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REMMEL, Randall James, 1949- PREPARATION AND NUCLEAR MAGNETIC RESONANCE STUDIES OF THE ANIONS DERIVED FROM THE DEPROTONATION OF HEXABORANE(IO) DERIVATIVES; NMR STUDIES OF THE ANIONS DERIVED FROM THE POLYHEDRAL EXPANSION OF BORON HYDRIDE ANIONS BY DIB0RANE(6).

The Ohio State University, Ph.D., 1975 Chemistry, inorganic

X©rOX UniVOrSlty Microfilms, Ann Arbor, Michigan 48106

0 1975

RANDALL JAMES REMMEL

THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED PREPARATION AND NUCLEAR MAGNETIC RESONANCE STUDIES OF THE

ANIONS DERIVED FROM THE DE PROTONATION OF HEXABORANE(IO)

DERIVATIVES; NMR STUDIES OF THE ANIONS DERIVED FROM THE

POLYHEDRAL EXPANSION OF BORON HYDRIDE ANIONS BY

DIBORANE(G)

DISSERTATION

Presented in Partial Fulfillment of the Requirements for

the Degree Doctor of Philosophy in the Graduate

School of The Ohio State University

Randall J. Remmel, B.S.

*****

Tne Ohio State University

1975

Reading Committee; Approved By

Dr. Daniel L. Leussing

Dr. Gary G. Christoph

Dr. Sheldon G. Shore A (Aviser Department of Chemistry DEDICATION

To Staci

ii ACKNOWLEDGMENTS

I sincerely thank Professor Sheldon Shore for his suggestions, support and encouragement during my tenure as a graduate student. I also thank my colleagues for their suggestions and discussions during the investigation. I also acknowledge financial support of this work by the National Science Foundation.

ill VITA

August 23, 1949 ...... Born - Peoria, Illinois

1 9 7 1 ...... B.S., Illinois State University

1971-1973 ...... Teaching Associate, Department of Chemistry, The Ohio State University, Columbus, Ohio

1973-1975 ...... Research Associate, Department of Chemistry, The Ohio State University, Columbus, Ohio

PUBLICATIONS

W.R. Clayton, A.V. Fratini, R.J. Remmel, and S.G. Shore, "2,6- Lutidine-Chloroborane, CyHgN- BH 2 CI, " Crystal Structure Communica tions , 3, 151 (1974).

R.J. Remmel and S.G. Shore, "Nuclear Magnetic Resonance Studies of 2 -CH 3 B5 H0 " and 2 -BrBgH0 ~, " Abstracts of Papers, 168th Meeting, American Chemical Society, Atlantic City, 1974, p. INOR 059.

R.J. Remmel, H.D. Johnson, II, l.S. Jaworiwsky, and S.G. Shore, "Pre paration and NMR Studies of the Stereochemically Nonrigid Anions: ^4^9~' ®5^12~' ®6^11~ ^ 7 ^ 1 2 ”' Syntheses of BgHii and BgHi2 ." J. Amer. Chem. Soc., in press (1975).

FIELDS OF STUDY

Major Field: Inorganic Chemistry

Studies in Nonmetal Chemistry. Professors Sheldon G. Shore and Eugene P. Schram

Studies in Transition Metal Chemistry. Professors Daryle H. Busch, Andrew A. Wojcicki, and Devon W. Meek iv TABLE OF CONTENTS

Page

DEDICATION...... 11

ACKNOWLEDGMENTS...... Ill

VITA ...... Iv

LIST OF TA BLES...... vll

LIST OF FIGURES ...... vill

INTRODUCTION...... I

I Background of Hexaborane(lO) C h e m is tr y ...... 1

II Brjz^nsted Acidity of the Boron H ydrides ...... 27

III Polyhedral Expansion of Boron Hydride A n io n s...... 33

IV The Existence of a Heptaborane Species ...... 39

V Background of Hexaborane(12) Chem istry ...... 41

VI Statement of the Problem ...... 46

EXPERIMENTAL...... 48

I Apparatus...... 48

II Reagents ...... 52

III Solvents 55 .

IV Preparation of Starting Materials ...... 58 TABLE OF CONTENTS (continued)

Page

V Reactions . 67

A. Deprotonation of Hexaborane(lO) Derivatives .... 67

B. Relative Acidities of the Bora ne s ...... 68

C. Preparation of KBgH^^...... 68

D. Preparation of KBgHj^j^ from B g H ^ g...... 69

E. Preparation of ByH 22 and CHgByH^^ Salts ...... 70

F. Tensimetric Titration of [(n"C: 4 Hg)^N^]

[a-CHgBgHg"] with BgHg...... 71

G. Protonation of CHgByH^^" ...... 71

RESULTS AND DISCUSSION...... 72

I NMR Spectra of K'^[2-BrBgHgl...... 72

II NMR Spectra of K+[2-CHgBgHgl...... 77

III NMR Spectra of K'*‘[2 , 3 -(CH 3 )2 B6 H7 ] ...... • 85

IV Relative Acidities of 2-BrBgHg and 2-CHgBgHg

with Respect to B gH ig...... 90

V NMR Spectra of KBgH^...... 93

VI Deprotonation of BgH]^2 ...... 101

VII NMR Spectra of B7 H1 2 ...... 103

VIII NMR Spectra of CH3 B7 H1 1 ...... I l l

REFERENCES...... 119

Vi LIST OF TABLES

Table Page

1 NMR Data for Hexaborane(lO)...... 6

2 NMR Data for KBgHg...... 10

3 NMR Data for BsHn'^Br" ...... II

4 NMR Data for 2-Bromohexaborane(10)...... 15

5 NMR Data for 2-Methylhexaborane(10) ...... 20

6 NMR Data for 2 -CH 2 BgHio"^Br"...... 23

7 NMR Data for 2 ,3-Dimethylhexaborane(10) ...... 26

8 NMR Data for KB^Hg...... 28

9 NMR Data for K+[2-CHgBgHyl...... 35

10 NMR Data for Hexaborane(12)...... 45

11 NMR Data for K'*'[2-BrBgHgl...... 74

12 NMR Data for K+[2 -CH 3 BgHg“] ...... 79

13 NMR Data for K+[2 , 3 -(CHg)2 BgHy-]...... ’ ...... 87

14 NMR Data for KBgH^i...... 95

vii LIST OF FIGURES

Figure Page

1 Molecular Structure of Hexaborane(lO) ...... 3

2 Valence Structure of Hexaborane(lO) ...... 3

3 Variable Temperature Boron-11 NMR Spectrum

o fB e H lO ...... 7

4 Variable Temperature Proton NMR Spectrum of « « « 8

5 Mechanism of the Bridging Hydrogen Tautomerism .... 9

6 Low Temperature Structures of 2-BrBgHg...... 14

7 Variable Temperature Boron-11 NMR Spectrum

of 2-BrBgHg...... 16

8 Variable Temperature Proton NMR Spectrum of

2-BrBgHg...... 17

9 Low Temperature Structures of 2-CHgBgHg...... 19

10 Variable Temperature Boron-11 NMR Spectrum of

2 -CH 3 B6 H g...... 21

11 Variable Temperature Proton NMR Spectrum of

2 -CH 3 B6 H g...... 22

12 Boron-11 and. Proton NMR Spectra of 2, 3-(CH3 )2 BgHQ. . . 25

13 Low Temperature Structures of l-CHgB^Hg"...... 29

viii LIST OF FIGURES (continued)

Figure Page

14 Variable Temperature Proton NMR Spectrum of

K+C2 -CH 3 B5 H7 "] ...... 31

15 Low Temperature Structure of K+EZ-CHgBgHy"]...... 32

16 Variable Temperature Boron-11 NMR Spectrum of

id-EZ-CHgBgHyl...... 34

17 Boron-11 NMR Spectrum of LiBgH^^ ...... 37

18 Valence Structure and Molecular Structure of BQH 22 .... 43

19 Boron-11 NMR Spectrum of BsH]^2 ...... 44

20 Boron-11 NMR Spectrum of K’^[2-BrBgHg~]...... 73

21 Proton NMR Spectrum of K^[2-BrBgHg“] ...... 76

22 Boron-11 NMR Spectrum of [2-CHgBgHg"]...... 78

23 Variable Temperature Proton NMR Spectrum of

K+CZ-CHgBgHgl...... 81

24 Low Temperature Structures of Z-CHgBgHg"...... 84

25 Structure of 2-CHgBgHg" Utilizing 3-Center Bonds .... 85

26 Boron-11 NMR Spectrum of K+[2,3 - (CH 3 )2 B5 H7 “] ...... 86

27 Proton NMR Spectrum of K‘‘'[ 2 , 3 -(CH 3 )2 B5 H7 "] ...... 89

28 Boron-11 NMR Spectrum of K‘*’[2-BrBgHg"] + BgH^g .... 91

29 Boron-11 NMR Spectrum of KBgHg + 2 -CH 3 B6 H9 ...... 92

30 Variable Temperature Boron-11 NMR Spectrum of KBsHjj . . 94

31 Topological Representations of BgHn“ ...... 96

Ix LIST OF FIGURES (continued)

Figures Page

32 Variable Temperature Proton NMR Spectrum of

K BsH ii...... 97

33 Low Temperature Structure of 100

34 Boron-11 NMR Spectrum of KBgHn + B^Hg . 102

35 Boron-11 NMR Spectrum of [(n-C^Hg)^N+][ByH 2 2 "] .... 104

36 Boron-11 NMR Spectrum of [(C 6 H5 )3 PCH3'^][B7 H i2 "J . . . 105

37 Proposed Structure of B 7 H1 2 " ...... 107

38 Proton NMR Spectrum of [(CgH5 )3 PCH3 '*'][B 7 H]L2 ''^...... 109

39 Topological Representation of B7 H2 2 ...... 110

40 Proton NMR Spectrum of Decomposing B7 H], 2 " ...... 112

41 Tensimetric Titration Curve for [(n-C^Hg)^N'^]

[2 -CH 3 BgHg"] plus B2 H g...... 114

42 Boron-11 NMR Spectrum of [(n-C^Hg)^N^][CH 3 B7 H11 ] . . 115

43 Proton NMR Spectrum of [(Cg 113)3 PCHg"^]%^7^11 ^ • H 6

44 Proton NMR Spectrum of Decomposing CH 3 B7 H22 .... 118

X INTRODUCTION

I. Background of Hexaborane(lO) Chemistry

A. Preparation of Hexaborane(lO)

Hexaborane(lO) was among the first boron hydrides isolated and

studied by Alfred Stock and his co-workers more than forty years ago.^

Until recently, however, BgHio remained unstudied due to the lack of ade quate preparative methods. Hexaborane(lO) chemistry has advanced ra pidly during the last decade as a result of improved synthetic procedures.

Stock's preparation of BgH^^g produced very low yields by the acid hydrolysis of magnesium boride. ^ This method was later improved to give a 5.5% yield .^ Very low yields of BgH^g have also been obtained from O the silent discharge of diborane( 6 ). The reaction of various Lewis bases with pentaborane(ll) has also been used as a synthetic route to but B5 H12 has itself been difficult to obtain until quite recently.^ Small quantities of BgH^g have also been isolated from the reaction of polyphos- phoric acid with (C2Hg)gNH^BgH2,2 Octaborane(12) may be hydrolyzed g almost quantitatively to BgH^g*

Hexaborane(lO) was made in quantities large enough for detailed in vestigation by Geanangel, Johnson, and Shore in 1971. They obtained a 25% yield from the reaction of LiBgHg, which is prepared from commer-

1 daily available pentaborane(9), with diborane( 6 ). Two years later a modi

fied preparation was reportedw hich gave a 75% yield of BgHig accord

ing to the following reaction:

K+tl-BrBjH;'] + 1/282% BgHio + KBr

This reaction represents a yield of at least 50% from B 5 H9 , the precursor of

K'^'[l-BrBgHy ], and the BgH^Q is easily purified.

B. Physical Properties of Hexaborane(lO)

Hexaborane(lO) is a colorless liquid which melts at -62.3°C^^ and has a vapor pressure of 7.5 torr at 0°C. ^ ^ In contrast to several other boron hydrides, hexaborane(lO) does not ignite or explode when exposed to air, although it decomposes with the evolution of hydrogen.

C. Structure of Hexaborane(lO)

The X-ray crystal structure of BgH^g was reported initially by 13 Lipscomb and co-workers in 1954. The boron atoms were found to be arranged in a pentagonal pyramid which was about 0.9^ deep. The refined structure was published in 1958.^^ Each boron atom was shown to have a single terminal hydrogen bonded to it. Four hydrogens occupy positions below the basal plane bridging adjacent basal boron atoms. A unique B-B bond thus remains in the base of the molecule. The length of this bond is only 1.60 % , making it the shortest B-B bond known in boron hydride chem istry. The molecular structure of BgHig is shown in Figure 1. The set of FIGURE 1. Molecular Structure of Hexaborane(lO) localized orbitals obtainedfor may be depicted as shown in

Figure 2.

H H

H"?

FIGURE 2. Valence Structure of Hexaborane(lO)

D. Nuclear Magnetic Resonance Spectra of Hexaborane(lO)

The boron-11 nmr spectrum of has been recorded at 12.8

32.1 and 70.6 MHz.^° In each case a low field doublet of relative area 5 and a high field doublet of relative area 1 are ob-

1 Q served with chemical shifts of -14.1 and +51.8 ppm , respectively> when

the spectrum is recorded at or near ambient temperature. Chemical shifts

are with respect to BF3 * 0 (0 2 1 1 5 )2 equals 0.0. It is important that these

results indicate that BgHiQ has symmetry while the crystal structure

has Cg symmetry.

The proton nmr spectrum has been recorded at 40 100

MHz 18,19 and 220 MHz.^^ These spectra also imply symmetry for

BgH^Q in solution at or near ambient temperature since they consist of only

terminal basal, terminal apical and bridging hydrogen resonances in the 19 expected ratios at 5.82 t , 11.22? and 11.10? , respectively.

The discrepancy between the solid-state and solution structures has

been rationalized in two ways. One rationale states that the three kinds

of basal boron atoms, and their terminal hydrogens, produce resonances in

their respective nmr spectra which coincidentally overlap exactly. 21 The

other is that the bridging hydrogen atoms exchange with,the basal B-B bond 22 23 at a rate which is rapid on the nmr time scale ' , thus time averaging

the chemical shifts of the resonances involved. Evidence that the latter rationale is correct was obtained in 1971.^^ At low temperatures the basal

boron resonance was observed to split into two peaks with relative areas

of about 4 to 1. This work was continued and appropriate proton nmr spec

tra recorded which definitely show that at very low temperatures the tautomerism of the bridging hydrogens is quenched. Table 1 presents

the boron-11 and proton nmr data for The variable temperature

boron-11 and proton nmr spectra are shown in Figures 3 and 4, respectively.

The assignments of these spectra will be discussed in a later section.

It has been proposed that this tautomerism proceeds through an inter-

o o p c p c mediate which contains a basal BH 2 group, as shown in Figure

It is clear from the drawing that the hydrogens of the BH 2 group would not

be equivalent. Isotope studies have shown that the interconversion of

basal terminal and bridging hydrogens in BgH^g is very slow even at ele- Ifl vated temperatures.

E. Reactions of Hexaborane(lO)

The Brjzfnsted acidity of BgHj^g was demonstrated in 1969.^7«28 The

deprotonation occurs according to the following reaction:

BjHio + MA an^ethe^^+BgH9~ + HA

MA = LiCHg, NaH, KH

Acidification of solutions containing the nonahydrohexaborate(l-) ion with

DCl yield hexaborane(lO) with deuterium in a bridging position, suggesting

that the proton which is removed from BgH^g is a bridging h y d r o g e n . ^7,28

This suggestion was confirmed when only CH 4 was evolved from the reac

tion of LiCHg with a hexaborane labeled with deuterium in the basal ter

minal p o sitio n s.M o re recently the bridging hydrogens of BgHig have TABLE 1

NMR Data for Hexaborane(10)'

100 MHz ^H^ Assignments 32.1 MHz

25°C -150°C 25°C -95°C

^^1 2.14 U3,4' ^S,6

11. 10-<'' (11. 00)® ail n

9.86 W2,3; H2 , 6 6.85 2 ^ 6.5

5.82-<'" (5.84) 2 ,3 ,4 ,5 ,6 -14.1-

\ 5.76 4.5 or 3,6 -18.6

5.42 3.6 or 4,5

11.22 11.27 1 51.8 51.8

^Reference 19

^Chemical shifts expressed in ppm relative to tetramethylsilane equals 10. 00. *"The number, n, denotes Bj^ or the terminal hydrogen attached to it.

The symbol y denotes a hydrogen bridging B^ and By.

‘^Chemical shifts expressed in ppm relative to BFg" 0 (C2 H5)2 equals 0.0.

®Values in parentheses are appropriately weighted averages. FIGURES. Boron-11 NMR Spectrum of B5 H1 Q (a )

(b )

FIGURE 4. Proton NMR Spectrum of

Basal ^^B atoms spin decoupled CO

b) All atoms spin decoupled FIGURE 5. Proposed Mechanism of the Tautomerism of the Bridging Hydrogen Atoms in

CO 10 been calculated to be slightly positive. Hexaborane(10) has also been 24 29 deprotonated by ammonia ' according to the following reaction: ' an ether + ■ BeHio + NH3 — NH^ B5 H9

The boron-11 nmr spectrum of BgHg" is qualitatively similar to that on of BgHio, as is the proton nmr spectrum. The boron-11 and proton nmr data are presented in Table 2. Apparent equivalence of the basal boron

TABLE 2

NMR Data for KBgHg®

100 MHz ^H^ Assignments 32.1 MHz l^Bf

6.9 base -10.1

12.4 apex +49.3

14.2 bridge

^Reference 30

^Chemical shifts expressed in ppm relative to tetramethylsilane equals

10. 00.

‘^Chemical shifts expressed in ppm relative to BFg" 0 (C2 Hg)2 equals 0.0. atoms and their respective terminal hydrogens is again attributed to time 31 averaging due to tautomerism of the bridging hydrogens.

Hexaborane(10) has recently been protonated according to the reac tions below to form the undecahydrohexaboronium ion.^'^'^^ 11

®6 ^ 1 0 -780(3^ % ^ 1 1

BeHio + BCI3 4 . HCl [BgH^/][BCl^-]

I o o The existence of the BgH^^ ion was predicted by Lipscomb in 1958.

Later this ion was proposed as an intermediate in the exchange of bridge

1 R O A hydrogens in BgH^g for deuterium from D 2 O or DCl. The boron-11 and proton nmr data, presented in Table 3, indicate that the proton has entered

TABLE 3

NMR Data for BgH^i'^'Br" ®

100 MHz Assignments 32.1 M H z

5.1 base -20.9 (179)^

9.9 apex 48.7 (173)

7.9® bridge

^Reference 30

^Chemical shifts expressed in ppm relative to tetramethylsilane equals

10. 00.

^Chemical shifts expressed in ppm relative to BFg " 0 (C2 Hg)2 equals 0.0,

"^Values in parentheses are coupling constants expressed in Hz.

®The relative area of this resonance is 5, as expected. the vacant bridge position of BgH^g.

The basal boron-boron bond of hexaborane(10) has been used as a 12 site of Lewis basicity for reactions with Lewis acids other than An

9 /Î adduct of hexaborane(10) with BCI 3 was reported , but it is thermally un stable. Recently i-BgHi^ has been used as a Lewis acid, reacting with 33 34 BgHjo to form the new boron hydride B 2gH2g, ' which is viewed as an adduct.

Hexaborane(lO) has also been shown to act as a Lewis acid, forming adducts with various Lewis bases. The adduct BgH^Q' was re- O C ported in 1965. Adducts of composition BgH^g'Lg, where L =

(CH3)3 N, 2^ '^ ^ (CH3)3 P,^^'^® or (CgHg)gP,^^ were reported later. The O J structure of the trimethylphosphine adduct has been determined.

P. Isotopically Labeled Hexaborane(10)

Hexaborane(10) has been labeled with deuterium in the basal termi nal positions and in the bridging positions. The reaction of BgH^o with

B2D5 at low temperature produces a molecule which is almost entirely 18 labeled in the basal terminal positions. Exchange with B 2Dg in a sol vent at low temperatures yields a basal terminally substituted hexaborane(lO) of high purity, BgHgDg.^^

Almost complete bridge labeling results from the reaction of BgH^g with D2O at ambient temperature.^^ Acidification of solutions containing.

9 ft BgHg~ with DCl results in the labeling of a bridging hydrogen , while more complete bridge labeling may also be accomplished by the reaction of

BgHio with DCl at ambient temperature in the gas phase. A product of 13

composition BgHyD^ is formed.

G. 2-Bromohexaborane

Hexaborane may be converted to 2-BrBgHg in less than 10% yield by

reaction with the 2 , 6 -lutidine-bromine complex in methylene chloride at

-97°C.^^ The proton nmr spectrum near ambient temperature indicates

that the bridging hydrogen atoms are exchanging with the basal B-B bond as was observed for BgH^g* Cooling the sample results in a partial quenching of the tautomerism at about -60°C and complete quenching at about -120°C.

The valence structures of the partially quenched and entirely quenched molecules are shown in Figure 6 . The basal boron-boron bond resides adjacent to the bromo-substituted boron atom, which is consistent with the electron withdrawing character of bromine. The boron-11 and pro ton nmr data are presented in Table 4. The variable temperature boron-11 and proton nmr spectra are shown in Figures 7 and 8 , respectively.

H. 2-Methylhexaborane(10)

The methyl-substituted derivative of hexaborane (10), 2-CHgBgHg, is prepared in 55% yield according to the following reaction:

K'^[l-Br-2-CH3BgHgl + l/2BgHg .(^^3)20 2-CH 3BgHg+ KBr —3 5^C

Low yields are obtained from the reaction of (CH 3)3 B with BgHg at 175°C in 38 the presence of (CH 3)3 Ga. Tautomerism also takes place in this mole cule at ambient temperature. Partial quenching occurs at about -50° and \ A ? ^ y (a) ir®\^ V-^-H

H ~ b ^ ^ b - h Br Br

H V - ^ - H ^ b - h I B i-

f ig u r e 6 . Struccures of 2-BrBgHg in Solution;

a) Partially quenched structure, -60°C •&> b) Static structure, -130°C 15

TABLE 4

NMR Data for 2-Bromohexaborane(10)^

100 MHz Assignments^ 32.1 MHz ^^B^

27°C -60°C -130°C 26°C -100°C

^ 1 1 .6 4 ^ 3 ,4

/ f~ 10.55 —( (10.58)® 1^3,4' i^5,6 / / / ^ 9.51 ^ 5 ,6 ! 10.23 4 (10.28) (10.29) ail |i

^ 10.02 10.00 ^2, 6' ^4,5

^ 6.80 5 ^ 5.9 / / / / 6.02 6.07-/ ( 6.14) 4,5 - 6.2 4 (-6) \ \ \ % 5.49 4 '\--18

^ 5.73 3 or 6 / / 5.48 5 . 5 4 Y 3,6 -18.1 -18 \ 5.35 6 or 3

10.42 10.61 1 48.3 49.9

2 -23.6 -18+1

^Reference 19.

^Chemical shifts expressed in ppm relative to tetramethylsilane equals 10.00,

®The number, n, denotes B^ or the terminal hydrogen attached to it. The

symbol |Jx,y denotes a hydrogen bridging B^ and By.

^Chemical shifts expressed in ppm relative to BFg'0(C2H5)2 equals 0.0,

^Values in parentheses are appropriately weighted averages. 16

(a )

(b )

(c )

I d )

FIGURE 7. Boron-11 NMR Spectrum of Z-BrBgHg;

a) All Protons spin decoupled

b,c,d) Undecoupled 17

(a)

(b)

(c)

FIGURE 8 . Proton NMR Spectrum of 2-BrBgHg;

a) Basal ^^B atoms spin decoupled

b,c) All ^^B atoms spin decoupled 18

complete quenching is observed at about -125°C.^^'^^ The valence struc

tures of the partially quenched and fully quenched structures are shown in

Figure 9. The basal boron-boron bond resides away from the electron re

leasing methyl group, but not so far away as to give the molecule a plane

of symmetry. The nmr data for this molecule are presented in Table 5.

The assignments will be discussed in a later section. Figures 10 and 11

show the variable temperature boron - 1 1 and proton nmr spectra, respective

ly.

The only published reactions of Z-CHgBgHg are protonation accord

ing to the equations below.

2 -CH 3 B6 H9 + HBrU) — ô-g> 2 -CH 3 B6 Hio+Br-

2 -CH 3 B6 H9 + BCI3 + HCl [2 -CH 3 BGHiQ+][BCl,l -780C

The nmr data for the 2 -CHgBgH2 Q^ ion are presented in Table 6 .

I. 2 ,3-Dimethylhexaborane(10)

The reaction of dimethylchloroborane with BgHg" and subsequent re arrangement of the resulting p-(CHg)2 BB3 HQ species in ether produces the only known multisubstituted hexaborane, 2 , 3 -(CH 3 )2 BgHg, in low yield.This compound was named 4 ,5-dimethylhexaborane(10) based upon the suspected position of the B-B bond in the base of the mole cule. The designation 2, 3 -(CH 3 )2 BgHg is proper, however, since proton nmr studies carried out in this laboratory indicate that at ambient tempera- B'"

, , / - C ' " ^ \ y ô . ‘“’ H'?-< yP'H ^ H'^ 1 f ' H y ~ h ” H—B— H H— B—H H—B’—^ CH3 CH3 CH3

H— B — H

CH 3

FIGURE 9. Structures of Z-CHgBgHg in Solution

a) Partially quenched structure, -50°C

b) Static structure, -115°C to 20

TABLE 5

NMR Data for 2-Methylhexaborane(10)^

100 MHz Assignments*^ 32.1 MHz ^^1

-5°C -50°C -115°C 25°C -80°<

/~ 1 2 . 2 0 N ,5 / 11.09-<'’ (11.04)® r~ \ ^^4,5; ki5,6 1 \ 1 \ 1 9.87 / ^^5,6 10.83-^ (10.83) (10.78) all [X \ \ \\ /—11.54 % / ^2,3 % 10.57-(' (10.52) V ^ 2 ,3 ' ^^2 , 6 \ \— 9.51 ^ 2 , 6

/“ 7.10 6 f~ 5.8 / /

6.44 6.52 ( 6.64) 3,6 - 6 .5 Y (- 6 . 0 ) \ \ N \ \_ 6.19 3 '— 18

/— 5.95 4 or 5 // 5.69 5.72 V ( 5.81) 4,5 -17.6 -18 \ \ \ 5.67 5 or 4

11.04 11.13 11.23 1 49.4 49.4

9.16 9.17 9.19 CH3 , 2 -2 9 .4 -29.8

^Reference 19- “Chemical shifts expressed in ppm relative to tetramethylsilane equals 10.00, “The number, n, denotes or the terminal hydrogen attached to it. The symbol Px,y denotes a hydrogen bridging B^ and By. ^Chemical shifts expressed in ppm relative to BFg«0(C2Hs)2 equals 0.0. “Values in parentheses are appropriately weighted averages. 21

-11 NMR Spectrum of 2 -CH 3 B6H9 figure 10. Boron 22

FIGURE 11. Proton NMR Spectrum of 2-CHgBgHg, Basal Boron-11 Atoms

Spin Decoupled 23

TABLE 6

NMR Data for Z-CHgBgH^Q^Br" ®

100 MHz ' Assignments*^ 32.1 MHz ^^B*^

5.20 4,5 or 3,6 -17.6 (149)® 5.32 3,6 or 4,5

8.78 CH 3 , 2 -34.1

9.85 1 48.3 (162)

7.45 li

8 . 1 0 \Jl

^Reference 30.

^Chemical shifts expressed in ppm relative to tetramethylsilane equals

10. 00.

®The number, n, denotes B^ or the terminal hydrogen attached to it. The

individual bridging resonances could not be assigned.

^Chemical shifts expressed in ppm relative to BF 3 • 0 (C2_Hg)2 equals 0.0.

^Values in parentheses are ^^B-^H coupling constants expressed in Hz. 24

ture the bridging hydrogens exchange with the B-B bond at a rate which Is

rapid on the nmr time scale. Figure 12 shows the boron-11 and proton nmr

spectra of this compound at ambient temperature.^^ The corresponding nmr

data are presented in Table 7.

J. Metalloboranes Containing the Hexaborane(10) Framework

The first metalloborane to be derived from the hexaborane (10) frame

work was [(C6 H5 )3 P]2 CuB6 Fl9 , formed from BgHg" and [(CgHg)2 P]gCuCl.^^

This was also the first air stable hexaborane derivative. Insertion of the

Cu into a basal B-B bond was proposed.

The reaction of Pe 2 (CO)g with BgH^g produced n-Fe(CO)/^BgHiO'^^''^'^

The only known apically substituted hexaborane (10) derivatives are

l-(C H 3 )3 SiB6 Hg and l-(CH 3 )3 GeB6 H g, prepared from H2 B C l'0 (C2 Hg)2

and 2-(CH3)3SiB5H7~ or 2-(CH3)3GeB3Hy Other recently reported com

pounds are trans-Pt(Bf^Hi 0 )2 ^ 7 ^^ , Rh(BgHj^Q)2 (acetylacetonate)^"^,

[Rh(B6Hio)2Cl]2^^' and [Ir(BgHj^Q)201]2It was proposed in each case that the transition metal occupies a bridging position between two basal boron atoms.

Other recently reported metallohexaboranes are prepared according to the reactions written below.

BeHio + (CH3)2M ^-> CH3MB6H9 + CH4

M = Mg, Zn, Cd THF ZBgHio + (CH3 )2 Mg Mg(BgHg)2 + 2 CH4 (b) L

FIGURE 12. NMR Spectra of 2 , 3 -(CH 3 )2 BgH8 a) Boron-11 spectrum b) Proton spectrum N3 en 26

TABLE 7

NMR Data for 2 ,3-Dimethylhexaborane'

60 MHz Assignments 32.1 MHz

' 2,3 - 20.2

6.40 (145)‘ 5 -17.8 (160)

4,6 -13.1 (152)

11.27 (153) 1 +48.4 (152)

9.60 CH3

10.80

Reference 41

^Chemical shifts expressed in ppm relative to tetramethylsilane equals

10. 00.

*^The number, n, denotes B^ or the terminal hydrogen attached to it.

^Chemical shifts expressed in ppm relative to BF 3 «0 (C2 H^)2 equals 0.0,

^Values in parentheses are ^^B-^H coupling constants expressed in Hz. 27

BsHio + CHaMgX 4 ^ BgHgMgX + CH4

X = Br, I

KBgHg + (hg-CgHg)2 TiCl > (hg-CgHg)2 TiBgHg + KCl

In each case it was proposed that the metal is covalently bonded to the

boron hydride fram ew ork.T he X-ray crystal structure of Mg(B 6 Hg)2 .

2THF in fact shows that each BgHg is coordinated to the magnesium at a

B-B bond site.^^ The compound Mg( 2 -CHgBgHg) 2 '2THF has also been

prepared.

11. Br;z^nsted Acidity of the Boron Hydrides

The Br^z^nsted acidity of Decaborane(14) was first demonstrated in

1956 This acidic character was verified by many workers during the

next several years.The pKg for B2 0 H14 was shown to be about

4 6 3 , 5 4 ^ and a recently reported X-ray crystal structure shows a B-B bond replaces the B-H-B bond at the site of proton abstraction.^^

This demonstration of Br;z^nsted acidity for B 2 QH24 led to speculation

that other boron hydrides might also be acidic.It was indeed proposed

that the relative Brjz^nsted acidities of the boron hydrides would increase as 59 the size of the framework increased for a given series of boron hydrides.

It was not until 1967, however, that Br/nsted acidity was demonstra

ted for a lower boron hydride, BgHg.®*^”^^ A typical reaction is as follows: 28

BjHg + MH — M+BgHg" + Hg —/ o O

M = N a,

Methyl lithium has also been used to deprotonate pentaborane(9). ®^

The salt is formed rapidly when pentaborane(9) and liquid am

monia are allowed to react at -78°C.®^ Several salts of octahydropenta-

borate(l-) have now been isolated and characterized,31,65 boron-11 and proton nmr spectra of B 5 H9 are qualitatively similar to those of

BgHg^^ , 62, 6 6 ^ although broadening of the basal resonance is observed at

o 1 low temperatures due to quadrupolar relaxation of the basal boron atoms while sharpening of the apical resonance occurs. The boron-11 and proton

66 nmr data for BgHg are presented in Table 8 .

TABLE 8

NMR Data for KBgHg^

100 MHz Assignments 32.1 MHz ^^B'^

8.53 base 17.1 (130)^^

10.41 apex 52.9 (150)

13.51 bridge

^Reference 66

^Chemical shifts expressed in ppm relative to tetramethylsilane equals 10.00.

"^Chemical shifts expressed in ppm relative to BFg' 0 (C2 Hg)2 equals 0.0.

^Values in parentheses are ^B-^H coupling constants expressed in Hz. 29

Shortly after BgHg was shown to be a Br/nsted acid, the acidity of

27 2 fl hexaborane(10) was established. ' The resulting boron hydride anion,

BgHg" has been discussed in section I.E. 1. The hexaborane(10) deriva tive ia-Fe(CO) 4 B6 H]L0 has recently been deprotonated by KH at low tempera ture.^^

Tetraborane(lO) has been deprotonated in ether solvents by methyl lithium®®'®^, KH^^, and Potassium hydride was successful in deprotonating I-CH 3 B4H 9 also. The tautomerism of the bridging 73 hydrogens in the resulting stereochemically nonrigid anion, l-CH 3 B4 Hg“ was observed to quench at about -85°C such that the two bridging hydro gen atoms reside adjacent to the methyl-substituted boron atom in much 19 39 the same way as was observed for 2 -CH 3 BgHg. ' Two resonance forms of I-C H 3 B4 H8 " are shown in Figure 13.

ÇH 3 ÇH3 H

B /\ H H H H

FIGURE 13. Resonance Forms of the Static Structure of l-CH 3 B4 Hg“

The boron hydrides '2(dioxane)^^, n-B^gH 2 2 ^^ 30

76 and i-B 2gH 22 have also been found to function as Br/nsted acids.

With regard to the relative acidities of the boron hydrides, the follow ing reactions were found to be complete by boron - 11 nmr spectroscopy:^7,28

LiBsHg + B2 0 H 14 - BgHô + LiBôîa

BgHio 4- LiBgHg LiBgHg + B^Hg

The relative acidities of the lower nido-boron hydrides, those having 2n+4 77 framework electrons , are thus > BgH^g > BgHg, in order of de creasing acidity. The octadecaborane(22)s are stronger acids than , having pKg =- -1.^® In the arachno-boron hydrides, those having 2n+6 77 framework electrons , pentaborane(ll) is a stronger acid than tetraborane(lO).

The pentaborane(9) derivatives l-CHgBgHg®^'^®, 2-CHgBgHg^^'^^, l-ClBgHg®^ and l-BrBgHg^^have been deprotonated by potassium hy dride at -78°C in tetrahydrofuran or dimethyl ether according to the follow ing reaction:

RB5 H8 + KH - K+CRBgHy"]

R = I-C H 3 , 2 -CH 3 , 1-C l, 1-Br

The resulting anions were shown by boron-11 and proton nmr spectroscopy to have pyramidal structures closely related to their parent neutral com pounds.^® These ions were found to be stereochemically nonrigid. The tautomerism of the bridging hydrogens in the 2 -CH 3 BgH7 " ion was observed to partially quench at temperatures below -90°C. Figures 14 and 15 show 31

CH:

FIGURE 14, Proton NMR Spectrum of K+EZ-CH^BgHyl, Basal ^^B11. Atoms

Spin Decoupled 32

H H

h - b^ b< Î ^ b - h ; ; = ± h - b — b b - h

"V" I I CH: >3 C H 3

FIGURE 15. Partially Quenched Structure of K^CZ-CHgBgHy"] 33

the proton nmr spectrum and the exchanging structure, respectively, for the

2 - C H 3 B 5 H 7 ion. The boron-11 nmr spectrum of this ion, shown in

Figure 16, exhibits loss of resolution of the basal resonances due to qua

drupolar relaxation at temperatures below -50°, while the apical resonance

sharpens. This sharpening has been attributed to thermal decoupling of

the basal boron atoms from the apex.The boron-11 and proton nmr data

for K'^'EZ-CHgB^Hy"] are presented in Table 9.

The relative acidities of the pentaborane(9) derivatives have also been

determined.The reactions listed below were determined to be complete

by boron - 11 nmr spectroscopy.

B5H9 + K+El-CHgBgHyl - KBgHg + l-CHgBgHg

B5 H 9 + K + [2-C H gB gH yl -* KBgHg + 2-CHgBgHg

l-ClBgHg + KBgHg - K’^Cl-ClBgHy"] +5 H B9

The reaction of l-CHgBgHg with 2 [-CH 3 B9 H7 "] yielded I-CH 3 B5 H3 and

2 -CH3 B5 H3 . Thus, the relative order of decreasing Brjzfnsted acidity is as follows:^^

I-CIB5H8 > B5H9 > l-CHgBgHg- 2-CH3B5H3

III. Polyhedral Expansion of Boron Hydride Anions

It was suggested by Lipscomb in 1959 that, on the basis of a then recent report of the addition of BH 3 to BH^ the addition of a BH 3 group

22 to boron hydride anions might be a general reaction. Shortly thereafter. 34

~45®C

FIGURE 16. Boron-11 NMR Spectrum of K^EZ-CHgBgHy"] 35

TABLE 9 -.a NMR Data for K'^CZ-CH^BgHy ]

100 MHz ^H^ Assignments’^ 32.1 MHz

-50°C -110°C -5°C

8.52 8.50 3,5 16.9

9.23 9.17 4 22.5

9.70 9.68 CH3 ,2 2.5

10.44 10.44 1 50.4 (148)®

^ 12.76 / ^^2,3' i^2,5 13.14 y [13.12]^ all p

13.85 ^*'exchanaina

Reference 6 6 .

^Chemical shifts expressed in ppm relative to tetramethylsilane equals

10. 00.

*^The number, n, denotes B^^ or the terminal hydrogen attached to it. The

symbol |ix,y denotes a hydrogen bridging B^ and By. The symbol ^exchanging

denotes the bridging hydrogen which exchanges between the |i 3 ^ 4 and g

positions.

"^Chemical shifts expressed in ppm relative to BF 3 * 0 (0 2 1 1 5 )2 equals 0.0.

®Value in parentheses is the coupling constant expressed in Hz.

^Value in brackets is the appropriately weighted average. 36

81 decaborane(14) and were combined to form a B 2 1 H24 salt. Several years later the reaction of CGH 5 BCI2 with Na2 BgC2 H2 2 was reported to 8 2 yield C 5 H5 B2 0 C2 H 2 1 .

Addition of the formal (CH 3 )2 B'*' moiety to boron hydride anions was re- 83 ported in 1969. The following reactions were observed:

(CH3)2BC1 + NaBH4 - 1 ,1-(CH3)2B2H4

(CH3)2BC1 + NaB3Hg - 2 , 2 -(CH 3 )2 B4 Hg

In another study chlorodimethylborane was used to insert the dimethylboryl moiety into the BgHg ion according to the following reaction:^^

(CH3)2BC1 + LiBgHg ^-[(CH3 )2 B]B3 Hg + LiCl

The product of this reaction rearranges to 2 ,3-dimethylhexaborane(10) at ambient temperature in an ether solvent.

The insertion of the BHg moiety into the pyramidal BgHg was inves tigated by Johnson^^ as a route to unsubstituted neutral boron hydrides.

The BgHg ion was found to cleave B 2 H5 symmetrically to yield 6 5 11 21 ".

This ion was then treated with liquid HCl to produce BgHi 2 5 to 10% yield. This preparation, currently the best available for B 5 H2 2 , has been found to produce yields in excess of 60% when the potassium salt of 7 BgHg is used.

The boron-11 nmr spectrum of BgHn was reported in 1971 by 7 Johnson and Shore. This spectrum is shown in Figure 17. The singlet at -2.3 ppm is assigned to the inserted BHg group and the high field doub- -2.3

“ 14.6 0 .3 33.5

FIGURE 17. Boron-11 NMR Spectrum of Chemical Shifts Expressed in ppm Relative to

BFg'OCCgHg)^ =0 . 0

w 38 let to the apical boron atom. The remaining doublets are due to the basal borons but cannot be assigned unambiguously. The lack of resolvable spin coupling of the inserted boron atom to its hydrogens was attributed to a rapid tautomerism which exchanges these hydrogens with the bridging hy- 7 drogens in the remainder of the anion , or to thermal decoupling.

Titrations of B 5 H3 with 8 2 Hg showed a sharp beak in the curve at

0.5 moles 8 2 Hg per mole 8gHg" when the titration was carried out in one day, but a 1:1 mole ratio was obtained if each increment beyond the ratio 7 of 0.5 was allowed sufficient time to react. The final products of the 1:1 reaction include and The reaction of 8 gHg" with one equi valent of 8 2 Hg was therefore used as a convenient preparation of BgHj^g in 25% yield.

The addition of one half equivalent of 8 2 Hg to 8^Hg and subsequent acidification is the most convenient preparation of pentaborane(ll).

Yields in excess of 60% are obtained.

The addition of the 8 Hg moiety to 8gHg salts to form heptaborane anions has also been reported.These reports will be discussed in a later section.

Trimethylborane has been reported to react with 8 gHg in the presence

30 of (CH3 )3 Ga to form 2 -CH 3 8 gHg in low yields. This insertion of BCH 3 is formally analogous to a carbene insertion reaction. As mentioned earlier, the reaction of H 2 8 C l ' 0 (C2 Hg)2 with (CH3 )3 M^^BgHy produces 39

the first apically substituted hexaborane(lO) derivatives, 1 -(CH 3 )3 M^^

T\7 3fi BgHg, where M is silicon or germanium.

The boron-boron bond site in the base of BgHg", resulting from the

removal of a bridging hydrogen from BgHg, has also been shown to be

susceptible to insertion of various electrophilic reagents which do not con

tain boron. These electrophiles contain silicon^^'®^'®^, germanium®®'®^,

tin®^, lead®®, or phosphorous.^^ The resulting compounds are usually 85 89 bridge-substituted BgHg" derivatives. ' The trimethylsilane moiety

has also been inserted into the — framework. 90

Insertion of the bis-triphenylphosphinecopper moiety into the bridg-

- _ Ay 70 q1 ing positions of BgHg and BgHg has also been reported.

pounds believed to be bridge-substituted BgHg derivatives containing

zinc, cadmium, magnesium and titanium have also been prepared.

These latter derivatives were discussed in section I.J.

IV. The Existence of a Heptaborane Species

92 In 1957 Dickerson and Lipscomb predicted, on the basis of their

semitopological approach to the structures of the boron hydrides, that no

heptaborane should exist.

Two years later Quayle reported that heptaborane(11) was present in low concentrations as an impurity in several boron hydrides, as evidenced

QO from mass spectral studies. The existence of B 7 H13 was also reported in 1959.94 This report was based on the observation of a B 7 H22 species 40

in the mass spectrum of tetraborane(lO) which was prepared from B 2 Hg in a hot-cold tube reactor. The following year Gibbins and Shapiro^^ re ported the observation of a heptaborane species, the number of hydrogen atoms was unspecified, in the mass spectrum of a sample of BgH 22 which was prepared from B2 K5 in electric discharge. This claim was later found to be in error when it was shown that 2 -ethylpentaborane gives the same 96 mass spectrum as the heptaborane species.

The products of the pyrolysis of 8 2 Hg in a shock tube reportedly con- 97 tained ByH^^ and B^H^^, as evidenced by mass spectroscopy. These boron hydrides were also reported to be present in the products of the 98 pyrolysis of B 4 H1 0 , according to mass spectral studies. An unknown By hydride was reported isolated from the products of the reaction of BgHg and

8 2 Hg at elevated temperatures in a flow-quench system.There was re portedly a By region in the mass spectrum and some boron - 1 1 nmr data were presented, although no spectra were published.

The first report of a heptaborane species which did not rely on mass 7 spectral evidence was published in 1971 by Johnson and Shore. The tensimetric titration of (n-C4Hg)4NBgHg in C H 2 C I2 solution with 8 2 Hg showed a sharp break in the curve at a mole ratio of 0.54 moles 8 2 Hg per mole

BgHg . Recovery of the excess diborane was achieved. This corresponds to the addition of BH3 to BgHg , thus forming ByH 2 2 ~* The boron-11 nmr spectrum of this new salt evidenced no B g H g " , but details were not repor ted. The treatment of B 7 H12 with HCl yielded BgH^Q as the major product. 41

The first characterization of a heptaborane species was recently re

ported. One half an equivalent of diborane was added to the potas

sium salt, or the tetra-n-butyl ammonium salt, of |i-Fe(CO),^BgHg to yield the [i-Fe( 0 0 ) 4 8 7 1 1 1 2 ion. The X-ray crystal structure of this ion reveals that a BH 3 group occupies a bridging position in the p-Fe(C 0 )4 BgHg ion.^^ Acidification of K^|pi-Fe( 0 0 ) 4 8 7 1 1 1 2 ] with liquid HCl yields KOI, hydrogen and Fe(CO) 4 B7 H i i .

The boron-11 nmr spectrum of K"**[ij-Fe(CO) 4 8 7 H i2 ] consists of 7 resonances of approximately equal areas. The bridging hydrogen region of the boron - 1 1 spin decoupled proton nmr spectrum of this salt consists of three relatively symmetrical resonances at 9 .9?, 10. 3t and 11 .4t . The remainder of the proton nmr spectrum is unreported.

Predictions of the stability, or lack of stability, of various hepta-

n c nn n o bora ne s have been published during the last two decades. ' ' Several alternative valence bond representations^^, 1 0 0 ^ called STYX^^^ notations, where S = number of bridging hydrogens, T = number of 8 - 8 - 8 bonds, Y = number of 8 - 8 bonds, and X = number of terminal hydrogens in excess of one per boron atom, as well as several geometries^^, have been advanced for these hypothetical compounds.

V. Background of Hexaborane(12) Chemistry

The first report of the isolation of hexaborane(lZ) appeared in 1912.

This report was, however, later withdrawn. ^ The existence of B 5 H22 was 42

95 97 103 later inferred from mass spectral data. ' ' Hexaborane(12) was pre pared in 4% yield from NaBgHg in 1964.^04 ^he only practical preparation 7 of BgH22 was reported by Johnson and Shore in 1971. This synthesis re sults in the isolation of 60 to 70 percent yields of B 0 H12 from the treat ment of KBgH^i with liquid HCl according to the following reaction:

KBjHii + HCl — BgHi2 + KCl

Hexaborane(12) is a colorless liquid which has a vapor pressure of

17 torr at It is stable at ambient temperature for short periods if it is quite pure.

The X-ray crystal structure of BgH]^2 has not been solved due to its tendency to form a glass at low temperatures. The structure has, how ever, been deduced from its boron-11 and proton nmr spectra. The valence bond structure, and probable molecular structure, are shown in

Figure 18. A boron-11 nmr spectrum of BgH%2 ' obtained in this laboratory, is shown in Figure 19. The boron-11 and proton nmr data are presented in

Table 10.

Exchange of hydrogens between BgH]^2 s^d B 2 Dg occurs, yielding

1, 1 , 4 , 4 - D ^ B g H g a t -30°C , and BgDi2 at ambient temperature. The boron atoms were determined not to be involved in this exchange.

The Lewis bases (CHg)2 0 ^^^ and (CHg) 2 N^^^ ' have been shown to cleave BgH22 to yield BgHg. Ammonia has been shown to react with

BgHi2 to yield [H 2 B(NH3 )2‘^][BgH^g"]. Attempts to prepare a brominated H- (a) (b)

FIGURE 18. Structures of BgH22 &) Valence structure b) Probable molecular structure

00 3 .6 1 ,4 2 ,5

figure 19. Boron-11 NMR Spectrum of BgH22 45

TABLE 10

NMR Data for Hexaborane(12)'

220 MHz Assignments 70.6 MHz

4.9 (160)® 3,6 -22.6 (156) f 5.8 (120) 1.4 equatorial - 7.9 (133) 6.1 (138) 1.4 axial^

7.9 (158) 2,5 +22.6 (158)

10.2

®Reference 2 0 .

^Chemical shifts expressed in ppm relative to te trame thylsilane equals

10. 00.

®The number, n, denotes or the terminal hydrogen attached to it.

^Chemical shifts expressed in ppm relative to BF^ « 0 (C2 Hg)2 equals 0.0.

®Values in parentheses are ^^B-^H coupling constants expressed in Hz.

^Reference 72. 46 hexaborane(12) from BgH^2 bromine failed. The only currently known derivative of hexaborane(12) is 3-methylhexaborane(12). This com pound is prepared by the addition of BH 3 to either the I-CH 3 B5 H7 or

2 -CH 3 B5 H7 ion and subsequent acidification with liquid

VI. Statement of the Problem

Derivatives of hexaborane(lO) have only recently been prepared^l'19,41^ their chemistry remains almost uninvestigated. It was of interest to determine whether Z-CH 3 B6 H9 , 2-BrBgHg and

2 , 3 -(CH 3 )2 BgHg could be deprotonated by an alkali metal hydride, as has been shown to be a general reaction of boron hydrides.

68-70,74-76 relative acidities of these derivatives with respect to

BgHpQ was also to be determined, as has been done for some derivatives of pentaborane(9)

It was expected that the bridging hydrogen atoms of the anions of hexaborane(lO) derivatives would undergo rapid tautomerism, as has been observed for their neutral counterparts^^ and for BgHg Low tempera ture nmr studies were to be carried out with the objective of quenching this tautomerism and determining the low temperature static structures of the new anions.

The anion BgH^ has been of interest for some time since it is an 7 intermediate in the only convenient synthesis of BgH ^2 « It was sug gested that the lack of observable B-H coupling in the peak assigned to 47

the BH3 boron atom was due to a rapid exchange of the hydrogens with 7 the bridging hydrogens. A test of this hypothesis was to be carried out by

investigating the variable temperature proton nmr spectrum of this ion. If

quenching of such a tautomerism occurred, then a low temperature static

structure would be assigned. An attempt was to be made to deprotonate

BeHi2 to yield a BgH^j." species which might be an isomer of the reported

No binary heptaborane species has been characterized to date. The only such species reported which has other than mass spectral data to _ 7 support it is ByH 22 • Since no nmr data has been published on this ion, it was of interest to obtain the appropriate spectra and attempt to assign a reasonable structure to this ion.

It was expected that the ByHi2 ion would be quite unstable with respect to temperature. Since it was reported that Z-CHgBgH^g"*' displayed greater thermal stability than BgH^^ an attempt was to be made to incorporate a stabilizing methyl group into a heptaborane anion. Thus the

ion was to be prepared from Z-CHgBgHg and diborane. This new ion was then to be examined by nmr techniques. An attempt was also to be made to protonate the ion to yield a neutral methyl- heptaborane. EXPERIMENTAL

I. Apparatus

A. Vacuum System

A vacuum system similar to that described by Sanderson^^? was uti lized in the manipulation of volatile materials. The system consisted of a pumping station, a distillation train, two reaction manifolds, a Toepler system, and a McLleod guage.

The pumping station consisted of a Welch Scientific Company model

1405 mechanical vacuum pump and a two stage mercury diffusion pump which were separated from the vacuum line and from each other by U traps maintained at liquid nitrogen temperature. The pumps could also be isola ted from the vacuum line and from each other by large bore stopcocks.

The distillation train consisted of four U traps which were connected to each other and to a glass manifold by Fischer and Porter Company 4mm

Teflon stopcocks. A glass partition divided the glass manifold into two equal parts. A Teflon stopcock was attached to the manifold near each end for the purpose of introducing materials into the train and withdrawing mater ials from it. Each stopcock was attached to a Fischer and Porter Company

9mm Solv-seal joint and a 6 mm mercury blowout. One trap had a mercury

48 49

manometer attached to it which was made of 16mm precision bore glass

tubing. This manometer allowed the pressure in this trap, or in one of

several combinations of traps, to be measured. A calibration of the train

was carried out in such a way as to allow the determination of the amount

of volatile material in a trap, or a combination of traps, by reading only the pressure and room temperature. Volatile reagents were measured in this

fashion during the investigation. Checks of the accuracy of the calibration were periodically made to insure precision. A Teflon stopcock separated the manometer from the traps in order to prevent excessive contamination of the mercury. Attached to the manifold via a Teflon stopcock was a three liter storage bulb for diborane. This bulb was equipped with a sidearm which was maintained at liquid nitrogen temperature. The bulb was wrapped with adhesive tape in order to reduce the amount of shattering glass in the event of an explosion.

Each reaction manifold contained several stations, each consisting of a Teflon stopcock, a mercury blowout, and a 14/35 inner Joint or a 9mm

Solv-seal joint. Each manifold was divided, by a glass partition, into two equal parts. The stopcocks nearest this partition were fitted with 18/9 ball joints in the case of the manifold which utilized the 14/35 joints. The manifold which was fitted with Solv-seal joints utilized these joints on either side of the partition also. The stations on either side of the parti tion could thus be joined by a U trap which was fitted with the appro- 50

priate joints. This U trap was often used to trap solvents which were to be

discarded.

The distillation train, including its manifold, and the reaction mani

fold which was equipped with Solv-seal Joints were entirely grease free.

They were connected to each other by glass tubing and could be isolated

from each other by closing Teflon stopcocks. The other reaction manifold .

contained a station with a 14/35 outer joint mounted horizontally for use

with extractors. Materials were transferred from one reaction manifold to

the other by the use of either a transfer manifold or a U trap which could be

fitted to the appropriate end stations.

The Toepler system was used to measure quantities of noncondensible

gas which was generated in various reactions. The Toepler pump dis

placed the noncondensible gas to a calibrated volume. There were two

calibrated volumes in order that reasonable pressures could be obtained

from large and small samples alike. The volumes were calibrated in much

the same fashion as the traps on the distillation train. - Only the pressure

and ambient temperature needed to be read in order to determine the amount

of gas present. Checks of the accuracy of the calibration were periodically

made to insure precision.

B. Glove Box

A Vacuum Atmospheres glove box was utilized in the manipulation of air sensitive nonvolatile materials. Continuous recirculation of the nitro- 51 gen atmosphere through Linde 4X molecular sieve and Dow Q-1 oxygen scavenger maintained the water and oxygen concentrations below 1 ppm.

Periodic regeneration of the molecular sieve and Q-1 was accomplished by heating the purification system to 300°C, purging it with hydrogen for one hour, and then evacuating it for twelve hours.

C. Glassware

Reaction vessels were constructed of Pyrex glass and equipped with standard taper or Solv-seal joints. Stopcock adapters were constructed utilizing standard taper or Solv-seal joints and were often used to attach reaction vessels to the reaction manifolds. Storage vessels were also made of Pyrex glass. Each storage vessel was equipped with a Teflon stopcock and either a 14/35 outer joint or a 9mm Solv-seal joint.

The cleaning of glassware was accomplished by soaking overnight in a concentrated solution of potassium hydroxide in ethanol and rinsing with hot water. When necessary, three percent HP was used to remove stains prior to rinsing. Glassware was dried for several hours in an oven maintained at 110°C.

D. Nuclear Magnetic Resonance Spectra

Proton and boron-11 nmr spectra were recorded on a Varian HA-100 high resolution nmr spectrometer operating at 100 MHz in the HA mode and at 32.1 MHz in the HR mode, respectively. Proton chemical shifts are 52

reported in tau units relative to tetramethylsilane equals 1 0 . 0 0 t using the

internal standards CgHg = 2.74 t , CHCI3 = 2.75 t , CHCIF2 = 2.76 t ,

CH2 CI2 = 4.67 T, or (0 1 1 3 ) 2 0 = 6.76 t . These shifts are accurate to

T + 0.03. Boron-11 chemical shifts are reported in ppm relative to

BF3 "0 (C2 Hg)2 equals 0.0 ppm using the external standard BCI 3 equals

-46.8 ppm^*^^ and are accurate to + 0.2 ppm. Coupling constants, ^^B-^H,

are accurate to + 5 Hz.

Decoupling experiments were carried out using a General Radio

Company 1164A Frequency Synthesizer, a Hewlett Packard 3722A Noise

Generator, and an Electronic Navigation Laboratories 3100L Power Ampli

fier. The decoupling apparatus was assembled by Mr. John Kelley.

Proton and boron-11 nmr spectra of several samples were also re corded with a Bruker HX-90 nmr spectrometer operating at 90 MHz and

28.87 MHz, respectively. Heteronuclear broadband decoupling was accomplished by using the B-SV3-B noise decoupler set at maximum width.

Spectra were obtained in the FT mode using 100 pulses per spectrum.

II. Reagents

A. Aluminum chloride

Aluminum chloride, anhydrous, purified, was purchased from

Matheson, Coleman and Bell and was sublimed into the reaction bulb where it was to be used. 53

B. Boron tribromide

Boron tribromide was purchased from Research Organic/inorganic

Chemical Corporation. It was condensed into a storage vessel and stored at ambient temperature. The vessel was wrapped with aluminum foil when in storage.

C . Bromine

Reagent grade bromine was purchased from the J. T. Baker Chemical

Company and used as received. It was stored in the hood.

D. Chloromethane

Chloromethane was purchased from Matheson Gas Products. It was used directly from the cylinder.

E. Diborane ( 6 )

Diborane was purchased from Callery Chemical Company and frac tionated thru a U trap maintained at -145°C before use. It was stored at

-196°C in the sidearm of the 3 i storage bulb which was described in section I.A.

F. Hydrogen chloride

Anhydrous hydrogen chloride was purchased from the J. T. Baker

Chemical Company. It was fractionated thru a U trap maintained at -126°C prior to use and was stored in a glass storage vessel at -196°C. 54

G. Lithium aluminum hydride

Lithium aluminum hydride was purchased as a powder from Alfa In

organics. It was used as received to dry solvents.

H. 2 , 6 -Lutidine

2 , 6 -Lutidine was purchased from the Aldrich Chemical Company. It

was dried over sodium at 110°C and condensed into a U-shaped storage

vessel for storage at ambient temperature. The vessel contained a Teflon

coated magnetic stirring bar.

I. Methanol-d^

Methanol-d^ was purchased from Stohler Isotope Chemicals. It was

condensed into a storage vessel and stored at ambient temperature.

J. Methyl iodide

Reagent grade methyl iodide was purchased from the J. T. Baker Chem

ical Company. It was used as received.

K. Methyl iodide-dg

Methyl iodide-dg was purchased from Stohler Isotope Chemicals. It was condensed into a storage vessel and stored at ambient temperature.

L. Pentaborane(9)

Pentaborane(9) was purchased from the Callery Chemical Company,

It was condensed into a storage vessel and stored at -78°C. 55

M. Potassium hydride

Potassium hydride was purchased from Research Organic/inorganic

Chemical Corporation as a fifty percent suspension in mineral oil. It was

freed of oil by repeated washings with anhydrous pentane. The activity of

the KH was determined by measuring the amount of hydrogen liberated in a

methanolysis reaction. A sample of KH so calibrated was then reacted with

BgHg to verify its activity. Samples found to be less than 90% active were

discarded. It was stored in a glass vial in the glove box.

N. Tetra-in-butyl ammonium iodide

Tetra-n-butyl ammonium iodide was purchased from Matheson, Cole

man and Bell. It was used as received.

O. Triphenylphosphine

Triphenylphosphine was purchased from Chemical Samples Company.

It was used as received.

III. Solvents

A. Benzene

Reagent grade benzene was purchased from the Fisher Scientific

Company. It was dried over LiAlH^, condensed into a storage vessel and stored at ambient temperature. 56

B. Chlorodifluoromethane

Chlorodifluoromethane was purchased from Matheson Gas Products.

It was used directly from the cylinder.

C. Dichloromethane

Reagent grade dichloromethane was purchased from Mallinckrodt Chem

ical W orks. It was dried over LIAIH^, condensed into a storage vessel

and stored at ambient temperature.

D. Dichloromethane-d 2

Dichloromethane-d 2 was purchased from Stohler Isotope Chemicals.

It was dried over LiAlH^, condensed into a storage vessel and stored at ambient temperature.

E. Diethyl ether

Reagent grade diethyl ether was purchased from the J. T. Baker Chem- . ical Company. It was dried over LiAlH^, condensed into a storage vessel and stored at ambient temperature over NaK.

F. Dimethyl ether

Dimethyl ether was purchased from Matheson Cas Products. It was dried over LiAlH^ at -78°C, condensed into a storage vessel and stored at

-78°C . 57

G. Dimethyl ether-dg

Dimethyl ether-dg was prepared from CD 3 OD and CD 3 I in tetrahydrofuran according to the following equations:

CD3 OD + KH CD3 0 "K'*' + HD

CD30"K'^ + CD3 I - CD3 OCD3 + KI

In the glove box, 4.25 g KH was placed into the removable, rotatable sidearm of a 1 0 0 ml reaction vessel which was fitted with a stopcock adapter and contained a Teflon coated magnetic stirring bar. Condensed in was

3.7 ml CD 3 OD and 50 ml tetrahydrofuran. At ambient temperature the KH was added in small amounts. The HD thus evolved was removed from the system periodically by passing it thru a U trap maintained at -196°C.

When evolution of HD ceased, the vessel was cooled to -196°C and evacuated. The volatiles from the U trap and 5.8 ml CD 3 I were then condensed in. The vessel was then filled with dry nitrogen gas at 1 atm pressure and allowed to warm to ambient temperature. The reaction was allowed to proceed with stirring while open to a U trap,maintained at

-196°C. After 12 hours the vessel was cooled to -196°C, evacuated, and the volatiles from the U trap condensed in. The system was again charged with 1 atm of dry nitrogen and allowed to react at ambient temperature.

After 24 hours the vessel was cooled to -196°C and evacuated. The vola tile contents of the vessel and the U trap were then condensed into the fractionation train and passed thru U traps maintained at -111°C and -196°C 58 while the originating trap was maintained at -45°C. The CD^OCD^ was isolated in the -196°C U trap. The yield, 93%, was determined gaseometrically. Storage was at -78°C.

H. Tetrahydrofuran

Reagent grade tetrahydrofuran was purchased from the J. T. Baker

Chemical Company. It was dried over LiAlH^, condensed into a storage vessel and stored at ambient temperature.

IV. Preparation of Starting Materials

A. 2-Bromohexaborane(10)

In a typical preparation of 2-BrBgHg, 4.24 mmol BgH^g and 6.36 mmol

BBrg were condensed into a 25 ml reaction vessel containing a Teflon coated magnetic stirring bar. The vessel was warmed to ambient temperature and stirred for 60 hours. Initially a white solid precipitated, but it disappeared after about 10 hours, at which time the solution was quite yellow. After

60 hours had elapsed an ice bath was placed around the reaction vessel and the volatiles pumped thru U traps maintained at -35° and -196°C while the vessel slowly warmed to ambient temperature. The fractionation was terminated after 8 hours. Isolated in the -35°C U trap was 2-BrBgHg,

2.49 mmol, which was shown to be pure by its boron-11 nmr spectrum.

This represents a 59% yield, a six fold increase over the previously re ported synthesis. The product was stored in a U trap storage vessel at

-78°C . 59

B. Chlorodimethylborane

Chlorodimethylborone was prepared by a method similar to that of

W iberg.^^^ The reaction of (CHg)gB with a 100% excess of HCl at 180°C

for 18 hours produced an essentially quantitative yield of (CHg) 2 BCl. The

volatile products of the reaction were passed thru U traps maintained at

-63°C, -126°C and -196°C. The (CH 3 )2 BC1 was isolated in the -126°C

U trap. Its vapor pressure was 625 torr at 0°C (lit. 634 torr) and re

mained constant in different volumes. It was stored at ambient tempera ture.

C. 2,3-Dimethylhexaborane(10)

The method of Gaines and lorns^^, somewhat modified, was used to prepare 2 , 3 -(CH 3 )2 BgHg. The condensation of 12 mmol (CH 3 )2 BC1 Into 31 9.90 mmol KB5 H3 in 8.5 ml (CH 3 ) 2 0 was followed by warming from

-78°C to -40°C over a one hour period. The ether was then removed at

-78°C and the remaining volatiles passed thru U traps maintained at -35°C,

-63°C, and -196°C while the vessel warmed to ambient temperature. The product, p-[(CH 3 )2 B]B3 H g^\ was recovered as a solid in the -63°C trap.

The yield was 59%. Its purity was verified by its boron-11 nmr spectrum.

For the rearrangement of |a-[(CH 3 )2 B]B5 H0 , a IM solution in

(CH3 ) 2 0 was prepared and allowed to warm to ambient temperature. This solution was stirred for 21 hours before the volatiles were passed thru U traps maintained at 0°C , -35°C and -196°C. The fraction collected at 60

-35°C had a vapor pressure of 3.5 torr at 19°C (llt.^^ 3.5 + 0.5 at 19°C).

Pure 2 , 3 -(CH 3 )2 BgHg was obtained by using the low temperature fractiona tion column. This column is similar to that described by Dobson^ex cept that a helix of 3 mm tubing serves as the inner tube. The second frac tion (about 80% of the material) which came off the column when the top of the column was maintained at -40°C was shown to be pure by its boron-11 nmr spectrum.The pure product was stored at -78°C.

D. Hexaborane(lO)

The method of Johnson, Brice, and Shorewas used to prepare

BgHjQ. In a typical preparation, 80 mmol Br 2 was syringed into a 1 reaction bulb which contained a Teflon coated magnetic stirring bar. The bulb was then cooled to -196°C and evacuated. Pentaborane(9), 78 mmol, was then condensed in and the vessel allowed to warm to ambient tempera ture, with stirring, while a -196°C bath was close at hand in the event the reaction proceeded too vigorously. After several hours only a slight color remained. The volatiles were then passed thru a U trap maintained at -30°C, which was equipped with Teflon stopcocks in order that it could be removed from the vacuum line, and another U trap maintained at -196°C. The mass of the 1 -BrBgHg^^^ was thus determined by taking the difference between • the mass of the removable U trap before the fractionation and its mass after the fractionation.

The 54 mmol l-BrBgHg thus obtained was then passed into a removable 61

U trap similar to the one described above, except that it was of larger volume, contained a Teflon coated magnetic stirring bar, and was fitted with a rotatable sidearm which contained 54 mmol active KH. The KH was, of course, placed there while the apparatus was in the glove box. Di methyl ether, 42 ml was then condensed in and the vessel allowed to warm to -78°C. The KH was tipped into the stirred solution a few millimoles at a time. The hydrogen evolved was periodically pumped away. When all the KH had been added, the solution was allowed to stir at -78°C for one hour.

Diborane, 27 mmol, was then allowed to expand into the vessel at

-78° and the vessel was warmed to -35°C for one hour. During this period a white solid, KBr, precipitated. The dimethyl ether was then pumped into a U trap maintained at -196^C while the reaction vessel re mained at -78°C.

The reaction vessel was warmed to -35°C and opened to U traps n o maintained at ambient temperature, -78 C and -196 C. The bulk of the

BgHio was collected in the -78°C trap at this time. The -35°C bath was then transferred from the reaction vessel to the ambient temperature trap and the vessel was allowed to warm to ambient temperature while pumping thru the -35°C, -78°C and -196°C U traps. The vapor pressure of the product was 7.5 torr at 0°C (lit. 7.5 torr) and no impurities were de tected by boron-11 nmr. Typical yields were in excess of 70% based on 62 l- B r B g H g . Storage was at -78°C.

E. Hexaborane(12) 7 Hexaborane(12) was prepared by the method of Johnson and Shore.

In a typical preparation, 15 mmol active KH was placed into a reaction vessel which contained a Teflon coated magnetic stirring bar. The vessel was then sealed with a stopcock adapter and removed from the glove box to the vacuum line and evacuated. Pentaborane(9), 10.0 mmol, was then con densed into the vessel, followed by 8 ml (CHg)2 0 . The vessel was allowed to warm, with stirring, to -78°C for one hour. The hydrogen which was evolved was measured to verify quantitative deprotonation.

Diborane, 5.0 mmol was allowed to expand into the reaction vessel which was maintained at -78°C. After about one hour the dimethyl ether was removed by pumping into a U trap maintained at -196°C. The last traces of

(Cl^ ) 2 0 were pumped away when the vessel was warmed to -30°C for an hour.

Ten milliliters of HCl was condensed into the vessel, which was then allowed to warm to -110°C while the contents were stirred for one hour.

The volatiles from the vessel were passed thru U traps maintained at -78° and -196°C while the vessel was allowed to slowly warm from -110°C to ambient temperature. The fraction isolated in the -78°C U trap was then fractionated thru U traps maintained at -63°C, -78°C and -196°C. The

®6^12 isolated in the -78°C U trap was determined to be pure by its 63 boron-11 nmr spectrum. It was stored at -78° and fractionated again before use.

F. 2-Methylhexaborane(10)

The method of Johnson, Brice, and Shorewas used to prepare

Z-CHgBgHg. In a typical preparation, a small amount of AICI3 was sub limed into a 1 X reaction bulb. Pentaborane(9), 25 mmol, was then con densed in, followed by 30 mmol CH^Cl. The bulb was then heated to

80°C for 12 hours. The bulb was then cooled to -196°C and the volatiles passed thru U traps maintained at -45°C, -78°C and -196°C while the bulb warmed to ambient temperature. Two such preparations of l-CHgBgHg^^^ afforded 33 mmol of product which was isolated as a solid in the -78°C U trap.

The 33 mmol of l-CHgBgHg were then condensed into the U-shaped

2,6-lutidine storage vessel, which contained 30 ml 2 , 6 -lutidine, and the solution was stirred at ambient temperature for 18 hours.The reaction vessel was cooled to 0°C and its entire volatile contents was fractionated thru U traps maintained at 0°C, -63°C, -95°C and -196°C. Several days were required for completion of this fractionation. The product, 22 mmol of 2 -CH 3 B5 H8 / was isolated as a solid in the -95°C U trap.

The 2 -CH 3 B5 H8 was then condensed into a vessel containing a stoichiometric amount of bromine and a Teflon coated magnetic stirring bar.

The vessel was allowed to warm to ambient temperature and stirred. The 64

HBr which was evolved was allowed to expand into the vacuum line. After

five hours the volatiles were fractionated thru U traps maintained at -35°C,

-78°C and -196°C. The contents of the -78°C U trap were refractionated

to insure complete separation. The product, 18.4 mmol of l-Br-Z-CHgBgHy, was isolated in the -35°C U trap. This procedure for the bromination of

2 -CHgBgHg is superior to that described in the literature^^ since separa

tion of the product is easily accomplished.

The l-Br-Z-CHgBgHy was condensed, with pumping, into a removable

U trap equipped with a Teflon coated magnetic stirring bar and a rotatable

sidearm charged with KH similar to that described in section IV.D. above.

The deprotonation of the l-Br-2-CHgBgHy, subsequent addition of diborane, and purification of the final product, 2 -CH 3 BgHg, is strictly analogous to the procedure used for BgH^g in section IV.D. above. The 2-CH^BgHg thus obtained in 74% yield had a vapor pressure of 6 torr at 0°C (lit.

6 torr). No impurities were detected by boron-11 nmr. The pure product was stored at -78°C.

G. Methyltriphenylphosphonium iodide 113 The method of Michaelis and Soden was used to prepare

(0 5 1 ^5 )3 PCH3 I. The preparation involves the addition of CH 3 I to a diethyl ether solution of (CgHg) 3 P followed by stirring at ambient tempera ture for several days. The white product was isolated in almost quantita tive yields by filtration. It was washed with diethyl ether and dried under 65

vacuum.

H. [(C6H5)3PCH3'^][2-CH3B6Hg“]

A typical preparation of [(CgHg)3 PCH3^][2 -CH 3 B6 H8 "] was carried out as described below. In the glove box, a reaction vessel equipped with a rotatable sidearm and a Teflon coated magnetic stirring bar was charged with 3.92 mmol KH. The sidearm was charged with 3.89 mmol

(C6 H5 )3 PCH3 l. The vessel was then fitted onto an extractor and removed to the vacuum line and evacuated. Dimethyl ether, 3.5 ml, and 4.14 mmol

2 -CH 3 BgHg were condensed into the vessel and hydrogen was quantitatively liberated at -78°C. An additional 4.3 ml (CH3)20 was then condensed on to the clear solution and the (CgH 5 )3 PCH3 l was tipped into the reaction vessel which remained at -196°C. The resulting mixture was stirred for one hour at -30°C before the dimethyl ether was removed at -78°C. The white solid was then extracted with 7.0 ml CH 2 CI2 while warming to ambient temperature. Upon removal of the methylene chloride, the white, crystalline [(CgHg)3 PCH3 ^][2-CH3BgHg ] was isolated in 90% yield. No impurities were detected by boron-11 nmr. The product was stored at

-78°C in a vessel fitted with Solv-seal joints.

I. [(CgHg)3PCH3+][B6H9l

The preparation of [(CgHg)3 PCH3'*'][BgHg ] was carried out in a fa shion analogous to that of [(CgHg)3PCH3''3[2-CH3BgH8"] as described 66

above in section IV.H. , except that replaces Z-CH^BgHg. The

boron-11 nmr spectrum of a salt so prepared was identical to that of

KBgHg '^9 Storage was at -78°C.

J. [(n-C4Hg)4N+][2-CH3B6H8"]

The preparation of [(n-C4Hg)4N^][2-CH3BgHg ] was carried out in a

fashion analogous to that of [(C 6 Hg)3 PCH3^][2 -CH 3 B6 Hg"] as described

above in section IV. H. , except that (n-C 4 Hg)4 NI is placed in the vessel

with the KH rather than (CgHg)3 PCH3 l in a sidearm. The boron-11 nmr

spectrum of a methylene chloride solution of the white, crystalline solid revealed no impurities. Storage was at -78°C.

K. [(n-C4Hg)4N+][B6Hg-]

The preparation of [(n-C 4 H g )4 [BgHg ] was carried out in a

fashion analogous to that of [(n-C 4 Hg)4 N^][2 -CH 3 B6 H8 ~] as described above in section IV. J ., except that BgH^g replaces 2 -CH 3 BgHg. The boron - 11 nmr spectrum of a methylene chloride solution of the white, crystalline solid revealed no impurities. Storage was at -78°C.

L. Trimethylborane

Trimethylborane was generously supplied by I. Jaworiwsky of this laboratory. It was prepared by the method of Brown, and stored at

-78°C . 67

V. Reactions

A. Deprotonation of hexaborane(lO) derivatives

For nmr studies a reaction vessel was constructed from 16 mm Pyrex tubing. One end was sealed into a test tube bottom while the other was connected to a Teflon stopcock. The vessel was equipped with a sidearm made of 6 mm glass tubing attached to an nmr tube and contained a Teflon coated magnetic stirring bar.

In a typical reaction an excess of KH was placed in the vessel while utilizing the glove box. The vessel was removed to the vacuum line and evacuated. At -196°C, 0.40 mmol Z-CHgBgHg, 0.36 ml (0 0 3 )3 0 , and

0.04 ml CHCIF2 were condensed into the vessel, which was then warmed to -78°C. The reaction was allowed to proceed with stirring until the evolution of hydrogen ceased. The hydrogen evolved was measured with the Toe pier pump. Yields were in excess of 95% of the theoretical amount.

The solution was then decanted into the nmr tube taking care to maintain the vessel and the sidearm at -78°C. The vessel was then frozen and the nmr tube sealed with a torch and removed. The nmr tube was then stored at -196°C. Deprotonations of 2-BrBgHg and 2, 3 -(CH 3 )2 BgHg were carried out in similar fashion.

Pmr spectra at temperatures below -130°C were obtained untilizing samples which were 1:1 (CD3 )2 0 /CHC 1F2 (by volume at -78°C). These samples were prepared by removing one half of the (CD 3 ) 2 0 from a IM 68 solution of the appropriate hexaborane(lO) salt at -78°C and replacing it with a like amount of CHCIF 2 .

B. Relative acidities of the boranes

Proton competition reactions were carried out in dimethyl ether at

-78°C between various pairs of neutral boranes and anions. An anion was prepared on a 0.35 mmol scale at -78°C as described above in section

V.A., except a stoichiometric amount of KH was used. The appropriate neutral species was then condensed in at -196°C in an equivalent amount.

The reaction was allowed to proceed for one hour at -78°C before the solution was decanted and the nmr tube removed. The nmr tube was then stored at -196°C. The following pairs of reactions were carried out and followed by boron-11 nmr spectroscopy in the temperature range -78°C to

-20°C: Z-BrBgHg and KBgHg; K'^[2-BrB6H8“] and BgH^Q; BgH^g and

K^[2-CHgBgHg ]; KBgHg and 2-CHgBgHg. The species present in the re sulting solutions were identified by the chemical shifts of the resonances observed.

C. Preparation of KBgH^^

The preparation of nmr samples of KBgH^^ was typically carried out as described below. In the glove box, about 10 mmol KH was placed into a reaction vessel constructed from 25 mm Pyrex tubing. This vessel con tained a Teflon coated magnetic stirring bar and was equipped with a side- 69

arm made of 6 mm tubing which was attached to an nmr tube. The vessel was then fitted onto a stopcock adapter, removed to tne vacuum line.and

evacuated. Dimethyl ether, 5.6 ml, was condensed in, followed by 6.55

mmol BgHg, measured gaseometrically. The hydrogen evolution was

measured to be 6.53 mmol after the reaction proceeded for several minutes at -78°C. Diborane, 3.27 mmol, was allowed to expand into the stirred

solution of KBgHg at -78°C for about 1/2 hour. The last traces of 8 2 Hg were condensed into the vessel rapidly with the use of a piece of glass wool, held with the forcepts, which had been dipped in liquid nitrogen.

The clear solution was then allowed to stir a few minutes at -78°C before a portion of it was tipped, taking care to maintain the vessel and the sidearm at -78°C. The nmr tube was then sealed with the torch and re moved. The nmr tube was stored at -196°C.

D. Preparation of KBgH^^ from BgH^g

The deprotonation of BgH 22 was accomplished by KBgHg in the follow ing manner. The preparation of KBgHg in (CHg) 2 0 was’undertaken in the 31 usual manner on a 0.5 mmol scale. A stoichiometric amount of B 5 H12 was the condensed into the reaction vessel and the reaction was allowed to proceed at -78°C. After one hour the clear solution was poured into the nmr tube sidearm taking care to maintain the vessel and the entire sidearm at -78°C. The nmr tube was then sealed with the torch, removed, and stored at -196*^C. 70

E. Preparation of ByH 22 and salts

The preparation of ByH 2 2 " and salts was typically under taken as described below. In the dry box, 0.47 mmol [(C 5 115)3 PCH3 '’']

[BgHg ] was loaded into a reaction vessel made of 16 mm Pyrex tubing which contained a Teflon coated magnetic stirring bar and was equipped with a 6 mm sidearm attached to an nmr tube. The vessel was then fitted with a stopcock adapter, removed to the vacuum line and evacuated. Di- chloromethane, 0.45 ml, was condensed into the vessel, which was then warmed to -78°C with stirring. Allowed to expand into the reaction vessel at -78°C was 0.23 mmol diborane. The clear solution of [(CgHg) 3 PCH3 ^]

[B7 H1 2 ] was allowed to stir at -78°C for one hour prior to pouring into the nmr tube. Care was exercised to maintain the vessel and the entire sidearm at -78°C while pouring. The nmr tube was then sealed with the torch and removed for storage at -196°C. Dichloromethane-d 2 solvent was used in the preparation of proton nmr samples. Some boron-11 nmr samples were prepared which utilized a mixed solvent system consisting of equal volumes of CH 3 CI, CH2 CI2 and CHCIF 2 .

The salts [(n-C,^Hg)4 N+][B7 H1 2 I , [(CgHg)2 PCH2 '^][CHgByH^^l and

[(B."C,^Hg),^N'*'][CH3ByHn ] were prepared from the appropriate BgHg and 2 -CH 3 BgHg salts in an entirely analogous fashion.

Dichloromethane solutions of the various B gH g" and 2 - C H 3 B g H g “ salts were also treated with an excess of diborane at -78°C. The excess 71

B2 Hg was recovered by pumping on the vessel at -78°C and allowing the volatiles to pass thru U traps maintained at -110°C and -196°C. The re covery of 8 2 Hg in the -196° trap corresponded to a mole ratio of 8 2 Hg to

8 g H g ~ or 2-CHg8gHg of 0.45 to 0.51 for several determinations. All nmr samples of all 8 7 salts were stored at -196°C.

F. Tensimetric titration of [(n-C^Hg)/^N jCZ-CHgBgHg ] with 8 2 Hg

A solution composed of 0.54 mmol [(n-C^Hg)^N'*'][2-CHg8gHg"] and

0.54 ml CH2 CI2 was titrated tensimetrically with diborane at -78°C. The equilibrium pressure was measured on an absolute reading mercury manometer using a cathetometer after each measured increment of 8 2 Hg was allowed to expand into the reaction vessel and react for 1/2 hour at -78°C. The titra tion curve showed a sharp break in the curve at 0.50 moles 8 2 Hg per mole

2-CH3B6H8".

G. Protonation of CHgByH^]^

A methylene chloride solution of [ Hg)^N"*"] [CHgB7 H^ 2 ], pre pared as described above in section V.E., was reacted with 14 mmol HCl at -110°C. Hydrogen was liberated; 0.78 mol for each mol of CH^ByH^^ present initially. The clear solution was poured into the nmr tube sidearm of the reaction wnile at -78°C. The sample was then stored at -196°C. RESULTS AND DISCUSSION

I. NMR Spectra of K‘^[2-BrB6H8~]

The boron-11 nmr spectrum of K'^'EZ-BrBgHg"] is shown in Figure 20.

The nmr data for this salt are presented in Table 11. The high field apical doublet and the low field singlet, assigned to boron number 2 , are reminiscent of 2-BrBgHg. They are of equal area. The doublet at

- 6 . 6 ppm is assigned to the remaining boron atoms and has a relative area four times that of either smaller peak. The doublet character of appropriate resonances was verified by proton decoupling experiments.

The arrangement of the boron atoms in 2-BrBgHg" must be similar to that of 2-BrBgHg since the boron-11 nmr spectrum exhibits a high field doublet of relative area one and the five remaining boron atoms resonate at con siderably lower field. The pairs of boron atoms Bg, Bg and B 4 , Bg are thus said to be isochronous.

The resonance due to B 3 and Bg appears at 11.5 ppm higher field than in the neutral compound. This shift upon deprotonation is larger than has been reported for a pyramidal boron hydride. It is noteworthy that the resonance due to B 4 and Bg appears at lower field than the corres ponding resonance in 2-BrBgHg. The basal resonances of the anions of

-72- B-2 —B,

FIGURE 20. 28.87 MHz Boron-11 NMR Spectrum of K^[2-BrB6H8“]

w 74

TABLE 11

NMR Data for K+CZ-BrBgHgl-ia

90 MHz Assignments^ 28.87 MHz ^^B^

-30°C -63°C

6.54 3 ,4 ,5 ,6 - 6 . 6 ®

2 -22 .5

11.27 1 48.9 (142)^

12.84 H

®The solvent is 90% (CDg ) 2 0 and 10% CHCIF 2 , by volume.

^Chemical shifts expressed in ppm relative to tetramethylsilane equals

10. 00.

The number, n, denotes B^ or the terminal hydrogen attached to it.

Chemical shifts expressed in ppm relative to BF^' 0 (CgHg)2 equals 0.0.

® ^^B-^H coupling constant equals 130 Hz at -20®C.

^ Value in parentheses is the ^^B-^H coupling constant-expressed in Hz. 75

BgH^Q and of B^Hg and its derivatives appear at higher field than the

basal resonances of the respective neutral species.

As the temperature is lowered the resolution of the basal

coupling is lost at about -40°C. Further cooling results in additional

loss of resolution of the basal resonances while the apical resonance

sharpens. This loss of resolution is due to quadrupolar relaxation of the

basal boron atom sw hile the apical sharpening is probably due to ther

mal decoupling of the basal boron atoms from the apex.^^

The proton nmr spectrum, basal boron-11 atoms spin decoupled, of

K'^'LZ-BrBgHg"] is shown in Figure 21. The position of the protium im purity in the ( 0 0 3 ) 2 0 solvent is indicated by dashes. The basal termi

nal resonance is not observed in the absence of ^^B spin decoupling. In the spectrum shown the apical quartet is not visible above the baseline.

The basal terminal and bridging resonances have relative areas of 4 and

3 , respectively, indicating that deprotonation occurs with the removal of a bridging proton. That the bridging hydrogens in the 2-BrBgHg ion undergo rapid exchange with the B-B bonds in its base is evidenced by the presence of a single, time averaged bridging resonance. The peak composed of coincidentally overlapping basal terminal resonances began to broaden as the temperature was lowered to -130°C, but splitting of the peak did not occur. Further cooling, to -170°C, caused only slight broadening of the bridging resonance. Thus, attempts to quench the FIGURE 21. 90 MHz Proton NMR Spectrum of [2-BrBgHg"], Basai ^^B Atoms Spin Decoupled

cr> 77 tautomerlsm of the bridging hydrogens was unsuccessful.

The overlap of the resonances due to B 3 - Bg and their terminal hydrogens is probably coincidental rather than due to an exchange pro cess involving boron atoms. This is reasonable since a distinct reson ance due to Bg is observed in the boron - 1 1 nmr spectrum.

II. NMR Spectra of K+[2-0% BgHg 1

The boron-11 nmr spectrum of K"^[ 2 -CH 3 BgHg"] is shown in Figure 22

The nmr data for this salt are presented in Table 12. The boron-11 nmr spectrum is qualitatively similar to that of 2-CHgBgHg, indicating that the pyramidal arrangement of boron atoms is retained upon deprotonation.

The four resonances shown are in the area ratio 1:2:2;1. The assign ments indicated in the figure are unambiguous for Bj and Bg, but the re maining assignments are based on the assignments for the neutral parent compound.

The resonance assigned to Bg and Bg appears at 12.6 ppm higher field than the corresponding resonance for 2-CHgBgHg. This shift upon deprotonation is larger than for 2-BrBgHg. It is noteworthy that the resonances for 2-CHgBgHg"' which are assigned to Bg, and Bg appear at lower field than their counterparts in the neutral species. Recall that a similar phenomenon was observed for 2-BrBgHg .

The doublet character of the resonance assigned to B 4 and Bg is not readily discernable at 0°C. Proton decoupling does sharpen it, however. 0®C

02 B4S B5 B,

FIGURE 22. 28.87 MHz Boron-11 NMR Spectrum of K^[ 2 -CH 3 B6 Hg"]

00 79

TABLE 12

NMR Data for K+EZ-CHgBgHgl^

90 MHz Assignments^ 28.87 MHz ^^B^

-30°C -130°C -40°C

14.62 H4,5

13.18_<'' [13.25]® all|i

12.56 uoM2,3 Q and H2,6

7.68 7.76 3 and 6 6.1^

5.65 5.61 4 and 5 -18.6^

11.60 g 1 48.0 (133)^

9.19 ,9,18 CHg, 2 -32.5

®The solvent is 90% ( 0 0 3 ) 2 0 and 10% CHCIF 2 , by volume.

^Chemical shifts expressed in ppm relative to tetramethylsilane equals

10. 00.

®The number, n, denotes B^ or the terminal hydrogen attached to it. The

symbol iJx,y denotes a hydrogen bridging B^ and By.

‘^Chemical shifts expressed in ppm relative to BF 3 «0 (C2 H3)2 equals 0.0.

®Value in brackets is the appropriately weighted average.

Resolution of this resonance did not allow accurate measurement of the

coupling constant.

^The apical hydrogen was not visible above the baseline at this temperature.

^ Va lue in parentheses is the ^^B-^H coupling constant expressed in Jlz,. 80

Proton decoupling also collapses to singlets the peaks assigned to 8 3 ,

Bg and B]^. Lowering the temperature below 0°C initially results in the loss of resolution of the coupling in the resonance assigned to

Bg and Bg. The 4 separate resonances remain observable to -80°C, but loss of resolution of the basal resonances occurs below this temperature while the apical resonance sharpens. These observations are again due to quadrupolar relaxation and thermal decoupling.

The proton nmr spectrum, basal boron-11 atoms'spin decoupled, is shown in Figure 23. It is very similar to that of 2-CHgBgHg. The position of the protium impurity in the ( 0 0 3 ) 3 0 solvent is indicated by dashes. In the spectrum shown the apical quartet is not visible above the baseline. In the absence of boron-11 spin decoupling the basal terminal resonances are not observed. The resonances shown which are due to the hydrogens attached to boron have relative areas of 2,2 and 3, reading from low to high field. The presence of only three bridging hy drogens indicates that deprotonation occurs with the removal of a bridging proton.

The bridging hydrogens of 2 -CH 3 BgHg” undergo rapid exchange with the B-B bonds in the base of the ion, as evidenced by the variable temperature proton nmr spectrum. Only a single, time averaged bridging resonance is observed over the temperature range -40°C to -120°C. At

-130°C, however, the bridging resonance splits into two peaks in the -X r" \

/^ 4 ,5

FIGURE 23.23 90 MHz Proton NMR Spectrum of K"^[2 -CH 3 BgHg 3, Basal Atoms Spin Decoupled

00 82

ratio 2 : 1 . This change is reversible. No further changes in the spec trum occured to temperatures near - 1 6 0 ° C . The weighted average of the chemical shifts of these two new peaks is in good agreement with the chemical shift of the time averaged resonance, as shown in Table 12.

The basal terminal resonances do not shift position or split, indicating that the 2 -CHgBgHQ ion possesses a plane of symmetry over the tempera ture range studied.

In the cases of , 2 - B r B g H g and 2 - C H g B g H g , the basal resonance at highest field was assigned to the boron atom opposite the basal B - B bond at low temperature. This assignment was unambiguous for BgH^Q and its validity for the derivatives was shown by the consis tency of the assignments based on narrow line heteronuclear decoupling experiments. This phenomenon occurs in 2-CHgBQHg" also, as shown below.

The resonance at 6 .1 ppm in the boron-11 nmr spectrum was assigned

1 9 to B g and B g based on the assignments for 2 - C H g B g H g , as previously stated. Narrow line heteronuclear decoupling experiments showed that the higher field basal terminal hydrogens are attached to these boron atoms. Analogous results were obtained for B 4 , Bg and their terminal hydrogens. This is also in agreement with the results obtained for

BgHfo» 2-BrBgHg and 2-CHgBgHg, where the highest field basal terminal hydrogen was attached to the boron atom opposite the B - B bond in the base at low temperature.^^ 83

For Z-CHgBgHg it was found by heteronuclear decoupling experi

ments that the lower field bridging hydrogens were adjacent to the

methyl-substituted boron atom while the higher field ones were adjacent

19 to the B-B bond in the static structure. This is also the case for

Z-CHgBgHg" at -130°C. The unique bridging hydrogen, actually adjacent

to two B-B bonds, appearing at 14 .62 t is then assigned to g while the

resonance due to ^ 2 , 3 and 1^2 6 aPP^ars at 12.56? . These assignments

are consistent with the Cg symmetry of the ion over the temperature range

studied and place the B-B bonds between B 3 and B 4 and between B 5 and

Bg. Thus, these bonds are indeed opposite Bg and Bg.

The above discussion actually leads to two possible structures for

2 -CH 3 BgHg“ , as shown in Figure 24. Both structures have Cg symmetry

on the nmr time scale. A dynamic structure is shown in Figure 24(a). The

unique hydrogen, assigned above the 1^4 ^5 , migrates between the three

bridging positions not adjacent to Bg. The bridging hydrogens adjacent to

Bg do not exchange. Similar partial quenching of the bridging hydrogens

has been observed for 2 -BrBgHg^®, 2 -CHgBgHg^^ and 2 -CHgBgH2 '".

Figure 24(b) shows resonance forms of the static structure which is equi valent to the middle structure in Figure 24(a). The resonance forms are preferred over the single structure since no boron hydride has been re ported which has two adjacent boron atoms joined by a 2-center B-B bond and a 3-center B-B-B bond. ^^^ If the framework bonds were shifted in H - H - B — \ H H

(a) B H H H' ^3 H •^ \ I / "H H — h — b - ^ h

CH. CH, CH 3

(b) B B.

H —' g —’H

FIGURE 24. Structures of 2 -CH 3 B5 H3 ”; a) Dynamic b) Static

00 85 order to avoid this condition, then the Cg symmetry of the ion is lost.

The static structure of the ion may, however, be represented by a single lie structure in terms of fractional 3-center bonds, as shown in Figure

25. The pmr experiment is unable to distinguish between these structures

/T\ ■

H——

CH 3

FIGURE 25. Topological Representation of 2-CHgBgHQ Utilizing Frac tional 3-Center Bonds. over the temperature range studied due to the symmetry of the ion.

III. NMR Spectra of K+[2 , 3 -(CH 3 )2 BsH7 "]

The boron-11 nmr spectrum of K^[2, 3 -(CH 3 )2 B6 H7 ~] is shown in

Figure 26. The nmr data for this salt are presented in Table 13. The boron - 1 1 nmr spectrum is somewhat similar to that of 2 , 3 -(CH 3 )2 B6 Hg^^, indicating that the pyramidal arrangement of boron atoms is retained upon deprotonation. The three peaks observed are in the area ratio 3:2:1. The assignments are thus unambiguous. Proton decoupling verifies the doublet character of the two higher field resonances.

The coupling is not observed for the resonance assigned to COen FIGURE 26. 28.87 MHz Boron-11 NMR Spectrum of K+[2, 3 -(CH 3 )2 BeH7 "] 87

TABLE 13 “ia NMR Data for K+[2 , 3 -(CH 3 )2 B gH yl'

90 MHz Assignments^ 28.87 MHz

-3G°C

5.81 5 -17.3

6 . 8 8 4 and 6 - 4.0®

9.45 CH3 , 2 and 3 -17.3

10.58 1 46.8 (135)^

12.85 n

®The solvent is 90% ( 0 0 3 ) 2 0 and 10% CHCIF 2 , by volume.

, ^Chemical shifts expressed in ppm relative to tetramethylsilane equals

1 0 . 0 0 .

®The number, n, denotes B^ or the terminal hydrogen attached to it.

^Chemical shifts expressed in ppm relative to BF 3 - 0 (C2 Hg)2 equals 0.0.

®Resolution of this resonance did not allow accurate measurement of the

coupling constant.

^Value in parentheses is the ^^B-^H coupling constant expressed in Hz. 88

and Eg below about -20°C. The resonance assigned to 8 2 , 83 and Bg lacks observable doublet character since the bulk of its area is due to the large singlet assigned to 83 and B 3 . Also, it may be recalled that the basal coupling is not readily observed for the other ions discussed above. As the temperature is lowered further the resolution of the entire basal region of the spectrum is lost while the apical resonance sharpens.

These observations are again due to quadrupolar relaxation and thermal decoupling.

The resonance assigned to B^ and Bg appears at 8.9 ppm higher field than the corresponding resonance for 2 , 3 -(CH 3 )2 BgHg. This large upfield shift of the resonance assigned to the boron atoms adjacent to a substituent was also observed for 2 -BrB6 H8 ~ and 2 -CH 3 B8 Hg".

The proton nmr spectrum, basal boron-11 atoms spin decoupled, of

K"^[2 , 3 -(CH 3 )2 BgHy"] is shown in Figure 27. The position of the protium impurity in the ( 0 0 3 ) 3 0 solvent is indicated by dashes. The basal termi nal resonances are not observed in the absence of boron - 11 spin de coupling. In the spectrum shown the apical quartet is not visible above the baseline. The basal terminal peaks have relative areas of 1 and 2 wnile the bridging resonance has a relative area of 3. This indicates that deprotonation occurs with the removal of a bridging proton, as was the case for the other hexaborane(lO) derivatives described above.

The bridging hydrogens in 2 , 3 -(CH 3 )2 B6 Hy" undergo rapid exchange CH

FIGURE 27. 90 MHz Proton NMR Spectrum ofK+[ 2 , 3 -(CHg)2 BgH7 -]. Basai Atoms Spin Decoupled 00 (O 90 with the basal B-B bonds, as indicated by the observation of a single, time averaged bridging resonance at temperatures near -150°C. Thus, attempts to quench this tautomerism were unsuccessful.

IV. Relative Acidities of 2-BrBgHg and 2-CH^BgHg with Resepct to BgH^g

The reactions below were shown by boron-11 nmr spectroscopy to be complete, as shown in Figures 28 and 29. These reactions were studied

BgHio + K'^[2 -CH 3 BgH8 l -> KBgHg +2 -CH 3 BgHg

2-BrBgHg + KBgHg -» K+[2-BrBgHg"] + BgH^g over the temperature range -78°C to -20°C. The species in solution were identified by chemical shifts and coupling constants. The following reactions did not occur.

KBgHg + 2-CHgBgHg -$ no reaction

[2-BrBgHg"] + BgH^g -» no reaction

Figure 28 shows that a proton has been transferred from 2-BrBgHg to

BgHg , indicating that 2-BrBgHg is a stronger Br/z^nsted acid than BgHj^g.

Figure 29 shows that a proton has been transferred from BgH^g to

2-CHgBgHg", indicating that Bgll^g is a stronger Br/z^nsted acid than

2-CHgBgHg. Thus the order of decreasing Br/nsted acidity for the deri vatives investigated is 2-BrBgHg > BgH^g > 2-CHgBgHg. This order was expected on the basis of the electron withdrawing character of bromine and the electron releasing character of the methyl group. 91

(a)

(b )

B e H io B e H |0

FIGURE 28. 32 .1 MHz Boron-11 NMR Spectrum of K+[2-BrB6H8“] + BgH^g; a) Basal Region with Protons Decoupled ~ b) Undecoupled 92

(a)

(b)

B e H g ’

FIGURE 29. 32.1 MHz Boron-11 NMR Spectrum of KBgHg + 2 -CH 3 B6 H9 a) Basal Region with Protons Decoupled b) Undecoupled 93

V. NMR Spectra of KBgHj j

The boron-11 nmr spectrum of KBgH^j^ is shown in Figure 30. The nmr data for this salt are presented in Table 14. The boron-11 nmr spec tra at 25°C support a structure in which a borane group has entered the vacant bridging site in the BgHg ion, as shown in Figure 31(a). A spec- 7 trum identical to Figure 30(a) has been published by Johnson and Shore and the assignments are indicated. The lower field doublets cannot be unambiguously assigned. The proton decoupled spectrum, shown in

Figure 30(b), verifies the multiplicities indicated in Figure 30(a). Lower ing the temperature produces significant changes in the spectrum, as shown in Figure 30(c). The apex has shifted down field by 12.9 ppm and the basal region of the spectrum has become poorly resolved with the bulk of the area being in the lower basal region near -15 ppm rather than near

O ppm. These observations suggest that significant changes in the struc ture of BgHii have occured upon lowering the temperature. These changes are reversible.

The boron-11 spin decoupled proton nmr spectra of KBgH^i are shown in Figure 32. The two lower field resonances at -25°C are assigned to the basal^terminal hydrogens from the BgHg” framework. The lower field protons are attached to the boron atoms which appear at lowest field in the boron-11 nmr spectrum. The large proton resonance appearing at

9.29t in Figure 32(a) has a relative area of seven while the two lower 94

(Q) BH

APEX .

(b) -25®C

Id) -76°C

FIGURE 30. 28.87 MHz Boron-11 NMR Spectra of KBgHij;

a) -25°C, Undecoupled b) -25°C, Protons Decoupled

c) -76°C, Undecoupled d) -76°C, Protons Decoupled 95

TABLE 14 a NMR Data for KB^Hn' llBd 100 MHz iR b Assignments® 28.87 MHz

-25°0 125°0 -25°0 -76°0

r 12.35 / ^ 3 ,4 /9 11.16 W2,3 ^ 4 ,5

9.29 Y' [9.25]® all and BH 3

A ^ 7.89 \ ^ 2 , 6 \ u 6.47 BH2 - 1 . 6 f

8.57 2 or 5, or 3 or 4 /

6 . 6 8 -< ' [6.69]® 2 and 5 or 3 and 4 -14.0 (117) -15.2 \ SN 4.81 3 or 4, or 2 or 5

7.89 3 or 4, or 2 or 5 //"

7.23 [7.18]® 3 and 4 or 2 and 5 0.9 (125) - 1 . 0 \ N> AC 6.47 2 or 5, or 3 or 4

9.66 9.58 1 34.6 (117) 21.7 (117)

^The solvent is 85% ( 0 0 3 ) 2 0 and 15% CgHg by volume. ^Chemical shifts expressed in ppm relative to tetramethylsilane equals 10. 00. ^The number, n, denotes B^ or the terminal hydrogen attached to it. The symbol px,y denotes a hydrogen bridging B^ and By. ^Chemical shifts expressed in ppm relative to BF 3 '0 ( 0 2 115)2 equals 0.0. ^Values in brackets are appropriately weighted averages. ^Values in parentheses are coupling constants expressed in Hz. H H \/ B H B / .H B"

(b) (c) (a) /M/X /\V/\ H\ B H H B / \ H H 3222 4131 3222

FIGURE 31. Topological Structures of BgHii

a) 3222 b) 4131 c) 3222 , based on ^6^12 framework

VO o bfbfb b+^2,6

FIGURE 32. Proton NMR Spectra of KBgHj^l' Boron-11 Atoms Spin Decoupled a) 100 MHz Spectrum b) 90 MHz Spectrum 98

field peaks have a relative area of two. Decoupling at the boron-11

frequency corresponding to the apical boron atom resolves the apical hy

drogen, as shown in the inset to Figure 32(a). The resonance at 9.29?

is then due to six hydrogens while the apical hydrogen appears at 9.66?.

The six hydrogens are assigned to the three bridging hydrogens from

BgHg" and the three borane group hydrogens which are undergoing rapid

exchange giving rise to a single, time averaged resonance. This ex- n Change was originally suggested by Johnson and Shore to account for the

1 1 1 lack of observable B- H coupling in the resonance assigned to the

borane group in the boron-11 nmr spectrum. Evidence for such an ex

change process is provided by variable temperature proton nmr spectra.

As the temperature is lowered the resonances shown in Figure 32(a) broaden and then disappear until eight relatively sharp resonances can be discerned in the spectrum at -125°C, as shown in Figure 32(b). These changes are reversible. These new resonances have relative areas toward increasing tau of 1:3:2:1:1:1:1:1. The position of the protium impurity in the (CDg ) 2 0 is indicated by dashes. This spectrum represents an effectively static structure on the proton nmr time scale. The relation ships between the resonances observed at -125°C and those observed at

-25°C are indicated by dashed lines in the figure. The weighted averages of the chemical shifts of the resonances observed at -125°C are in good agreement with those of the time averaged resonances observed at -25°C, as indicated in Table 14. 99

The pyramidal framework remains effectively intact as indicated by only a small shift of the apical resonance, designated "a". The inset in

Figure 32(b) shows the apical proton resonance when the boron-11 de coupling frequency corresponds to the apical boron atom in the boron - 1 1 nmr spectrum.

The resonances assigned to the bridging hydrogens at -125°C are relatively insensitive to boron - 1 1 spin decoupling and have chemical shifts which are in the range commonly observed for pyramidal borane anions. That there are three separate bridging resonances and four termi nal resonances, designated "b", implies that the static structure of

BgHii is asymmetric. Two hydrogens of the borane group have the same resonance position, 6 .47 ?, while the unique one resonates at 7 .89t . It is proposed that the symmetry of the ion has been reduced by the act of the borane group assuming a static position such that one of its hydrogens is in what is nearly a bridging position analogous to the equatorial hy-

20 drogen on the apex of which resonates at 8.2?. The two remain ing borane group hydrogens are therefore stereochemically nonequivalent but their resonances nonetheless overlap. Figure 33 shows the proposed structure of B^H^i in solution at -125°C. The topological representa tion for this structure is shown in Figure 31(b). 100

FIGURE 33. Proposed Structure of BgHii at Low Temperature 101

VI. Deprotonation of Hexaborane(12)

The attempted deprotonation of BqHj^2 by KH was unsuccessful.

Only 50-70% of the theoretical amount of hydrogen was evolved in a typi cal reaction and the boron - 1 1 nmr spectra of the resulting solutions were unclean.

Hexaborane(12) is, however, deprotonated by BgHg according to the following proton competition reaction. This reaction was observed by

BgHiz + KBgHg -* KBgHii + BgHg boron-11 nmr spectroscopy over the temperature range -78°C to -20°C.

The reaction was complete in several minutes. Figure 34 shows the boron-11 nmr spectrum of the product mixture at -25°C. Pentaborane(9) is easily identified by the difference between the apical chemical shift and the basal chemical shift and by the coupling constants. 1 1 fi

It was initially expected that the BgH^i" which resulted from the deprotonation of BgHj ^2 niight be an isomer of the BgH^^ discussed above, and that its structure could be represented by the topological representa tion shown in Figure 31(c). The BgH^i actually derived from BgH ^2 is, however, the same as that prepared from BgHg and BHg. This is clear from the boron-11 nmr spectrum shown in Figure 34. The spectrum is somewhat out of phase with respect to BgH^j^ , but it is not highly un usual for phasing difficulties to occur in samples which contain neutral boranes and boron hydride anions. The three doublets not assigned to ,U[-1 y -" B5H9

11 NMR Spectrum of KBgH^^x figure 34. 32.1 MHz Boron-11

o CO 103

B^Hg are assigned to . Their chemical shifts are in good agree ment with those presented in Table 14. The assignments are further sub

stantiated by proton decoupling experiments.

VII. NMR Spectra of ByH^g

The boron-11 nmr spectrum of [{n-C^Hg)^N^][ByHj ^2 ] is shown in

Figure 35. The two peaks observed at -80°C are centered at 19.6 ppm and 44.4 ppm. Their relative areas are four and three, respectively. At

-80°C proton decoupling changes only the higher field peak. At -70°C, however, the lower field peak becomes slightly resolved with decoupling.

The small sharp peak and the upfield shoulder on the peak at 44.4 ppm are due to impurities. Since the downfield multiplet has a relative area of four and it is shown to be unsymmetrical when resolved, this multiplet must be composed of overlapping resonances with relative areas of one and three.

The boron-11 nmr spectrum of [(CgHg)gPCHg'*'][ByH^2 ] is more re solved than that of the tetra-n-butyl ammonium salt when undecoupled, as shown in Figure 36. The lower field peak is resolved for this salt whereas it was not for the salt discussed above. Proton decoupling collapses the downfield multiplet to two singlets of unequal area and collapses the up field peak to a singlet. The ratio of the areas of the downfield multiplet to the upfield peak is 4:3 for this salt also. The same impurities that were described above are present in this sample also. The downfield multiplet 104

(a)

(b)

(c)

FIGURE 35. 32.1 MHz Boron-11 NMR Spectra of [(n-C 4 Hg)4 N+][ByH 22 1

in a Mixed Solvent System Composed of CHgCl, CH 2 CI2 and

CHClFg; a) Undecoupled b,c) Protons Spin Decoupled 105

(a)

(b)

FIGURE 36. 32. 1 MHz Boron-11 NMR Spectrum of [(CgHg);^PCH3 +][ByH^ 2 "]

in a Mixed Solvent System Composed of CH 3 CI, CH2 CI2 and

CHClFg; a) Undecoupled b) Protons Decoupled 106 is then composed of two doublets centered at 17.9 and 22.4 ppm with relative area's of one and three, respectively. The upfield peak, at

46.2 ppm, is more difficult to assign. It contains no resonances of higher multiplicity than doublet, but it may contain a singlet also. The fact that contains a BHg group which produces a singlet in the boron - 1 1 nmr spectrum suggests that the ion may possess a BHg group which resonates at about 46 ppm. Recall from the experimental section that the reaction of BgHg" with excess B2 Hg and subsequent re covery of the unreacted B 2 Hg results in a mole ratio of B2 Hg to BgHg" of

0.5. This is not unreasonable since the coordinated BHg group in

C2 BgHio", the isoelectronic carborane analog of B7 H12 which is pre pared from C 2 B4 H7 ’' and 1/2 B 2 Hg, produces a quartet at 46.4 ppm.

The upfield peak in the spectrum may then be composed of a singlet of relative area one which coincidentally overlaps a doublet with twice the relative area.

The discussion above sets forth the suggestion that B 7 H2 2 ~ may contain a BHg group, that is, be composed of a BHg group inserted into one of the vacant bridging sites of BgHg , as shown in Figure 37. This proposed structure is not unreasonable since acidification of solutions

— n containing B' 7 Hj^2 yield BgH^g as the major product , suggesting that the BgHg" pyramid is not severely distorted upon the addition of diborane.

Also, a structure analogous to that shown in Figure 37 has been found in 107

FIGURE 37. Proposed Structure of 108

Fe(CO)^ByH 2 2 " which is prepared from Fe(CO)^BgHg and 1/2

The proton nmr spectrum of [(CgHg)gPCH2 '^[ByH 2 2 "], boron-11 atoms spin decoupled, is shown in Figure 38. The solvent is CD 2 CI2 .

The low field doublet is due to the methyl group in the cation. The resonances due to the ByH ]^2 appear at 7 .73 t , 8 .65 t , 9.66 t , 10.45t and 13.1 It- The BgHg ion is absent. The area ratios of the resonances varied widely with instrumental conditions. Thus the spectrum has not been completely assigned. The large peak at 10.45t is assigned to the borane group. This peak probably also contains the apical hydrogen since its relative area was usually greater than three. The highest field peak is assigned to the bridging hydrogens since its chemical shift is quite high and since it is less sensitive to boron - 1 1 spin decoupling than the other resonances. The proposed structure has three bridging protons, but the relative area of the peak assigned to the bridging hydrogens was usually nearer two than three. The bridging hydrogens probably undergo exchange with the remaining B-B bond in the base of the BgHg fragment, as shown in Figure 39. This type of exchange, although involving all bridging positions, could account for the single bridging resonance ob served. The three resonances due to B 7 H2 2 '' which are downfield of the

BH3 resonance are then assigned to basal terminal hydrogens. Their relative areas are 2 :2 :1 , reading from low to high field, which is in good agreement with the proposed structure. - 80®C

FIGURE 38. 100 MHz Proton NMR Spectrum of [(CgHg)2 PCHg ][ByH^2 ] / Boron-11 Atoms Spin

Decoupled

o to 110

\ / —\

■\" “-h - b \ ^=;______«î . r ®'H H ^ \ ' ^ H—B—H H—B I I H H

FIGURE 39. Topological Representation of ByH 22 Showing One Bridging

Hydrogen Exchanging With the B-B Bond I l l

The boron-11 and proton nmr spectra of are not readily compatable. This may be due to the difference between the boron-11 and proton nmr time scales. The Ion may be stereochemically nonrigid on the proton time scale but effectively static on the boron - 1 1 time scale. The proton nmr spectrum does not change when the tempera ture is lowered to -100°C, where the sample freezes. Quadrupolar re laxation precludes boron-11 nmr studies below -80°C while decomposi tion, discussed below, prevents nmr studies much above -75°C.

Thermal decomposition of ByH-^2 occurs at temperatures above about -75°C. Severe decomposition takes place with warming to +10°C over an hour, as shown in Figure 40. A major product of this decomposi tion is BgHg , as indicated in the figure. This result also supports the proposed structure for . The largest resonance in the spectrum now appears at 9.70 t while other peaks appear at 8 .58t / 9.26?, 10.47? and 13.2 6 t.

VIII. NMR Spectra of

The Br^z^nsted acidity of 2-CHgBgHg relative to BgHj^g indicates that Z-CHgBgHg is a stronger base than BgHg . Also,2 -CHgBgH2^Q^ was found to be more stable thermally than BgH^j^.^^ These observa tions suggested that the addition of 1/2 B£Hg to 2-CHgBgHg" might yield a heptaborane anion of greater thermal stability than ByH 22 '

A tensimetric titration of [^-C^Hgj^N"^][ 2 -CH3 BgHg ] in CH^Clg 1

FIGURE 40. 100 MHz Proton NMR Spectrum of [(CgHg)2 PCHg'^]' Boron-11 Atoms Spin De

coupled, at -80°C after Warming to +10°C ts3 113

by 6 2 Hg was carried out at -78°C. The titration curve is shown in

Figure 41. The sharp break in the curve at a mole ratio of B 2 H6 to

2-CHgBgHg" of 0.50 indicates the presence of CHgByH^^ in solution.

It is proposed that a borane group enters a vacant bridging site in the

2-CH3B5H3” ion. As described in the experimental section, the reaction of 2 -CH3 BgHg" with excess 2 BHg and subsequent recovery of the un reacted B2 H5 also corresponded to a product of composition CH^ByH^^ .

The boron-11 nmr spectrum of [(n^-C,^Hg)^N'''][CH 3 ByH 2 i"] in a mixed solvent composed of CH 3 CI, CHgClg and CHClFg is shown in

Figure 42. The spectra are very similar to those of ByH 2 2 " , suggesting that these ions have similar structures. The area ratio of the low field peak to the high field peak is 4:3. The peaks are centered at 21.3 and

40.9 ppm. The unsymmetrical nature of the upfield peak is the only difference between these spectra and those of ByH ]^2 ' This peak is composed of a doublet of area two and a singlet of area one which over laps the upfield arm of the doublet. It is not known whether this singlet is due to the methyl-substituted boron atom or to the borane group. The

ion is somewhat more stable than ByH]^ 2 ” as evidenced by the fact that clean boron-11 spectra could be obtained at -60°C.

The proton nmr spectrum of [( 0 3 1 1 3 )3 ], boron-11 atoms spin decoupled, is shown in Figure 43. The sharp doublet at low field is due to the methyl group in the cation. The peaks indicated by o

_ 3 o> X s 3 2

-o o

0.2 0 .4 0.6 0.8 1.0 mmol B2H 0y/m m ol Z-CH^BgH^

FIGURE 41. Tensimetric Titration of [(n-C 4 Hg)4 N*-][ 2 -CH3 BgHg"] in CHgClg by BgHg at -78°C it. 115

(a)

(b)

FIGURE 4 2 . 32.1 MHz Boron-11 NMR Spectrum of [(n-C^Hg)^N+][(n C4Hg)4N+] [CH3 B7H1 1 "] in a Mixed Solvent System Composed of CH 3 CI, CH 2 CI2 and CHCIF 2 ; a) Undecoupled b) Protons Decoupled I 111

FIGURE 43. 100 MHz Proton NMR Spectrum of [(CgHgj^PCH^"*"], Boron-11 Atoms Spin

Decoupled

C l 117

vertical lines in the figure appear at 8.16? , 8.94%, 9 .34t , 9.62 t , 9.78 t ,

10.61? and 12.76 t . The peak at 9.34? is probably due to the methyl group of the ion. The peak at 9 .78 ? may be due to the apical hydrogen. All other resonances due to boron-bonded hydrogens are very similar to those of ByH ^ 2 •

The CHgByH^i ion is more stable thermally than ByH 2 2 , as evi denced by its proton nmr spectrum at -15°C after the sample had been warmed to +10°C. This spectrum is shown in Figure 44. The resonances indicated by arrows are assigned to 2 -CH3 B6 H8 ” , a major decomposition product. The peaks indicated by vertical lines are assigned to remain ing CHgByH^^ • As in EyB.-^2 the resonances near 9.7 ? increase in size with decomposition. I I 4

FIGURE 44, 100 MHz Proton NMR Spectrum of [(CgHg)g PCH^^] [CHgByH^ % ], Boron-11 Atoms Spin

Decoupled, at -15 C after Warming to +10 C

CO REFERENCES

1. A. Stock, Hydrides of Boron and Silicon, Cornell University Press, Ithaca, New York, 1933.

2. P. L. Timms and C. S. G. Phillips, Inorg. Chem ., 297 (1964).

3. W. V. Kotlensky and R. Schaeffer, J. Amer. Chem. Soc., 8 £, 4157 (1958).

4. J. L. Boone and A. B. Burg, ibid., 8£, 1519 (1958).

5. J. L. Boone and A. B. Burg, ibid., 1766 (1959).

6 . J. L. Boone and American Potash and Chemical Corp., U. S. Pat. 3,110,565, (Nov. 12, 1963).

7. H. D. Johnson, II, and S. G. Shore, J. Amer. Chem. Soc., 93, 3798 (1971).

8 . H. A. Beall and W. N. Lipscomb, Inorg. Chem. , 1783 (1964).

9. J. Dobson and R. Schaeffer, ibid., 1_, 402 (1968).

10. R. A. Geanangel, H. D. Johnson, II, and S. G. Shore, ibid., 10, 2363 (1971).

11. H. D. Johnson, II, V. T. Brice, and S. G. Shore, ibid., 1^, 689 (1973).

12. A. B. Burg and R. Kratzer, ibid., 1^, 725 (1962).

13. K. Eriks, W. N. Lipscomb and R. Schaeffer, J. Chem. Phys., 754 (1954).

14. P. L. Hirshfeld, K. Eriks, R. E. Dickerson, E. L. Lippert, Jr., and W. N. Lipscomb, ibid., 56 (1958).

15. I. R. Epstein, J. A. Tossell, E. Switkes, R. M. Stevens and W. N. Lipscomb, Inorg. Chem., 10^, 171 (1971).

119 120 16. R. E. Williams, S. G, Gibbins and I. Shapiro, J. Chem. Phys., 333 (1959).

17. T. P. Onak, H. Landesman, R. W. Williams and I. Shapiro, J. Phys. Chem., 6 ^ , 1533 (1959).

18. J. D. Odom and R. Schaeffer, Inorg. Chem., 9^, 2157 (1970).

19. V. T. Brice, H. D. Johnson, II, and S. G. Shore, J. Amer. Chem. S oc., 9^, 6629 (1973).

20. J. B. Leach, T. Onak, J. Spielman, R. R. Reitz, R. Schaeffer and L. G. Sneddon, Inorg. Chem., 2170 (1970).

21. H. Steinberg and A. L. McClosky, Editors, Progress in Boron Chemistry, Vol. 1, Macmillan Co., New York, 1964, Chapter 10, R. Schaeffer.

22. W. N. Lipscomb, J. Inorg. Nuc. Chem., 1 (1959).

23. R. E. Williams, ibid ., 20, 198 (1961).

24. G. L. Brubaker, Ph. D. Thesis, The Ohio State University, 1971.

25. W. N. Lipscomb, Inorg. Chem., 1683 (1964).

26. J. C. Carter and N. L. H. Mock, J. Amer. Chem. S oc., 5891 (1969).

27. H. D. Johnson, II, Ph.D . Thesis, Tne Ohio State University, 1969,

28. H. D. Johnson, II, S. G. Shore, N. L. Mock, and J. C. Carter, J. Amer. Chem. Soc., 2131 (1969).

29. G. L. Brubaker, M. L. Denniston, S. G. Shore, J. C. Carter, and F. Swicker, ibid., 7216 (1970).

30. H. D. Johnson, II, V. T. Brice, G. L. Brubaker, and S. G. Shore, ib id ., 9±, 6711 (1972).

31. H. D. Johnson, II, R. A. Geanangel, and S. G. Shore, Inorg. Chem., 9, 908 (1970). 121 32. W. N. Lipscomb, J. Chem.. Phys., 170 (1958).

33. J. Rathke and R. Schaeffer, J. Amer. Chem. Soc., 3402 (1973).

34. J. Rathke and R. Schaeffer, Inorg. Chem., ÎJ_, 3008 (1974).

35. R. E. Williams and F. J. Gerhert, J. Amer. Chem. Soc., 82, 3513 (1965).

36. M. L. Denniston, Ph. D. Thesis, The Ohio State University, 1970.

37. M. Mangion, M. L. Denniston, J. R. Long, R. K. Hertz, W. R. Clayton, and S. G. Shore, Abstracts of Papers, 169th Meeting, American Chemical Society, Philadelphia, 1975.

38. D. F. Gaines, S. Hildebrandt, and J. Ulman, Inorg. Chem., 13, 1217 (1974).

39. V. T. Brice, H. D. Johnson, II, and S. G. Shore, Chem. Comm., 1128 (1972).

40. T. V. lorns and D. F. Gaines, Abstracts of Papers, 157th Meeting American Chemical Society, Minneapolis, 1969, p. INOR 030.

41. D. F. Gaines and T. V. lorns, J. Amer. Chem. Soc., 4571 (1970).

42. V. T. Brice and S. G. Shore, Chem. Comm., 1312 (1970).

43. A. Davison, D. D. Traficante and S. S. Wreford, ibid., 1155 (1972).

44. A. Davison, D. D. Traficante and S. S. Wreford, J. Amer. Chem. Soc., 25, 2802 (1974).

45. J. P. Brennan, R. Schaeffer, A. Davison and S. S. Wreford, Chem. Comm., 354 (1973).

46. D. L. Denton, Ph. D. Thesis, The Ohio State University, 1973.

47. D. L. Denton, W. R. Clayton, and S. G. Shore, to be published.

48. G. A. Guter and R. Schaeffer, J. Amer. Chem. S oc., 78,, 3546 (1956). 122

49. G. A. Guter and R. Schaeffer, Abstracts of Papers, 131st Meeting, American Chemical Society, Miami, 1957, p. 3R.

50. W. V. Hough and L. J. Edwards, Abstracts of Papers, 133rd Meeting, American Chemical Society, San Fransisco, 1958, p. 28L.

51. M. F. Hawthorne and J. J. Miller, J. Amer. Chem. Soc., 80, 754 (1958).

52. B. Siegel, I. L. Mack, J. U. Lowe, Jr., and J.Gallaghan, ib id ., 8^, 4523 (1958),

53. R. W. Atteberry, J. Phys. Chem., 1458 (1958).

54. G. W. Schaeffer, J. J. Burns, T. J. Klingen, L. A. Martencheck and R. W. Rozett, Abstracts of Papers, 135th Meeting, American Chemical Society. Boston, 1959, p. 44M.

55. M. F. Hawthorne, A. R. Pitochelli, R. D. Strahm and J. J. Miller, J. Amer. Chem. S oc., 1825 (1960).

56. R. T. Holtzman, R. L. Hughes, I. C. Smith and E. W. Lawless, Production of Boranes and Related Research, Academic Press, New York, 1967.

57. S. Hermanek and H. Plotova, Collect. , Czech. Chem. Commun., 1639 (1971).

58. L. G. Sneddon, J. C. Huggman, R. O. Schaeffer and W. E. Streib, Chem. Comm., 474 (1972).

59. R. W. Parry and L. J. Edwards, J. Amer. Chem. S o c., 8J^, 3554 (1959).

60. T. P. Onak, G. B. Dunks, I. W. Searcy and J. Spielman, Inorg. Chem., i5, 1465 (1967).

61. D. F. Gaines and T. V. lorns, J. Amer. Chem. Soc., 89, 3375 (1967).

62. R. A. Geanangel and S. G. Shore, ibid., 6771 (1967). 123

63. R. A. Geanangel. Ph. D. Thesis, The Ohio State University, 1968.

64. G. Kodama, U. Englehardt, C. Lafrenz and R. W. Parry, J. Amer. Chem. Soc., 407 (1972).

65. V. T. Brice, H. D. Johnson, II, D. L. Denton, and S. G. Shore, Inorg. Chem., 11_, 1135 (1972).

6 6 . V. T. Brice and S. G. Shore, ibid., _12, 309 (1973).

67. C. Hollander, Ph. D. Thesis, The Ohio State University, 1975.

6 8 . A. C. Bond and M. L. Pinsky, J. Amer. Chem. Soc., 7585 (1970).

69. M. L. Pinsky and A. C. Bond, Inorg. Chem., 1^, 605 (1973).

70. H, D. Johnson, II, and S. G. Shore, J. Amer. Chem. Soc., 9^, 7586 (1970).

71. I. S. Jaworiwsky and S. G. Shore, Abstracts of Papers, 166th Meeting, American Chemical Society, Chicago, 1973, p. INCR 084.

72. I. Jaworiwsky, Ph. D. Thesis, The Chio State University, 1975.

73. E. L. Muetterties, Accounts Chem. Res., 266 (1970).

74. G. Kodama, J. E. Dunning and R. W. Parry, J. Amer. Chem. Soc., 91, 3372 (1971).

75. L. J. Edwards and J. M. Makhlouf, ibid., 4728 (1965),

76. F. P. Clsen, R. C. Vasavada and M . F. Hawthorne, ibid., 90, 3946 (1968).

77. R. E. Williams, Inorg. Chem., 10, 210 (1971).

78. V. T. Brice, Ph. D. Thesis, The Chio State University, 1971.

79. J. B. Leach and T. Cnak, J. Magn. R es., £, 30 (1971). 124

80. H. C. Brown, P. F. Stehie and P. A. Tiemey, J. Amer. Chem. Soc., 79, 2020 (1957).

81. V. D. Aftandilian, H. C. Miller, G. W. Parshall and E. L. Muetterties, Inorg. Chem., 734 (1962).

82. M. F. Hawthorne and P. A. Wegner, J. Amer. Chem. Soc., 896 (1968).

83. D. F. Gaines, ibid., 6503 (1969).

84. O. Hollander, R. W. Clayton, and S. G. Shore, Chem. Comm., 603 (1974).

85. D. F. Gaines and T. V. lorns, J. Amer. Chem. S oc., 89, 4249 (1969)

8 6 . D. F. Gaines and T. V. lorns, ibid., 90^, 6617 (1968).

87. D. F. Gaines and J. Ulman, Inorg. Chem. , 1_^, 2792 (1974).

8 8 . A. B. Burg and H. Keinen, ibid., 7_, 1021 (1968).

89. J. C. Calabrese and L. F. Dahl, J. Amer. Chem. Soc., £3, 6042 (1971).

90. E. Amberger and P. Leidel, J. Organometal. Chem. , %8 , 345 (1969).

91. V. T. Brice and S. G. Shore, J. Chem. S oc., Dalton Trans., 334 (1975).

92. R. E. Dickerson and W. N. Lipscomb, J. Chem. Phys., £7, 212 (1957).

93. A. Quayle, J. Appl. Chem., £, 395 (1959).

94. R. W. Schaefer, K. H. Ludlum and S. E. Wiberley, J. Amer.Chem. S oc., 81, 3157 (1959).

95. S. G. Gibbins and I. Shapiro, ibid., 81, 2968 (1960).

96. J. F. Ditter, J. R. Spielman and R. E. Williams, Inorg. Chem., 1, 118 (1966). 125

97. T. P. Fehlner and W. S. Koski, J. Amer. Chem. Soc., 8j6, 1012 (1964).

98. A. B. Bayliss, G. A. Pressley, Jr., M. E. Gordon and F, E. Stafford, ibid., M , 929 (1966).

99. J. Dobson, R. Maruca and R. Schaeffer, Inorg. Chem., 2161 (1970).

100. W. N. Lipscomb, J. Phys. Chem., 1064 (1961).

101. W. N. Lipscomb, Boron Hydrides, W. A. Benjamin, Inc., New York, 1963.

102. A. Stock and C. Massenez, Chem. Ber. , ;45, 3539 (1912).

103. T. P. Fehlner and W. Koski, Abstracts of Papers, 145th Meeting, American Chemical Society, New York, 1973, p. BN.

104. D. F. Gaines and R. Schaeffer, Inorg. Chem ., 2, 438 (1964).

105. A. L. Collins and R. Schaeffer, ibid., 2153 (1970).

106. J. Long, Ph. D. Thesis, The Ohio State University, 1973.

107. R. T. Sanderson, Vacuum Manipulation of Volatile Compounds, John Wiley and Sons, Inc. , New York, 1948.

108. T. Onak and J. Spielman, J. Magn. Res., 122 (1970).

109. E. Wiberg and coworkers, F.I.A.T. , Review of German Science, 1939-1946, Inorg. Chem. Part I, pages 235-238.

110. J. Dobson, Ph. D. Thesis, Indiana University, 1967.

111. L. H. Hall, V. V. Subanna, and W. S. Koski, J. Amer. Chem. Soc., 8 6 , 3969 (1964).

112. T. P. Onak and F. J. Gerhart, Inorg. Chem., 1^, 742 (1962).

113. A. Michaelis and H. V. Soden, Justus Liebigs Ann. Chem. , 229, 295 (1885).

114. H. C. Brown, J. Amer. Chem. Soc., 374 (1945). 126

115. W. N. Lipscomb, Accounts Chem. Res., 257 (1973).

116. P. M. Tucker, T. Onak and J. B. Leach, Inorg. Chem ., 2, 1430 (1970).

117. J. Ragaini, private communication.