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8703628

Wermer, Joseph Raymond

PREPARATION AND REACTIONS OF ANIONS DERIVED FROM PENTABORANE(9); PREPARATION OF NEW METALLABORANES

Ohio University Ph.D. 1986

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PREPARATION AND REACTIONS OF ANIONS DERIVED FROM

PENTABORANE(9 ); PREPARATION OF NEW METALLABORANES

DISSERTATION

Presented in Partial Fulfillment of the Requirements for

The Degree of Doctor of Philosophy in the Graduate

School o f the Ohio State U niversity

By

Joseph Raymond Wermer, B.A., M.S.

The Ohio State U niversity

1986

Reading Committee: Approved by:

Dr. Eugene P. Schram

Dr. Daniel L. Leussing

Dr. Sheldon G. Shore

Advisor

Department of Chemistry to Mary,

Michael Joseph and Daniel John

i i ACKNOWLEDGEMENTS

I wish to thank the Army Research Office, Durham, North Carolina for financial support. I also wish to thank Professor Shore for his help and guidance in this project. I am especially thankful to my wife, Mary, for her understanding support during my graduate studies. Special thanks are also extended to Dr. Steven Lawrence and

Mr. Thomas Getman who helped me a great deal with my research. I wish also to acknowledge the help o f other members of the Shore research group, especially Ms. Jeanette Krause who helped me to prepare th is manuscript. Finally, I wish to thank Kathy Curry for her patience in typing this dissertation. VITA

November 5, 1954 Born - M ontpelier, Ohio

1978 B.A. (German), The College of Wooster, Wooster, Ohio

1979-1980 Graduate Teaching Associate, Department of German, The Ohio State U nive rsity, Columbus, Ohio

1980-1983 Graduate Teaching Associate, Department of Chemistry, The Ohio State U n ive rsity, Columbus, Ohio

1983-1986 Graduate Research Associate, Department of Chemistry, The Ohio State U n ive rsity, Columbus, Ohio

1984 M.S. (Chemistry), The Ohio State U n ive rsity, Columbus, Ohio

PUBLICATIONS

Wermer, J. R.; Shore, S. G. "Classical Pentaborane(9) Chemistry for the Preparation of Higher Boron Hydride Systems; Some New Aspects of the Chemistry of Pentaborane(9) and Decaborane(14)," Molecular Structures and Emergencies, accepted for publication.

Wermer, J. R.; Hosmane, N. S.; Siriwardane, U.; Alexander, J. J.; Shore, S. G. "Synthesis and X-ray Crystal Structure of arachno- 6 - ((CH3)3Si )-6,9-CoBqH 1 3 through a Cage-Expansion Reaction o f jTi_do- 2,3-((CH?)3 Si)g-2,3-CgB/|H6," Inorg. Chem., 1986, 25, 4351.

Lawrence, S. H.; Wermer, J. R.; Boocock, S. K.; Banks, M. A .; K e lle r, P. C.; Shore, S. G. "Pentaborane(9) as a Source fo r Higher Boron Hydride Systems. A New Synthesis o f nido- 5 , 6 -(CH

iv VITA (CONTINUED)

FIELDS OF STUDY

Major Field: Inorganic Chemistry

Studies in Non-Metal and Organometal1ic Chemistry: Professors Sheldon G. Shore, Eugene P. Schram, and Andrew W ojcicki.

Studies in Transition Metal and Bioinorganic Chemistry: Professors Daryle H. Busch, Bruce E. Burster, Daniel L. Leussing, and Devon W. Meek.

v TABLE OF CONTENTS

Page

DEDICATION i i

ACKNOWLEDGEMENTS i i i

VITA iv

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF ABBREVIATIONS xiv

INTRODUCTION 1 I. H isto rica l Background to the Preparation of the Boron Hydrides. 1

I I . P ractical Syntheses o f Tetraborane(lO), Pentaborane(ll), Hexaborane(lO), and Decaborane(14). 3

III. Physical Properties and Stabilities of the Boron Hydrides. 6

IV. Structures of the Boron Hydrides. 8

V. Bronsted Acidities of the Boron Hydrides. 11

VI. The Chemistry of Pentaborane(9). 13

A. Reactions w ith Lewis Bases. 13

B. Reactions w ith Strong Bronsted Bases. 14

C. Halogenation and Alkylation Reactions. 18

D. Reaction of Pentaborane(9) with Alkali Metals. 24

v i V II. Statement o f the Problem. 2b

RESULTS AND DISCUSSION 28

I. Reduction of Pentaborane(9) with Alkali Metals to Form the Nonahydropentaborate(2-) Dianion. 28

A. Preparation and Characterization. 28

B. Protonation of LB^Hy]2“ with HC1 and HBr. 3b

C. Reaction of LBgHg]^- w ith B£Hg and BgHg. 39

D. Other Reactions of Alkali Metal Napthalides and Pentaborane(9). 42

II. Production of the Tetradecahydrononaborate(l-) Anion from Deprotonation Reactions of Pentaborane(9) 44

A. Reaction of Pentaborane(9) with Sodium and Potassium Hydride. 44

B. The Reaction of Pentaborane(9) with the Borohydride Ion. 55

C. Preparation of the Tetradecahydrononaborate(l-) anion from Pentaborane(9). 60

D. The Preparation of Decaborane(14) from Pentaborane(9). 62

E. Preparation of j]j-0ctadecaborane(22) from Pentaborane(9). 6 8

F. Other Related Reactions. 69

III. Formation of Triosmium Carbonyl Methylidyne D erivatives o f Boranes and Carboranes. 71

A. Preparation of Derivatives of Pentaborane(9) 71

B. Preparation of Derivatives of Decaborane(14) 76

C. Preparation of Derivatives of ^-Carborane 78

EXPERIMENTAL 8 b

I . Apparatus and Equipment. 85

A. Vacuum Line. 8 b

B. Dry Box. 8 6 v ii C. Reaction vessels. 8 6

D. Nuclear Magnetic Resonance Spectra. 87

E. Mass Spectra 90

F. Infrared Spectra. 90

G. High Pressure LiquidChromatography. 91

I I . Reagents. 91

III. Reactions. 96

A. Reaction of B^Hg w ith two equivalents o f potassium napthalide. 96

B. Preparation o f the crown ether complex [K(dibenzo-18-crown-6)]2B5Hg. 97

C. "One-pot synthesis" o f BgHji from K 2 [BgHg] by protonation with HC1 in Butane. 97

D. Preparation of ®5«U from C s2[B 5H g ] by protonation with liquid HC1. 98

E. Preparation of B 5 H jj from K 2 [B 5 Hg] by protonation with liquid HBr. 99

F. Reaction of BcHg with 1 equivalent of Na+(CioH8r . 100 G. Reaction of BcHg with 1/2 equivalent of

Na+(cioH8)‘ . 1 0 0 H. Low Temperture Reaction of [(n-C/iHobNXBcHo] w ith B5 Hg. 101

I. Low Temperature Reaction o f K[BgHg] with B^Hg. 102

J. Reaction of B^Hg with Li[BH^]. 102

K. Preparation of K[Bj j H ^ ] from B^Hg. 103

L. Attempt to prepare K[BiiH^] by a stoichiometric reaction of BgHg with Kfl. 104

M. Preparation of B^H 2 2 isomers from CB^H^]". 104

N. Improved preparation of B^qH ^ from B^Hg. 10b

0. Preparation of ^v-B^gH 2 2 from BgHg. 109 v i i i P. Reaction of BgH^Q with one-half equivalent of KH in glyme. 1 1 0

Q. Preparation of (u-H) 3 (C0 )g 0 s 3 (p^-C-l-B^Hg). Ill

R. Preparation of (u-H^COjgOs^p-j-C-^BgHj^). 112

LIST OF REFERENCES 114

ix LIST OF TABLES

Table Page

1. Some physical properties of selected boron hydrides. 7

2. A Comparison of Properties and Reactivities of [BjjHg] and [BgHg] . 3 4

3. Boron-11 NMR Chemical S h ifts , Coupling Constants and Assignments 9 for jr-BjgF^. 107

4. Boron-11 NMR Chemical S h ifts and Coupling Constants

fo r _L~Bi 3 H2 2 - 108

x LIST OF FIGURES

Figure Page

1. One possible mechanism fo r polyhedral expansion from diborane( 6 ) pyrolysis. 4

2. Cross-sectional view of a Pyrex hot-cold reactor. 5

3. The molecular structure of diborane( 6 ). 9

4. Structural classes of boron hydride clusters. 12

5. Structures and boron-11 NMR spectra of BcHg and [B5H8r 15

6 . Higher boranes and carboranes derived from [B gH ^] . 17

7. The structure and boron-11 NMR spectrum for [B9 H14] - . 19

8 . The structure of l, 2 '-(B 0 Hg)j>. 23

9. Infrared spectrum of Rb 2 [B 5 Hg] (nujol mull). 30

10. Boron-11 NMR spectrum o f Na 2 [B 5 Hg] in glyme. 32

11. Expected stru ctu ra l change in the boron framework by a two-electcon reduction of nido-B^Hg to arachno-CB^Ho] . 33

12. ^H NMR spectrum of the reduction of pentaborane(9) with sodium napthalide-dg(a) vs pure napthalene-dg(b). 36

13. Boron-11 NMR spectrum o f the CH 2 CI2 soluble material from the protonation of KgCBgHg] with HC1 in CH2 CI2 - a = 8 5 ^ 1 1 * 38

14. Boron-11 NMR spectrum o f BcH^j obtained from the protonation of I^CBgHgJ with HC1 in butane. 40

x i 15. Gas phase (12 to rr) infrared spectrum o f BgH,. obtained from the protonation of ^[BgHg] with HC1 in butane.

16. Boron-11 NMR spectrum o f the reaction of ^[BgHg] with B2 Hg in THF.

17. Boron-11 NMR spectrum o f the reaction of 1.8 equivalents of BgHg with sodium hydride in glyme a fte r 1 2 hours.

18. Boron-11 NMR spectrum of the low temperature reaction of [(n-Bu) 4 N][BgHg] w ith BcHg in glyme showing The presence of the CBinH17^" intermediate species, a = BgHg; b = [BgHg]- ; c = [BgHj^]- ; d = [BgH]^]- ; e = [BjqHjj] .

19. Sequential boron-11 NMR spectrum of the low temperature reaction of [(n-Bu) 4 N][BcHg] with BcHq in glyme. a = BeHq ; TT = [B c H g ] ; c = [BgR14r ; d = [B 6 Hn ] a; e = [B 1 0 R17] " .

20. Boron-11 NMR spectra o f the decomposition of

K[B6 hi i ] - 21. Boron-11 NMR spectrum o f the reaction o f 1.5 equivalents of BgHg with KH.

22. Boron-11 NMR spectrum o f the reaction o f BcHg with Li[BH4] in glyme. a = [BqH14] “ , b = [BgHg]", c = compound _I.

23. ^B -^B COSY experiment for the reaction of BgHg with Li[BH4] in glyme. Signals marked with an asterisk (*) are from [BqHi4]~ and [BgHg]". A proposed structure fo r [BgR^g]" is shown.

24. Boron-11 NMR spectrum o f KC B^H ^] in glyme.

25. Boron-11 NMR spectrum o f the B^gHgp isomer mixture obtained from pyrolysis o f [ B u H ^ j .

26. Boron-11 NMR spectrum o f Jj-BigHgg*

27. Boron-11 NMR spectrum and assignments fo r jT-BjgH 2 2 »

28. ^B -^B COSY experiment for _n.-BigH 2 2 .

29. Boron-11 NMR spectrum of the reaction of 2 BgH 1 0 + KH in THF. a = [B j^H j4] ; b = [BgH^4] . 30. Molecular structure of [(r -H^COjgOsg^ 3 -CO)]3 (B3 O3 ) . 72

31. Boron-11 NMR spectrum of the reaction of BgHg with [(p-HlglCOjgOsgCu 3 “C0 )] 3 (B3 O3 ) in the presence of BF 3 . 74

32. Boron-11 NMR spectrum o f the a p ic a lly substituted (g- H)g(C0)g0s3(g 3 -C-l-BgHg). 75

33. Ft-ICR mass spectrum and proposed structure o f (p- H)g(COjgOSgfgg-C-l-BgHg). 77

34. FT-ICR mass spectrum o f (p-H) 3 (C0 )g 0 s3 (g g ^ B g H n ) . 79

35. Boron-11 NMR spectrum of (p-H ) 3 (C0 )g 0 s3 (gs-CgBgH^). 81

36. Boron-11 NMR spectrum and molecular structure o f ^-carborane. 82

37. ^B-^B COSY experiment for o^-carborane. 83

38. ^B-^B COSY experiment for (p-H^COjgOsgfpg-CgBgHjj). 84

39. Vessel used to prepare NMR samples o f a ir-s e n s itiv e materials. 8 8

40. A vacuum extractor. 89

41. Boron-11 NMR spectrum of an attempt to prepare [B 1 1 H1 4 ]" using a stoichiometric quantity of pentaborane(9). BcHq :MH = 2.2:1. a = [ B n iH 1 4 ] " ; b = [BgH14] - . 105

x i i i LIST OF ABBREVIATIONS

jt-Bu _n-butyl, _n-C^Hg-

Et ethyl , C2 H5- glyme 1 , 2 -dimethoxyethane, H3C0CH2CH20CH3

L Lewis base

M metal atom

Me m ethyl, CH3-

NMR nuclear magnetic resonance ppm parts per million—unit for chemical shift in NMR spectra.

THF tetrahydrofuran

x iv INTRODUCTION

I. Historical Background to the Preparation of the

Boron Hydrides

The firs t definitive account of the preparation of boron hydrides

(boranes) appeared in 1912 in a report by Stock and Massenez.* By reacting magnesium boride with hydrochloric acid, they produced a mixture of volatile, air-sensitive compounds. The mixture required tedious separation techniques to obtain reasonably pure materials. p Over a period of about twenty years, Stock and his co-workers isolated and characterized seven boron hydrides which he classified into two series, the BnHn+g series (B^Hjq, BgH^, and BgH^)* This represented a remarkable achievement, since it required Stock to firs t invent the glass high vacuum line and to develop techniques for working with small amounts of highly air-sensitive materials.

Although Stock's original preparation was later improved with the use of phosphoric acid, the yields of product never exceeded 1 1 % and s till required tedious separation procedures. The firs t major breakthrough in the synthesis of boron hydrides came in the early

1930's when Schlesinger and Burg obtained diborane( 6 ) , B2 Hg, in about

75% yield by passing boron trichloride and hydrogen gas through a high O voltage electric discharge . Modifications of this technique provided routes to other boron hydrides as well^. Although the total amount of

1 diborane ( 6 ) produced was s till quite small, it was sufficient to allow detailed studies on the reactivities of these materials.

Substitution reactions were developed to produce alkylated derivatives of diborane( 6 )®»® and other higher boron hydrides.

Cleavage reactions using Lewis bases led to the isolation and characterization of a number of borane derivatives including trim e th yl amine borane, carbon monoxide borane, OCBH 3 ,® and dimethyl ether borane, ( 0 1 1 3 ) 2 0 8 1 1 3 .® The discovery of metal borohydrides®"** in 1940 was one of the most notable outcomes of this study. The use of metal borohydrides led to later, high-yield

1 O preparations of B 2 Hg.

Pyrolysis reactions involving diborane( 6 ) using hot-cold reactor techniques provided routes to many of the other neutral borpn hydrides, including B^H^q, BgHg, BgHjj, and B jqH ^.^ The high energy fuels projects of the 1950's brought process for the preparation of diborane( 6 ), pentaborane(9), and decaborane(14) into industrial scale production. Although these programs were la te r scrapped, they le f t behind large reserves of BgHg and B 1 QH1 4 1 3 which were important for the further development of this area of chemistry.

The mechanism of higher borane formation from B 2 H0 pyrolysis has been o f considerable in te re s t. 14-16 There seems to be agreement th a t the firs t step in the pyrolysis is the formation of a B 3 Hg species, however, it is not clear whether this is followed firs t by dissociation of B 2 Hg in to two BH 3 fragments (equations 1_ and 2) or whether the formation of B 3 Hg is a concerted process (equation _3). 3

» 2 BH3 (1)

(2 ) or

* b3 h9 + bh3 (3)

There seems to be general agreement th a t the cage expansion to form higher borane species is the result of a series of BH 3 a ddition or BH 3 transfer steps. Figure _1_ depicts one possible mechanism for the polyhedral expansion from B3Hg pyrolysis. Many of the postulated intermediates including B 3 H y ,^ B^Hg,*® and BH3, ^ " ^ have been observed using mass spectroscopy giving some credence to this mechanism. For the present discussion, however, i t is noteworthy th a t the expansion of the boron cage takes place through a series of reactions which add one cage atom at a time to the cluster.

II. Practical Syntheses of Tetraborane(lO), Pentaborane(ll),

Hexaborane(lO), and Decaborane(14)

As mentioned above, traditional syntheses of a number of boron hydride systems including B / ^q, BgH^, BgH^0, and BjqH ^ have been

1 *? based on pyrolysis of diborane( 6 ) in hot-cold reactors. Figure^ shows a cross-sectional view of a Pyrex hot-cold reactor. During the operation of these reactors, the inner wall of the reactor is heated w hile the outer wall is immersed in a cooling bath. Boranes are pyrolyzed on the inner wall and the products condense on the outer wall of the vessel. A number of boron hydrides can be obtained in B2H6 BHXl (B3 H7 ) < • * - =* (B3H9)

(B4 H8) < - - b 4 H10 BH BH

H B

Figure 1. One possible mechanism for polyhedral expansion from diborane( 6 ) pyrolysis. Teflon Stopcock

to vacuum line

to m a n o m e te r

Figure 2. Cross-sectional view of a Pyrex hot-cold reactor. good yield by varying such parameters as the reactor dimensions,

pressure, and the temperatures of the inner and outer wall. Good

y ie ld s of B4H jq ^ “ 24 anc| BgH ^ 5 have also been achieved by the

protonation of salts of [BgHg]" and [BgHjg]", respectively. One of

the firs t useful routes to BgH^g was obtained by treatment of the

[ B g H n ] " anion with B g H g , producing B g H jg and the borohydride anion as

products.^® An improved preparation of BgH^g was later developed

0 7 based on the thermal decomposition of KCBgHjgBr]. These routes to

B gH io are p a rtic u la rly useful because they employ BgHg, a readily

available material, as the primary starting material.

More recently, systematic routes to most of the lower boron

hydrides have been developed utilizin g hydride abstraction

OO 01 reactions. x Using th is method, B-^qH^ can be prepared in high yield from [ B g H ^ ] " which in turn can be readily obtained from BgHg.

Presently, the best no n-p yro lytic methods fo r making BgHjj have been based on [B 4H g ]" and [ B g H i g ] - , substances which are best produced from

*28-30 Tetraborane(lO)» B 4 H^q, is thermally unstable and not commercially available.

III. Physical Properties and Stabilities of the

Boron Hydrides

As pure compounds, the boron hydrides are colorless, volatile, and generally highly toxic materials. Table l_ gives some physical data fo r a number of these compounds. The lower boron hydrides such as BgHg, B^Hjq, BgHg, and BgH^g are spontaneously flammable in air and Table 1. Some physical properties of selected boron hydrides . 3

Boron Hydride boiling point melting point

b2 h6 -93°C -165.5°C

B4H10 18°C -120°C

B5 H9 57°Cb -4 6 .8°C

B5H11 63°Cb -122°C

B6H10 108°C -62°C

B10H14 231°C 99.5°C

aS hriver, D. F. "The Manipulation of A ir-S e n sitive Compounds," McGraw- H ill Book Company, New York, 1969.

^Extrapolated values. rapidly hydrolyzed by water. Many of the lower boron hydrides exhibit limited thermal stability as well. At the other end of the scale,

B1 0 H1 4 and BjgH 2 2 are unaffected by air or water and are quite thermally stable as well. The properties of BgHg lie somewhere in the middle, being very a ir se n sitive while showing high thermal s ta b ility .

IV. Structures of the Boron Hydrides

The boron hydrides have been of considerable in te re s t because o f their apparent electron deficient character. In other words, there are too few electrons to explain the bonding in these compounds using conventional two-electron, two-center ( 2 e - 2 c) bonds such as those occurring in hydrocarbons. Diborane( 6 ), B2 Hg, is the classic example of this dilemma. Early attempts to explain the bonding in diborane( 6 ) centered on treating it as a structural analog of ethane, C 2 Hg.

•3 0 Indeed early structural studies by electron diffraction supported the conclusion that B2Hg had an ethane-like structure. A number of attempts were made to explain the apparent electron deficiency arising from this model.33-35 nowever> others such as P itzer^ and Longuet-

0 7 OO Higgens * 0 proposed a structure having bridging hydrogen atoms. oq 4,n Later electron diffraction and X-ray crystallographic studies showed beyond doubt that B2Hg had a bridged structure having four terminal and two bridging hydrogens. The structure of B2Hg is shown in figure_3. Each bridging hydrogen participates in a three-center, two-electron (3c-2e) bond in which one pair of electrons is shared between three atomic o rb ita ls . 9

H

H-

Figure 3. The molecular structure of di'orane(6). 10

Lipscomb and co-workers determined the structures of a number of boron hydrides beginning w ith the structu re of BgHg in 19514* and found that the description of bonding used for B 2 Hg could be extended to many other boron hydride systems as w e ll . 4 ^ * 4 8 The bonding in these systems was considered to be a combination of 2c-2e and 3c-2e bonds. In some cases such as BgHg and BgH^g, a number o f resonance forms of the bonding description were invoked to explain the lack of asymmetry which would be expected from the combination of 2 c- 2 e and

3c-2e bonds. Williams recognized that the structures of the boron hydrides could be related to triangular-faced polyhedra . 4 4 , 4 8 From

Williams' and Lipscomb's observations, Wade 4 ® - 4 8 was able to relate molecular formulas to known structures of boron hydride and transition metal clusters. He devised empirical rules to directly relate observed structures to the number of skeletal electrons in the molecule, i.e . the number of electrons free to bind the cluster framework. For boron hydride clusters, the number of skeletal electron pairs is l/ 2 ( 2 m+n+p) for clusters of the general formula

[BmHm+n ]p"* These observations, commonly known as "Wade's Rules," show that a molecule having_n skeletal electron pairs has a structure which is based on a polyhedron having n-1 v e rtic e s . For example, BgHg has 7 skeletal electron pairs, and is thus related to the 6 -vertex octahedron. Since there are 5 vertex atoms in B gH g, the structure is an octahedron with one missing vertex, or a square pyramid. For

BgHn, there are 8 skeletal electron pairs which means that the structure is based on the pentagonal bipyramid. However, the number of vertices remains 5, so the actual structure is derived from the 11

pentagonal bipyramid with two missing vertices. The addition of an

electron pair in going from BgHg to BgHjj, in this case in the form of two hydrogen atoms, caused the stru ctu re to open up.

Four stru ctu ra l classes o f boron hydrides are now known and classified according to their molecular formulas and structures . ^ 9

These are commonly known by the Greek p re fixe s: c lo so -, n id o -, arachno-, and hypho-. A fifth possible class is the conjuncto-class which has structures formed by linking two of the preceeding types of clusters together. The four classes are formally related by series of

redox processes:

2 e” 2 e" 2 e~ closo- * nido- * arachno- hypho-

The nido- and arachno-classes correspond to Stock s BnHn+4 and ®n^n + 6 series, respectively. The closo-boranes have the general formula

[BnHn]2" and the hypho- class has the general formula BnHn+8. There are cu rre n tly no known examples of neutral hypho-boranes, although a few hypho- anions are known. Figure_4 shows the relationship between these classes and th e ir re la tio n sh ip to "Wade's Rules."

V. Bronsted Acidities of the Boron Hydrides

Although the hydrogen atoms in the neutral boron hydrides are generally considered to be hydridic in character, it has been known for some time that these compounds could also function as Bronsted 12

NIDO

+ > a r a c h n o

Figure 4. Structural classes of boron hydride clusters. 13

acids. Decaborane(14), was shown to function as a monoprotic

Bronsted acid in 1956.5B Many other lower boron hydrides, including

their halo- and alkyl- derivatives, have more recently been shown to

function as Bronsted acids. Among these are B4H10,25»5/* B g H g ,5 5 - 5 7

b5^11’2^ b6^1 0 *^'^ b6h12»2^ and j>BgH^.5B Within a given series of boron hydrides (e.g. nido- or arachno-series) Bronsted acidity

increases as the size of the boron cage increases. This gives the

following order of acidities:

BgHg < B6H10 < B10H14 < _n-B18H22

B4 H1 0 < b5H11 < B6H12

In general, the arachno- series is more acidic than the nido- series, so th at B 4 H1 Q is more acid ic than BgH^g.

V I. The Chemistry of Pentaborane(9)

A. Reactions with Lewis Bases. Many of the investigations

into the chemistry of pentaborane(9), B gH g, have centered on its acidic character. In the presence of Lewis bases such as trialkyl or triaryl phosphines 5 * - 5 7 and amines55-7*, Lewis acid-Lewis base adducts are formed. In some cases, the adduct formation can be reversed by applying vacuum to the system. The formation of these adducts involves the a ddition of two Lewis base molecules to BgHg to produce adducts of the general formula BgHgL 2 (L = PR3 , NR3 ). The Lewis base adds electrons to the boron skeleton, effectively reducing it to a 14 hypho- species. This has been confirmed by the X-ray structural determination of BgHg(P(CH 3 ) 3 ) 2 .®*

B. Reactions with Strong Bronsted Bases. Another aspect of the chemistry of pentaborane(9) has centered on its ability to function as a Bronsted acid. In the presence of strong Bronsted bases such as sodium or potassium hyd rid e,55»57»58,72 ammonia , 7 3 , 7 4

NaCC(CH 3 ) , 7 2 or organolithium compounds ,5®’37,72,73 BgHg is deprotonated to form the octohydropentaborate(l-) anion, [BgHg]- . The deprotonation reaction has also been extended to numerous derivatives of BgHg such as 1-C1B 5 H8, 1-BrBgHg, l-(CH 3 )-B 5 Hg, 2-{CH 3 )-B 5 Hg, and 1-

( ( CH3 ) 3 Si)-BgHg . 7 5 The structures and boron-11 NMR spectra of BgHg and [BgHg]" are given in figure _5.

Deprotonation of BgHg occurs by removal of a basal bridge proton, producing a boron-boron bond which is subject to insertion by electrophilic reagents. Thus 1/2 equivalent of B3Hg readily adds to

[BgHg]", forming the [BgH^]" anion which is believed to contain a BH 3 nc nc group bridging two basal boron atoms. ’ Other in se rtio n reactions of this type involving heteroatoms are also known. For example,

Gaines and co-workers successfully introduced a trim eth yl s ily l group into the basal bridging position to form u-((CH 3 ) 3 Si)-BgHg. Similar d e riva tive s were formed containing group IV substituents such as

(CH3 ) 3 Ge, (CH 3 ) 3 Sn, and (CH 3 ) 3 Pb. 7 7 , 7 9

Alkali metal salts of [B g H g ]" do not possess the high thermal stability of the conjugate acid, BgHg, and are unstable at room 15 Structure and ffB NMR Spectra of B 5H9

p 2-5 Undacouplad 6= -13.3 ppm

JI^B-’Hlsiei Hz 1*1 Hzl

B, 6= -53.2 ppm Jl11B-1HI=173 Hz I l±1 HzJ

Structure and 11B NMR Spectra of [B 5H8]'

B 2 -5 6= -17.1 ppm j ,11b .1H |=134 H z 1*1 Hzl

B,

6 s -53.0 ppm JI^-Vl^lSO Hz Jt 1*1 Hzl

Figure 5. Structures and boron-11 NMR spectra of B^Hg and LByHy] 16 temperature. The [BgHg]" anion is noticeably more stable both in solutions and in the solid state as tetraalkylammonium , 8 8 81 81 tetraalkylphosphonium, or tetraalkylarsonium salts. Within 24 hours at room temperature, K[BgHg] is nearly completely decomposed, producing primarily [BgH^]", [BgHg]", [BH4]", and unidentified cc 70 on species as decomposition products. * * The tetradecahydrononaborate(l-) anion, [BgHj4]“ is a particularly desirable product since it is stable in air and since it has been shown to be an useful precursor in the synthesis of a number of higher boron hydride and carborane systems including BjqH 1 4 , ^ 8 " 3 1 BgH ^ 2 , 8 3 j_-

b9H15»84,85 b 9 h1 3 l »31,6° JL-b18h22»31,6° and_nido-5,6-RR'-5,6-C 2 BgH 1 0 carboranes . 3 1 , 8 4 Figure 6 _ illustrates routes to a number of higher boranes and carboranes from [BgHj4]". In addition, the [BgH^]" anion has also proved to be a useful reagent for the preparation of many metallaboranes . 8 8 - 9 8 The original preparation of the [BgH^]" was based on base degradation of BjqH^, followed by acid hydrolysis of the [B^H^gOH]^- intermediate to form [BgH14]", boric acid, and water . 9 8 This method is s till widely employed.9^ Savory and

Wall bridge 8 4 found that this anion could also be produced in good yield from the reaction of a 1 : 1 molar ra tio o f BgHg and sodium hydride in glyme. This is essentially a decomposition reaction of

[B gH g]", since this anion is formed very rapidly from BgHg and NaH in glyme. Another preparation involved the reaction of equimolar ratios of BgHg and the [BH4] “ io n . 9 8 , 9 9 Both of these preparations provided

[BgHi4]" in moderate yields (40-60%). More recently, Toft ^ 8 and

Lawrence 1 8 8 found th a t [BgHj4] " could be produced in good yie ld s (ca. 1.8 B ,H , + MH

s > \

+ HCI Et,0 B10H1 0 n 14

OEt • -B9 H15

+ RC =CR' \ + L

R

B8H)2

B 5, 6 —RR'-C7 B,H 10

Figure 6 . Higher boranes and carboranes derived form LB 75%) from the room temperature reaction of BgHg with alkali metal hydrides (sodium or potassium hydride) in a 1 . 8 : 1 molar ratio

(BgHg:MH). Although neither the formation of [BgH^]” nor the formation of the minor species is understood, it was assumed that the firs t step was a simple deprotonation of BgHg to form [ B g H g ] " , since this was known to be a fast process.55,57,58,72 Syntheses of [BgH^]" from BgHg suffer from the fact that the [ B g H ^ ] " product is only about

75% pure, the main impurities being [B^H]^]", [BgHg]", and at least one unidentified species. However, methods for extracting and purifying the product obtained from this reaction have been developed to minimize th is problem.31*100

Although the X-ray crystal structure 1 0 1 of C s[B gH ^] indicates the presence of three BH 2 groups, no triplets are observed in the boron-11 NMR spectrum . 1 0 1 In fact, the spectrum is much simpler than would otherwise be expected, showing only three doublets of equal intensity. Using a series of deuterium labelling experiments,

Keller10^ was able to assign the boron-11 NMR spectrum. Figure _7 shows the molecular structure and boron-11 NMR spectrum of the

[B gH14]" anion.

C. Halogenation and Alkylation Reactions. Pentaborane(9) reacts with elemental chlorine , 1 0 "1 bromine,10^ and iodine 1 0 *1 in the presence of Friedel-Crafts alkylation catalysts to form apically substituted derivatives of the general formula 1-XBgHg according to equation _4. 19

STRUCTURE OF [B9H14]

BORON-11 NMR SPECTRUM

Boron u JP’B-’H), Atom ppm Hz -23.6 13712

84 ,6, e -20.4 12813

B5 7 9 - 8.0 14013

B

Figure 7. The structure and boron-11 NMR spectrum for [BgHj^] 20

BgHg + X 2 » 1-XBgHg + HX (4)

X2 = C l2, Br2, I 2, IC1

The ease of halogenation decreases from Cl 2 to I2. Chlorination and bromination also occur in the absence o f a Lewis acid c a ta ly s t, producing a small amount of 2-XBgHg substituted derivatives along with the apically substituted 1-XBgHg product.104,105

In the presence o f weak Lewis bases such as dimethyl ether, diethyl ether, or hexamethylenetetramine, reversible isomerization of

1-XBgHg to 2-XBgHg occurs . * 0 0 However, some o f these isom erizations using methyl ether are complicated by side reactions which produce 2 - methoxypentaborane(9) and alkylated derivatives.*00’*0^ The apical position can also be halogenated in basally substituted pentaborane(9) derivatives . * 0 0 * * 0 0 Thus, successive chlorination and isomerization reactions have been successfully employed in the preparation of di- and trichloropentaboranes.*0^ Friedel-Crafts catalyzed halogenation has also been shown to occur at the B(2) basal position when the apical position is blocked by an ethyl group (equation_5 ) . 1 0 6

A1C1 3 1-Et-BgHg + I2 » l-Et-2-I-BgH 7 + HI ( 5)

Pentaborane(9) can also be alkylated by reaction with alkenes or halogenated hydrocarbons in the presence of a Friedel-Crafts 21

c a ta ly s t. 1 1 0 , 1 1 1 pr 0 (jUCt j s an apically substituted 1 -

alkylpentaborane(9). Isomerization to the 2-alkylpentaborane(9)

derivative occurs at elevated temperature (ca. 150-200°C),*10 but the

y ie ld s of isomerized product often do not exceed 50%. However, in the

presence of Lewis bases such as 2,3-dimethyl pyridine or

hexamethylenetetramine, 1 -alkylpentaboranes are quantitatively

isomerized to 2-alkylpentaboranes.11^7,11'* Pentaborane(9) also has

been shown to react with alkenes at elevated temperatures in the

absence of Lewis acid ca ta lysts to produce 2-alkylpentaboranes,

however, only a small amount of the starting material is actually

consumed in th is re a ction . * * 4 Also of interest in this study are the

reactions of CH 3 CI with 2 -(CH3 )-BgHg and of CH 2 CI2 with BgHg in the

presence of AICI 3 . The former reaction produced low yields of

products containing both methyl and chloro substitutents , * * 4 while the

la tte r reaction produced the methylene bridged system (l-BgHg ^ ^ . * * 5

A reaction which is apparently related to the alkylation

reactions discussed above is the formation of a bipentaborane, 1 , 2 '-

(B 5 H8 ) 2 by the reaction of 2 -B rB g H g with BgHg under Friedel-Crafts

co n d itio n s , * * 6 according to equation^.

A1C1, 2-BrB5 H8 + B5 H9 ------> 1,2*-(B&H8 ) 2 + HBr ( 6 )

Although the product had previously been isolated and characterized, this represented the firs t rational synthesis of this 22 compound. Interestingly, another high yield, albeit slow route 1 1 7 , 1 1 8 to l , 2 '-(BgHg ) 2 was recently reported in the PtBr 2 catalyzed dehydrodimerization reaction shown in equation^.

PtBr9 2 BgHg 5 ------> 1 .2 '-(B 5 H8 ) 2 + H2 (7)

The 1,2' isomer was the exclusive bipentaborane product from this reaction. The structure of l,2'-(BgHg ) 2 is shown in figure 8 ^.

1 1 Q Sneddon and co-workers recently reported that the reaction of 1,2 -

(b5h8)2 with lithium triethylborohydride provided [BgH14]" in high yield, according to equation 8 ^.

1 ,2 '-(B 5 H8 ) 2 + Li[B E t3 H] ------> L i[B gH14] + THFBH 3 ( 8 )

+ BEt3

The mechanism of this reaction is not clear, although it should be noted that the reaction of B5Hg with lithium triethylborohydride 1 Of) has been found to result in ethylation and not deprotonation, according to equation _9.

B&Hg + Li[B E t 3 H] -> 2,3,4-Et 3 -B 5 H6 + Li[BH] 4 ( 9) 23

Figure 8. The structure of l,2'-(Bc)Hy)2. 24

In studies of the reactivity of these bipentaborane(16) species,

Gaines and co-workers found that the chemistry of the 1,2' isomer is

1 pi dominated by reactions which cleave the B-B a bond. A

D. Reaction of Pentaborane(9) with Alkali Metals. Stock 1 2 2 initiated the investigation of this area by studying the reaction of pentaborane(9) with postassium amalgam. A large excess of potassium amalgam reacted with BgHq at room temperature. After the reaction was complete the mercury and unreacted potassium metal were removed by d is t illa tio n under high vacuum at temperatures up to 265°C, leaving a non-volatile white material. Elemental analysis of this material was consistent with the formula KgBgHg. However, later investigations of the material obtained from this reaction showed that it contained i p o large amounts of borohydride and other materials. In a brief note,

Lipscomb 1 2 4 reported that the reaction of B 5 H9 with potassium in THF led to the formation of a s a lt formulated as K tB gH ^]. However, besides a poor NMR spectrum, no other data is reported. The only 1 pt other inve stig a tio n in to th is area has been the work of Lockman, who studied the reaction of pentaborane(9) with potassium and lithium metals in various solvents. Pentaborane(9) was found to react at low temperature (-78°C) with approximately 1.8 equivalents of lithium in liquid ammonia, discoloring the in itia lly deep blue solution. The reaction did not evolve hydrogen. Upon warming to -60°C the compound decomposed. The product was not id e n tifie d and the boron-11 NMR spectrum resolved only a low field doublet at -51.7 ppm. The high field region was not resolved. The reaction of pentaborane(9) with 2b

lith iu m in dimethyl ether was observed to proceed w ithout hydrogen

evolution, the main product being identified as Li [B g H g ] on the basis

of the boron-11 NMR spectrum ( 6 = -17.2 ppm, -53.2 ppm; 4:1 ratio).

Lockman believed that this may have been due to the in itia l reduction o f B5 H9 to form the [B g H g ]2 - anion, which then deprotonated BgHg in

solution to form [BgH^Q]- and [ B g H g ]- , as illu s tra te d below in equations _ 1£ and _U.

2 Li + B5 Hg ------> L i2 [B 5 Hg] (10)

L i2 [B 5 Hg] + B 5 H9 ------> L i[B 5 H8] + L1[B 5 H1()] (11)

Signals which could be assigned to [BgH^g]- were not observed.

Reaction of pentaborane(9) with potassium in various solvents was observed to evolve hydrogen and produce I ^ B g H ^ ] and K[BH4 ] as the major products. Hydrogen evolution was greatest in the most basic solvent used, ammonia, where two equivalents of hydrogen were evolved per mole of BgHg consumed. The amount o f hydrogen evolution was never reproducible.

V II. Statement of the Problem

Attempts to reduce boron hydride clusters with akali metals have met little success, possibly the only exception being the reduction of decaborane(14) with sodium in liquid ammonia and with sodium amalgam12^ to form the dianion. At least in theory it should be 26 possible to reduce a boron c lu s te r by two electrons and go from one structural class to another. This has been achieved by the addition of Lewis bases which act as ligands or electron donors to the cluster cage, and effectively reduce it, causing a structural transformation of the cluster framework. This study was undertaken to try to reduce pentaborane(9) and form a [B g H g ]2 " dianion. Dianions of the lower boron hydrides were unknown at the time th is study was begun. I t was hoped that the [BgHg]2- dianion might be a useful synthetic reagent.

Previous studies of the reaction of pentaborane(9) with alkali metals have centered on the use of amalgams and ammonia reductions. Neither of these proved satisfactory. It was hoped that the use of an electron carrier might facilitate the reduction reaction since these have been used successfully in transition metal cluster chem istry . 1 2 8 " 1 3 1 Electron carriers have also been shown to be useful in the preparation of diborane( 6 ) from sodium borohydride . 1 3 2

A second project in this thesis has been the study of the formation of the tetradecahydrononaborate(l-) anion, [BgH^]", from deprotonation reactions of pentaborane(9). This anion had been previously synthesized from pentaborane(9) and has been shown to be a useful intermediate in a number of syntheses. However, little was known about the pathways o f th is reaction which led to the distribution of products. The scope of the present study has been to elucidate the pathways o f th is reaction and to attempt to iso la te intermediate species, as well as to attempt to improve the syntheses of [BgH^]", B 1 0 H ^ , _n-BigH 2 2 » and other important derivatives. 27

A third project in this thesis has involved the preparation of new metallaborane species using Friedel-Crafts reactions on boron hydrides and carboranes using the boroxine supported triosmium cluster, [( 11- ^ 3 ( 0 0 ) 9 0 5 3 ( 113- 0 0 ) 3 3 ( 6 3 0 3 ) . * 3 3 It was of interest to see whether the triosmium carbonyl methylidyne unit might undergo these types o f reactions, implying th a t a non-planar carbocation is formed as an intermediate. RESULTS AND DISCUSSION

I. Reduction of Pentaborane(9) with Alkali Metals to Form

the Nonahydropentaborate(2-) Dianion.

A. Preparation and Characterization. Pentaborane(9) is cleanly

reduced by two equivalents o f sodium, potassium, rubidium, or cesium

napthalide, M+(C 1 QHg)_ (M = Na, K, Rb, Cs), in THF or glyme to form a new nonahydropentaborate( 2 -) dianion, [BgHg]^- , according to equation

12 .

B5H9 + 2 M+(C10H8)" ------> M2[B5H9] + C1qH8 (12)

M = Na, K, Rb, Cs C._H 0 = napthalene 1 U O

No hydrogen is evolved in this reaction. These salts can be isolated by washing w ith pentane and f ilt r a t io n to remove napthalene or by pumping the napthalene away at room temperature under high vacuum.

The Na, K, and Rb sa lts are red-brown or burgandy red in co lo r. The

Cs salt is grey-black. The sodium salt is soluble in THF or glyme, while the other salts are insoluble.

The product yield for the potassium salt is nearly quantitative, however, yields for the sodium salt could not be accurately determined

28 29

due to a high degree of solvation. These salts appear to be quite

stable under vacuum in both the so lid state or in so lu tio n s, showing

only minimal decomposition after one week, as judged from physical

appearance, lack of gas evolution, and boron-11 NMR spectra. The IR

spectrum (nujol mull, figure_9) exhibits B-H stretches of 2400 and

2290 cm"*. This is very low compared to the B-H stretches for BgHg

(2598, 2610 cm"1, gas ) 1 3 4 and K[B 5 H8] (2540, 2470 cm"1, nujol m u ll ) . * ’ 3 In the presence of air Na 2 [B 5 Hg], I^LB^Hg] and Rbgl^Hg]

fume and are quickly discolored.

Slightly soluble potassium, rubidium, and cesium salts for

boron-11 NMR spectroscopy were obtained using the crown ether, dibenzo-18-crown-6. The crown ether was also found to act as an electron carrier like napthalene if a trace amount of napthalene were added to a reaction vessel containing the crown ether, potassium or

rubidium metal, and THF or glyme. This complex was also e ffe c tiv e in

reducing B 5 Hg to form [M(dibenzo-18-crown-6)]2[B5Hg] (M = K, Rb,

Cs). This sequence of reactions is shown below in equations 13 and

14.

napth. M + dibenzo-18-crown-6 ------> M (dibenzo-18-crown-6)“ (13)

2 M+(dibenzo-18-crown-6)” + BgHg (14)

THF or glyme

[M(dibenzo-18-crown-6)]2CB5 Hg]

M = K, Rb, Cs; napth. = napthalene 30

(B-H) Rb2[B5H9]

2200 2401 2295

2500 2000

- 1

Figure 9. Infrared spectrum of (^[B^Hg] (nujol mull). The boron-11 NMR spectra of NagCByHg] and

[M(dibenzo-18-crown-6)]2[BjjH

show two doublets in at -16.1 and -51.7 ppm in a relative rati,o of 4:1

(figure J^). A two-electron reduction of nido-BgHg to the arachno-

[B 5 H9 ]2- dianion is expected to open one face of the cage as shown in

figure_U. The fact that only two NMR signals are observed indicates that the [BgHg]2" molecule is highly fluxional at room temperature.

Low temperature boron-11 NMR spectra did not reveal any additional signals, but only broadening of the signals. The **B NMR spectrum of

[ B 5 H g ] 2 - is, in fact, nearly identical to the spectrum of the [B g H y ]" anion. This in itia lly cast doubt on whether the compound which had been synthesized was actually the dianion. However, aside from the

NMR spectrum, all the other evidence clearly supports the formulation of [B g H g ]2 " for this anion. The sodium and potassium salts of [B g H y ]" are colorless salts, which undergo rapid decomposition at room temperature (both in solution and as solids) to form the [B g H 1 4 ] " anion as the major product. Protonation of [B g H y ]" salts generates the conjugate acid BgHg in nearly quantitative yield. On the other hand, the decomposition products of K 2 [BgHg] do not contain [B g H ^]" and protonation of K2 [B g H g ] , discussed below in detail, has provided

BgHn in good yield. Table Z_ shows a comparison of some of the physical properties, spectroscopic properties, and reactivities of

[B g H g ]2 - and [B g H g ]" . It should be noted that the * * B NMR spectrum of another pentaborane anion, [BgHjy]" (obtained from deprotonation of

BgHn), also shows two doublets at -13.2 and -52.3 ppm in a relative 32

r T T T T T -10 -20 -30 -40 -50 PPM

Figure 10. Boron-11 NMR spectrum of Na 2[B£Hy] in glyme. 33

NIDO-

+ 2 M

i f

ARACHNO-

Figure 11. Expected stru ctu ra l change in the boron framework by a two- electron reduction of nido-B^Hg to arachno-LB^Ho]^". 34

Table 2. A Comparison of Properties and Reactivities

of [BjHg]^ and [BgHg]

Properties [B 5 H9] 2" Cb5 h8] -

Color Red-brown Colorless

Solubilities (K+ sa lts ) insoluble in ethers soluble in ethers

IR Spectrum v (b- h ). cm" 2400, 2290, 2210(sh) 2540, 24701 NMR Spectrum -16.1, -51.7 ppm -17.1, -52.9 ppm (4:1 ratio) (4:1 ratio)

Stability/ Decomposition prod. L it t le change a fte r Decomposes w ith in 1 wk.; no [BgH^]" 24 hours to form formed. primarily [B 9 H14] “

Protonation rxn. Forms B 5 H1:l in good Forms B5Hg in y ie ld quantitative yield

■^Johnson, H. D., I I ; Geanangel, R. A.; Shore, S. G. Inorg. Chem. 1970, 4, 908. 35 ratio of 4:1 . 2 5 , 1 3 5 Like [BgHg]2", [BgH1Q]" is expected to have three signals in a ratio of 2 : 2 : 1 .

A further experiment was used to provide more evidence that

Eb5h8^~ 1S not Producecl f r o n 1 ttie reaction of 2 equivalents of alkali metal napthalide with BgHg. If the [BgHg]" anion were indeed produced, then reduction of the napthalene must have occurred, since there was no hydrogen gas evolution. To test this, BgHg was reduced w ith two equivalents of perdeuterated sodium napthalide. The reaction p mixture was then studied using deuterium NMR spectroscopy. The ^H NMR spectrum (figure JL 2 ) shows that only a slight reduction of the napthalene has occurred.

Attempts to metathesize [B g H g ]2 - using tetraalkylammonium salts, tetraalkylphosphonium salts, and bis(triphenylphosphine)imminium chloride ( [PPN]C1) were unsuccessful. In each case, 1 1 B NMR spectra revealed large quantities of [B g H 1 4 ] " and [ B g H g ] " . This result seems to indicate that the [B g H g ]2 " is strongly basic and abstracts a proton from the metathesis salt to form [B g H 1 0 ] " , the thermal decomposition products of which are primarily [ B g H ^ ] " and [B g H g ]" .

B. Protonation of [B g H g ]2 - with HC1 and HBr. The [B g H g ]2 " dianion has proven to be an excellent route to pentaborane(ll), BgH^.

Protonation of ^[BgHg] or Cs 2 [BgHg] w ith hydrogen chloride or hydrogen bromide has provided a high yield route to BgH^, as illu s tra te d below in equation 15. 36

76 S 4 3 PPM

Figure 12. NMR spectrum of the reduction of pentaborane(9) with sodium napthalide-dg(a) vs pure napthalene-dg(b). 37

M2 [B 5 Hg] + 2 HX ------> B5 Hn + 2 MX (15)

M = K, Cs X = C l, Br

Yield = 38% in butane with HC1, 21% with liquid HC1

Initial investigations were carried out using liquid HC1 or

liq u id HBr. This produced BgH^ in yie ld s o f about 20% based on

BgHg. The product was isolated by trap to trap fractionation on the

vacuum lin e . A f a ir amount o f B 2 Hg, as well as a considerable

quantity o f hydrogen gas were also produced in the reaction. The diborane recovered from this reaction was assumed to be a result of cleavage of B5H11 by residual solvent. Pentaborane(ll) is known to be

re a dily cleaved by Lewis bases such as THF . 1 3 6

In an attempt to minimize the problem with solvent cleavage, the protonation of K 2 [BgHg] was carried out in an in e rt solvent. Butane was chosen because i t is chemically in e rt toward the boron hydrides and because it s low b o ilin g point allows easy separation o f the BgH-^ product on the vacuum line fractionation train. Boron-11 NMR studies also showed that methylene chloride is also a good medium for the protonation reaction. However, BgH^ could not be as easily separated from methylene chloride. The boron-11 NMR spectrum of the crude

(unseparated) product from protonation in CH 2 CI2 is shown in figure

13. This shows that BgHjj is by far the major product. When the protonation was carried out in butane at -78° using a 50% molar excess of HC1, BgHjj was isolated in 38% yield based on the BgHg starting material by trap to trap fractionation on the vacuum line. This represents the best preparative method to date for BgH^, provided a a

20 10 0 -10 -20 -30 -40 -50 -60 PPM

Figure 13. Boron-11 NMR spectrum o f the CHgC^ soluble material from the protonation of with HC1 in CH 2 CI2 - a = BbHll * 39

that BgHg is readily available. Figures and JJS show the NMR

and gas phase IR spectra of BgH^ obtained from this reaction.

C. Reaction of [BgHg]2- with B2Hg and BgHg. S alts o f [BgHg]2"

react rapidly with 1 equivalent of pentaborane(9) resulting in the

discoloration and dissolution of the red-brown dianion and the

formation of a light yellow solution. After standing at room temperature for 2 days, the boron-11 NMR spectrum of this solution

showed that the major species in solution were the [BgH-^]",

[B 1 1 H1 4 ]", and [BgHg]” anions. This is believed to occur through the deprotonation of BgHg by the anion to form [BgHg]” and [BgH10]" according to equation 16.

[B^Hg] + B5Hg > [BgH^g] + CB 5 Hg] ( 16 )

These anions are both thermally unstable species and decompose to form the observed products.B5>73,80,100,135 j^g [BgHg]2" anion also readily reacts with 1/2 equivalent of B 2 Hg. The product mixture, as studied by boron-11 NMR spectroscopy, did not contain [BgH^]", nor its decomposition products. The boron-11 NMR spectrum of the product mixture from the reaction of K 2 [BgHg] with 1/2 equivalent of diborane( 6 ) is shown in figure JJ[. The reaction occurred at low temperatures (< -45°C) resulting in the formation of a light yellow solution. Although the reaction appears to be quite complicated, producing a large number of products, the dominant species in solution 40

L _L_ X Xi I_ X_I_ XX XX X 20 -10 -20 -30 -40 -50 PPM

Figure 14. Boron-11 NMR spectrum o f obtained from the protonation of ^[B^Hg] with HC1 in butane. 41

60 —

55 —

50 —

40 —

30 —

25 —

15 —

10 —

Wovenumbers

Figure 15. Gas phase (12 torr) infrared spectrum of B 5 HU obtained from the protonation of with HC1 in butane. 42

were id e n tifie d as [BgHg]- , [BgHg]- , and [B g H ^]- by boron-11 NMR

spectroscopy.

D. Other Reactions of Alkali Metal Napthalides and

Pentaborane(9). The reactions of alkali metal napthalides with 1 and

2 equivalents of pentaborane(9) was also investigated. (Section

above describes the reaction of alkali metal napthalides with 1 / 2

equivalent of BgHg.) These reactions appear s im ila r to deprotonation

reaction involving BgHg, which are discussed in detail in the next

section of this thesis. When equimolar amounts of pentaborane(9) and

sodium napthalide were stirred at room temperature, the dark green

napthalide color quickly dissipated, leaving a clear, colorless

solution without any gas evolution. After 3 days, the color had

changed to a light yellow. Boron-11 NMR spectra revealed a mixture of

6 8 % [B g H ^ ]- , 1 2 % [BgHg]-.^»73>80,100 stirring potassium napthalide with 2 equivalents of BgHg in THF at room temperature produced an

in itia lly clear, colorless solution which turned yellow after a few

hours. The **B NMR spectrum of the solution (figure ^ 6 ) showed th a t

it contained primarily [BgH^]-, BgHg, [B^H-^]- , THFBHg, plus a small amount of [BgHg]- . This is a similar product mixture to that obtained

from the reaction of BgHg with potassium or sodium hydride in a 2:1 molar ratio (BgHg:MH) in THF or glyme.*^ Both of these reaction

solutions are similar to those from deprotonation reactions of BgHg and indicate the probable formation of the [BgHg]- anion which then either decomposes or reacts with additional BgHg in solution. 43

a = [B 6 H9]

b = [B9 H i4]-

= [b3 h8]-

I * 1 ■ I ■ I * l-i I i I . i l.i 1 20 10 0 -1 0 -2 0 -30 -40 -50 PPM

Figure 16. Boron-11 NMR spectrum of the reaction of ^[BgHg] with B£Hg in THF. 44

I I . Production of the Tetradecahydrononaborate(l-) Anion

from Deprotonation Reactions of Pentaborane(9)

A. Reaction of Pentaborane(9) with Sodium and Potassium Hydride.

Reacting pentaborane(9), BgHg, and potassium hydride (or sodium

hydride) in a 1.8:1 molar ratio (BgHg:MH) in glyme at room temperature

results in the complete consumption of the BgHg and the formation of

the tetradecahydrononaborate(l-) anion, [BgH^]“ , in 70-75% yield

1 1 based on the BgHg s ta rtin g m a te ria l. As analyzed by AAB NMR

spectroscopy, the other 25-30% of the boron in the product mixture

consists of [B 1 2 .H1 4 ]” , [BgHg]", [BH4]“ , [BgHg]", and a number of

unidentified, apparently anionic species according to equation 17.

1.8 BgHg + MH ------> M[BgH14] + + minor products (17)

M = Na,K

The boron-11 NMR spectrum of the products from reaction J7 is

shown in fig u re l]_ . The relative amounts of [BgH^]" and the minor

products vary slightly as a function of reaction time and have been

previously described in detail.The scope of the present study has

been to isolate intermediate species, as well as to improve the

syntheses of [BgH^]", B^qH^, Jl-B^gHgg. and other important

derivatives.

The in itia l reaction was presumed to be a simple deprotonation of

BgHg to form the octahydropentaborate(l-) anion, [BgHg]", (reaction

_18). 45

~ T ~ T “I— 1------1— — I— 10 0 ■10 -20 -30 -40 -50 PPM

Figure 17. Boron-11 NMR spectrum of the reaction of 1.8 equivalents of

w ith sodium hydride in ylyme a fte r 1 2 hours. 46

B5 H9 + MH - •> m[b5 h8] + h2 (18)

M = Na,K

This reaction has been well-studied with metal hydrides such as potassium hydride and sodium hydride and with a variety of other strong Bronsted bases.85-8,72-74 y^g [B^Ha3“ anion was then thought to react with additional B 5 H9 and also to decompose thermally, leading in both cases to the formation of the [BgH-^]" anion as the major product. This was confirmed by low temperature investigations of the reactions of K E B g H g ] w ith B5 H9 in THF and [(rv-C/jHg^NDLBgHg] w ith B g H g in glyme. Both reactions produced nearly id e n tica l re s u lts . At temperatures below 240 K, [BgHg]" and BgHg were found to co-exist in solution without reacting, as followed by high-field ^B NMR spectroscopy. This is consistent with observations by Grimes and co- w o rk e rs ^ th at temperatures below 253 K are necessary to produce pure

[ B g H g ] " from deprotonation of B g H g w ith sodium hydride. As the temperature of the solution was slowly raised, the two species began to react, forming an intermediate species thought to be Cbioh 1 7 ^"*

Attempts to isolate this intermediate were unsuccessful, as it rapidly decomposed. However, i t was possible to obtain ^ B NMR spectroscopic data on this species. The NMR spectrum clearly shows an intermediate species having six signals at 10.5, 0.6, -11.0, -22.2, -24.7, and

-31.9 ppm in a relative ratio of 2:2:1:1:2:2 (figure _18). After 30 minutes at 273 K, this intermediate had completely disappeared and the reaction solution consisted of [ B g H - ^ ] " , [BgH^]", an^ unreacted

B g H g . The results of this study are shown in figure _19. The / 47

a ,b

T T T T TTTT 20 10 0 -10 -20 -30 -40 -50 PPM

Figure 18. Boron-11 NMR spectrum of the low temperature reaction of

C(jv-Bu) 4 N][BgHy3 with B5 H9 in glyme showing the presence o f the

[B 1 0 H1 7 ]" intermediate species, a = BgHg; b = [BgHy]- ; c = [BgH^]- ; d = [BgHjj] ; e = [B^gH^y] • 48

A Ia Ju LA

^ v_a _a> L J L

20 10 0 -10 -20 -30 -50-40 PPM

Figure 19. Sequential boron-11 NMR spectrum of the low temperature reaction of [(_n-Bu)^N][B 5 Hg] w ith BgHg in glyme. a = BgHg; b =

[BgHg] ; c = [BgHj^] ; d = [BgH^] ; e = . 49 formation of [ B g H ^ ] " and [BgHn]” in the reaction of [B g H g ]" w ith

BgHg is thought to occur according to reactions ^9., ^ 0 , and 2 1 .

[BgHg]" + BgHg > "Ebioh17^”" ( 19)

"tB10H17] “" ------> EBgH14]" + “BH3" ( 2 0 )

C W + "BH3" ------* CB6Hll 3 ' (21)

Reaction ^1_ has been well-studied and is known to be very fast.

The reaction of [B g H g ]" w ith BgHg (equation_20) is the major process leading to the formation of [B g H 1 4 ] " . This is a particularly interesting reaction in view of the previously studied cage expansion reactions. The NMR spectroscopic data shows the presence of only one intermediate species, “[BigH^y]"," t *1us indicating that the cage expansion is a concerted process which combines two Bg u nits to form a

B1Q cage. This process is in contrast to cage build-up sequences which add one boron atom at a time to the cluster cage such as those proposed for the pyrolysis of B 2 Hg to higher boranes. Reaction _2L is also interesting in that it is a reaction of a conjugate acid with its conjugate base. The proton exchange reaction is slow on the NMR time scale, resulting in the observation of two signals for BgHg and

[ B g H g ] " . I f the [ B g H j ^ ] - synthesis reaction (equation 21) is carried out at room temperature, signals for [B g H g ]" are never observed in the boron-11 NMR spectrum, apparently due to its rapid consumption in reactions 19 and 21. As part of this study, the decomposition of the and

[B 5 H8 ]” anions was investigated. Although decomposition products of these species had previously been reported, it was re-evaluated here using high field boron-11 NMR spectroscopy. The contribution of each of these species to the overall product distribution was also studied. The decomposition reactions of both species were found to be very complex, and many of the signals observed in the 11B NMR spectra represent unidentified species. The sodium and potassium salts of

[B 5 H8]- decompose thermally in solution and in the solid state to form primarily [BgH-^]" along with [BgHg]", [BH^]“ , unidentified species, and insoluble material. The potassium salt of [BgHj^]" is likewise unstable in solution and as a solid. It decomposes slowly to firs t form a complex m ixture containing p rim a rily [ B ^ H ^ ] " , [B g H ^ ]",

[BgHg]", and unknown species, the boron-11 NMR spectrum of which has two doublets centered at -35.9 and -41.6 ppm and a broad singlet at

-4.7 ppm. For the present discussion, this unknown species is referred to as compound _I_. After several hours at room temperature, the amounts of [B ^H ^]" and [BgH^]" relative to the other species had noticeably increased. Compound _I_ appears to be an unstable species, and its disappearance from the solution leads to increase in the [BgH^]" content, and perhaps also the [B ijH ^]" content. The main long-term (3 months) decomposition products of [BgH^]" are

[B 1 1 H1 4 ]", [BgH^]", and [BgHg]". Results of the boron-11 NMR spectroscopic study of the decomposition of K[BgHu] in THF are shown in figure _20. Compound _I_ was also observed from the reaction of

[BH4 ]" with BgHg and is discussed in detail below in section _B. This 51

K[®6 H]l] decomposition in THF

K [b 11h m ]

K[b9h i 4]

3 mo k [b3h8]

JV\ ____

t------r -20 -40 ppm

Figure 20. Boron-11 NMR spectra of the decomposition of K[B 6Hll3 . 52 species was also observed by Savory and Wall bridge, 64,98,99 an(j ^

Lawrence.100 The known (identified) products from the decomposition of [BgHg]" and [BgH^j]" are illustrated in equations 22 and 23.

respectively.

M[B5H8] ------> M[B9H14] + M[B3H8] + M[BH4] (22)

M[B6Hn ] ------> M[Bn H14] + M[B3H8] + M[B9H14] (23)

M = Na, K

From reactions _1£ and Z\_ listed above, both of which are very fast reactions, it seemed unlikely that reaction j?2_would have a very large effect on the product yield. This was confirmed by experiment. When the [B9Hj4]" synthesis reaction (equation IT) was run at low temperature (< -10°C) in the in itia l stages of the reaction

(firs t 5 hours) and then warmed to room temperature for the remainder of the reaction time (KM2 hours), the product distribution did not change from previous tria ls at room temperature. At low temperatures, the [BgHg]" anion possesses good thermal s ta b ility , so th a t its decomposition in the early stages of the reaction should not have been a factor here. The fact that there was no observable difference between the room temperature and low temperature tria ls thus indicates that [BgHg]" is being consumed in reactions ^0 and ^1_ much faster than i t decomposes. 53

A summation of reactions _1£[, _19, _20, and 21_ yields equation _24.

3 BgHg + 2 MH ------> M[B 9 H14] + M[B6 Hn ] + 2 H2 (24)

M = Na, K

Therefore, the reaction of 1.5 equivalents of BgHg with 1 equivalent of KH in THF or glyme at temperatures below the decomposition temperature of K[BgH^] should produce a solution containing only

K[B9H14] and K[BgH^]. This was confirmed by experiment, the results of which are shown in the ^B NMR spectrum in fig u re ^ . Only a small residual amount of BgHg was s till present after the reaction.

Based on reactions _19 and 20, an attempt was made to try to increase the purity of the [BgHj4]" by increasing the BgHg to KH ratio. Since reactions _1£ and ^ represent processes which compete for the available [BgHg]" in solution, an increase in the amount of

BgHg would be expected to favor reaction 21 over re a ctio n ^, and thus produce less ]“ impurity. This was confirmed by the reaction of

BgHg and KH in a 10:1 molar ra tio (BgHg: KH) in glyme at room temperature. Integrated boron-11 NMR spectra of the non-volatile reaction products showed that [BgH^4]" accounted for approximately 80% of the boron in solution. As expected, an increase in the [B ^H ^]" content was also observed. Although th is is a modest improvement over reactions employing a 1.8:1 molar ratio (BgHg:KH), the d ifficu lty in recovering the unreacted BgHg from the reaction solution does not offset the benefit of the increased product quality. 54

I 1-- 1-- 1-----1-1--- 1---- '-1-----1-1---- 1-1 ' I 1 I 20 10 0 -10 -20 -30 -40 -50 PPM

Figure 21. Boron-11 NMR spectrum of the reaction of 1.5 equivalents of

B5 H9 with KH. 55

B. The Reaction of Pentaborane(9) with the Borohydride Ion.

E a rlie r work by Savory and Walbridge showed th a t BgHg and [BH4] " react to form good yields of [BgH ^ ]" .64,98,99 Their work also suggested the formation of an adduct between BgHg and [BH4] _ at -78°C which decomposed at room temperature with evolution of hydrogen . 6 4 This work was repeated here to see whether the [BgH^]” ion could be formed directly from [BH4]~ and BgHg according to equation_25, as had on previously been suggested . 0 0

BgHg + [BH4r ------> [B6 Hn ] - + H2 (25)

S tirrin g Li[BH4] and BgHg overnight in glyme at -78°C did not produce gas evolution or any evidence of reaction. The boron-11 NMR spectrum showed only s ta rtin g m aterials to be present. Upon warming to room temperature, slow hydrogen evolution occurred, evolving approximately 1 equivalent of gas after 24 hours. The integrated boron-11 NMR spectrum of this solution (figure J22J shows signals for

[BgHj4] ” and [BgHg]- to be dominant in the system, accounting for 55% and 6 8 % o f the to ta l boron content in two d iffe re n t t r ia ls . Signals for [BgH^]" were never observed. Signals for a third species, referred to as compound J_ in this discussion, were observed at 7.6,

-4.3, -16.6, -35.7, and -41.5 ppm in an approximate area ratio of

1:2:1:2:2, perhaps meaning that this is a Bg anion. The signal at

-4.3 ppm is a broad singlet which sharpens with proton decoupling; the remaining four signals are doublets. Compound _I_ is of interest 56

b

J. ± ± J. X i i 10 0 -10 -20 -30 -40 PPM

Figure 22. Boron-11 NMR spectrum of the reaction of B^Hg with Li[BH^] in glyme. a = [BgH14] _, b = [B 3 H y]", c = compound J_. 57

because i t is also observed as one o f the main im p u ritie s in the

synthesis of from BgHg and KH (reaction _T7 ) . 1 0 0 It is also

one of the primary decomposition products of [BgHjj]” . However, in

both of these reactions, the spectrum is much too complicated to allow

many conclusions regarding this species. This species slowly

decomposes, forming [Bg hi4]" and [Bn H14]- as the major products.

Compound J_ was investigated using 2D ^B -^B NMR spectroscopy to

determine whether the signals were all from one species and what

structural information could be obtained. The results of the 2D **B-

**B COSY (correlated spectroscopy) experiment are shown in figure

23. The four signals^, c , and ji, are shown to be directly coupled to

_e. The f i f t h signal b^ does not show any B-B coupling w ith the other

signals. This was quite puzzling since it had been observed in many

experiments that th is signal always appeared together w ith and of the

same intensity as signals 6_ and e . Furthermore, signal _b is quite

broad and sharpens noticeably with the application of proton spin

decoupling, indicating that it is probably coupled to bridging

hydrogens. It has been previously observed that B-B coupling is

usually not observed in these experiments between boron atoms bridged by hydrogens. Thus, the five signals are believed to be from the same

boron hydride.

The formation of [BgH^]", [BgHg]", and the unknown Bg species

(Jj can be accounted for by the following reactions, the summation of which is given in equation 30. -4 3

-40

-33

-3 0 -25

-2 0 -15

-1 0 o O -5

0

5

10

15 Pf 1 1 -1 0 -2 0 -30 -4 0 PPM

Figure 23. 1 1 B- 1 1 8 COSY experiment for the reaction of with

Li[BH43 in glyme. Signals marked with an asterisk (*) are from

[B 9 H1 4 ]" and CB 3 Hq3~« A proposed structure fo r [BgH13] “ is shown. 59

B5 H9 + [BH4r > CB5 H8] - + H 2 + BH3 (26)

[B 5 H8r + B 5 H9 ------> [B 9 H14] - + BH3 (27)

[BH4r + 2 BH3 ------> [B3H8] “ + H 2 (28)

[B 3 H8] - + B 5 H9 ------> [B8 H13r + 2 H2 (29)

3 B5 H9 + 2 [BH4] ------> [B 9 H14r + CB8 H13] “ + 4 H2 (30)

S toichiom etric evolution o f hydrogen was not observed, however,

i t should be noted th a t a ll o f the B^Hg was consumed and 17% o f the

final product mixture consisted of [B3H8]” . The proposed structure of the [B8H13r product is shown in figure j?3. The signal labelled e^ is

coupled to signals a_, _c, and _d. Signa‘! _a is coupled to d_, and e, while signal c_is coupled to a_ and e_. The proposed stru ctu re is consistent with the observed coupling and may be considered as an

analogue of a B-jH^L adduct. The broad singlet in the NMR spectrum at

-4.3 ppm and the doublet at -16.6 ppm, which are assigned as boron atoms Jt^ and c_ respectively in the proposed structure, are sim ilar to i go signals found for B-jHyL ether adducts. Ligand adducts between boron hydrides to produce conjuncto-cage adducts have previously been proposed on the basis of molecular weight determinations and NMR spectra.*39-40 scheme proposed above (equations 26-30) might be formally analogous to a compound derived from the reaction of LBgHn]” with 1 equivalent of B 2 Hg, which might explain why this species is observed from the decomposition of [BgHjj]” . 60

C. Preparation of the Tetradecahydroundecaborate(l-) anion from

Pentaborane(9). It had earlier been observed that the presence of

excess amounts of pentaborane(9) in the synthesis of the [BgH^]"

anion resulted in a substantial amount of impurity due to the

tetradecahydroundecaborate(l-) anion, Also very

significant amounts of this anion were present if the reaction was run

at temperatures higher than room temperature. Based on these

observations, the reaction of [BgH^]" with BgHg was investigated.

When 1:1 molar ra tio s of these two compounds in glyme were allowed to

react in a sealed NMR tube, it was observed that [B uH ^]" was slowly

formed. When these reactants were heated at 80°C in glyme fo r 24

hours, the only non-volatile product observed in the boron-11 NMR

spectrum (figure ^4) was One equivalent of diborane( 6 ) or

2/5 equivalent of B&Hg were found to react as well with [BgH^]" under

these reaction conditions to form

The tetradecahydroundecaborate(l-) anion could be prepared in a

"one-pot" synthesis starting with B^Hg and sodium or potassium

hydride, according to equation _31.

2.4 B5 H9 + MH g1yme> 800C* 2 4 h> M[Bu H14] + 3.5 H£ (31)

M = Na, K

Attempts to use a stoichiometric ratio of B^Hg to hydride (BgHg:MH =

2 . 2 : 1 ) always resulted in a substantial amount of [BgH^]" in the

product. This was apparently due to the formation of borane

adducts. Various tetraalkylammonium, tetraalkylphosphonium, and

ra n also be added to the reactants to produce the cesium s a lts can 11B

n i------1------1------r " -5 -10 -15 -20 -25 PPM

Figure 24. Boron-11 NMR spectrum of K[B^H ^] in glyme. 62 corresponding metathesized products. The NMR spectrum of K[B^H ^] is shown in fig u re 25.

Pyrolysis of NatB^H^] and kCB 1 1 H14] produced low y ie ld s (4-6% based on BgHg) o f isomers of B 1 gH22. This was accomplished by heating these sa lts to 120-150°C under dynamic vacuum. The product was sublimed from the reaction vessels into a U-trap maintained at 0°C.

The ratio of the_n-B 1 8 H2 2 to_L-B 1 8 H2 2 isomers (fig u re _25) produced in this reaction was found to be about 1:1.5 (j^ - : _i_). The two isomers were successfully separated on an High Pressure Liquid Chromatograph

(HPLC) using a silica gel column. Although the yields of the isomer are low, this preparation is potentially useful since it provides a route to the _i^B 1 8 H2 2 isomer. Preparations of Bj 8 H2 2 based upon the pyrolysis of BgH^L compounds produce only the _n-Bi 8 H2 2 isom er.60,31

Figure 26_ shows the boron-11 NMR spectrum of _1“ B1 8 H22. Figures 27_ and

28 show the boron-11 NMR spectrum, 2D ^B -^B NMR spectrum, and assignments for_n-B^gH22.

D. Preparation of Decaborane(14) from Pentaborane(9).

Improvements in the "one pot" co n ve rsio n ^- ^ of BgHg to B^qH ^ have raised the product yield (based on BgHg) from 40-45% in the original preparation to 58% in the latest preparation (equation 32, 33).

1.8 B 5 Hg + NaH + [(CH 3 ) 4 N]C1 ------> [(^^[B gH ^] + H 2 (32)

+ NaCl + minor products

C(CH3 ) 4 N][BgH14] + BC1 3 > B1 qH1 4 + [(CH3 ) 4 N][BC13 H] + H2 (33) 63

a = ' “B18H 2 2 b= n-B|gH22

II

V_J

20 -10 -20 -30 -40 PPM

Figure 25. Boron-11 NMR spectrum o f the B 1 8 H2 2 isomer mixture obtained from pyrolysis of 64

11B

i ***%«)■

11bM J

J______L J______L 20 0 ppm 20 40

Figure 26. Boron-11 NMR spectrum of J_-B^gH 22« 5 ,6

-10 -20 -30 -40 ppm

Figure 27. COSY spectrum and assignments for _n-Bia H 66

I X X J l X x 20 -10 -2 0 - 3 0 -4 0

Figure 28. Boron-11 NMR spectrum of The y ie ld increase is a ttrib u te d p rim a rily due to improvements in the preparation of the [(CH 3 )^N]intermediate. Specifically the use of a 1.8:1- ratio of B^Hg to NaH in the firs t step of the reaction along with use of glyme is probably the major factor in the yield improvement. The 58% yield obtained in this reaction is interesting because it is better than the theoretical yield of 56% from the stoichiometry proposed by Toft. It was, therefore, of in te re s t to determine whether the proposed stoichiom etry was wrong, o r whether some other factor was responsible for the unexpectedly high yield. Reaction was studied using very pure [ (CH 3 J^N] [BgH-^^] which Q7 was prepared from B^qH^ by base degradation. Also investigated was the reaction of BC1 3 with the decomposition products of

[(CH3 )/jN][BgH^] since these species constitute the impurities in the

[BgH^]- preparation as described above.

Pure t(CH 3 )4 N][BgH14] was freshly prepared from BjqH^ using the

0 7 method of Gaines and Nelson, and was shown to be very pure by boron-11 NMR spectroscopy. The use of this freshly prepared material in reaction 33_ led to a B^qH^ y ie ld of 45-48% based on

C(CH3 . It reasonably might have been expected that this reaction would have produced an even higher y ie ld of B^qH^ than is obtained from the "one pot" procedure since at best only 80% of the in it ia l B 5 Hg is converted to the [(C^J^NjCBgH^] intermediate. The reaction of BC1 3 with the decomposition products of [(CI^J^NDCBgHj^] was also studied, since the decomposition of this species is the source for most, if not a ll, of the minor species arising in equation

32. This experiment produced a 30% y ie ld o f b10H14 based on 68

[(CHg^NDCBgHu]. Neither tria l provided an explanation for the "one

pot" preparation of B^gH^ from BgHg, however, it is clear that there

is no advantage to purify the intermediate [(C^J^NDCBgH^] anion, if

it is to be subsequently converted to BjqH ^ .

Other improvements were also made in th is preparation. Good yields of product were obtained. It was found that a higher quality product could be obtained if lower sublimation temperature (40-45°C) were employed in the fin a l step. A lte rn a tiv e ly , B 1 0 H1 4 could also be extracted from the final reaction mixture with hot jv-butyl ether.

This method would only be useful if the _n-butyl ether solution could be used directly, since there is no practical method for separating

B1 0 H1 4 from _rv-butyl ether.

E. Preparation of ji-0ctadecaborane(22) from Pentaborane(9).

Pentaborane(9) was converted to 2L~octadecarborane(22), in a

"one pot" procedure going through LBgH14]“ . The synthesis is described in equations V* J54_, and

Na[B 9 Hi 4] + HC1 + (n-Bu)20 ...... > B9 H1 3 0(n-Bu ) 2 + H2 (34)

+ NaCl

B9 H1 3 0(n-Bu)2 - heat- > n-B 1 8 H2 2 + 2 H2 + (n-Bu)20 (3b)

Reactions _2£ and ^0 have been previously described.6*^ Product yields of approximately 30% (based on BgHg) are obtained using this procedure. 69

F. Other Related Reactions. Hexaborane(lO) is known to undergo a number of reactions parallel to those of BgHg, particularly with respect to reactions w ith Lewis and Bronsted bases.131-147 was therefore of interest to see whether [BgHg]" might react with BgH^g in a fashion similar to the reaction of [BgHg]" with BgHg (equation

19). Thus, when 2 equivalents of BgH 1 0 was reacted with KH in THF over a period of 3 days, according to reaction 36^, KLB^H-^] was produced in about 70% yield based on integrated boron-11 NMR spectra

(figure 29).

2 B6 H1 0 + KH > K[BnH14] + KLBgH^] + K^Hy] (36)

> 70% 20-25%

This suggests a reaction parallel to reaction 22 in which two Bg un its combine to form a CBi 2 Hi 7 ^~ anion, followed by loss of "BHg" to form the major product [B ^H ^]" (equation 37).

[BgHg] + BgHj^g -----> "[Bj^H^] " —— > [Bj ^Hj^ ] + BHg (37)

This suggests that this type of reaction might be a general synthetic route to higher boron hydride systems. 70

- 3 5 - 2 5 - 3 0 -1 5 -2 0 PPM

Figure 29. Boron-11 NMR spectrum of the reaction of 2 B 6H10 + KH in

THF. a = [Bn H14]" ; b = [BgH14] . I I I . Formation of Triosmium Carbonyl Methylidyne Derivatives

of Boranes and Carboranes.

A. Preparation of Pentaborane(9) Derivatives. A Friedel-Crafts

type reaction of pentaborane(9) with the boroxine supported triosmium

carbonyl cluster [(u-H^COJgOsgfuj-COJ^BgOg) (figure _30) has

resulted in the preparation of a triosmium carbonyl methylidyne

derivative of B 5 Hg, (u-H) 3 (CO)gOs 3 (u 3 -C -l-B 5 H0 ), according to equation

38.

[ (u-H)3(C0)g0s3(u3-C0)]3(B303)

BF:

B5H9

( u - H ) 3 (C0 ) 90s3 ( u 3-C- 1-B 5H8 )

This s ta rtin g m aterial has previously been used to prepare phenyl and

1 QQ halo derivatives from Friedel-Crafts reactions.

This product was also obtained from the reaction of

(u-H) 3 (C0 )g 0 s3 (u 3 -CCl) with B&Hg in the presence of AICI 3 . This reaction is of particular interest because it implies the existence of the carbocation "[(u-H) 3 (C0 )g 0 s3 (u 3 -C)]+" as an intermediate in the 11

Os(2") 0s(3")

O --- Os(1")(

B(105) W V 0(104) Os(2')

0(106) B(103) 8(101) Os(l') \ 0 ( 102)

Os (2) fp i 0s(1)

0s(3)

Figure 30. Molecular structure of L(u-H) 3(C0)y0s3(u3-C0 )] 3(B303). 73

Friedel-Crafts reaction. This would be a non-planar carbocation. The

role of the boron trifluoride is thought to assist in cleaving the C-0

bond which-attaches the cluster to the boroxine ring by coordination

with the oxygen atom. Indeed, signals fo r BF3-oxygen species were

observed in the boron-11 NMR spectrum at about 0 ppm in many samples,

particularly in preparations of derivatives of decaborane(14) and j>carborane, which are described below. However, an intermediate

carbocation was not isolated, nor was evidence for its existence

observed other than the formation of the Friedel-Crafts product.

The reaction was carried out by stirring the boroxine supported

cluster in a pentaborane(9) slurry in the presence of 2-4 equivalents

of boron trifluoride. Pentaborane(9) was in greater than 50:1 molar

excess in this case, however, similar products were obtained by

running the reaction in methylene chloride with a 3-fold excess of

BgHg. The ^B NMR spectrum of the non-volatile products is shown in

fig u re JJ1_ and shows the presence of two isomers. The apical -1-BgHy

isomer was found to be insoluble in hexane while the second isomer,

possibly a basal -2-B5Hg isomer, was only slightly soluble in

hexane. Thus, f ilt r a t io n in hexane, followed by a second f ilt r a t io n

in methylene chloride to remove boric oxide isolated pure

(ii-H ) 3 (C0)g0s 3 (u 3 -C-l-BgHg). The boron-11 NMR spectrum of this isomer

is shown in figure_32. The spectrum consists of a signal due to the

basal B(2,3,4,5) boron atoms at -12.2 ppm (J = 140 Hz), and a singlet

attributed to the apical B(1) signal at -25.3 ppm. The proton NMR

spectrum shows a single metal hydride signal at -19.23 ppm, a broad

single resonance at -0.86 assigned to the B-H-B bridging hydrogens, 74

VkklkAU

I '-----1------•- 1----- 1------'-1------'-1------1-1------'-1------1-1-----r 20 10 0 -10 -20 -30 -40 -50 PPM

Figure 31. Boron-11 NMR spectrum of the reaction of BgHg with

[ ( u-H)3 (00)9053(M3-CO)33(6303) in the presence of BF 3. 75

i ------1------1------1------1------1------1------1------r ~ 0 -10 -20 -30 -40 PPM

Figure 32. Boron-11 NMR spectrum of the apically substituted

(ii-H)3(C0)90s3 (p3-C-l-B5 H8). 76 and a 1:1:1:1 quartet at 3.06 ppm (J = 168 Hz) due to the terminal basal B-H hydrogens. Both the boron and proton NMR spectra are in good agreement with an a p ic a lly substituted pentaborane(9) cage. The

FT-ICR mass spectrum showed a signal fo r the molecular ion at 906 m/z

(calculated:906) and the sequential loss of 9 carbonyls from the triosmium cage. Figure shows the FT-ICR mass spectrum and the proposed structure o f (u-H) 3 (CO)gOs 3 (u 3 -C -l-B 5 H8) .

The pentaborane(9) derivative (y-H^COJgt^^-C-l-BijHg) is very moisture sensitive. Reaction of this cluster with air resulted in the formation of trisomium carbonyl methylidyne, (u-H) 3 (C0 ) 9 0 s3 (u 3 -CH), and an unidentified boron residue. The formation of the C-H capped cluster could be detected by proton NMR spectroscopy ( 6 = 9.36 ppm fo r U 3 -CH, -20.02 ppm for Os-J^-Os)^® or by mass spectroscopy. The conversion to the methylidyne cluster was cleanly accomplished by heating with glacial acetic acid for 24 hours at 80°C. The moisture sensitivity of the cluster thwarted attempts to separate and isolate the two isomers using chromatographic techniques on silica gel. The second isomer was never isolated as a pure compound.

B. Preparation of Decaborane(14) Derivatives. Attempts to prepare similar triosmium carbonyl methylidyne derivatives of decaborane(14) resulted in a mixture of isomers which were not successfully separated due to their extreme air-sensitivity. The mass spectrum of the non­ volatile products from the reaction of 5 equivalents of B^qH^, 2 equivalents of BF 3 , and 1 equivalent of [(u-H ^C O Jgt^^-C O )^^!^) in methylene chloride showed the presence of (u-H^COjgC^^-CH). RELATIVE INTENSITY RELATIVE INTENSITY 5 0 0 5 0 100 78

This product was assumed to be formed due to the brief exposure to air while the compound was being loaded into the mass spectrometer.

C. Preparation of ^-Carborane Derivatives. Triosmium carbonyl methylidyne derivatives of_o-carborane were prepared by the reaction of j^-carborane with [(u-H) 3 (C0 )g 0 s3 (u 3 ~C0 )] 3 (B3 0 3 ) in the presence of

2 equivalents of BF 3 , according to equation 39.

C ( |J~H) 3 (CO) 9 0s 3 ( U3-CO ) ] 3 ( B3O3) (3 9 )

1»2-C2BqH12

BFo

(u~H)3(C0)gOS3(U3—C—CgBgH^ 2)

The in itia lly light yellow slurry gradually turned to a clear, red solution then slowly formed a lig h t yellow p re c ip ita te . This precipitate was isolated by filtra tio n , dissolved in acetone, and passed through a silica gel column. The light yellow solid was obtained in 47% yield (based on ^(^(CO Jiq used to make the starting boroxine compound). In contrast to the pentaborane(9) and decaborane(14) derivatives, the jo-carborane derivative was reasonably stable in a ir , showing l i t t l e decomposition a fte r 1 week in so lu tio n . The FT-ICR mass spectrum of th is compound (fig u re 34) iue 4 F-C ms setu o ( H^CUj C^ByHjj). H y B ^ -C ^ g s O jy U C ^ -H (M of spectrum mass FT-ICR 34. Figure

r c l a t w f : i N r c N S ' T f S I . U. M. . A IN ASS M 79 showed a molecular ion signal at 987 m/z (calculated: 987) and the sequential loss of 9 carbonyl ligands. The proton NMR spectrum showed one metal hydride signal at -18.93 ppm. Signals for the terminal B-H groups could not be resolved due to the expected overlapping quartets. The boron-11 NMR spectrum (figure J5) showed four signals, all doublets, at 0.97, -5.71, -10.65, and -13.73 ppm. However, six signals are expected for a mono-substituted o-carborane. The structure of the_o-carborane starting material is readily assigned on the basis of the 2D spectrum. The ^B -^B NMR spectrum, ID NMR spectrum, and structure of_o-carborane are shown in figures 36 and

37. An attempt to assign the structure of the carborane derivative

1 1 using a 2D NMR experiment, however, was not successful. The 2D AAB-

^B NMR spectrum is shown in figure 38. __L_ -10 -20 PPM

Figure 35. Boron-11 NMR spectrum of (u-H^COjgOsjtug-C-CgBgH^). T i — r ------r ~

5 0 - 5 -10 - 1 5 ppm

Figure 36. Boron-11 NMR spectrum and molecular structure of o-carborane. 83

1 0 -5 -10 -15 -20 PPM

Figure 37. ^B -^B COSY experiment for o-carborane. 84

Ji ------1______i______ii______li__ 5 0 - 5 -10 -15 ppm

Figure 38. COSY experiment for (u-H^COJgOsytijy-C-C^ByHii). EXPERIMENTAL

I. Apparatus and Equipment.

A. Vacuum Line. Because of the air sensitivity of the boron

hydrides used in this project, a Pyrex high vacuum line similar to

that described by Sanderson^® was used to manipulate volatile

compounds. The vacuum lin e consisted o f a pumping s ta tio n , a main

manifold, two reaction manifolds, a U-trap fractionation train, and a

calibrated Toepler system. One reaction manifold was equipped with a

4 mm Teflon stopcocks manufactured by Kontes and Fischer & Porter; the other reaction manifold was equipped with 4 mm ground glass stopcocks. Connections were made to the reaction vessels through standard taper 14/35 joints which were affixed to the reaction manifolds. The fractionation train was constructed of four U-traps with ground glass stopcocks and a mercury manometer connected to one trap. The reaction manifolds, fractionation train, and Toepler system were connected to the main manifold using 10 mm Pyrex tubing and yround glass stopcocks. Additionally, 10 mm crossover tubes connected the individu a l components so that gasses could be transferred between different parts of the vacuum line without using the main manifold.

The main manifold was evacuated to an ultimate pressure of 10"® mm Hy using a Welch Duo-Seal rotary vacuum pump and a two-staye mercury

85 86 diffusion pump. A liquid nitrogen trap between the reaction manifold and the diffusion pump protected the latter from solvent vapors. A dry ice-isopropanol trap was used between the diffusion pump and the mechanical pump to protect the latter from mercury.

B. Dry Box. The manipulation of non-volatile, air-sensitive m aterials was carried out using a Vacuum Atmospheres glove box (dry box). Constant circulation of Matheson prepurified nitrogen gas through a column containing Linde 13-X molecular sieves and Ridox oxygen scavenger maintained a dry, oxygen-free atmosphere. Entry into the dry box was achieved through a port which was twice evacuated and flushed with nitrogen gas. The design and operation of this dry box have been described elsewhere . ^ 9

C. Reaction vessels. Pyrex tubes and round bottom or Kjehdahl flasks fitted with either standard taper 14/35 joints or Fischer &

Porter Solv-Seal joints were used as reaction vessels. A stopcock adapter with a Kontes 4 mm Teflon stopcock, standard taper 14/35 jo in t, and a Fischer & Porter Solv-Seal joint were employed to connect the reaction vessels to the vacuum line or to take reaction vessels into the dry box. Stirring of the reactants was accomplished with the use of Teflon or glass-coated s tir bars driven by externa! rotating magnets.

A ir-s e n s itiv e samples were prepared fo r nuclear magnetic resonance spectroscopy in a reaction vessel having a side arm to which either a 5 mm or a 10 mm NMR tube was attached by glass blowing. The 87 reaction solution could then be tipped directly into the NMR tube and sealed off with a torch. A diagram of this type of vessel is shown in figure jJ9.

Filtrations of air-sensitive materials were achieved using a vacuum extractor such as the one illustrated in figure 40. The apparatus was rotated 180° about the standard taper 14/35 joint attaching it to the vacuum line to filte r the material in the reaction flask. Cooling the collection vessel speeded up the filtra tio n process. Alternatively, materials which were too fine to filte r with this type of apparatus were successfully filtered in the dry box using a Teflon filte r.

Solvents were f i r s t dried and d is t ille d , degassed under vacuum, and then stored in 500 mL round bottom solvent bulbs having Kontes 4 mm Teflon stopcocks and standard taper 14/35 joints. For use, the bulbs were attached directly to the vacuum line and the desired amounts of solvents could be transferred easily by condensation into the reaction vessels. Solvents of very low volatility such as jnbutyl ether were firs t distilled into sealed glass vessels and then transfered in the dry box.

Glassware was cleaned by soaking for a few hours in a potassium hydroxide/ethanol cleaning solution. Rinsing firs t with double distilled water and finally with acetone and drying in an oven at 85-

95°C prepared the glassware for use.

D. Nuclear Magnetic Resonance Spectra. Boron-11 Fourier Transform

Nuclear Magnetic Resonance (FT-NMR) spectra were recorded on either a NMR sam ple tube

reaction bulb

Figure 39. Vessel used to prepare NMR samples of a ir-s e n s itiv e m aterials. «9

reaction vessel

9 mmSolv-seal joint

Kontes stopcock

to vacuum line

glass frit

Kontes stopcock

9 mm Solv-seal joint

collection vessel

Figure 40. A vacuum extractor. Bruker WM300 or a Bruker MSL300 spectrometer. Both employed superconducting magnets and were equipped with boron - 1 1 fixe d frequency probes. Chemical s h ifts were referenced using an external sample of boron tric h lo rid e in methylene chloride-dg which was assigned a chemical shift of +46.80 ppm relative to boron trifluoride etherate at 0.00 ppm. For low temperature studies, the probe was cooled with a stream of cold nitrogen gas which was obtained by boiling off gas from liquid nitrogen in a sealed Dewar using an immersed heater. The temperature was monitored using a thermocouple placed near the probe and controlled using a BVT-1000 low temperature u n it. Boron-11 COSY spectra15^ correlated spectroscopy were obtained on the Bruker MSL300 spectrometer. Proton FT-NMR spectra were recorded on either a Bruker AM500 or a Bruker WM200 spectrometer.

Both employed superconducting magnets. The solvent signals in the spectra were used as internal chemical shift references.

E. Mass Spectra. Fourier Transform Ion Cyclotron Resonance (FT-

ICR) mass spectra 1 5 1 of organometallic clusters were obtained on a

Nicholet MS1000 spectrometer operated by Mr. Steven Mullen. Gaseous samples were analyzed fo r hydrogen and other lig h t gasses using an AEI

MS-10 mass spectrometer.

F. Infrared Spectra. Fourier transform infrared spectra (FT-ICR) spectra were recorded on a Mattson Cyngus or in a Perkin-Elmer 257 spectrometer. Spectra of gaseous samples were obtained using a 10 cm

Pyrex c e ll using KBr windows. The sample pressure used in these 91

experiments was approximately 8-14 mm Hg. Other spectra were obtained

either with a solution IR cell using KBr windows or with nujol mulls

between a ir - tig h t KBr plates.

G. High Pressure Liquid Chromatography. A Perkin-Elmer Series 2

High Pressure Liquid Chromatograph employing a s ilic a gel a n alytica l

and preparatory column and a LC-75 UV detector was used to separate

mixtures of compounds.

I I . Reagents.

A. Boron tric h lo rid e was obtained in a lectu re b o ttle from

Matheson and used without further purification.

B. Boron tr iflu o r id e was obtained in a le ctu re b o ttle from

Matheson. I t was passed through a -140°C trap p rio r to use and stored

in a Pyrex tube w ith a ground glass stopcock at -196°C.

C. o-Carborane was purchased from Alfa Products and used as

received.

D. Cesium metal (Gold Label) was purchased in a sealed glass ampule from A ld rich Chemical Company and used w ithout fu rth e r puri fic a tio n . 92

E. Cesium chloride was obtained from Alfa Products, Inc. It was

dried at 150°C under high vacuum and stored in the dry box.

F. Decaborane(14) was prepared according to the synthesis reported

in this thesis.

G. Dibenzo-18-crown-6 crown ether was purchased from Aldrich

Chemical Company and used without fu rth e r p u rific a tio n .

H. Diborane( 6 ) was prepared by the reaction of sodium borohydride

and boron t r iflu o r id e . 3 0 The boron trifluoride impurity in the

product was removed by stirring over ethyl ether at -78°C and

fra c tio n a tio n through a -140°C tra p .

I. Dihydridodecacarbonyltriosmium (H 2 0s3 (C0)10) was generously

supplied by Ms. Jeanette Krause and Dr. Deng-Yang Jan, who prepared it

1 W? from H 2 and 0s 3 (C0) 1 2 using the lite ra tu re method.

J. Hexaborane(lO) was prepared from pentaborane(9) and diborane( 6 ) 71 according to the lite ra tu re method.

K. Hydrogen bromide was obtained from Matheson. I t was p u rifie d by passing through a -111°C tra p and stored at -78°C in a Pyrex tube having a ground glass stopcock. 93

L. Hydrogen ch lo rid e was obtained from Matheson. I t was p u rifie d by passing through a -140°C trap to remove water and stored in a Pyrex tube with a Kontes Teflon stopcock at -78°C.

M. Lithium borohydride was purchased from Matheson, Coleman, and

Bell and used as received.

N. Napthalene was purchased from J. T. Baker Chemical Company and used as received.

0. Napthalene-dg was purchased from A ld rich Chemical Company. I t was sublimed before use and stored in the dry box.

P. Pentaborane(9) was obtained from C allery Chemical Company,

Callery, Pennsylvania. It was purified by passing through a -78°C trap and stored in an evacuated Pyrex tube at -78°C prior to use.

Q. Potassium metal was purchased from Aldrich Chemical Company as lumps of metal in mineral o il. In the dry box, the oil ws washed away with hexane. The metal was then stored in a sealed vessel in the dry box u n til use.

R. Potassium hydride was purchased from A ld rich Chemical Company as a 35% mineral oil dispersion. It was washed repeatedly with dry pentane to remove the oil and stored in the dry box. The activity was 94 determined by reaction w ith methanol and measurement o f evolved Hg gas.

S. Rubidium metal (99.9%) was purchased in a sealed glass ampule from A ldrich Chemical Company and used as received.

T. Sodium metal was purchased from J. T. Baker Chemical Company as lumps of metal in mineral o il. In the dry box, the oil was washed away with hexane. The metalwas then stored in a sealed vessel in the dry box u n til use.

U. Sodium borohydride was purchased from Matheson, Coleman, and

Bell and used without further purification.

V. Sodium hydride was purchased from A ldrich Chemical Company as a

50% mineral oil dispersion. It was washed repeatedly with dry pentane to remove the oil and stored in the dry box. Activity was determined by reaction w ith methanol and measurement of evolved H 2 gas.

H. Tetra-n-butyl ammonium iodide was obtained from J. T. Baker

Chemical Company. I t was dried at 150°C under high vacuum and then stored in the dry box.

X. Tetramethylammoniurn chlo rid e was obtained from A ldrich Chemical

Company. I t was dried at 150°C under high vacuum and then stored in the dry box. 95

Y. Acetonitrile was obtained from Fischer Scientific. It was distilled from calcium hydride and stored in a solvent bulb.

2. Butane was obtained in a lectu re b o ttle from Matheson. I t was dried by s tirrin g over potassium hydride and stored in a Pyrex tube at

-78°C.

AA. _n-Butyl etherwas purchased from A ldrich Chemical Company. I t was dried by d is t illin g from sodium benzophenone ketyl and stored in a sealed vessel in the dry box.

BB. Ethyl ether (d ie thyl ether) was purchased from Matheson,

Coleman, and Bell. It was stored in a solvent bulb containing sodium benzophenone ketyl p rio r to use.

CC. Glyme (1,2-dimethoxyethane) was purchased from Matheson,

Coleman, and B e ll. I t was d is tille d f i r s t from potassium hydride and then from sodium benzophenone k e ty l. The solvent was stored in a solvent bulb containing sodium benzophenone k e ty l.

DD. Hexane and pentane were purchased from Matheson, Coleman, and

Bell. These solvents were distilled from calcium hydride and stored in solvent bulbs. 96

EE. Methylene chloride was purchased from Fischer S c ie n tific . I t was distilled from calcium hydride and stored in a solvent bulb prior

to use.

FF. Methyl ether (dimethyl ether) was obtained in a gas cylinder

from Matheson. I t was p u rifie d by s tir r in g over potassium hydride at

-78°C for several hours. The dried solvent was stored in a Pyrex tube without drying agent at -78°C.

GG. Tetrahydrofuran (THF) was obtained from Fischer Scientific.

I t was d is tille d from sodium benzophenone ketyl p rio r to use and stored in a solvent bulb containing sodium benzophenone ketyl.

I I I . Reactions

A. Reaction of B 5 H9 with two equivalents of potassium napthalide. In the dry box, a 30 mL fla sk was charged w ith 107.5 mg K metal (2.749 mmol) and 366.5 mg napthalene (2.86 mmol), and a glass- coated magnetic s tir bar. The reaction flask was attached to a Solv- seal extractor. On the vacuum line, the vessel was evacuated and 10 mL THF was condensed in to the vessel at -196°C. The vessel was stirred at room temperature for 12 hours to form the napthalide. The vessel was once again cooled to -196°C and 1.38 mmol BgHg was admitted by condensing. After 30 minutes of stirring at room temperature, the color had changed from dark green to burgandy-red. Stirring was continued for 2 hours. The colored solid was filtered on the frit of 97

the extractor and washed several times with THF to remove

napthalene. V o la tile s were then pumped removed by continuous pumping

for 30 hours. In the dry box, 182 mg of product (1.29 mmol, 94%

yield) was scraped from the extractor. IR spectrum (nujol mull):

V( b_h) 2400 (s, b), 2290 (s, b), 2210 (sh). Solubilities: insoluble

in ethers, hydrocarbons, and methylene chloride.

B. Preparation of the crown ether complex [K(dibenzo-18-crown-

6) ] 2 B5 H g . In the dry box, a 50 mL reaction vessel with an NMR side

arm and a Teflon-coated magnetic s tir bar was charged with 11.7 mg K metal (0.299 mmol), 109 mg dibenzo-18-crown-6 (0.302 mmol), and a

trace amount o f napthalene (<5 mg). The vessel was removed from the

dry box and evacuated on the vacuum lin e . Glyme, ca_. 1 mL, was

condensed into the vessel. As the mixture firs t began to stir at room temperature, a green napthalide color was visible. This faded after

2-3 hours leaving a yellow solution and a light yellow precipitate.

The reaction vessel was then cooled to -196°C and 0.150 mmol B5Hg

(measured as a gas) was condensed in to the vessel. Warming to room temperature with stirring quickly consumed the yellow solid, forming a clea r yellow s o lu tio n . However, a fte r a few minutes, a yellow solid began to appear again. The solution was then tipped into the NMR tube

and the sample was sealed with a torch. NMR spectrum at 96.27

MHz: -11.5 ppm (J = 132 Hz); -51.0 ppm (J = 157 Hz).

C. "One-pot synthesis" of 5 BHh from t^CBgHg] by protonation with

HC1 in butane. In the dry box, a 250 mL reaction flask containing a glass coated magnetic s tir bar was charged with 872 mg K metal (22.3 mmol) and 2894 mg napthalene (22.6 mmol). The vessel was removed from the dry box and evaucated on the vacuum lin e . 15-20 mL glyme was distilled in. The flask was warmed to room temperature and stirred overnight to form the dark green napthalide. The reaction vessel was then cooled to -196°C and 11.2 mmol BgHg (measured as a gas) was condensed into the vessel. The vessel was then allowed to warm to room temperature with stirring. After 2 hours, the reaction mixture appeared as a burgandy red suspension. Solvent and other v o la tile s

(napthalene) were removed by pumping for 3 days, leaving a free- flowing brown powder in the vessel. The vessel was then cooled to

-196°C and 5-8 mL of butane and 30 mmol HC1 (measured as a gas) were admitted by condensing. The temperature was raised to -78°C and maintained there for 30 minutes. After this time, the solid material was cream-colored. The volatile products were fractionated through U- traps held at -95°C, -111°C, and -196°C. (3.80 mmol, 38% yield based on B^Hg) collected in the -111°C and -95°C traps and was identified by its IR and boron-11 NMR spectra and by its vapor pressure at 0°C of 52 mm H g .^-4 gutane and an undetermined amount of HC1 and B 2 Hg (identified by gas IR spectroscopy) passed through the

-111°C tra p and collected at -196°C.

D. Preparation of from Cs 2 [BgHg] by protonation with liquid

HC1. In the dry box, 188.0 mg Cs metal (1.41 mmol) and 186 mg napthalene (1.45 mmol) were weighed in to a 250 mL reaction vessel containing a glass-coated magnetic s tir bar. The vessel was removed 99 from the dry box and evacuated on the vacuum line. After cooling to

-196°C, 10-12 mL THF was d istille d into the vessel. Warming to room temperature and s tir r in g fo r 24 hours formed the dark green napthalide. BgHg (0.70 mmol, measured as a gas) was then condensed in to the vessel at -196°C followed by warming to room temperature. As the reaction proceeded, the color gradually changed from dark green to grey-black. After 3 1/2 hours, the volatile products were removed by pumping. Pumping was continued fo r 20 hours. The vessel was cooled to -196°C, and 4.0 mmol HC1 (measured as a gas) was condensed in to the vessel. The vessel was warmed to -78°C. H 2 gas evolution (0.41 mmol) was measured after once again cooling to -196°C. The volatile products were then fractionated through traps held at -140°C and

-196°C. The -140°C trap contained 0.150 mmol BgHu (21% yield based on BgHji) which was identified from its gas IR spectrum.^2 The gas

IR spectrum of the contents of the -196°C trap showed that it contained a mixture of B 2 Hg and HCl.^®

E. Preparation of BgHjj from l^CBgHg] by protonation with liquid

HBr. 4.00 mmol I^CBgHg] was prepared from 314.6 mg K metal (8.04 mmole), 1060 mg napthalene (8.28 mmol), and 4.00 mmol BgHg in a 250 mL reaction vessel as described above in _A. Removal of the napthalene from the I^CBgHg] product was achieved by continuous pumping for 3 days. A few glass beads were added in the dry box to aid in s tir r in g the solid. The reaction vessel was then evacuated and cooled to

-196°C and 15.0 mmol HBr (measured as a gas) was d is tille d in to the vessel. The vessel was then allowed to warm to -78°C for 30 minutes 100 with vigorous stirring. The solid was rapidly discolored. The vessel was again cooled to -196°C and 4.25 mmol H 2 gas was measured on a

Toepler system and pumped away. The v o la tile components were then fractionated through traps held at -111°C, -160°C, and -196°C. The

-111°C trap contained 0.35 mmol B5H11 ( 8 % y ie ld based on BgHg), which was identified by its gas IR spectrum.15^ jhe -160°C trap contained

1.40 mmol o f pure B 2 Hg, identified by its IR spectrum . 1 5 5

F. Reaction of BgHg with 1 equivalent of Na+(CjQHg)” . In the dry box, 48.7 mg Na metal (2.12 mmol) and 266 mg napthalene (2.08 mmol) were weighed in to a 100 mL reaction vessel containing a glass-coated magnetic s tir bar. The vessel was removed from the dry box and evacuated on the vacuum line. 10 mL THF was d istille d into the vessel which was cooled to -196°C. The vessel was warmed and stirred for 24 hours to form the sodium napthalide. The vessel was then once again cooled to -196°C and 2.12 mmol BgHg (measured as a gas) was d is tille d in to the fla s k . Warming and s tir r in g produced immediate d isco lo ratio n to form a clear, colorless solution. Only a trace amount of gas, identified as H 2 by mass spectroscopy, was evolved. The reaction solution was stirred at room temperature for 3 days. An NMR sample was prepared in the dry box. The ^B NMR spectrum showed the solution to contain 6 8 % [BgH^]", 12% [BgHg]", and a number of unidentified species.

G. Reaction of BgHg with 1/2 equivalent of Na+(C!QHg)". In the dry box, a 10 mL NMR sample vessel was loaded w ith 13.6 mg Na metal (0.587 mmol) and 79 mg napthalene (0.617 mmol). The vessel was

evacuated on the vacuum line and cooled to -196°C. THF (1-2 mL) was distilled into the flask and the mixture was stirred for 24 hours at

room temperature to form the dark green napthalide. The vessel was then cooled to -196°C, and 1.174 mmol BgHg, measured as a gas, was condensed in to the vessel. Warming and s tirrin g produced immediate discoloration of the green color, producing a clear, colorless solution. After 2 days time, the solution had yellowed. The boron - 1 1

NMR spectrum showed the [BgH^]" anion to the predominant species, along with [B ^H ^]- and BgHg. Only small amounts of other species were observed in the NMR spectrum. Among these were BH 3 THF and

[B 3 H8] " .

H. Low Temperature Reaction of [(n-fyHgJ^XBgHg] with BgHg. In the dry box, 15.0 mg KH (97%, 0.359 mmol) and 141.6 mg [(n ^H g ^N ]!

(0.384 mmol) were weighed in to a 10 mL reaction fla s k . A Teflon- coated magnetic s tir bar was added and the flask was attached to a greased standard taper 14/35 vacuum extractor. The receiving vessel . was a standard taper 14/35 tube having a 5 mm NMR tube sidearm. On the vacuum line, the vessel was evacuated. After cooling the reaction fla sk to -196°C, 1-1.5 mL glyme followed by 0.360 mmol BgHg, measured by gas volume, were condensed in to the vessel. The vessel was s tirre d fo r 6 h at -78°C, after which time 0.34 mmol or 94% of the expected H 3 gas had been evolved. The product was filtered at low temperature to remove KI and washed in to the NMR tube sidearm. The NMR tube was then cooled to -196°C and an additional 0.360 mmol BgHg was then admitted 102 by condensing. The NMR tube was sealed o ff with a torch and stored at

-196°C until use. Before the NMR spectrum was recorded, the sample tube was warmed to -78°C in a dry ice-isopropanol bath. It was then quickly inverted to ensure thorough mixing and placed immediately into the probe of the spectrometer. The NMR spectrum was followed as the sample was slowly warmed from -70°C to 0°C in the spectrometer. This resulted in a series o f sequential spectra showing the course of the reaction. These spectra are shown in figure 19.

I . Low Temperature Reaction of K[BgHg] with BgHg. In the dry box,

23.8 mg KH (97%, 0.576 mmol) was weighed in to a 50 mL NMR vessel

(reaction vessel having a 5 mm NMR sidearm) containing a Teflon-coated magnetic s tir bar. The vessel was evacuated on the vacuum line and cooled to -196°C. THF (ca. 1 mL) and BgHg (0.576 mmol, measured as a gas) were condensed in to the vessel. The vessel was s tirre d 4 hours at -78°C. After cooling once again to -196°C, H 2 gas (0.580 mmol,

100%) was measured. The vessel was returned to -78°C, and the solution was tipped and washed in to the NMR tube. The NMR tube was cooled to -196°c, an additional 0.550 mmol BgHg was condensed into it , and the sample was sealed with a torch. Sample storage and recording of the NMR spectrum was identical to that described above in _H. The

NMR spectra from this sample were nearly identical to those obtained above in 2 1 .

J . Reaction of BgHg with LiCBH^]. In the dry box, 37.8 mg Li[BH4]

(1.74 mmol) was weighed in to a 50 mL NMR vessel containing a Teflon- 103

coated magnetic s tir bar. The vessel was evacuated on the vacuum line

and cooled to -196°C. Glyme (ca. 1 mL) and 1.75 mmol BgHg (measured

as a gas) were condensed in to the vessel. The vessel was warmed to

room temperature and stirred for 18 hours. During this time, slow H 2

evolution was noted as well as a gradual .yellowing of the solution.

The vessel was cooled to -196°C and 2.18 mmol H 2 was measured and

pumped away. The sample was then tipped in to the NMR tube and sealed

with a torch. The 96.3 MHz boron-11 NMR spectrum showed three

doublets from LiCBgH^] at - 6 . 8 , -19.0, and -22.3 ppm, a nonet at

-28.8 ppm (J = 33 Hz) from LiCBgHg], and fiv e signals from an unknown

species at 7.6 (d, J = 132 Hz), -4.3 (s, br), -16.6 (d, J = 120 Hz),

-35.7 (d, J = 140 Hz), and -41.5 (d, J = 140 Hz) ppm.

K. Preparation of from BgHg. A 500 mL reaction vessel

was loaded in the dry box with 372.8 mg of KH (97% active, 9.018

mmol). A Teflon-coated magnetic s tir bar was placed into the vessel, which was then sealed with a stopcock adaptor, removed from the dry

box, and evacuated on the vacuum line. The vessel was then cooled to

-196°C using a liquid nitrogen bath, and 10 mL glyme and 22.0 mmol

BgHg (measured by its gas volume at room temperature) was condensed

into the vessel. This gives a BgHg to KH ratio of 2.4:1. The vessel was allowed to warm to room temperature and stirred for 2 hours.

Vigorous H 2 evolution ensued upon warming, but subsided within a few minutes. The vessel was again cooled to -196°C and 9.9 mmol H 2 gas was measured on the Toepler system and pumped away. The vessel was

then heated for 16 hours at 85°C using an oil bath heater, during which time the color gradually changed from nearly colorless to deep yellow. The vessel was then cooled to -196°C and an additional 22.4 mmol H 2 gas was measured and pumped away. Total H 2 evolution was 32.3 mmol. Removal of v o la tile s by pumping le f t a solvated, yellow gum.

The NMR spectrum of the product in glyme showed three signals at

-12.5 ppm (J = 146 Hz), -14.1 ppm (J = 156 Hz), and -14.9 ppm (J = 138

Hz) in a relative ratio of 1:5:5, and was identified as [Bi jH -^]" by comparison with spectra in the lite ra tu re .^

L. Attempt to prepare by a stoichiometric reaction of

BgHg with KH. In a procedure similar to that described above in _A,

86.3 mg o f KH (97%, 2.09 mmol), 4.60 mmol BgHg, and 10 mL glyme were reacted in a 100 mL reaction vessel. The BgHg to KH ratio was

2.2:1. The reaction mixture was stirred for 1 hour at room temperature followed by 16 hours at 85°C, during which time a total of

6.57 mmol H 2 gas was evolved. A total of 7.11 nmol H 2 was expected from the reaction stoichiometry. The NMR spectrum of the product

(fig u re _41) showed i t to be a mixture o f KC B^H ^] and K[BgH14] , No other species were observed.

N. Preparation of *somers ^rom 9 , 0 0 ,1 , 0 ^ oir k^B11h14^ was PrePared ,n a 250 mL reaction vessel as described above in_C. As much solvent as possible was removed by continuous pumping for 3 days. In the dry box, a U-trap was connected between the reaction flask and stopcock adaptor. The vessel was again evacuated on the vacuum line. An ice bath was placed on the U-trap. With 105 a

IMM

0 - 5 10 15 20 25 -3 05 35 PPM

Figure 41. Boron-11 NMR spectrum of an attempt to p re p a re [B j 1 h1 4] “ using a stoichiometric quantity of pentaborane(9). B 5 H9:MH = 2.2:1. a = ; b = [BgHj^]". continuous pumping, the fla sk was gradually heated to 145°C. Hydrogen appeared to be continuously evolved during th is process, but was not measured. After heating was discontinued, the reaction vessel was opened in air. The U-trap contained 50.0 mg of a mixture consisting of a 3:1 m ixture o f JL"B18^22 t 0 _2_”®18^22 based on B^Hg), as identified by boron-11 NMR spectroscopy. The two isomers were separated on an HPLC using a silica gel column and eluted using a 15%

CH2C12/85% hexane m ixture. Figures _2i5, ^ 6 and ^7 show the boron-11

NMR spectra of the isomer mixture and the separated isomers. Tables _3 and _4 presents boron-11 NMR chemical sh ift data and coupling constants

fo r _n."Bl 8 ^ 2 2 ancl -L“ B18^22’

N. Improved preparation of B^qH^ from BgHg. In the dry box,

372.4 mg NaH (95%, 14.74 mmol) and 1709 mg [(CH 3 )^N]C1 (15.6 mmol) were weighed in to a 500 mL reaction vessel containing a Teflon-coated magnetic s tir bar. The vessel was evacuated on the vacuum line. The vessel was cooled to -196°C and 5 mL glyme and 26.3 mmol B 5 Hg, measured as a gas, (B 5 Hg:NaH = 1.8:1) were condensed in to i t . The vessel was warmed to ambient temperature and stirred for 24 hours, forming a light yellow slurry. The vessel was again cooled to -196°C, and 17.2 mmol H 3 gas were measured on a Toepler system and pumped away. V o la tile m aterials were then removed by continuous pumping at room temperature for 8 hours. In the dry box, the reaction vessel was disassembled and a U-trap was connected between the reaction flask and the stopcock adaptor. The solid was also broken up with a spatula and a few glass beads were added to aid in stirring the solid. The vessel 107

Table 3. Boron-11 (MR Chemical Shifts, Coupling Constants

and Assignments 3 for JL-Bis^*

Assignment Chemical S h ift (ppm) J(B-H)

B( 3) 14.91 149 Hz

B( 10) 9.62 159 Hz

B(5,6) 5.85 sin g le t

B(9) 3.91 162 Hz

B( 1) 1.05 147 Hz

B(8 ) -3.69 149 Hz

B(7) -11.25 156 Hz

B(2) -31.40 158 Hz

B( 4) -39.46 164 Hz

Assignments based on 2D ^B -^B NMR spectrum. 108

Table 4. Boron-11 NMR Chemical Shifts and Coupling

Constants J.~^18^22*

Chemical S h ift ^(B-H)

14.68 ppm 150 Hz

10.46 ppm 141 Hz

4.20 ppm 148 Hz

2.78 ppm 148 Hz

-0.90 ppm 162 Hz

-2.95 ppm s in g le t

-14.53 ppm 154 Hz

-26.93 ppm 159 Hz

-38.88 ppm 142 Hz was removed from the dry box and evaucated on the vacuum lin e . BCI 3

(15.0 mmol, measured as a gas) was admitted by condensing i t at

-196°C. The vessel was warmed and stirred for 1-1/2 hours. The solid

turned yellow during this reaction. The vessel was then cooled to

-196°C and 10.8 mmol H 2 was measured and pumped away. An ice bath was

placed on the U-trap and using an oil bath heater, the reaction flask

was slowly heated to 40-45°C and maintained there fo r 3 hours. The

temperature of the flask was then very slowly raised to 120°C over a

period of 4 hours. The system was under dynamic vacuum during the

entire sublimation process. Slightly yellow B^gH^ (939 mg, 58.4%

yield based on the total boron content from BgHg) was recovered in the

U -trap.

0. Preparation of JL~B18H22 from t B9H14^” « In the dry box» I " * 3 mg NaH (93%, 7.72 mmol) was weighed in to a 500 mL reaction vessel

equipped with a Teflon-coated magnetic s tir bar. The vessel was

removed from the dry box, evacuated on the vacuum line, and cooled to

-196°C. THF (ca. 10 mL) and 1.48 mL BgHg (14.0 mmol, measured as a

liquid at 0°C where its density is 6 6 mg/mL) were condensed in to the

vessel. The vessel was allowed to return to room temperature and

stirred for 30 hours leaving a clear yellow solution. Hydrogen gas

(8.3 mmol) was measured on the Toepler system and pumped away. A fte r warming, the volatiles were removed by continuous pumping for 1 2

hours. Approximately 30 mL of (jt-Bu^O was added in the dry box and a water condenser was attached between the reaction flask and the stopcock adaptor. The vessel was once again returned to the vacuum 110

line, evacuated, and cooled to -196°C. HC1 (8.0 mmol, measured as a

gas) was condensed into the vessel. Upon warming, H 2 evolution

began. After stirring 2 hourc the solution had turned from yellow to white. The vessel was once again cooled to -196°C, and 9.45 mmol Hg

gas was measured and pumped away. With cold water flowing through the

condenser, the reaction vessel was slowly heated from room temperature to 145°C over a period of three hours. During this time, the pressure was c a re fu lly monitored on a Hg manometer. Most of the Hg evolution occurred between 90°C and 130°C. 7.0 mmol of H 2 was evolved. The product was extracted using 1 N aqueous NaOH. This was then c a re fu lly acidified to pH = 1 using 12 N HC1 and extracted again with benzene.

The benzene was removed by pumping and the product was sublimed at

120-130°C under high vacuum and id e n tifie d by it s m elting point and

NMR spectrum. Yield: 233.8 mg (1.08 mmol), 27% based on total boron from B 5 Hg.

P. Reaction of BgH^Q with one-half equivalent of KH in glyme. In the dry box, a 30 mL reaction vessel was loaded with 34.8 mg KH (95%,

0.824 mmol) equipped with a Teflon-coated magnetic s tir bar. The vessel was removed from the dry box, evacuated on the vacuum lin e , and cooled to -196°C. THF (1-2 mL) and 1.65 mmol BgHjg, measured as a gas, were condensed in to the vessel. The vessel was then allowed to return to room temperature and stirred for 18 hours. The vessel was then cooled to -196°C and H 2 gas was measured (0.824 mmol) and pumped away. Stirring was continued at room temperature for 2 additional days, after which time an additional 0.37 mmol of H 2 was measured and I l l

pumped away. The v o la tile products were removed by pumping and

fractionated through a -78°C trap in to a -196°C tra p . The -196°C

fraction contained a trace amount of t^Hg, identified by the IR

spectrum. No BgH^g or other boron hydrides were detected in either

fraction. An NMR sample in THF was prepared in the dry box. The

boron-11 NMR spectrum showed the product to be 70-80% [B u H ^]". The only other reaction product in any substantial amount was [BgH^]- , which accounted for 20-25% of the total boron content.

Q. Preparation of (u-H^COlgOsjfyj-C-l-BgHg). A 10 mL reaction vessel was loaded with 117.1 mg HgOsj^OJig (0.137 mmol) and a Teflon- coated magnetic s tir bar. The vessel was evacuated on the vacuum line and 2 mL dry CHgC^ was condensed in to the vessel at -196°C. This was followed by 0.548 mmol THF and 0.0687 mmol B 2 Hg, both measured as gases. The vessel was warmed to room temperature and stirred for 5 hours. After about 1 hour, the boroxine supported cluster had begun to precipitate leaving a light yellow solid and a yellow solution.

A fte r 5 hours, the v o la tile components were removed by continuous pumping fo r 1 hour. The vessel was cooled to -196°C and 1.0 mL BgHg

(ca. 10 mmol) and 0.274 mmol BF 3 were condensed in to i t . The vessel was returned to room temperature and stirred for 40 hours. The resultant mixture consisted of an orange solution and an off-white precipitate. Only 0.08 mmol of non-condensible gas was evolved. The volatile materials were removed by pumping for 1 hour. In the dry box, the reaction flask was attached to a vacuum extractor. The vessel was then again put on the vacuum lin e and the compound was 112 washed with hexane. The vessel was then taken into the dry box once more and a new collection flask was attached. Finally, the compound was dissolved in CH 2 CI2 and filtered, leaving behind boric oxide on the fr it. The methylene chloride soluble compound was isolated in 33% yield (41 mg) and identified as (p-H^COjgC^^-C-l-BgHg). Boron-11

NMR spectrum (CHgC^. room temperature): -12.2 ppm (4B, d, J = 140

Hz), -23.85 ppm (s, IB); proton NMR spectrum (CD 2 Cl2 » room temperature): 3.06 ppm (4H, q (1:1:1:1), J = 140 Hz, B-_H), -0.86 ppm

(4H, s (b r), B-JT-B), -19.23 ppm (3H, s, 0s-_H-0s); FT-ICR mass spectrum, m/z, found: 906, calculated: 906.

R. Preparation of (y-H^COjgi^^-C-Cg Starting with

187.5 mg HgOs^COJig ( 0 . 2 2 0 mmol) the boroxine supported cluster

[ (vj —H)g( C0)g0s3(yg-CO)] 3 (B3 O3 ) was prepared according to the procedure above in_Q. A fte r the v o la tile s had been removed by pumping, the vessel was taken into the dry box and charged w ith 32.0 mg _o-carborane

(0.226 mmol). The vessel was removed from the dry box, evacuated on the vacuum line, and cooled to -196°C. Dry CH 2 CI2 (1-2 mL) was condensed into the reaction vessel along with 0.440 mmol BF 3 . The vessel was allowed to return to room temperature with stirring. The light yellow precipitate gradually disappeared, forming an in itia lly clear, orange solution. After a few minutes, an off-white precipitate began to appear again. Over a period of 3 days, the amount of precipitate became noticeably larger. After stirring for 6 days, the v o la tile components were removed, the vessel was taken in to the dry box, and attached to a vacuum extractor. The orange CHgClg solution was filtered, leaving behind a slightly soluble (in CH 2 CI2 ) lig h t yellow material. In the air this material was dissolved in acetone and eluted from a s ilic a gel column w ith acetone and methylene ch lo rid e . Y ield: 72 mg (33% based on ^ O s ^ C O )^ ). FT-ICR mas spectrum, m/z, found: 987, calculated 987. Loss of 9 carbonyls from

OS3 framework was observed in mass spectrum. IR spectrum (f^ S O , room temperature): qq = 2011, 2076 cm-1. Boron-11 NMR spectrum: 0.97 ppm

(J = 129 Hz), -5.71 ppm (J = 148 Hz), -10.65 ppm (J = 164 Hz), and

-13.73 ppm (J = 151 Hz). Proton NMR spectrum: -19.23 ppm (s,

Os-H-Os), B-H region not resolved. 114

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