Title: Boron hydride chemistry of n-substituted-iminotriphenylphosphoranes
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Title: Boron hydride chemistry of n-substituted-iminotriphenylphosphoranes
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Language: English
Creator: Holley, William Keith, 1960-
Copyright Date: 1986
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BORON HYDRIDE CHEMISTRY OF N-SUBSTITUTED-
IMINOTRIPHENYLPHOSPHORANES








By

WILLIAM KEITH HOLLEY


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


1986
















ACKNOWLEDGEMENTS


The author wishes to express his deepest appreciation

to Dr. George E. Ryschkewitsch, for his guidance, super-

vision and encouragement during the period of this research

program. The interaction with him, both as a student and a

friend, will always be remembered.

The author wishes to express his gratitude to the

members of his advisory committee for their help and sup-

port. He is also thankful to Donald S. Swieter for his help

throughout this study.

The author would also like to thank Dr. W.S. Brey and

his associates for obtaining the high field B11 P31 and 1

nmr spectra reported in this study. Special thanks are due

to Dr. R.W. King for obtaining the mass spectra in this

study and for the instrumental instruction that the author

received from him. The author extends thanks to Mr. Mel

Courtney for obtaining the elemental analyses used in this

study. The author would also like to thank Dr. G.J. Palenik

for obtaining the crystal structures reported in this study.

The author gratefully acknowledges the financial

support of this research by the Department of Chemistry,

University of Florida.









Finally, the author expresses his gratitude to his

parents for their support and encouragement during the

course of study and to Dr. Donald F. Clemens for getting him

started.


iii


















TABLE OF CONTENTS


Page


ACKNOWLEDGEMENTS.. . . . .

LIST OF TABLES . . . . .

LIST OF FIGURES . . . . .

ABSTRACT . . . . . . .

CHAPTERS

I INTRODUCTION . . .

II MATERIALS AND PROCEDURES


. . . . . .


xii


. . . . . 1


Materials . . .
Procedures . . .


S . . . . 13
S . . . . 15


SYNTHESES OF BORANE ADDUCTS AND BORON
CATIONS . . . . . . . ... 19


Syntheses of Borane Adducts . .
Syntheses of Boron Cations .


* . 21
* . 30


:V PHYSICAL, CHEMICAL AND SPECTRAL PROPERTIES
OF BORANE ADDUCTS AND BORON CATIONS . .

Physical and Chemical Properties . .
Spectral Properties . . . . .

V DISCUSSION ON SYNTHESES OF BORANE ADDUCTS
AND BORON CATIONS . . . . . . .

Syntheses of Borane Adducts . . .
Synthesis of Boron Cations . . .

TI MEASUREMENT OF EQUILIBRIUM CONSTANTS FOR
THE EXCHANGE OF BH BETWEEN N-ALKYLIMINO-
TRIPHENYLPHOSPHORAAES AND BORANE ADDUCTS
OF TRIMETHYLAMINE AND 4-METHYLPYRIDINE .

Preparation to Measure Exchange of BH
Between N-Methyliminotriphenylphos-
phorane and Trimethylamine Borane .


III


36

36
46


98

98
106




116



116










Results and Treatment of Data ... .119
Discussion and Errors . . . .. 138


VII DETERMINATION OF THE AMOUNT OF PI-BONDING
BETWEEN PHOSPHORUS AND NITROGEN . . .. .149

Pi-Bond Character Measured from
Phosphorus-Nitrogen Bond Distances 149
Pi-Bond Character Measured from P
NMR Chemical Shifts . . . .. .169
Conclusion . . . . . ... 177

VIII REDUCTION OF IMINOTRIPHENYLPHOSPHORANE AND
N,N-DIMETHYLAMINOTRIPHENYLPHOSPHONIUM ION 178

Reaction of Iminotriphenylphosphorane
With Tetra-n-Butyl-Ammonium Boro-
hydride . . . . . . . 179
Reaction of N,N-Dimethylaminotriphenyl-
phosphonium Iodide With Sodium
Dimethylaminoborohydride . . .. .193
Reaction of N,N-Dimethylaminotriphenyl-
phosphonium Iodide With Lithium
Borohydride . . . . . ... .196
Conclusion . . . . . ... 203

IX SUMMARY . . . . . . . .... .. 207

APPENDIX COMPUTER PROGRAM USED IN CALCULATION OF n
FOR N-ETHYLIMINOTRIPHENYLPHOSPHORANE .. . 211

REFERENCES .. . . . .. . . . . . 213

BIOGRAPHICAL SKETCH . . . . . . . ... 219

















LIST OF TABLES

Table Page

1. Yields and Melting Points of N-Alkylimino-and
B-N-Substituted-Aminoimino-triphenylphosphorane
Boranes . . . . . . . . ... .. . 24

2. Analyses of N-Alkylimino-and s-N-Substituted-
Aminoimino-Triphenylphosphorane Boranes . .. 25

3. Comparison of the Two Methods Used to Synthesize
Borane Adducts . . . . . . . . 31

4. Yields and Melting Points of Bis(N-Alkylimino-
triphenylphosphorane) Boronium Iodides . . 34

5. Analyses of Bis(N-Alkyliminotriphenylphos-
phorane) Boronium Iodides . . . . ... 34

6. Infrared Data of N-Alkylimino-and 8-N-
Substituted-Aminoimino-Triphenylphosphoranes . 50

7. Infrared Data of N-Alkylimino-and B-N-
Substituted-Aminoimino-Triphenylphosphorane
Boranes . . . . . . . . ... .. . 51

8. Infrared Data of Bis-(N-Alkyliminotriphenyl-
phosphorane) Boronium Iodides . . . ... 53

9. Mass Intensity Data for N-Ethyliminotriphenyl-
phosphorane Borane . . . . . . ... 63

10. Proton and P31 NMR Data of N-Alkylimino-and
8-N-Substituted-Aminoimino-Triphenylphos-
phoranes . . . . . . . . .. .. . 68
31
11. Proton and P31 NMR Data of N-Alkylimino and
B-N-Substituted-Aminoimino-Triphenylphosphorane
Boranes . . . . . . . . ... .. . 70

12. Proton and P31 NMR Data Qf Bis-(N-Alkylimino-
triphenylphosphorane) BH2 I Salts . . . .. 72

13. B NMR Data of Borane Adducts and Boron
Cations . . . . . . . . ... .. . 73










Table

14. Line Positions and Intensities for the A2 X
Case . . . . . . . . .

15. Line Positions of the a Protons . . .

16. Line Positions of the B Part . . . .

17. Starting Concentrations of Reactants in the
Exchange of BH Between N-Alkylimino-
triphenylphospAorane and Trimethylamine
Borane . . . . . . . .

18. Starting Concentrations of Reactants in the
Exchange of BH Between N-Alkylimino-
triphenylphosp orane and 4-Methylpyridine
Borane . . . . . . . . .

19. P31 and 11 NMR Data for Exchange of BH3 .

20. H1 NMR Data for Exchange of BH . . .

21. Equilibrium Constants for Exchange of B3 .

22. Equilibrium Constants for Exchange of BH3 .

23. H1 NMR Data for Exchange of BH . . .

24. Calculated Values of KTP Using Equation (6.1

25. Enthalpies and Entropies of Reaction . .

26. Bond Lengths in N-Methyliminotriphenylphos-
phorane Borane . . . . . . .

27. Bond Angles in N-Methyliminotriphenylphos-
phorane Borane . . . . . . .

28. Bond Lengths in N,N-Dimethylaminotriphenyl-
phosphonium Tetrafluoroborate . . . .

29. Bond Angles in N,N-Dimethylaminotriphenyl-
phosphonium Tetrafluoroborate . . . .


Page


S. 77

. 79

. 83




. 118




. 118

. 120

. 121

. 134

. 134

. 135

) . 139

. . 145


S. 152


S. 153


S. 159


S. 162


30. Planar Angles in N-Methyliminoiriphenylphos-
phorane Borane . . . ... . . . .

31. Planar Angles in N,N-Dimethylaminotriphenyl-
phosphonium Ions . . . . . . . .

32. Parameters Used in and Results of Equation (7.2)
for (C6H5)3PM . . . . . . . . .


vii


167


167


173









Table Page

33. Change in Pi-Bonding on Coordination of
Phosphoranes by BH3 ........... . .174

34. Effect of Changing Angles EA and EP on the Value
of 1 for M = N(CH3)BH . .......... 176

35. Infrared Data of Iminotriphenylphosphorane and
Product from Reaction with Tetra-n-Butyl-
Ammonium Borohydride . . . . . . .. 183

36. C13 NMR Data of Solid Obtained by Reaction of
Iminotriphenylphosphorane with Tetra-n-Butyl-
Ammonium Borohydride . . . . . . .. 186

37. Mass Intensity Data of Solid Obtained by
Reaction of Iminotriphenylphosphorane with
Tetra-n-Butyl-Ammonium Borohydride . . ... .189

38. Mass Balance . . . . . . . ... 200

39. Possible Reaction Products Containing Boron . 202


viii

















LIST OF FIGURES


Figure Page

1. Apparatus for synthesis of phosphoranes . .. 20

2. Apparatus for synthesis of borane adducts . . 28

3. Infrared spectrum of N-ethyliminotriphenyl-
phosphorane .... . . . . . . . 54

4. Infrared spectrum of O-N-dimethylaminoimino
triphenylphosphorane . . . . . . . 55

5. Infrared spectrum of N-tert-butyliminotri-
phenylphosphorane borane . . . . . . 57

6. Infrared spectrum of B-N-phenylaminoimino-
triphenylphosphorane borane . . . . .. 58

7. Infrared spectrum of bis-(N-methyliminotri-
phenylphosphorane) boronium iodide . . .. 59

8. Mass spectrum of N-ethyliminotriphenylphos-
phorane borane . . . . . . . . 62

9. Symmetry and coupling constants of the A2B2
case . . . . . . . . . ... 75

10. Expansion of a protons in H nmr spectrum of
N-n-propyliminotriphenylphosphorane borane . 78

11. Expansion of B protons in H nmr spectrum of
N-n-propyliminotriphenylphosphorane borane . 81

12. Expansion of I protons, decoupled from methyl
protons, in H spectrum of N-n-propylimino-
triphenylphosphorane borane . . . . .. 82

13. H nmr spectrum of N-n-propyliminotriphenyl-
phosphorane . . . . . . . . . 84

14. H nmr spectrum of N-n-propyliminotriphenyl-
phosphorane borane . . . . . ... 85









Figure Page

15. H1 nmr spectrum of bis-(N-ethyliminotriphenyl-
phosphorane) boronium iodide . . . ... 87

16. Proton decoupled B nmr spectrum of N-methyl-
iminotriphenylphosphorane borane . . .. 90

17. Proton coupled B11 nmr spectrum of N-methyl-
iminotriphenylphosphorane borane . . ... 91

18. Proton coupled B11 nmr spectrum of N-ethylimino-
triphenylphosphorane borane . . . . ... 92
*1
19. Proton coupled B!' nmr spectrum of 8-N-phenyl-
aminoiminotriphenylphosphorane borane . . .. 93

20. Proton coupled B11 nmr spectrum of B-N-methyl,
phenylaminoiminotriphenylphosphorane
borane . . . . . . . . ... .. . 94

21. Proton coupled B11 nmr spectrum of bis-(N-n-
propyliminotriphenylphosphorane)boronium
iodide . . . . . . . . .. .. . 95

22. Proton decoupled B11 nmr spectrum of bis(N-n-
propyliminotriphenylphosphorane)boronium
iodide . . . . . . . . ... .. . 96

23. HOMO-LUMO interaction in Sn2 mechanism ... . 99

24. HOMO-LUMO interaction in Snl mechanism .. .. 100

25. Transition state for Sn2 reaction on
(C6H5)3PNRBH2I . . . . . . . 109

26. Transition state for trimethylamine displacement
in (trimethylamine)(pyridine)boronium iodide . 114

27. Transition state for trimethylamine displacement
in (trimethylamine)(N-n-propyliminotriphenyl-
phosphorane)boronium iodide . . . . ... .114

28. Expansion of H nmr spectrum for exchange of BH
between N-methyliminotriphenylphosphorane
and trimethylamine borane at 250 . . . . 123

29. Expansion of H nmr spectrum for exchange of BH3
between N-methyliminotriphenylphosphorane
and trimethylamine borane at 500 . . ... .124









Figure Page

30. Expansion of methyl resonances of phosphorane
and phosphorane borane in H nmr spectrum for
exchange of BH3 between N-methyliminotri-
phenylphosphorane and 4-methylpyridine borane
at 50 . . . . . . . . . 126

31. Expansion of methyl resonances of 4-methyl-
pyridine borane and 4-methylpyridine in H
nmr spectrum for exchange of BH between N-methyl-
iminotriphenylphosphorane and 4-methylpyridine
borane at 500 . . . . . . . ... 127

32. Expansion of H nmr spectrum for exchange of BH
between N-n-propyliminotriphenylphosphorane
and 4-methylpyridine borane . . . . .. 129
31
33. P nmr spectrum for exchange of BH between
N-ethyliminotriphenylphosphorane and 4-methyl-
pyridine borane at 250 . . . . . ... .131


34. Proton decoupled B11 nmr spectrum for exchange
of BH between N-n-propyliminotriphenylphos-
phoraRe and trimethylamine borane at 50 ...

35. Expansion of H spectrum for exchange of BH3
between 4-methylpyridine and trimethylamine
borane at 250 . . . . . . . . .

36. Structure of N-methyliminotriphenyl-
phosphorane borane . . . . . . . .

37. Structure of cation 1 in N,N-dimethyl-
aminotriphenylphosphonium tetrafluoroborate . .


38. Structure of cation 2 in N,N-dimethyl-
aminotriphenylphosphonium tetrafluoroborate


133


137


151


156


157


39. Structures of tetrafluoroborate anion
in N,N-dimethylaminotriphenylphosphonium
tetrafluoroborate . . . . . .

40. Infrared spectrum of [(C6H5)3PN]2BH . .

41. C13 nmr spectrum of [(C6H5)3PN]2BH . .

42. Mass spectrum of [(C6H5)3PN]2BH . . .


* . 158

S. 182

* . 185

S . 188


. .
















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



BORON HYDRIDE CHEMISTRY OF N-SUBSTITUTED-
IMINOTRIPHENYLPHOSPHORANES

By

William Keith Holley

December, 1986


Chairman: Professor G.E. Ryschkewitsch
Major Department: Chemistry

Borane adducts of N-substituted-iminotriphenylphos-

phoranes were prepared by two different general synthetic

methods. The first method involved displacement of tetra-

hydrofuran from borane tetrahydrofuran complex. The second

method employed in situ generation of diborane by reaction

of lithium borohydride with N-substituted-aminotriphenyl-

phosphonium bromides in diethyl ether. The two methods are

represented by the following equations:



D + C4H8OBH ----> DBH3 + C4H80
C4H80


DH + BH ------> DBH + H
4 (3 2
(C2H5)20
where D = a N-substituted-iminotriphenylphosphorane.


xii









A number of symmetrical cations were prepared which

contain a BH2 group coordinated with N-alkyliminotri-

phenylphosphoranes. They were synthesized by iodination of

the corresponding borane adduct followed by bimolecular

nucleophilic substitution. The reaction steps are repre-

sented by the following equations:



2DBH3 + 12 ---> 2DBH2I + H2



DBH2I + D ---> D2BH2 + I



where D = a N-alkyliminotriphenylphosphorane.

Physical, chemical and spectral properties of the

borane adducts and boron cations, namely thermal and hydro-

lytic stability, infrared and nmr spectra were discussed in

detail. In addition, the stability of the cations towards

Ag(I) and borohydride ions was studied.

Discussion on the synthetic methods includes steric and

electronic factors of the nucleophiles and substrates,

reaction mechanisms and comparison of reactivities of

boranes and boron cations, containing phosphoranes as

ligands, with the corresponding amine substituted entities.

Phosphoranes appear to be better nucleophiles than amines,

and phosphorane iodoboranes react faster than trimethylamine

iodoborane. Steric and electronic factors appear to play an

important role in defining the reactivity of the iodoborane


xiii









adducts. Comparison of the two methods to prepare borane

adducts showed that the second method was preferred.

Relative basicities of N-alkyliminotriphenylphos-

phoranes were determined by measuring equilibrium constants

for exchange of BH3 between phosphoranes and borane adducts

of trimethylamine and 4-methylpyridine. It was found that

the phosphoranes are less basic than trimethylamine.

The amount of pi-bonding between phosphorus and nitro-

gen was determined by crystallographic and P nmr data.

Reduction of iminotriphenylphosphorane and N,N-

dimethylaminotriphenylphosphonium ion by different reducing

agents was studied in detail. A new product was isolated

and characterized from the reaction of tetra-n-butyl-

ammonium borohydride with iminotriphenylphosphorane. The

compound was identified as [(C6H5)3PN]2BH.


xiv

















CHAPTER I

INTRODUCTION



Adducts of diborane (1) are characterized by having an

electron pair donor coordinated to a BII3 group. Burg and

Schlesinger (2) isolated the first adducts of diborane,

OCBH3 and trimethylamine borane. Since that time a large

variety of borane adducts has been synthesized employing

oxygen (3), nitrogen (2), sulfur (4), and phosphorus (5) as

electron donors. Their examples are represented as follows:



Ether Boranes

CH3 IH (3) (6)

:O:B- I : :B H

CH H



Thioether Boranes

CH3 H

: B=-- H\ (4)

CH3 H


1









Amine Boranes

CH3 H

CHH
CH---N: H

CH3 H



Phosphine Boranes

H H

H :B H

H. H


H H

H----N:B H

H





0 H



0 H


The most common route to borane adducts is direct combina-

tion of the donor and diborane at low temperature (2-6).

The class of borane adducts which has received the

largest amount of attention is the amine boranes. There are

numerous different procedures for synthesizing amine

boranes. Koster obtained them by high pressure hydrogenoly-

sis of amine trialkylboranes (9).


R3NBR' + 3H2 --> R3NBH3 + 3R'H


(1.1)


Ashby and Foster (10) prepared them by reduction of

alkoxyboranes with aluminum and hydrogen in an amine sol-

vent.

N(C2H5)3
N(C2H5)3 + 2B(OC6H5)3 + 3H2 + 2A1 -------> 2H3BN(C2H5)3


+ 2Al(OC6H5)3 (1.2)









Schlesinger et al. (2,11) produced them by displacement

of a donor attached to BH3.



OCBH3 + (CH3)3N --> (CH )3NBH3 + CO (1.3)

C5HNBH3 + (CH3)3N --> C H5N + (CH3)3NBH (1.4)



Schlesinger et al. (12) also obtained amine boranes by

reaction of an amine with an aluminum boron hydride.



(CH3)3N + A1B3H12 --> (CH3)3NBH3 + other volatile

solids (1.5)



Other procedures employ in situ generation of diborane

in the presence of an amine as follows:



DH+ + BH --> DBH + H2 (1.6) (13)

4R3N + BX3 + 3NaBH4 --> 4R3NBH3 + 3NaX (1.7) (14)

2D + 12 + 2BH4 --> 2DBH3 + 21 + H2 (1.8) (15)



Iminotriphenylphosphoranes represent an important class

of reactive intermediates in organic synthesis. Imino-

triphenylphosphoranes contain the basic structure of

(C6H5)3P = N-R. The nomenclature adopted in this text for

these compounds follows the rules agreed upon by The Organic

Division's Advisory Committee on the Nomenclature of Organic

Phosphorus Compounds (16). The parent structure on which

the names are based is taken as phosphorane, H5P. In









general cases, the compounds may be referred to as imino-

triphenylphosphoranes or phosphoranes for brevity.

The first iminotriphenylphosphoranes were made by

Staudinger et al. (17,18) by reacting triphenylphosphine

with an organic azide.



(C6H5)3P + RN3 --> [(C6H5)3P = N N = N R] -->

(C6H5)3P = N R + N2 (1.9)



Since that time a number of compounds with different R

groups have been reported (19-22). The preparations of

these compounds involve dehydrohalogenation of the corre-

sponding aminotriphenylphosphonium salts.

Horner and Oediger (21) carried out the dehydrohalo-

genation with triethylamine.



(C6H)3PBr2 + RNH2 + 2(C2H5)3N --> (C6H5)3P = N R

+ 2(C2H5)3NHBr (1.10)



Two separate research groups (19,23) have described the

dehydrohalogenation with sodamide in liquid ammonia.



liq. NH
(C6H5)3P = N HR + NaNH2 --> (C6H5)3P = NR + Na + NH3

(1.11)


Sisler et al. (24) have dehydrohalogenated amino-

triphenylphosphonium chloride with magnesium hydride.





5



250C
2[(C6H5)3P = NH2] Cl + MgH2 --> 2(C6H5)3P = N H

+ 2H2 + MgC12 (1.12)



During the current investigation, a new compound of the

aforementioned class, 6-N-phenylaminoiminotriphenylphos-

phorane, was synthesized and characterized.

Although several BF3 adducts of the iminotriphenyl-

phosphoranes have been reported in the literature (25,26),

the only BH3 adduct mentioned is that of the parent com-

pound, iminotriphenylphosphorane (25). Therefore, one of

the objectives of the present work was to prepare and

characterize a series of new borane adducts employing

N-substituted-iminotriphenylphosphoranes as ligands.

Little or no information on the IR (19), H -nmr

(20,27), and P 31-nmr spectra of the iminotriphenylphos-

phoranes used in this study was available. It was neces-

sary, therefore, during the course of this investigation, to

record infrared and nmr spectra on all the iminotriphenyl-

phosphoranes used in the current study.

Borane adducts are a basic starting material to other

boron compounds. Closely related to borane adducts, boron

cations constitute an important class of boron compounds.

Boron cations containing only one boron atom can be con-

sidered as coordination compounds of boron (III). There-

fore, when less than three negatively charged ligands are

completed to boron, a positively charged species is formed.









By varying the number of negatively charged ligands, mono-,

di-, and tri- cations are possible.

Boron cation chemistry developed after the elucidation

of the structure of the diammoniate of diborane (28). It

was found that the diammoniate of diborane is the tetra-

hydroborate salt of the boron cation, diaminedihydro-

boron(+1).



+


H3N
BH4







Since this time a number of boron cations have been

reported in the literature (29,30). The majority of the

boron cations reported contain a single positive charge.

There are several general methods for the preparation of

singly charged cations. A small number of boron cations

have been prepared by unsymmetrical cleavage of diborane

(28,31).



2H3N + B2H --> (HN) BH2 BH4 (1.13)



Miller and Muetterties (32) prepared boron cations by

reaction of borane adducts with onium salts of large anions.









100-1800
+ -+
ABH + AH X -> A B2X + H (1.14)

A = tertiary amine X = halogen



In general, boron cations are formed by the displace-

ment of an anion from an amine halo borane by a neutral

base. This method was pioneered by Douglass et al. (33,34)

to prepare boronium ions of the type (amine)2BRH+ where R

represents organo groups.


+ +
RBH (amine) + I, + 2 amine --> RBH(amine) I + amine H+I

(1.15)



The method was further developed by Ryschkewitsch (35)

to prepare the (C5H5N)2BH2 cation.



CH5NBH3 12 + 2C5H N --> (C5HN) BH I + C H5NH I

(1.16)



Since that time a number of boron cations of the type

(base)(base')BH where base=base' or base#base' have been

prepared by the aforementioned method (29,36,37).

Another objective of the present work was to prepare a

series of boron cations of the type (base)(base')BH employ-

ing N-alkyliminotriphenylphosphoranes as the bases.

Boron cations of the type (base)2BH in the presence of

borohydride ion can interconvert to borane adducts.









(base)BH + BH 2(base)BH (1.17)
(base)2 2 4 3


The more thermodynamically stable product should result.

For example, the borohydride salts of bis(monomethyla-

mine)boronium cation and bis(dimethylamine)boronium cation

do not transform into the corresponding amine boranes in

solution (38). However, the BH2 cation derived from tert-

butylamine reacts with lithium borohydride to produce

tert-butylamine borane (39).

A third objective of the present work was to investi-

gate the stabilities of the bis(alkyliminotriphenylphos-

phorane) boronium cations in the presence of borohydride

ion.

Iminotriphenylphosphoranes have been shown to be basic

materials. They act as Lewis bases to form adducts (25,26)

and as Bronsted bases reacting with hydrogen halides

(17,18,40). Information on their relative base strengths is

scant. It has been reported that the alkylaminotriphenyl-

phosphonium halides cannot be deprotonated by triethylamine

(21,41).

Johnson and Wong (42) determined pKa values of the

hydrochloride salts of a series of N-(substituted-phenyl)-

iminotriphenylphosphoranes by potentiometric titrations in

95% ethanol solution. Their results show that the

N-(substituted-phenyl)-iminotriphenylospshoranes are much

weaker bases than ammonia.









Graham and Stone (43) used BF3 and BH3 as reference

acids to measure the relative base strengths of some thio-

ethers, phosphines, and amines. The base strengths were

determined by measuring equilibrium constants for exchange

of BH3 between two different donors in the gas phase.



(base)BH3 + base' <_ (base')BH3 + base (1.18)



A fourth objective of the present work was to study the

relative basicities of the alkyliminotriphenylphosphoranes.

This was done by measuring equilibrium constants for

exchange of BH3 between the alkyliminotriphenylphosphoranes

and ordinary amines.

Iminotriphenylphosphoranes exhibit varying amounts of

multiple bonding between phosphorus and nitrogen. This

bonding is referred to as d -p bonding in which filled 2p

orbitals on nitrogen overlap with empty 3d orbitals on

phosphorus.







Three different resonance structures can be drawn to

represent bonding in the iminotriphenylphosphoranes.


+ R <> 0 R
3 P N R <--> -P N R <--> R
3 3 3









Craig and Paddock (44) published an excellent discus-

sion on electron distribution in cyclic d -p systems. They

attempted to correlate the amount of d -p overlap in cyclic

phosphazenes by comparing two different physical properties.

Phosphorus-nitrogen bond lengths are compared to the P-N

bond length in phosphoramidate ion of 1.78A (45) and to the
0
sum of single covalent radii of 1.76A. Also, the

dissociation energies for P-N are compared to a calculated

value of 65 kcal/mole (for a single bond) and an

experimental value of 66.8 kcal/mole in trisdiethylamido-

phosphine (46).

Claydon, Fowell, and Mortimer (47) determined the P-N

dissociation energy in N-ethyliminotriphenylphosphorane to

be approximately 125 kcal/mole. This would attribute

approximately 58 kcal/mole of energy to d -p interaction in

N-ethyliminotriphenylphosphorane.

Letcher and Van Wazer (48) present an elaborate quantum

mechanical theory to describe P nmr chemical shifts. They

demonstrate by examples that, to a first approximation, P3

chemical shifts are determined by the number and kind of

atoms immediately adjacent to the phosphorus in the mole-

cule. According to this theory, the P31 chemical shift, 6,

is attributable to two additive quantities. One involves

the occupation of the p orbitals on phosphorus, and the

other involves occupation of the d oribtals. It was con-

cluded that molecular structures based on triply and

quadruply connected phosphorus have a bonding involving only










s and p orbitals and that the d orbitals are reserved for r

bonding. For compounds based on quadruply connected phos-

phorus, the P31 chemical shift, 6, referenced to 85% phos-

phoric acid, is given by



6 = 11,828.5 7940a1 149n
1 iT


where n is the total occupation of the d orbitals of

phosphorus in electronic charge per phosphorus atom, and 6

is the P chemical shift in ppm which would be observed if

the occupation of the d orbitals of the phosphorus were

zero. A short computer program, which takes into account

the electronegativities of the groups attached to phosphorus

and the group bond angles around the phosphorus, is used to

calculate al. By rearranging the above equation, n can be

solved for.



-6 + 11,828.5 7940ac
n =
149



A final objective of the current investigation was to

determine the amount of 7 bonding between phosphorus and

nitrogen in the N-substituted-iminotriphenylphosphoranes and

their borane adducts by a combination of crystallographic

and P nmr data.

Phosphorus atoms in molecules can exist in a number of

oxidation states. The most stable oxidation state of









phosphorus in aqueous solution is +5. Iminotriphenylphos-

phoranes contain phosphorus in the oxidation state of +5.

Reduction of the +5 oxidation state of phosphorus even in

non-aqueous solutions is difficult. A subsidiary objective

of the current research program was to investigate the

possibility of reduction of iminotriphenylphosphorane and

N,N-dimethylaminotriphenylphosphonium ion with hydride ion.

Hydride ion was chosen because it is a strong reducing agent

and should be a good nucleophile toward phosphorus.

















CHAPTER II

MATERIALS AND PROCEDURES



Materials



Boranes

Borane-tetrahydrofuran complex was obtained from

Aldrich Chemical Company and was used without further

purification. Trimethylamine borane was obtained from

Callery Chemical Company. Dimethylamine borane was pur-

chased from Aldrich Chemical Company. The compound

4-methylpyridine borane was synthesized from 4-methyl-

pyridine and borane-tetrahydrofuran complex. The amine

boranes and 4-methylpyridine borane were sublimed prior to

use.



Amines

Amines were purchased from various commercial sources--

namely, Eastman Organic Chemicals, Aldrich Chemical Company,

and Matheson Gas Products. Amines were distilled prior to

use. The compound 4-methylpyridine was obtained from

Eastman Organic Chemicals and was distilled from barium

oxide.









Hydrazines

The various hydrazines purchased were unsymmetrical

dimethylhydrazine from FMC Corporation, phenylhydrazine from

Fisher Scientific Company, and N-methyl,N-phenylhydrazine

from Fluka Chemical Corporation. The hydrazines were used

without further purification.



Triphenylphosphine

Triphenylphosphine was obtained from Aldrich Chemical

Company, Peninsular ChemResearch, and Matheson Coleman and

Bell and was used without further purification.



Halogens

Iodine was purchased from Mallinckrodt Chemical Company

and bromine from Fisher Scientific Company.



N-substituted-Iminotriphenylphosphoranes

The N-substituted-iminotriphenylphosphoranes were

prepared by dehydrobromination of the corresponding

aminotriphenylphosphonium bromides by sodamide in liquid

ammonia (19,20) and were recrystallized from heptane.



N-substituted-Aminotriphenylphosphonium Bromides

The N-substituted-aminotriphenylphosphonium bromides

were synthesized according to the procedures of Zimmer and

Singh (19,20) and were recrystallized from chloroform-ethyl

acetate.









Solvents

All solvents, reagent grade, were supplied from various

commercial sources. They were used without purification

except when dry solvents were required. Solvents were dried

over sodium-benzophenone or phosphorus pentoxide and

distilled under dry nitrogen.



Other Compounds

Sodamide, sodium hydride, and proton sponge were

purchased from Aldrich Chemical Company and were used

without further purification. Sodium dimethylaminoboro-

hydride, as the dioxanate, was synthesized according to the

procedure of Aftandilian et al. (49). The compound N,N-

dimethylaminotriphenylphosphonium iodide was synthesized

according to the procedure of Zimmer and Singh (19).

Lithium borohydride was obtained from Metal Hydrides, Inc.

and was recrystallized from diethylether. Tetra-n-butyl-

ammonium borohydride was purchased from Aldrich Chemical

Company and was recrystallized from ethyl acetate (50).

Trimethylamine iodoborane was synthesized according to the

procedure of Ryschkewitsch and Wiggins (51) and was sublimed

prior to use.



Procedures

Protection from the Atmosphere

All syntheses were performed in glassware which had

been dried in an oven at 1300 and that were cooled to room









temperature under a steady stream of dry nitrogen. All of

the syntheses were performed either inside a dry box or in a

hood maintaining a constant flow of dry nitrogen through the

reaction flasks. Filtrations of water sensitive materials

were done inside a dry box or by using standard Schlenk ware

techniques.

Samples for nmr spectroscopy of water sensitive mate-

rials were prepared in a dry box, and the nmr tubes were

sealed by a flame when solutions were to be kept for long

periods of time.

Potassium bromide pellets for i.r. spectroscopy were

prepared in a dry box using oven dried KBr. Infrared

spectra were recorded under a stream of dry nitrogen.

All water sensitive materials were stored in dessica-

tors and handled in a dry box.



Infrared Spectra

Infrared spectra were obtained on a Nicolet 5DXB FTIR

spectrometer.



NMR Spectra
13
Proton and C1 nmr spectra were obtained at 99.55 and

25.00 MHz respectively on a JEOL FX-100 instrument with

tetramethylsilane as internal reference. Occasionally, H1

nmr spectra were obtained at 300 MHz on a Nicolet NT-300

instrument or at 60 MHz on a Varian EM360L when more or less

resolution was appropriate. Phosphorus-31 nmr spectra were









obtained proton decoupled at 80.984 MHz or 121.477 MHz with

85% phosphoric acid as the external reference. Boron-11 nmr

spectra were obtained at 64.184 MHz or 96.270 MHz with

trimethylborate as the external reference. Methylene

chloride, benzene, or monoglyme was used as the solvent.

Deuterated solvents were used for the HI nmr spectra.



Mass Spectra

Mass spectra were obtained on an AEI-MS30 with an

ionizing energy of 70 e.v.



Gas Chromatography

Gas chromatography was recorded on a Varian Model 3700

gas chromatograph using a 2.5 meter long 1/4 inch in diame-

ter column packed with Porapak Q.



Calculations

All computer programs were performed on an Apple II

computer.



Melting Point

Melting points of the various compounds were determined

in sealed capillary tubes on a Thomas Hoover apparatus and

were not corrected.






]8


Constant Temperature

Temperatures were kept constant in a Haake FJ constant

temperature bath.



Elemental Analyses

The elemental analyses were performed by Mr. Mel

Courtney of the University of Florida.
















CHAPTER III

SYNTHESES OF BORANE ADDUCTS AND BORON CATIONS



Syntheses of the N-alkyliminotriphenylphosphoranes and

the $-N-substituted-aminoiminotriphenylphosphoranes, used in

the borane adduct investigation, are represented by the

preparation of a new phosphorane, B-N-phenylaminoimino-

triphenylphosphorane. The apparatus consists of a nitrogen-

flushed 500 ml three neck flask immersed in a dry ice

acetone bath. The flask is fitted with a thimble, a dry ice

condenser and a gas addition tube which is connected to an

ammonia cylinder (see Figure 1).

To a suspension of B-N-phenylhydrazinotriphenylphos-

phonium bromide, 22.466 g (49.999 mmoles), in 300 ml of

anhydrous liquid ammonia, sodamide, 2.148 g (55.06 mmoles),

was added. The yellow mixture was stirred for one hour with

a magnetic stirrer. The ammonia was then evaporated under a

steady stream of dry nitrogen. The reaction flask was

transferred to the dry box and 300 ml of dry tetrahydro-

furan were added to the residue. The mixture was filtered

leaving a white solid behind. The yellow-brown filtrate was

evaporated under a steady stream of dry nitrogen to produce

a yellow-brown solid which weighed 14.7896 g (80% yield).




19















To hood


NaNH2 NH


\ \ //




Phosphonium bromide I -
in liquid NH3 .:i .
.... .. ...... Dry ice-
:iiiii::::: :: : acetone bath

Magnetic stirring bar

7 Magnetic
I stirring motor


Figure 1. Apparatus for synthesis of phosphoranes.









The crude product was recrystallized from a dry tetrahydro-

furan-heptane solvent mixture to produce large yellow cubic

crystals. The recovered material (9.7886 g, 66% yield)

melted at 132-1330. The analysis of the recrystallized

material was %C 78.05, %H 5.61, %N 7.41, calculated: %C

78.24, %H 5.75, %N 7.60.



Syntheses of Borane Adducts

Borane adducts of N-alkyliminotriphenylphosphoranes and

8-N-substituted-aminoiminotriphenylphosphoranes were

prepared by two simple synthetic methods. The first pro-

cedure employs displacement of a donor coordinated to BH3

using borane-tetrahydrofuran complex and an N-substituted-

iminotriphenylphosphorane (2,11).



C4H 8
(C6H5)3PNR + C4H OBH3 ---> (C6H5 )PNRBH3 (3.1)



The second procedure employs in situ generation of diborane

in diethyl ether by reaction of lithium borohydride with a

N-substituted-aminotriphenylphosphonium bromide.



(C6H5)3PNHR + BH4 --> (C6H5)3PNRBH + H2 (3.2)
6 5 3 6 5 3 3 2









Syntheses of N-Alkyliminotriphenylphosphorane Boranes
from Borane Tetrahydrofuran Complex and N-Alkylimino-
triphenylphosphoranes

In a typical experiment, twice the stoichiometric

amount of borane-tetrahydrofuran complex was added via a

syringe to a stirred saturated solution of a N-alkylimino-

triphenylphosphorane in tetrahydrofuran. Using this pro-

cedure, N-alkyliminotriphenylphosporane boranes were

synthesized where alkyl = methyl, ethyl, n-propyl, iso-

propyl, isobutyl and tert-butyl. The general workup of this

preparative method is represented by the synthesis of

N-methyliminotriphenylphosphorane borane.

To N-methyliminotriphenylphosphorane, 1.381 g

(4.740 mmoles), in 6 ml of dry tetrahydrofuran, borane-

tetrahydrofuran complex, 8.00 ml of 1.00 molar (8.00 mmoles

of BH3), was added. The mixture was stirred for 1.5 hours

with a magnetic stirrer. A white precipitate formed after

5 minutes of stirring. The product was further precipitated

by the addition of 150 ml of dry heptane. The crude product

was filtered and washed with four portions of 40 ml each of

dry heptane (160 ml total). The solid was dried in vacuo.

The product weighed 1.309 g (90% yield), mp 184-186 dec.

A portion of the crude product (0.269 g) was recrystal-

lized from a dry benzene-heptane solvent mixture producing

cubic crystals. The recovered material (0.170 g, 63%)

melted at 190-1910 with decomposition.









The yields of the N-alkyliminotriphenylphosphorane

boranes and the melting points of the crude and recrystal-

lized materials are given in Table 1. Analytical data for

the N-alkyliminotriphenylphosphorane boranes are listed in

Table 2.



Syntheses of 6-N-Substituted-Aminoiminoiriphenylphos-
phorane Boranes from Borane-Tetrahydrofuran Complex and
B-N-Substituted-Aminoiminotriphenylphosphoranes

In a typical experiment, three times the stoichiometric

amount of borane-tetrahydrofuran complex was added via a

syringe to a stirred saturated solution of a B-N-subsituted-

aminoiminotriphenylphosphorane in tetrahydrofuran. Using

this procedure, B-N-dimethyl, S-N-phenyl and B-N-methyl,

phenylaminoiminotriphenylphosphorane boranes were synthe-

sized. The general workup of this preparative method is

represented by the synthesis of B-N-phenylaminoimino-

triphenylphosphorane borane.

To S-N-phenylaminoiminotriphenylphosphorane, 1.8557 g

(5.0370 mmoles), in 35 ml of dry tetrahydrofuran, borane-

tetrahydrofuran complex, 15.00 ml of 1.00 molar (15.0 mmoles

of BH3), was added. The solution changed from dark yellow

to a very light yellow upon addition of the borane

tetrahydrofuran complex. The mixture was stirred for

2 hours with a magnetic stirrer. A yellowish precipitate










o o
) 0
SN UO U U U0 0 0 0
0- -) O C) a) c) C) C) C) a)
0 -14-
r-- 4-) ro ri r(:; ro rQ To rd



> I I I I I I >1
,-1-4 C),J 0) C r-I i
..i o-1 -11 0 0 l-l t--1 l- .-l4
H0 0 0 0 H
0
HI u


o
) 4-1
4J U c C) ) C)O ) ) U
j 4-41 a) D C ) a) a) ) a a "
4J Or00 0 re r, ra r r
J N e a- -,
S U c ) N 4l l
3HU 1 1 1 1 1 1 1 1

I U 2






0 4 4 r d o
0 H
O 0


4 S o M r tM ,o n CY) m om





>1 ,- 0 0 >-
r- a



-H IO
0
z a)


44 -rI O
0CO () 4 0 U2
C 0 O H) >1







C, a O (i n3 5 l C S
.Hn It O c 4J -rA H Or
) P O O O O C, d
C z Q) I 0 k H
P4 C Q.t 4 04 0 (z rCd q





4J40 02 04 a 04 4 H E -)
S0) Q I 0 H I >4 HI 04 l 04. 'zl >


) 04 >i >1 -44) -H- ) -HM Q H
O Q Z.) r o C) 0-. 0r c p )
>i H, r-4 a C) Ql C) r CdO z C 0 r0 V
Z2 a) r 4 -, E 0- 0 Ei a0 0 2
>1 >o 4 ) -H P .- I -Q -H Tj -H
z 04 4: o 4 4- > 4 r-i a 0 a E 0 _0
P 4- Pk -H !)0 + HC O Cd0J

0r C 0 >i P0 Q 0 -1 -z 0r O 0 Q ru
HO. 04 a P a r 0 fa z m J a)c04-4
C)-H 2 0 4J4 -H (0 -H -4 -HP 1 U>1 02
-H P 0 z 0 2 -H 2 -H o 0 04 .1 -i-H
U-, E u -H L -Ha Ha) ) a2 ) >- r Q) U 4J
2 z -H $: >- 0-4 -H- O24 H 4 0 rd
4 fo Q4 r o E o a 1 04 ra M
Q4 0 OP -4JIP >-,P *H 0 r -0 S -H -r-4 0



E-4 g z z z z ca ca
E Z Z Z Z C a < *









Table 2. Analyses of N-Alkylimino-and B-N-Substituted-
Aminoimino-Triphenylphosphorane Boranes.



Compounds %C %H %N


(C6H5)3PNCH3BH3 Calcd. 74.78 6.94 4.59
Found 75.00 7.09 4.54

(C6H5)3PN(CH2CH3)BH3 Calcd. 75.26 7.26 4.39
Found 75.15 7.31 4.26

(C6H5) 3PN(n-C3H7)BH3 Calcd. 75.69 7.56 4.20
Found 75.22 7.86 4.15

(C6H5)3PN(i-C3H7)BH3 Calcd. 75.69 7.56 4.20
Found 75.63 7.68 4.10

(C6H5) PN(i-C4H9)BH3 Calcd. 76.09 7.84 4.03
Found 76.13 8.09 3.83

(C6H5) PN(t-C4H9)BH3 Calcd. 76.09 7.84 4.03
Found 76.02 8.04 3.91

(C6H5) 3PNN(CH3) 2BH3 Calcd. 71.88 7.24 8.38
Found 71.63 7.38 8.10

(C6H5) 3PNNH(C6H5)BH Calcd. 75.41 6.33 7.33
Found 75.31 6.42 7.10

(C6H5)3PNNCH3(C6H5)BH3 Calcd 75.77 6.61 7.07
Found 75.49 6.69 6.85









formed after 30 minutes of stirring. The product was

further precipitated by the addition of 200 ml of dry

heptane. The crude product was filtered and washed with

four portions of 40 ml each of dry heptane (160 ml total).

The solid was dried in vacuo. The product weighed 1.3802 g

(72% yield), mp 126-1270 dec.

A portion of the solid (0.8643 g) was dissolved in

75 ml of dry tetrahydrofuran. The solution was filtered,

and dry heptane, 100 ml, was added slowly to the filtrate,

with stirring, to precipitate fine white needles. The solid

was filtered and washed with three portions of 50 ml each of

dry heptane (150 ml total). The solid was dried in vacuo.

The recovered material (0.6619 g, 77% yield) melted at

130-1310 with decomposition.

The yields of the B-N-substituted-aminoiminotri-

phenylphosphorane boranes and the melting points of the

crude and recrystallized materials are given in Table 1.

Analytical data for the B-N-substituted-aminoiminotri-

phenylphosphorane boranes are listed in Table 2.



Syntheses of N-Substituted-Iminotriphenylphosphorane
Boranes from Lithium Borohydride and N-Substituted-
Aminotriphenylphosphonium Bromides

Two experiments were carried out to demonstrate the

usefulness of this experimental method toward the

two classes of compounds, the N-alkylaminotriphenylphos-

phonium bromides and the B-N-substituted-hydrazinotri-

phenylphosphonium bromides. The apparatus consists of a









nitrogen-flushed 100 ml three neck flask equipped with a

pressure compensated addition funnel at A, a reflux con-

denser at B, and a nitrogen inlet tube at C, connected to a

mercury bubbler (see Figure 2). The top of the reflux

condenser is connected to a mercury bubbler.

Synthesis of N-methyliminotriphenylphosphorane borane.

To N-methylaminotriphenylphosphonium bromide, 1.893 g

(5.085 mmoles), a solution of 0.147 g (6.75 mmoles), of

lithium borohydride in 20 ml of dry diethyl ether was added

via the funnel. The mixture was stirred for 1 hour with a

magnetic stirrer during which time hydrogen gas evolution

was observed. To the mixture was added 25 ml of dry diethyl

ether. The funnel was removed and a stopper was placed at

A. The inlet tube was moved from C and connected to the top

of the reflux condenser, and a stopper was placed at C. The

mixture was then heated to reflux for 4 hours. The flask

was allowed to cool to room temperature, and the inlet tube

was moved back to C. The top of the condenser was connected

to a drying tube containing anhydrous calcium sulfate. The

ether was then evaporated under a steady stream of dry

nitrogen. The flask was transferred to a dry box. The

residue in the flask was extracted with two portions of

80 ml each of dry benzene (160 ml total). The solutions

were filtered, and the combined filtrate was evaporated

under a steady stream of dry nitrogen. After evaporation, a

yellowish white solid remained which weighed 0.916 g (59%

yield).


I












/ '-- To mercury bubbler


Pressure- --
compensated
dropping
funnel
LiBH solution
in diethyl ether




Phosphonium bromide




Magnetic stirring-
motor


Water cooled reflux
condenser








2








netic stirring bar


Figure 2. Apparatus for synthesis of borane adducts.










A portion of the solid (0.307 g) was recrystallized

from a benzene-heptane solvent mixture producing 0.189 g

(62% yield) of white cubic crystals. The melting point, H1

and B nmr spectra of the product were identical to a

previously prepared sample of N-methyliminotriphenylphos-

phorane borane.

Synthesis of g-N-Dimethylaminoiminotriphenylphos-

phorane Borane. To S-N-dimethylhydrazinotriphenylphos-

phonium bromide, 2.0200 g (5.0340 mmoles), a solution of

0.1591 g (7.304 mmoles) of lithium borohydride in dry

diethyl ether was added via the funnel. The mixture was

stirred for 2 hours with a magnetic stirrer, during which

time hydrogen gas evolution was observed. To the mixture

was added 60 ml of dry diethyl ether. The inlet tube was

moved from C and connected to the top of the condenser, and

a stopper was placed at C. The funnel was removed; a

stopper was placed at A. The mixture was then heated to

reflux for 4 hours. The flask was allowed to cool to room

temperature and the inlet tube was moved back to C. The top

of the reflux condenser was connected to a drying tube

containing anhydrous calcium sulfate. The ether was then

evaporated under a steady stream of dry nitrogen. The flask

was transferred to a dry box. The residue in the flask was

extracted with three portions of 50 ml each of dry benzene

(150 ml total). The solutions were filtered and the

combined filtrate was evaporated under a steady stream of









dry nitrogen. After evaporation, a white solid remained

which weighed 1.417 g (84% yield).

A portion of the solid (1.1264 g) was dissolved in

25 ml of dry tetrahydrofuran. The solution was filtered.

To the filtrate was added 150 ml of dry heptane to form a

white precipitate. The precipitate was filtered and washed

with four portions of 40 ml each of dry heptane (160 ml

total). The solid was dried in vacuo and weighed 0.7422 g

(66% yield). The melting point, H and B nmr spectra of

the solid were identical to a previously prepared sample of

g-N-dimethylaminoiminotriphenylphosphorane borane.

A direct comparison of the two methods used to obtain

borane adducts is given in Table 3. Materials used, yields,

reaction times, and total time spent to isolate a crude

product of N-methyliminotriphenylphosphorane borane are

listed in Table 3.



Syntheses of Boron Cations

Boron cations of the type (base)2BH+I where

base = N-alkyliminotriphenylphosphorane were synthesized by

displacement of iodide from an iodoborane prepared in situ

(36). The iodoborane adducts were prepared by a modifica-

tion of the method of Noth and Beyer (52).



2(C6H5)3PNRBH3 + 2 --> 2(C6H5)3PNRBH2I + H2 (3.3)

not isolated









Table 3. Comparison of the Two Methods Used to Synthesize
Borane Adducts.


Method 1


Materials used




Reaction time


Yield %


Method 2


THFa borane, THF, LiBH4, diethyl ether,
heptane, phosphorane phosphonium bromide,
benzene


1.5 hours


5 hours


Total time


15 hours


24 hours


a = tetrahydrofuran.








(C6H5)3PNRBH2I + (C6H5)3PNR --> [(C6H5 3PNR]2BH I-
(3.4)



In a typical experiment, a stoichiometric amount of

iodine was added to a solution of the borane in benzene.

After all the iodine had reacted, a stoichiometric amount of

the corresponding phosphorane was added, and the reaction

product was isolated. The reactions were run at room

temperature. In this manner boron cations of the type

bis(N-alkyliminotriphenylphosphorane)BH I where









alkyl = methyl, ethyl and n-propyl, were synthesized. The

general workup of this preparative method is represented by

the synthesis of bis(N-methyliminotriphenylphosphorane)

boronium iodide.



Synthesis of Bis(N-Methyliminotriphenylphosphorane)
Boronium Iodide

To N-methyliminotriphenylphosphorane borane, 0.341 g

(1.12 mmoles), in 60 ml of dry benzene, iodine, 0.124 g

(0.487 mmoles), was added. The solution was stirred with a

magnetic stirrer. The iodine reacted rapidly evolving

hydrogen gas. The iodine color disappeared after 10 minutes

indicating that all of the iodine had reacted. To the

yellowish cloudy solution, N-methyliminotriphenylphos-

phorane, 0.292 g (1.00 mmoles), was added. The mixture was

stirred for 1.5 hours. A white precipitate was observed

after 30 minutes of stirring. The precipitate was filtered

and washed with five portions of 20 ml each of dry benzene

(100 ml total). The solid was dried in vacuo. The product

weighed 0.669 g (93% yield), mp 164-1680.

A portion of the crude product (0.282 g) was dissolved

in a minimum amount of dry methylene chloride. The solution

was filtered, and dry diethyl ether was added to the fil-

trate to precipitate 0.275 g of white powder (98% yield)

mp 215-217.

The yields of the bis(N-alkyliminotriphenylphosphorane)

boronium iodides and the melting points of the crude and









reprecipitated products are given in Table 4. Analytical

data for the boron cations are listed in Table 5.



Attempted Synthesis of (Trimethylamine)(N-n-Propyl-
iminotriphenylphosphorane) Boronium Iodide

To trimethylamine iodoborane, 1.0012 g (5.0352 mmoles),

in 100 ml of dry benzene, N-n-propyliminotriphenylphos-

phorane, 1.6168 g (5.0622 mmoles), was added. The mixture

was stirred for 14 hours with a magnetic stirrer. A white

precipitate formed which was filtered and washed with

five portions of 20 ml each of dry benzene (100 ml total).

The solid was dried in vacuo. The product weighed 1.9025 g

(73% yield).

A H1 nmr spectrum of the solid in deuterated methylene

chloride was recorded. The spectrum showed two sets of

peaks. One set of peaks corresponded to bis(N-n-propyl-

iminotriphenylphosphorane) boronium iodide, and the sharp

singlet occurring at 6 = 3.00 ppm was identical with the

chemical shift for bis(trimethylamine) boronium iodide in

the same solvent. The ratio of the integrated areas under

the peaks showed that an equimolar amount of both products

was produced.

A portion of the solid (1.467 g) was added to 50 ml of

deionized water. The solid was sparingly soluble, and the

mixture was stirred for 10 minutes with a magnetic stirrer.

The mixture was filtered, and the remaining solid was dried

in vacuo. The recovered material weighed 1.202 g. A H nmr









Table 4. Yields and Melting Points of Bis(N-Alkylimino-
triphenylphosphorane) Boronium Iodides.



Mp, Co of
Compounds Yield of Mp,C of Recrystallized
Cation % Crude Product Product


Alkyl


Methyl 93 164-168 215-217

Ethyl 73 186-190 197-199

n-Propyl 91 190-194 200-202


Table 5. Analyses of Bis(N-Alkyliminotriphenylphos-
phorane) Boronium Iodides.



Compounds %C %H %N


[(CH PNCH ]2BH I Calcd. 63.18 5.30 3.88
Found 62.82 5.22 3.73

[(C6H5)3PN(C2H5 2BH I- Calcd. 64.02 5.64 3.73
Found 63.34 5.61 3.56

[(C6H5 )PN(n-C3H7 BH +I Calcd. 64.80 5.96 3.60
SFound 64.51 6.01 3.41









spectrum of the water insoluble material in deuterated

methylene chloride was recorded. The spectrum showed

two sets of peaks. One set of peaks corresponded to

bis(N-n-propyliminotriphenylphosphorane) boronium iodide,

and the other set corresponded to N-n-propylaminotri-

phenylphosphonium ion formed by the decomposition of the

boron cation in water.

To the aqueous filtrate was added 30 ml of a saturated

solution of ammonium hexafluorophosphate in deionized water.

A white solid precipitated from the mixture. The precipi-

tate was filtered and dried in vacuo. A H nmr spectrum of

the solid in methylene chloride was recorded. The spectrum

showed only one peak, a singlet at 6 = 2.50 ppm. The peak

corresponded to bis(trimethylamine) boronium hexafluoro-

phosphate (29). The recovered weight, 0.370 g, corresponded

to a 95% yield.
















CHAPTER IV

PHYSICAL, CHEMICAL AND SPECTRAL PROPERTIES OF BORANE
ADDUCTS AND BORON CATIONS



Physical and Chemical Properties



Borane Adducts

General properties. The borane adducts of various

N-substituted-iminotriphenylphosphoranes are white crystal-

line solids. They all have some solubility in methylene

chloride, benzene, tetrahydrofuran and chloroform. Their

solubility in various aliphatic hydrocarbons, namely

heptane, is very poor. Therefore, heptane could be used as

a precipitating agent. These compounds are also quite

insoluble in water.

Thermal stability. In general, thermal stabilities of

borane adducts vary according to which ligand group is

attached to BH3. It has been reported (53) that tri-

methylamine borane can be heated for several hours at 1250

without a detectable change in its physical properties. In

contrast to trimethylamine borane, the pyridine boranes

readily evolve hydrogen at temperatures below 1000 to form

red resins. Dimethylamine borane also evolves hydrogen at

2000 to form dimethylamino borane (54,55). A few of the









borane adducts which have been made, namely carbonyl borane

(2), dimethylether borane (3) and phosphine borane (5) are

only stable at low temperatures and dissociate into the free

bases and diborane below -200.

The borane adducts prepared in this study are stable at

room temperature. Samples stored for one year in closed

containers gave no noticeable change in appearance or in

their H1 nmr spectra. The adducts are unstable at elevated

temperatures, and all of the boranes decompose at their

melting points evolving hydrogen. The mode of decomposition

is represented by the pyrolysis of N-n-propyliminotriphenyl-

phosphorane borane.

A sample of N-n-propyliminotriphenylphosphorane borane

was heated to 1900 for 20 minutes under an atmosphere of dry

argon. Hydrogen evolution was observed at the melting

point. A H1 nmr spectrum of the recovered material in

deuterated benzene gave a complex spectrum with several new

overlapping peaks in the 0-3 ppm region. A P3 nmr spectrum

of the same material showed only two resonances: a major

peak corresponding to triphenylphosphine and a very minor

peak corresponding to triphenylphosphine borane. A B11 nmr

spectrum, proton decoupled, gave a peak corresponding to

triphenylphosphine borane and two broad humps in the region

0 to -30 ppm indicating sp2 bonded borons (56).

Hydrolytic stability. The stabilities of borane

adducts toward hydrolysis also depend upon which group is

coordinated to BH3. Phosphine borane (5) and borane









tetrahydrofuran complex react rapidly with water to form

hydrogen and boric acid. Reports indicate that pyridine

borane (57) and substituted pyridine boranes (58) react only

slowly with water. The kinetics of hydrolysis of trimethyl-

amine borane have been studied in detail by Ryschkewitsch

(59) and demonstrate that the reaction with water is quite

slow. Heal (60) reports that triphenylphosphine borane is

unaffected by moist air, water, 2N sodium hydroxide and 6N

hydrochloric acid solutions.

The borane adducts prepared in the current investiga-

tion are not stable towards hydrolysis, but react slowly

with water. Samples could be handled in a humid atmosphere

for short periods of time without evidence of decomposition.

A crystalline sample of N-methyliminotriphenylphosphorane

borane was allowed to sit out in a moist atmosphere for

two days. Examination of the crystals under a microscope

showed pitting of the surface indicating that some

decomposition had occurred.



Boron Cations

General properties. The boron cations of the type

bis(N-alkyliminotriphenylphosphorane) boronium iodide are

white solids. The iodide salts are very soluble in

methylene chloride and chloroform but are insoluble in

benzene, water, diethyl ether, heptane and tetrahydrofuran.

Their insolubility in benzene and diethyl ether made these

solvents ideal precipitating agents.









Thermal stability. The boronium iodides prepared in

this study are stable indefinitely at room temperature when

stored under a dry nitrogen atmosphere. The P3 nmr spectra

of these compounds, taken after 1 year, did not show any

change. On heating in sealed capillary tubes, the salts

changed color at their melting points. The change in the

color of the molten salt was irreversible on cooling,

probably due to decomposition.

Hydrolytic stability. Boron cations exhibit varying

stabilities toward hydrolysis. For example, the stability

increases with the base strength of the donor attached to

boron. Salts of the bisamine cations show remarkable

stability and have been recovered without change from

concentrated acids and from 10% sodium hydroxide, even when

heated to 1000 for prolonged periods (32). On the other

hand, cations containing tertiary phosphorus as a donor are

stable toward acid and neutral solutions but are decomposed

by hot aqueous base. Boron cations containing substituted

pyridines as donor groups have been reported to be slowly

attacked by boiling neutral and basic solutions (37).

Cations containing dialkyl sulfides are decomposed rapidly

in cold water. These observations show that generally, acid

in low concentrations retards decomposition while base

accelerates the reaction.

The boron cations prepared in this study are not stable

toward acid and neutral solutions but appear to be stable in

cold aqueous base for short periods of time.









In order to obtain detailed information regarding the

hydrolytic stability of the boron cations, the following

experiment was performed employing bis(N-n-propylimino-

triphenylphosphorane) boronium iodide as representative of

the group.

Three flasks were numbered and charged with the follow-

ing materials:


Flask 1.







Flask 2.







Flask 3.


0.6270 g (0.8056 mmoles) of

[(C6H5) PN(n-CH) ] BH2I + 50 ml

of 1 M HC1.



0.4761 g (0.6117 mmoles) of

[(C6H5)3PN(n-C3H7) BH I + 50 ml

of H20.



0.4531 g (0.5822 mmoles) of

[(C6H5)3PN(n-C3H7) ]BH2I- + 50 ml

of 1 M NaOH.


The mixtures were vigorously stirred for 15 minutes and

then rapidly filtered. The solids were dried in vacuo over

P205. Proton and P nmr spectra of the recovered materials

were recorded in deuterated methylene chloride, and the

following results were obtained:

(1) The H nmr spectrum showed only peaks in the

phenyl region. The P nmr spectrum showed only









one peak corresponding to triphenylphosphine oxide

in the same solvent.



(2) The H1 nmr spectrum showed two sets of peaks

corresponding to unreacted boron cation and to

N-n-propylaminotriphenylphosphonium ion. The P31

nmr spectrum showed two peaks corresponding to the

same materials identified in the H spectrum. The

integrated areas of the peaks in the P31 spectrum

showed that the ratio of boron cation to

phosphonium ion was 3:1.



(3) The HI nmr spectrum showed one set of peaks

corresponding to unreacted boron cation. The P31

nmr spectrum showed only one peak also correspond-

ing to unreacted boron cation.



In conclusion, the boron cation was completely decom-

posed by cold 1 M HC1, partially decomposed by neutral water

and was recovered unreacted from 1 M NaOH. The triphenyl-

phosphine oxide recovered from reaction 1 weighed 0.369 g

(82% yield). This product is not an unexpected one, since

some iminotriphenylphosphoranes are known to be decomposed

by water to the corresponding amines and triphenylphosphine

oxide (19,20,22,23,41). The above observations are surpris-

ing in that they contrast boron cation stability data

reported in the literature. The observations indicate that









the mode of decomposition of the cations must be different

than in bis(amine) boronium ions. The observation that hot

aqueous acid does not attack bis-amine boron cations indi-

cates that either the hydrogens on the boron are shielded by

the bulky amine groups or that the hydridic character is

reduced by the positive charge on the molecule (61).

Separate experiments show the N-alkylaminotriphenylphos-

phonium ions to be stable in cold aqueous neutral and acidic

solutions for short periods of time. Therefore, the differ-

ent reaction products from the acidic and neutral solutions

described before indicate that two different mechanisms must

occur both following initial attack of the hydridic

hydrogens by acidic protons.

Attack of a hydridic hydrogen by a hydronium ion would

produce hydrogen gas and a dication having water bound to

the boron. The oxygen bound protons would be expected to be

quite acidic because of the positive formal charge on the

oxygen.

In the neutral solution, the hydronium ions would come

from the autoionization of water. Thus, for every hydronium

ion that reacted, a hydroxide ion must be produced. The

hydroxide ion would be expected to abstract an acidic proton

from the dication to produce a mono cation containing a

B-O-H group. A lone pair on the oxygen could then donate

electrons to the boron and cause the coordinated phosphorane

to leave. The resulting boron fragment would most likely be

coordinated by water and contain a single positive charge.









The free base would react with the water to form the

corresponding phosphonium ion and hydroxide ion. The

hydroxide ion would be expected to attack the boron cation,

removing the acidic proton. Thus, hydroxide ion would not

be expected to attack the phosphonium ion in neutral

solution to produce triphenylphosphine oxide. The net

equation for decomposition in neutral solution is as

follows:



[(CH5) 3PNR]2BH2 + 4H20 --> 2(C6H5) 3PNHR + H2 + B(OH)4

(4.1)



In the acidic solution, the hydroxide ion concentration

would be neglible. Therefore, the coordinated phosphorane

would not be expected to free itself from the dication. The

high positive charge on the ion would be expected to

activate the phosphorus toward attack by water through

delocalization of charge by resonance. Thus, attack of

phosphorus by water would produce the observed product,

triphenylphosphine oxide.

Stability towards oxidizing agents. To a solution of

bis(N-ethyliminotriphenylphosphorane) boronium iodide in dry

methylene chloride, silver hexafluorophosphate was added.

Rapid hydrogen evolution was observed immediately. A black

solid remained which was filtered and then dissolved in 15 M

nitric acid with evolution of NO2. The resulting solution

was mixed with a solution of HC1 to precipitate white silver









chloride. This result contrasts reports (37,61) on the

properties of bis(amine) boronium ions which are unaffected

by Ag(I) ion. Therefore, our boron cations possess

substantial hydridic character.

Stability towards borohydride ion. In general, solu-

tions of the three bis(N-alkyliminotriphenylphosphorane)

boronium iodides were treated with stoichiometric amounts of

tetra-n-butyl-ammonium borohydride. The following experi-

ment is representative of the group.

To N-methyliminotriphenylphosphorane borane, 0.4560 g

(1.494 mmoles), in 25 ml of dry methylene chloride, iodine,

0.1884 g (0.7423 mmoles), was added. The solution was

stirred with a magnetic stirrer. Rapid hydrogen evolution

was observed, and the iodine color disappeared after 10 min-

utes indicating that all of the iodine had reacted. To the

solution, N-methyliminotriphenylphosphorane, 0.4298 g

(1.475 mmoles), was added. The solution was stirred for

1 hour under an inert atmosphere of dry nitrogen.

Approximately one half of a milliliter of the solution

was transferred to a nmr tube. Phosphorus-31 and B nmr

spectra were recorded proton decoupled, and both showed only

one peak corresponding to bis(N-methyliminotriphenylphos-

phorane) boronium iodide.

To the solution, tetra-n-butyl-ammonium borohydride,

0.3750 g (1.457 mmoles), was added. The solution was

stirred for seven days under an inert atmosphere of dry

nitrogen. After three hours of stirring, approximately









one half of a milliliter of the solution was transferred to

a nmr tube. A B nmr spectrum was recorded proton

decoupled and showed only two peaks corresponding to the

boron cation and to borohydride ion. A P nmr spectrum was

recorded and showed only one peak corresponding to the boron

cation.

The reaction was monitored periodically over the 7 day
11 31
reaction time via B and P nmr. The spectra showed that

the boron cation and borohydride ion reacted slowly to form

the corresponding borane adduct exclusively. The final

spectra obtained after 7 days showed only one peak each

corresponding to the borane adduct.

In conclusion, all the boron cations reacted slowly

with borohydride ion to form the corresponding borane

adducts. The results show that the borane adducts are more

stable thermodynamically than mixtures of the boron cations

and borohydride ion. Although no specific kinetic studies

were done, the sluggishness of the reactions between the

boron cations and borohydride ion indicates that the

transition state must be a high energy situation. The

general equation for the transformation is as follows:



D2BH + BH --> 2DBH (4.2)
2 2 4 3









Spectral Properties



The Infrared Spectra of Phosphoranes, Borane Adducts
and Boron Cations

The infrared spectra were obtained in KBr pellets using

the Nicolet 5DXB FTIR spectrometer.

All of the phosphoranes, borane adducts and boron

cations exhibit complex infrared spectra. In each spectrum,

characteristic peaks corresponding to P-C, C-N and P=N

stretching frequencies were assigned.

In general, the vibrational frequencies of the P-C

groups are sharp and of moderate intensity. In all cases

the P-C stretching frequencies are between 1432 and
-1
1442 cm The observed peaks are in good agreement with

observations made by Daasch and Smith (62). They examined

the infrared spectra of a considerable series of aryl

phosphorus compounds containing the P-aryl group.

The vibrational frequencies of the C-N groups are not

as sharp as the P-C peaks and vary in intensity from very

intense to moderately intense. Two different sets of C-N

peaks were identified corresponding to aliphatic and

aromatic groups attached to nitrogen. In general, the

vibrational frequencies of the aliphatic C-N groups lie in

the region between 1105 and 1117 cm- The vibrational

frequencies of the aromatic C-N groups lie in the region
-1
between 1302 and 1312 cm The observed C-N stretching

frequencies are in good agreement with the correlations made

by Colthup (63) for aromatic and aliphatic amines.









It was observed in the current study that by progress-

ing through a series of free base to borane adduct to boron

cation that the P-C and C-N stretching frequencies do not

change to any significant extent.

In general, the vibrational frequencies of the P=N

groups are broad and vary in intensity from very intense to

weak. The stretching frequencies of the P=N group were

assigned by straightforward comparisons between the spectra

of the boronium cations, borane adducts and the uncoordi-

nated phosphoranes. The assignments were made by finding

peaks which changed to a significant extent along the series

of free base to borane adduct to boron cation. This corre-

sponds to the reasoning that by adding a BH3 unit, the

increase in mass and decrease in d -p bonding should cause

a shift to lower wavenumbers. The assigned frequencies for

P-N stretching are in the broad region between 879 and
-1
1335 cm1.

Several workers have attempted to identify a charac-

teristic P=N stretching frequency. Horner and Oediger (21)

made assignments in a series of N-(substituted phenyl)-

iminotriphenylphosphoranes for the P=N stretches between
-I
1160 and 1180 cm1. Allcock (64) presents an excellent

discussion of P=N vibrational assignments. The collective

data presented in his discussion show that, in cyclic

structures, the absorptions are found at higher frequencies

in the 1200 to 1400 cm- region. The data also show that









many mono-iminophosphoranes have a characteristic P=N

stretching vibration in the 1325 to 1375 cm-1 region.

By attaching BH3 units to the N-alkyliminotriphenyl-

phosphoranes, a shift toward lower wavenumbers of between 31
-1
to 105 cm in the P=N stretching frequency is seen. By

attaching BH3 units to the B-N-substituted-aminoimino-

triphenylphosphoranes, a smaller shift toward lower wave-
-1
numbers of between 0 to 27 cm- is seen. When comparing

borane adducts to the corresponding boron cations, a shift

on the order of 7 to 15 cm- in the P=N vibrational fre-

quencies is evident, and the direction is random.

Presumably, there is a rough correlation between

increasing coordinate i character and increasing vibrational

frequency for P=N vibrations. Any correlation for the P=N

link, however, must be expected to be mass sensitive and

therefore liable to considerable frequency shifts with minor

alterations in structure. This correlation is also only

valid if the P=N vibrations do not participate in combina-

tion vibrations with the groups attached to phosphorus or

nitrogen. The correlation is not, therefore, a particularly

useful one in interpreting small frequency differences.

Two B-H stretching vibrations, symmetrical and antisym-

metrical, are expected for a BH3 group. In addition to

these, two B-H deformation modes, bending and wagging, are

also expected. In general, the asymmetrical stretch will

occur at a higher frequency than the symmetric stretch, and

the bending mode will occur at a higher frequency than the









wagging mode. Also, the stretching vibrations will occur at

much higher frequencies than the deformations. In general,

the vibration frequencies of the BH3 groups of the borane

adducts in this study are similar to the infrared data

reported in the literature (65,66).

Symmetrical and antisymmetrical stretching vibrations

are also expected for a BH2 grouping as well as a symmet-

rical deformation vibration. The B-H stretching frequencies

appeared in the region between 2274 and 2329 cm- and the

deformation vibrations appeared in the region between 1185
-I
and 1210 cm1 (32,37). Compared to the borane adducts, the

B-H stretching and deformation frequencies of our boron

cations occur at higher wavenumbers, but at lower

wavenumbers than in bis-amine cations (29).

The B-N stretches in the borane adducts and boron

cations appeared in the region between 882 and 936 cm-.

The B-N stretching frequencies of the cations were not much

different from the corresponding borane adducts.

All of the assignments for the B-H and B-N modes were

made by straightforward comparisons between the spectra of

the borane and boronium complexes and the spectra of the

uncoordinated phosphoranes.

Various infrared assignments are given in Tables 6, 7

and 8. Spectra of N-ethyliminotriphenylphosphorane and

8-N-dimethylaminoiminotriphenylphosphorane are reproduced in

Figures 3 and 4 respectively as examples for infrared








Table 6. Infrared Data of N-Alkylimino-and -N-Substi-
tuted-Aminoimino-Triphenylphosphoranes.



P-C Stretch P-N Stretch C-N Stretch
Compounds cm-1 879-1335 cm 1105-1311 cm-
broad

(C6H5)3PN(CH3) 1435 1230 1108

(CH5) 3PN(C2H5) 1434 1228 1106

(C6H5)3PN(n-C3H7) 1432 1204 1106

(C6H5) 3PN(i-C3H7) 1434 1335 1105

(C6H5) 3PN(i-C4H9) 1434 1224 1107

(C6H5)3PN(t-C4H9) 1440 1281 1106

(C6H5)3PNN(CH3)2 1434 941 1114
1440 1107

(C6H5)3PNNH(C6H5)b 1437 908 1305

1311c
(C6H5)3PNN(CH3) (C6H5) 1436 879 1117d


adoublet; b he NH stretching
aromatic; aliphatic.


frequency is 3186 cm-1
frequency is 3186 cm ;




















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spectra of phosphoranes. Spectra of N-tert-butylimino-

triphenylphosphorane borane and P-N-phenylaminoimino-

triphenylphosphorane borane are reproduced in Figures 5 and

6 respectively as examples for infrared spectra of borane

adducts. The spectrum of bis(N-methyliminotriphenylphos-

phorane) boronium iodide is reproduced in Figure 7 as an

example for infrared spectra of boronium iodides.



The Mass Spectrum of N-Ethyliminotriphenylphosphorane
Borane

The mass spectrum was obtained on an AEI-MS30 instru-

ment employing an ionizing energy of 70 e.v. The spectrum

was recorded using a crystalline sample. The mass spectrum

is quite complex, and more than one fragmentation pattern

appears. The parent ion peak is found at 319. Two differ-

ent fragmentation patterns can be postulated which are

consistent with the mass spectral data. In the first, the

molecular ion loses hydrogen stepwise to form the fragment

located at 316 corresponding to (C6H5)3PN(C2H5)B This

fragment then loses boron to form the fragment

(C6H5)3PN(C2H5) located at 305. Loss of a methyl group

from this fragment forms the fragment (C6H5)3PNCH2 found at

290. The fragment at 290 then loses NCH2 to form (C6H5)3P+

located at 262. The second fragmentation pattern is much

simpler than the first. The molecular ion loses an ethyl

group to form (C6H5)3PNBH3 found at 290. This fragment then

loses NBH3 to form (C6H5)3P+. The rest of the fragmentation




















C


I i.I

























o
0


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o ~e


-o r-0
>1


0

o
0









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o
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aa
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pattern is almost identical to the mass spectrum of tri-

phenylphosphine (67). The peaks at 28 and 18 correspond to

nitrogen and water respectively from the atmosphere. The

two fragmentation patterns are represented by the following

equations:



(C6H5)3PN(C2H5)BH3 --> (CH5) 3PN(C2H5)BH2

319 -H 318


--> (C6H5)3PN(C2H5)BH --> (C6H5)3PN(C2H5)B+

-H 317 -H 316



--> (C6H5)3PN(C2H5)+ --> (CgH5)3PNCH

-B 305 -CH3 290



--> (C6H5)3P (4.3)

-NCH2 262




+ +
(CH5) 3PN(C2H)BH --> (C6H5 3PNBH

319 -C2H5 290



--> (C6H5) 3P+ (4.4)

-NBH3 262



The second fragmentation pattern is similar to the

fragmentation pattern of trimethylamine borane (68).









Trimethylamine borane loses a methyl radical to form a very

stable fragment corresponding to (CH )2NBH3 at 58. The mass

spectrum of N-ethyliminotriphenylphosphorane borane is

reproduced in Figure 8 and the intensity results are pre-

sented in Table 9.



Nuclear Magnetic Resonance Spectra

Proton nmr spectra of the phosphoranes, borane adducts

and boron cations were taken on the JEOL FX-100 instrument

with tetramethylsilane as an internal reference. The

compounds N-n-propyliminotriphenylphosphorane borane and

N-isobutyliminotriphenylphosphorane borane required higher

resolution to determine their coupling patterns. Conse-

quently, the HI nmr spectra of these two materials were

taken on the Nicolet NT-300 instrument. Phosphorus-31

spectra were obtained proton decoupled at 80.984 MHz or

121.477 MHz with 85% phosphoric acid as the external refer-

ence. Boron-11 spectra were taken at 64.184 MHz or

96.270 MHz with trimethylborate as the external reference.

Shifts for the P31 and B spectra are reported with nega-

tive ppm downfield from the corresponding references.

Deuterated methylene chloride was used as the solvent for

the H1 and B11 spectra. Benzene was used as the solvent for

the P31 spectra except in the case of the boron cations in

which methylene chloride was used. The chemical shifts, 6,

in parts per million and coupling constants, J, in hertz, of

H resonances plus the chemical shifts, 6, in parts per











290


183


152


316


50 100 150 200 250 300


Figure 8. Mass spectrum of N-ethyliminotriphenylphos-
phorane borane.










Table 9. Mass Intensity Data for N-Ethyliminotriphenyl-
phosphorane Borane.



Absolute % Intensity of
Mass Intensity 290


320 231 0.53
319 2403 5.54
318 10230 23.60
317 6792 15.67
316 20889 48.20
315 145 0.33
315 5387 12.43
314 447 1.03
306 817 1.89
305 3928 9.06
304 5778 13.33
294 229 0.53
293 184 0.42
292 918 2.12
291 9265 21.38
290 43341 100.00
289 664 1.53
288 2213 5.11
287 546 1.26
286 505 1.17
278 401 0.93
277 804 1.86
276 712 1.64
264 379 0.87
263 4396 10.14
262 22343 51.55
261 4812 11.10
260 442 1.02
259 314 0.72
Continued









Table 9. Continued.


Absolute % Intensity of
Mass Intensity 290


229 198 0.46
212 418 0.96
211 266 0.61
210 200 0.46
200 178 0.41
198 256 0.59
186 1434 3.31
185 3989 9.20
184 5286 12.20
183 24079 55.56
182 314 0.72
181 490 1.13
170 788 1.82
165 634 1.46
164 160 0.37
163 372 0.86
159 251 0.58
157 1245 2.87
154 698 1.61
153 863 1.99
152.5 397 0.92
152 2954 6.82
151 501 1.16
141 407 0.94
139 493 1.14
134 420 0.97
133 1074 2.48
131 895 2.07
128 241 0.56
122 269 0.62
Continued


--









Table 9. Continued.


Absolute % Intensity of
Mass Intensity 290


115 1005 2.32
110 236 0.54
109 1530 3.53
108 9703 22.39
107 3894 8.98
104 130 0.30
91 515 1.19
89 906 2.09
88 170 0.39
83 420 0.97
81 380 0.88
78 1761 4.06
77 1510 3.48
74 200 0.46
65 508 1.17
63 496 1.14
57 293 0.68
57 755 1.74
56 174 0.40
55 394 0.91
54 234 0.54
52 515 1.19
51 2214 5.11
50 745 1.72
46 162 0.37
44 474 1.09
43 227 0.52
42 908 2.10
41 670 1.55
40 712 1.64
Continued









Table 9. Continued.


Absolute % Intensity of
Mass Intensity 290


39 1222 2.82
32 1912 4.41
30 427 0.99
29 644 1.49
28 10261 23.68
27 1459 3.37
26 513 1.18
19 464 1.07
18 86396 199.34
17 18562 42.83
16 1110 2.56
15 383 0.88
13 580 1.34









million of the P31 resonances are reported in Tables 10 to

12. The chemical shifts, 6, in parts per million and

coupling constants, J, in hertz of the B resonances are

reported in Table 13. The integrated intensities of the H1

spectra correspond well with the expected values. The

borane hydrogens were not resolved in the H spectra due to

broadening by the boron quadrupole moment. The integration

in the region 0-5 ppm did reflect their presence in the

baselines. Proton, P31 and B11 nmr spectra were extremely

useful in characterizing the compounds and in studying

various reactions.

The coupling patterns in the H1 spectra of the various

alkyl groups of the phosphoranes are what is expected for

their corresponding structures. One special addition to

these patterns, however, is long range coupling from the

phosphorus atom of spin one half (27). This coupling is

seen to the a and 6 protons through three and four bonds

respectively. The phosphorus coupling constant to the a

protons is on the order of between 15.39 and 24.54 Hz and to

the 8 protons is on the order of between 1.04 and 1.54 Hz.

The H1 nmr spectra of N-methylimino, N-tert-butylimino and

B-N-dimethylaminoiminotriphenylphosphoranes have been

reported by Kaplan et al. (27), and their results agree well

with the data presented in this study.

In general, there is a definite upfield chemical shift

in the resonances of the protons attached to the a and y

carbon atoms of the ligand on coordination to BH3. The

















































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11
Table 13. B NMR Data of Borane Adducts and Boron Cations.



Chemical
Shift J
Compounds 6, ppm Multiplicity Hz


(CH5) 3PN(CH3BH3 33.981 4 88.53

(C6H5)3PN(C2H5)BH3 35.520 4 84.59

(C6H5)3PN(n-C3H7)BH3 35.104 4 84.74

(C6H5) 3PN(i-C3H7BH3 39.498 4 82.76

(CH5) 3PN(i-C4H9)BH3 35.792 4 86.49

(C6H5) 3PN(t-C4H9)BH3 35.142 4 88.54

(C6H5)3PNN(CH3) 2BH3 44.173 4 91.74

(CH5) 3PNNH(C H )BH3 35.472* 4 66.24

(CH5) 3PNN(CH3) (C6H5)BH3 40.299 1 **

[(C6H5) 3PN(CH3) ] BH2I 25.842 1 **

(C6H5)3PN(C2H5) 2BH I 29.715 1 **

[(C6H5) PN(n-C3H7 2BH2 27.513* 1 **



Note. All the 6 values represent the proton decoupled
peaks; B spectra were run in methylene chloride;
11
B chemical shifts are measured relative to
trimethylborate, external; B shifts are reported
with negative shifts downfield from trimethylborate;
11 **
B nmr obtained at 64.184 MHz; coupling in these
peaks was complete collapsed by quadrupole relaxa-
tion.









resonances of the protons attached to the @ carbon atom of

the ligand show a shift downfield on coordination to BH3.

The upfield chemical shift of the a proton resonances on

coordination to BH3 is just the opposite of what is seen

with amine boranes (15). When amines are coordinated to

BH3, a positive formal charge is assigned to the nitrogen

atom, and thus a downfield shift for the protons closest to

the nitrogen is expected.



+ -
R3N: + BH3 --> R3N:BH3 (4.5)



When N-alkyliminotriphenylphosphoranes are coordinated to

BH3, a positive charge is also assigned to the nitrogen

atom. In this case, however, a resonance structure can be

drawn placing the positive charge on the less electronega-

tive phosphorus atom. This would cause a shift upfield for

the proton resonances due to the buildup of electrons on the

nitrogen atom.



+ -
(C6H5)3P=N-R + BH3 --> (CH)3 P=N:BH3
R

+
--> (C6H5)3P--:BH 3 (4.6)
R



A general decrease of the long range phosphorus

coupling constant is observed in the proton resonances of

the ligand on coordination to BH3. A decrease in the









phosphorus coupling constant is also seen upon protonation

and methylation of the nitrogen atom (27), and in these

respects the behavior on BH3 coordination is analogous.

The H nmr spectrum of N-n-propyliminotriphenylphos-

phorane borane is noteworthy because the coupling pattern of

the n-propyl group is non-first order. The coupling pattern

falls into the special category of A2B2 (69). This type of

coupling pattern is sometimes seen with n-propyl groups.

The spin coupling of identical protons leads to the A2B2

case. The symmetry and coupling constants are represented

in Figure 9.


JAA'


A





JAB


BB'


Figure 9. Symmetry and coupling constants of the
A2B2 case.









There are four coupling constants, JAA' JAB' AB and
AA" AB' "ABD
JBB,. Because of symmetry, JA'B = JAB' and JA'B' = JAB. To

simplify solving the various coupling constants, four new

quantities are defined: K = JAA' + BB'; L = JAB -JAB

M = JAA BB'; and N = JA + J A much simpler subcase
AA' BB AB AB'
of A2 B2 is A2X2 in which the chemical shift between A and X

is large compared to the various coupling constants. This

is the case in the spectrum of N-n-propyliminotriphenyl-

phosphorane borane. The A and B parts will be identical

minus coupling from the phosphorus and from the methyl

protons. There should be ten lines in each of the

two parts, and each part will be symmetrical about its

center. The line positions and intensities are given in

Table 14 (70).

The A part of the pattern will be treated first. The

coupling pattern of the A protons, the protons attached to

the a carbon atom, is reproduced in Figure 10. In general,

the pattern consists of a quintet split into two by the

phosphorus coupling. The line positions in hertz and

intensities of the ten lines along with the line positions,

minus the phosphorus coupling constant, are given in

Table 15.

From the spectrum, only five peaks besides the phos-

phorus coupling, and not the expected ten, are observed for

the A part. In order to collapse ten peaks into five, some

assumptions can be made. Assuming that JAA' = JBB and that
AA' iix









Table 14. Line Positions and Intensities for the A2X2Case.



Position Relative Relative Intensity
Transition to V or V
A X

1 1/2 N 1

2 1/2 N 1

3 -1/2 N 1

4 -1/2N 1

5 1/2K + 1/2(K+L2)1/2 sin2
S
6 -1/2K + 1/2(K+L2)1/2 cos2
s
7 1/2K 1/2(K2+L2)1/2 cos2
2 2 1/2 2
8 -1/2K 1/2(K +L2) 2 sin2
s
2 2 1/2 .2
9 1/2M + 1/2(M +L)12 sin
a
10 -1/2M + 1/2(M+L2)1/2 cos2

11 1/2M 1/2(M+L2)1/2 cos2
a
12 -1/2M 1/2(M2+L2) 1/2 sin28



6 = 1/2 cos- [K/(K2+L2)1/2]



ea = 1/2 cos-1 M/(M2+L2)1/2





78












5


1 36 8 10
1 \






2 4 7
9





















Figure 10. Expansion of a protons in H1 nmr spectrum of
N-n-propyliminotriphenylphosphorane borane.












Table 15. Line Positions of the a Protons.


Position of Lines Intensity Position of Lines in
in Part A Hz Part A Minus Phosphorus
Coupling Hz


1) 849.27 462.87

2) 843.47 325.78

3) 841.84 474.89 1) 840.93

4) 839.91 322.21 5) 835.09

5) 834.20 535.11 833.48

6) 832.59 492.01 8) 831.53

7) 826.70 320.87 3) 825.86

8) 825.11 478.98

9) 823.15 310.49

10) 817.51 490.21










JAB AB'' then both M and L are equal to zero, and five

peaks result. The rest of the calculation is as follows:



1) 3) = 1/2 N (-1/2 N) = N

1) 3) = 15.07 Hz = N = JAB + JAB'

AB = AB' = 7.535 Hz

5) 8) = K (-K) = 2K

5) 8) = 3.55 Hz = 2K

K = JAA + BB = 1.78 Hz

JAA = BB' = 0.888 Hz



The B part of the pattern will be treated next. The

coupling pattern of the B protons, the protons attached to

the 8 carbon atom, is reproduced in Figure 11. A selective

decoupling experiment was performed by irradiating the

methyl protons to collapse their coupling in the B part.

The resulting coupling pattern is reproduced in Figure 12.

In general, the pattern consists of the expected quintet.

The peak positions in hertz and intensities of the five

lines are given in Table 16.

The calculation for the B part is as follows:



1) 3) = 15.21 Hz = N = JAB + JAB'

JAB = AB' = 7.605 Hz

5) 8) = 3.59 Hz = 2K

K = JAA + BB = 1.80 Hz

JAA' = JBB = 0.900 Hz




















































Figure 11. Expansion of B protons in H1 nmr spectrum of
N-n-propyliminotriphenylphosphorane borane.





82











1


3
8


5



























Figure 12. Expansion of q protons, decoupled from methyl
protons, in H spectrum of N-n-propylimino-
triphenylphosphorane borane.









Table 16. Line Positions of the B Part.


Position of Lines Hz Intensity


1) -761.18 257.07

5) -766.70 191.87

-769.08 292.89

8) -770.29 216.96

3) -776.39 229.57


*
The values are relative to an unknown reference.







The values for the coupling constants calculated for

parts A and B agree well with each other, as expected.

Average values for JAB' JAB AA' and JBB' are reported in

Table 11. The spectrum of N-n-propyliminotriphenylphos-

phorane is reproduced in Figure 13 as an example for proton

spectra of the phosphoranes. The spectrum of N-n-propyl-

iminotriphenylphosphorane borane is reproduced in Figure 14

as an example for proton spectra of the borane adducts.

In general, there is a definite upfield chemical shift

in the resonances of the alkyl protons of the ligand on

going from borane adduct to boron cation. Since a positive

charge is assigned to the boron containing unit, an

enhancement of the delocalization of positive charge to the

phosphorus atoms could explain the observed phenomenon. A






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change in the spatial positions of the alkyl groups cannot

be overlooked, however, due to the various ring currents

from the phenyl groups.

The H1 nmr spectrum of bis(N-n-propyliminotriphenyl-

phosphorane) boronium iodide also exhibits an A2B2 coupling

pattern. The same treatment described for the corresponding

borane adduct was used to solve for the various coupling

constants. The spectrum of bis(N-ethyliminotriphenylphos-

phorane) boronium iodide is reproduced in Figure 15 as an

example for proton spectra of the boron cations.

In general, the B resonances are quartets, with

varying degrees of collapse, for all the borane adducts, as

expected. Boron-11 nuclei, with a spin of 3/2, possess an

electric quadrupole moment due to nonsphericity of the

electric charge distribution within the nucleus. These

nuclei interact with the fluctuating electric field

gradients produced at the nucleus by other molecular degrees

of freedom. These interactions lead to smaller values of

Tl, the spin-lattice relaxation time (70). Since the line

width measured on a frequency scale is proportional to 1/T1,

then smaller values of T1 lead to broadening of the line.

If a boron nucleus is coupled to another spin nucleus,

simple multiplets will occur in the absence of quadrupolar

relaxation. If the rate of relaxation of the boron nucleus

becomes rapid enough, the multiple will coalesce into a

broad signal.




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