 mol)
_3
dry lithium chloride, 0.47 g (1.6 x 10 mol) 2-pyridyl-4-methylphenyl-
4-fluorophenylmethanol, and 50 ml acetone. This mixture was stirred
magnetically as it was refluxed for a period of 2 hours resulting in the
dissolution of all solids and the formation of a deep red-brown solution.
The acetone was then removed by distillation yielding some red gummy
material. The gummy semisolid was redissolved by the addition of 10 ml
fresh acetone reproducing the red-bro’m solution. A heaping micro-
spatula of tetramethylammonium chloride was dissolved in a mixture of
2 ml acetone and 1 ml methanol. This colorless salt solution was added
to the red-brown solution (above) producing no apparent change. The
addition of 2 ml dichloromethane induced the separation of a reddish
oily material which clung to the inner walls of the flask. After standing
overnight the oily material had failed to crystallize and was redissolved
by the further addition of 20 ml fresh acetone. This solution was heated;
following 30 minutes reflux a salmon-colored crystalline solid separated
with the solution phase now being yellow-orange in color. A second
microspatula of tetramethylammonium chloride was added, and the reaction
mixture was returned to reflux for a period of 2 hours. After cooling,
the salmon-colored solid was separated by filtration. (This solid was
laLer shown to be tetramethylammonium tetrachloropalladate(I£).) The

38
yellow-orange acetone filtrate was flooded with deionized water result¬
ing in the separation of a yellow crystalline solid. This solid was
filtered by suction through a medium frit, washed with deionized water,
and air dried to yield 0.52 g (43%) of a material characterized as the
"bis" alcohol complex (PdL^Cl^) . This material decomposed to a black
oil above 195°.
Anal. : Caled for C38H32N2°2F2PdC12: C, 59.74; H, 4.22; N, 3.67.
Found: C, 59.56; H, 4.39; N, 3.70.
II. The Preparation of the "Mono" Alcohol Complexes of Palladium(II),
(Pd(IT) (pyLOH) (lSr)Cl 0], where L,, is Diphenyl-4-pyridylmethane. (See
also p. 33).
The Preparation of Pd (II) (pyLOH) (LyQCl? , where pyLOH is 4-Pyridylnhenyl-
4-fluorophenylmethanol. In a dry environment 0.01 g (5.6 x 10 ^ mol)
palladium chloride powder was transferred to a 259-m.l round bottom
flask together with 0.16 g (5.8 x 10 ^ mol) dried Letca-n-butylammoniunv
chloride and 100 ml acetone. This mixture was stirred magnetically as
it was refluxed for 72 hours to dissolve all solids, producing a deep
red-brown solution. To this solution was added 0.14 g (5.7 x 10 ^ mol)
purified diphenyl-4-pyridylmethane (p. 33). As the alkane dissolved
the color of the solution changed from red-brown to red-orange. This
solution was refluxed for 2 hours and cooled. To this was added 0.16 g
(5.7 x .10 * mol) 4-pyridylphenyl-4-fluorophenylmethanol; as the alcohol
dissolved,the color of the solution changed from red-orange to yellow-
orange. This solution was refluxed for 1 hour after which acetone was
removed by distillation until a solution volume of cji. 30 ml vías attained.

39
The: mixture was now distinctly yellow with incipient precipitation of a
yellow solid having begun. Sufficient deionized water (ca. 10 ml)
was added until permanent cloudiness was produced. Tiie mixture was
allowed to stand 48 hours to promote crystal growth, and was then filtered
by suction through a tared frit (medium). The collected yellow solid
was washed with deionized water and dried on. the frit at 130° for a
period of 1 hour. A yield of 0.35 g (89%) of well defined yellow
needles was obtained. This material darkened above 245° and decomposed
to a black oil above 270°.
Anal.j Caled for c36H2gN2OFPdCl2: C, 61.60; H, 4.16; N, 3.99.
Found: C, 61.34; H, 3.93; N, 3.83.
The Preparation of Pd(ll)(pyLOH)(Lv)Cl?, where pyLOH is 4-Pyridy]-4-
met.hylphenyl-4-fluorophenylmethanol. This complex was prepared in exactly
the same fashion as that for the 4-pyridylphenyl-4-fluorophenylraethanol
complex (above). The same quantities of materials were employed together
with 0.17 g (5.7 x 10 ^ mol) 4-pyridyl-4-methylphenyl-4-fluorophenyl-
methanol. A yield of 0.35 g (87%) of well defined yellow needles was
obtained. This material decomposed to a brown-black oil above 245°.
Anal.: Caled for c37H31N2OFPdCl2: C, 62.07; H, 4.36; N, 3.91.
Found: C, 62.20; H, 4.32; N, 3.77.
The Preparation of Pd(II)(pyLOH)(Ly)Cl?, where pyLOH is 4-Pyridvl-4-
mcthnxyphenyl-4-fluorophenvlmethanol. This complex was prepared in
exactly the. same fashion as that for the 4-pyridylphenyl-4-fluorophenyl-
me Annual complex (above). The same quantities of materials were employed

40
togrthc* with 0.18 g (5.7 x 10 ^ mol) 4-pyridyl-4-inethoxyphenyl-4-
fluo ro phenylme t h a a o 1. A yield of 0.35 g (S4%) of well defined yellow
needles was ohrained. This naterial darkened above 180° and decomposed
to a brown oíL above 210°.
Anal.: Caled for C37tI31N202FPdCl2: C, 60.71; H, 4.77; N, 3.83.
Found: C, 60.94; H, 4.46; N, 3.83.
i'e.tra-x\-butylan¡monium Trichloro- (4-pyridylphenyl-4-fluorophenylmethanol)-
pa'lladaLe(Il) . This "salt-like" complex was prepared separately in order
to establish the fact that it was a stable, isolable intermediate. (See
Results and Discussion, p. 58.)
-4
Tn a. dry environment 0.12 g (4.3 x 10 mol) tetra-n-butylammonium
chloride, 0.075 g (4.2 x 10 ^ mol) palladium chloride powder, and 100 ml
acetone were placed together in a 250-ml round bottom flask. This
mixture was stirred magnetically as it was refluxed for a period of 24
hours. The reaction mixture now consisted of a deep red-brown solution
phase containing traces of undissolvcd white and red-brown solids. The
solution phase was carefully decanted into a clean flask, and to this
-4
was added 0.12 g (4.2 x 10 mol) 4-pyridylphenyl-4-fluorophenylmethanol.
As the alcohol dissolved the solution changed color from red-brown to
orange. This mixture was stirred magnetically at ambient temperature
for a period of 1 hour and was then heated to reflux. Acetone was re¬
moved by distillation during reflux until a solution volume of ca. 30 ml
was attained. To the hot red-orange acetone solution was added 30 ml
ether, and this solution was allowed to cool without stirring. To the
cooled solution n-pentane was added in small portions until permanent
cloudiness was attained. Upon stirring for a period of a few hours a

41
small quantity of yellow-orange crystals developed and settled to the
bottom of the flask. The solution phase, which was now slightly yellow,
was treated again with n-pentane to reinduce cloudiness. After standing
overnight the mixture was gravity filtered through a fluted filter, and
the virtually colorless filtrate was discarded. The crystals which
wete collected were air dried, examined under a microscope, and found
to he thin, transparent gold-orange sheet-like needles. This material
melted at 150° to a red-brown oil. A yield of 0.29 g (94%, as based
on palladium) was obtained.
Anal.: Caled for C34H50N20FPdcl3: C, 55.60; H, 6.86; N, 3.81.
Found: C, 55.35; H, 6.87; N, 3.77.
Elemental Analyses
Catbon, hydrogen, and nitrogen elemental analyses for ligands and
complexes were performed either by PCR Incorporated, P. 0. Box 466,
Gainesville, FL, 32601, or by Atlantic Microlab, Incorporated, P. 0.
Box 54306, Atlanta, GA, 30308. No special handling techniques were
required for either the ligands or the complexes.
Reagents and Solvents
The special, coimnerdaily obtained reagents which were employed
in this research are listed in Table I (p. 42). These materials were
used without further purification unless otherwise specified. The

Tab It* I
Special, Commercially Obtained Reagents - - and Suppliers
Reagent
Supplier
£-bromoanisole (l-bromo-4-
nethoxybenzene)
Aldrich Chemical Co., Inc.,
Milwaukee, WI, 53233
4-bromof luorobenzene
Aldrich
2-broroopyridine
Aldrich
2-cyanopyridine (picolino-
uitrile)
Aldrich
4-cyanopyridine (isonicotino-
nitrile)
Aldrich
diphen.yl-4-pyridylcarbinol
K & K Laboratories, Inc.,
Plainview, NY, 11303
diphenyl-4-pyridylmethane
Aldrich
phenyl--2-pyridy] ketone
(2-benzoylpyridine)
Aldrich
tetra-n-butylammonium chloride Eastman Kodak Co.,
jp-tolunitr ile (j^-methylbenzo-
nitrile)
Rochester, NY, 14650
Aldrich
additional reagents and solvents which were employed were readily
available, reagent grade quality materials, and were used without
further purification.

Instrumental Analytical Methods
1
Proton Magnetic Resonance Spectra. The II nmr spectra were obtained
usl.UK a Varian Associates Model A-60A nmr spectrometer operating at 60
MHz. The spectra were taken as saturated carbon tetrachloride solutions
using tetromethylsilane (TMS) as internal standard. The spectra were
examined principally with respect to integrated peak intensity ratios
for the purposes of ascertaining sample homogeneity and molecular
composition.
Mass Spectra. Mass spectra were obtained using an AEI MS-30 mass
spectrometer equipped with a DS-30 data system. Solid and oil samples
were introduced into the ionization chamber via direct insertion probe
at 2.00° and run at an ionizing voltage of 70 eV.
Infrared Spectra. The IR spectra were obtained using a Perkin-Elraer
Model 337-B grating infrared spectrophotometer scanning the region
4000 -- 400 cm Solid samples were intimately ground with oven dried
reagent potassium bromide and run as pressed semimicro discs. Oily
samples were run as follows: A neat potassium bromide disc was pressed
and supported horizontally. The oil was warmed until it became fluid,
and a drop of the oil was added to the surface o£ the salt disc. This
technique deposited the oil as a uniform thin film on the disc. The
spectrum was x'ecorded as soon as the oil cooled sufficiently to become
viscous.
The IR spectra were used to provide evidence of ligand homogeneity
by establishing the absence of a carbonyl stretching vibration (ketone),

44
Lhe presence of a hydroxyl band (alcohol), and to confirm the presence
of both ligands in the "mixed" mono-alcohol complexes (pp. 38-40).
19
Fluorine Magnetic Resonance Spectra. The F rur.r spectra were obtained
using a Varian Associates Model XL-100-15 nm;r spectrometer operating
at 94.1 MHz in either continuous wave or Fourier transform pulse mode.
Fourier transform capabilities were provided with a Nicolet TT-100
computer system equipped with a 16 K capacity memory. All spectra were
recorded using external 1^0 as a lock signal. Fluorine resonances were
recorded relative to 10% CFCl^ in acetone and to neat trifluoroacetic.
acid as external reference standards. Operation at a sweep width of
5000 Hz afforded an uncertainty of ±15 Hz (±0.16 ppm) in the position
19
of observed F signals.
Ligand spectra were recorded as 0.05 M acetone solutions, as 0.05 M
10% HCIO^ solutions, and as saturated 70% HCIO^ solutions. Spectra of
complexes were recorded as saturated acetone solutions and as saturated
70% HCIO^ solutions. All solutions were filtered through a coarse frit
directly into the nmr sample tube just prior to recording of spectra.
HCIO^ solution spectra of the complexes were run in large capacity
nmr tubes employing Fourier transform techniques exclusively to facilitate
signal detection for these very dilute samples. All samples were air
cooled in the sample holder during the recording of spectra in order
to maintain ambient temperature.
Visible Spectra and Molar Absorptivity Coefficient Determination. Vis Lble
spectra were obtained using a Beckman Model DB-G grating spectrophotom¬
eter equipped with a Sargent Model SR recorder. Molar absorptivity

45
coefficients (c, Table II, p 77) were determined fur carbenium ion
â– species derived from each of the free and complexed alcohols dissolved
-4 -5
in 70% HCIO^. Samples of appropriate size (10 to 10 g) were weighed
to three significant figures using a Cahn Model 1501 Gram Electrobalance
calibrated in the 1 mg range. Oily samples had to be weighed by dif¬
ference. This was done by taring a small finely drawn glass whisker
and then carefully touching the glass whisker to the oil until a very
small bit of the oil adhered to the x^hisker. The weight of the oil
was obtained from the combined weight of the oil and whisker. The
veighed samples were stirred in ca. 9 ml of the acid to complete dis-
sclution and then made to 10.0 ml xjith fresh acid. These acid solutions
were scanned vs. the neat acid as blank spanning the region 760 — 320
mn to ascertain the position of X for the various carbenium ion
max
species. Each ionic species exhibited two main absorption bands with
the more intense band appearing at lower energy. If the absorption
maxima x^ere "off-scale", the acid solutions xvere diluted with the
necessary quantity of fresh acid to produce "on-scale" readings x-rithin
acceptable sensitivity limitations of the spectrophotometer readout,
yin., >10% T (<1.0 absorbance units).
Visible Spectra and the "Peno" Titration Technique. The equilibrium
constant (K^)+) datum pertaining to the thermodynamic stability of each
of the carbenium species x/hich have been considered in this x/ork x-:as
experimentally obtained as follows: a 70% IICIO^ solution of the alcohol
(ligand) or complex under investigation xjas prepared and diluted (if
necessary) with fresh acid until an "on-scale" (yñz.- > 15 — 25% T)
spectrophotometer reading was obtained x;ith the instrument set at X
r 1 ° mai:

46
for chat particular Ionic species. It is not necessary to fix the
concentration of this solution. (See Results and Discussion, p. 92.)
A predetermined quantity of this solution (c.a. 5 gj was weighed to five
significant figures into the special cuvette (described below). (By
amploying the same sample size for each titration, data treatment was
greatly simplified.) In order to obtain exactly the same weight for
each sample, very minute quantities of the parent acid solution could
be transferred to or from (as necessary) the contents of the cuvette
with the tip of a finely drawn glass rod. The acid solution in the
special cuvette was then transferred to the cell compartment of the
spectrophotometer and "read" at X relative to a samóle of the neat
max
acid used as blank. The cell compartment was thermostatted at 20 — 25°
by the circulation of tap water. The special cuvette was removed
from the cell compartment, and the parent acid solution of the carbenium
ion was diluted by the. addition of a measured increment (ca. 0.02 —
0.03 g) of deionized water from the special burette (described below).
Following each addition of water the acid solution was carefully mixed
in the cuvette; the cuvette was returned to the spectrometer, and the
absorbance reread. This procedure was repeated until the absorbance
of the acid solution had fallen off considerably (<0.20 absorbance
units) thereby indicating a reconversion of carbenium ion to alcohol
(or complexed alcohol) precursor in excess of 50%. Data treatment is
considered in Results and Discussion (pp. 83-103).
The specific gravity (p) of the reagent 70% HCIO^ was determined
before performing the titrations by weighing accurately (5 sig. fig.)
a measured volume of the acid in a 10 ml volumetric flask which had
bteu voiumetrically calibrated (to 4 sig. fig.) with a weighed sample

47
of distilled water. Prior to calibration the neck of the flask v;a:;
heated and drawn to a fine bore of sufficiently large inner diameter to
permit insertion of a Pasteur pipette for liquid transferral. The flask
was then calibrated by marking the drawn neck at a volume dictated by
the weighed sample of water contained in the flask. Specific gravity
data for water at ambient conditions were used to calculate the volume
of the flask at the calibration mark.
Special Cuvette. A 1.00 cm path length quartz cell fitted with a quartz/
Pytex graded seal stem was obtained from Pyrocell Manufacturing Co.,
Inc., Westwood, NJ, 07615, The stem was shortened so that the cell
fitted conveniently into the sample compartment of the spectrometer.
A standard taper size 13 ground glass neck was added to the top of the
stem to facilitate the direct dropwise addition of water to the acid
solution of the carbenium ion contained in the body of the cell during
titration. A side arm of ca_. 4 ml capacity was fused to the stem at an
angle of ca. 75° to the cell. Thus the thorough mixing of water with
the acid solution during titration was readily accomplished by rocking
the cell after each addition of water through an angle of 90°. This
particular cell design also eliminated any problems associated with
sample less upon removal of the cell stopper prior to each addition of
titrant (water) since none of the liquid sample was in contact with the
stopper throughout the titration.
Special burette. A 5.00 ml capacity semimicro burette equipped with an
automatic refilling reservoir and side arm was fitted with a 5 cm length
of surgical tubing at the drip tip. A 12 cm length of 6 mm (o.d.)

AS
rap ill ary tubing was drawn to a very fine bore pipette tip at one end.
Pie opposite end of the capillary was inserted snugly into the open
end of the surgical tubing. A small screw clamp was affixed to the
surgical tubing. With the stopcock opened on the burette, the screw
clamp was adjusted until drops of uniform size were discharged at a
convenient rate from the drip tip of the capillary. It was found that
during a citrimetric run (ca. .30 minutes) drops of water could be col¬
lected from this burette assembly which differed in weight by not more
than ±0.0002 g for drops averaging 0.0190 to 0.0230 g, provided the
tip of the capillary was wetted prior to drop size calibration. This
obviated the need to weigh the sample in the cell following each addition
of rrater; that is, it was necessary only to count the number of drops
collected in order to determine the total quantity of added water at
any given time during the titration.

RESULTS AND DISCUSSION
Synthetic Consideration
On the Preparation of Ligands. The pyridine alcohol carbenium ion
precursors employed as ligands in this work were found to be con¬
veniently preparable by the Grignard reagent synthetic routes, outlined
in the experimental section. It was discovered, however, that con¬
sistently better yields of product were obtained when the Grignard
reagent was prepared from 4-bromofluorobenzene followed by the addition
of the appropriate pyridyl ketone. That is, in attempts to prepare the
identical alcohol from a 4-fluorophenylpyridylketone and the required
phenyl-type Grignard, much poorer yields were got. These results suggest
that 4-brorcofluorobenzene Grignard was readily prepared in good yield as
a reactive intermediate and was a sufficiently potent carbanionic reagent
co attack the carbonyl carbon of the ketone. The difficulties encountered
in the alternate synthetic route leading to acceptable quantities of
product are attributed to the preparation in poor yield of the necessary
Grignard intermediate. This was particularly obvious in the case for
which 4-methyl phenyl Grignard or 4-methoxyphenyl Grignard were the
required earbanion. Thus, ketones prepared from these Grignards cou.ld
usually be obtained only in poor yield. None the less this \;as not a
problem of consequence since the desired material (the ketone) was
49

10
easiLy separated from the uareactcd starting materials. However, the
separation of alcohoL from parent ketone was very difficult, and it x^as
necessary therefore to convert ketone precursor to alcohol as completely
as possible in order to isolate the desired alcohol as a ketone-free
product. Thus, the preparative route for the alcohols employing 4-bromo-
fiuorobenzene Grignard was the better method.
The filter stick filtration technique employed prior to hydrolysis
|n the synthetic procedures for the preparation of alcohols facilitated
the removal of unreacted ketone from the reaction mixture. This technique
utilized the fact that the ketone — Grignard addition compound was
sparingly soluble in the ether solvent x^hereas the ketone itself v;as
moderately to readily soluble. Therefore prior to hydrolysis unreacted
ketone x^hich was dissolved in the ether layer could be drax-m off by
suction through the filter stick. Repeated washings of the reaction
mixture with fresh ether, followed by filter stick filtration, afforded
essentially complete removal of unreacted ketone.
On the Choice of Palladium(II). The most obvious reason for the incorpo¬
ration of palladium(Il| as the central metal species into the complexes
considered in this research is to permit a direct and immediate extension
upon the related work of previous investigators. Richardson (6) and
Wentz (8) both pointed out the suitability of palladium(II) to such
investigations oxrlng to its low oxidation state and high penultimate
d-oibitai occupancy. These factors would be expected to contribute
to metal stabilization of a coordinated carbenium ion via back donation
of petal 4d electron density into the a-framexv'ork of the carbenium ion
provided the ligand donor atom and carbenium ion carbon atom xjere both

51
meflSbets of ijb ligand w-system. The relative inertness of pa Had Him (XI)
complexes also suggests that such complexes would be amenable to these
types of studies. Finally, the diamagnetic nature of 4-coordinate
pal.ladiam(ri) stemming from its square planar complex geometry, makes
it convenient for nmr investigations on the stability of a coordinated
carbenium ion since no paramagnetic contribution to measured chemical
shifts would be observed.
On the Selection and Preparation of Complexes. The results of previous
investigations of bis palladium(II) complexes of ionizable pyridyi and
tMazoly.1 alcohols demonstrated the suitability of coordinated carbenium
ions derived from these complexes for thermodynamic stability studies
upon such ions. Therefore, the bis palladium(II) complexes were prepared
in order to enlarge the scope of earlier work through similar studies
upon carbenium ions derived from the fluorine-tagged pyridylmethanols.
The palladium(II) complexes containing but one ionizable ligand
molecule per complex were prepared so that a one-to-one relationship
could be established between a coordinated carbenium ion and the stabi¬
lizing effects exerted by the metal-containing moiety. Indeed, the
development of such a synthetic method would in itself be a novel
contribution to that area of preparative coordination chemistry embody¬
ing palladium(II) as the central metal species. This follows in that
there are known many "mixed" neutral complexes of palladium(I[) of the
type [Pd (II)XYL^L,2J , where X and Y are anionic groups, and and
aue neutral donor ligands. In none of these complexes, however, are
the L ligands pyridine homologs; rather they are usually donors which
cxnibit particularly strong r-acid character. Examples of those ligands

52
which ate usually found in these complexes are P& (R = alkyl or aryl),
CO, and various alkenes. Actually, work has been reported con¬
cerning the preparation of such mixed complexes wherein pyridine donors
•have been incorporated into the coordination sphere as neutral ligands,
but the bulk of this work has focused upon the use of platinum(TI) as
the central metal species.
In 1936 Mann and Purdie (24) reported the preparation of mixed
complexes of palladium(II) having the general formula [Pd(II)(Bu^P)(ara)-
C^] > where Bu^P is tri-n-butylphosphine, and am is either aniline,
pBtoiuidine, or pyridine. These complexes were obtained via the initial
preparation of the bi.nuclear chloride-bridged trans bis (Bu,,P) complex
I P¿2 (Bu0jP) 2^4] , followed by cleavage of the chloride bridges with the
required molar ratio of the amine of choice. However, an examination
cf the information cited in the experimental section of this article
revealed that accounts are given only for the preparation of the complexes
which incorporated aniline and p-toluidine as the nitrogen donors.
Investigations by Chatt and Venanzi (2b) in 1957 upon similar complexes
of p-illadium(II) again served to demonstrate that the neutral chloride-
bridged, binuclcar compounds could be converted to the corresponding
mononuclear complexes via rupture of the bridging bonds of the halide
ions with triphenylphosphine. The parent bridged materials had been
preparable with di-n-pentylamine or piperidine as the nitrogen donor
ligands Ln trans positions; but these workers reported that they were
• 101 able' to obtain the related bridged compounds using pyridine or
pyridine-containing ligands. Obviously, therefore, neutral mononuclear
complexes with pyridine in the coordination sphere had not been isolated
during these investigations.
In 1969 Chatt and Mingos (26) reported

53
che successful preparation of neutra], square planar, mixed, mononuclear
complexes of palladium(II) which had pyridine included within the
coordi.nation sphere of the metal. Again the synthetic route to these
mixed mononuclear materials relied upon the cleavage of bridging bonds
in binuclear precursors wherein the bridgixig species were either
chloride ions or p-toluenesulfinate ions. In 1975 Boschi and coworkers
(27) succeeded in preparing some neutral, square planar, mixed,mononuclear
complexes of palladium(II) with coordinated pyridine. They also employed
a chloride-bridged binuclear precursor [Pd^L^Cl^] wherein the neutral
L groups were aromatic isonitriles. Treatment of the bridged compound
with the required molar ratio of pyridine afforded the isolation, in
good yield, of the corresponding trans mononuclear complex. The results
of both of these studies (viz., Chatt and Mingos, and Boschi and co¬
workers) therefore indicated that a general route towards the synthesis
of mixed mononuclear complexes of palladium(II) which included pyridine-
type ligands required initially the preparation of a suitable halide-
bridged binuclear complex, followed by the rupture of the bridging
bonds with the selected pyridine donor(s).
So, in order to obtain the desired pyridine-containing, mixed
mononuclear complexes in this research, it was first attempted to
prepare the binuclear chloride-bridged dimeric materials [1121.2^14]
with the L groups as the pyridine methanols. This method depended upon
the direct combination of the mononuclear bis-a.lcohol complexes [PdL^C^]
2-
witli the complex anion [PdCl^j on a 1:1 mole basis with respect to
palladium. The bridged dimer, however, could not be obtained by this
method. Therefore, the chloride bridged complex I phc.ny 1 phosphine (Ph^P) ligands incorporated as the neutral I. groups was

54
pr pared according to the method outlined by Chatt and Venanzi (25).
The- Ph.,? was employed because of its structural, similarity to the pyr~
icly lute than© Is. This bridged material, which was a red-brown solid,
was slurried in refluxing acetone and treated with 4-pyridyl-4-fluoro-
phenyImethanol (4-pyLOH) on a 1:1 r.ole basis with respect to palladium.
An reflux was continued (ca. 3 hours) the bridged material dissolved
and a yellow solution resulted. When this solution was saturated with
n-pentane a pale yellow crystalline solid settled out. Characterization
of this solid indicated that the desired mixed mononuclear complex
[Pd(II)(Pb^P)(4-pyLOH)Cl^] had been obtained. This result suggested
that the problem of preparing the mononuclear mixed complexes containing
the pyridine alcohols had been solved. However, when this material was
treated with 70" HCIO^ for the purpose of carrying out stability in¬
vestigations upon, the "coordinated" carbenium ion it was discovered that
the coordinate bond between the ionized pyridine alcohol and the palladium
metal center was quickly ruptured (ca. 5 minutes or less). It was pre¬
sumed that this bond breaking was a consequence of the effective trans
labilizing effect exerted by the strong TT-aci.d ligand, triphenylphosphi.ne.
This result therefore dictated the necessity to prepare the mixed mono¬
nuclear complexes with a neutral, nonionizable counter ligand, which
would not exhibit particularly strong ir-acid behavior in these complexes.
The selection of 4-pyridyldiphenylnethane as an appropriate counter
ligand was clearly a good choice. This is attributable to the structural
comparability of the alkane to the pyridine alcohols, and to the antic¬
ipated similarity in chemical behavior of the alkane to pyridine it¬
self. Thus, the problem at hand was the development of a synthetic
procedure through which a molecule of the alcohol as well as a molecule

op the allot no could bo. systematically introduced into the coordination
Sphere of the metal in the mononuclear complex. The following con¬
siderations were pertinent: 1) The inability to prepare the chloride-
bridged binuclear complexes containing pyridine donors in trails positions
¡ Pd9 (pyLOH) jjCl ] (vide supra) ruled out the use of such a material as
a precursor. The bridging bonds in this dimer would presumably have
been susceptible to attack by the "second" pyridine donor thereby
yielding the mixed pyridine mononuclear complex. 2) In view of the
anticipated similarity in donor character of the pyridine alkane to the
pyridine alcohols there appeared to be no method by which these two
pyridine ligands could be added directly to the palladium metal center
in the required stoichiometric ratio.
The synthetic finds of Goodfellow, Goggin, and Duddell (25) provided
reasonable prospects for the preparation of the desired complexes. These
workers recognized that there are many complex anions of the type
[Ft(II)LCl^] (L = CO, NO, NH^, or pyridine; references for the
preparation of this complex anion with these respective ligands are
cited in this article) v7hich are well known. They discovered that such
complex anions were also preparable with L as PR^, ^2’ or ^ =
alkyl or aryl), and that a similar series of complexes (excluding
pyridine) was preparable as well with palladium(II). This was the first
general account given for the successful preparation of such types of
complex anions of palladium(II). The usual synthetic route which these
workers employed was characterized by refluxing the chloride-bridged,
binuclear material [P^L^Cl^], M equals Pt(EI) or Pd(II), with the re¬
quired stoichiometric quantity of tetra-n-propylammonium chloride in an
inert organic solvent such as dichloromethane. The complex anion which

was Cocmetl upon rupture of the chloride bridges was apparently stabilized
in solution by the large tetraalkylammonium counterion. The complex
|man was found to be isolable as the tetraalkylammonium salt via treat¬
ment of the dichloromethane reaction mixture with excess ether which
resulted in crystallization of the desired product. The salient aspect
of this preparative method is that it permitted the controlled inclusion
of a particular neutral ligand into the coordination sphere of the metal
acorn. However, as previously indicated, this particular method was not
directly applicable to the situation involving the pyridine donors
since the necessary bridged precursors with trans pyridine donors had
not been prep-arable. Nevertheless, further considerations paralleling
this synthetic approach were certainly warranted in that this technique
served to reinforce the possibility of being able to investigate stabil¬
ity relationships between the metal center and a singly charged co¬
ordinated pyridine carbonium ion provided [Pd (II)LCl-j] complex anions
of the pyridine alcohols could be prepared.
Goodfellow, Goggin, and Duddell had also reported the preparation
of the anionic complexes [Pd (II) (G^H^Cl^] , and [Pd(II) (CO)Cl^] , by
2-
reacting the binuclear anion [Pd7Cl,.] with the required molar quantity
of the neutral ligand in the presence of tetra-n-butylarrunoniun ion
using cls-1,2-dichloroethylene as solvent. Again treatment of the
reaction mixture with excess ether induced the separation of the desired
product as a crystallines solid. Infrared spectroscopic investigations
by Adams and coworkers (29) also served to indicate the potential use-
2-
fulness of the binuclear anion [Pd9Cl^] as a precursor to mononuclear
complexes of palIndium(IT) of the type [Pd(II)LCl^] by demonstrating

57
that the force constant for the terminal metal-halide stretching
vibration was greater than that for the bridging metal-halide vibra-
2-
tl.on. Thus, it would be expected that the dimeric anion [Pd0Cl,]
l o
would be attacked at the bridging positions by incoming ligands.
It appeared, therefore, to be reasonable to treat polychloropalla-
uate(IT) anions with the pyridine alcohols in an appropriate solvent in
the presence of tetraalkylammonium cations with the anticipation of sus¬
taining the stability of the [Pd(II)(pyLOH)Cl^] complex anions. In
conjunction with this, palladium chloride powder was stirred in re¬
fluxing acetone with tetramethylammonium chloride (tMACl) on a 1:2
mole basis. A red-orange solution initially resulted as the solids
began to dissolve, but as reflux was continued the color of the solution
disappeared and a salmon-colored solid separated. This solid was slur¬
ried with 4-pyridylpheny3ra4-fluorophenylmethanol in refluxing solvent but
no additional change occurred. Nevertheless, the incipient formation
of the red-orange solution indicated the presence of a solution-stable
chloroanion of palladium(II). Further investigations indicated that
2-
the solution-stable species was [Pd0Cl,l and that the salmon-colored
/ b
solid was the acetone-insoluble salt [(tMA)^PdCl^]. Thus, the nature
of the palladium(II) polychloroanion was dependent upon the concentra¬
tion of the ammonium salt. Studies by Henry and Marks (30) upon
glacial acetic acid solutions of palladium(II) in the presence of
various alkali metal chlorides served to indicate that with readily
2_
soluble chlorides such as LiCl, [PdCl^] was the commonly encountered
palladium(II) anion, whereas with moderately soluble chlorides such
2-
as NaCl, the binuclear species [Pd^Cl^] ' was got. Therefore, it
appeared that regulation of the tetraalkylammonium chloride concentration

afforded a method by which the nature of the paliadiuin(TI) poiychloro-
rjnion could be controlled. The combination of palladium chloride
powder with tMAGl (1:1) in refluxing acetone did in fact yield complete
dissolution of all solids and a stable red-orange solution. Treatment
of this solution with a typical 4-pyridylmethanol (1:1 with respect
to palladium) again resulted in the separation of a salmon-colored
precipitate [(tMA)9PdCl^] and a yellow solution. Workup of the yellow
solution yielded the bis-alcohol complex [Pd(II)(pyLOH)2^-2!* Thus,
the tMA cation did not appear to be capable of stabilizing the desired
anionic mono-alcohol complex regardless of the nature of the polychloro-
paliadate(II) precursor.
Palladium chloride powder was then combined with tetra-n-butyl-
arnnonium chloride (1:1) in refluxing acetone again resulting in the
dissolution of all solids and a stable red-orange solution. Treatment
of this solution with a typical 4-pyridine methanol (1:1 with respect
to palladium) induced an immediate color change in the solution from
red-orange to yellow-orange with the separation of no solids. Workup
of this solution (see Experimental p. 40) revealed that the desired
anionic complex [Pd(II)(4-pyLOH)Cl^] had been obtained. Further
studies showed that this anionic complex was readily converted to the
desired mixed, neutral, mononuclear complex by treatment (1:1) with
the 4-pycidyl alkane in acetone solution (see Experimental pp. 38-40).
(Note: During the course of this research all synthetic procedures
involving palladium(II) were run using acetone as solvent. There are
many standard methods for the preparation of complexes of palladium(II)
employing alcohol (usually methanol or ethanol) as solvent, but in this
work it was discovered that in the presence of alcohol pallndiura(TI)

59
was frequently reduced to palladium black. Ho similar difficulty was
encountered with acetone.)
On the Suitability of 4-Pyridyldiphenylmethane as a Counter!igand in the
Nixed Complexes. As reported previously (see Experimental p. 33) the
commercially obtained alkane was found to be contaminated with trace
quantities of the corresponding 4-pyridyl alcohol. To be sure that
the alkane was not converted to the alcohol (carbenium ion) via oxida¬
tion in 70% HCIO^. a solution of the purified alkane in the acid was
stirred at ambient temperature in the open environment of the laboratory.
After stirring for a period of 2 hours this solution was scanned in the
visible region of the spectrum and was found to be transparent. There¬
fore no complications were expected to arise during thermodynamic
studies upon complexes which contained the alkane since all such mea¬
surements were made within a 2 hour time span.
The similarity in donor behavior of the alkane to the 4-pyridyl
alcohols was demonstrated by the preparation of the anionic complexes
fPd'LCl^] (in situ) with either the alkane or the alcohol, followed by
conversion to the mixed complex. Thus, the mixed complexes were
preparable independent of the order of addition of the respective pyr¬
idine donors.
Finally, a small sample of mixed complex (any) was triturated in
70% IICIO^ for a period of ca. 1 hour. The acid was removed by filtra¬
tion and the residue was washed with deionized water and dried. An IR
scan of the residue revealed it to be of the same constituency as the
original mixed complex. This indicated that both pyridine ligands re¬
mained coordinated during thermodynamic stability investigations and

GO
again demo Lir.tr a ted Che suitability of 4-pyridyidi phcnylmethane as an
appropriate counterligand. When the complex [Pd(II)(Ph^P)(4-pyLOH)Cl?]
had been treated in a similar fashion (1.e., triturated in 70% HCIO^)
j t v/as found that the pyridine ligand (carbenium ion) was discharged
from the. complex (p. 54).
Concerning Carbenium Ion Salts. Various synthetic routes are available
for the preparation of stable salts of trityl-type carbenium ions (see,
for instance, the methods given in the papers by Sharp and Sheppard
(31), by Dauben et al. (32), or by Olah et_ aJL. (33)). It may certainly
prove to be interesting and profitable to investigate the stability of
the. free and complexed carbenium ions which have been dealt with in this
work as discrete salt-like species in aprotic, nonrcactive solvents.
Current considerations however, have exclusively involved the use of
70% IlC10^ as an ionizing medium in order to provide a direct extension
to previous work upon trityl-type carbenium ions derived from the
pyridyldiphenylrnethanol s.
Thermodynamic Investigations and Measurements
Electronic Spectra and Carbenium Ton Constitution and Structure. Con¬
siderable work has been done on the electronic, spectra of trityl-type
carbenium ions Ln the 200 — 750 nm (50.0 — 13.3 kK) spectral region.
The majority of this work, however, has been focused upon the transitions
exhibited by these ions in a rather limited portion of this region,
vis. 300 — 550 nm (33.3 — 18.2 kK), because the electronic bands found

01
hete are those which are characteristic solely cl the carbenium loa.
'he higher energy transitions (50.0 — 33.3 kK) exhibited by these ions
are normally present in the spectrum of the precursor molecules (i.e.,
tertiary alcohols) and are characteristic of the electronic absorptions
of the isolated conjugated systems which are bound to the carbinol
carbon in the unionized alcohol. Previous electronic absorption studies
on these types of ions (e.g., Richardson (6) and Wentz (8)) including
similar studies performed during the course of this work have demon¬
strated that the higher energy (ultraviolet) spectral region of these
alcohols remains virtually unchanged for a given alcohol independent
of the nature of the solvent. Thus, the significant electronic changes
which occur ju these systems upon carbenium ion generation are not
directly reflected by these higher energy transitions. The dramatic
changes which do take place in the electronic spectrum of these alcohols
upon ion formation are illustrated by the development of two intense
A 5 _;]
(e ca. 10 — 10 liter mol cm ), broad absorption bands ordinarily
max —
appearing between 300 and 550 run. This spectral region is transparent
for the alcohols dissolved in a nonionizing solvent, e.g., acetone,
alcohol, or 1 M HCIO^. The extreme intensities of these bands are ex¬
pected for strongly allowed n +- rr charge transfer type transitions.
As pointed out by Dunn (34) based upon considerations of the classical
theoretical work of Mulliken (35) on electronic spectroscopy, the
intensity of a charge transfer band is expectably large since the
charge transfer phenomenon occurs over at least one interatomic dis¬
tance in the absorbiirg species. Thus, the radius vector (r) of the
transition is relatively large. Since the magnitude of the transition
moment integral is directly proportional to r, and in turn directly

62
proportional Lo r.he oscillator strength (jf) of the transition, f rniist
¿•l.se be large. Hence, the intensity of the transition is considerable.
The general positions of these trityl-ion charge transfer bands have
beer, rationalized by considering that alcohol ionization is accompanied
by the conversion of the system from a quasi even-alternant benzene
hydrocarbon to an odd-alternant, fully conjugated benzene hydrocarbon.
According to various workers (see, for instance, Deno e_t al. (36))
based on simple LCAO HO calculations this transformation introduces a
zero energy (nonbonding) m-symmetry orbital into the molecular orbital
scheme of the previously unionized alcohol intermediate between the
highest energy filled vr-orbitals and the lowest energy unfilled tt*-
orbitals. Thus, the energy of the longest wavelength (lowest energy)
electronic transition observed for these ionic species should be on the
order of half the energy of the longest wavelength transition exhibited
by benzene, the model compound. Since the wavelength of this transition
for benzene is 256 nm it is expected that the longest wavelength electron¬
ic transition of the trityl-type ions would appear in the vicinity of
512 nm. As pointed out by Richardson (6:153) the rather inexact nature
of this treatment is revealed by the fact that the longest wavelength
electronic absorption exhibited by triphenylcarbenium ion is 431 nm
(in 96% H^SO^) which is at considerably shorter wavelength than that
predicted from the benzene model.
A.n eclectic account of previous investigations upon the electronic
nature of arylearhenium ions reveals that extensive considerations have
been made, but that these considerations are not without certain per¬
plexing aspects. In 1932 Schoepfle and Ryan (3?) reported that the two
s-bstances, triphenylchloromethane and methyldiphenyIchloromethane, yield

essentially the same visible spectrum when dissolved Ln dj.ch.loroethylene
in the presence of stannic chloride. This prompted Newman and Deno (38)
to conclude that this was evidence indicating that in triarylcarhenium
ions no mote than two (and perhaps just one) of the aryl rings could
simuitaaeouHly participate in resonance interactions with the carbenium
ion center (the cxocyclic carbon atom). Completely synchronous resonance
stabilization of a triarylcarbsnium ion involving all of the aryl rings
would of course require an all-planar molecular ion configuration of
symmetry. Lewis eh. a^. (39) had already reported as a consequence of
studies on crystal violet ion (tris-(dimethyl-jj-aminophenyl)-methyl ion),
that the. all-planar configuration of the ion is not possible owing to
steric. interactions between the ortho hydrogen atoms on the phenyl rings.
These workers had speculated on the existence of two isomers of the ion
having structures akin to a symmetric and an asymmetric propeller wherein
the phenyl rings were the blades of the propeller. The presence of two
intense bands in the electronic spectrum of crystal violet ion supported
the proposal that each of the two isomeric forms of the ion was a distinc
chromophoric system. Additional evidence cited by Newman and Deno which
suggested the structural uniqueness of trityl-type ions was the following
Tri-o-tolylcarbenium ion was reported to be as stable as tri-p-tolyl-
carbenium ion and to exhibit essentially the same electronic spectrum.
TJiis was an unexpected result owing to the considerably greater degree
of inhibition towards ring resonance stabilization of the ion anticipated
for the tri-cv-tolyl ion as a consequence of steric iv>teractiou between
the cx-methyl groups. Also, van' t Hoff i-factor data on solutions of tri-?.
g-dimethylaminophenylcarbinol in 100% indicated that even in this
strongly acidic medium one of the _p-amino groups was not protonated.

64
This suggested that only one of the rings was involved substantially in
resonance: stabilization with the cation center. Other investigations
i'/ Newman and lleno on the electronic spectra of various carbenlutn ions
revealed that the observed band positions were sensitive to changes in
phenyl ring substitution. Attempts to rationalize these band shifts
premised mainly on resonance considerations were inconclusive, further
attempts to rationalize the observed differences in band intensity and
position in the electronic spectra of various series of related aryl-
carbenium ions by Deno, Jaruzelski, and Schriesheim (40), met with
limited success. These workers discovered a systematic spectral trend
characterized by an increase in X as well as in band intensity re-
suiting from, singular substitution of any of the groups, -NCCH^)^, -NH ,
-OCH^ or -Cl, into the para position on one of the phenyl rings in
triphenyicarbcrpum ion. The trend appeared to coincide with expecta¬
tions contingent upon simple extension of the x-electron donating, con¬
jugated system of the substituted cation relative to the triphenyl ion.
However, successive para substitution of these groups on subsequent
phenyl rings in a given ion resulted in discontinuous shifts in v and
max
in molar absorptivity. In 1954, Branch and Walba (41) studied the
electronic spectra of various para-aminotriphenylcarbinols in 96% I^SO^.
They reported that each of the carbinols which was converted to its
corresponding carbenium ion upon dissolution in the acid exhibited two
intense bands in the visible region of the spectrum which had not been
found to be present in the spectrum of the parent carbinol. It is
interesting to note, however, that these workers reported no such bands
for tr.i-p-dimethylaminophenylcarbinol in the acid and concluded in this
instance that: carbenium ion formation had not occurred (cf. the results

oí Ncwmaft and Deno (.above) with respect to their investigations on this
particular carbinol). Branch and Walba also isolated a trend in band
position shifts from their data. They rationalized that increases in
resonance stabilization of a given carbenium ion resulted in an increase
in the frequency of the band associated with that particular carbenium
ion chromophora. The simplest example of their consideration is illus¬
trated by comparing the relative positions of v for the ionic species
max
(C.Iic)„GK+ and (C.H,-)0C+ wherein v (diphenyl ion) < v (triphenyl
6 5 2 653 max max J
ion). Branch and Walba had attributed this absorption to the (C^-H,.)
chromophcre. Thus, these workers concluded that resonance stabilization
of the (Ci.llc.)^C 3 chromophore in the trityl ion by the presence of the
"third" phenyl ring resulted in a blue shift of v . Branch and Walba
max
also contended that trityl carbenium ions exhibited two visible region
absorption bands (instead of but one) because of two carbenium ion con¬
taining c.hromophores believed to exist in the sterically hindered parent
ion. This was in basic agreement with similar considerations made
previously by Lewis e_t all. (39) . Related studies in this area by Evans
and coworkers (42) provided evidence pointing to the existence of a
relationship between band intensity and resonance interactions in tri-
arylcarbenrum ions. These investigators reported that para substitution
of a given group on a phenyl ring in tripheny.lcarbenium ion resulted in
a notable increase in a for the main absorption band of Chat particular
ion, whereas the corresponding ortho substitution of the same group
resulted in a marked decrease in e for the same band.
Studies ty Dehl el^ al. (43), and by Dcno et al. (36) served to in¬
validate a number of the earlier arguments concerning the interpretation
oF the electronic spectra of trityl carbenium ions. Dehl et al.

60
concluded from pmr Investigations on various deliberated triphenyl-
carbenium ions that the three phenyl rings in the cationic aggregate,
were equivalent. This result suggested that analyses of the electronic
spectra of such ions would require the attribution of any trityl car-
beaium ion chromophore to the ion as a whole, therefore denying the
possibility of simultaneous existence of two (or more) chromophores in
the molecular framework of the ion. Deno et^ al. performed simple LCAO
MO calculations on aryl cations and found that the results of these
calculations predicted identical v positions for the principal elec¬
tronic absorption exhibited by related mono-, di-, and triaryl cations.
Thus, inhibition of resonance in a sterically hindered carbenium ion
would still leave v (calculated) unchanged. Also, these calculations
max
indicated that the intensity of the principal absorption for such ions
is ir.variaut to phenyl ring rotation (due to steric interaction). Hence,
these authors concluded that electronic absorptions exhibited by such
ions could not be used as a measure of steric inhibition to resonance
interaction existing within the ion. In yet a later article, Deno (44)
has again pointed to the irresolute nature of the situation in commenting
that much of the work on the electronic spectra of arylcarbenium ions
still requires revision. Olah et al. (45), as well have concluded that
there is a great deal of uncertainty in the literature citations con¬
cerning the visible and ultraviolet spectra of carbenium ions. Interest¬
ingly enough, however, in order to rationalize some of their results
these workers employed the notion that in a sterically crowded triaryl-
eerhenium ion only two of the aryl substituents are part of the absorbing
chromophore, while the third functions as a cross-conjugating electron
donor or acceptor moiety. So, once again the possiblity of the existence

67
of multipJe cliromophores in trityl-type carbeniun ions is considered,
'bus, as late as 1966, many of the problems resulting from unsatisfactory
interpretation of the. electronic spectra of carbenium ions remained.
To a large degree, recent investigations in this area rely heaviLy
upon molecular orbital treatments of the electronic structure of aryl-
arbenium ions. Streitwicser (46:226-230) has shown that in the 1IM0
approximation the lowest energy transition exhibited by triphenyl-
carbcnium ion can be considered to he associated with the passage of
an electron from the highest occupied bonding MO to the vacant nonbond-
i.ng MO in the odd-alternant hydrocarbon created upon cation generation.
To a first approximation the energy level diagram associated with this
transition is the same as for the benzyl cation. Various, more sophisti¬
cated MO treatments (46:360-362) however, reflect the complex and imbro¬
glio tic nature of this approach to the problem by calculating rather
grossly different charge densities for the ir-framework carbon atoms in
the ground state of the trityl ion.
By employing MO and resonance theory Waack and Doran (47) attempted
to correlate the effects of methyl group substitution in odd-alternant
anions with the resultant band shifts of the main absorption hands
found in the electronic spectra of these ions. They noted that this
type of substitution (i.e., methyl or alkyl) on an even-alternant hydro¬
carbon had - - in the absence of steric affects - - always induced a red
shift in the electronic conjugation bands, whereas similar substitution
on a nonalternant hydrocarbon had induced cither a red or blue shift
depending upon the site of substitution. They reported spectral
changes for the odd-alternant anions to be similar to those for the
nonalternants and experienced qualitative success in applying the

Jefiat-lts of their calculations to the prediction of the spectral behavior
Of odd-alternant ions. A particular highlight of this effort was the
prediction that «--alkyl substitution on an odd-alternant cation would
result in a blue shift of which is in agreement with reported data.
A rather comprehensive MO treatment by Grinter and Mason (48) yielded
a symmetry-based energy level diagram for structurally comparable aryl-
rrictbyl ions. An examination of this energy level diagram revealed that
the longest wavelength, lowest frequency transitions for a related bis¬
and trisarylnethyl ion pair should be approximately identical (¿f. the
conclusions reached by Deno ert aJL. (36)). However, stemming from more
acute considerations, these authors showed that the ground state
charge stabii izati.ion of a given triaryl ion was greater than that for
the corresponding bisaryl ion (recall the conclusions of Branch and
Wfilba (41), pp. 64-65). Thus, the highest occupied bonding MO's for
the trisaryl ion were somewhat lower in energy than the related MO's
of the bisaryl ion, and therefore, the longest wavelength transition
of the trisaryl ion was of slightly greater energy than the correspond¬
ing transition for the bisaryl ion. The dual nature of the visible
region absorption envelope of the trisaryl ions was also considered by
Grinter and Mason. Their explanation ran as follows. Tn the point
group "C3" (following from the anticipated propeller shape of these
ions) the highest bonding MO's of the trisaryl ions are "five-fold
degenerate," with the attendant symmetries e, e, and The MO's of
the first excited state(s) are likewise five-fold degenerate, and are
of a.p a^, a3, and e symmetries. Again, provided that the ion is
propeller shaped, transitions to the 'and 'E excited terms are
allowed and should be polarized parallel and perpendicular respectively,

69
co che. principal three-fold symmetry axis of the ion. This appeared to
be in basic agreement with similar considerations which had been made by
Lewis and Bigele.isen (49) on the phenomenon of polarization upon the
transit:ions in the electronic spectrum of crystal violet and malachite
green. Thus, Grinter and Mason concluded that two low energy transitions
of high intensity are expected (and are found) for such ions. (It is
here appropriate to point out that results of newer studies on the elec¬
tronic absorption spectra and magnetic circular dichroism (MCD) of tri-
phenvlcarbenium ions have suggested refinements of certain of the con¬
siderations made by Grinter and Mason. Mo eh: al. (50) found three MCD
bands in the near UV, visible spectrum of triphenylc.arbe.nium ion. This
result indicated the existence of three electronic transitions in this
spectral region for trityl-type carbenium ions whereas only two such
bands were proposed to exist by Grinter and Mason. Dekkers and Kielman-
van Luyt (51) in fact have stated that MO theory does predict three nearby
singlet -a singlet transitions for a triaryl ion of symmetry. Two
of these three transitions are to excited states of e symmetry and are
polarized in the x,y-plane of the ion. (This plane is defined for an
assumed coplanar arrangement of the aryl rings and the exocyclic carbon
atom. Thus, the aryl rings are perpendicular to the principal symmetry
axis of the molecular ion, the z-axis.) The third transition, however,
which is to a state of a^ symmetry and z-polarized, would not be observed
rf the cation were completely planar. Since the cation is propeller¬
shaped and not planar, this transition is observed (at slightly higher
frequency than the higher energy intense band), but it is considerably
weaker than either of the highly allowed transitions to the e states.
It is also noteworthy that these investigators were not able to resolve

70
the two c state transition! which are observed to overlap rather severe¬
ly (maxima are at 23.2 and 24.6 kK respectively with a reported e of
33,700 tor each band (45)). This suggests an inherent relationship
between the electronic states in the ion from which these two bands
originate. Consequences of this implication concerning the chromo-
phoric nature of triarylcarbenium ions lie in the forthcoming text,
vide infra.
It is now interesting and profitable to examine the. wave functions
for the molecular orbitals which were considered by Grinter and Mason
to correspond to the energy levels which arise upon generation of a tris-
arylmethylcarbenrium ion. The forms of these wave functions are:
’’’'i = a<’c +
^ . , + if;
aryl Yaryl aryl
(5)
n
= (’-7 i - ^ , ,) / /2
aryl Yaryl
(6)
and
l^TT, = (\p 1 + \¡) - , - 2l¡) Tli)/^
YII Yaryl Yaryl’ Yaryl
{7}
where <¡> is the wave function of the 2p state of the exocyclic carbon
atom. The functions represent the highest occupied bonding states
of the ion, and their forms indicate that the bonding contribution of
the "third" aryl ring ('l’aryj_n) is °f principal significance in •
(Note: The basic forms of these wave functions are virtually identical
to the corresponding wave functions used in the calculations by Dekkers
and Kidman-van I.uyt (51) ) Since the degeneracy of the i!; functions

71
has been removed co an appreciable degree by virtue of the nonplanarity
oi ihe ion (48) and by configuration interaction effects (46:227), (51),
.it follows that only one of the long wavelength, low energy transitions
should reflect significant electronic contributions to carbenium ion
stability (or instability, as the case may be) by the so-called "third"
ring which is denoted above as aryl" in equations {5} arid {7}. This
consideration is given additional substance from the results of various
investigations. Barker and coworkers (52) studied the electronic spectra
of derivatives of malachite green produced by substitution in the "non-
anilrno" phenyl ring. They showed that the longest wavelength absorption
band, recorded for each derivative reflected primarily a flow of electrons
from the two para-N,N-dimethy1 substituted rings towards the exocyclic
carbon atom. This is in keeping with MO calculations which have estab¬
lished that this carbon atom bears the principal degree of positive
charge in the ground state of the ion (53), (an expected result). There¬
fore, replacement of the para-N,N-dimethyl groups with poorer electron
releasing substituents resulted in a blue shift of v . These workers
max
also demonstrated the existence of a linear relationship between the
appropriate Hamnett constant for the phenyl ring substituent and the
magnitude of shift in v induced by that particular substituent. Thus,
a type of cross-conjugation seems to exist between the phenyl ring and
the remainder of the conjugated system with respect to the energy of
the longest wavelength transition. The results of studies by Hopkinson
and Wyatt (54) concerning substituent effects upon the electronic ab¬
sorption; of phenolphthalein nonopositive ions (Figure 5) allowed these
â– workers to conclude that v of the second longest electronic transition
max
exhibited by these ions reflected primarily a shift in electron density

72
fTiirn the "third'1 ring towards the exocyellc carbon atom. In phenol¬
phthalein this "third" ring is the ring to which the ortho-carboxylic
acid group is attached. Hopkinson and Wyatt also compared the elec¬
tronic absorption spectra of phenolphthalein and phenolsulphonphthalein
and observed a considerable blue shift of the second band for the
"eulpho" containing pnthalein. This was expected owing to the apprecia¬
ble electron withdrawing power of the sulphonie acid group. These results
were corroborated via extended HMO calculations to resolve the electronic
effects which arise from para-substitution of Tr-eleetron donating groups
on two of the phenyl rings in triphenylearbeniun ion. Furthermore, the
results of these calculations were found to be in agreement with the
results of the HMO calculations which had been carried out by Mason and
Orinter (48). These calculations also verified that such substitution
of Tr-el&ctron donating groups served to remove still further the de¬
generacy of the two highest occupied MO’s in triaryl-type earbenium
ions (see p. 70) with the higher energy occupied MO acquiring a greater
R
- -C00H
R*
" -CH3’
-Cl,
-hr,
e tc
R"
= -ch3,
-Cl,
-Br,
etc
Fig. 5.
Phenolphthalein monopositive ions

73
•n-eloctron contribution from the rings which hear the more potent elec¬
tron releasing substituents. Consequently, the conclusions reached
which qualitatively associate the two principal electronic absorptions
of criarylcarbenium ions with the MO's from which these transitions
originate (p. 70) have been upheld. In addition, Hopkinson and Wyatt
also isolated from their spectral data a linear variation between
Hammett c-meta substituent constants and shift magnitudes of the higher
energy electronic band produced upon the. substitution of groups ortho
to the ring hydroxyl groups in phenolphthalein. Thus, whereas the
results obtained by Barker and coworkers (52) indicated a cross-con¬
jugation effect to exist upon the frequency of the lower energy band
and the "third" aryl ring, Hopkinson and Wyatt showed a similar effect
upon the frequency of the higher energy band by the two rings in a
given triaryl-type carbenium ion which are the primary (as compared
to the remaining ring) r-electron donating moieties.
Finally, it is still not clear whether the high intensity electronic
absorption bands exhibited by triarylcarbenium ions may or may not be
considered rigorously as charge transfer transitions! This concern is
not crucial to the considerations made in this work; but for complete¬
ness a few remarks shall be tendered. Initially, in this discussion of
electronic, spectra, it was assumed rather tacitly that these electronic
bands arc charge transfer in nature (pp. 61-62). However, these ab¬
sorptions do not meet with certain of the criteria (55) which have been
«employed for classifying electronic transitions as "charge transfer."
Couch (56:65-66) for instance, has pointed out that the factors tending
to indicate charge transfer interactions in monoaryl tropylium ions

71
(pFbvud by Couch to exhibit intramolecular charge transfer) are either
not present, or are opposite, in monoe.rylcarbenium ions. Furthermore,
related studies by Couch (57:113-122) have suggested that triarylcor-
beriiur.i ions as well do not exhibit bona fide charge transfer interactions.
L'aubcn and Wilson (58) have at last demonstrated the existence of au¬
thentic charge transfer interactions for systems containing triaryl-
caubenium ions. They accomplished this via the preparation of various
pyrene-triarylcarbenium ion complexes wherein the coordinated carbenium
ion was found to function as a particularly potent ir-acceptor. The
electronic spectrum of any of these complexes gave a very intense band
at relatively low energy (viz. 14.1 kK for coordinated triphenylcarbenium
ion) which was not present in the spectrum of either component. These
results imply that the existence of a "true" charge transfer inter¬
action in a system requires an appreciable shift of electron density
from a specific location in the ground state of the parent molecule
(ion, etc.) to a new (and removed) location in the excited state.
Perhaps then, it is in fact not extremely unrealistic to treat the
principal electronic absorptions of arylcarbenium ions as charge trans¬
fer. Ramsey (55) has alluded to this assumption by suggesting that a
charge transfer transition in a triarylborane can be associated with
the promotion of an aryl ring ir-electron into the empty available £
orbital on the boron atom. Similarly, since the results of various
studies on the electronic spectra of arylcarbenium ions have associated
the main absorption bands with transfer of aryl ring m-electron
density to tire exocyclic carbon, those transitions may, at least broadly,
be categorized as charge transfer. Arguments contrary to this classi¬
fication can be registered based upon degree of charge transfer. For

75
Instance, work by Olah et al. (59) on the pmr and F nmr spectra of
an 1 ifluorccnrbeciura ions has demonstrated that the degree of charge
delocalisation into the aryl rings in these ions is substantial. Thus,
electronic ground state charge delocalization in these ions appears
to be considerable. Extended HMD calculations (54), however, have
indicated an appreciable difference in carbon atom charge densities
between the ground and first excited states in arylcarbenium ions.
Let it suffice, therefore, to say that this aspect of arylcarbenium ion
electronic spectral investigations remains largely a moot issue.
An examination of the electronic spectra and attendant data collected
during this \7ork is now in order. Examples of electronic spectra ob¬
tained for carbenium ions derived from a related series of compounds,
namely pyLOH, Pd(Tl) (pyLOH) (1^)01^, and Pd(II) (pyLOII)£^12 (w^ere pyLOH
equals 4-pyridyl-4-methylphenyl-4-fluorophenylmethancl, and equals
diphenyl-4-pyridylmethane) , have been presented in Figures 6 — 8, p. 7(5.
As these spectra are representative of all electronic spectra recorded
for the carbenium ion species considered herein, no other electronic
spectra are presented. Pertinent electronic spectral data are given
in Table II, pp. 77-78).
The carbenium ion electronic spectra obtained in this work are
found to be very similar to the related spectra (in the same spectral region)
which have been reported by previous investigators (Richardson (6) and
Wentz (8)). An examination of these spectra reveals the presence of two
broad, intense absorption bands located within the 33.3 — 18.2 kK range.
The lower energy band found in the spectrum of a given carbenium ion is
always the more intense. The e values reported in Table II indicate

76
1.0
A 0.5
0.0
A
A
33.3 28.6 25.0 _ 22.2 20.0 18.2 17.4
v (kK)
Fig. 6. Visible spectrum of the carbenium ion derived from 4~pyridyl-4-
methylphenyl-4-fluorophenylmethanol, in 70% IICIO^. v , 20.2,
?q 7 max
i.o tlii:
a ~ —
33.3
Fig. 7.
0.0
33.
J
28.6 25.0 _ 22.2 20.0 18.2 17.4
V (kK)
Visible spectrum of the carbenium ion derived from Pd (II)(pyLOH)
(Ljj)C12> where pyLOH is 4-pyridyl-4-methylphenyl-4-fluorophenyl-
nethanol, in 70% HCIO^. vna:., 20.6, 27.6.
28.6 25.'o _ 22.2 20*.0 18.2 17.4
v (kK)
Fig. 8. Visible spectrum of the carbenium ion derived from Pd(II)(pyLOH)2
CI2, where pyLOH is 4-pyridyl-4-methylphenyl-4-fluorophenyl¬
methanol, in 70% HCIO4. 57 , 20.6, 27.7.
5 max

Table II
Electronic Spectral Data for the Various Carbenium Ion Species, in 70% HC10, at 23"
Catbenium Ion Precursor X (nm) V (kK) e x 10 ('1 mol cm-1) Cation Color
m3X (in 70% PX104)
x-band
y-band
x-band
y-band
x-band
y-band
a
Alcohols: 2-pyLOII =
2-pyridyl~R-4-fluorophenyl-
methanol
R = -phenyl
490
371
20.4
27.0
(2.73)
(1.32)a
orange-pink
R - -4-mathylphenyl
507
373
19.7
26.8
4.56
1.75
red-pink
R = -4-methoxyphenyl
505
361
19.8
27.7
5.87
2.30
red-orange
Alcohols: 4-pvLOH =
4-pyridyl~R-4-fluorophenyl-
methanol
R = -phenyl
482
340
20.7
29.4
4.21
1.34
pale yellow
R = -4-methylphenyl
496
337
20.2
29.7
3.58
1.93
orange-pink
R = -4-methoxyphenyl
495
337
20.2
29.7
3.58
1.09
orange-pink

Table II
Extended
Carbenium Ion Precursor \ (nm) V (kK) c x 10 ^ (1 mol cm Cation Color
maX (in 70% rlCiO.
.. i j .. i ... , j .. i 4'
x-band
y-band
x-band
y-band
x-band
y-band
Complexes
: Pd(II)(4-pyLOH)
R =
-phenyl
471
357
21.2
23.0
-
b
pale yellow
R -
-4-methylphenyl
485
362
20.6
27.6
(2.28)
(1.12)C
yellow-gold
R =
-4-methoxvphenyl
492
346
20.3
28.9
(2.71)
(1.37)°
blood orange
Complexes
: Pd(II)(4-DyL0H)2Cl2
R =
-phenyl
470
363
21.3
27.5
6.52
3.97
pale yellow
R =
-4-methylphenyl
485
361
20.6
27.7
9.58
4.24
yellow-orange
R -
-4-methoxyphenvl
492
353
20.3
23.3
8.03
3.11
blood orange
These va
lues are apparent eTs as
this alcohol was
not completely conv
erted to
carbenium ion
in 70% HCIO^.
°The extremely limited solubility of this complex in 70% HCIO^ prevented any value from being obtained,
c
These complexes were completely converted to carbenium ion in 70% HCIO^ but their limited solubility prevented
reliable c values from being determined.

79
tuls directly. This band is the so-called "x" electronic band so
classified by Lewis 3nd Calvin (60) in an elegant work on the color of
organic compounds. Similarly, the higher energy, less intense (in this
case) band, is labeled the "y" band (60). Certain relevant trends are
established by the spectral position shifts of these main absorption
bands which occur upon proceeding from R = phenyl to R = 4-methoxyphenyl
(see Table II) for a related series of carbenium ions; and from the
comparison of the spectrum of a free alcohol carbenium ion to that of
the corresponding complexed carbenium ion. An inspection of the
respective v values (Table II) reveals these trends to be the
* max
following:
(i) For carbenium ions derived from a family of precursors (e.g.,
the 2-pyridyl alcohols, the 4-pyridyl alcohols, etc.), in proceeding
from R =•• phenyl to R = 4-methoxyphanyl v of the x-band decreases ca.
max —
0..4 — 0.5 kK for the free alcohol ions and ca_. 0.9 — 1.0 kK for the
complexed alcohol ions, find for the 4-pyridyl ions the x-band v for
max
a given free alcohol ion is lower than that for the corresponding
complexed ion, w’ith the difference in related x-band frequencies dimin¬
ishing in going from R = phenyl to R = 4-methoxyphenyl. Thus, whereas
the x-band v is at 20.7 kK (free alcohol ion) and 21.3 kK (bis-
max
complexed ion) respectively for R = phenyl, it is at 20.2 kK (free
alcohol ion) and 20.3 kK (complexed ion) for R = 4-methoxyphenyl.
(ii) Making the same comparisons as in (i) (above) on the relative
y-baad v values reveals that proceeding from R = phenyl to R = 4-
•nechoxyphenyl results in a concomitant increase in v of ca. 0.7 kK;
but. this does not include the free 4-pyridyl ions where an increase in
v-band v of only ca. 0.3 kK is encountered. And, in this case the
max —

80
y-band \> _ for a given 4-pyridyl ion is found to be liigher (usually
0.7 ^ 1.0 kK) than the y-band of the corresponding completed ion.
Here, however, no apparent trend exists in the magnitudes of observed
difference in y-band v values for a related free ion — completed ion
pni r.
(iii) A comparison of the x- and y-band v values of a free
max
2-pyridyl ion and corresponding 4-pyridyl ion shows that for a given R
group v is always lower for both the x and y absorptions. (Note:
This particular trend was also exhibited by a related series of 2-thi-
azoiyl vs. 5-thiazolyl carbenium ions (8). That is, the x and y ab¬
sorptions exhibited by a 2-thiazolyl ion were always found to be at
lower v than the same absorptions for the corresponding 5-thiazolyl
ion.)
For convenience and simplicity these spectral trends are summarized
in the immediately succeeding statements. The effect of proceeding from
R = phenyl to R = 4-inethoxyphenyl is reflected by a bathochromic (red)
shift of the x-band and an hypsochromic (blue) shift of the y-band.
And, the effect of coordinating the carbenium ion always results in an
hypsochromic x-band shift and a bathochromic y-band shift. It can
now be shown that these results are qualitatively in accord with con¬
siderations made previously concerning the electronic spectra of aryl-
carbenium ions. For instance, if the energy of the x-band transition
exhibited by pyridylcarbenium ions is dependent primarily upon a floxv
of electrons towards the exocyclic carbon atom from the aryl group(s)
which are of predominant electron releasing capability, it is expected,
and found, that the energy of this transition is reduced upon replacing
R phenyl with R - 4-methylphenyl, or R = 4-methoxyphenyl. The

81
subsequent cross-conjugation'll effect of this R substitution on the
energy of the y-band transition is illustrated by the corresponding
y-band blue shift in the spectra of a related series of ions. More
important to this work, however, are the band shifts which take place
as a consequence of complexation of a given carbenium ion. It follows
that if the transition energy of either or both of the bands (x, and
or, y) in the spectrum of a pyridylcarbenium ion is associated, at
least to a degree, with a flow of electrons from the pyridine ring to
the exocyc.lic carbon atom, any change in the electronic nature of the
pyridine ring making it a more effective electron releasing moiety
shot»Id result in a lowering in energy of that (those) electronic band(s) .
Furthermore, it. is reasonable to expect that the coordinated pyridine
ring would in fact be a better donor than the pyridine ring in the
uncomplexed ion as in 70% HCIO^ the ring nitrogen is certainly protonated
in the free ion, vide infra. Clearly then, any difference in these
situations should reside in the fact that in the coordinated pyridine
case electrons flow from an ostensibly neutral ring towards the exocyclic
carbon; whereas in the uncoordinated pyridine carbenium ion electrons
are required to flow from a ring which already bears a positive charge
(the proton) resulting in a comparably unfavorable energetic trans¬
formation. Now, since coordination of a given pyridylcarbenium ion
results in a blue shift of the x-band, and a relatively substantial red
shift of the y-band, it appears to be the case that the y-band transi¬
tion energy is, to an appreciable degree, paronymnusly related to the
pyridine ring, and therefore dependent upon its electronic nature.
These arguments, of course, serve to indicate that the pyridine ring
is the so-called aryl" which appeared in the wave equation, ^
= Í5),

82
and •{/ t - (7), presented previously (p. 70). So, from a qualitative
Standpoint it is reasonable that the m-electron energy level of ,
.■.‘Guiri be lowered with the pyridine ring protonated relative to the energy
level of tj; , with this ring coordinated, as in the protonated situation
the pyridine cing would be expectedly more electronegative. Hence, if
the energy level of is not altered as much as that of for each
of these two possibilities, the y-band should (and does) shift red for
the coordinated carbenium ion relative to the "free" ion. It is also
suggested that these assessments are correct owing to the magnitude of
sk.if t in energy observed for the y-band upon pyridylcarbenium ion co¬
ordination. An inspection of the v data (Table II, pp. 77-78) for the
4-pyridyi ions reveals that coordination induces a red shift in the
energy of the y-band proportional to as much as 2.1 kK for the palladium
complexes of the R - 4-methylphenyl ion vs. the corresponding "free" ion.
Similarly, for this ion, the x-band is blue shifted only 0.4 IcK. (This
trend is also realized by the remainder of the data found in Table II.
Furthermore, related data reported previously by Richardson (6) and
by Wentz (8) support this trend.) Consequently, the electronic energy
changes which are produced in the ion via coordination appear to be
related principally to the attendant changes in the transition energy
of the y-band. This engenders the speculation that relative energetic
contributions provided by coordinated metal species towards stabilizing
"complexable" carbenium ions would be reflected in a comparison of the
respective y-band transition energies for a given complexed ion. Per¬
haps future work will furnish this possibility with substance.

Carbenium Ion Stability in IICIO4 — II7O ¿is Determined by the "Peno"
Titration Method. The suitability of the Deno titration method (10,11)
for the determination of the thermodynamic stabilities of the carbenium
ions investigated in this study has been aptly demonstrated by Wentz (8)
The interested reader is referred to this work for a salient discussion
of the necessary and pertinent experimental considerations. Reagent
perchloric acid, 70% HC10,, has proved to be a most appropriate ioniza¬
tion medium for these titrimetric stability determinations. It is
a potent mineral acid as reflected by its thermodynamic ionization
constant reported to be 3800 (61). In fact, as pointed out by
Gillespie (62), IIC10,. — H,,0 systems can be more acidic than reagent
i^SO, , and only certain, nonaqueous superacid systems afford higher
acidity than aqueous HCIO^. Indeed, HCIO^ — H^O is found to be uniquely
between neat and superacid systems such as HSO^F — SbF,. (used
by Olah (63) to prepare many relatively unstable carbenium ions) as a
useful solvent for the generation of trityl-type carbenium ions.
Freedman (64:1535) has commented that carbenium ion investigations in
concentrated Il^SO^ can be complicated by side reactions such as sulfona-
tion or oxidation which in turn can destroy either the parent carbinol
or the carbenium ion. Problems such as these are without a doubt respon
sibie for much of the confusion found present in earlier studies on
carbenium ions. The superacid system HRO^F — RbF^ as well, recently has
been shown to generate carbenium ions as a consequence of oxidation by
SbF.. or S0_ (65). Thus, previously devised methods and mechanisms of
-J ^
carbenium ion generation in this solvent may require extensive modifica¬
tions. Furthermore, the use of superacids for the preparation of these
types of carbenium ions would certainly require modifications of the

84
Heno tit'ration method to take into account the fact that superacid media
«■tro nonaqucous. Therefore, at the minimum, the definition of new acidity
/unction parameters would be requisite, as well as drastic alterations
*Sf the mechanics of the aqueous titration technique.
A consideration of the equilibria which pertain upon carbenium
ion generation is in order. An examination of the literature in this
area reveals that on occasion various authors are wont to write H+ as
the. acid species responsible for the conv -yion of carbinol to carbenium
ion. Albeit convenient, this practice is certainly not rigorous, and
can frequently be misleading. In the present situation where perchloric
acid has been employed as the ionizing medium it is necessary to choose
between HC.10^ or 11^0 as the principal proton source towards the ion
precursor carbinois, assuming, of course, that other complex or unusual
acid species do not exist in this system in appreciable concentration.
Since concentrated solutions of such mineral acids as i^SO^, HHO^, or
MCI, are not capable of carbenium ion generation in instances where
ÍÍClQjj — H^O is, it follows that HCIO^ is the acid species responsible
for carbenium ion formation in those systems in which these other
acids produce little or no carbenium ion. As a result of mar studies
on. 1IC10^ — f^O, Redlich and Hood (6b) reported that reagent 70-72%
|C10A (ca. 11.8 M) is approximately 75% ionized. Hence, sufficient
molecular 11C]0^ is present in 70% HCIO^ — 1^0 for carbenium ion genera¬
tion in systems which contain as solute limited quantities of ion
precursor pyriJylmethanol. And here, concentrated solutions of TU0+
do not convert carbinol to carbenium ion to any appreciable extent,
except for the relatively more stable cations such as those which contain
stiongly electron l'clensing phenyl ring substituents such as 4-methoxy

85
groups. Thus, the ionization of triphenylcarbinol in HCIO^ — 1^0 may
be written appropriately as:
(C6H5)^COH + 2 HC104 -> (C6H5)C+ + H^o'1' + 2 C10~ {8}
And, even though ring nitrogen protonation of the free alcohol ions
tends to complicate the attendant equilibria, the pyridylmethanols
should be ionized similarly. (Also, see the discussion which ensues
(p. 98) in reference to the stability data contained in Table V.)
The equation for the Deno acidity function (H ) may be written as
Rr - PV + log-^Sfl {51
where the values of H for a particular acid medium are a measure of
the capability of that medium at various concentrations to ionize a
given alcohol (R-OH) generating the corresponding carbenium ion (R+).
Since this equation is of the fora, y = b + mx, it follows that if a
series of values for H are known, and if the respective concentrations
of R-OH and R+ for a related alcohol — carbenium ion pair can be ex¬
perimentally determined at the different H^'s, pK^.p may be obtained
as a quantitative measure of the thermodynamic stability of a given
carbenium ion. Of course, it is required therefore that the acid medium
be capable of measurably ionizing the alcohol over a range of acid
concentrations; and it is also inherently i*equxred that in order for
the H relationship to hold, the slope (m) of the curve got by plotting
Hjj vs. the log term be equal to 1.00. Wentz (8) showed that both of

156
these condit i.ons were met in HCIO^ H^O for the pyridylmethanols
which are considered in this work.
A list of R^ values for aqueous HCIO^ and the corresponding wt %
acid are given in ’Cable III, p. 87. A plot of -i: vs. wt % acid
(Figure 9, p. 3S) yielded a smooth curve of approximately constant
slope which was easily extrapolated (as shown in Figure 9) to 70.0%
HC-LO^ in order to obtain IL^ values for acid concentrations greater than
60.0%. Employment of the fact, that Beer's law (A. = ecb) directly
relates the absorbance (A) of an absorbing species to its molar con¬
centration (c), allows values for [R-0H]/[R+] in equation {9} to be
obtained by measuring the absorbance (to ±0.001 absorbance units) of the
carbeniutn ion at various HCIO^ concentrations. The absorbance (con¬
centration) of R.-0H was then taken as the difference between the Beer's
law absorbance of the carbenium ion (see Dilution Curves, p. 93) and
the actual absorbance of the ion at a given acid concentration. This
method of data treatment is valid since R-OH does not absorb at X
max
of the carbenium ion. Consequently, it is justifiable to assume that
xrtien the actual absorbance of the carbenium ion matched the expected
absorbance as predicted from Beer's law, the alcohol was ionized to an
extent of ca. 100%. Naturally then, as the ionizing acid was systemat¬
ically diluted (actually, at the onset of the titration molecular HCIO^
is also converted to II^0+, CIO^) by the addition of measured increments
of water, the absorbance fall off was linear (Beer's law dependent) as
long .as the alcohol remained essentially 100% ionized. However, as soon
a.s the carbenium ion became t Ltrimetrically reconvert ed to alcohol pre¬
cursor as a result of further addition of water, absorbance fall off
was no longer linear; and indeed, it was greater than that predicted

—1
o 7
Values
Table III
of Hp in Aqueous HCIO^ at 25°
-«R
Wt % HC10.a
4
3.79
30.0
4.61
35.0
5.54
40.0
5.95
42.0
ó. 38
44.0
6.82
46.0
7.31
48.0
7.86
50.0
8.45
52.0
9.05
54.0
9.63
56.0
10.37
58.0
11.14
60.0
Deno et al.
(11)

17. OCT:
15.00..
1
j
/
i
i
-H
R
13.00-
11.00-
9.00-
7.00—!
5.00-j
3.00-- —
30.0
i l ’ “ 1
40.0 50.0 60.0
Wt % RC10.
H
I
I
i
I
i
I
t
I
t
70.0
Values of 11^ in aqueous HC'10^ at 25°
Fig. 9.
CO
(X

89
|t om lln extrapolated Beer's Law straight line. An examination of the
dLLution curves (Figures 10-12, p. 93) illustrates this straightforwardly.
Thus, for each carbenium ion so titrated, a collection of absorbance
data was obtained as a function of changing wt % HClO^.
Data treatment was carried out using the methods employed by Wentz
(8) with some minor modifications. These methods may be described con¬
veniently in conjunction with a stepwise examination of the pertinent
arithmetic relationships required for data treatment. Initially, an
unv:eighed sample of ion precursor pyridylmethanol (free or complexed)
is dissolved in sufficient reagent HCIO^ (determined as 70.87%, see
bellow) to produce an acceptable on-scale (viz., 15-25% T) spectrophotom¬
eter reading at X for the absorbing species (the carbenium ion). The
in 3.x
total solution sample is now weighed and the absorbance recorded. Then,
measured increments of deionized water are added to the carbenium ion
solution and, after thorough mixing, the absorbance of the sample is
reread. The wt % of the acid solvent resulting from dilution is calcu¬
lated from:
Wt % acid
wt (g) of acid
wt (g) of sample + st (g) of L^O added
{10}
where wt of acid = original wt % acid (70.87%) x original total sample
wt. Thus, the wt % of the acid can be determined following each dilution
by simply noting the cumulative quantity of water which has been added
to that sLage in the titration. The volume of the sample following
each addition, of water is then determined from:

yo
Sample. volume (ral)
cumulative sample wt (g)
corresponding p (g/ml) of the sample
(11}
where p “ specific gravity of the acid solvent. And therefore, it is
obviously necessary to have values of p for aqueous HCiO^. (Wentz had
obtained this information from a plot of p (4 sig. fig.) vs. wt % (4
sig. rig.) for solutions of aqueous HCIO^ (see Table IV, p. 91).)
However, since the volume of an aqueous HCIO^ solution does nol increase
linearly upon dilution with water (i.e., the volumes of water and parent
acid solution are. not additive), Wentz found it necessary to "blow up"
this plot in the region of each wt % datum point in order to obtain
the corresponding value for p. This procedure was found to be extremely
tedious owing to the difficulty found in obtaining 4 sig. fig. accuracy
(to insure reliability of related data to 3 sig. fig.) for a considerable
amount of wt 7, data from such a graphical readout. This particular
problem was conveniently alleviated by taking a "least squares" curve
fit of Brickweude’s data (67), (Table IV, p. 91) to yield a "printed
out" series of values for p spanning the range 0.00 wt % HCiO^ to 75.00
wt % iiCiO^. (The details of this least squares treatment are given in
the Appendix.) Thus, having experimentally determined p of the original
reagent, acid, the corresponding wt % of the original acid was obtained
from this p — wt % tabulation. The use of equation {10} then yielded
wt % data for subsequent dilutions, in turn for which corresponding p
values were available from the p — wt % tabulation. Finally, it is
necessary to determine the dilution fraction (D.F.) for each dilution.
This is obLained from:

91
Table IV
Specific Gravity of Aqueous HCIO^ Solutions at 25°
Specific Gravity (g/ml) Wt: % HCIO^
0.997 0.00
1.026 5.00
1.056 10.00
1.088 15.00
1.123 20.00
1.160 25.00
1.200 30.00
1.244 35.00
1.291 40.00
1.343 45.00
1.400 50.00
1.462 55.00
1.527 60.00
1.596 65.00
1.664 70.00
aBriekwedde (67)

D. i7.
112}
or íginal sample volume (mi)
cumulative sample volume (mí)
Again, inspection of equation {9} reveals that the required values for
the log terra are ratios of concentrations (of alcohol to corresponding
carbenium ion), and not absolute concentration values. Thus, it is
not necessary to determine the concentration of the absorbing species
at. any time during the titration. It is only necessary to measure
absorbances throughout the titration at the various, knovm dilution
fractions, which are proportional to changes in the concentration of the
absorbing species. Hence, a plot of absorbance (A) vs. dilution fraction
(D.F.) yields a plot which reflects the decrease in concentration of
carbenium ion as a consequence of dilution as well as of reconversion
to alcohol precursor. And, the only requirement which must be met in
order for this treatment to hold is that the alcohol be ionized com¬
pletely at the onset of the titration. An examination of the dilution
curves for free and complexed carbenium ions derived from the same al¬
cohol precursors (Figures 10-12, p. 93) clarifies thc.se considerations.
In each case the beginning of the titration (i.e., in the. vicinity of
D.F. - 1.00) corresponds to a linear fall off of absorbance with dilu¬
tion. Tims, at this juncture of the titration the alcohol precursor
species is essentially completely ionized; and, to repeat, the effect
of the addition of titrant (water) is to titrate molecular HCIO^ while
only diluting the carbeiiium ion. V.'hen the equilibrium reconversion of
cutbeirium ion to aic.ohol (described by equation {1}, p. 9) becomes mea¬
surable the titration curve begins to slope down and away from the
extrapolated Beer's law straight line as seen in the dilution curves.

93
Fig. 10. Dilution curve for the titration of 4-pyridyl-4-methylphenyl-
4-fluorophenylcarbenium ion
where 4-pyL = 4-pyridyl-4-methylphenyl~4-fluorophenylcarbenium
ion
l i ¡ 1
1.0G 0.90 0.80 0.725
D.F.
2-1-
Fig. 12. Dilution curve for the titration of [Pd(II)(4-pyL)2CI2] ,
where 4-pyL = 4-pyridyl-4-methylphenyl-4-fluorophenylcarbeniutn
ion

?4
1! «_ lower straight lino shown (which praoticaily bisects the plot
horizontally) corresponds to the so-called "1/2" Beer's lav; line. Tnis
second line has been drawn by considering that if at the onset of the
titration the concentration of the absorbing species (the carbenium
ion only) were divided by two, its absorbance would also be divided
by two. Thus, this "1/2" Beer's law line may be constructed from a
series of points got by halving the absorbance values which served to
establish the initial (upper) Beer's law line. Consequently, the
intersection of this second Beer's law line with the dilution curve for
a given carbenium ion marks the D.F. location at which [R-OH] is ex¬
pected to equal fR*1] during the titration of that Ionic species. The
point of this graphical treatment resides in the fact that the log term
-f
in equation {9} is equal to zero for equal values of [R-OH] and [R ].
Hence, vertical extrapolation from this intersection point to the ab¬
scissa of the plot yields the D.F. at which the corresponding value of
Hj, equals pK. of that carbenium ion. Of course, H^ is obtained after
relating D.F. to the appropriate wt % HCIO^, (note: here, simple
arithmetic interpolation is usually necessary to obtain the required
values for wt % HCIO^ since the data points used to plot the dilution
curve seldom include the exact D.F. values at which [R-OH] = [R ]),
which in turn is related to H (see Figure 9, p. 88).
The thermodynamic stability data resulting from these titrixnetric
measurements upon the. pyridylcarbenium ions investigated in this study
are presented in Table V, pp. 95-96. The following considerations which
are in respect to this data are relevant.
The reliability of the data was corroborated through a titrimetric
measurement of pK + for triphenylcarbeni.um ion. The value obtained
K

fable V
Thermodynamic Stability Data Resulting from
Various Fyridylcarbcnium Ion Species,
the ”Deno" Titration, of
in. HC10. — II 0 at 25°
4 2
Carbenium
Ion Precursor
] pK
AG° (kcal mol ±)
AG° (kJ mol 1)
Alcohol:
triphenylmethanol
1.7 x 10~7 b
6.76b
9.21
38.53
Alcohols:
pyridyl-R-
methanol
2-pyLOH =â–  2-
â–  4-fluoropheny1-
R = -
■phenylC’G
2.1 x 10"16
15.68
21.36
89.37
R = -
â– 4-ir.ethylphenyl
-14
2.1 x 10
13.67
18.62
77.91
R = -
-4-methoxyphenyl
5.1 x 10-11
10.29
14.01
58.62
Alcohols: 4-pyLQlI = 4-
pyridyi-R-4-fluorophcnyl-
methanol
d
R = -phenyl
R = -4-methylphenyl
R = -4-methoxyphenyl
3.4
x 10~1A
13.47
IS.35
76.78
2.2
x 10"12
11.66
15.88
66.44
1.0
x 10"9
9.00
12.26
51.30

Tab!o V -
Extended
Carbenium Ion Precursor
PK
AC0 (kcal mol ^)
AGC (kJ mol"1)
Complexes: Pd(II)(4-pyLOH)-
(VC12
K[Pd(II)(4-pyL)(Ln)C19]+
e
R = -phenyl8
-12
2.0 x 10
11.70
15.94
66.69
R = -4-methylphenyl
2.6 x 10-11
10.58
14.41
60.29
R = -4-methoxyphenyl
1.5 x 10_S
7.82
10.65
44.56
Complexes: I’d(11) (4-pyi.Oll)
C12
K[Pd(II)(4-pyL)2C12]2+
R = -phenyl8
-13
6.2 x 10
12.21
16.63
69.58
R - -4-met'nylphenyl
2.7 x 10-11
10.57
14.40
60.25
R = -4-methoxyphenyl
1.2 x 10-8
7.93
10.80
45.19
n ,
is the stability constant for a "free" alcohol carbenium ion.
b HpyL -7 _! +
Compare to K^+ = 1.4 x 10 , pK^+ = 6.89, AG° = 9.37 kcal mol ; for R = triphenylcarbenium ion; Dono et
_al. ill) .
Q
Stability data for this alcohol were not obtainable by the "Reno" titration method. The values provided
follow from -^F nmr studios and appropriate LFE relationships (p. 119).
Q .i-i O
See the. discussion (pp. 103-106) concerning rearrangement of the carbenium ions derived from these, alcohols cn
and the complexes thereof.
Glhesc are the stability constants for the "mono" and "bis" complexed carbenium ions.

97
(Table V) ia in good agreement with pK measured Cor this ion in 60Z
llClU^ by Tieno and coworkers (11) using the titration technique.
A. requirement which obviously must be met by the complexed carbenium
ions to insure that the corresponding stability data be meaningful is
that the coordinate bond between the palladium metal center and the
pyridine ring remains intact throughout titration. Undoubtedly, the
protonic solvent will compete strongly for the basic ring nitrogen site(s)
as evidenced by the fact that the pj'ridine ring is protonated for the
"free" alcohol ions in 70% HCIO^ (shown below). The simplest demonstra¬
tion of the stability of the coordinate bond during titrimetric (and
1 9
J"'F nmr chemical shift) measurements stems from the fact that the
electronic spectrum of a given complexed 4-pyridylcarbenium ion in HCIO^
— 11^0 remains unchanged for a period of at least a few hours. In fact,
the electronic spectrum of the bis complex of 4-pyridyl-4~methvlphenyl-
4-fluorophenylcarbenium ion in HCIO^ — 1^0 was found to remain intact
for 12 hours as evidenced by the fact that during this time no appreciable
change in band intensity could be observed; and, more importantly ab¬
solutely no shifts of the x- and y-absorption bands had taken place.
Furthermore, the solution color of the complexed ion did not deteriorate
to the solution color of the corresponding "free" ion. Additional
investigations on the intact nature of complexed carbenium ion electronic
spectrum in HC.10^ — H^O upon the lone 2-pyridylmethanol complex isolated
(see Experimental, p. 36) revealed that as soon as this compound was
dissolved in the acid the intensities of the x- and y-absorptions began
t.o increase steadily; and also, the x- and y-absorptions began to shift
immediately towards the respective positions of these absorptions
characteristic of the uncoordinated, "free” 2-pyridylcarbenium ion.

98
Thu , this 2-pyrifiylo*rbeniutu ion complex was insuftic Lently stable to
be studied using liClU^ H^O as an ionizing medium. A comparison of the
stability data for a related free ion — complexed ion series also
§orves to establish that the metal — nitrogen bond(s) remaiu(s) intact
during thei-rcudynajuic measurements, and that coordination certainly
stabilizes a given carbenium ion relative to the corresponding free ion.
An examination of the respective AG° values (Table V) indicates that
the degree of stabilization afforded by coordination is greatest for the
4-pyridylphenylcarbenium ion. Although the thermodynamic titration
data for the unsubstituted phenyl carbenium ions is somewhat suspect
owing to rearrangement of these ions in HCIO^ — H^O (discussed, pp. 103-
19
106), F nmr chemical shift measurements in conjunction with relevant
free energy relationships substantiate the reliability of the reported
stability data, vide infra. The stabilizing influence of coordination
upon a g.iven carbenium ion is also seen on inspection of the dilution
curves for a free iou — complexed ion related series (see Figures 10-12,
p. 93). Here, the Beer's law dependence of the plot reflects the
relative stability of a given carbenium ion. That is, a relative com¬
parison of the D.F. values corresponding to that point in the titration
at which each dilution curve no longer adheres to F>eer’s law, allows an
ordering of the stability of all carbenium ions investigated by the
titration method. This particular D.F. for the free A-pyridyl-4-methyl-
phenyl-4-fluoropbenylcorhenium ion is ^a. 0.92, whereas the corresponding
D.F. values for the complexes of this ion are ca_. 0.87, thereby showing
that the coordinated ions are more stable.
The stability constant values (K) found in Table V correspond <.o
the equilibria which are established upon the. tjgtrimetri c reconversion

99
of a particular pyridyloarbenium Ion to its free or complexed precursor.
The equations for these equilibria have been presented previously (p. 16)
but for expedient purposes they are repeated in the order in which they
are discussed. The equilibrium titration of a free alcohol ion is
represented by:
HipyL+ + 2 H20 t K+pyLOH + H30+ { 2}
This statement is consistent with the fact that the unionized alcohol is
protonated. This is certainly expected for pyridine in such strongly
acidic media as 45-70/ IICIO^ (these values correspond to the acid con¬
centration ranges spanned during the titration of the more stable car-
beniura ions). Moreover, Wentz (8) demonstrated that equation {2} was
the correct equilibrium statement for describing the titrimetric re¬
conversion of an uncoordinated thiazolylcarbenium ion to its alcoholic
precursor. This was accomplished by titrating the N-methyl iodide salt
of a particular 2,4-dimethyl-5-thiazolylcarbenium ion yielding a K value
which was identical to that which he had obtained for the titration of
the original alcohol ion. Clearly then, in each instance the thiazole
ring nitrogen must have borne a unit positive charge throughout titra¬
tion. Also, by assuming that the pyridylmethanol pyridine ring is of
-9
similar basicity as pyridine itself (K^ pyridine = 2.3 x 10 ), it
can be shown from simple acid-base equilibria that a given pyridyl-
methanol dissolved in 1 M H~0+ at an .initial alcohol concentration of
0.01 M, is protonated to an extent in excess of 99.99%! (This calcula¬
tion Is given in the Appendix.) Since, for the HC10, — I^O — pyridyl-
nethanol systems considered, the combined concentration of IiClO^ —

100
iu always much greater than 1 M, and the concentration of a pyridyl-
)§tfuhrnoi is very small comparatively, the pyridine, nitrogen is protonated
',cs. .100%) for a free alcohol enrbenium ion. A direct effect of ring
nit logon protonation on carbenium ion stability is indicated from a
comparison of the data in Table V for a structurally related pair of
.free 2- and 4-pyridylearbenium ions. That is, a 2-pyridyl ion is seen
to be considerably less stable than its 4-pyrLdyl congener. The only
significant difference between such a related pair of cations should
reside in the disproportionate degree of positive charge separation in
tne 2-pyridyl vs. the 4-pyridyl ion. Hence, it appears that the de¬
stabilizing consequence of like-charge repulsion on the stability of a
given 2-pyridylcarbenium ion is relatively substantial in that the
positive charge on the 2-pyridyl nitrogen is in much closer proximity
to the carbenium ion center than in the corresponding 4-pyridyl ion
s.i tuation.
The equilibrium titrations of the coordinated carbenium ions may
be represented by:
Cl2(LN)Pd(Tl)pyL+ +2H20 ± Cl2(LN)Pd(II)pyLOH + H30+ {3}
and
C.l2Pd(Il)(pyL)2+ + 4 H20 t Cl2Pd(Il) (pyL0H)2 + 2 1130+ {4}
Statement {3} designates the reconversion of a singly charged coordinated
carbenium ion to its complexed ''nono" alcohol precursor. The stability
data associated with this transformation therefore afford a reflection

101.
of r.l'ci stabilizing effect exerted by the metal on a single p/ridy.lcar-
beniud ion. Statement. {4} corresponds to the reconversion of a "bis"
ravoeniwn ion complex to its alcoholic precursor and is premised upon
complete ionization of both of the coordinated alcohols in 70% HC10,
4
(i - c.l prior to titration). The £ data (Table II, pp. 77-73) indicate
that both coordinated alcohols are ionized for the bis complexes in the
IS
acid. The F nrar chemical shift data (vide infra) also corroborate
this consideration stemming from the fact that the absorption position
11
or tne F nvnr signal for a mono complexed ion is identical to that
found for the corresponding bis complexed ion. If both the coordinated
alcohols in the bis complex were not ionized, either a time averaged
signal, would be expected or two signals would be observed in the spectrum
corresponding respectively to an ionized and an unionized ligand mole-
19
cule. That is, the F nmr spectrum should reflect the presence of
either tvTo rapidly equilibrating, or two distinctly different, fluorine
nuclei. Furthermore, as previously indicated, the dilution curves re¬
sulting from the titrations of the bis complexed ions all exhibit
appreciable Beer's law dependency at the onset of the titration. If
the bis complexes had not been ionized completely upon dissolution in
70% HCIO^, an immediately detectable equilibrium would have been estab¬
lished upon addition of the initial quantities of tiirant (water), and
no Beer's law dependence would have been illustrated by the Beer's law
plot at the beginning of the titration. This consideration alone does
not preclude the unique possibility of having ionized only one of the
coordinated alcohols in a bis complex in 70% HCIO^. .However, the e data,
which indicate multiple ionization of the bis complexes in the acid,
provide rather forcing evidence substantiating the assertion that both

LO?
oí Hie coordinated alcohols are converted to carbenium ion in 70% HL’10, .
4
lrdeed, as the bin complexes dissociate in the acid, no increase in
absorption intensity is detectable. Thus, both coordinated alcohols
must have been ionized. Of course, this contention could be. definitively
established by titrating a weighed sample of a bis complex vs_. the
corresponding mono complex, for which twice the quantity of water would
be required to reconvert the bis complexed ions to tlie neutral precursor
if both coordinated alcohols had been ionized initially.
It is also pointed out that tlie values for the thermodynamic data
in Table V correspond to the reverse of the titration equilibria
(equations (2), (3), and {4}) as written. Hence, an examination of
these data in relation to the relative ease of carbenium ion formation
affords a measure of the stability (as opposed to instability) of that
ion. In w’riting these equilibria it was tempting to consider the equa¬
tions which obtain upon carbenium ion generation; viz. , for a free
alcohol ion:
H+pyLOH + 2 HCIO^ -> H+pyL+ + ll30+ + C10~ {13}
That is, this statement illustrates the net chemical change which occurs
upon dissolving a protonated pyridylmethanol in 70% HCIO^ and obviously
corresponds to carbenium ion formation. (It is not germane to consider
the proton source required for the initial protonation of the pyridine
ring.) It must be emphasized, however, that the carbenium ion stability
data were obtained from the aqueous titrations which are correctly
described by equations {2}, {3}, and {4}: and it is for this reason
that this distinction has been made.

103
Finally, a comparison of the stability data for the mono complexes
to the data for the corresponding bis complexes proves worthwhile. These
data suggest that related mono -- bis cornplexed carbenium ions are of
practically identical thermodynamic stability. In the absence of charge
effects tills would have been an expected result. However, based upon
the consequence of like-charge repulsions on the stabilities of related
free 2-pyridyl ví¿. 4-pyridylcarbenium ions, it seems reasonable that a
given bis cornplexed ion would be somewhat less stable than the correspond¬
ing mono cornplexed ion. Apparently, therefore, the degree of charge
separation in the bis complex '’di''-carbenium ion is sufficiently great
that there is no residual ion destabilizing effect exerted mutually
upon one another by the two coordinated ions in the complex. This
stability similarity is also reflected by a virtual superimposability
of the dilution curves for a related pair of these cornplexed carbenium
ions. Thus, the stabilizing influence exerted by the metal center on
the stability of such 4-pyridyl cornplexed ions appears to be independent
of mono ví^. bis coordination. Although, it may be the case that de-
stabilization arising through charge repulsions in the bis ions is
counterbalanced by enhanced stabilization through solvation in the highly
polar HCIO^ — l^O solvent system. This possibility is suggested as a
consequence of the considerably greater solubility of the bis vs. the
mono complexes in HCIO^ — K^O. Additional studies are required to test
and confirm the validity of this explanation.
The Vroblen; of Carbenium Ion Rearrangement in HC10/t — HpO. Initial
attempts to gather stability information for the carbenium ions derived
from the free and cornplexed unsubstituted phenyl pyridylmethanols led

104
t.o rather unusual and unanticipated results. For instance, it was dis¬
covered that the dilution curves for the HC10. — H O titrations of these
H Z
carben turn ions could not be treated by the ”1/2" Beer's law line extra¬
polation technique in order to get the corresponding stability constant
anta! That is, the second portion of the dilution curves (cf., Figures
10-12) obtained for any of these particular ions never fell off suffi¬
ciently to intersect with the '’1/2" Beer's law line. In other words,
the intensities of the principal electronic absorptions of these ionic
species were found to grow steadily on standing (until the intensities
had magnified by a factor of ca. 1.5 of original). In relation to this
19
unanticipated result was the fact that the F nmr signal initially ex¬
hibited by 11010 ^ — i^O solutions of these ions was found to disappear
with time (ca. within 1-2 hours to 24 hours depending upon the original
concentration of the carbenium ion under investigation). The nmr result
suggested therefore that the para-fluorine phenyl ring substituent was
discharged kinetically. Shutske's results (68) verified this contention.
Shutske studied the reduction of various fluorospiro(isobenzofuran-
piperidine)s in 97% formic acid and discovered that on standing fluorine
was lost as a phenyl ring substituent in the parent compound. This
result prompted Shutske to repeat the investigations of Dayal ejt _al_. (69)
on the reduction of 4-fluorophcnyldiphenylmethanol in 97% formic acid —
sodium formate solution. Shutske recognized the similarity of this
investigation to the fluorospiro study with respect to the anticipated
ejection of the Para-fluorine substituent. Dayat ct al. had reported
the isolation of only 4-fluorophonyldiphenylmethane as the reduction
product. Shutske, however, found that although this alkane was the
principal reduction product, 4-hydroxydiphenylmethane was also obtained

â– > n a yield of .13%.
Consequently, the loss of the paia-f1uofine sub-
stunellt fros) the. unsubstituted phenyl pyridylmethanols in 1IC1()¿ —
P «waffle led Shutske's results. And. in retrospect, this result indicates
8hat the ability of a 4-fluorophenyl group to participate in conjugations
interaction with the ex.oc.yc.lic carhenium ion carbon via tt—electron
release is more substantial than is that of unsubsticuted phenyl. This
is, in fact, borne out by the results of various studies on the thermo¬
dynamic stabilities of trityl-type carhenium ions which also contain
4-fluorophenyl rings (18,19,70,71), etc. Hence, the degree of positive
charge which migrates by resonance into the 4-fluorophenyl ring in these
particular carhenium ions is significantly greater than for either of
the ion systems containing 4-methylphenyl, or 4-methoxyphenyl substituted
rmgs. Thus, in these latter cases the fluorine nucleus was not lost
during studies on carhenium ions in HCIO^ — H^O.
The ’’Deno" titration stability data (Table V) for the unsubstituted
phenyl pyridyicacbenium ions were obtained in the following fashion.
The initial, portion of the dilution was plotted as usual (vis. absorbance
vs. D.F.) to yield the Beer's law dependent region followed by the
normal smooth curve deviation from the extrapolated Beer's law straight
line. It can he seen by inspection of the dilution curves (Figures 10-
12) that the plot is then again linear over a substantial region of
the titration until a smooth curve upswing of the plot is reached which
thereby establishes that the titration is virtually complete. That, is,
these curves are very similar to those got from ordinary acid — base
titrations, with the difference that the pertinent carhenium ion equi¬
libria persist over a rather substantial concentration range of the
lionizing medium (ca. 10 wt / IICIO^) , resulting in a titration curve

10b
with considerably less dr.ir.tic changes in slope chan ate customarily
o::hibj ted by acid — base titration curves. So, since the dilution curves
tor these carbeuium ions (i.c. , the ions which rearrange in HCIG^ — U^O)
exhibit curve upswing prior to intersection with the "1/2" Beer's law
â– line, the so-called second straight line portion of the curve (that
portion between curve downswing and curve upswing) was extrapolated
to intersect with the "1/2" Beer's law line. Ihis simple technique
facilitated the isolation of the D.F. value for which [R-OK] = [R+],
and thereby allowed the determination of K _j_ for the unsubstituted
phenyl carbenium ion in question. The reliability of the data ob¬
tained by this method was tested by precalculating appropriate wt %'s
KC-K>¿ required to yield D.F. samples whose carbenium ion absorbance
would tentatively lie on the extrapolated dilution curve in the region
of interest. The D.F. samples tested in this fashion gave absorbances
which coincided very well with absorbances predicted from the extrap¬
olated plot. Hence, the stability data so obtained are considered
19
to be very satisfactory. It will also be shown that F nrar chemical
shift data, in conjunction with attendant free energy relationships,
serve to establish that these data are acceptable, vide infra. (Note:
Certain experiments were performed in attempts to determine the nature
of the species which resulted upon fluorine atom ejection. A brief
account of this work is provided in the Appendix.) Furthermore, it
i.s potentially of interest to study the stability of such f 1 uorophenyl-
pyrJcívica rhenium ions as a function of the rate of discharge of the
fluorine substituent. Indeed, these experiments should he relatively
straightforward to monitor via *nmr, and could provide additional
information concerning the catbeni.urr ion stabilizing influence as exerted
by various coordinated metals.

J 07
JQ
F UheEu.cal Shift's and Carbenium Ion Stability. To repeat, the results
19
of previous F nmr investigations have demonstrated that a juirn-sub-
stituted fluorine nucleus on an aryl ring is a highly sensitive probe in
regard to the stability of carbenium ions which are conjugated with
the fluorine nucleus. Hence, further discussion respecting the appro¬
priate nature of this nmr technique shall not be presented, excepting,
19
of course, as it pertains to the F nmr data obtained during the course
of this work.
19
The use of F nmr chemical shifts as a criterion for the stability
of coordinated carbenium ions is, in itself, a novelty. Past studies
19
which have employed F nmr measurements for the purposes of elucidating
the stability and structure of coordination compounds have normally
incorporated fluorine into the system as a ligand itself, i. e. , fluoride
ion (see, for instance, the nmr studies by Dixon and McFarland (72),
and references to related work cited therein). Also, fluorine in this
capacity has been used for nmr investigations as a substituent on a
ligand moiety bound directly to the metal center such as in the contro¬
versial studies by Parshall (73,74). This author proportioned the
19
measured F chemical shift of 3- and 4-fluorophenyl groups coordinated
to platinum(II) to the trans-directing abilities of ligands in the
complex located trans to the fluorophenyl groups. In any event, it is
believed that the current work embodies the first attempts to correlate
19
F chemical shifts with the thermodynamic stabilities of metal-complexcd
trity1-type carbenium ions.
19
The F nmr spectra which were recorded for the free and complexed
pyridylmethanol — carbenium ions are uncomplicated and highly similar.

Each absorption pattern ..'ns characterised by the presence of a
non tuple r. fluorine signal which is predicted for 'll — 19F coupling in
these sjsteras by the relationship:
Number of peaks = (2 In. + 1)(2 T n_ + 1) • • • (2 I n 4-1)
11 2 2 n n
UA}
where 1^ - 1^ = 1/2 for hydrogen, and n^ = n£ = 2 for the two pairs of
hydrogens situated ortho and nieta respectively, to the single fluorine
nucleus present in each species investigated. (The basic form of this
equation is given in (75).) The center peak of the 9-fold absorption
was expectedly the most intense. The only difference of consequence
resulting from a comparison of all the spectra lies in the relative
positions of the signals for each species. For simplicity, the center
19
of the 9-fold resonance pattern is taken as the F absorption position.
Hence, the position of the fluorine signal, recorded relative to an
appropriate reference standard, provides an indication of the stability
cf the carbeniura ion under investigation relative to the degree of
¡¡-electron delocalization present within the structural framework of
each carbenium ion species. The reference standards employed were ex¬
ternal CFCl^ external trifluoroacetic acid (TFA) . The use of two
standards afforded a double check on the reliability of the obtained
shift data. External referencing procedures were used for all carbenium
ion spectra owing principally to the extremely reactive nature of the
ion and cf the HCIO^ — H^O solvent. Consequently, the absorption position
cf any interna] standard might have been appreciably affected by inter¬
actions with soluLe, or solvent. Nonreactive, nonpolar materials, ob¬
viously could not bo satisfactorily employed as internal references

109
because of their immiscib.ility with HCÍ®| -- IJLO. Referencing against
the sane external standards also facilitated the comparison of chemical
shift data obtained for the unionized ligands and complexes in acetone
to the related data for the corresponding carbenium ions in HG3M, — 1^0.
bulk susceptibility contributions by the solvent to carbenium ion chemical
shifts were expected to be unimportant in that each ion spectrum was
recorded in 70% HCIO^. Hence, solvent chemical shift susceptibility
contributions were leveled for each nmr measurement.
19
The shift data resulting from these F nmr investigations are
1 19
given in Table. VI, pp. 110-111. Since H -- F coupling is of no
19
particular concern to this work, examples of the F spectra are not.
given.) The following statements in relation to the relevant trends
established by these data are in order. A comparison of 6 values for
the alcohols in acetone, 1 HCIO^ and 70% HCIO^, systematically shows
the effect of proceeding from an aprotic solvent, to a protonating
solvent, to a solvent capable of carbenium ion generation. Consequently,
a small downfieid shift of the resonance for a given alcohol is detected
upon protonation (i. e., acetone vs_. 1 M HC10^ as solvent) ; whereas
transformation to carbenium inn is accompanied by a relatively substantial
19
downfieid shift in the F signal. This same trend is exhibited by the
complexes but, of course, no 1 K HC10^ spectrum was recorded for these
materials as they are not soluble at this acid concentration. Hence,
as expected, conversion to carbenium ion results in appreciable resonance
del ocaiizat.ion of positive charge throughout the conjugated molecular
framework. In proceeding from R = -phenyl to R = -4-methoxyphenyl for
any related series of carbenium ions an appreciable upfield shift of
the ^91' signal is observed. This reflects the substantial capacity of

Table VI
F nmr Chemical Shifts (6) for Carbcnium Ion Precursors in Acetone and 1 M HC10. .
and for Carbenium Ions in 70% HC10. at 25°
‘4
Solvent3
Ext
. Standard
Carbeniurn
Ion Precursor
Acetone13
TFA
1 .M HC104C
cfci3
1 M HC10aC
TFA
70% HC10/,
CFCI3
70% HCIO4
TFA
/.lcoho Ls : 2-pyLOK = 2-pyridyl-R-
4-fluorophenylmethanol
R =
-phenyl
39.2
111.9
35.0
66.6
-10.2
R =
4-n;e thylphenyl
39.4
111. 9
35.1
75.5
-] .3
R =
- 4-:ne thoxypheny 1
39.7
112.0
35.1
90.5
13.6
Alcohols: 4-pyLOH = 4-pyridyl-R-
4-fiuorophenylraethanoi
R =
-phenyl
39.1
112.6
LO
Kjl
CO
68.7
-8,1
R =
-4-me thylphenyl
39.2
112.8
35.9
77.3
0.4
R =
-4-nethoxypheny1
39.4
112.7
35.8
91.5
14.8

Table VI ••
Extended
Solvent:5
Ext. Standard
Carbenium Ion Precursor
Acetone^
1 M HC.lO/jC
1 R KC10/,C
70% HC10/,
70% HC10/.
TFA
cfci3
TFA
CFCI3
TFA
Complexes: Pd(II) (4-pyLOH) (L^C^
R = -phenyl
38.6
d
d
R = -4-methylphenyl
38.6
-
-
80.4
3.5
R = -4-nothoxyphenyl
38.7
-
-
92.5
15.6
Complexes: Pd(II)(4-pyLOH)2CI2
R = -phenyl
38.4
-
-
73.1
-3.8
R = -4-methylphenyl
38.6
-
-
80.4
3.5
R = -4-methoxyphenyl
38.6
-
-
92.4
15.5
a6 values are in parts per million(ppm), and are upfield relative to the external reference signal unless the
value is negative, in which case ó is downfield relative to the external reference.
k
Acetone solution spectra were recorded relative to external TFA only,
c *
6 values in these columns refer to the protonated alcohols.
C*No ^F carbenium ion signals were detectable for this species saturated in 70% HC10¿ following 5000 scans
with the Fourier transform synthesizer.
Ul

a [.-ara-mcthoxyphenyl substituent relative to hydrogen, • • • and in turn
relate ve to a para-fluorine substituent, to remove positive charge from
the cxoeyclic carbon via conjugational interaction. A comparison of 6
tor the 2-pyridyl vs_. the corresponding 4-pyridy.l.carbenium ions shows
the destabilizing effect of like-charge repulsions on carbenium ion
stability to be more significant in the 2-pyridylcarbcnium ions, hence,
IS.
the F signal for a given 2-pyridylcarbenium ion is downfield relative
to its more stable 4-pyridylcarbenium ion congener. This is in keeping
with the. thermodynamic data which have been considered previously.
19
lhe consequence of coordination on a given F resonance is reflected
by a substantial increase in 6 found in proceeding from a free to the
corresponding complexed ion(s). This trend also parallels related
thermodynamic data obtained from the titrimetric investigations and
again indicates that complexation stabilizes unsubstituted phenyl-
earbenium ions to the greatest extent.
19
For the data reported, it can be seen that the F signals for
a related mono- and bis-complexed carbenium ion pair are virtually
19
identical. Since two F resonances were not initially detectable for
the bis complex ions, it is clear that both coordinated alcohols are
converted to carbenium ion in 70% HCIG^; and again, a related mono-
r.ncl bis-complexed carbenium ion pair are predicted to be of essentially
equal thermodynamic stability. Here, it is conveniently pointed out
19
that when the 70% HC.10^ F nrrir samples of the mono and bis complexes
(of R = -4-methyiphenyl, for example) were allowed to stand, eventually
two signals developed. One of the signals coincided with the original
coordinated carbenium ion absorption, whereas the newly developed signal
coincided with the free carbenium ion resonance. These data verify the

113
ItiÉpcPf naimre of Lhe coordinate5, bond between palladium and the pyridine
ring in 70% liClG,^ as the second signal was not detectable within the
first. few hours of sample preparation. Furthermore, for the mono-
coraplexad Ion, the intensity of the free ion signal was not equal
(approximately) in magnitude to that of the completed ion until the
sample had stood ca. 24 hours. Again, this demonstrates the stability
of the coordinate bond.
19
The F nmr shift data reported for the earbenium ions derived
from the free and complexed unsubstituted phenyl pyridylmethanols are
considered to be reliable for the following reasons. Principally, the
19
detection of a F signal in these systems for a freshly prepared sample
essentially guaranteed that the nmr measurement was made on the species
19
ot interest. This follows since the originally detectable F signal
disappears only after rearrangement of these earbenium ions takes
place. Free energy correlations (considered in the forthcoming section)
also served to corroborate the credibility of the nmr data; and, as
lq
well, instated the use of appropriate F chemical shifts for the deter¬
mination of the thermodynamic stability of 2-pyridylphenyl-4~fluoro-
phenylcarbenium ion (recall that the stability of this earbenium ion
species was not titrimetrically measurable). As this particular
earbenium ion was allowed to stand, several poorly resolved signals
1 9
developed in the F spectrum. An attempt was made to fingerprint
19
these absorptions via comparison with the F nmr spectrum of 1:5 48%
HF - 70% HC10.. The 19F signal for HF in 96% H_S0. reportedly exists
4 ¿ H
at -116.9 ppm relative to external TFA (76), but no similar absorption
detectable in the HF — HCIO^ spectrum. Presumably, the HF reacted
with the glass nmr tube to produce, silicon fluorides or fluorosilicates.

114
Sira.Lar side products were expecced for the remaining unsubstituted
phony Lea rhenium ion samples where HF was also the initialLy anticipated
fluorine containing rearrangement product. A comparison of all un-
subst itute.d phenylcarbenium ion nmr spectra, however, yielded little
correspondence of resonance positions for the signals which developed
upon rearrangement. (For the concerned reader: the 2-pyridylphenyl-
4-flucrophenylcarbenium ion spectrum degenerated upon standing into two
ill-resolved signals at ca^. 52.3 and 68.9 ppm relative to external TFA;
and the HF — HCiO^ spectrum exhibited four principal absorptions, at
52.6 (very broad), 63.1, 64.3, and 66.6 ppm, respectively, relative
to external TFA. And, the intensity of the signal at 64.3 ppm grew
rapidly during scanning of the sample.)
One final set of nmr experiments was performed in an attempt to
19
relate carbenium ion — carbinol precursor equilibria to associated F
chemical shift data. The vt % UCIO^ datum for 50% ionisation of a given
carbenium ion species was obtained from the appropriate dilution curve
— D.F. plot. A F spectrum of a carbenium ion system in this wt % HCIO^
was expected to exhibit either two principal signals corresponding to
ion and alcohol, respectively, or one signal arising from rapid solution
equilibration of ion and alcohol (see p. 101). To carry out this in¬
vestigation a solution of 4-pyridyl-4-methoxyphenyl-4~fluorophenyl-
methanol was prepared using 53.8% HC10 , . This is the so-called 50%
ionising acid for this carbenium ion precursor. The nmr spectrum of
this solution, however, exhibited only a single resonance which córre¬
la
sponded with the position for the F signal of this ion in 70% KCIO^.
Moreover, no additional resonance was detectable for this system until

Ill
the acid vas diluted to £a. 46%. At this acid concentration a second
resonance finaiJy developed which corresponded to tne signal exhibited
by the. protonated pyridylmethanol precursor. These signals became of
approximately equal intensity at jna. 44.5% acid, and at _ca. 43% acid
the carbenium .ion resonance disappeared entirely. This result is
unusual for the following reasons. First, the dilution curve — D.F.
data for this carbenium ion indicate that the carbenium ion — protonated
alcohol equilibrium is measurably significant over a minimum range of
8-10% acid (this is, in fact, the case for each of the titratable
carbenium ion species, see p. 105), whereas the nmr result suggests
that this equilibrium is measurable only over a rather limited range
of ca. 3%. Secondly, the nmr result indicates that this particular
carbenium ion is essentially 50% reconverted to protonated alcohol
precursor at 44-45% HCIO^ which is much less than the 53.8% value pre¬
dicted from the titrimetric investigation. Hence, the nmr measurement
suggests that a considerably less concentrated ionizing medium is
capable of producing substantial conversion of protonated pyridylmethanol
to carbenium ion, and, as yet, this result is unexplainable. It should
be noted, however, that there is a significant difference in concentra¬
tion required for carbenium ion nmr investigations compared to concentra¬
tions necessary for carbenium ion electronic spectral investigations.
That is, in order to obtain acceptable nmr spectra for materials of
relatively high molecular weight which are dilute in the absorbing
nucleus (viz., one fluorine atom per pyridylmethanol of M.W. jra. 280-
-2
300 amu), it is necessary to maintain solute concentrations at 10 it,
19
or higher, in order to obtain detectable F resonances, even with
currently available Fourier transform techniques.
In fact, the

116
4--liet'.hoxyphenyl sebSt United carbenin» ion was visually detectable in
43% JiClO^ by virtue of the characteristic solution color of the ion,
even though n.o nmr resonance could be obtained. Thus, concentration
requirements for nmr studies are considerably greater than for elec¬
tronic spectral measurements on pyridylcarbenium ions. Hence, the two
experimental methods cannot be cross-checked quantitatively owing to
tiic grossly different concentration ranges necessary for each measure¬
ment. (Note: The same nmr dilution experiment was performed on the
bis complex of 4-pyridyl-4-methoxyphenylr4-fluorophenylmethanol (carbenium
ion). However, this investigation proved futile as dilution induced the
prec.ipitation of the complex.)
Although additional studies are required to resolve the problems
encountered in the so-called nmr dilution experiments, a potentially
fruir.fui study is suggested concerning the carbenium ions which eject
fluorine in HCIO^ — H^O. That is, presume it is possible to fix a known
concentration ratio of a given unsubstituted phenylpyridylmethanol and
corresponding carbenium ion via appropriate manipulation of HCIO^ con¬
centration. This should establish two simultaneous equilibria: a) al¬
cohol interconversion with carbenium ion; and, b) carbenium ion inter¬
conversion with the species resulting after fluorine atom loss. This
19
investigation would obviously be monitorable by F nmr, and perhaps
new information concerning the stability of such types of carbenium
ions would be afforded from kinetic, as well as from thermodynamic
standpoints.
Linear Free Energy (I.FE) Correlations and Carbenium Ton Stability. A
number of analytical free energy correlations have been successfully

117
applied to the thermodynamic data obtained for the pyridylcarbenium
Iohss considered in this work. These correlations are presented graphi¬
cally (whére appropriate) in this section and discussed principally in
terms of the relative stabilities of the various carbenium ion species.
A significant outgrowth of these considerations is the indication that
coordination, which has been shown to stabilize a given carbenium ion
relative to the protonated ion, destabilizes the ion relative to the
unprotonated, uncoordinated ion (vide infra). This implies, rather ob¬
viously, that the localized removal of "sigma" electron density occurring
upon coordination to the palladium containing moiety cannot be separated
from a concomitant reduction of 77-electron density in the pyridine ring.
Consequently, it appears that complexation (for the cases considered
herein) does in fact destabilize the pyridylcarbenium ions.
Various studies (see, for instance, (12), (19), (77), (78), and
(79)) have demonstrated the suitable application of the famous Hammett
equation (80), log K = log K° + pa, towards the correlation of thermo¬
dynamic parameters for arylcarbenium ions. Therefore it was reasonable
to analyze the thermodynamic data obtained for the pyridylcarbenium
ions by similar methods.
The plots which are presented in Figures 13, 14, and 15, p. 118,
established the following relationships to be linearly dependent:
(i) Hammett "exalted" To . constants vs. AG° of carbenium ion
P —
formation. (The. a^.p values employed were 0.00 for para-H; -0.07 for
para-F; -0.31 Cor para-CH.,; and -0.78 for para-OCH^ (81). Curves 1, 2,
and 3, are for protonated 2-pyridyl, protonated 4-pyrldyl, and bis-
palladium(II) ecmplexed 4-pyridylcarbenium ions respectively.)

.118
Fig.- 13. Hammett £0^4. vs. AG0(carbenium ion formation). See p. 117 for
explanation
Fip,. 14. Carbenium ion 6 relative to external CFCI3 vs. AG° of same.
See p. 117 for explanation.
Fi . 15. Hammett £0 -|- \ns. carbenium ion 6 relaLive to external CFCl^.
See p. 117 lor explanation.

U9
19
(ii) Carbenium ion F nmr chemical shifts recorded relative to
¿Ar.ei.nal CFCl^ vs. related values of AG°. (Curves 4, 5, and 6, corre¬
spond to tin' same carbenium ion sequence as in (L) above. The point
on curve 4 designated by the * is extrapolated to the abscissa to yield
AG° for the formation of unsubstituted phenyi-2-pyridylcarbenium ion.)
19
(iii) Hammett "exalted" constants vs. carbenium ion F
nmr chemical shifts relative to external CFCl^. (Curves 7, 8, and 9,
correspond to the same carbenium ion sequence as in (i) above.) The
ensuing discussion is in respect to these relationships. The appropriate
application of Hammett a _j. constants (rather than the usual a constants)
in free energy correlation analyses for arylcarbenium ions upon varia¬
tion of electron donating, para-phenyl substituents has been established
principally through the work of Deno and Evans (78), and Brown and
Ckaucto (82) . Therefore it was expected that these parameters were
found to correlate exceptionally well with the pyridylcarbenium ion
stability data. Admittedly, it is seen that in each case the curves
have been drawn employing only three data points. None the less, the
degree of linearity obtained for all correlations considered is aston¬
ishingly good. And, although in certain instances nonlinear free energy
correlations may prove to be interesting and important, a linear correla¬
tion is the required sine qua non for the immediate and direct prediction
of interrelated but otherwise "unknown" thermodynamic information.
Indeed, it is on this basis that the stability constant data reported
for 2-pyridy.l.phenyl-A-f luorophenylcarbenium ion (Table V, pp. 95-96)
have been obtained and deemed reliable. That is, plots 2 and 3 in
Figure 13 served to establish the linear interdependency of Jjkx + and
AG° for carbenium ion formation for the various 4-pyridyl species.

1.20
Similarly, plots 7, 8, and 9, have demonstrated the linear relation¬
ship of Zo t and ó for each carbenium ion species investigated. Hencej
as shown, the construction of plot 4 in Tigure 14 using the nmr and
40° data for the 2-pyridyl-4-methylphenyl, and 2-pyridyl-4-inethoxyphenyl
protonated carbenium ions, allowed the determination of AG° for the
corresponding unsvbstituted phenyl ion. (Note: For these analyses the
tun;, data recorded relative to external CFCl^ were used exclusively
owing to the greater significant figure accuracy obtained for carbenium
.¡.on chemical shifts measured relative to this standard. Viz. , as in¬
dicated by the data contained in Table VI, pp. 110-111, the positions
of the sample and reference signals with external TFA as standard were
relatively close. Consequently, only two significant figure reliability
could be obtained for the nmr data measured relative, to external TFA.
Nevertheless, to check these LFE analyses, similar plots were drawn
using the TFA. referenced nmr data, and these plots also were linear.)
Two additional LFE plots of interest are illustrated in Figures
16 and 17, p. 121. The linearity of these plots suggests a proportionate
change in carbenium ion stability throughout the related 4-pyridyl vs.
2-pyridyl (Figure 16), and 4-pyridyl v£. bis-complexed 4-pyridyl (Figure
17), series of ions. The slope (= 0.829) of the line in Figure 16 re¬
flects the lower stability of a given 2-pyridylcarbenium ion compared to
its 4-pyridyl congener. Extrapolation of this curve to the intercept,
however, yields an inexplicable result from which it j's implied that
for relatively stable pyridylcarbenium ions (i.e., AC° very small, or
negative) the 2-pyridyl ions are ultimately the more stable. Consequently,
it appears that extrapolation of this curve to a considerable extent
beyond the data points is not warranted. The slope (= 1.04) of Figure 17

Fig. 16. AG°(uncoordinated 4-pyridylcarbenium ions) vs_. AG°(uncoordi¬
nated 2-pyridylcarbenium ions).
AG
.kcal.
^ mol '
* i T i
0.00 10.00 20.00 24.00
AG° (kcal/rnol)
Fig. 17. AG° (uncoordinated 4-pyridylcarbeuiuru ions) vs. AC»° (bis-com-
plexed 4-pyridy]carbenium ions).

122
uo-Toborates r.lie conclusion previously arrived upon that complexation
stabilizes the least stable 4-pyridylcarbonium ion l;o the greatest
extent. In this case the intercept value implies that a coordinated
pyridylearbeniuir ion is inherently more stable than the corresponding
nrotonated icn. This is a reasonable result:. Of course, identical
analyses of new, related data are required before more exacting con¬
clusions can be drawn. (Note: Several other linear plots are construct-
ihie using the accumulated thermodynamic data owing to the established
linear interdependencies (as shown) of AG°, and 6. These plots can
be synthesized as necessary for supplementary correlation studies.)
An examination of the slopes of the curves of Figures 13, 14, and
15 (1/p % -9.42 for curve 1; 1/p = -7.82 for curve 2, and 1/p = -7.48
for curve 3; these slopes are reported as 1/p for the comparisons which
«.re to be made) affords a simple method for comparing the stabilities
of ihe pyridylcarbenium ions to related systems of arylcarbenium ions
which have been investigated previously via similar techniques. That
is, as pointed out by Freedman (64:1548), a plot of AG° vs. ^op+ for
a series of structurally and substitutionally related arylcarbenium ions
yields a straight line whose slope reflects the degree of electronic
demand at the carbenium ion center. And, in these cases, a negative
slope indicates that the presence of electron releasing substituents
capable of interacting conjugationally with the carbenium ion positive
charge facilitates the development of that charge. Thus, carbenium ion
stability is enhanced by substituents such as para-methyl and para-
methoxy relative Lo para-II, etc. Also, the magnitude of the slope is
a relative measure of the stability of the particular family of ions
under consideration. For example, p for plots of AGp+ vs. Ea q. is on

the order of -2.5 for a series of malachi.ce green carbenium ions, -4.5
for a series of tritylcarbenium ions (64:1.749), and -8 for para-sub-
stituted diphenylmethylcarbeniuro ions (64:1550). Therefore the sta¬
bilities of the pyridylcarbenium ions are again shown to be in the order:
Coordinated 4-pyridyl > protonated 4-pyridyl > protonated 2-pyridyl;
and furthermore, these results imply that the 4-pyridyl ions are but
minimally more stable than diphenylmethylcarbenium ions, whereas the
2-pyr.idyl ions are appreciably less stable.
Finally, the use of certain, appropriate arguments permit a reason¬
able comparison of the stability of the protonated and complexed 4-pyr-
i.dylcarbenium ions to the stability of such ions premised upon a non¬
bound pyridine nitrogen. That is, although it. is not possible, obviously,
to investigate an unprotonated free ligand pyridylcarbenium ion in
strongly acidic media, it is necessary to speculate on the stability of
this ion in order to estimate the net stabilizing effect exerted by
the metal containing moiety on the coordinated ion. This is done in
the following fashion. The contribution to the stability of a triaryl-
type carbenium ion by an unprotonated pyridine ring may be approximated
using the literature pKp+ values for malachite green (MG) carbenium
ion (pK_j. = 7.07) and 4-pyr.idine malachite green (4-pyMG) carbenium
ion (pKj>-f “ 5.66). These data have been taken from the compilation of
Nemcova et al. (83). (Note: Here pKj,+ corresponds to the equilibrium
reconversion of carbenium ion to precursor alcohol: R+ + 2 ^0 J R-OH
3- H,,0‘ ; and 4-pyMG is simply MG with the unsubstituted phenyl ring re¬
placed with a 4-pyridyl ring.) An examination of these pK^_j. values
indicates that exchange of a phenyl ring for a 4-pyridyl ring induces
a net carbenium ion destabilization of 1.41 pK units (1.92 kcal) in

124
the MG so. 1/5.*«; of ions. This destabilization may be quantitatively
loinLed to strictly triphenyl-type carbenium ions (1. e. , tiiose without
pat a--anil no substituents) by comparing the slopes (p's) of the plots
of log K vs. >Ja j. for the MG series of ions (p = -1.4) to that for the
triphenyl ions (p - -3.5), (S4:101-102) . That is, as pointed out by
Mine, phenyl ring substitution in the triphenyl ions induces a consider¬
ably greater change in carbenium ion stability than does the identical
substitution in the MG series of ions. Hence, the larger negative slope
of this plot for the triphenyl ions reflects the greater sensitivity of
the stability of these ions to electronic effects. This consideration
is illustrated through a simple analysis of the pK data given below.
These data are in respect to the general equilibrium described above.
(i) pKp+ of triphenylcarbenium ion = -6.63; and pK^+ of para-
nitrotriphenylcarbenium ion = -9.15 (10).
(ii) pKp^-i- of MG carbenium ion = 7.07; and pK^+ of para-nitroMG
carbenium ion = 6.00 (64:1534). Thus, as expected, the destabilizing
effect exerted by a para-nitro substituent is much greater in the tri¬
phenyl scries of carbenium ions (-2.52 pK units) than in the MG series
of carbenium ions (-1.07 pK units). And, the ratio of these desta¬
bilizing contributions, 2.52/1.07 = 2.36, is certainly comparable to
that predicted from the slope ratio, 3.5/1.4 = 2.5. Now, in that pyr¬
idine exhibits tendencies towards electrophilic aromatic substituti.on
which are similar to nitrophcnyl rings, and since both of these systems
destabilize trityl-type carbenium ions, it is reasonable to predict pK^p
for unprotonated 4-pyridyldiphenylcarbenium ion to be on the order of
-6.82 - 2.5(1.41) = -10.34 = pK^j.. (Note: For this approximation -6.82
is Lhe value for of triphenylcarbenium ion. This is the average of

125
the pK_,_|_ values cited in Table V, pp. 95-90, for this ionic species
in 70% RCIO^.) A comparison of this value (-10.34) to the pK+ values
which have been determined for the protonated (pKR+. - -13.47) and bis-
compiexed (pK + = 12.21) 4-pyridylphenyl-4-fluorophenylcarbeniom ion,
strongly suggests that the unprotonated ion is appreciably more stable
than either the protonated (obviously) or the palladium complexed ion.
Moreover, the para-fluoro substituent would contribute additional sta¬
bilisation. to this ion such that the actual pK_^+ i^ould be slightly
greater (less negative) than the speculative value of -10.34. This
further substantiates the validity of the hypothetical stability com¬
parison.
Suitable use of the log K vs_. ZcTp_|_ plots given by Hine (84:101)
in conjunction with the results of Barker et_ jfL. (52) affords another
simple corroboration of this consideration. That is, examination of
the plot for the MG series of ions (Hine) reveals that for MG with pK^+
= 7.C7, £°p+ = -3.4; and for 4-pyMG with pK^+ = 5.66, Zcjp.p = -2.5. Thus,
with Op4. = -1.7 for para-N(CH^)^, a hypothetical value of a = 0.9 is
predicted for a 4-pyridyl ring, thereby demonstrating the electron
withdrawing capacity of a pyridine ring taken as an arylcarbenium ion
substituent. This value is comparable to = 0.78 for a nitro group
as a para-phenyl substituent; and the ratio 0.9/0.78 = 1.2 is in good
agreement with the ratio 1.41/1.07 = 1.3 which is obtained from the
respective energetic destabilizations of a 4-pyridyl ring and a 4-nitro-
phouyl ring in MG carbenium ion. Similarly, the linear correlation of
v (kK) with Hammett a substituent constants discovered by Barker
and coworkers for a series of phenyl substituted MG carbenium ions

126
yHows a prodiction of a of ca. 1.0 - L.l for the 4-pyridyl ring in
4-pyMC. This t or re] at ion is mide by using the value oí 3.5.4 kK re¬
ported for v at X for 4-pyMG (83). Furthermore, use of the second
max
linear plot presented by Hine of log K vs. £o + for triphenylcarbenium
ions, and the provisional value of ca. -10.3 for pK^+ of unprotonated
4-pyridylphenylcarbenium ion, allows a value of o of ca. 1 to be ob¬
tained for the 4-pyr.idyl ring. Tims, the hypothetical a values which
are predicted for a 4-pyridyl ring treated as a substituent in arylcar-
benium ions are found to be in very good agreement. Therefore, on this
basis, it is reasonable to conclude that an unprotonated pyridine ring
is of approximately the same electron withdrawing capacity as a nitro-
phenyl ring, but, as suggested previously, is not as electron withdrawing
as the palladium complexed pyridine ring.
A last extension of these considerations can be made employing
the results of Atkinson et_ aT. (85). These workers satisfactorily
demonstrated the existence of a linear correlation between the frequen¬
cies (v, kK) of the longest wavelength electronic absorptions and Taft
a* polar substituent constants for a family of diphenylmethylcarbenium
+
ions ((J^-C-X) generated in 96% H^SO^. The group X is the substituent
which is varied in this series of ions. Here, a* reflects the electron
releasing or withdrawing capacity of X depending upon the exertion of
polar effects by X. Since the 4-pyridylcarbenium ions are of comparable
stability to the diphenyl ions (p. 122) and have exhibited about the
same sensitivity to changes in electronic environment at the carbeniutn
ion center as these ions (recall the similar p values for plots of AG°
vs. Zo + for these ions), it is reasonable to estimate values of a* for
p
the protonated and coordinated pyridine rings taken as polar substituents.

127
un fact, tHti treatment may indeed be more logical than the a evaluation
ov/iv'.g to the polar character produced in the pyridine ring by pro fona¬
ción (and, apparently, by coordination as well). Inasmuch as the elec¬
tronic spectral investigations have indicated that the absorption at
A reflects principally electronic interactions between the carbenium
man
ion center and the phenyl rings, it is necessary to consider the fre¬
quencies at A fot the protonated and bis-palladium complexed unsub¬
stituted 4-pyridyldiphenyIcarbenium ion. The frequencies are 21.0 kK
and 21.4 kK, respectively, for these ions in 96% H^SO^ (7). (Note:
The electronic spectra of these ions are not changed in 70% HCIO^.)
Using the v — e* correlation plot (85) hypothetical values of a* of cn.
1.0 for protonated pyridine, and a* of cji. 0.85 for palladium-conplexed
pyridine are obtained. These a* values indicate rather substantial
electron withdrawing capacities for these pyridine moieties. Again,
based upon the comparable stabilities expected for 4-nitrotriphenyl-
earbenium ion and unprotonated 4-pyridyldiphcnylmethylcarbenium ion,
a speculative value of a* can be estimated for the unprotonated pyridyl
ring. That is, since v at A for the nitro ion is 22.0 kK, which
max
correlates with, a* of £a. 0.6, a value of a* of ca_. 0.6 — 0.7 is pre¬
dicted for the unprotonated pyridyl ring. Of course, this speculation
rests on the assumption that these two ring systems influence the fre¬
quency at A to approximately equal extents. This contention is
supported by the fact that these ring systems have been shown to be of
comparable electron withdrawing capacity. Therefore, as indicated
previously, the palladium(II) containing moiety employed in this work
as the coordinating agent, aopears to contribute an overall thermo¬
dynamic destabilization to trityl-type pyridylcarbenium ions.

IN CONCLUSION
The experimental bases which have been established for the investi¬
gation of heteroaromatic carbenium ions (6, 7, and 8), have been re¬
inforced and expanded by this work. The achievements which are felt to
be of principal significance are the following:
(i) The preparation of the mixed "mono" alcohol complexes (denoted
in the text as [I’d (II) (pyLOH) (L^) C^] ) appears to be the first success¬
ful application of a synthetic method generally suitable for the selec¬
tive incorporation of strong 7r-acid ligands into the coordination sphere
of palladium(II), to include pyridine-type donors. Consequently, it is
now expected that pyridine containing arylcarbenium ion precursors can
be introduced as ligands ad_ libitum into palladium(II), as well as
certain other, metal centers. Therefore, many additional, related
studies on ccmplexed carbenium ions have been made feasible by the
development of this synthetic technique.
(ii) The thermodynamic stabilities determined for the various
carbenium ion species considered herein provide strong evidence to in¬
dicate that charge repulsion effects tend to destabilize the 2-pyridyl
ions to a considerable degree. On the other hand, the very similar
stabilities found for related "mono" and "bis" complcxed carbenium ions
indicate that charge repulsion effects in the doubly ionized "bis" ion
systems are no longer sufficient to destabilize, these ions. So, it is
128

1.29
potent:.iaily of value to prepare several "bis" carbeniura ion complexes
v.'Ltt the interesting prospect of determining the sensitivity of the
stabllJ-ty of a particular complexed carbenium ion to intra-species
charge repulsion effects. Moreover, carbenium ion stabilization provided
by various metal-containing coordination centers can be considered in
respect to this possibility. That is, effects on carbenium ion stability
resulting from variation of the central metal species, variation of
the oxidation state of the metal species, variation of the counter ligands,
etc., can now be investigated with similar intent.
(iii) Again, the results obtained from the "Deno" titration
stability measurements, established to be reliable by appropriate LFE
analyses, have shown that this titrimetric technique is a suitable
method by which to evaluate the thermodynamic stabilities of protonated
and complexed pyridylcarbenium ions. Furthermore, successful electronic
spectral interpretations have provided experimental and theoretical
substance towards correlating arylcarbenium ion electronic absorptions
with the aromatic ring systems which comprise the carbenium ion entity.
Consequently, it has been made possible to assess tentatively the con¬
tribution to coordinated carbenium ion stability exerted by various
metal containing moieties in terms of the relative degree of influence
upon the frequency of the so-called y-band electronic absorption as
measured for the different metal centers.
19
(iv) The applicability of F nmr chemical shift measurements as
a criterion of the stability of pyridylcarbenium ions has been established.
That is to say, a fluorine nucleus para substituted on a phenyl ring
has been shown to be a suitably sensitive probe for the purpose of
quantitatively estimating the stabilities of these types of carbenium

no
lone. A possibly fruitful extension of this work might well be provided
1 9
by ‘ f nmr measurements with the fluorine nucleus incorporated as a
nera phenyl substituent in the carbenittm ion molecular framework. By
a compra Lson of the results of these nmr investigations with the nmr
data at hand, 1 separation of a- vs. Tf-electronic effects within the
pyridylcarbenium ions is potentially achievable.
(v) The LFE correlations which have been applied to the thermo-
19
dynamic stability data, F nmr data, and the appropriate Hammett-type
substituent constants, have proved to be exceedingly good even though
only three data points were used for each analysis. Obviously, the
preparation and investigation of additional pyridylcarbenium ion species
by varying para phenyl ring substituents, affords a simple means of
exclusion of the current work. The stability predictions made in
reference to uuprotonated 4-pyridyldiphenvlcarbenium ion could be pursued
o .perimentally via the syntheses of salts of the various pyridylcarbenium
ions, followed, of course, by appropriate measurements to determine the
stability of these ions. The preparation of stable salts of the coor¬
dinated carbenLum ions could well be stimulating and provocative owing
to the stringently anhydrous, nonbasic, conditions required in order
to sustain the existence of such materials. Consequently, it could
prove difficult to develop a preparative route during which the metal
containing moiety would remain coordinated during the conversion of
alcohol t:o carbenium ion salt.
To recapitulate then, the experimental studies on the various
carbenium ion species which have been carried out during this v/erk have
been very successful. It is therefore proposed that the scope of
thermodynamic investigations upon free and complexed heteroaronatic

33
carbaniam ions can now be. broadened considerably by extending these
r.cndiet: to include related systems of arylcarbenium i ons.

APPENDIX

I. _ Spec it: ic Gray it y of Aqueous HClU^ Determined as a Function o f
Wt_%_ ilClO/t. By employing the specific gravity (0) — wt % HCIO^ data in
Table TV, p. 91, a computer fitted "least squares" estimate of p as
a .function of wt % UCIO^ was obtained. This was carried out by assuming
the functional relation y(p) = f(x) (x = wt %) to be of the form:
2 3 4
y --- aQ + a^x + a2x + a^x + a^x {15}
ter y vs. x which yields a smooth curve plot over the entire range of
experimental (x,y) values. Then, the values of the coefficients (a's)
for this polynomial are obtained from a least squares estimates analysis
by minimizing the sum of the squares of the deviations which result
from:
(deviation)2 - [y(calcd from {15}) - y(exptl)]2 {16}
summed over all the experimental points. With the a's calculated,
equation {15} is:
y = 0.996357669170ex 00 + (0.606617i34345ex - 02)x -
(0.171560538090ex - 04)x2 + (0.164401851371ex - 05)x3 -
(0.98 L691970813ex - 0S)x4 {17}
from which a complete series of p values as a function of wt % HCIO^
3 4
is obtained. (Note: it was found that the x and x terms may be
neglected with no loss in data precision to 4 significant figures.)
These data were processed at intervals of 0.010 wt % spanning the range
133

136
P ~ 0.996357 aL wt % HCIO^ = 0.000 (i. e., pure water at 25°), to p =
1.737627 at wt % UCIO^ = 75.000. The p values '-;ere rounded to 4
significant figures for the required D.F. calculations. The program
employed was: WANG Series 700 V 1. General Library, Program 1063A/ST3
til
— "N ' order regression analysis". A general description of the method
is provided by Kuo (86).
2. Degree of Protonation of a Pyridylmetnanol (pyLOH) in Aqueous
IICIO4. In reference to the assumption that a pyridylmethanol is of
approximately the same basicity as pyridine (p. 99), straightforward
3t.id-!>ase equilibrium calculations may be employed showing that the
degree of pyridine ring protonation is virtually 100%:
(i) In connection with this assumption the following equilibria
can be written:
pyLOH + H20 t H+pyL0H + 0H~ {18}
and
H+pyL01I + H20 t pyLOH + 1I30+ {19}
-9
(ii) Using {19} and = 2.3 x 10 for pyridine, the equilibrium
constant for {19} can be evaluated:
= IPVLOII] [thO+] [OH ] =
{19} [H+pyLOH] ‘ [0H“]
and

:¡ 3á
kw 1.0 >: 10~x4
1C,' 2.0 x 10-9”
f)
4.3 x 10
-6
(iij) Now, with the conditions specified as [H^0+] = 1 and
[pvLQH]. - 0.01 (p. 99), it follows that for
Snxt. r
,.+
pyLOH + li30 t H pyLOH +
O
{20}
v{20}
K{19}
4.3 x 10-6 2,3 x 10
and. if [H pyLOH] = x,
K
/oof
1 C. KJ J
[H+pvL0H]
[pyLOH][K30+]
x
(0.01 - x)(1 - x)
= 2.3 x 10'
ana
x
(0.0.1 - x)(l - x)
0.01 - x
since 1 >>0.01 > x
and for
x
0.01 - x
10'
10
-2
10-7
x is on the order of cxi. 0.0099999! Hence, within the limits of the
calculation, a given pyridylmethanol at ca. 0.01 M (initially) is
profonated togn extent of 100% in 1 M [H30+].

UG
3_. I|xoi «rímente Conducted upon the Carbenium Ion Species Found
to_ Exhibit PLearrsngo.tient in 70% HCIO4. As indicated by previous in¬
ves ti f>?. Lions which have employed acidic media to generate arylcarbenium
ions containing pa r a-1: lucro phenyl substituents, the fluorine atom
may eventually he displaced resulting in the formation of either an
alcohol (68) or a quinone (79). Consequently, loss of the para-
fluorine substituent from the pyridylphenyl--4-f luorophenylcarbenium
ions in the HCIO — Ho0 was not unusual since in these carbenium ion
systems the para-flucro substituent: is the predominant electron-
donating entity involved in conjugational interaction with the car¬
benium ion center. Therefore positive charge build-up at the para-
positicn in the fluorine-containing ring ultimately results in nucleo¬
philic displacement (presumably by solvent molecules) of the fluorine
substituent.
Tn recording the electronic spectra of these pyridylphenyl-4-
fluorophenylcarbenium ion species it was observed that the intensity
of the main absorption bands (the x and y bands) grew steadily upon
standing until the intensities had approximately doubled. Moreover,
it was observed that the positions of these bands remained essentially
unchanged during rearrangement of the uncoordinated ions, whereas the
mono-complexed [Pd(II) (L^)C].2PyL]+ carbenium ion exhibited an x-band
shift to 494 nn after standing a period of 12 days. (Recall that
\ for this carbenium ion as the protonated species is 482 nm, and
max
for this particular complexed ion is 477 nm) . Thus, it is seen
max 1 r
that the "new" A (494 nm) is appreciably longer even than A for
the free (protonated) Lon (482 nm). Also, the bis-complex of this ion
exhibited a shift in A from 470 nm to 482 nm after standing a period
max

¡8f £> days; this species, however, exhibited no further red shift of
the x-band absorption as did the corresponding mono-complexed ion
(.above). These results are as yet not explicable.
In an attempt to estimate the relative stability of the rearranged
product, assuming it to be a new arylcarbenium ion, this species was
titrated via the usual method. This was carried out by preparing a
fresh sample of 4-pyridylphenyl-4-fluorophenylcarbeni.um ion in 70%
IIC10 and titrating immediately. The sample was then allowed to stand
ca. 24 hours during which time the intensity of the x-band absorption
had essentially doubled. This result indicated that although the orig¬
inal carbenium ion had been substantially reconverted to protonated
alcohol precursor by titration, the protonated precursor was still
capable of rearranging to the new species thereby implying that the
new species was a more stable carbenium ion. After the intensity of
the x-band had become constant, indicating that rearrangement was
complete (under these conditions), the titration was repeated. This
second titration required approximately three times as much titrant
(water) in order to effect the same absorption fall-off as compared to
the initial titration. So, again, this species appeared to be a more
stable carbenium ion than the original pyridylphenyl-4-fluorophanyl
ion from which it was derived.
Finally, a sample of 4-pyridylphenyl-4-fluorophenylmethanol
(ca. 100 mg) was dissolved in 70% HC.10^ (ca. 10 ml of acid) to complete!
covert it to carbenium ion. Rearrangement was again monitored spec¬
troscopically, and after it was apparent that no further changes in the
electronic spectrum of the sample were occurring, the acid was neutral¬
ised by the careful addition of reagent NII^.
This resulted in the

133
separa Li on. of a Mixture ot n white crystalline solid and a rather gummy
yellow solid. The mixture of solids was transferred to a filter and
washed with copious quantities of deionized water. The white solid
was readily removed by the washing, and the yellowish material remained
on the filter. The contents on the filter were, air dried to yield ca.
15 mg of a yellow-orange amorphous solid. This material exhibited
decomposition to a brown-black oil above 140° and an 1R analysis
revealed that this material was different than the original alcohol.
A visible spectrum of this material in 70% HCIO^ was identical to that
19
previously obtained for the so-called rearrangement product. The F
nmr spectrum of this material in 70% IICIO^ was also recorded. Following
3000 scans with the Fourier transform synthesizer two weak signals
(at 37.7 ppm and 68.9 ppm upfield with respect to external TFA) were
detected. These signals did not correspond to any of the nmr signals
which had been recorded relative to external TFA during previous
ea,rhenium ion nmr analyses; and the very low intensities of these signals
indicated the absence of any appreciable concentration of fluorine in
the sample. Hass spectral cracking analyses of this material revealed
the presence of molecular ion fragments of nominal mass as high as 520.5
armi; and, at relatively low probe temperatures (200° or less) a 259 amu
base peak was consistently observed. Interestingly, the 259 peak
corresponds to the mass of the quinonc. species which would result from
the combined effects in the parent alcohol, of quinonc formation at the
original fluorine site and hydroxyl loss at the exoc.yclic carbon. Care-
!cl analyses of these spectra, however, suggested the presence of as
runny as four new compounds with the distinct possibility of one or
more of these materials existing as a polymer. Rather obviously

139
therefore,, the nature of the materialfs) produced upon fluorine atom
displacement, from the pyridylphenyl-4-fluorophenylcarhenjum ions in
UC10. — H?0 remains to be ascertained.

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BIOGRAPHICAL SKETCH
James Chañes Horvath was born June 29, 1942
lie was very fortunate to recognize that learning
experience which life forever offers. Who knows
, in Toledo, Ohio,
is a wonderful
what may lie ahead?
145

i certify that I have read tnis study and that in my opinion
it c Oi it orris to acceptable standards of scholarly presentation and
if) fulry adequate, in scope and quality, as a dissertation for the
degree of Doctor of Philosophy.
R. Carl Stoufer, Chairir.aii/y
Associate Professor of Chenistry
I certify that I have read this study and that, in ray opinion
it conforms to acceptable standards of scholarly presentation and
is fully adequate, in scope and quality", as a dissertation for the
degree of Doctor of Philosophy.
Merle A. Battiste
Professor of Chemistry
I certify that I have read this study and that in my opinion
it conforms to acceptable standards of scholarly presentation and
is fully adequate, in scope and quality, as a dissertation for the
degree of Doctor of Philosophy.

I certify that 1 have read this study and that in ny opinion
it conferías to acceptable standards of scholarly presentation and
Ls fally adequate; in scope and quality, as a dissertation for the
degree of Doctor of Philosophy.
Professor of Chemistry
I certify that 1 have read this study and that in my opinion
it conforms to acceptable standards of scholarly presentation and
is fully adequate, in scope and quality, as a dissertation for the
degree of Doctor of Philosophy.
Professor of Electrical Engineering
of the Departirían
the Graduate
requirements
March 1978
Tills dissertation was submitted to the Graduate Faculty
of Chemistry in the College of Arts and Sciences and to
Council, anc was accepted as partial fulfillment of the
for the. degree of Doctor of Philosophy.
Dean, Graduate School