Syntheses and ring-opening reactions of alpha-fluorocyclopropyl sigma-complexes of iron

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Title:
Syntheses and ring-opening reactions of alpha-fluorocyclopropyl sigma-complexes of iron syntheses and fluxionality studies of iron and ruthenium cyclic allenes
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xiii, 143 leaves : ill. ; 29 cm.
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English
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Omrcen, Tatjana, 1961-
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Subjects / Keywords:
Iron   ( lcsh )
Ruthenium   ( lcsh )
Complex compounds   ( lcsh )
Organic compounds -- Synthesis   ( lcsh )
Chemistry thesis Ph.D
Dissertations, Academic -- Chemistry -- UF
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bibliography   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph.D.)--University of Florida, 1992.
Bibliography:
Includes bibliographical references (leaves 138-142).
Statement of Responsibility:
by Tatjana Omrcen.
General Note:
Typescript.
General Note:
Vita.

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University of Florida
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SYNTHESES AND RING-OPENING REACTIONS OF ALPHA-
FLUOROCYCLOPROPYL SIGMA-COMPLEXES OF IRON. SYNTHESES AND
FLUXIONALITY STUDIES OF IRON AND RUTHENIUM CYCLIC ALLENES















BY


TATJANA OMRCEN


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY



UNIVERSITY OF FLORIDA

1992


UNIVERSITY OF FLORIDA LIBRARY;















ACKNOWLEDGEMENTS


I would like to thank Dr. W. M. Jones for his guidance

on this project, for the time spent discussing chemistry and

many other topics, and for being there for me.

Thanks also go to Rhonda Trace for her support,

understanding and the fun times.

Special thanks to my parents who taught me all the

important values in life.

I would finally like to thank all the great people I

have met here, who have made my arrival and stay in the

United States a pleasant and unforgettable experience.















TABLE OF CONTENTS

ACKNOWLEDGEMENTS ............................................ii

LIST OF TABLES .............................................vi

LIST OF FIGURES ...........................................vii

LIST OF ABBREVIATIONS ........................................x

ABSTRACT ................................................. ...... xi

CHAPTER

1 INTRODUCTION.........................................1

2 SYNTHESES AND PHOTOLYSIS REACTIONS OF a-
FLUOROCYCLOPROPYL Fp SIGMA COMPLEXES ............... 6

3 SYNTHESES OF IRON AND RUTHENIUM ALLENE COMPLEXES.... 41

4 FLUXIONAL PROCESSES IN IRON AND RUTHENIUM CYCLIC
ALLENES ........................................... 93

5 EXPERIMENTAL.......................................111

Syntheses of 1,l-dibromo-trans-2,3-
dimethylcyclopropane and 1-bromo-l-fluoro-
trans-2,3-dimethylcyclopropane .................112

Synthesis of dicarbonyl (r5-cyclopentadienyl)(1-
fluoro-trans-2,3-dimethylcyclopropyl)iron
2 .2 8 ........................................... 113

Thermal decomposition of dicarbonyl(T5-
cyclopentadienyl)(l-fluoro-trans-2,3-
dimethylcyclopropyl)iron 2.28 .................. 114

Photolysis of dicarbonyl(15-cyclopentadienyl)(1-
fluoro-trans-2,3-dimethylcyclopropyl)iron
2.28 .......................................... 115

Thermal rearrangement of syn-anti dimethyl 13-n-
allyl complex 2.32 to syn-syn dimethyl T3-K-
allyl complex 2.33 .............................115


iii










Synthesis of l-bromo-trans-2,3-dimethyl-
cyclopropane .................................... 116

Synthesis of dicarbonyl(15-cyclopentadienyl)
(trans-2,3-dimethylcyclopropyl)iron 2.36 ....... 116

Photolysis of dicarbonyl(15-cyclopentadienyl)
(trans-2,3-dimethylcyclopropyl)iron 2.36 .......117

Synthesis of 7-bromo-7-fluorobicyclo[4.1.0]
heptane 2.41 ...................................117

Synthesis of dicarbonyl(T5-cyclopentadienyl)(7-
fluoro-7-bicyclo[4.1.0]heptyl)iron 2.39 ........118

Photolysis of dicarbonyl(T5-cyclopentadienyl)(7-
fluoro-7-bicyclo[4.1.0]heptyl)iron 2.39 ........ 119

Synthesis of dicarbonyl(95-cyclopentadienyl) (2-
1,3-dimethylallene)iron tetrafluoroborate
1 .0 7 ......................................... 119

Synthesis of dicarbonyl(T5-cyclopentadienyl)(4-
hydroxy-2-penten-3-yl)iron 2.31 ................ 120

Synthesis of dicarbonyl(15-cyclopentadienyl)(112-
1,2-cycloheptadiene)iron tetrafluoroborate
3 .02 ......................................... 121

Synthesis of 6-bromo-6-fluorobicyclo[3.1.0]
hexane 3.11 .................................. 122

Synthesis of dicarbonyl(15-cyclopentadienyl)(6-
fluoro-6-bicyclo[3.1.0]hexyl)iron 3.10 ......... 122

Attempted synthesis of dicarbonyl(55-
cyclopentadienyl) (12-1,2-cyclohexadiene)iron
tetrafluoroborate 3.08 .........................123

Synthesis of dicarbonyl(T5-cyclopentadienyl) (6-
hydroxy-cyclohexen-1-yl)iron 3.13 .............. 124

Synthesis of dicarbonyl(15-cyclopentadienyl)(6-
methoxy-cyclohexen-1-yl)iron 3.09 from
dicarbonyl(T5-cyclopentadienyl)(6-hydroxy-
cyclohexen-1-yl)iron 3.13 ...................... 125









Synthesis of (COD)CpFeLi(DME) 3.16 ............... 126

Attempted synthesis of bistrimethylphosphine(15-
cyclopentadienyl)(7-fluoro-7-bicyclo[4.1.0]
heptyl)iron 3.19 ............... .............. 127

Attempted synthesis of bistrimethylphosphine(T5-
cyclopentadienyl)(7-methoxy-cyclohepten-l-
yl)iron 3.20 ................................... 128

Synthesis of l-bromo-6-methoxy-cyclohexene ........ 128

Attempted synthesis of bistrimethylphosphine (T5-
cyclopentadienyl)(6-methoxy-cyclohexen-l-
yl)iron 3.21 ................................... 129

Attempted synthesis of dicarbonyl(T5-
cyclopentadienyl)(7-fluoro-7-bicyclo[4.1.0]
heptyl)ruthenium 3.22 .......................... 129

Synthesis of dicarbonyl (l5-cyclopentadienyl) (7-
methoxy-cyclohepten-1-yl)ruthenium 3.23 ........ 130

Synthesis of dicarbonyl(15-cyclopentadienyl) (T2-
1,2-cycloheptadiene)ruthenium
tetrafluoroborate 3.24 ......................... 131

Synthesis of dicarbonyl (5-cyclopentadienyl)(6-
methoxy-cyclohexen-1-yl)ruthenium 3.27 .........132

Attempted synthesis of dicarbonyl(T5-
cyclopentadienyl) (12-1,2-cyclohexadiene)
ruthenium tetrafluoroborate 3.26 ...............133

Attempted synthesis of carbonyl(15-
cyclopentadienyl)(7-methoxy-cyclohepten-l-
yl)triphenylphosphineruthenium 3.28 ............ 135

Attempted synthesis of bistrimethylphosphine (5-
cyclopentadienyl)(7-methoxy-cyclohepten-l-
yl)ruthenium 3.29 .............................. 136

Attempted synthesis of bistrimethylphosphine(55-
cyclopentadienyl)(6-methoxy-cyclohexen-l-
yl)ruthenium 3.30 .............................. 137

LIST OF REFERENCES .................... ....................138

BIOGRAPHICAL SKETCH ....................................... 143
















LIST OF TABLES


Table 4.01.




Table 4.02.


The experimentally determined exchange
rate constants kr/s-1 at various
temperatures t/oC for Rp allene 3.24 in
methylene chloride-d2. ....................... 100

The experimentally determined exchange
rate constants kr/s-1 at various
temperatures t/oC for Fp allene 3.02 in
methylene chloride-d2 ...................... 102















LIST OF FIGURES


Figure 2.01.



Figure 2.02.



Figure 2.03.



Figure 2.04.


Figure 2.05.


Figure 2.06.




Figure 2.07.





Figure 2.08.





Figure 2.09.


1H NMR spectrum of C-fluorodimethyl-
cyclopropyl Fp complex 2.28 in benzene-
d6 ....................................... 27

19F NMR spectrum of a-fluorodimethyl-
cyclopropyl Fp complex 2.28 in benzene-
d6 (fluorobenzene ref.) ..................... .28

13C NMR spectrum of a-fluorodimethyl-
cyclopropyl Fp complex 2.28 in benzene-
d6 .......................................... 29

1H NMR spectrum of dehydrohalogenated
compounds 2.29 and 2.30 in benzene-d6 ..... .30


13C NMR spectrum of dehydrohalogenated
compounds 2.29 and 2.30 in benzene-d6


..... 31


1H NMR spectrum of syn-anti dimethyl 13-_-
allyl complex 2.32 (kinetic product) in
benzene-d6. (*) indicates a small amount
of thermodynamic product 2.33 ..............


.32


19F NMR spectrum of syn-anti dimethyl T3-_-
allyl complex 2.32 (kinetic product) in
benzene-d6 (CFCl3 ref.). (*) indicates a
small amount of thermodynamic product
2 .3 3 ....................................... 33


Time resolved 1H NMR spectrum of the
thermal rearrangement of syn-anti dimethyl
13-t-allyl complex 2.32 at 70 C in
benzene-d6 .................................


.34


1H NMR spectrum of the thermodynamic
mixture after the thermal rearrangement of
syn-anti dimethyl r13-K-allyl complex 2.32
(x) in benzene-d6. (o) indicates presence
of endo, syn-syn compound 2.33a ............ .35









Figure 2.10.






Figure 2.11.


Figure 2.12.


Figure 2.13.


Figure 3.01.





Figure 3.02.


Figure 3.03.


Figure 3.04.


Figure 3.05.


Figure 3.06.


Figure 3.07.


Figure 3.08.



Figure 3.09.


19F NMR spectrum of the thermodynamic
mixture after the thermal rearrangement of
syn-anti dimethyl T13-K-allyl complex 2.32
in benzene-d6 (CFC13 ref.). (o) indicates
presence of endo, syn-syn compound 2.33a ... .36

1H NMR spectrum of a-fluoronorcaryl Fp
complex 2.39 in benzene-d6 ................. .37


19F NMR spectrum of a-fluoronorcaryl Fp
complex 2.39 in benzene-d6 (CFCl3 ref.)


... 38


13C NMR spectrum of a-fluoronorcaryl Fp
complex 2.39 in benzene-d6 .................

1H NMR spectrum of silica gel induced
ring-opened product 2.31 (a), compared to
previously proposed ring-opened product
3.05 (b) (Spectrum (b) reproduced from N.
Conti's Ph.D. Dissertation) .................

1H NMR spectrum of a-fluorobicyclohexyl Fp
complex 3.10 in benzene-ds .................

13C NMR spectrum of a-fluorobicyclohexyl
Fp complex 3.10 in benzene-dg ..............

19F NMR spectrum of a-fluorobicyclohexyl Fp
complex 3.10 in benzene-d6 (CFCl3 ref.).....

1H NMR spectrum of 6-hydroxycyclohexenyl
Fp complex 3.13 in benzene-d. .............


.39





.80


.81


.82


.83


.84


13C NMR spectrum of 6-hydroxycyclohexenyl
Fp complex 3.13 in benzene-dg. ............. .85

1H NMR spectrum of 7-methoxycycloheptenyl
Rp complex 3.23 in benzene-d6. ............. .86

13C NMR and APT spectra of 7-
methoxycycloheptenyl Rp complex 3.23 in
benzene-d ................ .................... 87

1H NMR spectrum of BF4- salt of 1,2-
cycloheptadienyl Rp+ allene complex 3.24
in methylene chloride-d2 at room
temperature .................................. 88


viii









Figure 3.10.



Figure 3.11.



Figure 3.12.


Figure 3.13.



Figure 4.01.


Figure 4.02.



Figure 4.03.


Figure 4.04.



Figure 4.05.


Figure 4.06.



Figure 4.07.



Figure 4.08.


Figure 4.09.


1H NMR spectrum of BF4- salt of 1,2-
cycloheptadienyl Rp+ allene complex 3.24
in methylene chloride-d2 at -40 OC. ......... .89


13C NMR spectrum of BF4- salt of 1,2-
cycloheptadienyl Rp allene complex 3.24
in methylene chloride-d2 at -40 oC. .........

1H NMR spectrum of 6-methoxycyclohexenyl
Rp complex 3.27 in benzene-d6. .............

13C NMR and APT spectra of 6-
methoxycyclohexenyl Rp complex 3.27 in
benzene-d6 ..................................

A pulse sequence used to perform the spin
saturation transfer experiment. .............


.90


.91



.92


.98


A plot of In[(H1+H3)/(H1-H3)] against the
delay time T in seconds for Rp allene
3.24, at four different temperatures. ...... 100

The Eyring rate plot for Rp allene 3.24
in methylene chloride-d2. ................... 101

A plot of ln[(H1+H3)/(H1-H3)] against the
delay time Z in seconds for Fp allene
3.02, at four different temperatures. ...... 102

The Eyring rate plot for Fp allene 3.02
in methylene chloride-d2 .................... 103

Temperature dependent 1H NMR spectra of
1,2-cycloheptadienyl Rp allene complex
3.24 in methylene chloride-d2. ............. 107

Expanded 1H NMR spectrum of BF4- salt of
1,2-cycloheptadienyl Rp allene complex
3.24 in methylene chloride-d2 at -40 OC. ... 108


Time course of the difference spectrum of
Rp allene complex 3.24 obtained after the
irradiation of H1, recorded at -30 oC. The
times shown correspond to the delay T
between the selective pulse and the
observation pulse ..........................


109


Temperature dependent 13C NMR spectra of
1,2-cycloheptadienyl Rp allene complex
3.24 in methylene chloride-d2 ..............110

















LIST OF ABBREVIATIONS


cyclooctadiene

cyclopentadienyl

pentamethylcyclopentadienyl

dimethoxyethane

(dicarbonyl)(cyclopentadienyl) iron

(dicarbonyl)(pentamethylcyclopentadienyl) iron

carbonyl(cyclopentadienyl)triphenylphosphine iron

highest occupied molecular orbital

lowest unoccupied molecular orbital

(dicarbonyl)(cyclopentadienyl) ruthenium

spin saturation transfer

tetrahydrofuran

trimethylsilyl trifluoromethanesulfonate


COD

Cp

Cp*

DME

Fp

Fp*

Fpp

HOMO =

LUMO =

Rp

SST

THF

TMSOTf=















Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy


SYNTHESES AND RING-OPENING REACTIONS OF ALPHA-
FLUOROCYCLOPROPYL SIGMA-COMPLEXES OF IRON. SYNTHESES AND
FLUXIONALITY STUDIES OF IRON AND RUTHENIUM CYCLIC ALLENES

By

Tatjana Omrcen

May, 1992




Chairman: William M. Jones
Major Department: Chemistry


There are no known a-fluoro substituted cyclopropyl

complexes of iron nor, to our knowledge, of any transition-

metal. These compounds are interesting in view of the

potential for fluorine to be abstracted with electrophiles to

give allenes, and to act as an electron donor which may

accelerate carbene and/or n-allyl formation.

The l-fluoro-2,3-dimethylcyclopropyl Fp complex [Fp =

dicarbonyl(T5-cyclopentadienyl)iron] and its 7-fluoro-7-

bicyclo[4.1.0]heptyl and 6-fluoro-6-bicyclo[4.1.0]hexyl

analogues have been synthesized as the first examples of a-

halocyclopropyl a-complexes of iron.

Under photolytic conditions, the 1-fluoro-2,3-

dimethylcyclopropyl-Fp complex undergoes a ring-opening to










give a centrally substituted X-allyl complex. The ring-

opening is stereospecific, facilitated by the a-fluorine, and

occurs disrotatorily and away from the metal.

Reaction of the 2,3-dimethylcyclopropyl- and

bicycloheptyl-Fp complexes with BF3-OEt2 leads to fluoride

abstraction and ring-opening to give n2-1,3-dimethylallene

and T2-1,2-cycloheptadiene Fp tetrafluoroborate complexes,

respectively. Attempts to synthesize the first example of a

six-membered cyclic allene complex of a transition-metal by

this method were not successful.

In an attempt to extend our studies to ruthenium, 7-

methoxy-cyclohepten-l-yl- and 6-methoxy-cyclohexen-l-yl-Rp

[Rp = dicarbonyl(T5-cyclopentadienyl)ruthenium] complexes

were synthesized. Methoxy abstraction with HBF4 from the

former led to a formation of T2-1,2-cycloheptadiene Rp

tetrafluoroborate as the first example of a cyclic allene

complex of ruthenium. The same reaction with the six-

membered analogue did not lead to the formation of the T2-

1,2-cyclohexadiene Rp complex.

The seven-membered Rp allene complex demonstrates

fluxional behavior caused by a migration of the Rp group

between the two allene double bonds. Spin saturation

transfer studies were done to determine kinetic parameters of

the rearrangement. Parallel measurements were performed with

the analogous Fp complex for comparison purposes. The value

for AH* for the Rp allene was determined to be 14.13 0.15

kcal/mol, and AS* = -1.15 0.99 eu. In the case of the Fp


xii










analogue, AH* was determined to be 14.59 0.06 kcal/mol and

AS* = 0.65 0.22 eu. The fluxionality mechanism of the Rp

complex involves an asymmetric 1,2-Rp shift as determined

from the variable temperature 13C NMR studies.


xiii














CHAPTER 1
INTRODUCTION

Cyclopropyl derivatives of the transition-metals have

only recently received significant attention, and a variety

of the transition-metal complexes with this ligand have

appeared in the literaturel-4 since the first report for the

synthesis of (dicarbonyl) (5-cyclopentadienyl)cyclopropyl

iron complex 1.01 appeared in 1972.5


Cp





1.01

Because of the significant ring strain associated with the

cyclopropyl ligand (28.3 kcal/mol),6 its transition-metal

complexes undergo a variety of rearrangements, depending on

the metal and the reaction conditions used, in order to

relieve some of the strain.

In contrast to unsubstituted cyclopropyl complexes, the

a-substituted analogues of these compounds have not been

studied extensively. It has been found in Jones's group that

under appropriate conditions (-alkoxy cyclopropanes sigma

bonded to an Fp group (Fp=(dicarbonyl)(cyclopentadienyl)

iron) can become a source of carbene, allene and X-complexes.

The first example of this work was carried out by Lisko.7 He

reported that photolysis of the dimethyl-a-methoxycyclopropyl










Fp sigma complex 1.02 led to a-elimination of carbon to give

a ring expanded carbene complex 1.03.


Fp

p..OMe


1.02


hv
-CO


1.03


Later work with a-ethoxy compound 1.04 has shown that the a-

elimination to 1.05 is accompanied by a formation of a K-

allyl complex 1.06.8,9


hv I
OEt c-CO


1.04


1.05


oc\


1.06


In addition, reaction of the methoxy compound 1.02 with

TMSOTf resulted in a methoxy abstraction reaction that led to

cyclopropyl ring-opening to a corresponding allene 1.07.10


Fp

OMe


TMSOTf
-OMe


1 Fp+




H3C
If-l


1.07


1.02








This opened a door to an exciting area of chemistry of the a-
substituted cyclopropyl sigma complexes of transition-metals,
and it was followed by the preparation of other analogues
with (-substituents such as alkyl,8 phenyl,11 and thiophenyl.8
In general, a-alkoxy cyclopropyl complexes of Fp were

synthesized from the corresponding l-alkoxy-l-cyclopropyl
acid chloride and Fp anion, followed by photo-decarbonylation
of the acyl complex to give the desired sigma complex.

O 0
CCl Fp- C .hcFp hv Fp
OR OR OR



An important drawback of this procedure is a lengthy and
tedious synthesis of these precursors. For example, the
reaction sequence shown in Scheme 1.01 was employed for the
synthesis of the trans-2,3-dimethyl-l-methoxycyclopropyl Fp
sigma complex 1.02.10

S SPh SPh SPSPh


o 1
:C^c -ec. *,1\OM.



"II
Fp Fp COC COOH

OMe %. OMe OMe OMe
1.02
Scheme 1.01










In principle, a-halocyclopropyl Fp sigma complexes could

lead to chemistry similar to their C-alkoxy counterparts.

Furthermore, they could be much easier to prepare from the

corresponding 1,1-dihalocyclopropanes, which are easily

available by dihalocarbene addition to olefins. However, it

has been reported that reaction of Fp~ with a 1,1-

dichlorocyclopropane led to reduction rather than

substitution,12 and it was anticipated that the corresponding

dibromide may be reduced even more readily. Indeed, the only

product isolated in high yield from reaction of a variety of

gem-dibromocyclopropanes with the Fp- was the oxidation

product Fp2; no trace of the desired a-complex could be

detected. However, briefly before completing his Ph.D.,

Conti13 found preliminary evidence that this substitution may

have occurred in the bromo, fluorocyclopropane case, without

further reduction of the carbon-fluorine bond. This was

important because l-bromo-l-fluorocyclopropanes can be

prepared relatively easily by the addition of bromo, fluoro

carbene to a desired olefin by a variety of methods described

in the literature,14 thus providing easy access to a variety

of a-fluoro substituted cyclopropyl sigma complexes of iron

(and possibly other metals).


R ~R R1 R1
Br R Br Fp


SR3 R3
R3 R4 RA R4








5

In view of the fact that fluorine should be abstracted

readily with electrophiles, to give cyclopropylidenes and

allenes and, as an electron donor, may accelerate carbene

and/or X-allyl formation, a study of the preparation and

properties of a-fluorocyclopropyl sigma complexes of iron,

and its possible expansion to ruthenium, was undertaken. The

results of these studies are the principal focus of this

dissertation.















CHAPTER 2
SYNTHESES AND PHOTOLYSIS REACTIONS OF a-FLUOROCYCLOPROPYL Fp
SIGMA COMPLEXES

The first example of a unimolecular rearrangement of a

cyclopropyl sigma complex of a transition-metal was reported

by Mushak and Battiste in 1969.15 The authors proposed the

cyclopropyl palladium complex 2.01 as a possible intermediate

to rationalize formation of l-allyl palladium complex 2.02 as

a product of reaction of a cyclopropene derivative with

palladium(II) chloride.





Ph Ph
Ph ") >H + PdCl2(PhCN)2 Cl2Pd- > H

Ph Ph 2




-o

Ph
Ph
C\ H* Ph
Pd- Ph C--
C1 PdC1

Ph 2 Ph
Ph 2

2.02 2.01

In the same year, Bruce et al.16 published work on the

decarbonylation of a series of cyclopropyl acyl complexes of

6










transition-metals 2.03, 2.04, 2.05 in an attempt to

synthesize the corresponding cyclopropyl sigma complexes and

to further study various transformations of the three

membered ring.


0 0 0


^> Mn (CO)5 e Re (CO) 5 FeCp (CO) 2

2.03 2.04 2.05



They showed that all the compounds were extremely inert, and

attempts to decarbonylate them were generally unsuccessful.

No decarbonylation occurred on prolonged heating or UV

irradiation. However, when 2.03 was reacted with

triphenylphosphine, decarbonylation and ring-opening did

occur to give the x-allyl complex 2.06. The cyclopropyl

sigma complex was not isolated or observed.


0


SMn (CO)5 + PPh3 PPh3 (CO) 3Mn >


2.03 2.06



Compounds 2.04 and 2.05, however, did not show the same

reactivity.* Since these initial results, occasional other

reports have appeared in the literature. In 1972 Rosenblum5


* Some years later in 1982, Manganiello et al.17 showed that,
upon change of solvent, 2.05 did decarbonylate under
photolytic conditions to give the sigma complex, but it did
not ring-open.










reported the synthesis of the parent cyclopropyl-Fp compound

1.01 as the first isolated transition-metal complex having a

sigma-bonded cyclopropane ring. This was followed by Brown's

and Mertis'si report of the synthesis of the cyclopropyl

nickel derivative 2.07. However, neither of those complexes
has been shown to rearrange to the corresponding t-allyl

derivative.




H N.R.


1.01

SNNiCpPPh3
hvor A


2.07



The first unequivocal evidence that such a rearrangement can

occur readily was published by Phillips and Puddephatt in

1977.2 The authors were able to synthesize

chlorocyclopropyl-platinum complex 2.08 which, on treatment
with silver nitrate, rapidly ring-opened to give the i-allyl

platinum complex 2.09.





Pt-Cl Pt-c PF6
[ I [NH4PF6 PhMe2
PMe2Ph
2.08 2.09









The work by Jones and Ibers, published in 1983,3 has shown

that the iridium cyclopropyl compound 2.10 can be reduced

readily with potassium benzophenone ketyl to the isolable 16

electron derivative 2.11, which however, does not show any
tendency toward rearranging to the t-allyl complex 2.12.




CO

C '.. ..,,PMePh2 K (C6H5) 2CO COI,. ..I*%PMePh2 Ph2Me
I o >-Ir
Ph2MeP Ph2MeP 2Me Ph2MePI -
Cl

2.10 2.11 2.12


On the other hand, Periana and Bergman4 reported in 1986 that

iodocyclopropyl Rh complexes 2.13 reacted rapidly and

quantitatively with AgBF4 to give the r-allyl complexes 2.14.


R

Me3. -I AgBF4_ CI P +

R R Me3/R BF4
R
R=H, CH3
2.13 2.14


Jones's group has been interested in the rearrangements

of cyclopropyl sigma complexes of iron for some time now. As
already mentioned in Chapter 1, photolysis of the a-ethoxy Fp

sigma complex 1.04 leads primarily to a-elimination of carbon

to give the ring-expanded carbene complex 1.05, with a slower










side reaction of ring-opening to the R-allyl complex 1.06.8,9

The same kind of reactivity was observed with a-methoxy

substitution.8


QOEt -CO
OEt


1.04


1.05


oc \
+ Fe OEt


1.06
1.06


Photolysis of the a-thiophenylcyclopropyl Fp sigma complex

2.15 leads to the chelate 2.16 which, upon warming,

rearranges to its n-allyl isomer 2.17.8 In this case no

formation of carbene complex 2.18 was observed.


CO
/- Cp
Fp Fe
hV f
SPh SPh


2.15


2.16


oc \

Fe- SPh
/
cp 2

2.17


hVf
C co



SPh

2.18


Trace and Jones11 have found that substitution of phenyl group

for hydrogen at the a-carbon of cyclopropyl-Fp complex, to










give 2.19, induces the ring-opening to a n-allyl complex

2.20 upon photolysis, but alkyl migration to form the carbene

complex 2.21 was not observed.


CO
CP hv Fp

22 2 Ph

2.21 2.19


hv


oc\
Fe- Ph


2.20


Under the analogous photolysis conditions, the a-

methylcyclopropyl Fp complex 2.22, as well as the P-methyl

2.23, did, although slowly, give small amounts of the ring-

opened products 2.24 and 2.25, respectively.18


Fp h
CH3


2.22


oc\


2.24


oc\


hv


CHFp

CH3


2.23


2.25


And finally, photolysis of the parent cyclopropyl Fp complex

1.01, as already mentioned, shows no net reaction,5,13 nor

does thermolysis of its triphenylphosphine derivative 2.26.13










> Fe(CO)PPh3 OC
Cp

2.26



From these results it appears that the alpha alkoxy group is

the only substituent that induces a-elimination, probably

because of its strong stabilizing effect on the carbene that

is being formed. Apparently, neither a-phenythio nor a-

phenyl is a strong enough electron donor to induce this kind

of rearrangement.

The question we can ask ourselves is whether there is

any generality that can emerge from these results about the

cyclopropyl ring-opening. One, which has been proposed by

Jones and Ibers,3 stated that the presence of an open

coordination site at the metal center is a necessary, but not

sufficient condition, for the ring-opening to occur. It also

appears that the metal itself plays some role. We can

conclude that the more electron-donating group in the a-

position seems to facilitate formation of the T-allyl

complex. By now it is pretty certain that photolysis simply

induces dissociation of a CO ligand to form a reactive,

electron deficient intermediate. Once the intermediate is

formed, the reactions that follow are thermally induced.

This is supported by the finding that, if one of the CO

ligands on the metal is substituted by a phosphine ligand,

known to be thermally rather than photochemically labile, the

entire reaction takes place under thermal conditions. The










role of the a-substituent may simply be the coordination of

its lone pair to the electron deficient metal, therefore

retarding back-reaction with CO, thus stabilizing the 16-

electron intermediate. Support for this speculation was the

isolation and characterization of the chelate 2.16 which,

upon warming, undergoes ring-opening to 2.17. Additionally,

during the ring-opening process, the Cl-Fe bond is partially

breaking, but whether the substituent on the C1 plays a

significant role in the bond breaking is as yet unclear.

Solvolysis experiments on cyclopropyl derivatives have shown

that carbocation stabilizing substituents produce abnormally

small rate enhancement when substituted for hydrogen at Cl.

For example, the acetolysis of 1-methylcyclopropyl tosylate

is only 180 times faster than the parent cyclopropyl tosylate

at 150 oC.19 It would be interesting to see where an a-

halogen, which is both an electron-withdrawing group and a 7-

electron donor, as a substituent stands in this spectrum of

reactions.

As a starting point of this work, trans-l-bromo-l-

fluoro-2,3-dimethylcyclopropane 2.27 was prepared20 in an

attempt to submit it to a substitution reaction with Fp-.

Indeed, reaction with KFp in THF gave 33% of the desired

sigma-complex 2.28 as air-sensitive reddish-yellow crystals

that are reasonably stable at -30 oC but decompose rapidly if

allowed to warm above 0 oC. The substitution is believed to

go by a single electron transfer process.









Br Fp
SCHBF tBuOK KFp
THF,00C


2.27 2.28



The structure of 2.28 was determined from the NMR data. Its

1H NMR spectrum (Figure 2.01) shows two high field complex

multiplets from the ring protons. A peak at 0.3 ppm was

assigned to the proton trans to the fluorine since the 3JHF is

smaller than in the case of the cis proton.21 This proton is

also expected to be more shielded by the Fp group situated on

the same side of the ring. The trans proton peak at 0.7 ppm

is a doublet of pentets, with a 3JHF=27 Hz, which is a typical

value for the cis F-C-C-H coupling in cyclopropyl systems.21

The two methyl groups are nonequivalent, producing two

doublets in the 1H NMR: one at 1.0 ppm is assigned to the

methyl group trans to the fluorine (shielded by the Fp group)

and the one at the lower field cis to the fluorine. The Cp

peak appears at 4.35 ppm which is within the range for sigma

Fp complexes. The 19F NMR resonance (Figure 2.02) is a

doublet of doublets with a 3JHF=26.9 Hz for the proton cis to

the fluorine and a smaller 3JHF=8.4 Hz for the proton trans to

the fluorine. The 13C NMR (Figure 2.03) contains four high

field peaks which correspond to C2, C3 and the two methyl

groups. They show characteristic long range coupling to

fluorine.21 The peak belonging to Cl is farther downfield and

it is a large doublet due to the one bond coupling to

fluorine, with a coupling constant 1JcF=284.0 Hz. As










mentioned earlier, sigma complex 2.28 is very thermally

unstable; it decomposes at room temperature within an hour,

whether in solution or neat. It was normally stored frozen

in benzene. The products of the thermal decomposition of

2.28 varied somewhat, but we were able to isolate a mixture

of two major components in an essentially 1:1 ratio which, on

the basis of 1H and 13C NMR spectra, are assigned the

dehydrohalogenated isomeric structures 2.29 and 2.30.







Fp -HF


2.28 2.29 2.30



Attempts to separate these isomers were unsuccessful although

column chromatography led to partial enrichment which

permitted unique assignment of both 1H and 13C NMR resonances.

The peaks that decrease in intensity belong to one set and

those higher in intensity to another. The two high field

doublets in the 1H NMR (Figure 2.04) belong to the methyl

groups. The two quartets at 5.75 and 6.55 ppm come from the

vinyl hydrogen alpha to the methyl group. The higher field

quartet is assigned to compound 2.30 because this hydrogen is

expected to be more shielded by the Fp group. The two low

field doublets of doublets belong to the vinyl protons on C2.

These peaks show different couplings to the cis and trans










terminal vinyl protons, respectively. Complex multiplets

around 5 ppm belong to the terminal vinyl protons. The 13C

NMR shown in Figure 2.05 additionally supports these

assignments. Furthermore, the 19F NMR does not show the

presence of fluorine, which is in agreement with the assigned

structures. Our attempts to initiate the same reaction by

the use of catalytic amounts of acid or base were

unsuccessful. It does not appear that the ring-opening is

either acid or base catalyzed. The rate of the decomposition

did, however, depend on the purity of the starting bromo,

fluorocyclopropane, but that could be explained by the fact

that the less pure compound melted below room temperature and

was, therefore, more susceptible to decomposition. One

possible initiator of the decomposition could be silicon from

glass, which could act as a fluoride abstracting agent.

Attempts to purify 2.28 by chromatography on silica gel led

to a complete ring-opening reaction to give the alcohol 2.31

as a major product. Additionally, a small amount of the

dehydrohalogenated compounds 2.29 and 2.30 was observed as

well.





sFp p p
silica gel H +

F


2.31 2.29


2.30


2.28










The ring-opening reactions and the mechanisms for their

formation will be discussed in detail in Chapter 3.

With the a-fluorocyclopropyl Fp complex now available,

it was possible to determine the impact of a-fluorine on n-

allyl formation. Sigma complex 2.28 was photolyzed for 6

hours in benzene-ds, at ice temperature. The conditions used

were standard ones employed for the other compounds7-11 (low

pressure Hg lamp and a Pyrex filter). The compound underwent

a fast ring-opening reaction to give the 13-t-allyl iron

complex 2.32 as a major product.




/Fe (CO) Cp
Fp
hv 3 F
S -C H3


2.28 2.32



The structure of the compound 2.32 was determined from the

NMR data. The compound was assigned the syn-anti

configuration because there are two different vinyl and two

different methyl peaks present in the 1H NMR spectrum (Figure

2.06), indicating a lack of a plane of symmetry in the

molecule. The low field doublet of quartets belongs to the

proton syn to the fluorine, and the other one at 1.9 ppm to

the more shielded anti proton. Its 19F NMR (Figure 2.07)

shows a triplet at -143.9 ppm. Coincidentally, the coupling

constants to the syn and anti proton are the same. After a










careful analysis of the NMR spectra, in addition to 2.32 a

small amount of another compound was observed. The syn-anti

13-t-allyl complex 2.32 is expected to be the kinetic product

videe infra), and it apparently slowly rearranges to the

thermodynamic isomer, expected to be the symmetric syn-syn

compound 2.33. The rearrangement presumably occurs by

dissociation of one terminus of the allyl ligand to give a

sixteen electron 'l-C-allyl intermediate, followed by

rotation around the new carbon-carbon single bond and

subsequent collapse back to the r13-7-allyl complex.22






Fe (CO) Cp H3 / Fe(CO)Cp

H3 C Hn W







H3
-->-F F
HH3c Hc

2.32 2.33





[H3C'V~, F]






To confirm that this is a thermal rearrangement, 2.32 was

heated at 70 oC in benzene-d6, and changes during the

reaction process were monitored periodically by the 1H NMR.

The peaks assigned to 2.33 grew in, at the expense of the

peaks belonging to 2.32. Since 2.33 has a plane of










symmetry, only one methyl and one high field vinyl peak were

expected. Coincidentally, the methyl doublet at 1.65 ppm in

the 1H NMR of 2.33 (Figure 2.09) overlaps with one of the

methyl peaks belonging to the kinetic product. To our

initial confusion, another Cp and corresponding methyl

doublet also appeared. This compound reached a steady

concentration at an early stage of the thermolysis and did

not change during the remaining course of the rearrangement.

This finding can be explained in light of the previous work

in Rosenblum's group on the thermal and photochemical

interconversions of similar X-allyl complexes of iron.23

Since there is no free rotation between the allylic and the

FeCpCO moiety, both 2.32 and 2.33 can exist in exo or endo

stereoisomeric forms, depending on the orientation of the Cp

ring relative to the allyl group. Of the two isomers, the

exo isomer is expected to be more stable than its endo

counterpart. Thus, the new compound is predicted to be the

endo, syn-syn 7-allyl 2.33a, since only one methyl and one

vinyl peak is present, indicating the symmetric isomer.






co Co \


HCH F3
F .H-- F
H3C H3CV


2.33


2.33a










There are controversial reports in the literature on the

existence of the exo and endo isomers.23 It seems that under

certain conditions the endo isomer is completely unstable and

only the more stable exo isomer can be isolated. This could

explain why we did not observe the endo counterpart of the

syn-anti isomer. It may have decomposed when the crude

product of the photolysis was submitted to the column

chromatography. Crowther has observed similar behavior on

syn and anti crotyl allyl complexes 2.34 and 2.35;




Fe(CO)Cp /Fe(CO)Cp

-js -^ 2-


H3C
2.34 2.35



if the mixture of exo and endo isomers is subjected to column

chromatography, only the exo isomer can be isolated.18

Figure 2.08 represents the time resolved 1H NMR of the

thermal rearrangement of 2.32. After 2 hours approximately

55% of 2.32 had rearranged to 2.33, but even after 24 hours

approximately 10% of the kinetic isomer remained present.

Figures 2.09 and 2.10 show the 1H and 19F NMR, respectively,

of the thermodynamic mixture. In the 1H NMR, the major

doublet at 1.70 ppm and the corresponding major Cp peak at

4.1 ppm belong to 2.33. In addition, small amounts of 2.32

(methyl doublets at 0.8 ppm and the other at 1.65 ppm which

is overlapping with the methyl doublet belonging to 2.33) and










2.33a (methyl doublet at 1.85 ppm and Cp at 4.0 ppm) are

present as well. The 19F NMR shows the presence of three

triplets belonging to 2.32 (-143.9 ppm), 2.33 (-159.5 ppm)

and 2.33a (-143.0 ppm). The ratio of syn-syn (exo+endo) to

syn-anti isomers calculated from peak area from the 19F NMR

was found to be 2.3. The conclusion is that 2.32 and 2.33

probably exist as an equilibrium mixture, with the

equilibrium significantly shifted towards 2.33. To be able

to draw valid conclusions about the mechanism of the ring-

opening, we must be sure that 2.33 is stable under photolytic

conditions, i.e., that 2.33 is not the direct product of the

ring-opening which, under the same conditions, rearranges to

2.32. Therefore, 2.33 itself was photolyzed under the

original conditions, and it was found that it did not

isomerize back to 2.32. This confirms that 2.32 is the

kinetic product of the ring-opening process. The only change

observed after several hours of photolysis was the increased

amount of 2.33a relative to 2.33, as expected, since this

isomerization is photo-initiated.23

Before discussing the mechanism of X-allyl formation

further, let us consider the results of the photolysis of the

unsubstituted trans-dimethylcyclopropyl Fp complex 2.36.

This compound was prepared for a comparison with the a-fluoro

substituted analogue according to the following scheme.









Br Br Fp
(nBu)3SnH KFp, RT
Br H H


2.36



The complex 2.36 was submitted to photolysis under identical

conditions as the fluoro analogue. No ring-opening products

were observed after a short photolysis time, while prolonged

photolysis (30 h) gave about 40% of ferrocene, 50% of the

starting material and 10% of two other compounds, which were

the expected X-allyl products, as determined by 1H NMR

analysis. They were present in amount too small to be

isolated. From this result, it is quite obvious that an a-

fluoro substituent significantly facilitates the ring-opening

process relative to its unsubstituted analogue. One reason,

as we predicted, is fluorine's ability to act as a t-electron

donor in much the same way a-alkoxy or a-thiophenyl do.

Additionally, it is known that fluorine substituted at C1 of

cyclopropane significantly weakens the C2-C3 bond.24

As mentioned earlier, the ring-opening is a thermal

process. According to the Woodward-Hoffman rules,25 if it

resembles a solvolysis, it should occur disrotatorily. There

are two possible ways this opening could occur. One was

first suggested, but not elaborated, by Phillips and

Puddephatt2,26 for the opening of 2.08 where a vacant metal

orbital inserts into the C2-C3 bond of the cyclopropane.













L P-------**
H J

2.08 2.09



The alternative possibility was suggested by Crowther for the

ring-opening of 2.23.8,18 Even though the compound

photolyzed very slowly and gave only a small amount of the

ring-opened product, Crowther was able to isolate the

products and she found that only the trans isomer reacted and

the ring-opening occurred exclusively as depicted.




Fp OC
-p hv 1 o c Fe-

H
CH3 CH3

2.23 2.25



To explain this, a disrotatory opening of the cyclopropane

ring was proposed as an interaction of the HOMO of the

breaking C2-C3 cyclopropane bond with the LUMO of the

partially breaking carbon-iron bond. This can find an

analogy in solvolytic ring-opening of cyclopropyl derivatives

to allyl cations, the mechanism which was extensively studied

by many research groups in the 1960s.27 Additionally, it is

possible that the process is assisted by a filled metal d-

orbital mixing with the LUMO of the breaking C2-C3 bond.






















Both mechanisms presume disrotatory ring-opening, but the

first suggests the disrotation towards the metal, while the

second requires the ring-opening away from the metal.

Even though the results of the ring-opening of 2.23 are

consistent with the latter mechanism, they do not exclude the

possibility of conrotatory ring-opening. The fact that the

photolysis of 2.28 gives 2.32, the syn-anti X-allyl complex

as the exclusive product is the first clear evidence for

disrotatory ring-opening of Fp cyclopropyl complexes.

However, its substitution pattern still does not require

disrotation away from the metal ("the solvolysis mechanism").

A compound which can only open away from the metal is

the endo a-fluoro Fp norcarane 2.37 which should give R-allyl

2.38. Alternatively, compound 2.39 should be inert if the

aforementioned mechanism for the photolytic ring-opening is

correct. In the latter case, the carbon-iron bond breaking

cannot be assisted by ring-opening of the cyclopropane

because that process would give the prohibitively strained K-

allyl complex 2.40.









F
F Fe (CO) Cp
H
Fhv
Fp hv




2.37 2.38



F
Fp Fe(CO)Cp

F X hv



2.39 2.40



The a-fluoronorcaryl complex was synthesized following the

same general procedure described for 2.28, using the

unseparated mixture of exo and endo bromo, fluoronorcarane

2.41 as the starting material that was reacted with KFp. The

1H and 19F NMR spectra shown in Figures 2.11 and 2.12 contain

only one Cp proton resonance, and one fluorine peak,

indicating that only one isomer of a-fluoro Fp norcarane was

formed. The stereochemistry of the product was determined

from the coupling constant between the F and the bridghead H

in the 19F NMR. In the cyclopropyl system, the H beta to the

fluorine will have a larger coupling constant if it is cis to

the fluorine (typically 20-40 Hz), than if it is trans to it

(typically 0-20 Hz),21 as illustrated in the case of complex

2.28. The value measured for 2.39 was 12.7 Hz, which is

within the range for the trans configuration, indicating the

exo stereochemistry.







26
Fp


+ CHBr2F KtBuOK Br KFp F
C>F THF

2.41 2.39



Rosenblum has observed the same selectivity in the

preparation of a-unsubstituted Fp-norcarane.5 Only the exo

isomer was obtained from the mixture of stereoisomeric

bromides. A steric argument was used to account for the

selectivity. Figure 2.13 shows the 13C NMR spectrum of

2.39, which shows typical long range couplings of the ring

carbons to fluorine.21 The compound 2.39 appears to be more

thermally stable than 2.28, but it does decompose after few

days at room temperature. No attempt was made to identify

the decomposition products.

Attempts to photolyze 2.39 showed that it is, indeed,

completely photo-stable. When 2.28 and 2.39 were photolyzed

side-by-side at comparable concentrations, the norcarane

complex showed no detectable reaction in the same time period

that 2.28 showed approximately 50% conversion to the E-allyl

complex 2.32. Even though the negative result does not carry

the same significance that a positive one would, this

experiment is an important contribution to our suggestions

about the mechanism of the cyclopropyl ring-opening reaction.



















'I.


Figure 2.01.


1H NMR spectrum of a-fluorodimethylcyclopropyl

Fp complex 2.28 in benzene-d6.


-:





.

















.




















-t-U
-w


















.



m


,,,~PFCIT~










































Figure 2.02. 19F NMR spectrum of (a-fluorodimethylcyclopropyl
Fp complex 2.28 in benzene-d6 (fluorobenzene ref.).


---L- i
'-~ --- --


rT_









29










((O






.*






0
















'"



































Figure 2.03. 13C NMR spectrum of a-fluorodimethylcyclopropyl

Fp complex 2.28 in benzene-d6.












4I





j


Figure 2.04.


1*4
0
0







0











0
Cl














I-
I *
1 .





1H NMR spectrum of dehydrohalogenated compounds
2.29 and 2.30 in benzene-d6.













4-L







9


0
X 1
0




o
i
I


Figure 2.05.


13C NMR spectrum of dehydrohalogenated compounds
2.29 and 2.30 in benzene-d6.


x
0


0


-0
in
-,










0O


-In
O





i

P
'I-^

iIr j

t..
i
r


m












I-a-
C

_-


x









-m-
^ \ a x





o <
O








I-
L
TE

-u
i
"AI-:










ii
L





t






















Figure 2.06. IH NMR spectrum of syn-anti dimethyl 13-2t-allyl
complex 2.32 (kinetic product) in benzene-d6. (*) indicates
a small amount of thermodynamic product 2.33.
f-r







r







c.
-r











Figure 2.06. 1H NMR spectrum of syn-anti dimethyl ^1-it-ally 1
complex 2.32 (kinetic product) in benzene-d6* (*) indicates
a small amount of thermodynamic product 2.33.





























0


-I


Figure 2.07. 19F NMR spectrum of syn-anti dimethyl T)3-7c-allyl
complex 2.32 (kinetic product) in benzene-d6 (CFCl3 ref.).
(*) indicates a small amount of thermodynamic product 2.33.


____


























































SII I I 1 I If l I 1 i I I I I I I I
S3 0 i PPM


Figure 2.08. Time resolved 1H NMR spectrum of the thermal
rearrangement of syn-anti dimethyl 113-n-allyl complex 2.32
at 70 oC in benzene-dg.



























0





0 jI :N
li-













I-

























Figure 2.09. 1H NMR spectrum of the thermodynamic mixture
after the thermal rearrangement of syn-anti dimethyl T3-X-
allyl complex 2.32 (x) in benzene-d6. (o) indicates
presence of endo, syn-syn compound 2.33a.


































O


(W,
N














:


x-J.5
o-y


r'
-n.







*
0 "0







-
0















0








U
















-I




'9


Figure 2.10. 19F NMR spectrum of the thermodynamic mixture

after the thermal rearrangement of syn-anti dimethyl T13--

allyl complex 2.32 in benzene-d6 (CFC13 ref.). (o) indicates
presence of endo, syn-syn compound 2.33a.
































































Figure 2.11.


1H NMR spectrum of a-fluoronorcaryl Fp complex
2.39 in benzene-dE


















































Figure 2.12.


II

,t

t?


19F NMR spectrum of (-fluoronorcaryl Fp complex
2.39 in benzene-d6 (CFCl3 ref.).





















































































































Figure 2.13.


13C NMR spectrum of a-fluoronorcaryl Fp complex

2.39 in benzene-d6


___ __ __


"O
n.







: .










.o
--0o














'* .
.0





-- 0






-0
-cu








-. 0



0



- 0














-o
.












CHAPTER 3
SYNTHESES OF IRON AND RUTHENIUM ALLENE COMPLEXES
Transition-metal complexes of acyclic allenes are well
known and have been reviewed extensively.28 However, only few
complexes of cyclic allenes have been reported, and among
them only few examples of 1,2-cycloheptadiene as the smallest
ligand; a Pt(0)29 (3.01) and Fe(II) (3.0230 and 3.0331)
complexes. In addition, Oon was able to trap 3.04, claiming
it as the first transition-metal complex of 1,2-
cyclohexadiene but the compound could not be characterized.31b



Pt(PPh3)2 FP Fpp pp



0( 00
3.01 3.02 3.03 3.04


The transition-metal allene complexes have been most commonly
prepared by the displacement of another ligand on the metal
by the allene which is added to or generated in situ, or by
the incorporation of the allene into a vacant coordination
site on the metal. This factor limits the choice of allenes
to those reasonably stable to be trapped by the metal during
the course of the synthesis. One example is the synthesis of










a series of allene Fp+ complexes by ligand exchange between

Fp+ isobutylene complex and an appropriate allene.32



Fp + ALLENE Fp+ (ALLENE) +





Cationic allene complexes can also be obtained via

protonation of the corresponding sigma-propargyl complexes.33


M --M
HClO
or HBF4



R
R



Another way to prepare allene complexes is a methoxy

abstraction from the corresponding methoxy olefin,34 a method

used in Jones's group for the synthesis of 3.02.30


Fp

-OMe F


OMe



Later in this chapter we describe the application of this

method to a synthesis of the first example of a seven-mebered

cyclic allene complex of ruthenium.

Transition-metal complexes of allenes, in which the

metal is t-bonded to one of the double bonds have a different









geometry than uncomplexed allenes.28 Acyclic, uncomplexed
allenes are linear, with the central carbon atom sp-
hybridized. The remaining two p-orbitals are perpendicular
to each other, and each overlaps with the p-orbital of an
adjacent carbon atom, forcing the two remaining bonds of each
carbon into a perpendicular plane.








The coordination of allenes to a transition-metal
leads to a considerable distortion of the linear unit. The
bonding in transition-metal allene complexes can be explained
using the Dewar-Chatt-Duncanson model developed for metal-
olefin complexes.35





I -COMPONENT
> -" sit


t-COMPONENT










The bond is formed by the interaction of the HOMO of a double

bond of the allene with an empty orbital on the metal (a-

component). Additionally, a filled metal d-orbital back

bonds with the LUMO of the allene (N-component). The result

is that the electron density in the X-orbital of the

coordinated olefin is withdrawn by the donation to the metal

atom, and at the same time electrons are returned to the

antibonding N*-orbital of the olefin. As a result, the C=C

bond of the coordinated olefin weakens and the bond length

increases. The weakening can be detected and investigated

through vibrational spectroscopy. The weakened bond becomes

more susceptible to addition reactions; for this reason

transition-metal allene complexes are generally more

electrophilic than the corresponding free allenes. Other

important structural aspect of this type of bonding is the

loss of linearity of the olefin upon coordination to a

transition-metal. The linear allene bends, and as a result

C1 becomes more sp3 in character, and C2 more sp2 in

character. The degree of this deformation will depend on the

degree of back donation from the metal. The presence of

electron-withdrawing groups on the olefin encourages back

donation, as well as strong electron-donating ligands on the

metal.

Incorporating a linear allenic unit into a relatively

small ring introduces considerable strain.36 The allene bends

at the middle carbon forcing it out of linearity. This has a

dramatic effect on the ground state energy, and the stability










of the cyclic allene decreases as the ring size is reduced.

For these reasons the smallest isolated cyclic allene is a

1,2-cyclooctadiene. Complexing the cyclic allene to a

transition-metal reduces this strain because of the geometry

changes mentioned earlier. As a result of this, the smallest

isolated transition-metal completed cyclic allenes are the

1,2-cycloheptadiene complexes.29-31 Additionally, as

previously mentioned, Oon3lb reported the possible existence

of an example of a 1,2-cyclohexadiene complex.

A relatively easy access to the a-fluoro substituted

cyclopropyl Fp complex 2.28 and the initial indications that

the fluorine could be abstracted readily may give rise to a

new synthetic approach to the cationic allene complexes of

iron and possibly other transition-metals. Especially

interesting would be the application of this kind of reaction

to bicyclic compounds containing such a three-membered ring,

since the fluoride abstraction would lead to the formation of

a cyclic allene complex. This method could possibly be used

as a general synthetic approach for obtaining strained and

otherwise inaccessible cyclic allene.


-F










The first attempt to synthesize an alpha fluoro sigma

complex 2.28 was done by Conti in Jones's group, but under

the conditions which generally produce a sigma complex, a

compound with some unusual properties was isolated.13 We now

know that the expected sigma complex 2.28 was initially

formed but, during its purification on a silica gel column,

it ring-opened to give a compound which Conti described as

the allene Fp fluoride complex 3.05, as the only isolated

product. At that time it was not determined whether the

compound was completely ionic or not. The compound was only

slightly soluble in hexane, but soluble in benzene, ethyl

acetate and diethyl ether.




H CH3

\ Br \ /P __ F F-
Br Fp silica gel F

F [Fj



H H3
2.27 2.28 3.05



The purpose of the initial phase of this research was to

determine the structure of the ring-opened product with more

certainty. We expected that the molecule should be

fluxional* if the predicted structure 3.05 was indeed


* See Chapter 4 for fluxional behavior of the transition-
metal allene complexes.










correct, but no changes were observed in the 1H NMR when the

compound was cooled to 2 OC, or heated to 60 oC. Since the

analogous tetrafluoroborate salt of the Fp dimethylallene

1.07 is known,32 (it exists as a 1:2.4 equilibrium mixture of

syn and anti isomers) 2.28 was reacted with BF3-OEt2 in an

attempt to prepare it. To avoid the ring-opening on silica

gel column, 2.28 was isolated from the crude reaction mixture

by extraction with cold hexane to remove Fp2 as a major

impurity. When 2.28 was reacted with BF3-OEt2, a yellow

solid precipitated immediately from the ether solution.

After recrystallization, its 1H NMR was compared to the

literature data32 for the authentic sample of 1.07. They

appeared identical.




H CH3 H CH3








Fp AH3 +
F BF4



L H CH3 H3C H
2.28 1.07 syn 1.07 anti



When 3.05 was compared to 1.07, the most significant

difference was observed in the position of the Cp peaks. In

the compound 3.05 the Cp peak is approximately 1.5 ppm

further upfield than it is in the case of the positively

charged Fp of 1.07. This, along with the solubility










properties, indicates that the compound 3.05 is probably not

ionic as originally thought. It is also unusual that 3.05,

as opposed to 1.07, exists only as one isomer. The biggest

surprise occurred after a 19F NMR of compound 3.05 was taken

more carefully--no fluorine peaks were observed. Clearly the

structure assigned to 3.05 is incorrect. Since 3.05 was

isolated from silica gel, it is possible that the silica gel

acted as a fluoride abstracting agent and that some kind of

ion exchange occurred when 2.28 was in contact with it.

Since we know that the Si-F bond is among the strongest bonds

known, this exchange would not be unreasonable. The most

reasonable group for exchange with fluoride ion in this case

is the hydroxy group. Therefore, 2.28 was stirred with a

small amount of silica gel (the silica gel used had been

vacuum dried and degassed by a standard procedure) for 30 min

and after additional purification on a silica gel column, a

light yellow solid was obtained. Its 1H NMR was very similar

to the spectrum of 3.05, except in the position and

multiplicity of one peak. The two spectra are compared in

Figure 3.01. In the former case the peak appears at 4.35

ppm, which is 0.6 ppm further downfield from its position in

the spectrum of 3.05, and it is a broad singlet rather than a

quartet. In addition, a doublet, corresponding to one

hydrogen, at 1.05 ppm is missing in the spectrum of the

compound 3.05. The 13C NMR spectra are identical, and the

19F NMR shows no presence of fluorine. The structure that is

consistent with all these facts is the hydroxy compound 2.31.










In addition to 2.31, small amounts of dehydrohalogenated

compounds 2.29 and 2.30 were observed in the 1H NMR of the

crude product after the reaction of 2.28 with silica gel.





Fp p p P
F silica gel H + +



2.28 2.31 2.29 2.30

MAJOR MINOR

When 2.31 was stirred with D20, the doublet at 1.05 ppm,

assigned to the OH group disappeared and the multiple at

4.35 ppm became a quartet. The quartets at 6.40 ppm and 4.35

ppm are assigned to vinyl and alkyl hydrogen, respectively.

Conversion of 2.28 to 2.31 probably arises from the initial

silica gel induced ring-opening to the allene cation 1.07,

possibly tightly bound onto the silica gel surface, followed

by attack of water on the terminal carbon of the completed

double bond.* To test this as a viable possibility,

authentic allene complex 1.07 was treated with water and was

found to give 2.31, again as a single stereoisomer, in 78%

isolated yield. Moreover, sigma complex 2.28 does not react

at all when stirred with water for 30 min. Small amounts of

dehydrohalogenated compounds were probably formed by a loss

of proton from the allene, competitive with attack of water.


In general, the addition of nucleophiles, including
hydroxide ion, to Fp(allene) cation has been shown to occur
preferentially at C1.37









Fp
silica geq H H20 1.07
F

2.28 2.31

SH20



N.R.

We can with some certainty assign the stereochemistry as

depicted to 2.31, based on Klemarczyk's and Rosenblum's38

work on the hydration of Fp+ complex of 2,3-propadiene. Even

though the nucleophile can, in principle, attack both the syn

and the anti isomer of 1.07, there is a considerable steric

hindrance by the anti methyl group to the nucleophilic

attack. Unlike the uncomplexed ligand, allenes bound to

transition-metals through a t-bond are not linear, with the

uncoordinated carbon atom bent away from the iron atom. The

consequence of this distortion is to increase the steric

hindrance of an anti substituent at C3 for nucleophilic

addition to Cl, since such reaction takes place trans to the

iron-olefin bond.


H H H
PREFFERED SITE OF
1 NUCLEOPHILIC ATTACK
Fp+ Fp+

H3 2 H 2
3 3
H CH3


anti


syn









Therefore, the syn isomer of 1.07 will preferentially undergo

nucleophilic attack but, since the two isomers are in
equilibrium, all of the allene will be transformed into the
final product.




ScH3 cH3

-FP+ _____ +--p+




H CH3 H3C H
1.07 syn 1.07 anti



I t
P P
H H


2.31



We consider that the thermal decomposition of 2.28 to give

2.29 and 2.30, which we have mentioned in Chapter 2, follows
a similar mechanism. Silicon from glass initiates the ring-
opening to the allene, and since the conditions are water
(nucleophile) free, rather than undergoing a nucleophilic
attack, the allene intermediate 1.07 loses a proton to give
the isolated dehydrohalogenated products 2.29 and 2.30.










The slow reaction step is the loss of fluorine with ring-

opening, which is not expected to be base or acid catalyzed.

Only two other examples of the ring-opening of a

transition-metal complex of cyclopropane to an allene complex

have been reported in the literature. The treatment of 1.01

with 3.06 gave the allene Fp+ complex, in a reaction that was

suggested to have proceeded through a cyclopropylidene

complex 3.06a.39




S+ F + F +III Fp


1.01 3.06 3.06a


In another case, methoxy abstraction from 1.02, the a-methoxy

analogue of 2.28, gave the dimethylallene Fp complex 1.07.

Chirality studies showed that the ring-opening probably does

not proceed through the cyclopropylidene, but presumably

through the planar allyl cation 3.06b instead.10



S -OMe



1.02 3.06b



Considering the complicated, multi-step synthesis involved in

preparation of 1.02, the fluoride abstraction induced ring-

opening of 2.28 seemed like a preferable alternative.











Therefore, we considered it as a general synthetic method for

the preparation of other, possibly otherwise inaccessible

cyclic allenes. We first applied it to the norcaryl Fp

complex 2.39 which we had synthesized for the purpose of the

photolytic ring-opening studies (Chapter 2). As expected,

the reaction with BF3-OEt2 went smoothly and quantitatively

gave the T2-1,2-cycloheptadiene Fp tetrafluoroborate complex

3.02.


Fp






2.39


BF3'OEt2


Fp+ BF4






3.02


The compound had previously been prepared in our group via

several different routes based on the methoxy abstraction

from the 7-methoxy-cycloheptenyl Fp complex 3.07.


Fp

OMe Me
1. nBuLi,-780C
2. FpBr, -780C -OMe



3.07 3.02


Initially, Manganiello et al.30 prepared a triflate salt of

3.02 by using TMSOTf as a methoxy abstracting reagent. The

allene complex formed was thermally unstable in methylene










chloride solution at room temperature. The major

decomposition products were identified as Fp trifluoromethane

sulfonate and 1,3-cycloheptadiene. On the other hand, the

T2-1,2-cyclononadiene Fp tetrafluoroborate shows remarkable

thermal stability. It did not decompose for days in

methylene chloride at 40 oC, or for at least 30 min in

nitromethane at 80 C.32 The conclusion was that the triflate

anion caused the decomposition. The mechanism shown below

has been proposed to account for the products formed.30


OTf -TfOH


1.05


TfOH


OTf












OTf


FpOTf +


Manganiello's attempt to abstract the methoxy group from 3.07

with HBF4 was completely unsuccessful.40 Oon was able to

carry out a successful methoxy abstraction with

trimethyloxonium tetrafluoroborate. The allene formed in










such a way is much more stable than the triflate, showing no

decomposition after 16 h at 40 OC in methylene chloride. The

drawback of this procedure was that the product was sometimes

contaminated with the unreacted trimethyloxonium

tetrafluoroborate, since it has very similar solubility

properties to those of the allene. The alternative way of

accessing the tetrafluoroborate allene complex is by the

anion exchange from the initially formed triflate salt.30 The

advantages of the fluoride abstraction method described in

this work are in the clean reaction conditions. The sigma

complex can be dissolved in diethyl ether and reacted with

BF3-OEt2 which is ether soluble. The resulting product

precipitates from the solution immediately as a pure allene,

with no additional byproducts. Simply washing the solid with

diethyl ether removes the unreacted BF3-OEt2.

A major interest of this research was the successful

synthesis of the analogous 1,2-cyclohexadiene Fp+ allene

complex 3.08, as no transition-metal complex of such a

strained allene has ever been prepared.


3.08











The methoxy abstraction methods described previously for the

seven-membered analogue were unsuccessful in the case of 6-

methoxycyclohexenyl Fp complex 3.09. Only the decomposition

products similar to those from the decomposition of 3.02

were isolated as a result of the reaction of 3.09 with

trimethylsilyl trifluoromethanesulfonate.40


OMe
1. nBuLi,-780C
2. FpBr, -780C


3.09


TMSOTf


3.08


+ FpOTf


Additionally, attempts to trap the product of the methoxy

abstraction at low temperature were unsuccessful. When

trimethylsilyl bromide was used as a methoxy abstracting

reagent, and at the same time the internal trap, no expected

6-bromocyclohexenyl Fp complex or its elimination product

were observed.31b











OMe TfOBr Br
TfOBr
X OR



3.09



When triethyloxonium tetrafluoroborate or triphenylcarbenium

tetrafluoroborate were used as methoxy abstractors, only the

decomposition products were formed. Considering the clean

reaction conditions for fluoride abstraction by BF3-OEt2 it

was thought that, if the decomposition was caused by the side

products, this new method should eliminate this possibility.

We decided to synthesize the a-fluorobicyclo Fp complex 3.10

as the initial aim of this work, following the same general

procedure employed for the preparation of 2.39.

The bromo, fluorobicyclohexane compound 3.11 was synthesized

by the method of Reinhard41 to give, after vacuum

distillation, a 52.5% yield of the desired product as a

mixture of exo and endo isomers (ratio exo/endo=1.2). The

method used for the seven-membered analogue20 was unsuitable

in this case, since it gave a complex mixture of various

unidentified compounds and a poor yield of the desired

product. To further purify compound 3.11, it was submitted

to GC and, surprisingly, only the exo isomer was isolated at

a column temperature higher than 100 oC. The decomposition

product from the endo isomer of 3.11 was identified as the

ring-opened compound 3.12. The same decomposition happened











if the compound was kept at room temperature for a prolonged

period of time. Additionally, 3.12 further eliminated to

give the 2-fluorocyclohexadiene.


+ CHBr2F 50% NaoH
CH2C12/H20


Br A

F >1000C


3.11


3.11 exo


3.12


This behavior is not unusual, since similar reactivity has

been reported for the analogous chloro, fluorobicyclohexane.42

It has been shown that the cyclopropane ring-opening occurs

much easier in the case where the better leaving group (Cl or

Br, as opposed to F) is endo rather than exo to the rest of

the ring, as well as that much higher temperature is required

for the same reaction to occur in the case of the analogous

bicycloheptane system. Since only the exo bromo,

fluorobicyclohexane 3.11 is probably the isomer that reacts

with KFp, we consider the decomposition of the endo isomer an

excellent method for purification of the starting material.










The synthesis of the Fp sigma complex 3.10 was carried out

under similar conditions as for its seven-membered analogue.

It was found, however, that in the six-membered case a

prolonged reaction period is required for successful

substitution to occur. A significantly lower yield was

obtained if the reaction was run at 0 oC, rather than at the

room temperature for at least 4 hours. Too long a reaction

time, on the other hand, caused a significant amount of

decomposition which presumably arose from the thermal

instability of the product. The crude reaction mixture

contained only the desired sigma complex and some Fp2, which

could be completely separated by cold hexane extraction.




Br Fp


KFp, THF-60 r
250C, 4h


3.11 3.10



The product is red, square-like, air and temperature

sensitive crystals which can be additionally purified by slow

crystallization from hexane under a nitrogen atmosphere at

-30 C. The structure of 3.10 was determined from its NMR

data, and on comparing with the norcaryl analogue 2.39. The

1H NMR, shown in Figure 3.02, qualitatively looks very

similar to the 1H NMR of 2.39, with a group of ring protons

in the high field region of the spectrum, and a Cp peak at










4.22 ppm. The 13C NMR (Figure 3.03) shows the expected number

of carbon peaks, and the long range couplings to fluorine are

similar to those observed for 2.39. The 19F NMR (Figure

3.04) peak appears at 148.6 ppm, which is very similar to the

value of -144.6 ppm observed for 2.39. The compound is, as

seen for the previous examples of a-fluoro cyclopropyl Fp

complexes, thermally unstable, decomposing after few hours at

room temperature and thus was stored as a solid in the

freezer.

In an attempt to synthesize the desired allene complex

3.08, 3.10 was reacted with BF3-OEt2. As soon as the

BF3-OEt2 was added to the diethyl ether solution of 3.10, at

0 oC, an orange powder precipitated. The solvent was

filtered via a filter cannula and the remaining solid was

washed with diethyl ether to remove excess BF3-OEt2. The

room temperature 1H NMR of the solid in CD3NO2 showed a

complex spectrum broadened by the presence of paramagnetic

impurities. It contained a mixture of compounds, which we

were unable to separate and identify. In an attempt to

recrystallize it, the compound was dissolved in methylene

chloride, but no solid reappeared upon the addition of

diethyl ether. After evaporation of the solvent, a red paste

remained which we did not attempt to further identify. The

orange powder from the reaction of 3.10 with BF3-OEt2 was

added to methanol in a slurry of sodium carbonate at -78 C

in an attempt to trap the allene, but the 6-methoxy-









cyclohexenyl Fp complex 3.09 could not be detected by a

comparison with the data for the known compound.40


SFp+
pOMe
Fp Fp
F BF3.OEt[ eOH



3.10 3.08 3.09


The difference in the results of fluoride abstraction

between the seven and six-membered rings could be attributed

to the actual ground state configuration of the allenes.

Another isomeric form of cationic allene complexes of Fp is

their allyl cation form. In the case of Fp+ complex of

propadiene, the allyl cation form is about 25 kcal/mol higher

in energy than the allene form, as predicted by EHMO

calculations.43 For a seven-membered cyclic allene complex

EHMO calculations predict that the allyl cation form should

be only 17 kcal/mol higher in energy than the linear allene.43

One would expect that, as we go to the smaller ring size, the

energy separation between the two isomeric forms should

decrease, as the ring strain should be reduced in the case of

the allyl cation relatively to the allene. The EHMO

calculations predict that, in the case of the Fp+ complex of

1,2-cyclohexadiene this order is reversed, and the allyl

cation is a ground state, about 14 kcal/mol more stable than

the allene isomer.43











+ AFp






25 kcal/mol 17 kcal/mol 14 kcal/mol


+ P
Fp+







Even though the energies derived from EHMO should not be

accepted as absolute values, the change in the ground state

structure is significant. The failure to isolate or to trap

the six-membered allene suggests that the allyl cation may

have been formed upon fluoride abstraction from 3.10, but is

extremely unstable yielding only decomposition products.

In light of the reaction of a-fluorodimethylcyclopropyl

Fp complex 2.28 with silica gel, we anticipated that it might

be possible to generate and trap the six-membered allene 3.08

in the same way. The complex 3.10 was stirred with silica

gel for 30 minutes in dry diethyl ether, and after column

chromatography a pale green-yellow solid was obtained as a

major product. The compound is rather polar, and pure

methylene chloride was required to elute it from the column.

It is moderately soluble in hexane, soluble in benzene,

methylene chloride and diethyl ether. Its 19F NMR shows no

fluorine resonance. The 1H NMR and 13C NMR spectra are shown










in Figures 3.05 and 3.06, respectively. By analogy with 2.31

the product was tentatively assigned structure 3.13.


P


f OH




3.13


The doublet at 1.0 ppm in the 1H NMR was assigned to the

hydroxy proton. Just as in the case of 2.31, the doublet

disappeared when D20 was added. The low field triplet is

assigned to the vinyl hydrogen, and the quartet at 3.85 ppm

to the hydrogen alpha to the OH group. The 13C NMR shows six

different carbon resonances, in addition to Cp and CO,

indicating that the symmetry of 3.10 has been lost. The two

different CO peaks indicate that the metal center has became

prochiral by introducing an asymmetric center in the ring, so

the carbonyls are no longer equivalent. As an additional

proof of the proposed structure, 3.13 was treated with NaH,

followed by Mel to give the known methoxy compound 3.09 as a

major product.


P P
OH OMe
S 1. NaH
2. CH3I
1


3.13


3.09










Sigma complex 3.10 itself does not react with water. The

result of the reaction between 3.10 and silica gel indicates

that the six-membered allene complex (or its allyl cation

isomer) was indeed formed, and furthermore, it was stable

long enough to react with the water present in silica gel to

give the isolated hydroxy compound 3.13.






Fp Fp+ ( O

F silica gel 0 H20



3.10 3.08 3.13


H20


N.R.



When Oon3lb replaced one of the carbonyl ligands of the

Fp group in 3.09 by a triphenylphosphine ligand to get 3.14

and treated the compound with TMSOTf in pentane, a green-

yellow solid precipitated which was too unstable to be

further characterized. However, addition of the solid to

ethanol at -78 oC yielded 6-ethoxycyclohexenyl Fpp complex

3.15 as the only isolated product, suggesting that the solid

formed might have been the expected six-membered allene

complex 3.04.










Fpp PP
OMe OMe OEt
hv TMSOTf EtOH
PPh3 [


3.09 3.14 3.04 3.15



One explanation for the difference in behavior between

1.07 and the dicarbonyl analogue could be the fact that the

triphenylphosphine ligand is a better electron donor than the

CO ligand.


Cp

LJ L
L








In the allyl cation form the metal is substituted at the

nodal carbon. As a result, electronic changes on the metal

should not have a strong influence on the stability of the

allyl cation. The electronic changes will, however,

significantly influence the strength of the X-bond in the

allene form. By substituting a strongly electron withdrawing

CO ligand by an electron-donating phosphine ligand the metal

becomes more electron rich. The metal can redistribute some

of this electron density by stronger backbonding to the

allene ligand making the X-complex stronger and, therefore,

more stable. This being the case, two phosphine ligands on










the metal would have an even more stabilizing effect on the

allene form, possibly making it stable enough to be isolated

and characterized. Since we also wanted to take advantage of

the fluoride abstraction with BF3-OEt2 and the cyclopropyl

ring-opening, we sought ways to prepare the

bistrialkylphosphine analogue of 3.10. In addition to the

six-membered case, we were also interested in preparing the

analogous seven-membered compound for the purpose of

comparative fluxionality studies, discussed in Chapter 4.

It is known that the photolysis of Fp sigma alkyl

compounds in the presence of phosphine ligands leads to the

substitution of one of the carbonyl groups, but the second

ligand can not be substituted the same way, one reason being

that the phosphine substitution will cause the strengthening

of the metal-carbonyl bond, making it photo-inert at the same

wavelength.44 One possible way to avoid this problem and to

access the bistrialkylphosphine iron system could be by using

the appropriate metal anion and reacting it with the desired

bromo, fluorocyclopropane in a way similar to the reaction

with Fp-. These anions are expected to be extremely reactive

since the phosphine ligand, as a strong electron donor, will

highly destabilize the negative charge on the metal.

CpFe(PMe3)2 anion, as well as a series of anions with a

variety of phosphine ligands, can be generated in situ as

lithium salt from Cp(COD)FeLi(DME) (3.16), by the method of

Lehmkuhl et al.45 The compound 3.16 was prepared following

the procedure of Jonas et al.46










DME \O
Fe + Li + Fe- Li + CpLi
I / o
Cp COD

3.16



The compound is a black, highly reactive, pyrophoric solid.

The weakly 7E-bonded cyclooctadiene ligand can be easily and

quantitatively replaced by CO, even at -78 oC to give the

FpLi.46 Lemhkuhl used this fact to substitute COD by a

variety of phosphine ligands. In the general procedure, 3.16

is dissolved in toluene, and reacted with two equivalents of

the desired phosphine ligand. The metal anion generated in

such a way is then allowed to react with an appropriate alkyl

halide to give the substitution product. We decided to

prepare a bistrimethylphosphine substituted compound 3.17,

according to the general procedure. Trimethylphosphine was

used because it is the least bulky, and also the best

electron donor in the trialkylphosphine series.




Cp r Cp
toluene e
Fe L( + 2 PMe3 tu Fe Li
/ o Me3P e
COD I PMe3

3.16 3.17



Since neither 3.16 nor 3.17 could be characterized easily by

spectroscopic methods, we initially attempted to use 3.16 as

a precursor for the synthesis of the known










bistrimethylphosphine(cyclopentadienyl)methyl iron complex

3.18,47 following the procedure of Lehmkuhl.


3.16 + 2 PMe3 3.17 ] CHl Fe-CH3
~,,.Fe CH3
Me3Pi "
PMe3
3.18


The 1H NMR spectrum of the product agrees completely with the

literature data for 3.18.45,48 With the starting material

characterized, we attempted to synthesize the bistrimethyl-

phosphine(cyclopentadienyl)iron complex 3.19. The reaction

was carried out in toluene at room temperature for 10 hours,

similar to the conditions that Lehmkuhl used for a variety of

alkyl halides. The crude product was analyzed by 19F NMR

which revealed no fluorine containing products.


+ [ 3.17 ]


FeCp (PMe3)2
toluene
10h, RT F



3.19
3.19


The 1H NMR showed that three compounds containing Cp

resonances were present: ferrocene, another that looked like

the methyl complex 3.18 by comparison with the previously

prepared compound and the third compound containing only Cp


Br
F










and PMe3 resonances, which was not characterized. We are not

certain what is the source of the methyl group for the

formation of 3.18. The failure to synthesize 3.19 was very

discouraging since it suggested that we may not be able to

generate the a-fluorocyclopropyl systems with electron rich

iron centers. A possible alternative would be to use an

appropriate metal halide, rather than metal anion and

reacting it with an appropriate 1-fluorocyclopropyl anion.

Unfortunately, 1-fluoro substituted cyclopropyl anions are

known to be extremely unstable. The only two literature

reports49 claiming the existence of the anions, used

temperatures below -105 OC in order to generate them which

are highly impractical conditions for syntheses involving

organometallic compounds, particularly considering solubility

problems. Therefore, this alternative approach was

abandoned. Since the cyclopropyl system did not look

promising, we decided to use the method of Lehmkuhl to try to

synthesize 3.20 and 3.21 from the corresponding bromides.




FeCp (PMe3)2 eCp (PMe3)2

Me 5 OMe





3.20 3.21



Support for this reasoning was the fact that Lehmkuhl had

reacted vinylchloride, among other compounds, with 3.17, yet











we did not find any examples of its reaction with a

cyclopropyl halide. Therefore, l-bromo-7-methoxycycloheptene

was reacted with 3.17 generated in situ, according to the

general procedure. Unfortunately, the 1H NMR of the crude

mixture looked complex. The mixture was separated into three

different fractions by flash column chromatography. The 1H

NMR of 3.20 would be expected to show two sharp singlets

corresponding to the Cp and OMe peaks. However, we did not

detect any such peaks in the 1H NMR spectra for all three

fractions. No attempt was made to identify the products.

Similar results were obtained when the same reaction was

repeated with l-bromo-6-methoxycyclohexene.


Br FeCp(PMe3)2

Me Me

+ [ 3.17 ] )(


3.20



r eCp (PMe3)2

OMe OMe

+ [ 3.17 ] (



3.21



The reason for the unsuccessful substitutions may be

explained by using steric arguments. It is possible that the

methoxy-cyclohexenyl or methoxy-cycloheptenyl group is too










large to be accommodated as a ligand on the metal already

crowded by two phosphine ligands. Even though we were using

trimethylphosphine, which is the least sterically demanding

in the series of trialkylphosphines, it is still

significantly larger than CO. The largest example of an

alkyl substituted bistrimethylphosphine (cyclopentadienyl)

iron that we came across was the 2-phenylethyl substituent.45

Furthermore, we did not find any examples of secondary

substituents. If this explanation is correct, it may not be

possible to access the precursors for the syntheses of 1,2-

cycloheptadiene and 1,2-cyclohexadiene complexes of electron

rich iron.

Discouraged by the results of the iron chemistry, we

decided to look at ruthenium. The reasoning behind this

decision was that the chemistry of ruthenium should be pretty

similar to iron, considering that both are in the same group

of the periodic table, but since the ruthenium atom is larger

than iron, it might be possible to overcome the steric

problems encountered with smaller iron. A review of the

literature shows that there are no known cyclic allene

complexes of ruthenium, and furthermore, we did not come

across any acyclic allene complexes of ruthenium either.

Therefore, we decided to begin this project with the

synthesis of compound 3.22, a ruthenium analogue of 2.39, in

an attempt to generate a precursor for preparation of the

first example of a cyclic allene complex of ruthenium. The

bromo, fluoronorcarane 2.41 was treated with NaRp but under










the conditions similar to those used for the synthesis of

2.39, none of the desired sigma complex was found. From the

19F NMR of the crude reaction mixture, only the starting

mixture of exo and endo bromo, fluoronorcarane was present,

and no new fluorine containing compound was formed. After a

prolonged reaction time the exo/endo ratio had changed

slightly but it appeared that the endo isomer was

disappearing rather than the exo isomer. Since the Rp- is

generated in situ,50 in order to confirm its formation, Rp-

prepared under exactly the same conditions as above, was

reacted with methyl iodide. The Rp methyl complex was indeed

formed, as expected.51


Rp

Br THF, OOC F
F + NaRp -X


2.41 3.22



Since we had already experienced the unpredictable

nature of the fluorocyclopropyl systems, we abandoned this

approach, and turned back to the synthetic scheme developed

in Jones's group for the synthesis of 3.07 and 3.09.30 The

l-lithio-7-methoxycycloheptene, generated in situ from the

corresponding bromide, was reacted with Rp bromide at -78 oC,

to give a 58% yield of the desired sigma complex 3.23, as an

orange oil, which is reasonably air stable (it decomposes

after few days of exposure to air at room temperature).









Br Li Rp

Me Me ME

nBuLi, -700C RpBr, -70C



3.23


The compound's structure was determined from its NMR data,

and by comparison with the iron analogue. The 1H NMR,

presented in Figure 3.07, shows the presence of two sharp

singlets at 4.7 ppm and 3.1 ppm in a 5:3 ratio, belonging to

the Cp and the methoxy group, respectively. The hydrogens at

C2 and C7 show characteristic couplings (triplet and doublet,

respectively) which are comparable to the iron analogue.40

The 13C NMR, accompanied by the APT sequence (Figure 3.08)

further support the proposed structure.

With the sigma complex 3.23 in hand we are now in

position to examine the methoxy abstraction process. Even

though methoxy abstraction with HBF4 was not successful in

the iron case40 we decided to try it with 3.23, because of

its potential advantages over other methoxy abstracting

reagents. The trimethyloxonium or triphenylcarbenium

tetrafluoroborate salts had similar solubility properties as

allenes formed in the reactions with them, making their

separation difficult, while TMSOTf caused the decomposition

of the iron allene, and we were concerned that the same would

occur in the ruthenium case. HBF4 is, on the other hand,

soluble in diethyl ether and can be easily removed from the

ether insoluble allene complex. The first attempt to










abstract the methoxy group was not successful. Comparable to

the same reaction of the iron analogue,30 upon the addition of

HBF4 to the diethyl ether solution of 3.23 at 0 OC, some of

the expected allene 3.24 was formed videe infra) but, by

analogy with the iron case,30 the major product was identified

as the methoxy substituted X-complex 3.25. This was

discouraging, although perhaps not surprising. However, a

reverse addition of two equivalents of HBF4 in ether solution

yielded the allene 3.24 as the major product along with only

a small quantity of 3.25 as an impurity. We could not find

the reaction conditions which would completely eliminate the

formation of 3.25, so the product generally contained

approximately 5% of the impurity. Furthermore,

recrystallization of the crude product did not remove 3.25

from the allene since, apparently, both compounds have

similar solubility properties.




Rp RRp+ Rp+
Me /- OMe

HBF4 BF4 + BF4


3.23 3.24 3.25
TRACES



The complex 3.24 is an off white powder, which is

stable to a brief exposure to air, but decomposes noticeably

after prolonged exposure. It is soluble in methylene










chloride, acetone and nitromethane, slightly soluble in

chloroform, and insoluble in diethyl ether. Its methylene

chloride solution is stable for days at room temperature, and

for at least 2 hours at +50 oC. It is less stable in

nitromethane or acetone solutions, decomposing significantly

after a day at room temperature. A room temperature 1H NMR

spectrum of 3.24 in CD2Cl2 (Figure 3.09) shows a sharp

singlet at 5.90 ppm assigned to the Cp peak, while all the

other signals are broadened, indicating fluxional behavior of

the compound. The 1H NMR of the same compound at -40 OC is

shown in Figure 3.10. The peaks that were broad or lost in

the baseline at room temperature have appeared because the

fluxional process is now slowed down significantly. The

spectrum compares quite well to the iron analogue 3.02.30

The two multiplets at 4.45 ppm and 6.25 ppm belong to H1 and

H3, respectively. The former is further upfield because the

K-bonding to the metal reduces the K-character of the allene

C=C bond. The complex splitting of each peak is caused by

coupling to the nonequivalent vicinal hydrogens, and

additionally, by the long range coupling between the two

allene hydrogens. The remainder of the ring protons appear

in the high field region of the spectrum. Small amounts of

impurities are also present in the 1H NMR, the major one

being 3.25, with its Cp peak at 5.65 ppm, and the

corresponding methoxy resonance at 3.6 ppm (Figure 3.10).

The 13C NMR spectrum of 3.24, recorded at -40 oC, is shown in

Figure 3.11. The methylene carbons are present in the high










field region of the spectrum. The two carbonyl groups are

diastereotopic, since the allene ligand is chiral, causing

the distinctly different chemical shift for each carbon atom,

one at 194.5 ppm and the other at 192.6 ppm. The central

carbon atom of the allene appears at 145 ppm, a typical value

for the transition-metal allene complexes. The completed and

uncomplexed allene carbons have distinctly different chemical

shifts for the same reason the corresponding protons do. The

19F NMR shows only one singlet at -150.6 ppm, corresponding to

the fluorine from the BF4- group. The fluxional behavior of

3.24 will be discussed in detail in Chapter 4. Compound

3.24 is, to date, the first reported cyclic allene complex of

ruthenium.

Encouraged by the successful synthesis of 3.24, we

decided to apply the same approach to the synthesis of the

the analogous six-membered ring allene 3.26.




/RP







3.26



The sigma complex 3.27 was synthesized in the same way as

3.23, in 48% yield. Its 1H and 13C NMR spectra are shown in

Figures 3.12 and 3.13, respectively. The compound is










reasonably air stable, and has similar properties as its

seven-membered ring counterpart.




r i p

OMe OMe OMe
nBuLi,-700C RpBr, -700C




3.27


When 3.27 was reacted with HBF4, in the same way as described

for 3.23, in an attempt to prepare the allene complex 3.26,

a yellow-brown powder precipitated immediately. The solvent

was filtered, and the solid was washed with diethyl ether and

dried under vacuum. The solid turned into a brown paste

immediately upon exposure to air or within a few hours at

room temperature under nitrogen. When the solid was

dissolved in CD3NO2, in an attempt to prepare an NMR sample,

it briefly changed color from yellow to red, to give a yellow

solution. The room temperature 1H NMR spectrum of the

solution looked very complex. Nevertheless, the solid could

still be the expected allene complex 3.26 but it may have

decomposed when dissolved in nitromethane. We decided to

prepare an NMR sample in CD2Cl2 at low temperature with the

hope that the spectrum could be recorded before the compound

had a chance to decompose. The solid formed in the reaction

of 3.27 with HBF4 was placed in an NMR sample tube fitted











with a stopcock, and methylene chloride-d2 was condensed in

it at liquid nitrogen temperature. The tube was sealed and

placed in the NMR probe, precooled to -60 oC. To our

disappointment, the 1H NMR spectrum of the compound looked as

complex as the one recorded previously at room temperature in

nitromethane. In the last attempt to identify the yellow

solid, it was added to a slush of sodium carbonate in ethanol

at -78 oC, in order to trap the allene 3.26, but no ethoxy

analogue of 3.27 was isolated or detected as a product of the

reaction.


SRp+
OMe / +OEt
SHB4EtOH
HBF4
BF4 X



3.27 3.26



After the successful syntheses of the Rp sigma complexes

3.23 and 3.27, we decided to try to synthesize their mono-

and bistrialkylphosphine analogues, considering that the

steric problems we had encountered in the iron case would not

be so severe. Since the carbonyl (15-cyclopentadienyl)

triphenylphosphine ruthenium bromide (Cp(CO) (PPh3)RuBr)52 and

the bistrimethylphosphine(15-cyclopentadienyl)ruthenium

chloride (Cp(PMe3)2RuCl)53 are easily available, we decided to

employ the same synthetic approach used for the syntheses of

3.23 and 3.27.










First, l-lithio-7-methoxycycloheptene was reacted with

CpRu(CO)(PPh3)Br, according to the procedure described

earlier, in an attempt to prepare 3.28. In this case,

however, no reaction was observed, and only CpRu(CO)(PPh3)Br

and some organic products were recovered. The organic

compounds are expected to be the decomposition products

formed upon warming l-lithio-7-methoxycycloheptene to room

temperature.




Br Li CpRu(CO) (PPh3)

Me Me Me

nBuLi,-700c CpRu(CO) (PPh3)Br

-700C

3.28



Very similar reactivity was observed when both l-lithio-7-

methoxycycloheptene and l-lithio-6-methoxycyclohexene were

reacted with CpRu(PMe3)2C1. In this case, in addition to the

recovered CpRu(PMe3)2C1, another similar compound was formed

in approximately the same amount, identified as CpRu(PMe3)2Br,

upon comparison of its 1H NMR spectrum with the literature

data for this compound.54 Knowing that the CpRu(PMe3)2Br is

normally prepared by anion exchange from the corresponding

chloride,54 the ruthenium bromide was probably formed from

reaction of CpRu(PMe3)2Cl with some source of bromide probably












generated in the reaction mixture as a result of

decomposition of the methoxy-lithio compound.


SOMe

nBuLi, -70C
M


CpRu (PMe3) 2


CpRu (PMe3) 2C1

-700C


3.29


OMe


CpRu (PMe3) 2C1

-700C


3.30


nBuLi, -700C
0







80



H
(a) 4r


2.31






.! / .1



r'- '- -) -- r -r- r -r-- T -I I .I.I. I r -.-r'-L-A--r--l-- '--
7 6 5 4 3 2 1 PFM 0





H CH3


(b) --






3.05










Figure 3.01. 1H NMR spectrum of silica gel induced ring-
opened product 2.31 in benzene-d6 (a), compared to previously
proposed ring-opened product 3.05 (b). (Spectrum (b)
reproduced from N. Conti's Ph.D. Dissertation.)



















0.
ru r


N


CIj


Figure 3.02. 1H NMR spectrum of a-fluorobicyclohexyl Fp
complex 3.10 in benzene-d6


-------~-----i
















C-
a-

-0




0

































L


L
.CM



0


























L
0













L
i-






L
L


Figure 3.03. 13C NMR spectrum of a-fluorobicyclohexyl Fp

complex 3.10 in benzene-d6.







83










o
w*I
















Figure 3.04. 1F NMR spectrum of a-fluorobicyclohexyl Fp
-- i
F



-o
Lg

K.








Er
[i




















Figure 3.04. 19F NMR spectrum of a-fluorobicyclohexyl Fp
complex 3.10 in benzene-d6 (CFCI3 ref.).













































Figure 3.05.


>0
-I)





.,
i,-i







1H NMR spectrum of 6-hydroxycyclohexenyl Fp
complex 3.13 in benzene-d6.


d































































Figure 3.06.


13C NMR spectrum of 6-hydroxycyclohexenyl Fp
complex 3.13 in benzene-d6.





Figure 3.07.


~Cv)


d











4
,i
i




















cJ
ij


1H NMR spectrum of 7-methoxycycloheptenyl Rp
complex 3.23 in benzene-d6.


I


-LL~)




-(0










87










-






m ye L
(11















-o0



0
0
-c



0




0










0C




















Figure 3.08. 13C NMR and APT spectra of 7-
methoxycycloheptenyl Rp complex 3.23 in benzene-d6.