Chemistry of Deca- and Dodeca-Closo-Borate Bearing Three Exopolyhedral Sulfur Substituents

CHEMISTRY OF DECA- AND DODECA-CLOSO-BORATE BEARING THREE EXOPOLYHEDRAL SULFUR SUBSTITUENTS

DISSERTATION

Presented in Partial Fulfillment of the Requirements for

the Degree Doctor of Philosophy in the Graduate

School of The Ohio State University

Hoitung Terry Leung

*****

The Ohio State University 2004

Dissertation Committee: Approved by Professor Sheldon Shore, Advisor

Professor Ross Dalbey ______Professor Claudia Turro Advisor Department of Chemistry

ABSTRACT

Chemistry of mercaptan-closo-decaborate was extended from mono-substituted isomers to a new tri-substituted species. The previously reported procedure of

2- synthesizing 1,10-(Me2S)2-2-MeS-B10H7 from [B10H10] was found irreproducible. The method was modified and the overall yield was improved. Even though the degree of substitution was found to be controlled by time and temperature, the increase of reaction time and temperature did not produce further (or tetrakis) substituted product. The tri- subsituted compound of closo-dodecaborate system, 1,7-(Me2S)2-9-MeS-B12H9, was synthesized from 1,7-B12H10(SMe2)2. Analogously halogenations of 1,10-B10H8(SMe2)2 and 1,7-B12H10(SMe2)2 produced compounds with a general formula of 2-X-1,10-

(Me2S)2-B10H7 and 9-X-1,7-(Me2S)2-B12H9, respectively. The existence of cationic

+ + intermediates, [1,2,10-B10H7(Me2S)3] and [1,7,9-(Me2S)3-B12H9] , were examined and witnessed by 11B and 11B{1H} NMR. Dealkylation of these boron cages led to the corresponding tri-thioether as well as tri-thiol products. They were found reacted with methylene chloride. Due to the decrease of reactivity by gradual substitution of the boron cage, the reaction was not complete. Mono-substituted compounds were employed to demonstrate this unusual nucleophilicity of decaborane(10).

1- The isolation procedure of [2-B10H9SMe2] was previously reported with a small

1- contamination of [1-B10H9SMe2] . This was when they were synthesized from DMSO

2- and [B10H10] . We discovered that this isomer can be purified by dealkylating to [2-

2- B10H9SMe] and realkylating with methyl iodide. Both of the isomeric thioethers of

2- [B10H9SMe] demonstrated their nucleophilicities in the formation of

1- [B10H9SMe((CH2)nX)] by reacting with alkyl chloride and other halides. Subsequently,

2- the thioethers led to the production of the corresponding thiols, [1-B10H9SH] and [2-

2- B10H9SH] , with combined yield of over 60% isolated, significantly higher than other synthetic methods.

All new compounds have been characterized by multinuclear NMR and either mass-spactrometry or elemental analysis. Some of their molecular structures have been obtained by single-crystal X-ray diffraction studies.

iii

DEDICATION To My Parents and family

ACKNOWLEDGMENTS

I would like to thank my advisor, Professor Sheldon G. Shore, for his support intellectually and financially in all these years. He has given me a lot of freedom in my research. He guided me to the right directions with his patience and experiences, not only on my work, but also on how to be a better person.

I am very thankful to everyone who had helped me or been my companions in the Department of Chemistry here in The Ohio State University, especially the Shore group members. My friends and co-workers have taught me a great deal of chemistry as much as some valuable lessons in life. I would like to thank Dr. Roman Kultyshev especially for being a great friend as well as a mentor. I am grateful to Drs. Xuenian

Chen, Biu Du, Shengming Liu, and Edward A. Meyers who did most of the work on the crystal structures contained herein, sometimes even sacrificing their own work. I would also like to thank my friends and coworkers Drs. Errun Ding and Christine Plečnik for their help and support. Special thanks go to Dr. Ewan Hamilton, Seth Kerechanin and

Duane Wilson for proofreading this dissertation.

I extend my gratitude to the Department of Chemistry of The Ohio State

University for providing the opportunity to grow as a scientist.

VITA

May 28th 1974...... Born – Hong Kong

May 1998...... Bachelor of Science University of Hawaii at Manoa

1998 – 2002...... Teaching Asst. The Ohio State University.

2002 – 2004...... Reasearch Asst. The Ohio State University.

PUBLICATIONS

Research Publications

1. Kultyshev, Roman G.; Liu, Shengming; Leung, Hoitung T.; Liu, Jianping; Shore, Sheldon G., “Synthesis of Mono- and Dihalogenated Derivatives of (Me2S)2B12H10 and Palladium-Catalyzed Boron-Carbon Cross-Coupling Reactions of the Iodides with Grignard Reagents.” Inorg. Chem., 42, 3199-3207, (2003).

FIELDS OF STUDY

Major Field: Chemistry

TABLE OF CONTENTS

P a g e

Abstract ...... ii

Dedication ...... iv

Acknowledgments ...... v

Vita ...... vi

List of Tables ...... x

List of Figures ...... xii

List of Schemes ...... xv

Chapters:

1. Introduction

2- 2- 1.1 Structure and properties of [B10H10] and [B12H12] ...... 1

2- 2- 1.2 Synthesis of [B10H10] and [B12H12] ...... 2

1.3 Stereochemistry on the boron clusters substituents

1.3.1 Dodecaborane(12) ...... 5

1.3.2 Decaborane(10) ...... 6

1.4 Charge-compensated closo-borane compounds and reaction properties. . . 8

vii 2- 2- 1.5 Selectivity in reactions of [B10H10] and [B12H12]

1.5.1 Halogenation ...... 9

1.5.2 Diazonium derivatives ...... 11

1.5.3 Carbonyl derivatives ...... 11

1.5.4 Sulfonium derivatives ...... 13

1.5.5 Mercapto derivatives ...... 15

2. Result and Discussion

A. Synthesis of Metal Linker and Potential Formation of Linkages

A2.1 Synthesis of 1,10-B10H8(N2)2 and Reactions ...... 16

2- A2.2 Development in Synthesizing [1,10-B10H8(CN)2]

A2.2.1 Through 1,10-B10H8(N2)2 ...... 20

A2.2.2 Through 1,10-B10H8(IPh)2 ...... 21

B. Chemistry of inner sulfonium derivatives of deca- and dodeca-closo-borate

B2.1 1,10-(Me2S)2-2-MeSB10H7 ...... 36

+ B2.2 First Cationic Trisubstituted Isomers [1,2,10-B10H7(SMe2)3] ...... 40

B2.3 Neutral Icosahedral closo-dodecaborane bearing

3 exopolyhedral sulfur substituents ...... 51

B2.4 Halogenation of 1,10-B10H8(SMe2)2,

1,10-B10H8(N2)2 and 1,7-B12H10(SMe2)2 ...... 62

2- B2.5 Dealkylation of 1,10-(Me2S)2-2-MeSB10H7 to [1,2,10-B10H7(SMe)3] . . 66

B2.6 Reduction and oxidation of 1,10-(Me2S)2-2-MeSB10H7 ...... 73

1- B2.7 Isolation and characterization of 1- and 2-[B10H9SMe2] ...... 82

B2.8 Synthesis of methyl thioether and thiols from inner sulfonium salts . . . . .90

viii B2.9 Reaction of methyl thioethers with electrophilic reagents ...... 101

B2.9.1 Reaction of [Me4N]2[2-B10H9SMe] with methyl iodide ...... 102

2- B2.9.2 Reaction of isomeric [B10H9SMe] with dihaloalkanes ...... 105

2- B2.9.3 Reaction of isomeric [B10H9SMe] with alkyl halides ...... 119

2- B2.9.4 Tertiary Alkylation of [1-B10H9SMe] by Michael Addition . . . .122

2- B2.9.5 Reaction of [1-B10H9SMe] with 1,1-Dichloroacetone ...... 124

2- B2.9.6 Reaction of [1(2)-B10H9SMe] with unsaturated alkyl halides . . .129

3. Experimental

3.1 Apparatus ...... 136

3.2 Reagents ...... 138

2- A3 Synthesis of [1,10-B10H8(CN)2] ...... 140

B3.1 Reactions of 1,10-(Me2S)2-2-MeSB10H7 and 1,7-(Me2S)2-9-MeSB12H9 . 141

B3.2 Halogenation of boron cages ...... 148

1- B3.3 Synthesis of 1- and 2-[B10H9SMe2] and related reactions ...... 150

1- B3.3.1 Dealkylation of [2-B10H9SMe2] ...... 151

2- B3.3.2 Alkylation of [1(2)-B10H9SMe] ...... 154

List of References ...... 163

LIST OF TABLES

Table Page

1 Crystal data and structure refinement for 1,10-B10H8(IC6H5)2 ...... 27

2 Selected Bond Distances of 1,10-B10H8(IC6H5)2...... 29

3 Selected Bond Angles of 1,10-B10H8(IC6H5)2 ...... 30

4 Crystal data and structure refinement for [1,2,10-B10H7(SMe2)3]BF4 . . 46

5 Selected Bond Distances of [1,2,10-B10H7(SMe2)3]BF4 ...... 47

6 Selected Bond Angles of [1,2,10-B10H7(SMe2)3]BF4 ...... 48

7 Crystal data and structure refinement for 1,7-(Me2S)2-9-MeSB12H9 . . . 57

8 Selected Bond Distances of 1,7-(Me2S)2-9-MeSB12H9 ...... 58

9 Selected Bond Angles of 1,7-(Me2S)2-9-MeSB12H9 ...... 59

10 Crystal data and structure refinement for 1,10-(Me2S)2-2-MeSO2-B10H7 ...... 77

11 Selected Bond Distances of 1,10-(Me2S)2-2-MeSO2-B10H7 ...... 79

12 Selected Bond Angles of 1,10-(Me2S)2-2-MeSO2-B10H7 ...... 80

13 Crystal data and structure refinement for [Bu4N][2-B10H9SMe2] . . . . . 88

14 Selected Bond Distances and Angles of [Bu4N][2-B10H9SMe2] ...... 89

15 Crystal data and structure refinement for [MePPh3]2[2-B10H9S] . . . . . 98

16 Selected Bond Distances and Angles of [MePPh3]2[2-B10H9S] ...... 100

17 Varied chemical shifts of alkylated products with different dihaloalkanes ...... 109

1- 18 Structure refinement for 1- and 2-[(MeSCH2Cl)-B10H9] ...... 113

1- 19 Selected Bond Distances of [1-(MeSCH2Cl)-B10H9] ...... 115

1- 20 Selected Bond Distances of [2-(MeSCH2Cl)-B10H9] ...... 116

1- 21 Selected Bond Angles of 1- and 2-[(MeSCH2Cl)-B10H9] ...... 117

22 Varied chemical shifts of alkylated products with different alkyl iodides ...... 120

23 Crystal data and refinement for Me4N [1-(MeSCH2CHCH2)-B10H9] ...... 132

24 Selected Bond Distances and Angles Me4N [1-(MeSCH2CHCH2)-B10H9] ...... 134

LIST OF FIGURES

Figure Page

2- 2- 1 Convention of labeling closo-[B10H10] and closo-[B12H12] ...... 4

14 2 N NMR spectrum of 1,10-B10H8(N2)2 ...... 18

3 11B-11B COSY NMR spectrum of reaction solution between 1,10-B10H8(N2)2 / KCN ...... 22

4 Mass spectrum of products in 1,10-B10H8(N2)2 reaction with KCN . . . .23

11 5 B NMR spectrum of 1,10-B10H8(IC6H5)2 ...... 26

6 Crystal structure of 1,10-B10H8(IC6H5)2 ...... 28

7 Packing of 1,10-B10H8(IC6H5)2 in a single crystal ...... 31

2- 8 Mass spectrum and IR of [1,10-B10H8(CN)2] ...... 34

11 11 1 1- 9 B and B{ H} NMR spectra of [1,PhI-6,7,8,9,10-I5-B10H4] ...... 35

10 Synthesis of Mono-/Di-substituted Inner Sulfonium closo-decaborate .. 36

11 1 11 B{ H} NMR spectrum of 1,10-(Me2S)2-2-MeSB10H7 ...... 39

11 1 + 12 B{ H} NMR spectra of [1,2,10-B10H7(SMe2)3] ...... 42

13 Crystal structure of [1,2,10-B10H7(SMe2)3]BF4 ...... 45

14 Mass spectrum of reaction between 1,10-(Me2S)2-2MeSB10H7 and ethyl iodide ...... 50

11 1 15 B{ H} NMR spectra of 1,7-(Me2S)2-9-MeSB12H9 ...... 55

xii 16 Single crystal structure of 1,7-(Me2S)2-9-MeSB12H9 ...... 56

+ 17 The existence of C3 symmetry in [1,7,9-B12H9(SMe2)3] ...... 61

11 1 18 B{ H} NMR of 2-X-1,10-(Me2S)2-B10H7 ...... 63

11 1 19 B{ H} NMR of 9-X-1,7-(Me2S)2-B12H9 ...... 64

1 1 11 20 H and H{ B} NMR spectra of [Me4N]2[1,2,10-B10H7(SMe)3] ...... 70

11 1 21 B { H} NMR spectra of [Bu4N]2[1,2,10-B10H7(SMe)3] in CD3CN and CD2Cl2 ...... 71

22 11B{1H} NMR spectra + 2- from [1,2,10-(Me2S)3-B10H7] to [1,2,10-(HS)3-B10H7] ...... 72

1 1 11 23 H and H{ B} NMR spectra of [Bu4N]2[1,2,10-B10H7(SH)3] ...... 75

11 1 + 24 B{ H} NMR spectra from [1,7,9-B12H9(SMe2)3] to dithiol ...... 76

25 Single crystal structure of 1,10-(Me2S)2-2-MeSO2B10H7 ...... 78

11 11 1 26 B and B{ H} NMR spectra of impure [NBu4][2-Me2SB10H10] . . . . 86

27 Crystal structure of [Bu4N][2-B10H9SMe2] ...... 87

1 1 11 28 H and H{ B} NMR spectra of [Me4N]2[2-B10H9SMe] ...... 92

11 11 1 29 B and B{ H} NMR spectra of [Me4N]2[2-B10H9SMe] ...... 93

11 11 30 B- B COSY NMR spectrum of [NMe4]2[2-MeSB10H9] ...... 94

1 11 2- 2- 31 H{ B} NMR spectra of [1-HSB10H9] and [2-HSB10H9] ...... 97

32 Crystal structure of [MePPh3]2[2-SB10H10] ...... 99

11 11 1 1- 33 B and B{ H} spectra of pure [2-B10H9SMe2] ...... 104

11 2- 34 B NMR spectra of [1-B10H9SMe] and reaction with CH2Cl2 . . . . . 107

1 1- 35 H NMR spectrum of [1-(MeSCH2Cl)-B10H9] ...... 108

36 Crystal structure Bu4N[1-(MeSCH2Cl)-B10H9] ...... 112

37 Crystal structures MePPh3[2-(MeSCH2Cl)-B10H9] ...... 114

xiii

1 11 1- 38 H{ B} NMR spectrum of [1-(MeSCH2CH2Cl)-B10H9] ...... 118

1 11 1- 39 H{ B} NMR spectrum of [1-(MeSCHMe2)B10H9] ...... 121

1 11 1- 40 H{ B} NMR spectrum of [1-(MeSCMe2CH2COMe)-B10H9] . . . . 123

11 1 1- 41 B{ H} NMR spectrum of [1-(MeSCHClCOMe)-B10H9] ...... 126

1 1- 42 H NMR spectrum of [1- MeSCHClCOMe)-B10H9] ...... 127

43 Stereoselectivity in formation of [1-MeSCHClCOMe]1-...... 128

44 Crystal structure of Me4N[1-(MeSCH2CHCH2)-B10H9] ...... 133

45 1H NMR spectrum of propargyl-allene isomerization ...... 135

xiv

LIST OF SCHEMES

Scheme Page

2- 1 Formation of [B10H10] by reacting with amine bases and B10H14 . . . . .3

2 Formation of 1,10-B10H8(N2)2 and its subsequent displacement reactions ...... 12

1- 3 Selective synthesis of [B10H9SMe2] isomers ...... 14

4 Equilibria existing between dialkylsulfide and alkyl halide ...... 49

1- 5 Separation of apical and equatorial isomers of [B10H9SMe2] ...... 84

LIST OF ABBREVIATIONS

ο degrees

α alpha

Ac acetyl

Å Angstoms br broad (IR and NMR)

β beta n-Bu normal-butyl t-Bu tert-butyl

°C degrees Celsius cal. calculated

δ chemical shift in parts per million downfield from tetramethylsilane d doublet (spectra); day(s)

DMF N,N-dimethylformamide

DMSO dimethylsulfoxide eq. equivalent

Et ethyl g gram(s)

xvi h hour(s)

IR infrared

J coupling constant in Hz (NMR)

K Kelvins

L liter(s) m milli; multiplet (NMR)

Me methyl

MHz megahertz min minute(s) mol mole(s)

MS mass spectrometry; molecular sieves m/z mass to charge ratio (MS)

NMR Nuclear Magnetic Resonance p para

Ph phenyl ppm parts per million q quartet (NMR) rt room temperature s singlet (NMR); second(s) t tertiary (tert) t triplet (NMR)

TLC thin layer chromatography

xvii

CHAPTER 1

INTRODUCTION

2- 2- 1.1 Structure and properties of [B10H10] and [B12H12]

2- 2- [B10H10] and [B12H12] are included in the family of closo-polyhedral boranes.

2- With the general formula [BnHn] , there are (n+1) skeletal electron pairs which hold

2- the borane frameworks together. The [B10H10] ion is a bicapped square antiprism containing eight equivalent BH units in the equatorial positions and two in the apical

2- positions. The overall symmetry is D4d. The structure of [B10H10] was first deduced by 11B NMR1 and confirmed by single crystal X-ray diffraction.2 The negative charge

2- 2- 2- of [B10H10] as well as [B12H12] are highly delocalized. [B12H12] is recognized as an icosahedral arrangement of BH units. The molecular orbital calculation for the

2- 3 [B12H12] system was carried out in 1955. It was predicted that the maximum

2- stabilization would be achieved with 13 skeletal electron pairs before [B12H12] was structurally characterized.4

2- All of the closo-[BnHn] (where n = 6 to 12) had been isolated and characterized by 1967.5 Their stabilities were characterized thermally by the decomposition of cesium salts under vacuum at about 600 oC.6 When strongly basic

1 aqueous basic solutions at 95 oC were used, no observable effects on their degradation

2- 2- were observed. At the same temperature, [B10H10] , but not [B12H12] , slowly reacts with 3M HCl(aq). These materials represent the “aromatic” class of the boron hydride species and may be analogous to the well known planar aromatic hydrocarbons, cations, and anions found in organic chemistry. Interestingly though, the structures of less stable, but more reactive nido- (n+2) and arachno- (n+3) species were discovered in earlier decades.7

2- 2- 1.2 Synthesis of [B10H10] and [B12H12]

8 In 1957, Schaeffer discovered that decaborane(14), B10H14, reacts with acetonitrile and forms B10H12(NCCH3)2 (Scheme 1). Similar reactions (1.1) were

9 found where different bases quantitatively replace hydridic hydrogens of B10H14.

10 Reaction of B10H12(ligand)2 with amines has been studied (Eqn. 1.2). It was found that decaborane(14) reacts with triethylamine (Eqn. 1.3 and 1.4) at high temperatures

2- directly forming [B10H10] ion with over 90% yield.

B10H14 + 2 ligands → B10H12(ligand)2 + H2 (1.1)

+ 2- B10H12(ligand)2 + 2R3N → 2R3NH + B10H10 + 2 ligands (1.2)

B10H14 + 2Et3N → B10H12(Et3N)2 + H2 (1.3)

+ 2- B10H12(2Et3N)2 → 2Et3NH + B10H10 (1.4)

N N

+ N reflux

2- N N

+Base

(NEt3, NH3)

2- Scheme 1. Formation of [B10H10] by reacting with amine bases and B10H14

2- 2- The convention for labeling the cluster ions, [B10H10] and [B12H12] , was

11 2- 2- concurrently developed (Fig. 1) . Unlike [B10H10] , [B12H12] ion was first obtained as a minor product from the reaction between triethylamine with 2- iododecaborane(14).12 The two preparations describing the quantitative formation of

2- 13 14 [B12H12] from simple borohydride or amine boranes with B2H6 at high temperature were later reported by Miller, Miller, and Muetterties in 1963.

2- ]

12 2- ] H 12 12 X 12 [B and [B 2- ] 10 H 10

Fig. 1 Convention of labeling [B

2- ] 10 X 10 [B

4 1.3 Stereochemistry on the boron cluster substituents

Stereochemical characterization of B10 and B12 derivatives has been achieved by X-ray analysis in many cases.15 However, most characterizations are currently based on 11B NMR spectroscopy and chemical arguments. Complex 11B NMR spectra result because of small chemical shifts and large peak widths are common. However, relatively simple 11B NMR spectra occur for mono and most disubstituted species

2- 2- 16 because of the relatively high symmetries of [B10H10] and [B12H12] . Boron NMR spectroscopy has been particularly useful in distinguishing apical from equatorial

2- substitution in [B10H10] .

1.3.1 Dodecaborane(12)

2- When a single substitution occurs on the icosahedral [B12H12] , only 1 compound can result since all 12 BH units are identical. As shown below, there are

n-2 three possible disubstituted isomers, namely 1,2-; 1,7-; and 1,12-[B12H10X2] (where n is the number of charge-compensated ligand – see Sec. 1.4). To date, there is only one

17 series, where X is a SMe2, reported where all three isomers are fully characterized.

Most of the other series lack the 1,2- isomer, probably due to steric effects.

X X X X

X X

n-2 n-2 n-2 1,2-[B12H10X2] 1,7-[B12H10X2] 1,12-[B12H10X2]

5 2- Nevertheless, the regiochemistry of the second substitution on [B12H12] was analyzed by Hoffmann and Lipscomb based on calculations of the ground state.18

According to their prediction, electrophilic substitution proceeds consistent with the nature of the substituent. For example, electron-withdrawing substituents like iodine19 tend to be direct succeeding electrophilic substituents to positions 7 and 12 in a ratio of

5:1 consistent with ratio of boron atoms. For the same reasons, electron-donating ligands would be directed to position 2.

1.3.2 Decaborane(10)

There are two different boron environments, 1- (or apical) and 2- (or equatorial) positions, due to the reduced symmetry within the boron cage itself. Subsequently,

2- there are two unique substitution positions. Mono subsitution of [B10H10] can lead to one of the isomers below. When substitution occurs at the apical position, C4 symmetry is retained. However, the equatorial isomer reduces the symmetry to Cs.

Therefore, more stereoisomers result at the same level of substitution, relative to

2- [B12H12] .

2- 2- 1-[B10H9X] 2-[B10H9X]

2- 2- [B10H10] (X = H) [B10H10] (X = H)

X X X

X X X X

2- Top: 1,2-, 1,6-, 1,10-; Middle: 2,3-, 2,4-; Bottom: 2,6(9)-, 2,7(8)- [B12H10X2]

As shown above, for a disubstituted species, seven isomers are possible: 1,2-, 1,6-,

2- 1,10-, 2,3-, 2,4-, 2,6(9)-, and 2,7(8)-[B10H8X2] . To the best of our knowledge, no single series has been reported to have all seven isomers isolated and characterized.

Similar to the case of B12, steric hindrance could be responsible for unobserved isomers. In addition to this, there is a selectivity of reagents toward nonequivalent

2- boron atoms, which is not a factor in the case of [B12H12] .

1.4 Charge-compensated closo-borane compounds and reaction properties

When unbound substituents are neutral, they become positively charged when they replace the H- group. The substituent takes on the “-onium” ending when on the closo-borate. The substituted boron cage compounds are subsequently less anionic

2- 2- than [B10H10] and [B12H12] . They have frequently been coined “charge- compensated” species. Charge-compensated closo-borane compounds, however, can technically be considered into two extreme categories. The first category involves the

2- displacement of hydride by a neutral ligand in [BnHn] as illustrated above. The second category occurs when a vertex in the cage is a more electronegative heteroatom.

Carborane is a classic representative of this group.

Since a substituent does not necessarily create a charged-compensated species, the boron cages compounds are mostly anionic. These are relatively more difficult to

2- handle. The pace of ongoing research of carboranes has clearly surpassed [B10H10]

2- 20 and [B12H12] due to its neutrality and comparable stability, as well as the already established collection of organic reactions. Nonetheless, the existence of an example including both categories has also been discovered.21

The reactions of boron clusters can also be separated into two categories.

When the BH units are modified, generally it involves either gradual hydride displacements by electrophiles or vertex removal by strong bases. This is classified in the first category. The second category involves the modifications of substituents

(other than hydride) while keeping the boron cage intact.

2- 2- 1.5 Selectivity in reactions of [B10H10] and [B12H12]

In general, there are two approaches to prepare substitution derivatives. The ligand can be introduced to the clusters by means of a precursor. The second approach involves the direct substitution on the boron cages. This has a broader scope due to the limited number of appropriately substituted decaborane derivatives. Reactions of the title clusters mostly involve the second approach, by an acid-catalyzed nucleophilic substitution;19 the mechanisms of which are still not understood.

1.5.1 Halogenation

Partially or completely brominated, chlorinated and iodinated derivatives of the boron cages have been prepared by reaction of the parent anions with elemental halogen, interhalogens, or N-halosuccinimide in a variety of solvents. These reactions always occur on the boron cage. Modification of existing substituent with halogenation was never reported. The order of reactivity with elemental halogen is:

2- 2- 19 [B10H10] > [B12H12] and F > Cl > Br > I. Initial halogenation rates in all cases are

2- extremely rapid. Iodine halogenation of [B10H10] with the three slowest rates were kinetically indistinguishable at low temperature. However, the iodination of

2- 2- [B12H11I] was slow enough to observe 5:1 product ratio of 1,7- to 1,12-[B12H10I2] .

Since the halides are not charged-compensated, the overall charge of the compound remained the same.

Muetterties and coworkers in 1965 discovered another “iodinated” product.22

The unique aspect of the compound was the oxidation state (+3) of iodine. This hypervalent iodine compound is quite interesting in terms of stereochemistry. When a

23 stoichiometric amount of iodosobenzene, C6H5IO,

NaOH(aq) I(OAc)2 I (1.5) O

2- that was synthesized by reaction (1.5), reacted with B10H10 in acetonitrile, [1-

1- B10H9(IPh)] formed selectively (Eqn. 1.6). No observation of equatorial substitution was detected by 11B NMR spectroscopy. Pure 1-iododecaborate was subsequently obtained in 1974 by UV radiation cleavage of the phenyl group.24

2- 1- 2-

PhIO UV

(1.6)

I I

1.5.2 Diazonium derivatives

2- The reaction of [B10H10] with excess nitrous acid forms a very explosive, uncharacterized product that can readily be reduced to a nonexplosive bis-inner-

25 diazonium salt, 1,10-B10H8(N2)2. However, this reaction does not apply to the

2- icosahedral analog. Equatorial substitution of [B10H10] has not been observed in this direct diazotization reaction. The selectivity was further demonstrated by the fact that no reaction occurred with a 1,10 isomer of any kind since both apices are blocked. It is uncertain why the reduction step was not required in the same reaction with organic aromatic species.26

1.5.3 Carbonyl derivatives

The diazonium derivatives are important as synthetic intermediates. Nitrogen was the only ligand that could be displaced by a variety of nucleophiles from the B10 polyhedron. The displacements had been reported on several occasions.25, 27 The most important among those products is that obtained with carbon monoxide. 1,10-

B10H8(CO)2 is not only stable indefinitely under ordinary conditions, but also has extensive flexibility in its chemistry (Scheme 2).28 These carbonyls are anhydrides of carboxylic acids. They can be converted to amides and esters with amines and

29 alcohols, respectively. Thermal dehydration of Cs2[1,10-B10H8(CONH2)2] to the corresponding dinitriles proceeds at 300o without oxidative degradation.30

N2 2-

HONO Explosive NaBH4 XS Intermediate

CO N2 N2 OC CO

O O

NH3 OC CO C C

H2N NH2

2- O O heat C C NC CN

H2N NH2

Scheme 2. Formation of 1,10-B10H8(N2)2 and its subsequent displacement reactions

Alternatively, carbonyl ligand can be introduced onto the cluster selectively at the equatorial position by using oxalyl chloride (Eqn. 1.7). Unlike the apical isomer, this is a single step reaction that does not utilize any intermediate.29

2- 2- -

O (COCl) (COCl)2 2 (1.7)

Cl CO O + CO + Cl-

1.5.4 Sulfonium derivatives

Unlike dodecaborane(12) chemistry, in which sulfonium derivatives are the most studied category,31 there is a limited number of reactions involving exopolyhderal sulfur substituents in decaborane(10). Among these the most well known reaction involves DMSO.27 The products are predominately mono, apical substituted [1-

- - B10H9SMe2] with small amounts of the equatorial isomer, [2-B10H9SMe2] , when the reaction is performed in DMSO with hydrogen gas. When the solvent is changed to acetic acid, only neutral products 1,10-B10H8(SMe2)2 with small amounts of 1,6-

B10H8(SMe2)2 and 2,7(8)-B10H8(SMe2)2 are observed. Nonetheless, the isomeric

- - mono-anions, [1-B10H9SMe2] and [2-B10H9SMe2] , can be selectively synthesized by utilizing the diazonium derivative and tetramethylthiourea, respectively32 (Scheme 3).

1- 1- 1- 2-

N - S OH

N N N S Me3SI SH NR N 1-

+ RN2

Me2SO, HCl SMe2 1-

NMe2 S SMe2 NMe2

Me3SI

1- 2-

NMe2 OH-

S SH NMe2

1- Scheme 3 Selective synthesis of [B10H9SMe2] isomers

14 Muetterties and coworkers reported that other dialkyl sulfoxides reacted

2- 2- similarly with [B10H10] , but the procedure was not applicable to [B12H12] .

- [B12H11SR2] and B12H10(SR2)2 (where R in Me, Et, …) were synthesized from diborane and the corresponding alkyl sulfide.33 However, Wright and Kaczmarczyk later found that by using acetic anhydride as the solvent the reactions occur in a similar

2- 34 fashion to [B10H10] . Most recently, in 1997, Shore and coworkers had developed a more advanced method in obtaining the same compounds through pyrolysis of borane dimethylsulfide complex in a high pressure stainless steel vessel.35 The enlarged scale of this reaction eventually permitted the completion of the first series of disubstitued isomers that contain two identical substiutents.17

1.5.5 Mercapto derivatives

In contrast to sulfonium, only two mercapto derivatives had been reported

2- 2- before the millennium. They are [B12H11SH] (BSH) and [1,10-B10Cl8(SH)2] , which

2- were prepared by reacting the conjugate acid of [B12H12] and 1,10-B10Cl8(N2)2 with hydrogen sulfide, respectively.36 Recently Shore and coworkers have found that alkali

n-2 metal in amines can remove alkyl groups from [B12H12-n(SR2)n] gradually. Sodium and potassium in ammonia could only dealkylate sulfoniums to thioethers. However, lithium in methylamine could reduce them further to sulfide anions.37 Upon washing

2- 2- of aqueous acid, about 90% yield of [B12H11SH] and [B12H10(SH)2] (bis-BSH) could be obtained. The sodium salt of bis-BSH was recently observed in vivo studies to have similar toxicity, but better uptake in tumor cells than BSH for boron neutron capture

38 therapy (BNCT).

CHAPTER 2

Result and Discussion

Synthesis of Metal Linker and Potential Formation of Linkages

A2.1 Synthesis of 1,10-B10H8(N2)2 and Reactions

The compound of 1,10-B10H8(N2)2 is probably the most studied and well known species in dianionic closo-borate chemistry because of its displaceable nitrogen ligands.39 However, it has never been utilized to form a linkage between metal compounds. In fact, this compound has not been involved in any chemical studies since the early 1980s. More recently calculations showed comparable conductivities of

2- 40 B10H8(N2)2 and [B10H8(CN)2] to organic analogs.

41 1,10-B10H8(N2)2 was synthesized by Knoth (Eqn. 2.1). Derivations from procedure include the use of the cesium salt of decaborate(10) in repeating experiments. The total yield obtained was only about 15-18%, which was slightly lower than reported.

HNO2 (aq) NaBH 4 N N N N -5 oC (2.1)

11 The synthesis of 1,10-B10H8(N2)2 was characterized by MS-EI and IR, B,

11B{1H}, 1H, 1H{11B}, and the previously unreported 14N NMR spectroscopy. The IR showed 2 very strong signals in the region of 2200-2600 cm-1 as reported. They were assigned to the dinitrogen at 2255 and boron hydrogens at 2545 cm-1, respectively. A singlet at 5.0 ppm and a doublet at -17.3 ppm were observed in the 11B{1H} NMR spectrum as previously reported. The doublet collapsed into a singlet upon proton decoupling, which implied D4d symmetry of the intact boron cage. This is consistent with the locations of the substitutent, which was in agreement with 1,10-B10H8(N2)2.

No signal appeared in the 1H NMR spectrum, but upon 11B decoupling, a broad singlet showed up at 1.56 ppm. This is consistent with the equivalence of all hydrogen atoms.

The MS-EI showed a typical boron cage pattern with molecular weight ranging from

169.2 to 175.2 with the center at 172.2. The average mass of B10H8 was subtracted leaving a mass of 56. Therefore, the 2 ligands remaining must each have a mass of 28.

This as well as 14N NMR confirmed the existence of 2 types of nitrogen atoms in the compound (Fig 2). Broadness of the signal at 235.6 ppm was assumed due to the coupling of 11B, as the slimmer signal at 290.5 ppm was assigned to the terminal nitrogen atom.

-Acetone -Acetone 6 in d 2 ) 2 (N 8 H 10 N NMR spectrum of 1,10-B 14 Fig. 2

18 Two different metal containing compounds, namely iron nonacarbonyl and platinum(II) chloride, were chosen to react with 1,10-B10H8(N2)2 under vacuum. The anticipated reaction in toluene with Fe2(CO)9 did not occur at room temperature even after 24 hours as monitored by 11B NMR spectroscopy (Eqn. 2.2) . It is known that the organic analog, 1,4-dicyanobenzene, reacts with PtCl2 to form a square planar

42 complex, (C6H5CN)2PtCl2. When PtCl2 was used to react with the inner diazonium salt, new, but small, signals were observed on the 11B NMR spectrum. The reaction was warmed to 80 oC for 2 hours in toluene. Additional signals were observed in the

11B NMR spectrum. The strongest signal was a singlet dominating at 45 ppm. A few other signals from the boron cages were also observed. When it was heated to a higher temperature for longer period of time, the boron cage decomposed totally. Only a few trialkylborane signals were observed in the spectrum (Eqn. 2.3). Seemingly the boron cage reacted with the solvent, toluene. This is not surprising, however, because of the similarity in chemistry between palladium and platinum. The palladium compound,

H2PdCl4, in methyl alcohol was used as the stain solution for TLC. The boron cage is destroyed upon heating after it is soaked in palladium solution.

Fe2(CO)9 N N N N N.R. (2.2)

PtCl2 (2.3) N N N N Decomposition Heat

The failure to form a linkage between metal and 1,10-B10H8(N2)2 was due to the positively charged nitrogen atom of the inner dizaonium substituent. The nitrogen atom, which is bonded directly to the boron cage, is electron withdrawing. This causes reducd electron density on the terminal nitrogen atom. As a result, the weak basicity hinders formation of desired product. Subsequently, our attention turned to [1,10-

2- B10H8(CN)2] , which was believed to be a better choice for forming a linkage with metal because of its dianionic nature and stronger basicity.

2- A2.2 Developments in Synthesizing [1,10-B10H8(CN)2]

A2.2.1 Through 1,10-B10H8(N2)2

The original synthesis of dicyano-closo-decaborate dianion, [1,10-

2- B10H8(CN)2] , utilized the lability of dinitrogen in 1,10-B10H8(N2)2 as the starting material (or intermediate). However, a step that requires carbon monoxide a high pressure made it impractical to carry out the synthesis in this laboratory.28

Unfortunately, no other synthetic route has been reported for this compound.

Therefore, we intended to develop a new method to explore this potential linker.

6 Nitriles had been reported to displace the dinitrogen of 1,10-B10H8(N2)2.

Nevertheless, attempts to use alkali metal cyanide were unreported. After refluxing potassium cyanide with diazo-closo-decaborate in an ethanol/water mixture for 3-7 days, the product was examined by 11B, 11B{1H}, and 11B-11B COSY NMR spectroscopy (Fig. 3). From the repeated reactions, the 11B-11B COSY suggested that there are at least two or more compounds or anions. Unfortunately, there is not enough

20 information for individual peaks assignment. At least 3 signals evidently belong to the product. The other signal at about 1 ppm is assigned to impurities. The desired dianion should, in principle, have only 2 signals like that of 1,10-B10H8(N2)2. The signal of an apical boron atom (bonded to carbon) typically appears between 5 and -5 ppm in 11B{1H} spectrum. Therefore, due to the observation of 3 peaks and the chemical shifts, the product must not be the desired dianion. In fact, the mass spectrum later showed 3 anionic boron cages. Nonetheless, none of them matched the anionic

2- mass of [1,10-B10H8(CN)2] . (Fig. 4)

A2.2.2 Through 1,10-B10H8(IPh)2

Iodobenzene can be converted into cyanobenzene by using a palladium catalyst along with trimethylsilyl cyanide43 (Eqn. 2.4). It was uncertain if 1-iodo-closo-

2- decaborate, [1-B10H9I] , could be synthesized in a pure form. However, its preparation was attempted. Iodination with 1 equivalent of sublimed iodine19 at the equatorial position was reported as the main product. However, upon repeating this experiment, the apical isomer formed substantially. We found that the ratio of isomers is temperature dependent. Unfortunately, the reaction was still not selective enough to fulfill our purpose.

o Pd , Me3SiCN I CN (2.4)

11 11 Fig. 3 B- B COSY NMR spectrum of reaction solution 1,10-B10H8(N2)2 / KCN

Fig. 4 Mass spectrum of products in 1,10-B10H8(N2)2 reaction with KCN

23 The hypervalent iodine compound, PhIO, is interesting in terms of stereochemistry and displacement reactions. Not only does iodosobenzene react specifically at the apical boron atoms of the decaborane(10), but C6H5I is also a good leaving group as known in organic syntheses. Grushin and co-worker21 reported the

+ successful displacement of iodobenzene by cyanide on C2B10H11(IC6H5) (Eqn. 2.5).

C C C C C C - C6H6 CN [O] I I NC (2.5)

Bis(iodophenyl)closo-decaborate, 1,10-B10H8(PhI)2, was discovered during

1- attempts to synthesize [B10H9CN] . The route used involved the reaction of

2- iodosobenzene with [B10H10] followed by C6H5I displacement with cyanide. When a

2- little excess iodosobenzne was used to react with [B10H10] , a very small amount of the di-substituted compound was observed by 11B{1H} NMR. The major product was the

1- mono-substituted species, [1-B10H9IPh] . 1,10-B10H8(IPh)2 was found to uniquely dissolve in methylene chloride which allowed for its isolation. If necessary, the compound could be further purified by wash it through silica gel. Its yield could be increased from 17% to 34% when the amount of iodosobenzene was increased from 2 to 10 times in excess. However, the mono-substituted product remained the major product (Eqn. 2.6). The small increase in disubstituted product clearly indicated the 24 1- equilibrium is shifting toward the anionic mono-substituted [1-B10H9IPh] . However, using excess amounts of PhIO in the reaction leads to a large amount of an explosive side product. This was insoluble in all of the common solvents, and believed to be

PhIO2. Nonetheless, the mono-substituted species recovered could not be used to react with additional iodosobenzene again. The boron cage decomposed, determined by 11B

NMR, when the route was tried.

- IPh IPh 2-

PhIO (2.6) 45 oC

IPh

11 Two signals were observed in the B NMR spectrum of 1,10-B10H8(IPh)2. The apical boron atom signal was difficult to observe because of its broadness (very close to baseline) at about 7 ppm (Fig. 5). Only the phenyl groups were observed on 1H

NMR spectrum. The hydrogens were observed in the 1H{11B} NMR spectrum. This was consistent with selective apical substitutions. MS-EI confirmed the correct molecular weight with a typical boron cage pattern ranging from 544.0-551.4 mass units. The compound was crystallized from methyl alcohol allowed for single crystal

X-ray diffraction analysis (See Table 1 for the crystallographic data). 1,10-B10H8(IPh)2 crystallizes in the triclinic space group Pī with six crystallographically independent molecules.

2 Cl 2 in CD 2 (IPh) 8 H 10 B NMR spectrum of 1,10-B 11 Fig. 5

Empirical formula C12 H18 B10 I2

Formula weight 524.16 Crystal system, space group Triclinic, Pī Unit cell dimensions: length(Å) a 8.72140(10) b 16.0725(2) c 22.0926(2) angle(deg) α 109.95 β 100.27 γ 91.6340(10) Volume, (Å3) 2850.82(5) Z, Calculated density (g cm-3) 6, 1.832 Crystal size (mm) 0.23 x 0.19 x 0.12 Temperature 150(2) K Absorption coefficient (mm-1) 3.299

R1 [I > 2σ(I)] 0.0807 wR2 (all data) 0.2249

Table 1 Crystal data and structure refinement for 1,10-B10H8(IC6H5)2

Fig 6. Crystal structure of 1,10-B10H8(IC6H5)2

Axial-Equatorial B-B Distances (Å)

B(21)-B(22) 1.675(19) B(30)-B(26) 1.692(18) B(21)-B(23) 1.668(19) B(30)-B(27) 1.681(18) B(21)-B(24) 1.68(2) B(30)-B(28) 1.683(19) B(21)-B(25) 1.671(19) B(30)-B(29) 1.669(19)

Equatorial-Equatorial B-B Distances (Å)

B(22)-B(23) 1.877(19) B(24)-B(27) 1.835(19) B(22)-B(25) 1.89(2) B(24)-B(28) 1.83(2) B(22)-B(26) 1.821(19) B(25)-B(28) 1.80(2) B(22)-B(29) 1.82(2) B(25)-B(29) 1.817(19) B(23)-B(24) 1.88(2) B(26)-B(27) 1.872(18) B(23)-B(26) 1.790(18) B(26)-B(29) 1.87(2) B(23)-B(27) 1.837(19) B(27)-B(28) 1.884(19) B(24)-B(25) 1.86(2) B(28)-B(29) 1.88(2)

Other Distances (Å)

I(5)-B(21) 2.191(12) I(6)-B(30) 2.183(12) I(5)-C(51) 2.122(12) I(6)-C(61) 2.124(13) C(52)-C(53) 1.40(2) C(61)-C(62) 1.384(19) C(53)-C(54) 1.38(2) C(61)-C(66) 1.36(2) C(55)-C(56) 1.370(19) C(62)-C(63) 1.40(2)

Table 2 Selected Bond Distances of 1,10-B10H8(IC6H5)2

Angles (o)

Substituted Boron Geometry

B(22)-B(21)-I(5) 126.6(9) B(26)-B(30)-I(6) 126.1(8) B(23)-B(21)-I(5) 128.5(9) B(27)-B(30)-I(6) 131.2(9) B(24)-B(21)-I(5) 127.7(9) B(28)-B(30)-I(6) 129.8(9) B(25)-B(21)-I(5) 127.1(9) B(29)-B(30)-I(6) 124.4(9)

Iodine Geometry

B(21)-I(5)-C(51) 97.4(5) B(30)-I(6)-C(61) 99.3(5)

Phenyl Carbon Geometry

C(56)-C(51)-C(52) 124.0(12) C(66)-C(61)-C(62) 123.4(14) C(56)-C(51)-I(5) 118.1(9) C(66)-C(61)-I(6) 118.8(10) C(52)-C(51)-I(5) 117.9(9) C(62)-C(61)-I(6) 117.8(11)

C(51)-C(52)-C(53) 117.2(13) C(61)-C(62)-C(63) 117.0(14) C(52)-C(53)-C(54) 119.5(13) C(62)-C(63)-C(64) 120.1(14) C(53)-C(54)-C(55) 121.0(13) C(63)-C(64)-C(65) 121.6(14) C(54)-C(55)-C(56) 121.0(14) C(64)-C(65)-C(66) 119.8(14) C(55)-C(56)-C(51) 117.2(13) C(65)-C(66)-C(61) 118.1(13)

Boron Cage Geometry

B(23)-B(21)-B(25) 104.3(9) B(26)-B(30)-B(28) 104.0(9) B(22)-B(21)-B(24) 105.7(10) B(27)-B(30)-B(29) 104.2(9) B(22)-B(21)-B(23) 68.3(8) B(26)-B(30)-B(27) 67.4(8) B(22)-B(21)-B(25) 68.9(8) B(26)-B(30)-B(29) 67.5(8) B(21)-B(22)-B(26) 108.3(10) B(30)-B(26)-B(22) 110.1(10) B(21)-B(24)-B(28) 109.4(10) B(30)-B(28)-B(24) 109.7(10)

Table 3 Selected Bond Angles of 1,10-B10H8(IC6H5)2

Fig 7. Packing of 1,10-B10H8(IC6H5)2 in a single crystal

31 Figure 6 displays one of the 6 molecules in the unit cell. The molecule is slight disordered. The equatorial B-B bond distances in these molecules range from

1.790(18) to 1.884(19) Å. The B-I and C-I bond distances range from 2.183(12) to

2.191(12) and 2.122(12) to 2.124(13) Å, respectively. The B-B-I bond angles are between 124.4(9) and 131.2(9) Å (Table 2 and 3). An interesting aspect of this structure is the orientation of the phenyl groups. Both aromatic rings in a molecule are facing in the same direction. The pairing partner is an identical molecule rotated 180o, which docks at about half a length below its counterpart (Fig. 7). This arrangement seemingly facilitates the π-π interaction between the phenyl rings of the two molecules.

However, these electron densities are farther than the typical distance of 3.5 Å, about

4.8 Å apart from each other. The phenyl rings were found stacked not directly on each others, but rather the six membered ring interacts partially with one another. Similarly a lone pair of electrons (3.7 Å) of the closest iodine atom interacts with the phenyl ring in the same way. This is facilitated by the serious distortion of bond angle C-I-B, less than 100o, as well as the slightly distorted B-B-I bond angle. Otherwise, the π electrons could only be interacting with either the iodine or another phenyl group, but not both.

The neutral disubstituted 1,10-B10H8(IPh)2 complex turned out to perform

+ similarly to the cationic [9-C2B10H11IPh] . After refluxing 1,10-B10H8(IPh)2 for about

1 week with cyanide, removal of solvent (toluene-chloroform) left a muddy red paste material in the reaction flask. Upon recrystallization in water, the 11B NMR solution spectrum, contained two signals at -4.5 and -24.7 ppm representing the apical and equatorial boron atoms. Nonetheless, positive identification was confirmed by electron

32 impact mass spectroscopy. The mass was determined to be in the range 82.6 to 85.1 mass units with the highest abundance at 84.6. The interval between signals was only

0.5, which implied the charge, z, to be 2. The actual weight is projected to 165.2-170.2

2- mass units, which is equivalent to [1,10-B10H8(CN)2] (Fig. 8). IR spectrum further indicated the formation of a B-CN bond at 2305 cm-1 since pure cyanide has a stretching frequency at about 2150 cm-1. Unfortunately, this synthesis was not reproducible. The reason for the failure is unknown. This reaction was not pursued further.

1- The remaining mono-substituted intermediate, [1-B10H9IPh] , was used stirred with sublimed iodine in ten-fold excess in chloroform continuously for 3 weeks. It is not surprising to find that the reaction was not selective in displacing hydrides. But it was surprising to find that only the hydrogen atoms at the bottom half of the boron cage could be displaced. As seen in the 11B and 11B{1H} NMR spectra, only 1 set of hydrogen bonded to boron are intact at about 15 ppm (Fig. 9). Incidentally it was

44 1- reported by Xie that [CB9H9] heated with iodine in a sealed NMR tube would

1- produce the analogous [7,8,9,10,11,12-CB12H5I6] . This directly showed the similarity between carborane and charge-compensated closo-dodeca- or deca-borate.

2- 2- ] 2 (CN) 8 H 10

(toluene solution) of [1,10-B Fig. 8 Mass spectrum and IR

1- 1- ] 4 H 10 -B 5 H} NMR spectra of [1-PhI-6,7,8,9,10-I 1 B{ 11 B and 11 Fig. 9

Chemistry of inner sulfonium derivatives of deca- and dodeca-closo-borate

B2.1 1,10-(Me2S)2-2-MeSB10H7

Knoth, Hertler, and Muetterties observed substitutions upon reaction of

2- 27 [B10H10] with DMSO under acidic conditions. Two reaction conditions, as seen in figure 10, are practically identical. DMSO was only the reagent in one, but also solvent in the other reaction. The important difference between the two reactions is the ratio of mono- and di-substituted products. Reactions in DMSO is to a large extent time dependent, the longer the reaction runs the higher the yield of II. Reaction in acetic acid is quite different in that the di-substituted product II is preferentially formed; seemingly, the reaction is independent of the reaction time.45 For the final step, both methods require the addition of water after the reaction takes place in order to precipitate the desired products.

2- [B10H10] HC l DM (g) SO

- [B10H9SMe2] + [B10H8(SMe2)2]

g) cid l ( A III C tic H ce A ial 2- lac [B10H10] + DMSO G

Fig. 10 Synthesis of Mono- / Di-substituted Inner Sulfonium closo-decaborate

It was reported that 1,10-(Me2S)2-2-MeSB10H7 was produced, if the temperature was allowed to spike while keeping all other conditions constant.46

Although the newly discovered compound was fully characterized, the reported procedure proved to be unreliable. Therefore, reinvestigation of the synthesis was undertaken.

2- 2- Reactions of the closo-borates [B9H9] and [B12H12] are also known with

2- 2- 47 DMSO. [B9H8SMe2] and [B9H7(SMe2)2] were synthesized under mild conditions.

Their reasoning is that these boron cage analogs are relatively sensitive to acidic media. Reactions were performed under ambient conditions for a few hours to a few weeks. The effect of time on the displacement of hydrides was shown to be important.

2- When DMSO was used as the solvent in the earlier studies with [B10H10] , the authors did not report any observations regarding further substitution beyond the formation of II. This is the case even if a prolonged period of reaction time was applied. Even if a more acidic solvent was used, II was observed as a predominant product. Although it was claimed that II was preferentially formed, the effect of extended reaction time was unknown.

We attempted to duplicate the reaction with a longer reaction time while maintaining other conditions. Normally the isomeric mixture of neutral di-substituted solids, 1,10- and 1,6-B10H8(SMe2)2, are observable in the reaction solution within an hour. It is because that they are partially insoluble in glacial acetic acid. The white solid disappeared and the solution became clear colorless 1 ½ to 2 hours after the reaction was initiated. 11B{1H} NMR was used to monitor the reaction. The signals

37 that belong to the di-substituted compounds were observed in the spectrum along with some others. These extra signals were in the vicinity of where the reported product would appear. If the reaction was allowed to continue, the solution eventually turned clear light yellow then cloudy almond after about 2 ½ to 3 hours. The 11B{1H} NMR spectrum of this solution was very similar to that of 1,10-(Me2S)2-2-MeSB10H7 except with slight differences in chemical shifts. Upon addition of distilled water, a white color flashed and disappeared while stirring the solution. Eventually bright white solid

11 1 precipitated, the isolated product in CD3CN had the exact B{ H} NMR spectrum of

1,10-(Me2S)2-2-MeSB10H7 as reported (Fig. 11). The overall yield was between 40 to

60%, about 3 to 4 times higher than previously recorded. Thus demonstrating that time is an important factor for further substitution on the boron cage. Nevertheless, further substitution was not observed, even when the reaction solution was heated for 24 hours at 55-60 oC.

2 Cl 2 in CD 7 H 10 -2-MeSB 2 S) 2 H} NMR spectrum of 1,10-(Me 1 B{ 11 Fig. 11

When Cs2B10H10 was allowed to react with DMSO at room temperature in the presence of HCl gas for 6 hours (or till saturation), the reaction solution contained

11 1 mainly B10H8(SMe2)2 as monitored by B{ H} NMR spectroscopy. The reaction was found to contain a mixture of di- and tri-substituted species, when the reaction solution was allowed to stir for another 18 additional hours after shutting off the supply of HCl gas. By repeating the same procedure for another 24 hours, the reaction was complete with slight impurities. Although the published procedure by Shore and coworkers was irreproducible, the effect of increasing temperature was legitimate. Unfortunately, the time allowed for temperature increase was probably too short to make the procedure effective. Another possibility of such production might be due to the increase HCl gas flow, for the reaction is very exothermic.

+ B2.2 First Cationic Trisubstituted Isomers [1,2,10-B10H7(SMe2)3]

The production of 1,10-(Me2S)2-2-MeSB10H7 raises a question since only a single methyl group bonded to the sulfur atom (a thioether) instead of two (a di-methyl sulfide) is presented in the molecule. This seemingly automatic loss of a methyl group is unprecedented in inner sulfonium closo-borate chemistry. The three previously reported tri-substituted compounds of decaborane(10) are all neutral: 1-N2-2-NCO-10-

48 Me2SB10H7, 1-N2-2-COOH-10-Me2SB10H7, and 1-H5C5N-2-COOH-10-Me2SB10H7.

Coincidentally, none of the charge-compensated substituents are at the equatorial

+ position. Muetterties and Knoth claimed to observe [B10H7(Me2S)3] . However,

40 “unpublished data” was cited in their references.39 And there has not been a publication that reported that such cation was found in the past 35 years.

To the best of our knowledge, there was never any evidence regarding a loss of methyl group in DMSO. Furthermore, the reaction proceeded and produced isolable di-substituted inner sulfonium neutral intermediates. Therefore, it was quite certain

+ that the cationic species, [1,2,10-B10H7(SMe2)3] , existed at some point (Eqn. 2.7). The point at which the methyl group became labile has been determined to be after the reaction stopped. Furthermore, water will cause a loss of a methyl group.

2- + SMe2 SMe2

SMe2 SMe HCl (g) -Me (2.7) DMSO Cl-

SMe2 SMe2

In comparing of 11B{1H} NMR spectra, the reaction solution has slight differences in chemical shifts to the isolated product. Although it was thought to be due to solvent effect, the assumption turned out to be incorrect. When only only a few drops of water was added, white solid flashed briefly and the solution returned to clear colorless instantly and the 11B{1H} NMR spectrum showed a few new signals (Fig. 12 top asterisks) after a flash. These signals match exactly where the signals of 1,10-

(Me2S)2-2-MeSB10H7 would appear. (Fig. 11)

rse reaction (bottom) (bottom) reaction rse direct (top) and reve + ] 3 ) 2 (SMe 7 H 10 H} NMR spectra of [1,2,10-B 1 B{ 11

Fig. 12

42 Apparently the compound in solution and the isolated product were quite different. Although chemically, there seems to be no other precursor than [1,2,10-

+ B10H7(SMe2)3] ; its existence cannot be positively concluded. Therefore, it was thought that the most direct way of obtaining the cationic intermediate would be to simply remove acetic acid from the reaction solution. After evaporating the acetic acid

1 to dryness, the residue dissolved in CD2Cl2 and a H NMR spectrum was obtained.

There were 3 major signals observed with a ratio of about 2:2:1. Those peaks are identical to the neutral compound obtained earlier, 1,10-(Me2S)2-2-MeSB10H7. This directly implies that the addition of water was unnecessary to cause the loss of an equatorial methyl group. Not only does this show the function of water in shifting the equilibrium, but it also displays the limited timeframe of the cationic species existence.

Since a direct route to the desired cationic intermediate was not achieved, an indirect reverse process was attempted by reacting 1,10-(Me2S)2-2-MeSB10H7 with

Me3OBF4 in methylene chloride for 3 hours to form 1,2,10-B10H8(SMe2)3BF4. After the filtration and workup, the 11B{1H} NMR spectrum of the pure isolated product in

CD3CN was obtained. The spectrum is identical to the acetic acid reaction solution

- except for the extra signal of BF4 (Fig. 12 bottom). Apparently the solvents did not affect the chemical shifts as much as originally thought. This compound was recrystallized from methyl alcohol. It was further characterized by mass spectroscopy and its structure was determined by single crystal X-ray diffraction (See Table 4 for the crystallographic data). 1,2,10-B10H8(SMe2)3BF4 crystallizes in the monoclinic space group P21/c with four crystallographically independent molecules. Figure 13 displays one of the 4 molecules. The apical-equatorial B-B bond distances in these

43 molecules range from 1.674(3) to 1.687(3) Å. The equatorial-equatorial B-B bond distances range from 1.785(3) to 1.869(3) Å. Those involved B(2) are slightly shorter than others. For example, the bond distances of B(2)-B(3) and B(2)-B(5) are 1.833(3) and 1.834(3) Å, respectively. However, B(4)-B(3) and B(4)-B(5) are slight longer with bond lengths of 1.856(3) and 1.859(3) Å, respectively. The apical boron atom B(1) does not seem to experience any sterics from B(2). The B-B(1)-S(1) bond angles range from 128.15(15) to 129.67(15) which are similar to B-B(10)-S(3) bond angles ranging from 127.53(15) to 129.53(15). Other selected bond distances and angles of the crystal structure of [1,2,10-(Me2S)3B10H7]BF4 are given in Table 5 and 6, respectively.

The characterizations have indirectly proved the existence of the cation. Since chloride was the only nucleophile existing in the acetic acid solution, it can simply be concluded that chloride abstracts a methyl group from equatorial sulfonium (Eqn. 2.8).

Chloromethane is a gas at room temperature. It may be removed along with acetic acid. Unlike in reaction solution, [1,2,10-B10H7(SMe2)3]BF4 does not break down into its neutral form in an acetic acid/water solution. Only when hydrogen chloride was added while heating the solution, the 11B{1H} NMR spectrum of this solution showed a long shoulder next to each signals of 1,2,10-B10H7(SMe2)3]BF4. This indicates the important role of chloride in obtaining the neutral compound.

+ SMe SMe2 2

SMe SMe 2 -Me (2.8) +Me, acetic acid Cl- SMe SMe2 2

Fig. 13 Crystal structure of [1,2,10-B10H7(SMe2)3]BF4

Empirical formula C6 H25 B11 F4 S3

Formula weight 388.35

Crystal system, space group Monoclinic, P21/c Unit cell dimensions: length(Å) a 6.8974(10) b 14.8720(10) c 19.7272(10) angle(deg) α 90 β 91.093(10) γ 90 Volume, (Å3) 2023.2(3) Z, Calculated density (g cm-3) 4, 1.275 Crystal size (mm) 0.50 x 0.50 x 0.35 Temperature 200(2) K Absorption coefficient (mm-1) 0.387

R1 [I > 2σ(I)] 0.0365 wR2 (all data) 0.1010

Table 4 Crystal data and structure refinement for [1,2,10-B10H7(SMe2)3]BF4

Axial-Equatorial B-B Distances (Å)

B(11)-B(12) 1.682(3) B(10)-B(16) 1.681(3) B(11)-B(13) 1.679(3) B(10)-B(17) 1.685(3) B(11)-B(14) 1.674(3) B(10)-B(18) 1.682(3) B(11)-B(15) 1.687(3) B(10)-B(19) 1.678(3)

Equatorial-Equatorial B-B Distances (Å)

B(12)-B(13) 1.833(3) B(14)-B(17) 1.805(3) B(12)-B(15) 1.834(3) B(14)-B(18) 1.812(3) B(12)-B(16) 1.785(3) B(15)-B(18) 1.816(3) B(12)-B(19) 1.786(3) B(15)-B(19) 1.823(3) B(13)-B(14) 1.856(3) B(16)-B(17) 1.852(3) B(13)-B(16) 1.825(3) B(16)-B(19) 1.869(3) B(13)-B(17) 1.804(3) B(17)-B(18) 1.865(3) B(14)-B(15) 1.859(3) B(18)-B(19) 1.861(3)

Other Distances (Å)

S(1)-C(11) 1.796(2) B(1)-F(1) 1.315(4) S(1)-C(12) 1.797(2) B(1)-F(1') 1.458(8) S(2)-C(21) 1.792(3) B(1)-F(2) 1.257(7) S(2)-C(22) 1.790(2) B(1)-F(2') 1.412(6) S(3)-C(31) 1.795(2) B(1)-F(3) 1.311(3) S(3)-C(32) 1.790(2) B(1)-F(4) 1.382(3)

B(11)-S(1) 1.861(2) B(12)-S(2) 1.876(2) B(10)-S(3) 1.862(2)

Table 5 Selected Bond Distances of [1,2,10-B10H7(SMe2)3]BF4

Angles (o)

Substituted Boron/Sulfur Geometry

B(12)-B(11)-S(1) 129.58(15) B(16)-B(10)-S(3) 129.19(15) B(13)-B(11)-S(1) 128.15(15) B(17)-B(10)-S(3) 127.61(15) B(14)-B(11)-S(1) 129.67(15) B(18)-B(10)-S(3) 127.53(15) B(15)-B(11)-S(1) 128.79(15) B(19)-B(10)-S(3) 129.53(16)

B(11)-B(12)-S(2) 116.93(14) B(11)-S(1)-C(11) 103.52(11) B(13)-B(12)-S(2) 126.39(14) B(11)-S(1)-C(12) 103.33(11) B(15)-B(12)-S(2) 132.07(14) B(12)-S(2)-C(21) 103.66(13) B(16)-B(12)-S(2) 118.04(14) B(12)-S(2)-C(22) 106.64(11) B(19)-B(12)-S(2) 121.75(14) B(10)-S(3)-C(31) 103.06(11) B(10)-S(3)-C(32) 102.56(10) C(11)-S(1)-C(12) 100.67(12) C(21)-S(2)-C(22) 101.27(15) C(31)-S(3)-C(32) 100.79(13)

Boron Cage Geometry

B(12)-B(11)-B(13) 66.12(13) B(16)-B(10)-B(17) 66.76(14) B(12)-B(11)-B(15) 65.95(13) B(16)-B(10)-B(19) 67.62(14) B(12)-B(11)-B(14) 100.76(15) B(16)-B(10)-B(18) 103.25(16) B(13)-B(11)-B(15) 103.04(16) B(17)-B(10)-B(19) 102.85(16) B(11)-B(12)-B(16) 112.83(16) B(10)-B(16)-B(12) 109.17(16) B(11)-B(13)-B(17) 110.49(16) B(10)-B(17)-B(13) 111.26(16) B(11)-B(14)-B(17) 110.86(16) B(10)-B(18)-B(14) 110.40(16) B(11)-B(14)-B(18) 111.17(16) B(10)-B(19)-B(15) 110.50(16)

Table 6 Selected Bond Angles of [1,2,10-B10H7(SMe2)3]BF4

48 Alkylation of 1,10-(Me2S)2-2-MeSB10H7 was also performed with ethyl iodide in acetonitrile at room temperature for 3 hours. The cationic compound, 1,10-(Me2S)2-

2-(MeSEt)-B10H7I, was predicted to form. The residue was a pasty dark orange material after the removal of acetonitrile and other volatile components. 1H NMR revealed the expected cation with some impurities even after washing with acetonitrile repeatedly. The simple ethylation at the equatorial thioether caused the expected downfield shift of equatorial methyl group to 2.31 ppm. This is identical to [1,2,10-

B10H7(Me2S)3]BF4. The methylene of ethyl group was observed as two doublets of quartet at 2.76 ppm. The mass spectrum revealed that the impurities were related compounds (Fig. 14). They are believed to be of the [B10H7(S3Me(6-x)Etx)]I family members. However, they could not be identified by 1H NMR. Nonetheless, the observation of extra ethyl groups was not unexplainable.

S + R2I S I- R1 R1 R1 R1 - R2I

+ R1I - R1I

R2 S + R2I S R1 R2 - R2I R1 R2

Scheme 4 Equilibria existing between dialkylsulfide and alkyl halide

Fig. 14 Mass spectrum of the reaction between 1,10-(Me2S)2-2MeSB10H7 and EtI

50 1,10-(Me2S)2-2-MeSB10H7 can be analyzed as a methyl alkyl sulfide, MeSR.

The reaction of methyl alkyl sulfide with alkyl iodide has been known since the 19th century to produce a mixture of compounds. However, the existence of equilibria49 between the dialkylsulfide and alkyl halide was not observed until 1937 (Scheme 4).

Halides could abstract alkyl groups from sulfonium, but tend to go after the smallest group, usually methyl. The methyl and ethyl groups show little distinction in reactivity. 1,10-(Me2S)2-2-(MeSEt)-B10H7I could partake in the reverse reaction to produce 1,10-(Me2S)2-2-MeSB10H7 and ethyl iodide. The forward reaction produces

1,10-(Me2S)2-2-EtSB10H7 and methyl iodide. Subsequently, 1,10-(Me2S)2-2-EtS-B10H7 could react further with ethyl iodide and form another cationic species, 1,10-(Me2S)2-

2-Et2SB10H7I. Similarly, 1,10-(Me2S)2-2-MeSB10H7 can react with methyl iodide to

+ form the already known [1,2,10-(Me2S)3B10H7] . Surprisingly, the mass spectrum showed that some of the boron cages contain more than 2 ethyl groups. This simply implies that more than one sulfonium substituent are involved. The formation of cationic species significantly weakens the electron density of B(1) and B(10) to allow the removal of methyl groups of the apical substituents by weak nucleophile like iodide under ambient conditions.

B2.3 Neutral Icosahedral closo-dodecaborane bearing 3 exopolyhedral sulfur substituents

The only existing icosahedral closo-dodecaborane50 bearing 3 exopolyhedral

sulfur substituents, 1,7-(Me2S)2-9-(S-2’,4’-(NO2)2C6H4)B12H9, was prepared from reaction (2.9). Even though with excess reagent, only a single displacement product

51 was obtained by this reaction. There was no evidence for further displacement. This compound was originally thought to be a good candidate for tris-BSH precursor.

Unfortunately, the sulfur-aryl bond of the thioether could not be hydrolyzed easily.

The use of KOH(aq) allowed the production of some pasty material, which was

- assumed to be [1,7-(Me2S)2-9-(S)-B12H9] . The methylation of this unknown paste with methyl iodide produced a brown pasty product. However, the 11B{1H} NMR

+ spectrum of this product showed a complelling indication of [1,7,9-(Me2S)3B12H9] .

Interestingly, when we followed the same procedure on 1,12-(Me2S)2B12H10 refluxed with 2,4-(NO2)2C6H4SCl in acetonitrile (Eqn. 2.10) for a long period of time brought no reaction, unlike halogenation.51

SMe2 SMe2

O2N 2,4-(NO2)2C6H3SCl (2.9)

SMe2 S SMe2

NO2 SMe2

2,4-(NO ) C H SCl 2 2 6 3 N. R. (2.10)

SMe2

DMSO N. R. (2.11)

SMe2

SMe2 SMe2

DMSO (2.12)

SMe2 S SMe2

There was no reaction with 2’,4’-(NO2)2C6H4SCl. This was believed to be due to steric problem. However, no reaction occurred after heating DMSO with 1,12-

(Me2S)2B12H10 in 1.0 M HCl-acetic acid solution for a few hours (Eqn. 2.11). This disapproves that steric hindrance alone is to blame. Therefore, electronic contribution must play a key roll as well. This is very consistent with the fact that a quaternary

2- product was not found after heating [B10H10] with DMSO for 24 hours.

Nevertheless, the major isomer, 1,7-(Me2S)2B12H10, started to react with DMSO after heating in acidic solution within an hour after heating (Eqn. 2.12). The reaction was monitored by 11B{1H} NMR spectroscopy. The spectrum showed 4 equivalent peaks. Upon addition of water, a white solid was obtained, isolated, and analyzed by

11B{1H} NMR spectroscopy. The spectrum had 8 peaks instead very similar to 1,7- 53 (Me2S)2-9-(S-2’,4’-(NO2)2C6H4)B12H9 (Fig. 15). The mass spectrum showed that the

+ parent mass, 333.21, is exactly the same as [1,7-(Me2S)2-9-MeSB12H9Na] . The compound was crystallized from methyl alcohol, and its structure was determined by single crystal X-ray analysis (See Table 7 for the crystallographic data). 1,7-(Me2S)2-

9-MeSB12H9 crystallizes in the monoclinic space group P21/c with eight molecules in the unit cell. The structure was slightly disordered. Figure 16 displays one of the 8 molecules. The B-B bond distances in these molecules are between 1.758(4) and

1.806(4) Å. It was found that the B-B bond distances involving sulfonium substituted boron atoms, B(1) and B(7), are slightly shorter than others. The shortened distances between B(1) or B(7) and its 5 neighboring boron atoms were compensated by the lengthening of the bond between their common neighbors, B(2) and B(3). The bond distance of B(2)-B(3) is 1.806 Å, which is the longest within the molecule. B(9) is bonded to methyl sulfide. Unlike sulfonium, the B-B bond distances between B(9) and its neighboring boron atoms are comparable to other B-B bond distances in the cage.

The distances of B-S bonds are ranging from 1.885(3) to 1.902(3) Å with some disorders (Table 8). The bond angles centered at the sulfur-bound boron atoms are slightly distorted. Two of the five angles of individual substitution are about 5o larger

(Table 9). This indicates that the substiuents are bending to a preferred direction.

Such increases are obviously to reduce the steric repulsion between the methyl groups.

CN 3 in CD 9 H 12 -9-MeSB 2 S) 2 H} NMR spectra of 1,7-(Me 1 B{ 11 Fig. 15

Fig. 16 Crystal structure (2 different views) of 1,7-(Me2S)2-9-MeSB12H9

Empirical formula C5 H24 B12 S3

Formula weight 310.14

Crystal system, space group Monoclinic, P21/c Unit cell dimensions: length(Å) a 13.86920(10) b 14.59720(10) c 18.26530(10) angle(deg) α 90 β 110.85 γ 90 Volume, (Å3) 3455.80(4) Z, Calculated density (g cm-3) 8, 1.192 Crystal size (mm) 0.22 x 0.19 x 0.18 Temperature 299(2) K Absorption coefficient (mm-1) 0.405

R1 [I > 2σ(I)] 0.0543 wR2 (all data) 0.1619

Table 7 Crystal data and structure refinement for 1,7-(Me2S)2-9-MeSB12H9

57 Distances

Substituted Boron Distances (Å)

B(1)-B(2) 1.759(3) B(7)-B(2) 1.756(4) B(1)-B(3) 1.765(4) B(7)-B(3) 1.764(4) B(1)-B(4) 1.766(4) B(7)-B(8) 1.758(4) B(1)-B(5) 1.755(4) B(7)-B(11) 1.764(4) B(1)-B(6) 1.761(4) B(7)-B(12) 1.766(4)

B(9)-B(4) 1.769(4) B(9)-B(5) 1.778(4) B(9)-B(8) 1.786(4) B(9)-B(10) 1.796(4) B(9)-B(12) 1.778(4)

Other Boron Distances (Å)

B(2)-B(3) 1.806(4) B(2)-B(6) 1.792(4) B(4)-B(5) 1.781(4) B(8)-B(3) 1.787(4) B(8)-B(12) 1.792(4) B(8)-B(4) 1.768(4) B(2)-B(11) 1.788(4)

B(10)-B(5) 1.775(4) B(11)-B(2) 1.788(4) B(10)-B(6) 1.785(4) B(11)-B(6) 1.771(4) B(10)-B(11) 1.780(4) B(11)-B(10) 1.780(4) B(10)-B(12) 1.786(4) B(11)-B(12) 1.790(4)

Other Distances (Å)

S(1)-C(11) 1.784(4) S(1)-C(12) 1.789(4) S(2A)-C(21) 1.745(4) S(2B)-C(21) 1.666(7) S(2A)-C(22) 1.777(4) S(2B)-C(22) 1.520(7) S(3A)-C(3A) 1.785(8) S(3B)-C(3B) 1.82(7)

B(1)-S(1) 1.892(3) B(7)-S(2A) 1.902(3) B(7)-S(2B) 2.038(6) B(9)-S(3A) 1.885(3) B(9)-S(3B) 1.795(14)

Table 8 Selected Bond Distances of 1,7-(Me2S)2-9-MeSB12H9

Angles (o)

Substituted Boron Atom Geometry

B(2)-B(1)-S(1) 123.46(16) B(3)-B(1)-S(1) 122.80(17) B(4)-B(1)-S(1) 116.03(16) B(5)-B(1)-S(1) 118.73(16) B(6)-B(1)-S(1) 118.82(17)

B(2)-B(7)-S(2A) 118.34(17) B(2)-B(7)-S(2B) 116.7(2) B(3)-B(7)-S(2A) 113.80(19) B(3)-B(7)-S(2B) 149.9(3) B(8)-B(7)-S(2A) 117.40(18) B(8)-B(7)-S(2B) 132.1(3) B(11)-B(7)-S(2A) 125.51(18) B(11)-B(7)-S(2B) 90.4(2) B(12)-B(7)-S(2A) 124.72(19) B(12)-B(7)-S(2B) 98.1(3)

B(4)-B(9)-S(3A) 118.09(17) B(4)-B(9)-S(3B) 126.0(11) B(5)-B(9)-S(3A) 119.96(17) B(5)-B(9)-S(3B) 110.4(8) B(8)-B(9)-S(3A) 121.17(19) B(8)-B(9)-S(3B) 136.0(12) B(10)-B(9)-S(3A) 124.28(19) B(10)-B(9)-S(3B) 109.4(14) B(12)-B(9)-S(3A) 125.17(19) B(12)-B(9)-S(3B) 124.2(8)

Sulfonium/Sulfide Geometry

B(1)-S(1)-C(11) 104.83(19) B(1)-S(1)-C(12) 105.19(15)

B(7)-S(2A)-C(21) 105.21(17) B(7)-S(2B)-C(21) 102.5(3) B(7)-S(2A)-C(22) 104.76(15) B(7)-S(2B)-C(22) 109.2(3)

B(9)-S(3A)-C(3A) 103.8(3) B(9)-S(3B)-C(3B) 101(2)

C(11)-S(1)-C(12) 102.2(3) C(21)-S(2A)-C(22) 102.5(3) C(21)-S(2B)-C(22) 120.6(4)

Table 9 Selected Bond Angles of 1,7-(Me2S)2-9-MeSB12H9

SMe2 SMe2

Me3OBF4 (2.13) BF4 CH2Cl2

MeS SMe2 Me2S SMe2

The reaction of 1,7-(Me2S)2-9-MeSB12H9 with Me3OBF4 in methylene chloride could serve as a tool to confirm the existence of the cationic intermediate (Eqn. 2.13).

The evidence of reaction was much more obvious due to the change in symmetry.

+ [1,7,9-B12H9(SMe2)3] has a local C3 axis (Fig. 17); 4 peaks should be observed by

11 1 B{ H} NMR spectroscopy. The loss of a methyl group reduced the symmetry to Cs and more signals could be observed. Not only had this proven the existence of cationic

+ [1,7,9-(Me2S)3-B12H9] , but it also indirectly supported the existence of the analogous

+ 2- intermediate, [1,2,10-B10H7(SMe2)3] . It is because [B12H12] is known to have lower

2- 52 electronic density than [B10H10] .

+ Fig 17. The existence of C3 symmetry in [1,7,9-B12H9(SMe2)3]

61 It seemed unlikely that a third exopolyhedral sulfur substituent could be added to 1,12-B12H10(SMe2)2. However, the reaction of dialkylsulfoxide with 1,7-

B12H10(SMe2)2 looked quite promising and could potentially be extended further.

More specifically, it should be investigated for the formation of sulfide linkage

2- between cages (Eqn. 2.14). [B12H11S(O)Me] was heated in acetic acid/HCl solution overnight with 1,7-(Me2S)2B12H10 in attempt to synthesize a sulfide bridge. Only starting materials were recovered. It is not known whether the failure is due to steric or electronic effects.

1- SMe2 SOMe

HCl (g) + N. R. (2.14) H3CCOOH SMe 2

B2.4 Halogenation of 1,10-B10H8(SMe2)2, 1,10-B10H8(N2)2 and 1,7-

B12H10(SMe2)2

Halogenation occurred in a similar fashion as the reaction between DMSO and

1,10-(Me2S)2B10H8 or 1,7-(Me2S)2B12H10. As expected, the new substituent underwent electrophilic substituted at the 2- or 9- position. The resulting products of such have the general formula of 2-X-1,10-(Me2S)2-B10H7 or 9-X-1,7-(Me2S)2-B12H9. The stack plot of 11B{1H} NMR spectra showed gradual changes caused by halides at the 2- and

9- position of 2-X-1,10-(Me2S)2-B10H7 and 9-X-1,7-(Me2S)2-B12H9, respectively (Fig.

18 & 19).

7 H 10 -B 2 S) 2 H} NMR of 2-X-1,10-(Me 1 B{ 11 Fig. 18

CN 3 in CD 9 H 12 -B 2 S) 2 H} NMR of 9-X-1,7-(Me 1 B{ 11 Fig. 19

64 One equivalent of 1,10-(Me2S)2B10H8 and N-bromo- or N-chloro-succinimde was refluxed in acetonitrile with stirring overnight. 2-Br-1,10-(Me2S)2-B10H7 and 2-

Cl-1,10-(Me2S)2-B10H7 were isolated, respectively. The analogous N-iodosuccinimide was not used because of its poor quality. Therefore, 1.0M iodine monochloride solution in methylene chloride was used instead. Nonetheless, the desired product, 2-I-

1,10-(Me2S)2-B10H7, could still be obtained. In fact, iodine monochloride had been

2- 2- used in the final step of iodinating [B10H10] to [B10I10] . This is because the initial iodination by sublimed iodine could only result in a mixture of partially iodinated closo-borates.19 Therefore, iodine monochloride has been claimed to be a better iodinating agent53 primarily because of its solubility in non-coordinating polar solvents. Under any circumstances, the displacement of the exopolyhedral sulfur substituents was not observed.

Analogous reaction conditions between N-halosuccinimdes and 1,10-

B10H8(N2)2 did not give analogous results. Succinimides are barely soluble in any non- coordinating or non-polar solvents dissolving primarily in water and ethanol. It is

6 known that acetonitrile can displace the nitrogen in 1,10-(N2)2B10H8. Although pure

1,10-B10H8(N2)2 was obtained by recrystallization in 95% ethyl alcohol, the effect in the presence of other reagents was unknown. Coordinating solvents could potentially displace the pre-existing ligands. This could be the case especially under the influence of basic succinimide anion, which is a strong coordinator. 1,10-B10H8(N2)2 was refluxed overnight with a N-halosuccinimide in ethanol. The 11B{1H} NMR spectrum suggested a mixture of compounds. The 2-D 11B-11B COSY NMR spectroscopy was not very helpful in the identification process. Column chromatography was unable to

65 isolate reasonable amounts of any product for further characterization. Chlorine or bromine could not be used for this reaction due to over-halogenation.19 The methods for placing bromide and chloride on the 1,10-B10H8(N2)2 in controllable fashion is limited. Iodine monochloride could be used because of its solubility in chloroform.

The halogen containing solvent did not react with the dinitrogen after refluxing for a few hours. Using this synthesis, 2-I-1,10-(N2)2B10H7 was isolated in 80% yield. In contrast to halogenation, not only 1,10-(N2)2-2-MeSB10H7 was not observed when

1,10-B10H8(N2)2 was heated in acetic acid with hydrogen chloride and DMSO for 3 hours. The electrophiles also did not have any effects whatsoever on the inner diazonium derivative either.

Excess reagents can multiply halogenate the bis-inner sulfonium neutral compound. In this case, only di-halogenation products were found. These compounds,

9,10-X2-1,7-(Me2S)2B12H8, contained halogens on neighbor boron atoms. When X is bromide or iodide, the halides can be displaced by different alkyl groups with the use of palladium catalysts.51 Dimethyl inner sulfonium is a very stable substituent. None of those reactions above had any effect on the sulfur atoms. The halogens remained in specific positions. 2-X-1,10-(Me2S)2B10H7 and 9,10-X2-1,7-(Me2S)2B12H8 are very

2- 2- useful in terms of synthesizing [2-B10H9X] and [1,2-B12H10X2] , respectively. This is when the exopolyhedral sulfur atoms can be removed from the boron cage.

2- B2.5 Dealkylation of 1,10-(Me2S)2-2-MeSB10H7 to [1,2,10-B10H7(SMe)3]

The chemistry of boron cages mainly occurs on either the boron atoms or substituents. The substitutions have already extended from mono-substitution to tri-

66 substitution, which is the end point of this category to date. The substituents are saturated with the exception of equatorial thioether. For further exploration of properties, the alkyl groups should be removed.

There are a few methods reported for removing alkyl groups on sulfonium derivatives including sodium phthalimide,54 sodium/potassium in ammonia, and sodium ethanethiolate generated in situ.46 Sodium phthalimide was found to be effective only in DMF.55 The complete removal of DMF from the ensuing deposit was quite tedious due to its low vapor pressure. The other two methods previously employed were found to be equally effective. However, sodium ethanethiolate

(ethanethiol and sodium hydride) is considerably easier in terms of quantitative measurement than sodium/potassium. This is the case for removing methyl groups gradually.

After refluxing 1,10-(Me2S)2-2-MeSB10H7 with 1 equivalent of EtSNa in acetonitrile for about 3 hours, the volatiles were removed. The resulting residue dissolved in water but could not be precipitated with tetramethyl, tetrabutyl or methyl triphenylphosphonium cations (Eqn. 2.15). However, the 11B{1H} NMR spectrum was obtained in water and 2 equivalent sets of signals were observed. They are assigned to

- - the predicted [10-Me2S-1,2-(MeS)2B10H7] and [1-Me2S-2,10-(MeS)2B10H7] .

Different solvents and ion exchange columns were used in attempt to separate these two isomers, but they were not successful.

If the reaction was stopped prematurely, the 11B{1H} NMR spectrum showed one set of signals predominant. This gave evidence of kinetic dependence. It is believed that the inner sulfoniums at B(1) and B(10) are sterically distinguishable by

67 the substituent at the 2-position. The eventual equivalence of signals indicated that a equilibrium exists between two mono anions. Therefore, it is not surprising that no single isomer could be isolated, even though they should theoretically have different physical properties. In fact, the similar phenomenon was observed in between

2- 56 [B12H10(MeS)2] and [B12H10(Me2S)2].

1- 1- SMe2 SMe SMe2

SMe SMe SMe 1 eq NaSEt (2.15) CH3CN, reflux

SMe2 SMe2 SMe

1- 1- 2- SMe SMe2 SMe

SMe SMe SMe ex NaSEt (2.16) CH3CN, reflux

SMe2 SMe SMe

When the reaction was allowed to reflux overnight with excess EtSNa, it was found that only 1 methyl group could be removed from each inner sulfonium

1 substituent (Eqn. 2.16). Taken in CD3CN, the H NMR spectrum showed 3 methyl groups. There were due to thioethers at 1.54 ppm for the preexisting equatorial position, and a broad signal at 2.22 ppm for both of the apical positions due to antipodal effect (γ coupling).57 The apical methyl groups were shifted upfield from

68 2.96 and 2.98 ppm after the reaction. Upon decoupling, the broad signal was resolved into two sharp singlets. The three hydride signals appear at about 0.5 ppm (Fig. 20).

Interestingly, the antipodal effect was not observed at the equatorial thioether as it is always observed in B12 cages.

1 The H NMR spectrum looked very different when obtained in CD2Cl2. In fact, the proton signals were hardly recognizable. It is somewhat surprising that the dianion reacted with a common solvent like methylene chloride (Eqn. 2.17). The broadness of

11 1 B{ H} signals and its relative insensitivity allowed the proposed [1-(MeSCD2Cl)-

- - 2,10-(MeS)2B10H7] and [10-(MeSCD2Cl)-1,2-(MeS)2B10H7] mixture to be observed

(Fig. 21). These compounds have some very similar chemical shifts to the most downfield B10”, B10’, B1”, and B1’ (20, 18, 11, and 4 ppm, respectively) of the

- mono-dealkyated anions, [1-(Me2S)-2,10-(MeS)2B10H7] and [1-(Me2S)-2,10-

- (MeS)2B10H7] . The reaction was allowed to continue for 1 week in the NMR tube and found to be incomplete. Failure to obtain the projected neutral 1,10-(MeSCD2Cl)2-2-

MeSB10H7 could be explained by the localization of electrons. The increase in substitutions on the boron cage with more electron withdrawing sulfur atoms reduces the reactivity. Therefore, a boron cage containing less substituents would likely enhance the probability of isolating a single product (see Sec B2.9).

2- 1- 1- SMe SMe SMe2

SMe SMe SMe CD2Cl2 (2.17)

SMe SMe2 SMe

] 3 (SMe) 7 H 10 [1,2,10-B 2 N] 4 B} NMR spectra of [Me 11 H{ 1 H and 1 Fig. 20

2 Cl 2 CN and CD 3 ] in CD 3 (SMe) 7 H 10 [1,2,10-B 2 N] 4 H} NMR spectra of [Bu 1 B { 11 Fig. 21

(bottom) 2- ] 7 H 10 -B 3 (top) to [1,2,10-(HS) + ] 7 H 10 -B 3 S) 2 H} NMR spectra from [1,2,10-(Me 1 B{ 11 Fig. 22

B2.6 Reduction and oxidation of 1,10-(Me2S)2-2-MeSB10H7

Sodium or potassium reacts with 1,10-(Me2S)2-2-MeSB10H7 in ammonia for about 30 mins at low temperature to produce the same result as sodium ethanthiolate.

This result did not change even as the reaction time was extended to 2 hours.

2- SMe2 SH

SMe SH Li (s) MeOH (2.18)

MeNH2, reflux HCl (aq)

SMe2 SH

However, if lithium granules were used in dry methylamine (Eqn. 2.18) refluxing for 2 hours, the 11B{1H} NMR spectrum looked quite different from that of any of the known species. This included the starting material and other dealkylated anions (Fig.

22). It was assumed that the rest of methyl groups were removed as the previously

1 reported B12H10(SMe2)2. Therefore, the H spectrum was obtained after acidification

(middle Fig. 23). The original methyl signals disappeared and the three new upfield signals at about zero ppm were observed. 11B{1H} NMR sharpened these peaks and allowed for observation of borohydride (bottom Fig. 23). Upon addition of D2O, all of the upfield signals vanished in the 1H NMR spectrum (top Fig. 23). This is due to H-D exchange. This directly proves those peaks were from protons (as well as thiol).

Furthermore, the shift of a small signal at 2.1 to 2.5 ppm was due to small amounts of water soluble in acetonitrile being converted to DOH. The yield of this reaction was

73 about 70%. This is relatively lower in comparison to the B12 analog (Fig. 24). This can be accounted for the fact that the B10 cage is more basic than the B12 cage; as a result, it is relatively more difficult to achieving the same outcome.

2- The anionic [B12H11SMe] was reacted with 1 equivalent of sodium periodate

2- 55 on alumina, to form the major product[MeS(O)-B12H11] after 27 hours. However, when it was heated in acetic acid/HCl solution with 1,7-(Me2S)2-B12H10, a sulfide linkage did not develop. In the hope of finding the right condition/system for the formation of a sulfide linkage, we turned our attention to a neutral and more electron deficient compound. For example, using 1,10-(Me2S)2-2-MeSO-B10H7 to react with

1 1,10-(Me2S)2-B10H8. As monitored by H NMR spectroscopy, oxidation of 1,10-

(Me2S)2-2-MeS-B10H7 produced a mixture of starting material, sulfoxide and sulfone.

Neither sodium meta periodate in alumina58 at room temperature nor sodium perborate in acetic acid59 at 50 oC produced the desired result. This phenomenon is similar to many reported examples in oxidizing neutral dialkylsulfides, which are easily over- oxidized to the corresponding sulfones. When 2 equivalents of sodium meta periodate was used, pure 1,10-(Me2S)2-2-MeSO2-B10H7 was obtained in 91% yield (Eqn. 2.19).

Upon recrystallization from acetonitrile, the structure of the pure compound was determined by single crystal X-ray diffraction (See Table 10 for the crystallographic data). 1,10-(Me2S)2-2-MeSO2-B10H7 crystallizes in the monoclinic space group P21/c with four crystallographically independent molecules. The structure was slightly distorted. Figure 25 displays one of the 4 molecules.

CN 3 ] in CD 3 -(SH) 7 H 10 [1,2,10-B 2 N] 4 B} NMR spectra of [Bu 11 H{ 1 H and 1 Fig. 23

to di-thiol + ] 9 H 12 B 3 S) 2

1,7,9

1,7,9 H} NMR spectra: From cation [1,7,9-(Me 1 B{ 11 1,7,9

Fig. 24 9 H

12 +

2- ] 9 ] 2- 9 ] H 9 H 12 H 12 B 12 3 B 3 -9-MeSB B S) 2 3 2 S) 2 [1,7,9-(Me (Me 1,7, [1,7,9-(MeS) [1,7,9-(HS)

Empirical formula C5 H22 B10 O2 S3

Formula weight 318.51

Crystal system, space group Monoclinic, P21/c Unit cell dimensions: length(Å) a 9.6442 (10) b 16.5462(10) c 10.6902(10) angle(deg) α 90 β 97.889(10) γ 90 Volume, (Å3) 1689.7(3) Z, Calculated density (g cm-3) 4, 1.252 Crystal size (mm) 0.27 x 0.23 x 0.19 Temperature 200(2) K Absorption coefficient (mm-1) 0.426

R1 [I > 2σ(I)] 0.0349 wR2 (all data) 0.1184

Table 10 Crystal data and structure refinement for 1,10-(Me2S)2-2-MeSO2B10H7

Fig. 25 Single crystal structure of 1,10-(Me2S)2-2-MeSO2B10H7

Axial-Equatorial B-B Distances (Å)

B(1)-B(2) 1.672(3) B(10)-B(6) 1.676(4) B(1)-B(3) 1.687(4) B(10)-B(7) 1.678(4) B(1)-B(4) 1.684(4) B(10)-B(8) 1.682(4) B(1)-B(5) 1.687(4) B(10)-B(9) 1.669(4)

Equatorial-Equatorial B-B Distances (Å)

B(2)-B(3) 1.831(4) B(4)-B(7) 1.809(4) B(2)-B(5) 1.842(4) B(4)-B(8) 1.814(4) B(2)-B(6) 1.789(4) B(5)-B(8) 1.810(4) B(2)-B(9) 1.795(4) B(5)-B(9) 1.823(3) B(3)-B(4) 1.863(4) B(6)-B(7) 1.845(4) B(3)-B(6) 1.815(4) B(6)-B(9) 1.868(4) B(3)-B(7) 1.806(4) B(7)-B(8) 1.864(4) B(4)-B(5) 1.858(4) B(8)-B(9) 1.851(4)

Other Distances (Å)

S(1)-B(1) 1.866(3) S(1)-C(11) 1.793(3) S(1)-C(12) 1.797(2) S(2)-B(2) 1.871(3) S(2)-C(21) 1.778(2) S(2)-O(21) 1.4476(18) S(2)-O(22) 1.4530(19) S(3)-B(10) 1.862(3) S(3)-C(31) 1.791(3) S(3)-C(32) 1.796(3)

Table 11 Selected Bond Distances of 1,10-(Me2S)2-2-MeSO2-B10H7

Angles (o)

Substituted Boron(Sulfur) Geometry

B(2)-B(1)-S(1) 127.23(17) B(6)-B(10)-S(3) 130.44(17) B(3)-B(1)-S(1) 127.17(18) B(7)-B(10)-S(3) 130.63(18) B(4)-B(1)-S(1) 131.77(17) B(8)-B(10)-S(3) 126.21(18) B(5)-B(1)-S(1) 129.84(18) B(9)-B(10)-S(3) 126.32(18)

B(1)-B(2)-S(2) 117.16(17) B(3)-B(2)-S(2) 129.60(17) B(5)-B(2)-S(2) 129.41(17) B(6)-B(2)-S(2) 120.01(16) B(9)-B(2)-S(2) 119.95(16)

Sulfur Geometry

B(1)-S(1)-C(11) 104.10(12) B(10)-S(3)-C(31) 104.91(12) B(1)-S(1)-C(12) 104.83(12) B(10)-S(3)-C(32) 103.16(12) C(11)-S(1)-C(12) 101.13(12) C(31)-S(3)-C(32) 102.35(12)

B(2)-S(2)-C(21) 108.07(12) B(2)-S(2)-O(21) 109.91(11) B(2)-S(2)-O(22) 109.32(11) C(21)-S(2)-O(21) 106.47(11) C(21)-S(2)-O(21) 106.47(11)

Boron Cage Geometry

B(2)-B(1)-B(3) 66.06(15) B(6)-B(10)-B(7) 66.74(16) B(2)-B(1)-B(5) 66.49(16) B(6)-B(10)-B(9) 67.91(16) B(2)-B(1)-B(4) 100.98(15) B(6)-B(10)-B(8) 103.31(19) B(3)-B(1)-B(5) 102.87(19) B(7)-B(10)-B(9) 102.98(19) B(1)-B(2)-B(6) 112.89(19) B(10)-B(6)-B(2) 109.32(19) B(1)-B(3)-B(7) 110.46(19) B(10)-B(7)-B(3) 111.15(19) B(1)-B(4)-B(7) 110.45(19) B(10)-B(8)-B(4) 110.3(2) B(1)-B(4)-B(8) 110.74(19) B(10)-B(9)-B(5) 110.74(19)

Table 12 Selected Bond Angles of 1,10-(Me2S)2-2-MeSO2-B10H7

SMe2 SMe2

SMe SO2Me

NaIO4 (2.19)

MeOH / CH3CN

SMe2 SMe2

The structural data reveals that all the B-S bond distances are relatively constant ranging from 1.862(3) to 1.871(3) Å. Other distances related to B(2) are significantly shorter due to the electrowithdrawing effect of the two oxygen atoms. As listed in Table 11, the bond distances of B(2)-B(6) and B(2)-B(9) (inter equatorial level distances) are 1.789(4) and 1.795(4) Å, respectively. The bond distances involving its neighbor atom like the ones of B(5)-B(8) and B(5)-B(9) are 1.810(4) and 1.823(3) Å, respectively. Moreover, the bond distances of B(2)-B(3) and B(2)-B(5) (intra equatorial level distances) are 1.831(4) and 1.842 Å, repectively. B(6)-B(9) bond length is as long as 1.868(4) Å. The bond distance between B(1) and B(2) is a bit shorter than others involving B(1). In fact, the C-S bond distance for the equatorial substituent is also slightly shorter. The shortening of distances directly caused the distortion of the boron cage, as it can be seen from the angles centered at B(1). The bond angles S(1)-B(1)-B(2) and S(2)-B(1)-B(3) are about 3 to 4 degrees smaller than the angles of S(1)-B(1)-B(4) and S(1)-B(1)-B(5). The distortion is accompanied on the opposite face of the boron cage. S(3)-B(10)-B(8) and S(3)-B(10)-B(8) and S(3)-B(10)-

S(9) are also about 3 to 4 degrees smaller than S(3)-B(10)-B(6) and S(3)-B(10)-B(7). 81 The angle B(1)-B(2)-S(2) is also smaller by about 3 degrees, but this is believed to be irrelevant since similar difference was observed in the case of [1,10-(Me2S)2-2-Me2S-

B10H7]BF4. The B(1)-S(1) axis of [1,10-(Me2S)2-2-Me2S-B10H7]BF4 is orthogonal to the square face of the antiprism. Even with two methyl groups on each sulfur atom, there is no significant repulsion. Therefore, this overall distortion of 1,10-(Me2S)2-2-

MeSO2-B10H7 might intend to facilitate the hydrogen bonding between O(22) and a hydrogen atom bound to C(12). This is because the distance between them is only

2.557 Å. Other bond distances and angles are listed in Table 11 and 12, respectively.

1- B2.7 Isolation and characterization of 1- and 2- [B10H9(SMe2)]

2- - -

HCl (g) + 55-60 oC (2.20) DMSO SMe2

SMe2

o After heating Cs2B10H10 in DMSO with dry HCl gas at 55-60 C for 5-10 minutes, the solution turned slight orange and then cloudy. The addition of water at room temperature caused a small amount of white solid to precipitate. More of the solid eventually precipitated out of the water-dimethyl sulfoxide solution after cooling in an ice bath for 1 hour. The filtered and isolated bright white solid was predominantly Cs[1-B10H9SMe2] with a small amount of di-substituted compounds,

B10H8(SMe2)2. Cs[1-B10H9SMe2] was purified by washing with dichloromethane and 82 cold acetonitrile. Contradictory to the previously published procedure27 which used

NMe4[B10H10] as starting material, NMe4[1-B10H9SMe2] would not precipitate without

60 the addition of NMe4X salt. Reaction (2.20) was repeated by other authors, and the same observation was reported.

1- The filtrate contained all of the [2-B10H9SMe2] and a small amount of the

1- remaining [1-B10H9SMe2] . The addition of water or tetramethylammonium salt could

+ + not remove the apical isomer. When the counterion is either Cs or NMe4 , [2-

1- B10H9SMe2] is too soluble in DMSO. This is the case even in a 9:1 (v/v) water-

DMSO solution. This isomer required a more bulky cation, NBu4Br in this case, to cause precipitation (Scheme 5). The remaining apical isomer was collected simultaneously. However, contradictions regarding the existence of equatorial isomer,

1- [2-B10H9SMe2] , existed. The original publication claimed that the reaction gave a

1- 1- mixture of isomers consisting of [1-B10H9SMe2] and [2-B10H9SMe2] . This was performed on an industrial scale as large as a quarter mole. On the contrary, the most recent result45 disagreed with the previous literatures.27 Hall claimed that no [2-

1- B10H9SMe2] could be found in an experiment scaled twentyfold smaller. This led to the development of an alternate route which employed the chemistry of Tolpin61 and coworkers’. This route eventually failed because of the low yield of reaction intermediates.

HCl (g) H2O Cs2 Cs +(MeS) B H 55-60 oC 0 oC 2 2 10 8 DMSO

SMe2

1.5 eq NBu4Br [NBu4]

SMe2

1- Scheme 5 Separation of apical and equatorial isomers of [B10H9SMe2]

Unfortunately, even though the authors27 recognized the impure minor product, they did not provide any resolution that could separate this mixture. The crystallization of contaminated NBu4(2-B10H9SMe2) in absolute ethanol or ethyl acetate could not single out the desired isomer from the impurity. It was always detected by using 11B and 11B{1H} NMR spectroscopy. The spectra showed the contamination at about 2.5 ppm (Fig. 26). Nonetheless, structural data of Bu4N(2-B10H9SMe2) could still be obtained by X-ray analysis since the compound crystallized more readily than the other components of the mixtures (Fig. 27 and Table 13-14).

Komura and coworkers32 had acknowledged the same problem and developed a unique synthetic route to bypass the obstruction. They utilized the lability and

62 - selectivity of the dinitrogen ligand of [1-B10H9N2] with N,N-dimethylthioformamide

- to obtain the precursor of [1-B10H9SMe2] . They also utilized the reaction selectivity of

84 2- tetramethylthiourea with [B10H10] to obtain the isomeric precursor, [2-

- - B10H9S(NMe2)2] , of [2-Me2SB10H9] . Unfortunately, the published procedural conditions were not optimized, and the overall production yield was diminished in the step of hydrolysis. Interestingly, Preetz and coworkers63 experienced a similar contamination problem of equatorial isomer by its counterpart in an analogous system,

- - - [1-B10H9SCN] and [2-B10H9SCN] . However, the purification of [2-B10H9SCN] was demonstrated by using an ion exchange column. The very slight contamination of its counterpart could still be observed in the 11B and 11B{1H} NMR spectra. Amazingly,

- the spectra looked exactly identical to the ones of [2-Me2SB10H9] .

2 Cl 2 ] in CD 2 SMe 9 H 10 N][2-B 4 H} NMR spectrum of impure [Bu H} NMR spectrum of impure 1 B{ 11 B and 11 Fig. 26

Fig. 27 Crystal structure of [Bu4N][2-B10H9SMe2]

Empirical formula C22.50 H63.75 B12.50 N1.25 S1.25

Formula weight 527.20

Crystal system, space group Monoclinic, P21/n Unit cell dimensions: length(Å) a 12.3507(10) b 11.9064(10) c 18.5360(10) angle(deg) α 90 β 97.327(10) γ 90 Volume, (Å3) 2707.4(3) Z, Calculated density (g cm-3) 4, 1.293 Crystal size (mm) 0.08 x 0.08 x 0.35 Temperature 293(2) K Absorption coefficient (mm-1) 0.158

R1 [I > 2σ(I)] 0.1105 wR2 (all data) 0.328

Table 13 Crystal data and structure refinement for [Bu4N][2-B10H9SMe2]

Axial-Equatorial B-B Distances (Å)

B(1)-B(2) 1.679(9) B(10)-B(6) 1.672(10) B(1)-B(3) 1.706(10) B(10)-B(7) 1.708(11) B(1)-B(4) 1.689(10) B(10)-B(8) 1.707(11) B(1)-B(5) 1.690(10) B(10)-B(9) 1.692(10)

Equatorial-Equatorial B-B Distances (Å)

B(2)-B(3) 1.797(10) B(4)-B(7) 1.803(10) B(2)-B(5) 1.816(9) B(4)-B(8) 1.826(10) B(2)-B(6) 1.789(9) B(5)-B(8) 1.793(10) B(2)-B(9) 1.804(10) B(5)-B(9) 1.829(10) B(3)-B(4) 1.831(10) B(6)-B(7) 1.834(10) B(3)-B(6) 1.842(10) B(6)-B(9) 1.840(10) B(3)-B(7) 1.822(11) B(7)-B(8) 1.833(10) B(4)-B(5) 1.841(10) B(8)-B(9) 1.812(10)

Other Distances (Å)

S(1)-B(2) 1.887(7) S(1)-C(1) 1.789(7) S(1)-C(2) 1.783(7)

N(1)-C(11) 1.515(7) C(11)-C(12) 1.535(8) N(1)-C(21) 1.532(7) C(21)-C(22) 1.504(8) N(1)-C(31) 1.522(7) C(31)-C(32) 1.532(9) N(1)-C(41) 1.523(7) C(41)-C(42) 1.540(8)

Selected Angles (o)

S(1)-B(2)-B(1) 113.8(5) C(11)-S(1)-B(2) 104.10(12) S(1)-B(2)-B(3) 129.1(4) C(12)-S(1)-B(2) 104.83(12) S(1)-B(2)-B(5) 127.8(5) S(1)-B(2)-B(6) 121.4(4) S(1)-B(2)-B(9) 120.1(4)

Table 14 Selected Bond Distances and Angles of [Bu4N][2-B10H9SMe2]

B2.8 Synthesis of methyl thioether and thiols from inner sulfonium salts

We intend to explore the chemistry of the dimethylsulfide substituent and the synthetic improvement for acquiring pure 2-mercaptan-closo-decaborate. The

2- 2- equatorial isomeric thioether [2-B10H9SMe] , the counterpart of [1-B10H9SMe] , was

- never characterized. We were first interested in its preparation from [2-B10H9SMe2] , which was in turn prepared via nucleophilic substitution of DMSO on closo- decaborate. A few reported methods had been described particularly in removing a single methyl group from the inner sulfonium substituent. It was noticed that if [1-

1- + 46 1- + 56 B10H9SMe2] (NMe4 salt) and [B12H11SMe2] (Me3S salt) were already negatively charged, they would react with nucleophiles such as potassium

54 1- phthalimide and sodium ethanethiolate. Therefore, [2-B10H9SMe2] was predicted to behave in a similar fashion. However, the level of impurity of the product, [2-

2- B10H9SMe] , was unknown (Eqn. 2.21). Slightly impure material was reluctantly

2- employed. The side product, [1-B10H9SMe] , could contribute to impurities.

SMe2 SMe NaH, EtOH, EtSH [Bu4N] [Bu4N]2 (2.21) CH3CN, reflux overnight

90 Sodium ethanthiolate generated in situ was chosen primarily due to the efficiency of subsequent procedures. After refluxing and the removal of volatiles, distilled water was added to the light brown residue. The residue only partially dissolved due to the pre-existing tetrabutylammonium cation. Addition of tetrabutylammonium bromide induced further precipitation of a grey solid with some yellowish impurities. A batch of bright white powdery product was obtained by re- precipitation of the impure material in hot absolute ethyl alcohol using tetramethylammonium hydroxide pentahydrate. The 1H spectrum of this salt showed that only a single product was isolated (Fig. 28). Other than the solvent itself, d6-

DMSO (with small amount of H2O) at 2.49 (3.30) ppm, there were two other signals located at 3.09 and 1.45 ppm with a ratio of 8:1. The signal at 3.09 ppm was assigned

+ 1 to the cation [Me4N] . The H NMR chemical shift of methyl groups in [2-

1- B10H9SMe2] occurs at 2.25 ppm, and the integrated ratio of cation/anion is 4:1. In addition, the methyl chemical shift, 2.14 ppm, previously reported would eliminate the

1- possibility of [1-B10H9SMe] . Therefore, the evidence suggested a positive

2- identification of the desired [2-B10H9SMe] . This new signal appeared at 1.45 ppm.

This was located in the projected proximity of equatorial thioether for 1,10-Me2S-2-

2- MeSB10H7 and [1,2,10-B10H7(SMe)3] (see Sec. B2.5). The discovery of [2-

2- 11 11 1 B10H9SMe] was confirmed by elemental analysis as well as B and B{ H} NMR

2- spectra (Fig. 29). Amazingly, the spectra are identical to [1,2,10-B10H7(SMe)3] .

-DMSO 6 SMe] in d 9 H 10 [2-B 2 N] 4 B} NMR spectra of [Me 11 H{ 1 H and 1 Fig. 28

-DMSO 6 SMe] in d 9 H 10 [2-B 2 N] 4 H} NMR spectra of [Me 1 B{ 11 B and 11 Fig. 29

11 11 Fig. 30 B- B COSY NMR spectrum of [Me4N]2[2-B10H9SMe] in d6-DMSO

94 All 11B signals collapsed from doublets to singlets other than the one at -15 ppm in

11B{1H} NMR. This singlet was assigned as B(2), assuming no re-arrangement occurred within the boron cage during the reaction.30 11B-11B COSY NMR was subsequently employed to determine the assignments of other boron signals (Fig. 30).

There were 3 signals observed besides B(2) which had an integration as expected for

B(1), B(4), and B(10). Two boron atoms are directly bound to each other in the pre- defined structure. The third peak assignment was trivial, B(10) (Fig. 28). B(1) and

B(4) were not labeled individually. We realized that B(1) and B(10) could not correlate to any common boron atoms. Therefore, the most upfield signal at -30 ppm was determined to be B(4) because of its trivial relationships to B(7) and B(8).

Sequentially, the unassigned peak at 0.5 ppm was identified as B(1). Since B(1), B(2), and B(4) were identified, in principle, B(3) and B(5) should be found by association.

The correlations between B(2) and some other neighbor boron atoms could not always be detected. However, we could rely on B(1) to locate B(3) and B(5). The remaining singlet was given to B(6) and B(9) by elimination of the other possibilities. The arrangement was identical to all of the compounds that contain a substituent at position-2. It is quite surprising that an expected contamination, the isomer [1-

2- B10H9SMe] , was rarely observed, even though the identical procedure for dealkylation was used.

2- Removal of the remaining methyl group of [2-B10H9SMe] could be accomplished by using Li refluxed in methylamine. The reaction shows dependence on the cation. The most efficient, tetrabutylammonium salt, could complete the reaction within 1-2 hours. In contrast, the tetramethylammonium salt would take about

95 3 hours for completion. In the case of the apical isomer, the same procedure could be

1- performed directly from [1-B10H9SMe2] since this anion was isolated in a pure form.

However, the synthesis was started with cesium as the cation. It was found that the cesium salt of this isomer is not soluble in methylamine. The removal of alkyl groups of this isomer did not occur unless ion exchange was performed.

The reported procedure required an oxygen free environment. Otherwise, the compound would be oxidized and appear blue.64 The synthesis performed as reported yielded only only clean thiol products as seen by 1H NMR (Fig. 31). Interestingly, both isomers were precipitated with MePPh3Br. The apical isomer appears to be orange in color while the equatorial isomer is white. The yields of both are over 85%.

2- Starting from [B10H10] , over 60% of the boron cage was recovered, including 46% of apical thiol and about 17% of the equatorial thiol. This is substantially higher than

Komura’s selective method that produced less than 20% of product.

The reaction performed with the addition of alcohol for destroying excess lithium did not result in a color change. The blue color did not appear until a sufficient amount of aqueous acid was added. It was claimed that the transient intermediate was a sulfur radical and disulfide chain would eventually be formed. A grayish blue solid was isolated by using excess methyl triphenyl phosphonium bromide. 1H and 11B

NMR spectra of this radical species in CD3CN had a poor signal to noise ratio. [2-

2- B10H9S] was crystallized from acetonitrile-isopropanol solution. The structure was determined by single crystal X-ray analysis (See Table 15 for the crystallographic data).

2- SH] 9 H 10 and [2-B 2- SH] 9 H 10 B} NMRspectra of [1-B 11 H{ 1 Fig. 31

Empirical formula C38 H45 B10 P2 S

Formula weight 703.90 Crystal system, space group Monoclinic, Cc Unit cell dimensions: length(Å) a 9.3287(10) b 32.7403(10) c 14.5737(10) angle(deg) α 90 β 109.786(10) γ 90 Volume, (Å3) 3901.0(5) Z, Calculated density (g cm-3) 8, 1.224 Crystal size (mm) 0.46 x 0.15 x 0.08 Temperature 200(2) K Absorption coefficient (mm-1) 0.337

R1 [I > 2σ(I)] 0.0508 wR2 (all data) 0.1159

Table 15 Crystal data and structure refinement for [MePPh3]2[2-B10H9S]

Fig. 32 Crystal structure of [MePPh3]2[2-B10H9S]

Axial-Equatorial B-B Distances (Å)

B(11)-B(12) 1.693(14) B(10)-B(6) 1.692(11) B(11)-B(13) 1.718(11) B(10)-B(17) 1.689(14) B(11)-B(14) 1.682(14) B(10)-B(18) 1.679(12) B(11)-B(15) 1.679(12) B(10)-B(19) 1.703(11)

Equatorial-Equatorial B-B Distances (Å)

B(12)-B(13) 1.825(10) B(14)-B(17) 1.801(14) B(12)-B(15) 1.814(10) B(14)-B(18) 1.817(14) B(12)-B(16) 1.804(12) B(15)-B(18) 1.798(12) B(12)-B(19) 1.797(11) B(15)-B(19) 1.835(13) B(13)-B(14) 1.827(10) B(16)-B(17) 1.781(9) B(13)-B(16) 1.782(11) B(16)-B(19) 1.838(10) B(13)-B(17) 1.768(15) B(17)-B(18) 1.815(8) B(14)-B(15) 1.801(11) B(18)-B(19) 1.805(10)

Other Distances (Å)

S(1)-B(2) 1.872(8) P(1)-C(1) 1.796(6) P(1)-C(121) 1.772(7) P(1)-C(131) 1.793(7) P(1)-C(141) 1.794(7)

Selected Angles (o)

S(1)-B(12)-B(11) 116.6(6) S(1)-B(12)-B(13) 131.4(5) S(1)-B(12)-B(15) 129.6(5) S(1)-B(12)-B(16) 121.4(4) S(1)-B(12)-B1(9) 119.3(4)

Table 16 Selected Bond Distances and Angles of [MePPh3]2[2-B10H9S]

100

[MePPh3]2[2-B10H9S] crystallizes in the monoclinic space group Cc with eight molecules in the unit cell. Figure 32 displays one of the 8 molecules. The hydrogen atom could not be located on the sulfur atom. The B-B bond distances in average are shorter than in other B10 cages. The decaborane(10) derivatives that were discussed in this dissertation have equatorial B-B bond distances ranging from 1.80 to 1.86 Å.

Most of the bond distances of those compounds are on the high end. The B-B bond distances of [MePPh3]2[2-B10H9S] are lower than typical. For example, the shortest

- distance of B-B bond in [2-B10H9SMe2] is 1.789(9) Å, but the shortest B-B bond

2- distance in [2-B10H9S] was 1.768(11) Å with many distances are shorter than 1.80 Å.

B2.9 Reaction of methyl thioethers with electrophilic reagents

Muetterties and co-workers were the first to demonstrate the exceptional nucleophilicity of methyl closo-dodecaboranyl thioether in the formation of sulfonium

2- 2- derivatives by reacting [B12H11SMe] and [B12H10(SMe)2] with trimethylsulfonium

36 1- iodide. Furthermore, the study of the alkylation involving [(MeS)(Me2S)B12H10] isomeric mixture was limited only to benzylic substrates.65 The research of alkylation was further extended to the pure isomer thioethers as well as the 1,2-, 1,7-, and 1,12-

2- 66 [B12H10(SMe)2] by Shore and coworkers.

101

2- 2- 1-

Me3SI (2.22)

SH SMe SMe2

Komura and coworkers32 obtained the corresponding sulfonium salts from [1-

2- 2- HSB10H9] and [2-HSB10H9] (Eqn. 2.22). We observed the unpredictable reaction

2- between [1,2,10-(MeS)3B10H7] and methylene chloride. Other than these, the

2- nucleophilicity of analogous [(MeS)xB10H10-x] system was almost unexplored. This is

2- due to the overwhelming popularity of [B12H12] derivatives for the potential use for

BNCT.67 Therefore, we became interested in exploring the properties and some other potential uses of this bicapped square anti-prismatic boron cluster.

B2.9.1 Reaction of [Me4N]2[2-B10H9SMe] with methyl iodide

The isolation of [Me4N]2[2-B10H9SMe] (see Sec. 2.8) provided a route to obtain

1- the uncontaminated [2-B10H9SMe2] by methylation. Referring to the previously mentioned examples, trimethylsulfonium iodide would be the logical choice (Eqn.

2.23). Nonetheless, the dimethylsulfide would inevitably be produced as a by-product.

Yet chemically the existence of the dimethylsulfide did not seem to facilitate or enhance the reaction. Therefore, a simple modification of using methyl iodide was considered and applied for an easier purification procedure (Eqn. 2.24).

102

2- 1- Me Me (2.23) + S I + S + I Me Me Me SMe SMe2

2- 1-

+ Me I + I (2.24)

SMe SMe2

1- 11 11 1 The desired product, [2-Me2SB10H9] , was obtained and analyzed by B and B{ H}

NMR. The impurity could no longer be observed as described in the previous section

(Fig. 33). The assignments of all the boron signals were made with the assistance of

11B-11B COSY NMR (see Sec. 2.8). To the best of our knowledge, this is the first time an equatorial substituted decaborane(10) derivative was “purified” chemically from its counterpart which was synthesized by a non-selective method

103

1- ] 2 SMe 9 H 10 H} NMR spectra of pure [2-B 1 B{ 11 B and 11 Fig. 33

104

2- B2.9.2 Reaction of isomeric [B10H9SMe] with dihaloalkanes

2- The unexpected reaction between [1,2,10-B10H7(SMe)3] and methylene chloride (see sec. 2.7) showed the underestimated basicity and nucleophilicity of bicapped antiprismatic closo-decaborate. There are limited numbers of organic reactions, especially in the formation of trialkylsulfonium derivatives involving methylene chloride. Reaction (2.25) and (2.26) have successfully produced the displacement product with dichloromethane.

CH2Cl SMe MeS

CH2Cl2 [NBu4]2 [NBu4] + NBu4Cl (2.25) CH3CN

CH2Cl2 [NBu4]2 [NBu4] + NBu4Cl CH3CN (2.26) SMe SMe

ClH2C

105

11 2- This conclusion based on the B NMR spectrum of [1-B10H9SMe] and [1-

1- (MeSCH2Cl)-B10H9] . The arrangement of chemical shifts between two apical boron atoms, B(1) and B(10), switched after reaction (Fig. 34). This phenomenon also occurs

1- in the dealkylation of [1-B10H9SMe2] . Additionally, the two hydrogen atoms were diastereotopically distinguished at 5.29 and 5.05 ppm on 1H and 1H{11B} NMR spectra

(Fig. 35). This is due to the anticipated chirality of inner sulfonium derivatives. These diastereotopic hydrogen atoms were verified by using 13C-1H HMQC and DEPT NMR spectroscopy to be bonded to the same carbon center.

The chemical shift of the α-proton is 5.29 ppm in this newly formed inner

1- sulfonium salt, [1-(MeSCH2Cl)-B10H9] . This comparable to the chemical shift of methylene chloride at 5.32 ppm. The similarity was also observed on the α-carbon chemical shift at 53.3 ppm compared to 53.8 ppm of CH2Cl2. Likewise, the α-carbon

1- of [1-(MeSCH2Br)-B10H9] was found at 37.7 ppm compared to 38.7 ppm in bromochloromethane.68 A gradual upfield trend of chemical shifts was observed from chloride to bromide to iodide. The same features on 11B, 1H, and 1H{11B} NMR spectra were repeatedly witnessed in the cases of dibromomethane, diiodomethane, and iodoacetonitrile (Table 17).

106

reaction product 2 Cl 2 -acetone and CH 6 in d 2- SMe] 9 H 10 B NMR spectra of [1-B 11 Fig. 34

107

CN 3 in CH in 1- ] 9 H 10 SMe B 2 H NMR spectrum of [1- ClCH of [1- H NMR spectrum 1 Fig. 35

108

65% 98% 87% 92% 91% Yield X 2 5.3 51.7 53.3 37.7 32.1 CH H} 1 C{ 13 23.9 26.9 27.9 29.8 28.4 MeS fferent dihaloalkanes 4.29 d 5.29 d 5.09 d 4.84 d 4.41 d X 2 CH B} 11 lated products with di H{ 1 4.52 d 5.05 d 4.81 d 4.49 d 4.30 d H/ 1 2.18 3.10 3.09 3.04 3.15 MeS H}

1 B{ S-B 2 0.9 -1.1 -0.2 -0.5 11 -17.8 R B/ 11

2- ] 2- 2- 2-

9 ] ] ] 2- 9 9 9 NMR: ] H 9 H H H 10 Table 17 Varied chemical shifts of alky H 10 10 10 10 I-B Cl-B Cl-B Br-B CN-B 2 2 2 2 2 [1-MeSCH [1-MeSCH Compounds [2-MeSCH [1-MeSCH [1-MeSCH

109 2-

S S

H H syn

S S

H H anti

Further replacement of chloride or halide was not achieved. Only one set of diastereomers was observed. The integral ratio between methyl and methylene was

3:(1:1). Assuming oligomers are formed, as shown above, they should have the proton ratio of 6:(1:1) for the syn isomer, but 3:1 for the anti isomer. Furthermore, the different chemical shift of diastereotopic α-protons from different dihaloalkane reactions indicated the differences between the alkyl groups on sulfonium. Finally, the single displacement was further supported by the crystal structure of Bu4N[1-

MeSCH2Cl-B10H9] (Fig. 36) and MePPh3[2-MeSCH2Cl-B10H9] (Fig 37). Both compounds were crystallized from methylene chloride. The structural data, bond distances and angles are given in Table 18-21.

The chemistry of the chloromethyl methyl boranyl sulfonium derivative,

- [ClCH2S(Me)B10H9] , is opposite to its organic analogue. The preparation of α- chloromethyl dialkyl sulfonium salt specifically required chlorination of dialkyl sulfide69 followed by application of the strong methylating agent, trimethyloxonium 110 tetrafluoroborate. Reagents like iodomethane failed as methylating agents. They also undergo halogen displacement reactions with nucleophiles.70 In contrast, alkyl or aryl sulfide could directly replace multiple chloride atoms in halogenoperfluoroalkanes

(Freons).71

Since the direct displacement of halide was discovered, we became interested in finding out the possible formation of a short alkyl linkage through the exopolyhedral sulfur atoms. The linkage could be potentially useful in understanding the communication between two closo-decaborate molecules via substituents as in the carborods.72 Therefore, 1,2-dichloroethane was used. It was successfully reacted with

- 11 11 1 [1-B10H9SMe] . B and B{ H} NMR showed the completion of the reaction from the arrangements of B(1) and B(10). 1H and 1H{11B} NMR spectra was used to determine the structure. The observation of 4 equivalent diastereotopic hydrogen atoms and the splitting of these multiplets proved that only the single displacement took place (Fig 38). If it were not the case, as shown below, simple doublets (for each set of protons) would be observed.

S S

H H H H

H S H

H H S

111

Fig. 36 Crystal structure Bu4N[1-(MeSCH2Cl)-B10H9]

112

Empirical formula C18 H50 B10 Cl N S C20 H30 B10 Cl P S

Formula weight 456.20 477.02 Isomer Apical Equatorial Crystal system, space group Monoclinic, Orthorhombic,

P21/c P212121 Unit cell dimensions: length(Å) a 21.0436(10) 11.1855(10) b 13.6040(10) 15.3187(10) c 20.6577(10) 16.0247(10) angle(deg) α 90 90 β 100.273(10) 90 γ 90 90 Volume, (Å3) 5819(6) 2745.8(3) Z, Calculated density (g cm-3) 9, 1.172 4, 1.154 Crystal size (mm) 0.35 x 0.19 x 0.15 0.80 x 0.15 x 0.12 Temperature 200(2) K 298(2) K Absorption coefficient (mm-1) 0.237

R1 [I > 2σ(I)] 0.0696 0.0514 wR2 (all data) 0.2119 0.1481

1- Table 18 Structure refinement for 1- and 2-[(MeSCH2Cl)-B10H9]

113

Fig. 37 Crystal structures Me3PPh[2-(MeSCH2Cl)-B10H9]

114

Axial-Equatorial B-B Distances (Å)

B(1)-B(2) 1.675(4) B(10)-B(6) 1.699(4) B(1)-B(3) 1.673(4) B(10)-B(7) 1.697(4) B(1)-B(4) 1.667(4) B(10)-B(8) 1.699(4) B(1)-B(5) 1.677(4) B(10)-B(9) 1.701(4)

Equatorial-Equatorial B-B Distances (Å)

B(2)-B(3) 1.846(4) B(4)-B(7) 1.824(4) B(2)-B(5) 1.857(4) B(4)-B(8) 1.818(4) B(2)-B(6) 1.810(4) B(5)-B(8) 1.811(4) B(2)-B(9) 1.809(4) B(5)-B(9) 1.805(4) B(3)-B(4) 1.852(4) B(6)-B(7) 1.881(4) B(3)-B(6) 1.796(4) B(6)-B(9) 1.848(4) B(3)-B(7) 1.807(4) B(7)-B(8) 1.851(4) B(4)-B(5) 1.850(4) B(8)-B(9) 1.836(4)

Other Distances (Å)

B(1)-S(1) 1.861(3) S(1)-C(1) 1.671(8) S(1)-C(2) 1.962(7) S(1)-C(1’) 1.959(7) S(1)-C(2') 1.718(7) C1(1)-C(1) 1.787(9) Cl(1’)-C(2’) 1.668(8) Cl(1B)-C(2’) 1.882(8)

1- Table 19 Selected Bond Distances of [1-(MeSCH2Cl)-B10H9]

115

Axial-Equatorial B-B Distances (Å)

B(1)-B(2) 1.675(6) B(10)-B(6) 1.680(7) B(1)-B(3) 1.689(7) B(10)-B(7) 1.685(7) B(1)-B(4) 1.702(7) B(10)-B(8) 1.704(7) B(1)-B(5) 1.717(7) B(10)-B(9) 1.695(7)

Equatorial-Equatorial B-B Distances (Å)

B(2)-B(3) 1.802(6) B(4)-B(7) 1.797(7) B(2)-B(5) 1.804(6) B(4)-B(8) 1.803(7) B(2)-B(6) 1.763(6) B(5)-B(8) 1.804(6) B(2)-B(9) 1.777(6) B(5)-B(9) 1.820(6) B(3)-B(4) 1.819(7) B(6)-B(7) 1.807(6) B(3)-B(6) 1.790(7) B(6)-B(9) 1.851(6) B(3)-B(7) 1.771(7) B(7)-B(8) 1.826(6) B(4)-B(5) 1.816(7) B(8)-B(9) 1.812(6)

Other Distances (Å)

B(2)-S(1) 1.889(4) S(1)-C(1) 1.751(5) S(1)-C(2) 1.805(5) C1(1)-C(2) 1.736(5)

1- Table 20 Selected Bond Distances of [2-(MeSCH2Cl)-B10H9]

116

Angles (o)

[Bu4N][1-MeSCH2Cl-B10H9] [MePPh3][2-MeSCH2Cl-B10H9]

B(2)-B(1)-S(1) 128.2(2) B(2)-B(1)-H(1) 123.7(15) B(3)-B(1)-S(1) 128.0(2) B(3)-B(1)-H(1) 133.7(16) B(4)-B(1)-S(1) 128.7(2) B(4)-B(1)-H(1) 139.2(15) B(5)-B(1)-S(1) 129.16(19) B(5)-B(1)-H(1) 129.2(16)

B(1)-B(2)-H(2) 121.5(14) B(1)-B(2)-S(1) 116.1(3) B(3)-B(2)-H(2) 131.2(14) B(3)-B(2)-S(1) 127.5(3) B(5)-B(2)-H(2) 132.1(14) B(5)-B(2)-S(1) 132.3(3) B(6)-B(2)-H(2) 119.1(14) B(6)-B(2)-S(1) 116.5(3) B(9)-B(2)-H(2) 119.7(14) B(9)-B(2)-S(1) 119.8(3)

S(1)-C(1)-Cl(1) 100.67(12) S(1)-C(2)-Cl(1) 113.4(3) C(1)-S(1)-C(2) 101.27(15) C(1)-S(1)-C(2) 100.7(3) C(1)-S(1)-B(1) 100.79(13) C(1)-S(1)-B(2) 102.8(2) C(2)-S(1)-B(1) 100.79(13) C(2)-S(1)-B(2) 104.2(2)

1- Table 21 Selected Bond Angles of 1- and 2-[(MeSCH2Cl)-B10H9]

117

CN 3 in CD 1- SMe] 9 H 10 Cl)-B 2 CH 2 B} NMR spectrum of [1-(MeSCH B} NMR spectrum 11 H{ 1

Fig. 38

118 2- B2.9.3 Reaction of isomeric [B10H9SMe] with alkyl halides

It was recognized that the reaction between thioether and dihaloalkanes had a high yield. However, the second halide could not be displaced in these reactions. The incapability to establish oligomers was believed to be due to steric hindrance. This effect was illustrated by the use of simple alkyl groups.

H H H

I I H Me Me H Me Me Br

Ethyl Iodide Isobutyl Iodide Isopropyl Bromide

Ethyl iodide, isobutyl iodide, and isopropyl bromide were stirred overnight (8-

2- 10 hours) each with [1-B10H9SMe] in acetonitrile. Identical workup processes were performed. As it could be seen from the yield of products (Table 22), the halide could be displaced easily in ethyl iodide. When a slightly bulkier isobutyl group was employed, the production was found to be about 25% lower than when a less hindered reagent was employed. The product yield increased from 69% to 71%, when the reaction was allowed to proceed for 24 hours. The cone angle is larger in the isopropyl group than those above. This has a more dramatic effect on the secondary carbon. The

1- corresponding product, [1-(MeSCHMe2)-B10H9] , observed was below 50% yield by

11B{1H} NMR. This is true even if the reaction was allowed to continue for 48 hours in room temperature. Two α-methyl signals (at 1.66 and 1.61 ppm) are observed in the

1 11 1- H{ B} NMR spectrum of [1-MeSCH(CH3)2-B10H9] (Fig. 39). Like the α-hydrogen atoms of dihaloalkyl group, the diastereotopic α-methyl groups are distinguishable.

119

77% 92% 69% 22% Yield

2 2 R 1 36.8 40.4 55.4 47.2 SCR H} 1 C{ 13 23.0 26.8 26.9 24.0 MeS fferent alkyl iodides

N/A 3-x 2.57 dq 3.27 dq 3.15 dd 1 R x B} 11 CH H{ 1 3.65 m 2.73 dq 3.42 dq 3.32 dd H/ lated products with di 1 2.18 2.89 2.90 2.86 MeS H}

1 B{ S-B 2 0.8 1.1 -0.4 11 -17.2 R B/ 11

2- ] 9

H NMR : 2-

10 ] 2- 2- 9 ] ] 9 9 -B H 2 ) H H 10 3 10 10 -B 2 Table 22 Varied chemical shifts of alky -B -B ) 3 3 3 Carbon o CH CH CH(CH (CH 2 2 2 – 1 3 Carbon CH CH CH o /CH – 2 2 (i-Butyl Iodide) Iodide) (i-Butyl [1-MeS Iodide) (i-Propyl CH CH [1-MeS (Ethyl Iodide) [1-MeS Compounds [2-MeSCH

120

CN 3 in CD 1- ] 9 H 10 -B 2 B} NMR spectrum of [1- MeSCHMe of [1- B} NMR spectrum 11 H{ 1 Fig. 39

121 Isobutyl iodide and isopropyl bromide reactions are analogous to dichloroethane and dichloromethane reactions, respectively. The dramatic change of product yield could be observed when the cone angle increase gradually. The boron cage is larger than the alkyl groups above, it is expected that the reactions between [1-

1- 2- (MeSCH2X)-B10H9] and [1-MeS-B10H9] would not proceed.

2- B2.9.4 Tertiary Alkylation of [1-B10H9SMe] by Michael Addition

The use of a secondary halide, isopropyl bromide, reduced the yield to 22%. A

2- tertiary halide, 2-bromo-2-methylpropane, did not to react with [1-B10H9SMe] . This result was expected. However, it was found that a Michael addition could easily introduce a tertiary alkyl substituent onto the thioether sulfur atom under acidic condition (Eqn. 2.27). The 1H NMR spectrum (Fig. 40) shows that the β-protons were

1- diastereotopic like the β-protons of [1-(ClCH2SMe)-B10H9] . Unlike [1-(iPrSMe)-

1- B10H9] , the α-methyl groups appear to be chemically equivalent. Their coincidental overlap signals in the proton spectra. The methyl carbon atoms (at 24.5 and 24.0 ppm) are distinguishable by 13C{1H} NMR.

SMe S

Me2CCHCOMe [NMe4]2 [NMe4] + NMe4Cl (2.27) HCl (aq), CH3CN

122

CN 3 in CD 1- ] 9 H 10 CHCOMe)-B 2 B} NMR spectrum of [1-(MeSCMe B} NMR spectrum 11 H{ 1

Fig. 40

123

The purpose of this reaction was to produce an appropriate precursor to investigate the possible removal of a methyl group while keeping the functional alkyl group.

Ethanethiolate was known to remove the methyl group as well as to attack the carbonyl group nucleophilically. Therefore, relatively less nucleophilic methoxide was applied as a protecting reagent in ketal formation before removing the methyl group.

Unfortunately, it was found that alkoxide would not fulfill the function. This base was found to undergo an the undesirable reverse Michael addition.

2- B2.9.5 Reaction of [1-B10H9SMe] with 1,1-Dichloroacetone

In section B2.9.2, dichloromethane was shown to react with isomeric

2- 2- [B10H9SMe] to form the corresponding [(MeSCH2Cl)-B10H9] . Since there are two

α-hydrogen atoms, only 1 set of enantiomers (due to the chirality of sulfonium) was obtained. When one of the hydrogen atoms was displaced with a functional group, R, as shown below, the resulting product would contain a second stereogenic center.

H H R H

C C C C BorateS H BorateS R BorateS H R SBorate

124 The prochiral reagent selected was 1,1-dichloroacetone (Cl2CHCOCH3) because of its acidic geminal hydrogen atom. The bromo- analog would have a better reactivity. However, it was not commercially available in a pure form. If this reaction proceeded as expected, it could be useful in generating an ylide. Monitoring by 11B

1- NMR, the spectrum of the product looked similar to [1-B10H9SR2] . However, the singlet of B(1) is overlapping with a smaller signal, B(1’), just upfield (Fig. 41).

Initially the reaction was mistakenly considered as incomplete. This is because the distribution of the two sets of diastereomers was not immediately recognized. The ratio was projected to be 50:50. The two chlorides of 1,1-dichloroacetone as well as the two electron pairs of thioether are chemically equivalent. Nonetheless, the 1H

NMR spectrum has revealed the ratio of 2 sets of diastereomers. One set of isomers was about 5 times in excess (Fig. 42). This moderate stereoselectivity could be explained by steric hinderance. The steric consideration forces the introduction of a larger group to the least crowded position (Fig. 43).

The methyl closo-decaboranyl thioether could have two possible faces of 1,1- dichloroacetone when they are parallel. When the thioether approaches, the sulfur atom is required to adjust the electron pairs. Since the size of hydrogen atom is smaller than chloride, it is more favorable for the methyl group to face the hydrogen. As a result, the enantiomeric excess (EE) can be observed by NMR.

125

CN 3 in CD 1- ] 9 H 10 H} NMR spectrum of [1-(MeSCHClC(O)Me)-B 1 B{ 11 Fig. 41

126

CN 3 in CD 1- ] 9 H 10 [1-(MeSCHClC(O)Me)-B H NMR spectrum of 1 Fig. 42

127

O O Cl Cl Cl Cl

H H O Cl Cl

Me S S Me H

Me Me

Major Product

O O Cl Cl Cl Cl

H H O Cl Cl Me S S Me Me H Me

Minor Product

1- Fig. 43 Stereoselectivity in formation of [1-(MeSCHClCOMe)-B10H9]

128

Nonetheless, we were interested in generating an ylide from this compound.

The subsequent procedure could remove the diastereotopicity by deliberately destroying the newly created stereogenic center (Eqn. 2.28). Many references described the formation of trialkyl sulfonium ylide under basic condition. The most commonly used reagent was found to be potassium tert-butoxide.73 This base was

1- allowed to react with [1-MeSCHClCOMe-B10H] in t-BuOH for 30 mins to 3 hours.

Although the solution color turned light yellow, the reaction was determined to be a failure. This is because the ratio between the isomers was unchanged as monitored by

1H NMR spectroscopy. It is believed that the unsuccessful trial was due to the strong repulsion between the base and the boron cage. Further investigation was not pursued.

1- 2- Cl Cl O O S S (2.28)

KOt-Bu t-BuOH

2- B2.9.6 Reaction of [1(2)-B10H9SMe] with unsaturated alkyl halides

2- Unlike the reaction with mesityl oxide, [1-B10H9SMe] was found only to displace the halides when reacting with unsaturated alkyl halide (Eqn. 2.29 and 2.30).

The double bond of allylic bromide (CH2CHCH2Br) and triple bond of propargyl bromide (HCCCH2Br) were not affected at all. Both reactions produce over 95% of product. 129

2- 1-

S S

Br + (2.29)

2- 1-

S S

Br + (2.30)

Polymerization of allylic derivative Me4N[1-(MeSCH2CHCH2)-B10H9], was attempted. No observed reaction was observe when catalytic ZrCp2Me2 and B(C6F5)3 was mixed in CH3CN at room temperature for 48 hours. The starting material was crystallized and recovered from acetonitrile solution. The structure was determined by single crystal X-ray diffraction (See Table 23 for the crystallographic data). Me4N[1-

(MeSCH2CHCH2)-B10H9] crystallizes in the monoclinic space group C2 with ten molecules in the unit cell. Figure 44 displays one of the 10 molecules. It is slightly distorted. The equatorial B-B bond distances in these molecules range from 1.797(12) to 1.883(14) Å with an average distance at about 1.84 Å. This is slightly longer than those having electrowithdrawing alkyl groups. The C-C bond distances show that

C(23)-C(24) is a double bond with the a bond length of 1.334(12) Å. The bond angle 130 124.8(8) of C(22)-C(23)-C(24) clearly indicates that C(23) is sp2 hybridized, which supports the existence of an allyl group. Other distances and bond angles are given in

Table 24.

It was reported that propargyl group isomerizes to allene in the presence of strong base. In the case of B12, 1,7-(MeSCH2CCH)2-B12H10 was found to preferably

50 isomerize to 1,7-(MeSCHCCH2)2-B12H10 upon crystallizing in ethyl alcohol. When

1- [1-(MeSCH2CCH)-B10H9] was allowed to heat in ethyl alcohol for 30 mins, only a small amount of allene was observed by 1H NMR spectrum (Fig. 45). The relatively low production (Eqn. 2.31) of allene in decaborate derivative is due to its stronger basicity than dodecaborate derivatives. This reduces the abstraction of the α-proton.

1- 1-

S C S

(2.31)

131

Empirical formula C8 H29 B10 N S

Formula weight 279.48 Crystal system, space group Monoclinic, C2 Unit cell dimensions: length(Å) a 14.5017(10) b 13.2987(10) c 20.7456(10) angle(deg) α 90 β 93.825(10) γ 90 Volume, (Å3) 3992.0(5) Z, Calculated density (g cm-3) 10, 1.163 Crystal size (mm) 0.19 x 0.15 x 0.15 Temperature 200(2) K Absorption coefficient (mm-1) 0.182

R1 [I > 2σ(I)] 0.0518 wR2 (all data) 0.1346

Table 23 Crystal data and refinement for Me4N[1-(MeSCH2CHCH2)-B10H9]

132

Fig. 44 Crystal structure of Me4N[1-(MeSCH2CHCH2)-B10H9] (2 views)

133

Axial-Equatorial B-B Distances (Å)

B(11)-B(12) 1.668(14) B(20)-B(16) 1.693(14) B(11)-B(13) 1.683(14) B(20)-B(17) 1.675(13) B(11)-B(14) 1.653(14) B(20)-B(18) 1.711(13) B(11)-B(15) 1.645(13) B(20)-B(19) 1.728(13)

Equatorial-Equatorial B-B Distances (Å)

B(12)-B(13) 1.863(15) B(14)-B(17) 1.853(11) B(12)-B(15) 1.827(15) B(14)-B(18) 1.823(13) B(12)-B(16) 1.825(12) B(15)-B(18) 1.797(12) B(12)-B(19) 1.798(14) B(15)-B(19) 1.814(13) B(13)-B(14) 1.856(14) B(16)-B(17) 1.825(14) B(13)-B(16) 1.833(13) B(16)-B(19) 1.878(14) B(13)-B(17) 1.832(12) B(17)-B(18) 1.849(14) B(14)-B(15) 1.838(13) B(18)-B(19) 1.883(14)

Other Distances (Å)

S(2)-B(11) 1.884(8) S(2)-C(21) 1.770(9) S(2)-C(22) 1.816(9) C(22)-C(23) 1.477(12) C(23)-C(24) 1.334(12)

Angles (o)

B(12)-B(11)-S(2) 131.2(7) B(11)-S(2)-C(21) 105.6(4) B(13)-B(11)-S(2) 125.4(7) B(11)-S(2)-C(22) 106.7(4) B(14)-B(11)-S(2) 125.2(7) C(21)-S(2)-C(22) 101.4(4) B(15)-B(11)-S(2) 131.1(7) S(2)-C(22)-C(23) 115.7(6) C(22)-C(23)-C(24) 124.8(8)

Table 24 Selected Bond Distances and Angles of Me4N[1-(MeSCH2CHCH2)-B10H9]

134

CN 3 gyl-allene isomers in CD gyl-allene isomers H NMR spectrum of propar 1 Fig. 45

135

CHAPTER 3

EXPERIMENTAL

3.1 Apparatus

3.1.1 Column chromatography

Chromatography was performed on Selecto silica gel (230-430 mesh) purchased from Fisher Sicentific. It was used as arrived. For the column separation of boron cages, fractions were obtained after preliminary analysis by TLC using the palladium dichloride stain. The stain was prepared by dissolution of 0.5 g of PdCl2 in

27 mL of concentrated HCl with slight heating followed by dilution to 1000 mL with methanol.

3.1.2 Nuclear magnetic resonance spectroscopy

NMR spectra were obtained on a Bruker DRX-500, DPX-400 and AM-250 spectrometers at 500.1, 400.1 and 250.1 MHz, respectively, for protons. They were referenced to residual solvent deuteriums. Operating at 125.8, 100.6 and 62.9 MHz

13C, NMR spectra were obtained on Bruker DRX-500, DPX-400 and AM-250 spectrometers, respectively, and referenced to deuterated solvent peaks. 11B spectra were obtained on the Bruker DRX-500, DPX-400 and AM-250 spectrometers at 160.5

136 128.4 and 80.3 MHz, respectively, and referenced externally to BF3.OEt2 complex in

31 C6D6 (δ = 0.00 ppm). P NMR spectra were obtained on a Bruker DRX-500 spectrometer operating at 202.5 Mhz, and referenced externally to 85% H3PO4.

Coupling constants are reported in Hertz, Hz.

3.1.3 Elemental analysis

Elemental analyses were performed by Galbraith Laboratories, Inc. at

Knoxville, Tennessee.

3.1.4 Mass spectra

The mass-spectra were recorded either on the Micromass QTOF Electrospray

(ESI) or VG-70 (EI) mass-spectrometers at the CCIC facility of The Ohio State

University.

3.1.5 Single-crystal X-ray diffraction

Single crystal X-ray diffraction data were collected on an Enraf-Nonius Kappa

CCD diffraction system, which employs graphite-monchromated Mo-Kα radiation. A single crystal was mounted on the tip of glass fiber coasted with Parabar. Unit cell parameters were obtained by indexing the peaks in the first 10 frames and refined employing the whole data set. All frames were integrated and corrected for Lorentz and polarization effects using DENZO. The structures were solved by driect methods and refined using SHELXTL.

3.1.6 Infrared spectra

The infrared spectra were recorded on a Mattson Polaris FTIR spectrometer with 2 cm-1 resolution.

137 3.2 Reagents

Reagents used as received:

Allyl bromide, CH2CHCH2Br, 97% (Aldrich)

Borane-methyl sulfide complex, BH3.SMe2, neat, contains 5% excess of methyl sulfide (Aldrich)

Borane-tetrahydrofuran complex, BH3.THF, 1.0 M solution in THF (Aldrich)

3-Bromo-1-propanol, Br(CH2)3OH, 97% (Aldrich)

N-Bromosuccinimide, 99%, (Aldrich)

N-Chlorosuccinimide, 98+%, (Aldrich)

2-Chloroethyl methyl sulfide, ClCH2CH2SCH3, 97% (Aldrich)

18-Crown-6, (CH2CH2O)6, 99% (Aldrich)

Dibromomethane, CH2Br2, 99+% (Aldrich)

1,1-Dichloroacetone, CH3COCHCl2, 98% (Aldrich)

1,2-Dichloroethane, ClCH2CH2Cl, 99% (Aldrich)

Diiodomethane, CH2I2, 99% (Aldrich)

Dimethylsulfoxide, (CH3)2SO, A.C.S. reagent (Aldrich)

2,4-dinitrobenzenesulfenyl chloride, 2,4-(NO2)2C6H3SCl, 96% (Aldrich)

Ethanethiol, C2H5SH, 97% (Aldrich)

Ethyl iodide, C2H5I, 99% (Aldrich)

Hydrogen chloride, HCl, 1.0M solution in acetic acid (Aldrich)

Iodine monochloride, ICl, 1.0M solution in dichloromethane (Aldrich)

Iodoacetonitrile, ICH2CN, 98% (Aldrich)

Iodobenzen diacetate, C6H5I(OAc)2, 97% (Aldrich)

138 1-Iodo-2-methylpropane, (CH3)2CHCH2I, 97% (Aldrich)

2-Iodopropane, (CH3)2CHI, 99% (Aldrich)

Lithium powder, 325 mesh, 99.9% (Aldrich)

Mesityl oxide, (CH3)2CCHC(O)CH3, 99%, mixture of α- and β-isomers, (93%

α-isomer) (Acros)

Methylamine, CH3NH2, 98% (Aldrich)

Methyl triphenyl phosphonium bromide, MePPh3Br, 98+% (Strem)

Palladium(II) chloride, PdCl2, 99.9% Pd (Strem)

Potassium cyanide, KCN, 97% (Strem)

Propargyl bromide, HCCCH2Br, 80% solution in toluene (Aldrich)

Sodium t-botoxide, NaOC4H9, 99% (Strem)

Sodium hydride, NaH, 95% (Aldrich)

Sodium hydroxide, NaOH, 98% (J. T. Baker)

Sodium meta periodate, NaIO4, 99% (Aldrich)

Tetrabutylammonium acetate, n-Bu4N(C2H3O2), 1.0 M solution in water

(Aldrich)

Tetrabutylammonium bromide, n-Bu4NBr, 99% (Aldrich)

Tetrabutylammonium hydroxide, n-Bu4NOH, 1.0 M solution in water (Aldrich)

Tetramethylammonium chloride, Me4NCl, 97% (Aldrich)

Tetramethylammonium hydroxide pentahydrate, Me4NOH.5H2O, 97%

(Aldrich)

Trimethyloxonium tetrafluoroborate, (CH3)3OBF4, (Aldrich)

139

2- A3 Synthesis of [1,10-B10H8(CN)2]

1,10-B10H8(IPh)2 The reaction is based on a reaction of Muetterties and coworkers’, but with slight modification.22 3.8431 g (10.00 mmol) of cesium closo- decahydrodecaborate74 was added with 50 mL of acetonitrile in a 125 mL Erlenmeyer flask followed by ~4.40 g of iodosobenzene (20.0 mmol). PhIO was prepared by hydrolysis of (diacetoxyiodo)benzene with 3.0 M sodium hydroxide solution.23 The reaction solution was added a few drops of water/ethanol and warmed to 45-50 oC and stirred for about 90 mins. After cooling the reaction mixture down to room temperature, the volatiles were removed under reduced pressure. The remaining residue was stirred in about 100 mL of methylene chloride for about 30 mins. The solution was filtered. The remaining solid was washed with 2 portions of 25 mL methylene chloride. The methylene chloride solution is combined with the filtrate.

After the solvent was removed, the residue was dried in a pre-heated oven at 70 oC overnight. 0.8858 g of pure compound (17%) was obtained. The title compound was sufficiently pure for preparative purposes. If not sufficiently pure, it could be dissolved in methylene chloride and be washed through a silica gel column. 11B NMR

1 (CD3CN): δ 6.5 (s B(1,10)), -22.7 (d, JBH = 140, B(2-8)). H NMR (CD3CN): δ 8.06

1 11 (s, 4H, JHH = 7.5), 7.61 (d, 2H, JHH = 7.5), 7.41 (t, 4H, JHH = 7.5). H{ B} 0.96 (br s,

+ 8H, BH). MS-EI (C12H18B10I2Na ) : 544.0-551.4 (547.0) cal. 547.17

140

[18-crown-6K]2[1,10-B10H8(CN)2] 0.5361 g (1.022 mmol) of 1,10-B10H8(IPh)2 was dissolved in a minimal amount of chloroform (about 15 mL) in a 100 mL round bottom flask. In a Erlenmeyer flask, 0.5501 g of 18-crown-6 was added with 0.1375 g of potassium cyanide. The contents of this flask were dissolved in toluene. The solution was added to the round bottom flask and the reaction mixture was allowed to reflux.

The solution was heated for about a week, occasionally a small amount of chloroform and toluene were added in order to compensate for evaporation of solvent. Afterward, the volatiles were removed under reduced pressure. The residue was recrystallized in

11 1 water. B NMR (CD2Cl2): δ -4.5 (s B(1,10)), -24.8 (d, JBH = 140, B(2-8)). H NMR

(CD2Cl2): δ 8.06 (s, 4H, JHH = 7.5), 7.61 (d, 2H, JHH = 7.5), 7.41 (t, 4H, JHH = 7.5). IR:

2305.48 cm-1 (CN), 2485.79 cm-1 (BH). MS-EI : 82.6 - 85.1 (84.6) cal. 168.20

B.3.1 Reaction of 1,10-(Me2S)2-2-MeSB10H7 and 1,7-(Me2S)2-9-MeSB12H9

1,10-(Me2S)2-2-MeSB10H7

Method A 3.840 g (10.0 mmol) of Cs2B10H10 was added with about 75 ml of glacial acetic acid to a 3-necked 250-ml round bottom flask. About 5.0 ml of dimethylsulfoxide (DMSO) was syringed into the reaction vessel. The mixture was stirred moderately for 2 to 3 hour with HCl gas slowly bubbling into the solution through a rubber septum that covered one of the necks of the flask. The reaction flask was equipped with a condenser, and a thermometer. The reaction solution was heated to 55-60 oC in an oil bath. The solution first turned clear light yellow after about 1 ½ to 2 hours. (Otherwise, the hydrogen chloride gas flow was too weak if solid remains,

141 or too strong if turned clear within 1 hour. That will result more impurities). A cloudy almond solution is obtained after heating and stirring for about 2 ½ to 3 hours.

(Both methods have the same work up procedure).

Method B A similar amount of Cs2B10H10 as stated above was charged in a

250-ml round bottom flask. About 5.0 ml of dimethylsulfoxide (DMSO) was syringed dropwise into the reaction vessel while stirring to avoid aggregation of the closo- decaborate. About 125-150 ml of new fresh 1.0 M HCl-acetic acid solution (Aldrich) was delivered into the flask. The flask was equipped with a condenser. The reaction solution was heated to 55-60 oC in an oil bath for 2-3 hours.

The reaction flask is removed from the heat source and allowed to cool down to room temperature. Acetic acid was then removed under reduced pressure. The residue was partitioned with water and methylene chloride in a separation funnel. The methylene chloride solution was washed with water. Then it was dried over magnesium sulfate, filtered, and was removed under vacuum. The color of the solution was white-light yellow due to slight contamination. The title compound was cleanly isolated by using silica gel column separation with using 1:1 (v/v) 1,2- dichloroethane/toluene solution. The total yield is ranged from 40 to 60%. The product was sufficiently pure for preparative purposes. The compound was

11 recrystallized by using 1:1 (v/v) acetonitrile/water solution. B NMR (CD2Cl2): δ 9.0

(s, B(10)), 5.2 (s, B(1)), -11.7 (s, B(2)), -20.9 (d, B(3,5)), -22.6 (d, B(7,8)), -24.1 (d,

1 B(6,9)), -25.9 (d, B(4)). H NMR (CD2Cl2): δ 3.01 (s, 6H), 2.99 (s, 6H), 1.67 (s, 3H).

1 11 H{ B} NMR (CD2Cl2): δ 1.40 (br s, 2H, BH), 1.19 (br s, 2H, BH), 1.07 (br s, 2H,

BH), 0.81 (br s, 1H, BH). MS-EI: 286.1895 (± 3ppm) cal. 286.5097

142

o 1,7-(Me2S)2-9-MeSB12H9 A pre-heated oil bath was set to 55-60 C. 0.2641 g of

1,7-(Me2S)2B12H10, obtained by pyrolysis of BH3.SMe2, was added with 15 ml of fresh

1.0 M HCl-acetic acid solution (Aldrich) to a 25 mL round bottom flask. Next 0.2 ml of dimethylsulfoxide (DMSO) was syringed into the reaction flask was equipped with a condenser and placed into the oil bath. The solution was heated and stirred for 2 hours.

The resulting clear solution was cooled down to room temperature. Acetic acid was then removed under reduced pressure. The white solid residue was partitioned with water and methylene chloride. The methylene chloride solution was washed with water. It was then dried over magnesium sulfate, filtered, and with solvent removed under vacuum. 0.2069 g of pure product was obtained (67%) without further

11 purification. B NMR (CD3CN): δ -3.2 (s, B(9)), -9.2 (s, B(1,7)), -13.0 (d, JBH = 157,

B(10)), -14.1 (d, JBH = 121, B(4,8)), -14.6 (d, JBH = 135, B(5,12)), -15.6 (d, JBH = 152,

1 B(6,11)), -17.0 (d, B(3)), -19.2 (d, JBH = 138, B(2)). H NMR (CD3CN): δ 2.49 (s,

1 11 6H), 1.88 (q, JBH = 4.1, 1H). H{ B} NMR (CD3CN): δ 1.70 (s, 2H, BH), 1.67 (s, 2H,

13 1 BH), 1.62 (s, 1H, BH), 1.57 (s, 1H, BH), 1.48 (s, 3H, BH). C{ H} NMR (CD3CN): δ

+ 25.9 (4C, SMe2), 15.5 (1C, SMe). MS-ESI (1,7-(Me2S)2-9-MeSB12H9Na ): 333.2140

(± 2.1ppm) cal. 333.2133. Elemental Analysis: C 19.25%, H 7.76%, cal. 19.36%, H

7.80%.

143 [1,2,10-B10H7(SMe2)3]BF4 0.1894 g (1.28 mmol) of trimethyloxonium tetrafluoroborate, Me3OBF4, was charged in a 14/20 25 ml round bottom flask in the dry box. It was capped with a glass stopper that was wrapped with Teflon tape.

0.2852 g (0.995 mmol) of 1,10-(SMe2)2-2-SMe-B10H7 was washed into the flask with about 15 ml of methylene chloride. The reaction solution was stirred for about 3 hours.

The resulting clear, colorless solution contained a very small amount of jelly-like material. The volatiles were removed under reduced pressure. The residue was washed with cold distalled water through a glass funnel that is equipped with a frit.

The solid was recrystallized with ethyl alcohol. 0.3114 g of pure compound was

11 - obtained (80%). B NMR (CD3CN): δ 12.5 (s, B(10)), 5.62 (s, B(1)), -1.0 (s, BF4 ), -

14.1 (s, B(2)), -22.3 (d, JBH = 126, B(3,5)), -23.1 (d, JBH = 123, B(4,7,8)), -25.7 (d, JBH

1 1 11 = 146, B(6,9)). H NMR (CD3CN): δ 3.04 (s, 6H), 3.00 (s, 6H), 2.31 (s, 6H). H{ B}

NMR (CD3CN): δ 1.42 (br s, 2H, BH), 1.14 (br s, 3H, BH), 1.04 (br s, 2H, BH). MS-

+ ESI ([1,2,10-B10H7(SMe2)3] ): 301.2115 (± 3.7ppm) cal. 301.2126.

[1,7,9-B12H9(SMe2)3]BF4 0.1566 g g (1.059 mmol) of trimethyloxonium tetrafluoroborate, Me3OBF4, was handled in the dry box and placed into a vial, which was equipped with a screw cap. In a separate flask, 0.2712 g (0.8744 mmol) of 1,7-

(SMe2)2-9-SMe-B10H7 was dissolved in about 15 ml of methylene chloride. Me3OBF4 was then added to the solution. The reaction was allowed to stir for about 3 hours.

The resulting clear colorless solution had its volatiles removed under reduced pressure.

The residue was washed with 25 ml of cold, distilled water through a glass funnel with a frit. The solid was scraped into a solv sealed flask. The solid was heated in a warm

144 water bath for ½ hour to allow the removal of water vapor. 0.280 g of pure solid was

11 1 - obtained (79%). B{ H} NMR (CD3CN): δ -1.8 (s, B(1,7,9)), -8.9 (s, BF4 ), -15.2 (d,

1 13 3B), -15.9 (d, 3B), -16.6 (d, 3B). H NMR (CD3CN): δ 2.61 (s, 18H). C NMR

+ (CD3CN): δ 25.8. MS-ESI ([1,7,9-B12H9(SMe2)3] ): 325.2458 (± 3.7ppm) cal.

325.2470.

[Bu4N]2[1,2,10-B10H7(SMe2)3] 0.1749 g of 95% of sodium hydride was measured in the dry box and charged to a 100 mL 3 neck round bottom flask, which was equipped with a magnetic stir bar and a condenser at the central neck. A side neck was capped with septum. Both the remaining neck and condenser were equipped with grease joint adapters. Nitrogen gas was purged through the adapters. A minimal amount (~3 mL) of absolute ethanol was injected through the septum while stirring the solution until the bubbling ceased. 0.50 ml of ethanethiol, EtSH, was added afterward, the solution became light yellow. In a 50 round bottom flask, 0.6177 g of 1,10-

(SMe2)2-2-SMe-B10H7 dissolved in about 25 mL of acetonitrile. The solution was added into the reaction flask. The reaction solution was allowed to reflux overnight.

All the volatiles were removed under reduced pressure. The resulting residue could either be dissolved in distilled water or 95% ethanol. If the former was used, then the compound was precipitated with about 2-3 equivalent of Bu4NOH or Bu4N(C2H3O2)

+ solution. If the latter was used, the counterion Me4N was required. 0.8770 g (59%) of

11 tetrabutylammonium salt was obtained. B NMR (CD3CN): δ 7.8 (s, B(10)), 4.9 (s,

B(1)), -14.8 (s, B(2)), -24.2 (d, JBH = 138, B(3,5)), -25.2 (d, JBH = 140, B(7,8)), -26.7

1 + (d, JBH = 125, B(6,9)), -27.6 (d, JBH = 123, B(4)). H NMR (CD3CN): δ (Bu4N : 3.09

145 (m, 16H), 1.60 (m, 16H), 1.35 (m, 16H), 0.96 (t, JHH = 7.4, 24H)), 2.24 (s, 3H, SMe),

1 11 2.21 (s, 3H, SMe), 1.53 (s, 3H, SMe). H{ B} NMR (CD3CN): δ 0.69 (br s, 2H, BH),

0.44 (br s, 3H, BH), 0.43 (br s, 2H, BH), 0.22 (br s, 1H, BH). 13C{1H} NMR

+ (CD3CN): δ (Bu4N : 59.4, 24.4, 20.3, 13.8), 18.3, 17.5, 15.9. MS-ESI

+ ([Bu4N]2[1,2,10-B10H7(SMe)3]Na ): 764.7000 (± 0.4ppm) cal. 764.7003. Elemental

Analysis: C 34.05%, H 11.17%, cal. C 34.59%, H 11.46%.

[Bu4N]2[1,2,10-B10H7(SH)3] 0.2963 g (1.034 mmol) of 1,10-(SMe2)2-2-SMe-

B10H7 was charged in a 2-necked 9 mm solv seal 100 mL round bottom flask, which was equipped with a magnetic stir bar. 0.2315 g of lithium powder was added to the flask. After evacuation, about 25 mL of pre-dried (over sodium) methylamine,

MeNH2, was condensed into the flask. The solution was allowed to reflux at room temperature (with cooling of dry ice slush) for two hours. Occasionally liquid nitrogen is required to quench the reaction if the pressure builds up too quickly. After the reaction, excess MeNH2 was removed to a cool trap. One of the adapters of the reaction flask was hooked up to a bubbler, and another was to a source of nitrogen gas.

N2 was allowed to purge through for a few minutes. After removing the nitrogen source and closing the adapter valve, an addition bulb (a 100 ml 24/40 round bottom flask with a grease joint attached to the bottom) was connected to the adapter.

Degassed methanol was poured into the bulb, it was allowed to drip into the flask dropwise to destroy excess lithium. Hydrogen gas was produced and escaped through the bubbler. Once the process was complete, methanol was removed under reduced pressure. The resulting residue was bright white with a slight yellow tinge. Degassed

146 water was then slowly added until all solid dissolved. Hydrochloric acid was then added until the pH was just below 7. The solution was filtered. 0.8599 g pre-weighed

Bu4NBr was added into the filtrate and precipitation occurred. The solid was filtered through a glass funnel that was equipped with a frit. The solid was scraped into a solv seal flask. The flask was heated in an oil bath set at 70 oC overnight to completely dry

11 it. 0.5185 g (71%) of pure compound was obtained. B NMR (CD3CN): δ 3.1 (s,

B(10)), 1.9 (s, B(1)), -18.0 (s, B(2)), -23.4 (d, JBH = 131, B(3,5,7,8)), -24.3 (d, JBH =

1 + 119, B(6,9)), -27.5 (d, JBH = 142, B(4)). H NMR (CD3CN): δ (Bu4N : 3.09 (m, 16H),

1.60 (m, 16H), 1.35 (m, 16H), 0.96 (t, JHH = 7.4, 24H)), 0.33 (s, 1H, SH), 0.13 (s, 1H,

1 11 SMe), -0.13 (s, 1H, SMe). H{ B} NMR (CD3CN): δ 0.53 (br s, 3H, BH), 0.42 (br s,

13 1 + 2H, BH), 0.33 (br s, 2H, BH). C{ H} NMR (CD3CN): δ (Bu4N : 59.4, 24.4, 20.3,

13.8). Elemental Analysis: C 53.82%, H 11.84%, cal. C 54.96%, H 11.82%.

1,10-(Me2S)2-2-MeSO2-B10H7 0.1730 g of 1,10-(SMe2)2-2-MeS-B10H7 was obtained and placed into a 100 mL 14/20 round bottom flask. 50 mL of methanol was added to partially dissolve the starting material, followed by 20 mL of acetonitrile.

When the solution became homogeneous, 0.5815 g of sodium meta periodate was charged. The reaction flask was equipped with a condenser. The solution was heated to 65-70 oC for about 3 hours. After the removal of volatiles, the residue was washed with cold distilled water and ethanol on a glass funnel with a frit. The white solid was then dried in a pre-heated 70 oC oven. 0.1458 g (76%) of pure compound was

11 obtained. B NMR (CD3CN): δ 11.2 (s, B(10)), 6.0 (s, B(1)), -13.4 (s, B(2)), -22.6 (d,

1 B(3,5)), -23.5 (d, B(4,7,8)), -24.6 (d, B(6,9)). H NMR (CD3CN): δ 3.04 (s, 6H,

147 1 11 SMe2), 2.98 (s, 6H, SMe2), 2.34 (s, 3H, SO2Me). H{ B} NMR (CD3CN): δ 1.36 (br s, 2H, BH), 1.09 (br s, 2H, BH), 1.02 (br s, 3H, BH). MS-EI (1,10-(Me2S)2-2-MeSO2-

+ B10H7Na ): 341.1687 (± 0.0 ppm) cal. 341.1687.

B3.2 Halogenation of boron cages

General Procedure 1,10-B10H8(SMe2)2, 1,10-B10H8(N2)2, and 1,7-B12H10(SMe2)2 were synthesized by the previously published procedure.35,25,46 A 25 or 50 mL round bottom flask equipped with a magnetic starbar was charged with about 1 mmol of boron compound. 1 eq of chloro- or bromo-succinimide (or iodine monochloride 1.0

M solution in CH2Cl2 was used for iodination). About 15-20 mL of acetonitrile was used as solvent. The solution was refluxed for 1 hour for 9-Cl-1,7-(Me2S)2B12H9, overnight for 2-Cl- and 2-Br-1,10-(Me2S)2B10H8, and 3 hours for 2-I-1,10-

(Me2S)2B10H8 and 2-I-1,10-(N2)2B10H8. The residue was partitioned between dichloromethane (10 mL) and water (10 mL). The organic phase was washed twice with water (NaS2O3 solution if ICl was employed) and dried with MgSO4. After solvent removal the crude products were obtained as white powders except 2-I-1,10-

B10H8(N2)2 which is light yellow.

148 9-I-1,7-(Me2S)2B10H8 From 0.2640 g of 1,7-B12H10(SMe2)2 and 0.1337 g of N-

11 chlorosuccinimide 0.2778 g (93%) of pure product was obtained. B NMR (CH2Cl2):

δ -2.4 (s, B(9)), -10.7 (s, B(1,7)), -13.5 (d, B(10)), -14.9 (d, B(5,12)), -15.4 (d, B(4,8)),

1 -17.2 (d, B(6,11)), -18.6 (d, B(3)), -21.9 (d, JBH = 139, B(2)). H NMR (CH2Cl2): δ

13 1 2.54 (s, 6H, SMe2), 2.53 (s, 6H, SMe2). C{ H} NMR (CH2Cl2): δ 25.9 (SMe2). MS-

+ ESI (9-Cl-1,7-(Me2S)2-B12H9]Na ): 321.1860 (± 3.0 ppm) cal. 321.1871.

2-Cl-1,10-(Me2S)2B10H8 From 0.2435 g of 1,10-B10H8(SMe2)2 and 0.1337 g of N-

11 chlorosuccinimide 0.2196 g (79%) of pure product was obtained. B NMR (CD3CN):

δ 9.4 (s, B(10)), 5.9 (s, B(1)), -7.8 (s, B(2)), -20.9 (bd, B(3,5,7,8)), -23.2 (d, JBH = 139,

1 B(6,9)), -26.6 (d, JBH = 135, B(4)). H NMR (CD3CN): δ 3.00 (s, 6H), 2.94 (s, 6H).

2-Br-1,10-(Me2S)2B10H8 From 0.2456 g of 1,10-B10H8(SMe2)2 and 0.1819 g of N-

11 bromosuccinimide 0.2764 g (85%) of pure product was obtained. B NMR (CD3CN):

δ 9.8 (s, B(10)), 6.5 (s, B(1)), -13.4 (s, B(2)), -21.2 (d, JBH = 110, B(3,5)), -21.7 (d, JBH

1 = 137, B(7,8)), -22.9 (d, JBH = 161, B(6,9)), -25.7 (d, JBH = 143, B(4)). H NMR

(CD3CN): δ 3.01 (s, 6H), 2.95 (s, 6H).

2-I-1,10-(Me2S)2B10H8 From 0.2417 g of 1,10-B10H8(SMe2)2 and 1.03 mL of

11 1.0M ICl in CH2Cl2 solution 0.2180 g (59%) of pure product was obtained. B NMR

(CD3CN): δ 10.5 (s, B(10)), 8.0 (s, B(1)), -20.6 (d, JBH = 236, B(4)), -22.1 (bd, JBH =

1 139, B(3,5,7,8)), -24.4 (d, JBH = 135, B(6,9)), -27.6 (d, B(2)). H NMR (CD3CN): δ

3.03 (s, 6H), 2.95 (s, 6H).

149

2-I-1,10-(N2)2B10H8 From 0.1974 g of 1,10-B10H8(N2)2 and 1.05 mL of 1.0M ICl in

11 CH2Cl2 solution 0.2330 g (80%) of pure product was obtained. B NMR (CD3CN): δ

4.1 (s, B(1,10)), -15.5 (d, JBH = 152, B(3,5,7,8)), -17.2 (d, JBH = 149, B(4,6,9)), -25.7

1 1 (s, B(2)). H{ H} NMR (CD3CN): δ 2.11, 1.95, 1.63, 1.27. MS-EI (2-I-1,10-

(N2)2B10H8): 298.0708 (± 1.7 ppm) cal. 298.0713.

1- B3.3 Synthesis of 1- and 2-[B10H9SMe2] and related reactions

The reaction is based on the reported procedure of Muetterties and coworkers’,

27 but with slight modifications. 7.8491 g of Cs2[B10H10] was charged in a 250 ml 3- necked round bottom flask equipped with a magnetic stir bar. About 50.0 mL of

DMSO was added into the flask. The mixture was stirred at room temperature until it was a homogeneous solution. It was heated at 50-55 oC. HCl gas ran through the solution by bubbling with a 9 inch micropipette for a total of 10 mins. The solution appeared orange for a minute, the final solution was white cloudy. The solution was removed from the heat source. About 100 mL of distilled water was added into the solution. The reaction flask was cooled in an ice bath. White solid appeared at the bottom of the flask. After an hour, the solution was poured into 350 mL of distilled water in a 500 mL Erlenmeyer flask to allow extra precipitation. The solid was then filtered through with a glass funnel equipped with a frit. The filtrate was stored for further use. The filtered residue was washed with cold acetonitrile or methylene chloride into a new flask. The filtrate contains undesired di-substituted species. The solid was dried overnight in a pre-heated oven. Pure 3.4221 g (54%) of Cs[1-

150 1- B10H9SMe2] was obtained. The stored filtrate contained all of [2-B10H9SMe2] , 7.1104 g of Bu4NBr was added. 2.3569 g (27%) of impure material was obtained. Bu4N[2-

2- B10H9SMe2] was purified through dealkylation to [2-B10H9SMe] and methylation with methyl iodide (see Sec B3.3.1 and B3.3.2).

1- B3.3.1 Dealkylation of [B10H9SMe2]

[Me4N]2[2-B10H9SMe] 0.5437 g of 95% of sodium hydride was weighed in the dry box and charged into a 100 mL 3 neck round bottom flask, which was equipped with a magnetic stir bar. A side neck was capped with septum. A condenser and grease joint adapters with on the other necks. Argon gas was passed through the adapters. About 10.0 mL of absolute ethanol was injected through the septum while stirring the solution until the bubbling ceased. 1.05 mL of ethanethiol, EtSH, was added afterward, and the solution became light yellow. In a 50 mL round bottom flask,

5.3529 g of [Bu4N][2-B10H9SMe2] dissolved in about 25 mL of acetonitrile. The solution was added into the reaction flask once it became homogenous. An extra 25 mL of acetonitrile was used for solvent. The reaction solution was allowed to reflux overnight. All the volatiles were removed under reduced pressure. The resulting residue dissolved in 100 mL distilled water in a 125 mL Erlenmeyer flask. 6.2109 g of

Bu4NBr was added into the solution which was stirred. Precipitation occurred instantly. The muddy light yellow solid was washed with extra water through a glass funnel equipped with a frit. It dissolved in minimal amount of absolute ethanol at room temperature and was heated to its boiling point. About 30 mmol of NMe4OH-

5H2O was added and stirred. Bright white pure [Me4N]2[2-B10H9SMe] was obtained

151 from filtration. The solid was dried overnight in a preheated oven at 70 oC. 2.9095 g

11 (73%) of the compound was found. B NMR (d6-DMSO): δ -1.0 (d, JBH = 139,

B(10)), -3.2 (d, JBH = 143, B(1)), -15.3 (s, B(2)), -24.7 (d, JBH = 133, B(3,5)), -25.6 (d,

1 JBH = 141, B(7,8)), -27.8 (d, JBH = 120, B(6,9)), -29.3 (d, JBH = 126, B(4)). H NMR

1 11 (d6-DMSO): δ 3.09 (s, 24H), 1.45 (s, 3H, SMe). H{ B} NMR (d6-DMSO): δ 2.95 (br s, 1H, BH), 2.78 (br s, 1H, BH), 0.39 (br s, 2H, BH), 0.06 (br s, 2H, BH), 0.02 (br s,

13 1 + 2H, BH), -0.24 (br s, 1H, BH). C{ H} NMR (d6-DMSO): δ 54.4 (t, Me4N ), 16.9 (s,

SMe). Elemental Analysis: C 56.30%, H 11.88%, cal. C 56.70%, H 11.96%.

[MePPh3]2[1(2)-B10H9SH] (Remark: since Cs[1-B10H9SMe2] is insoluble in

MeNH2, [Bu4N][1-B10H9SMe2] was used instead. Cs[1-B10H9SMe2] dissolves only in

DMSO. The most straightforward method to change cesium to tetrabutylammonium was by a metathesis reaction. After dissolving the mono-anion in DMSO, excess tetrabutylammonium bromide was added and the mixture was allowed to stir overnight.

Depending on the amount of solvent and solute, a few drops of water might be required to dissolve Bu4NBr. Once the solution becomes homogeneous, it was added with significant amount of water, white solid appears immediately. (The solid should be soluble in CH2Cl2 or CH3CN). 0.7805 g (1.851 mmol) of [Bu4N][1-B10H9SMe2] was charged in a single necked 9 mm solv sealed 100 mL round bottom flask, which was equipped with a magnetic stir bar and tightened with two adapters. 0.1415 g of lithium powder was added to the flask. After evacuation of the flasks about 30 mL of pre- dried (over sodium) methylamine, MeNH2, was condensed into the flask. The solution was allowed to stir at -15 oC by using ethanol/ice bath for two hours. Occasionally

152 liquid nitrogen was required to quench the reaction if the pressure built up too quickly.

After the reaction, excess MeNH2 was removed into a cool trap overnight. Degassed

MeOH was added to the white residue in the glove bag, gas was produced. HCl(aq) was then added until the solution was neutral. Excess of MePPh3Br was then added, the solid was filtered and scraped into another solv seal flask. The volatiles were removed on a vacuum line, while heating the solid in an oil bath at about 60 oC.

1.1392 g of pure orange apically substituted mercaptan isomer was obtained. (87%)

11 [MePPh3]2[1-B10H9SH] B NMR (d6-DMSO): δ 4.1 (s, B(1)), -3.0 (d, JBH =

1 139, B(10)), -26.2 (d, JBH = 123, B(2-5)), -29.0 (d, JBH = 121, B(6-9)). H NMR (d6-

+ DMSO): δ (MePPh3 : 7.88 (br s, 6H), 7.76 (br s, 12H), 7.74 (br s, 12H), 3.14 (d, JPH =

1 11 14.5, 6H)), 0.21 (s, 1H, SH). H{ B} NMR (d6-DMSO): δ 2.84 (br s, 1H, BH), 0.11

13 1 (br s, 4H, BH), -0.12 (br s, 4H, BH). C{ H} NMR (d6-DMSO): δ 134.8 (d, JPC =

2.7, 1C), 133.2 (d, JPC = 10.8, 2C), 130.0 (d, JPC = 12.8, 2C), 119.8 (d, JPC = 88.1, 1C),

7.2 (d, JPC = 55.6, 1C). With the analogous procedure, the white equatorially substituted mercaptan isomer could also be obtained by using [Me4N]2[2-B10H9SMe]

11 as the starting material. [MePPh3]2[2-B10H9SH] B NMR (CD3CN): δ -0.8 (br d, JBH

= 102, B(1,10)), -19.0 (s, B(2)), -24.5 (d, JBH = 128, B(3,5,7,8)), -26.1 (d, JBH = 127,

1 + B(6,9)), -28.7 (d, JBH = 128, B(4)). H NMR (CD3CN): δ (MePPh3 : 7.85 (m, 6H),

1 11 7.71 (m, 12H), 7.68 (m, 12H), 2.85 (d, JPH = 20.2, 6H)), -0.64 (s, 1H, SH). H{ B}

NMR (CD3CN): δ 3.13 (br s, 1H, BH), 2.92 (br s, 1H, BH), 0.59 (br s, 2H, BH), 0.25

13 1 (br s, 2H, BH), 0.09 (br s, 2H, BH), -0.10 (br s, 1H, BH). C{ H} NMR (CD3CN): δ

136.0 (d, JPC = 2.9, 1C), 134.3 (d, JPC = 10.9, 2C), 131.2 (d, JPC = 12.7, 2C), 120.4 (d,

JPC = 88.8, 1C), 9.6 (d, JPC = 58.5, 1C).

153

1- B3.3.2 Alkylation of [1(2)-B10H9-SMe]

2- + + General procedure for [1-B10H9SMe] Either Bu4N or Me4N salt can be used as

2- starting material. About 1 mmol of [1-B10H9SMe] with 10-15 mL acetonitrile was added to a 25 ml round bottom flask equipped with a magnetic stir bar. 1.0-1.1 equivalent of the alkylating agents was added to the reaction flask while the contents was stirred. The reaction was allowed to stir overnight at room temperature. All volatiles were removed under reduced pressure. Two portions of 5 mL cold water was used to wash the residue through a glass funnel equipped with a frit. The remaining solid on the filter was washed with two portions of 5 mL diethyl ether. The solid was air dried for 30 min, then dried in a preheated oven overnight.

[Bu4N][1-(MeSCH2Cl)-B10H9] [Me4N]2[1-B10H9SMe] is not used because the

+ - [Me4N] salt of [1-(MeSCH2Cl)-B10H9] is quite soluble in water. From 0.6501 g

(1.001 mmol) of [Bu4N]2[1-B10H9SMe] and 5 mL of CH2Cl2 0.4470 g (98%) of pure

11 product was obtained. B NMR (CD3CN): δ 10.4 (d, JBH = 153, B(10)), -1.1 (s, B(1)),

1 -24.7 (d, JBH = 134, B(2-5)), -27.4 (d, JBH = 130, B(6-9)). H NMR (CD3CN): δ

+ (Bu4N : 3.07 (m, 8H), 1.59 (m, 8H), 1.34 (m, 8H), 0.96 (t, JPH = 7.4, 12H)), 5.29 (d,

1 11 JHH = 10.7, 1H), 5.05 (d, JHH = 10.7, 1H), 3.10 (s, 3H, SMe). H{ B} NMR (CD3CN):

δ 4.00 (br s, 1H, BH), 0.66 (br s, 4H, BH), 0.21 (br s, 4H, BH). 13C{1H} NMR

+ (CD3CN): δ (Bu4N : 59.4, 24.3, 20.3, 13.8), 53.3 (s, CH2Cl), 26.9 (s, SMe). Elemental

Analysis: C 47.09%, H 10.73%, cal. C 47.39%, H 11.05%.

154 [Me4N][1-(MeSCH2Br)-B10H9] From 0.2485 g (0.7951 mmol) of [Me4N]2[1-

11 B10H9SMe] and 0.08 mL of CH2Br2 0.2297 g (87%) of pure product was obtained. B

NMR (CD3CN): δ 10.3 (d, JBH = 146, B(10)), -0.2 (s, B(1)), -24.7 (d, JBH = 133, B(2-

1 5)), -27.4 (d, JBH = 131, B(6-9)). H NMR (CD3CN): δ 5.09 (d, JHH = 10.0, 1H), 4.81

1 11 (d, JHH = 10.0, 1H), 3.09 (s, 3H, SMe), 3.07 (s, 12H). H{ B} NMR (CD3CN): δ 3.99

13 1 (br s, 1H, BH), 0.67 (br s, 4H, BH), 0.23 (br s, 4H, BH). C{ H} NMR (CD3CN): δ

+ 59.3 (t, Meu4N ), 37.7 (s, CH2), 27.9 (s, SMe). Elemental Analysis: C 21.76%, H

7.71%, cal. C 21.68%, H 7.89%.

[Me4N][1-(MeSCH2I)-B10H9] From 0.2622 g (0.8389 mmol) of [Me4N]2[1-

11 B10H9SMe] and 0.10 mL of CH2I2 0.2940 g (92%) of pure product was obtained. B

NMR (CD3CN): δ 10.1 (d, JBH = 146, B(10)), 0.9 (s, B(1)), -24.7 (d, JBH = 132, B(2-

1 5)), -27.4 (d, JBH = 130, B(6-9)). H NMR (CD3CN): δ 4.84 (d, JHH = 10.0, 1H), 4.49

1 11 (d, JHH = 10.0, 1H), 3.07 (s, 12H), 3.04 (s, 3H). H{ B} NMR (CD3CN): δ 3.97 (br s,

13 1 1H, BH), 0.67 (br s, 4H, BH), 0.22 (br s, 4H, BH). C{ H} NMR (CD3CN): δ 56.3 (t,

+ Me4N ), 29.8 (s, SMe), 5.3 (s, SCH2). Elemental Analysis: C 18.85%, H 6.75%, cal. C

19.00%, H 6.91%.

[Me4N][1-(MeSCH2CN)-B10H9] From 0.2551 g (0.8162 mmol) of [Me4N]2[1-

B10H9SMe] and 0.09 mL of ICH2CN 0.2070 g (91%) of pure product was obtained.

11 B NMR (CD3CN): δ 10.5 (d, JBH = 146, B(10)), -0.5 (s, B(1)), -24.3 (d, JBH = 132,

1 B(2-5)), -27.2 (d, JBH = 130, B(6-9)). H NMR (CD3CN): δ 4.41 (d, JHH = 16.4, 1H),

1 11 4.30 (d, JHH = 16.4, 1H), 3.15 (s, 3H), 3.07 (s, 12H). H{ B} NMR (CD3CN): δ 4.03

155 13 1 (br s, 1H, BH), 0.70 (br s, 4H, BH), 0.24 (br s, 4H, BH). C{ H} NMR (CD3CN): δ

+ 113.9 (s, CN), 56.3 (t, Me4N ), 32.1 (s, SCH2), 28.4 (s, SMe). Elemental Analysis: C

30.17%, H 9.32%, cal. C 30.19%, H 9.41%.

[Me4N][1-(MeSCH2CH2Cl)-B10H9] From 0.3243 g (1.038 mmol) of

[Me4N]2[1-B10H9SMe] and 1.00 mL of 1,2-dichloroethane 0.2813 g (93%) of pure

11 product was obtained. B NMR (CD3CN): δ 9.0 (d, JBH = 146, B(10)), 0.1 (s, B(1)), -

1 24.9 (d, JBH = 131, B(2-5)), -27.5 (d, JBH = 131, B(6-9)). H NMR (CD3CN): δ 4.22

(m, 1H), 4.10 (m, 1H), 3.79 (m, 1H), 3.67 (m, 1H), 3.07 (s, 12H), 2.99 (s, 3H).

1 11 H{ B} NMR (CD3CN): δ 3.93 (br s, 1H, BH), 0.63 (br s, 4H, BH), 0.22 (br s, 4H,

13 1 + BH). C{ H} NMR (CD3CN): δ 56.3 (t, Me4N ), 48.4 (s, SCH2), 40.7 (CH2Cl), 27.9

(SMe).

[Me4N][1-(MeSCH2CH2SMe)-B10H9] This reaction is relatively slow. It is allowed to stir at room temperature for 48 hours. From 0.6463 g (2.068 mmol) of

[Me4N]2[1-B10H9SMe] and 0.30 mL of MeSCH2CH2Cl stirring 0.3553 g (55%) of pure

11 product was obtained. B NMR (CD3CN): δ 9.1 (d, JBH = 144, B(10)), -2.6 (s, B(1)), -

1 27.1 (d, JBH = 128, B(2-5)), -29.1 (d, JBH = 125, B(6-9)). H NMR (CD3CN): δ 3.63

(m, 1H), 3.51 (m, 1H), 3.12 (m, 2H), 3.07 (s, 12H), 2.95 (s, 3H), 2.18 (s, 3H). 1H{11B}

NMR (CD3CN): δ 3.89 (br s, 1H, BH), 0.62 (br s, 4H, BH), 0.20 (br s, 4H, BH).

13 1 + C{ H} NMR (CD3CN): δ 56.3 (t, Me4N ), 45.7 (s, SCH2), 30.2 (CH2), 27.7, 15.4.

156 [Me4N][1-(MeSEt)-B10H9] From 0.2501 g (0.8002 mmol) of [Me4N]2[1-B10H9SMe] and 0.08 mL of ethyl iodide, 0.1953 g (92%) of pure product was obtained. 11B NMR

(CD3CN): δ 8.3 (d, JBH = 144, B(10)), 0.8 (s, B(1)), -25.1 (d, JBH = 131, B(2-5)), -27.6

1 (d, JBH = 130, B(6-9)). H NMR (CD3CN): δ 3.42 (dq, JHH = 12.7, 7.5, 1H), 3.26 (dq,

1 11 JHH = 12.7, 7.4, 1H), 3.08 (s, 12H), 2.88 (s, 3H, SMe), 1.57 (t, JHH = 7.5, 3H). H{ B}

NMR (CD3CN): δ 3.87 (br s, 1H, BH), 0.61 (br s, 4H, BH), 0.20 (br s, 4H, BH).

13 1 + C{ H} NMR (CD3CN): δ 56.3 (t, Me4N ), 40.4 (s, SCH2), 26.8 (s, SMe), 11.4 (s,

Me). Elemental Analysis: C 30.92%, H 10.71%, cal. C 31.43%, H 10.93%.

[Me4N][1-(MeSCH2CHMe2)-B10H9] From 0.2537 g (0.8117 mmol) of

[Me4N]2[1-B10H9SMe] and 0.10 mL of isobutyl iodide, 0.1643 g (69%) of pure product

11 was obtained. B NMR (CD3CN): δ 8.2 (d, JBH = 146, B(10)), 1.1 (s, B(1)), -25.1 (d,

1 JBH = 131, B(2-5)), -27.7 (d, JBH = 130, B(6-9)). H NMR (CD3CN): δ 3.32 (dd, JHH =

12.5, 7.5, 1H), 3.15 (dd, JHH = 12.5, 7.5, 1H), 3.07 (s, 12H), 2.90 (s, 3H), 2.36 (m, JHH

1 11 = 6.9, 1H), 1.15 (t, JHH = 6.6, 3H). H{ B} NMR (CD3CN): δ 3.86 (br s, 1H, BH),

13 1 + 0.61 (br s, 4H, BH), 0.19 (br s, 4H, BH). C{ H} NMR (CD3CN): δ 56.3 (t, Me4N ),

55.4 (s, SCH2), 26.9 (CH), 28.1 (SMe), 21.9 (Me), 21.9 (Me). Elemental Analysis: C

34.60%, H 11.44%, cal. C 36.58%, H 11.26%.

[Me4N][1-(MeSCHMe2)-B10H9] From 0.2608 g (0.8344 mmol) of [Me4N]2[1-

B10H9SMe] and 0.10 mL of isopropyl iodide 0.0506 g (22%) of pure product was

11 obtained. B NMR (CD3CN): δ 8.6 (d, JBH = 144, B(10)), -0.4 (s, B(1)), -24.9 (d, JBH

1 = 131, B(2-5)), -27.5 (d, JBH = 129, B(6-9)). H NMR (CD3CN): δ 3.65 (m, 1H), 3.07

157 1 11 (s, 12H), 2.85 (s, 3H), 1.66 (d, JHH = 6.8, 3H), 1.61 (d, JHH = 6.7, 3H). H{ B} NMR

13 1 (CD3CN): δ 3.88 (br s, 1H, BH), 0.62 (br s, 4H, BH), 0.20 (br s, 4H, BH). C{ H}

+ NMR (CD3CN): δ 56.3 (t, Me4N ), 47.3 (s, CH), 24.0 (SMe), 20.2 (Me), 19.2 (Me).

Elemental Analysis: C 35.62%, H 10.95%, cal. C 34.13%, H 11.10%.

[Me4N][1-(MeSCMe2COMe)-B10H9] 0.6342 g (2.029 mmol) of [Me4N]2[1-

B10H9SMe] was obtained and placed in a 50 mL round bottom flask. 25 mL of CH3CN was added as solvent. While the solution was being stirred, 0.26 mL of mesityl oxide was syringed into the flask. 1.5 mL 1.0M HCl(aq) followed. Volatiles were removed after stirring the solution for 3 hours. After standard aqueous workup 0.6312 g (94%)

11 of pure product was obtained. B NMR (CD3CN): δ 9.5 (d, JBH = 142, B(10)), -2.0 (s,

1 B(1)), -24.5 (d, JBH = 130, B(2-5)), -27.4 (d, JBH = 130, B(6-9)). H NMR (CD3CN): δ

3.58 (d, JHH = 17.2, 1H), 3.22 (d, JHH = 10.9, 1H), 3.08 (s, 12H), 2.85 (s, 3H, SMe),

1 11 2.13 (s, 3H), 1.79 (s, 6H). H{ B} NMR (CD3CN): δ 3.96 (br s, 1H, BH), 0.64 (br s,

13 1 4H, BH), 0.22 (br s, 4H, BH). C{ H} NMR (CD3CN): δ 206.5 (s, CO), 56.3 (t,

+ Me4N ), 53.8 (s, SC), 50.2 (CH2), 32.0 (Me), 24.5 (CMe), 24.0 (CMe), 27.9 (SMe).

Elemental Analysis: C38.82%, H10.79%, cal. C39.14%, H10.45%.

[Me4N][1-(MeSCHClCOMe)-B10H9] From 0.6511 g (2.083 mmol) of

[Me4N]2[1-B10H9SMe] and 0.30 mL of 1,1-dichloroacetone 0.6609 g (96%) of pure

11 product was obtained. B NMR (CD3CN): δ 10.8 (d, JBH = 145, B(10)), -1.3 (s, B(1)),

1 -2.5 (s, B(1’)), -24.2 (d, JBH = 132, B(2-5)), -27.9 (d, JBH = 131, B(6-9)). H NMR

(CD3CN): δ 6.19 (s, 1H, CH), 6.08 (s, 1H, CH’), 3.11 (s, 3H, SMe), 3.10 (s, 3H,

158 1 11 SMe’), 3.07 (s, 12H), 2.54 (s, 3H, Me), 2.49 (s, 3H, Me’). H{ B} NMR (CD3CN): δ

4.03 (br s, 1H, BH), 0.64 (br s, 1H, BH), 0.23 (br s, 4H, BH). 13C{1H} NMR

+ (CD3CN): δ 197.1 (s, CO), 196.8 (s, CO’), 71.3 (s, CH’), 71.1 (s, CH), 56.3 (t, Me4N ),

28.9 (Me), 27.7 (Me’), 26.9 (SMe), 26.0 (SMe’). Elemental Analysis: C 28.27%, H

8.86%, cal. C 29.12%, H 8.55%.

[Bu4N][1-(MeSCH2CCH)-B10H9] From 0.5020 g (0.7733 mmol) of [Bu4N]2[1-

B10H9SMe] and 0.10 mL of propargyl bromide 0.3194 g (93%) of pure product was

11 obtained. B NMR (CD2Cl2): δ 8.8 (d, JBH = 144, B(10)), -0.1 (s, B(1)), -25.5 (d, JBH

1 + = 128, B(2-5)), -28.3 (d, JBH = 130, B(6-9)). H NMR (CD3CN): δ (Bu4N : 3.18 (m,

8H), 1.64 (m, 8H), 1.46 (m, 8H), 1.02 (t, JHH = 7.4, 12H)), 4.27 (dd, JHH = 16.6, 2.7,

1H), 4.12 (dd, JHH = 16.6, 2.7, 1H), 3.12 (s, 3H, SMe), 2.62 (t, JHH = 2.7, 1H).

1 11 H{ B} NMR (CD3CN): δ 4.06 (br s, 1H, BH), 0.72 (br s, 4H, BH), 0.30 (br s, 4H,

13 1 + BH). C{ H} NMR (CD3CN): δ (Bu4N : 59.4, 24.4, 20.1, 13.8), 74.9 (CH), 75.7 (C),

35.6 (SCH2), 27.2 (SMe). Elemental Analysis: C 53.67%, H 11.22%, cal. C 53.89%, H

11.53%.

[Bu4N][1-(MeSCH2CHCH2)-B10H9] From 0.5241 g (0.8073 mmol) of

[Bu4N]2[1-B10H9SMe] and 0.10 mL of allylic bromide 0.3621 g (99%) of pure product

11 was obtained. B NMR (CD2Cl2): δ 7.8 (d, JBH = 142, B(10)), 0.1 (s, B(1)), -25.7 (d,

1 + JBH = 127, B(2-5)), -28.4 (d, JBH = 130, B(6-9)). H NMR (CD3CN): δ (Bu4N : 3.17

(m, 8H), 1.62 (m, 8H), 1.45 (m, 8H), 1.01 (t, JHH = 7.3, 12H)), 6.15 (m, 1H), 5.52 (d,

JHH = 18.0, 1H), 5.49 (d, JHH = 10.6, 1H), 4.16 (dd, JHH = 13.4, 6.2, 1H), 3.91 (dd, JHH

159 1 11 = 13.4, 8.6, 1H), 2.87 (s, 3H, SMe). H{ B} NMR (CD3CN): δ 3.99 (br s, 1H, BH),

13 1 + 0.71 (br s, 4H, BH), 0.29 (br s, 4H, BH). C{ H} NMR (CD3CN): δ (Bu4N : 59.2,

24.3, 20.0, 13.8), 128.9 (CH), 123.3 (CH2), 50.0 (SCH2), 25.9 (SMe). Elemental

Analysis: C 34.05%, H 10.68%, cal. C 34.38%, H 10.46%.

2- + + General procedure for [2-B10H9SMe] Either Bu4N or Me4N salt can be used as

2- starting material. About 1 mmol of [2-B10H9SMe] was added to a 25 ml round bottom flask equipped with a magnetic stir bar. The solid was added with 10-15 mL of acetonitrile. About 1.1 equivlaent of the alkylating agents (usually liquid) was syringed into the reaction flask while the contents was stirred. The reaction was allowed to stir overnight. All volatiles were removed under reduced pressure. (Unless the procedure is specified, the compound is precipitated with MePPh3Br from an ethanol/water solution). To the residue was added about 15 mL of distilled water. It partially dissolved. Then 1 mL of 95% ethanol was added. 1.1 equivalent of

MePPh3Br was added to the alcohol-aqueous solution and stirred for about 2 hours.

Generally the equatorial isomer is considerably more soluble relative to the apical isomer. The precipitant was filtered through a glass funnel equipped with a frit, and it was washed with two portions of 5 mL 95% ethanol. The solid was then dried in a preheated oven overnight.

[Me4N][2-B10H9SMe2] From 0.3309 g (1.059 mmol) of [Me4N]2[2-B10H9SMe] and 0.06 mL of methyl iodide dissolved in 15 mL of CH3CN. The reaction flask was covered with aluminum foil since methyl iodide is light sensitive. After standard

160 11 aqueous workup 0.1741 g (65%) of pure product was obtained. B NMR (d6-DMSO):

δ 2.1 (d, JBH = 147, B(10)), -4.5 (d, JBH = 145, B(1)), -17.0 (s, B(2)), -26.0 (d, JBH =

1 134, B(3,5)), -26.9 (d, JBH = 135, B(4,7,8)), -30.2 (d, JBH = 116, B(6,9)). H NMR (d6-

1 11 DMSO): δ 3.09 (s, 12H), 2.17 (s, 6H, SMe2). H{ B} NMR (d6-DMSO): δ 3.38 (br s,

1H, BH), 2.99 (br s, 1H, BH), 0.61 (br s, 2H, BH), 0.24 (br s, 2H, BH), 0.19 (br s, 1H,

13 1 + BH), -0.11 (br s, 2H, BH). C{ H} NMR (d6-DMSO): δ 54.4 (t, NMe4N ), 25.7 (s,

SMe).

[MePPh3][2-MeSEt-B10H9] From 0.3398 g (1.087 mmol) of [Me4N]2[2-

B10H9SMe], 0.14 mL of ethyl iodide, and 0.5527 g of MePPh3Br 0.3804 g (77%) of

11 pure product was obtained. B NMR (CD3CN): δ 2.4 (d, JBH = 148, B(10)), -4.2 (d,

JBH = 148, B(1)), -17.2 (s, B(2)), -25.9 (d, JBH = 140, B(3,5)), -26.8 (d, JBH = 138,

1 + B(4,7,8)), -30.0 (d, JBH = 129, B(6,9)). H NMR (CD3CN): δ (MePPh3 : 7.86 (m, 3H),

7.70 (m, 6H), 7.65 (m, 6H), 2.79 (d, JPH = 13.9, 3H)), 2.73 (dq, JHH = 15.1, 7.6, 1H),

1 11 2.57 (dq, JHH = 14.8, 7.4, 1H), 2.18 (s, 3H, SMe). H{ B} NMR (CD3CN): δ 3.48 (br s, 1H, BH), 3.13 (br s, 1H, BH), 0.68 (br s, 2H, BH), 0.33 (br s, 2H, BH), 0.29 (br s,

13 1 1H, BH), 0.20 (br s, 2H, BH). C{ H} NMR (CD3CN): δ 136.1 (d, JPC = 2.9, 1C),

134.2 (d, JPC = 10.9, 2C), 131.2 (d, JPC = 12.7, 2C), 120.4 (d, JPC = 89.0, 1C), 36.8 (s,

CH2), 23.0 (s, SMe), 10.6 (s, CH3), 9.4 (d, JPC = 58.3, 1C). Elemental Analysis: C

29.62%, H 11.02%, cal. C 31.43%, H 10.93%

161

[Bu4N][2-(MeSCH2CCH)-B10H9] 0.5591 g (0.8607 mmol) of [Bu4N]2[2-

B10H9SMe] was stirred with excess propargyl bromide in 20 mL CH3CN overnight.

After the removal of volatiles, the residue was partitioned between water and chloroform. The organic layer was obtained and chloroform was removed. The product was washed with 2 portion of 5 mL cold water and dried overnight. 11B NMR

(CD3CN): δ 2.8 (d, JBH = 145, B(10)), -4.3 (d, JBH = 142, B(1)), -17.2 (s, B(2)), -25.8

1 (d, JBH = 131, B(3,5)), -26.4 B(4), -26.9 (d, ,7,8)), -30.2 (d, JBH = 124, B(6,9)). H

+ NMR (CD3CN): δ (Bu4N : 3.07 (m, 8H), 1.59 (m, 8H), 1.35 (m, 8H), 0.96 (t, JHH =

7.4, 12H)), 3.51 (dd, JHH = 16.6, 2.7, 1H), 3.31 (dd, JHH = 16.6, 2.6, 1H), 2.69 (t, JHH =

1 11 2.7, 1H), 2.37 (s, 3H, SMe). H{ B} NMR (CD3CN): δ 3.51 (br s, 1H, BH), 3.10 (br s, 1H, BH), 0.69 (br s, 2H, BH), 0.34 (br s, 2H, BH), 0.31 (br s, 1H, BH), 0.20 (br s,

13 1 + 2H, BH). C{ H} NMR (CD3CN): δ (Bu4N : 59.4, 24.3, 20.3, 13.8), 76.3, 75.6, 32.7.

[MePPh3][2-(MeSCH2CCH2)-B10H9] From 0.6779 g (1.044 mmol) of

[Bu4N]2[2-B10H9SMe] and 0.16 mL of allylic bromide and 0.5407 g of MePPh3Br

11 0.3239 g (67%) of pure product was obtained. B NMR (CD3CN): δ 2.6 (d, JBH =

143, B(10)), -4.1 (d, JBH = 143, B(1)), -17.1 (s, B(2)), -25.7 (d, JBH = 134, B(3,5)), -

1 26.6 (d, JBH = 136, B(4,7,8)), -29.9 (d, JBH = 133, B(6,9)). H NMR (CD3CN): δ

+ (MePPh3 : 7.86 (m, 3H), 7.70 (m, 6H), 7.66 (m, 6H), 2.81 (d, JPH = 13.9, 3H)), 5.84

(m, 1H)), 5.29 (m, 2H)), 3.43 (dd, JHH = 13.3, 6.5, 1H), 3.22 (dd, JHH = 13.3, 8.4, 1H).

1 11 H{ B} NMR (CD3CN): δ 3.49 (br s, 1H, BH), 3.14 (br s, 1H, BH), 0.70 (br s, 2H,

BH), 0.35 (br s, 2H, BH), 0.30 (br s, 1H, BH), 0.22 (br s, 2H, BH). 13C{1H} NMR

162 (CD3CN): δ 136.1 (d, JPC = 2.9, 1C), 134.2 (d, JPC = 10.7, 2C), 131.2 (d, JPC = 13.2,

2C), 129.9 (s, CH), 123.0 (s, CH2), 120.4 (d, JPC = 88.8, 1C), 46.7 (s, SCH2), 23.3 (s,

SMe), 9.4 (d, JPC = 58.5, 1C).

[MePPh3][2-(MeSCH2Cl)-B10H9] From 0.6546 g (1.008 mmol) of [Bu4N]2[2-

B10H9SMe], 10 mL of CH2Cl2 in 10 mL of CH3CN, and 0.5301 g of MePPh3Br 0.3170

11 g (64%) of pure product was obtained. B NMR (CD3CN): δ 2.9 (d, JBH = 147,

B(10)), -4.2 (d, JBH = 145, B(1)), -17.2 (s, B(2)), -25.9 (d, JBH = 132, B(3,5)), -26.1

1 + (B(4)), -27.1 (d, B(7,8)), -30.3 (d, JBH = 128, B(6,9)). H NMR (CD3CN): δ (MePPh3 :

7.86 (m, 3H), 7.70 (m, 6H), 7.66 (m, 6H), 2.81 (d, JPH = 13.9, 3H)), 4.51 (d, JHH =

1 11 10.9, 1H)), 4.29 (d, JHH = 10.9, 1H)), 2.40 (s, 3H, SMe). H{ B} NMR (CD3CN): δ

3.54 (br s, 1H, BH), 3.15 (br s, 1H, BH), 0.69 (br s, 2H, BH), 0.36 (br s, 3H, BH), 0.21

13 1 (br s, 2H, BH). C{ H} NMR (CD3CN): δ 136.1 (d, JPC = 2.9, 1C), 134.2 (d, JPC =

10.9, 2C), 131.2 (d, JPC = 12.7, 2C), 120.4 (d, JPC = 89.0, 1C), 51.7 (s, CH2Cl), 23.9 (s,

SMe), 9.4 (d, JPC = 58.3, 1C).

163

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