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A Journey Across the Periodic Table: The Synthesis and Characterization of Main Group Metals Supported by Nitrogen– or Sulfur–Rich Ligands

Neena Tiscza Chakrabarti

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Graduate School of Arts and Sciences

Columbia University 2014

A Journey Across the Periodic Table: The Synthesis and Characterization of Main Group Metals Supported by Nitrogen– or Sulfur–Rich Ligands

Neena Tiscza Chakrabarti

Abstract

In Chapter 1, I discuss the synthesis and characterization of lithium tris(pyrazolyl)hydroborato complexes, [TpR1,R2]Li. Group 1 [TpR1,R2]M complexes serve as key starting points to access many other main group and transition metal complexes; however, the synthesis and crystal structures of [Tp R1,R2]Li has not been reported.

t t Molecular structures of [TpBu ]Li and [TpBu ,Me]Li show these complexes are trigonal pyramidal, an unusual geometry for lithium. These complexes are also able to bind small molecules to form four-coordinate pseudo-tetrahedral complexes, [Tp]Li-L (L =

But MeCN, pz H, and H2O). The binding constants for the association of acetonitrile to

t t [TpBu ]Li and [TpBu ,Me]Li are 0.84M-1 and 0.96M-1, respectively, indicating that the

t dissociation of MeCN is facile in solution. In addition, [TpBu ,Me]Li serves as

t transmetallating agent to yield the cadmium halide complexes, [TpBu ,Me]CdX (X = Cl, Br,

I).

In Chapter 2, I discuss the synthesis and characterization of organometallic cadmium complexes supported by the nitrogen-rich multidentate ligands, tris(pyridylthio)methane, [Tptm]H; tris(1-methyl-imidazolylthio)methane, [TitmMe]H; and tris(1-methyl-benzimidazolylthio)methane, [TitmiPrBenz]H. These ligands are in the nascent stages of development and there are only a few metal [Tptm] and [TitmMe]

complexes in the literature. An investigation of the reactivity of [L]CdN(SiMe3)2,

Me iPrBenz [L]CdOSiMe3, and [L]CdOSiPh3 ([L] = [Tptm], [Titm ], [Titm ]) shows these complexes provide access to a variety of organometallic cadmium complexes, [L]CdX,

(X = OAc, Cl, Br, O2CH, NCO). The characterization of cadmium acetate and formate complexes is significant due to their structural similarity with the metal bicarbonate intermediate formed by zinc and cadmium-substituted carbonic anhydrase. In addition, the synthesis and characterization of cadmium methyl complexes, [L]CdMe, is

iPrBenz discussed. The application of heat to a mixture of [Titm ]H and CdMe2 results in

iPrBenz iPrBenz isomerization of the ligand to [S3-Titm ]CdMe. This sulfur-rich [S3-Titm ] ligand is not reported in the literature and is ripe for further investigation. The solid state structures of these compounds provide a comparison with biologically relevant [Tp] or

[Tm] cadmium methyl complexes in the literature.

In Chapter 3, I describe the synthesis and structural characterization of

ButBenz RBenz t [Bm ]M (M = Na, K) and [Bm ]Ca(THF)2 (R = Me, Bu ) are discussed. The sulfur- rich tripodal ligand tris(imidazolylthio)hydroborato, [Tm], was previously designed to serve as a softer version of the [Tp] ligand. Metal [Tm] complexes are prevalent in the literature and have often been used as molecular mimics of sulfur-rich enzyme active sites. Recently, the benzannulated [TmRBenz]M complexes were reported and were found to promote 3 coordination toward the metal center. To allow for an in-depth

t investigation of the newly synthesized [BmRBenz] class of ligand, the [BmBu Benz]M (M =

Na, K, Ca) complexes were synthesized and compared to previously reported metal

MeBenz BmMeBenz [Bm ]M complexes. Additionally, the [ ]2Ca(THF)2 was synthesized and

MeBenz characterized via X-ray diffraction. The molecular structure of [Bm ]2Ca(THF)2 shows the complex is monometallic with an uncommon eight-coordinate dodecahedral

MeBenz calcium center. [Bm ]2Ca(THF)2 is the first molecular structure of calcium coordinated to the [Tm] or [Bm] ligand class.

In Chapter 4, I discuss the synthesis and characterization of mercury alkyl complexes supported by the [TmMe], [BmR], [TmRBenz] and [BmRBenz] ligands (R = Me or

But). As previously mentioned, [Tm]M complexes are considered biologically relevant

t molecular models of enzyme active sites. With this in mind, [TmBu ]HgR (R = Me,Et)

complexes have served as mimics for the mercury detoxification enzyme MerB. A previous study by our group showed that the adoption of multiple coordination modes

t of the ligand in [TmBu ]HgR plays a significant role in the activation of the Hg-C bond toward protonolysis. The molecular structures of the [TmR], [BmR], [TmRBenz], and

[BmRBenz] mercury alkyl complexes show that they adopt various coordination modes, ranging from 1 to 3. Preliminary competition experiments in which benzenethiol was added to [TmR]HgEt and [TmRBenz]HgEt indicate that the Hg-C bond in [TmMeBenz]HgEt

t was cleaved faster than that in [TmMe]HgEt. Conversely, the Hg-C bond in [TmBu ]HgEt

t was cleaved faster than that in [TmBu Benz]HgEt, indicating that benzannulation and the size of the R-group on the [Tm] ligand play important roles in Hg-C bond cleavage.

TABLE OF CONTENTS

List of Schemes, Figures, and Tables v

Acknowledgements xviii

Chapter 1. Synthesis and Structural Characterization of Uncommon Trigonal 1

Pyramidal Lithium Tris(pyrazolyl)hydroboration Complexes, Their

Coordination to Small Molecules, and a Study of Their Reactivity

1.1 Introduction 4

1.1.1 Objective 4

1.1.2 The tris(pyrazolyl)hydroborato, [Tp], ligand 5

t t 1.2 Synthesis of [TpBu ]Li and [TpBu ,Me]Li Complexes 6

t t 1.3 [TpBu ]Li-L and [TpBu ,Me]Li-L Complexes 16

t t 1.3.1 Synthesis and Molecular Structures of [TpBu ]Li-L and [TpBu ,Me]Li-L 16

Complexes

t t 1.3.2 DFT Calculations of [TpBu ]Li-L and [TpBu ,Me]Li-L 29

1.3.3 Equilibrium Studies of [Tp]Li and [Tp]Li-L Complexes 32

1.4 Reactivity of [TpR,R]Li complexes with Cadmium Halides Salts 43

1.5 Conclusion 52

1.6 Experimental Section 53

1.7 Crystallographic Data 67

1.8 Reference and Notes 73

Chapter 2. Synthesis and Structural Characterization of Cadmium Complexes 80

Supported by Nitrogen-Rich Ligands: [Tptm], [TitmMe], and [TitmiPrBenz] and A

Study of Their Reactivity

2.1 Introduction 83

2.1.1. Objective 83

2.1.2 The Ligand Systems 84

2.2 Synthesis of [Tptm]CdX Compounds 86

2.3 Synthesis of [TitmMe]CdX Compounds 95

i 2.4 Synthesis of [TitmPr Benz]CdX Complexes 102

2.5 Discussion of [L]CdN(SiMe3)2 Complexes 105

2.6 Discussion of [L]CdOSiR3 (R = Me, Ph) Complexes 110

2.7 Discussion of [L]CdMe 121

2.8 Discussion of [L]CdNCO 131

2.9 Discussion of [L]CdO2CX (X = H, Me) Complexes 139

2.10 Discussion of [L]CdX (X – Cl, Br, I) Complexes 147

2.11 Conclusion 155

2.12 Experimental Section 156

2.13 Crystallographic Data 187

2.14 References and Notes 197

Chapter 3. Synthesis and Structural Characterization of Bis(2-mercapto-1- 210

ii benzimidazolyl)hydroborato, [BmRBenz] (R = Me, But), Compounds of Sodium,

Potassium and Calcium

3.1 Introduction 221

3.1.1 Objective 221

3.1.2 The tris(mercaptoimidazolyl)hydroborato, [Tm] and 222 bis(mercaptoimidazolyl)hydroborato, [Bm] class of ligands

t 3.2 [BmBu Benz]M (M = Na, K) Compounds 224

RBenz t 3.3 Synthesis and Molecular Structure of [Bm ]2Ca(THF)2 (R = Me, Bu ) 227

MeBenz 3.4 [Bm ]2Ca(THF)2 as a l Agent 244

3.5 Conclusion 245

3.6 Experimental Section 245

3.7 Crystallographic Data 256

3.8 References and Notes 257

Chapter 4. Synthesis and Structural Characterization of Mercury Methyl and 253

Ethyl Complexes Supported by Sulfur-Rich [Tm] and [Bm] Ligands

4.1 Introduction 256

4.1.1 Objective 256

4.1.2 Rationalization for the [Tm] ligand 257

4.2 [Tm]HgR (R – Me, Et) complexes 260

4.2.1 Synthesis and Molecular Structures of [TmMe]HgR 260

iii

4.2.2 Synthesis and Molecular Structures of [TmMeBenz]HgR and 269

t [TmBu Benz]HgR

4.3 [Bm]HgR (R = Me, Et) Complexes 277

t 4.3.1 Synthesis and Molecular Structures of [BmMe]HgR and [BmBu ]HgEt 277

4.3.2 Synthesis and Molecular Structures of [BmMeBenz]HgR and 286

t [BmBu Benz]HgR

4.4 NMR Characterization of Mercury Alkyl Complexes 288

4.4.1 NMR Characterization of [L]HgMe Complexes 288

4.4.2 NMR Characterization of [L]HgEt Complexes 293

4.5 Hg-C Bond Cleavage with Benzenethiol 296

4.5.1 Reactions with [TmMe]HgEt and [TmMeBenz]HgEt 296

t t 4.5.2 Reactions with [TmBu ]HgEt and [TmBu Benz]HgR 297

4.6 Conclusion 298

4.7 Experimental Section 298

4.8 Crystallographic Data 322

4.9 References and Notes 327

LIST OF SCHEMES, FIGURES AND TABLES

Chapter 1

t t Scheme 1. Synthesis of [TpBu ]Li and [TpBu ,Me]Li 7

But 16 Scheme 2. Addition of small molecules (L = MeCN, Pz H, and H2O) to

t t [TpBu ]Li and [TpBu ,Me]Li to obtain the [Tp]Li-L adduct

t Scheme 3. Synthesis of [TpBu ,Me]CdX (X = Cl, Br, I) 45

Figure 1. Structure of a metal tris(pyrazolyl)hydroborato complex, 4

[TpR3,R5]M

Figure 2. The cone angle () measured for [Tp]Co complexes 6

t Figure 3. Molecular Structure of [TpBu ]Li 8

t Figure 4. Molecular Structure of [TpBu ,Me]Li 8

Figure 5. Trigonal pyramidal coordination geometry 8

Figure 6. Variable temperature 1H NMR spectrum of the H-B bond in 12

But,Me [Tp ]Li in d8-toluene. (* = impurity)

t Figure 7. Molecular Structure of [TpBu ]Li-NCMe 17

t Figure 8. Molecular Structure of [TpBu ,Me]Li-NCMe 18

t t Figure 9. Molecular structure of [TpBu ]Li(pzBu H) 18

But,Me But But 19 Figure 10. Molecular structure of [Tp ]Li(pz H)•(pz H)

But 21 Figure 11. Molecular structures of [Tp ]Li(OH2)•2(THF) and

But [Tp ]Li(OH2). These two structures were obtained from the same unit

cell (THF molecules which do not participate in hydrogen bonding have

been omitted for clarity)

But,Me 22 Figure 12. Molecular structure of [Tp ]Li(OH2)

But,Me 23 Figure 13. Molecular structure of [Tp ]Li(OH2)•(pzH)

Figure 14. Plot of the 7Li NMR chemical shift versus concentration of 34

But But,Me acetonitrile in solutions of [Tp ]Li and [Tp ]Li in d6-benzene

Figure 15. Plot of the 7Li NMR chemical shift versus concentration of 34

But But,Me Pz H in a solution of [Tp ]Li in d6-benzene

Figure 16. Plot of the 7Li NMR chemical shift versus concentration of 36

But,Me water in a solution of [Tp ]Li in d6-benzene

Figure 17. Double reciprocal (top) and y-reciprocal plots (bottom) for the 37

t addition of acetonitrile to [TpBu ]Li

Figure 18. Double reciprocal (top) and y-reciprocal plots (bottom) for the 38

t addition of acetonitrile to [TpBu ,Me]Li

Figure 19. Double reciprocal (top) and y-reciprocal plots (bottom) for the 39

t t addition of PzBu H to [TpBu ,Me]Li

Figure 20. Double reciprocal (top) and y-reciprocal plots (bottom) for the 40

t addition of water to [TpBu ,Me]Li

But,Me 45 Figure 21. Molecular structure of [Tp ]CdCl●C6H6 (solvent is omitted for clarity)

t Figure 22. Molecular structure of [TpBu ,Me]CdBr (disordered atoms are 46 omitted for clarity)

But,Me 46 Figure 23. Molecular structure of [Tp ]CdI●C6H6 (solvent is omitted for clarity)

Table 1. Summary of lithium coordination numbers in structurally 8 characterized compounds listed in the Cambridge Structural Database

Table 2. The geometric classification of lithium complexes from the 10

Cambridge Structural Database

t t Table 3. Selected bond angles for 3-coordinate [TpBu ]Li and [TpBu ,Me]Li 11

t t Table 4. 11B NMR data for [TpBu ]Li and [TpBu ,Me]Li and selected [TpR,R’]M 13 compounds

t t Table 5. 15N NMR data for [TpBu ]Li and [TpBu ,Me]Li and selected [TpR,R’]M 14 compounds

t t Table 6. 7Li NMR data for [TpBu ]Li and [TpBu ,Me]Li and other selected 15 compounds

Table 7. Li-N and Li-L bond lengths in the three coordinate [Tp]Li and 24 four coordinate [Tp]Li-L complexes

Table 8. N-Li-N and L-Li-N bond angles in the four coordinate [Tp]Li-L 26 complexes

Table 9. τ4 parameters as calculated from the bond angle information 27 obtained from the molecular structures of the four coordinate [Tp]Li-L complexes

t t Table 10. 11B NMR for [TpBu ]Li-L and [TpBu ,Me]Li-L compounds 28

t t Table 11. 7Li NMR data for [TpBu ]Li –L and [TpBu ,Me]Li-L compounds 28

Table 12. DFT computed H energy changes (kcal mol-1) associated with 30 coordination of a ligand to [Tp]Li

Table 13. Binding association, Ka, values for the addition of MeCN to 41

t t [TpBu ]Li and [TpBu ,Me]Li

vii

Table 14. Experimentally determined free energy values (G) for the 42

t t addition of MeCN to [TpBu ]Li and [TpBu ,Me]Li

Table 15. DFT calculated thermodynamic values for the coordination of 42

t t MeCN to [TpBu ]Li and [TpBu ,Me]Li

Table 16. N-Cd-N and X-Cd-N bond angles in the four coordinate 48

[Tp]CdX complexes

Table 17. τ4 parameters as calculated from the bond angle information 49

obtained from the molecular structures of the four coordinate [Tp]CdX

complexes

Table 18. Cd-N and Cd-X bond lengths in the [Tp]CdX complexes 50

t Table 19. 11B NMR data for the [TpBu ,Me]CdX complexes 51

Table 20. Crystal, intensity collection and refinement data 67

Chapter 2

Scheme 1. Synthesis of [Tptm] cadmium complexes 87

Scheme 2. Mechanism for the formation of [Tptm]ZnNCO from addition 89

of CO2 to [Tptm]ZnN(SiMe3)2

i Scheme 4. Synthesis of [TitmPr Benz] cadmium complexes 103

3 iPrBenz 4 iPrBenz 104 Scheme 5. Synthesis of [ -N3-Titm ]CdMe and [ -S3-Titm ]CdMe

Scheme 6. Isomerization of the [TitmMe]H ligand 122

Scheme 7. Catalytic mechanism of the hydration of carbon dioxide by 146

zinc CA

Scheme 8. Synthesis of [L]CdI (L = [Tptm], [TitmMe]) 147

viii

Figure 1. The tris(pyridylthio)methane, [Tptm]H, tris(1- 83 methylimidazolylthio)methane, [TitmMe]H, and tris(1-

i isopropylbenzimidazolylthio)methane, [TitmPr Benz]H ligands

Me 85 Figure 2. Isomerized [S3-Titm ]H ligand

Figure 3. Molecular structure of [Tptm]CdN(SiMe3)2 (only one of two 88 crystallographically independent molecules is shown)

Figure 4. Molecular structure of {[Tptm]Cd(-NCO)}2●C6H6 (solvent is 90 omitted for clarity)

Figure 5. Molecular structure of {[Tptm]Cd(-OSiMe3)}2●2C6H6 (solvent is 91 omitted for clarity)

Figure 6. Molecular structure of [Tptm]CdOSiPh3●C6H6 (solvent is 91 omitted for clarity)

Figure 7. Molecular structure of [Tptm]CdCl (disordered atoms are not 92 shown)

Figure 8. Molecular structure of [Tptm]CdBr (disordered atoms are not 93 shown)

Figure 9. Molecular structure of [Tptm]CdOAc 94

Figure 10. Molecular structure of [Tptm]CdO2CH 95

3 Me 97 Figure 11. Molecular structure of [ -S2C-Titm ]CdMe

Me 98 Figure 12. Molecular structure of [Titm ]CdOSiPh3

Me 99 Figure 13. Molecular structure of [Titm ]CdNCO●2C6H6 (solvent is omitted for clarity)

Figure 14. Molecular structure of [TitmMe]CdOAc 100

Me 101 Figure 15. Molecular structure of [Titm ]CdCl●C6H6 (solvent omitted for

ix clarity)

Figure 16. Molecular structure of [TitmMe]CdBr (there are two 101 crystallographically independent molecules in the asymmetric unit)

Me Me Figure 17. Molecular structure of [Titm ]CdOPh ●p-TolOH 102

3 iPrBenz 104 Figure 18. Molecular structure of [ -N2C-Titm ]CdMe●2C6H6 (solvent atoms are omitted for clarity)

4 iPrBenz Figure 19. Molecular structure of [ -S3C-Titm ]CdMe●C6H6 (solvent atoms are omitted for clarity)

Figure 20. 1H NMR spectrum of the pyridylthio protons in 108

[Tptm]CdN(SiMe3)2 at various temperatures (* = d8- toluene)

Figure 21. 1H NMR spectrum of the imidazolyl protons in 110

Me [Titm ]CdN(SiMe3)2 at various temperatures (* = d8-toluene; † = unknown impurity)

Figure 22. The molecular structure of [Tptm]ZnOSiMe3 114

Figure 23. Structures of the DFT geometry optimized of monomeric 115

[Tptm]MOSiMe3 and dimeric {[Tptm]M(-OSiMe3)}2 (M = Cd, Zn) complexes

Figure 24. Molecular structure of [Tptm]ZnOSiPh3 119

Figure 25. 1H NMR spectrum of the Cd-Me resonance with cadmium 128

3 Me satellites in [ -S2C-Titm ]CdMe

3 PriBenz 4 130 Figure 26. Structures of the [ - N2C -Titm ]CdMe versus [ - N3C -

PriBenz 3 PriBenz 4 Titm ]CdMe (top) and [ - S2C -Titm ]CdMe versus [ - S3C -

i TitmPr Benz]CdMe (bottom)

Figure 27. Coordination modes of NCO observed in structurally 132 characterized metal complexes

Figure 28. Metal center in {[Tptm]Cd(-NCO)}2 showing a distorted 134 octahedral geometry

Figure 29. Molecular structure of [Tptm]ZnNCO●0.5C6H6 135

Figure 30. A view down the three-fold axis in an octahedron and trigonal 141 prism

Figure 31. Atoms coordinating to cadmium in [Tptm]CdOAc showing a 141 distorted trigonal antiprismatic geometry

Figure 32. Atoms coordinating to cadmium in [Tptm]CdO2CH showing a 143 distorted trigonal antiprismatic geometry

Figure 33. The cadmium center in [TitmMe]CdOAc showing the cadmium 145 in a distorted trigonal prismatic geometry

Figure 34. Molecular structure of [Tptm]CdI (disordered atoms are not 148 shown)

Figure 35. Molecular structure of [TitmMe]CdI 148

Table 1. Selected bond lengths and angles in [Tptm]CdN(SiMe3)2 106

Table 2. Cd-N(SiMe3)2 bond lengths in select compounds 107

Table 3. Selected bond lengths and angles in {[Tptm]Cd(- 111

OSiMe3)}2●2C6H6

Table 4. M-O-M angles and M-O bond lengths in dimeric main group 112

[M(-OSiMe3)]2 complexes

Table 5. DFT energy calculations of the formation of dimeric metal 115 siloxide complexes

Table 6. Select bond lengths in [L]CdOSiPh3 complexes 116

Table 7. Select bond angles in [L]CdOSiPh3 complexes 117

Table 8. Selected bond lengths and angles in [TitmMe]CdMe 122

3 124 Table 9. N-Cd-C and C-Cd-C bond angles and 4 parameter for [ -

i TitmPr Benz]CdMe

4 124 Table 10. S-Cd-S and C-Cd-C bond angles and 5 parameter for [ -

i TitmPr Benz]CdMe

Table 11. Bond lengths in complexes containing a C-Cd-Me moiety 125

Table 12. 1H NMR data for terminal cadmium methyl complexes 128

Table 13. Percent of structurally characterized metal complexes 132 containing an NCO moiety in CSD 1.16

Table 14. Selected bond angles in {[Tptm]Cd(-NCO)}2 133

Table 15. DFT energy calculations of monomeric and dimeric metal 136 isocyanate complexes

Table 16. Select bond lengths in the X-ray and the DFT optimized 138 structures of [TitmMe]CdNCO

Table 17. Select angles in the X-ray and the DFT geometry optimized 138 structures of [TitmMe]CdNCO

Table 18. Selected bond lengths in cadmium acetate and formate 140 complexes

Table 19. Selected dihedral bond angles in cadmium acetate complexes 140

Table 20. Cd-O bond distances in cadmium formate complexes 142

Table 21. Select bond lengths in [Tptm]CdX and [TitmMe]CdX 149

Table 22. Select bond angles in [Tptm]CdX and [TitmMe]CdX Complexes 149

Table 23. Select bond lengths in DFT optimized [Tptm]CdX and 152

xii

[TitmMe]CdX

Table 24. Select bond angles in DFT optimized [Tptm]CdX and 152

[TitmMe]CdX

Table 25. Crystal, intensity collection and refinement data 187

Chapter 3

Scheme 1. Synthesis of [BmButBenz]M (M = Na, K) 215

RBenz t Scheme 2. Synthesis of [Bm ]2Ca(THF)2 (R = Me, Bu ) 217

Scheme 3. Addition of RHgCl (R = Me, Et) to [BmMeBenz]2Ca(THF)2 234

Figure 1. The [TmR] and [BmR] class of ligands 211

Figure 2. The tris(pyrazolyl)hydroborato, [TpR,R’], ligand 212

Figure 3. {[BmMeBenz]Na(THF)2}2 complex 213

Figure 4. Molecular structure of [BmMeBenz]2Ca(THF)2 218

Figure 5. The two sets of planar atoms in a trigonal dodecahedron 221

Figure 6. The two sets of planar atoms in [BmMeBenz]2Ca(THF)2 221

Figure 7. DFT optimized structure of [BmMeBenz]2Ca(THF)2 227

Figure 8. [BoR]M and [BoRBenz]M complexes 228

Figure 9. One of two binding sites featuring seven-coordinate calcium in 230

subtilisin BPN’

Figure 10. Structure of the [ToRBenz]M complex (R = Ad, But) 231

Figure 11. Molecular structure of [ToAdBenz]2Ca 232

t Figure 12. Molecular structure of [ToBu Benz]2Ca●3(C6H6) (benzene omitted 233

for clarity)

Figure 13. Experimentally obtained mass spectrum for [BmButBenz]Na 238

Figure 14. Predicted isotope pattern for the parent ion in [BmButBenz]Na 239

Figure 15. Experimentally obtained mass spectrum for [BmButBenz]K 240

xiii

Figure 16. Predicted isotope pattern for the parent ion in [BmButBenz]K 241

Table 1. B-H stretching frequencies in the IR spectra in [BmR]M (M = Na, 216

K) compounds

Table 2. Selected bond lengths in [BmMeBenz]2Ca(THF)2 219

Table 3. Selected bond angles in [BmMeBenz]2Ca(THF)2 219

Table 4. Summary of calcium coordination numbers in structurally 222

characterized compounds listed in the CSD

Table 5. Selected M-S bond and M…B atom distances in 225

[BmMeBenz]2Ca(THF)2 and reported compounds

Table 6. Crystal, intensity collection and refinement data 246

Chapter 4

t Scheme 1. Cleavage of the Hg-C bond in [TmBu ]HgR (R = Me or Et) via 257

reaction with benzenethiol

Scheme 2. Synthesis of [TmMe]HgR (R = Me, Et) 259

Scheme 3. Synthesis of [TmRBenz]HgR’ (R = Me, But; R’ = Me, Et) 268

Scheme 4. Synthesis of [BmMe]HgR (R = Me, Et) 276

t Scheme 5. Synthesis of [BmBu ]HgEt 277

Scheme 6. Synthesis of [BmMeBenz]HgR (R = Me, Et) 286

t Scheme 7. Synthesis of [BmBu Benz]HgR (R = Me, Et) 286

Figure 1. The [Tm] and [Bm] class of ligands (R = Me, or But) 256

t Figure 2. [TmBu ]HgR complexes (R = Me and Et) 256

Figure 3. Interconversion from 1 (left) to 3 (right) coordination modes in 258

xiv

t [TmBu ]HgR complexes (R = Me or Et)

Figure 4. Molecular structure of [TmMe]HgMe 260

Figure 5. Molecular structure of [TmMe]HgEt 260

Figure 6. Relative energies between [1-TmR]HgMe vs. [3-TmR]HgMe and 267

[1-TmR]HgEt vs. [3-TmR]HgEt (R = Me and But)

MeBenz 269 Figure 7. Molecular structure of [Tm ]HgMe•HgCl2 (co-crystallized

HgCl2 is omitted for clarity)

MeBenz 269 Figure 8. Molecular structure of [Tm ]HgEt•EtHgCl/HgCl2 (co- crystallized EtHgCl/HgCl2 is omitted for clarity)

t Figure 9. Molecular structure of [TmBu Benz]HgMe 270

t Figure 10. Molecular structure of [TmBu Benz]HgEt (disordered atoms are 270 not shown)

Figure 11. Molecular structure of [BmMe]HgMe 277

Figure 12. Molecular structure of [BmMe]HgEt 278

t Figure 13. Molecular structure of [BmBu ]HgEt 278

Figure 14. Coordination motifs of the “boat” configuration in [BmR]Hg 282

But alkyl complexes (left) versus the “chair” configuration in [Bm ]2Hg (right)

Figure 15. 199Hg satellites in the 1H NMR spectrum of [TmMe]HgMe 287

Table 1. Selected bond lengths and atom distances in [TmMe]HgR (R = Me 261 or Et)

Table 2. Selected atom distances in 1-S mercury alkyl complexes 262

Table 3. S-Hg-C bond angles in mercury alkyl complexes 263

Table 4. Calculated bond lengths and atom distances from DFT geometry 266

t optimizations of [TmMe]HgR and [TmBu ]HgR

Table 5. Select bond lengths in [TmMeBenz]HgR (R = Me, Et) and 271

t [TmBu Benz]HgMe

Table 6. Select bond angles in TmMeBenz]HgR (R = Me, Et) and 271

t [TmBu Benz]HgMe

3 273 Table 7. 4 parameters for  -S mercury alkyl complexes

Table 8. Relative energies calculated by DFT of [3-TmRBenz]HgMe and Et 275 complexes with [1-TmRBenz]HgMe and Et set as the reference point

Table 9. Hg-S and Hg-C bond lengths in [BmMe]HgMe and [BmR]HgEt (R 279

= Me or But)

… … R 280 Table 10. H2B Hg and Hg Sshort distances in select [Bm ]M complexes

Table 11. Selected bond angles in [BmR]HgMe and [BmR]HgEt (R = Me or 282

But)

Table 12. DFT calculated bond lengths in the optimized [BmMe]HgR and 283

t [BmBu ]HgEt structures

Table 13. DFT calculated bond angles in the optimized [BmMe]HgR and 283

t [BmBu ]HgEt structures

Table 14. 1H NMR data for mercury methyl complexes 289

Table 15. 11B NMR data for mercury methyl complexes 291

Table 16. 1H NMR data for mercury ethyl complexes 292

Table 17. 11B NMR data for mercury ethyl complexes 294

Table 18. 1H NMR data for the addition of benzenethiol to [TmMe]HgEt 318 and [TmMeBenz]HgEt

xvi

t Table 19. 1H NMR data for the addition of benzenethiol to [TmBu ]HgEt 320

t and [TmBu Benz]HgEt

Table 20. Crystal, intensity collection and refinement data 321

xvii

Acknowledgements

First and foremost, I would like to thank Ged Parkin, my advisor over the past five years. Thank you Ged for taking me into your lab, I have learned so much during my time at Columbia.

I would like to acknowledge the U.S. National Institutes of Health and the U.S.

National Science Foundation for supporting portions of the research described in this thesis.

My graduate committee, Colin Nuckolls and Jon Owen, have been great supporters of my research while at Columbia. I have appreciated our conversations over the years, ranging from the details of my research to broad ideas for the future.

I am grateful for my thesis committee members Professors John Magyar and

Roberto Sánchez-Delgado taking the time to read through my work and provide valuable feedback.

The former members of the Parkin group were quite singular in their hands-on approach and willingness to teach. Kevin helped to get me set up in the lab when I first got here and showed me how much there was outside of lab to enjoy. Aaron showed me what now comes as second nature today, how to load a crystal and take care of the glovebox. Wes was invaluable to my graduate education as he suggested I work with the [Tptm] ligand. He provided mentorship and friendship which only grew stronger during his last few years here. Ahmed, my fellow “brown,” kept things light-hearted

xviii and fun, which was crucial especially when research wasn’t working all that well. Yi, was really a jack of all trades in the lab. She had a solution for all the different types of questions I asked and took the time to teach me new techniques.

My present labmates make coming to work everyday fun. Our group lunches could go down in history, with stimulating discussions that serve as a much-needed break. I thank my fellow classmate, Ava, for a lasting friendship in an especially hard situation. Thank you for being a great listener and support. I owe a big thanks to Serge for all his original ideas and input that he offered for my research. Especially when he let me use his [TitmiPrBenz] ligand for my cadmium project. Serge has also been a great friend and deskmate over the years. Michelle has done a great job of keeping the lab going. Not just through being organized with the chemical orders but, more importantly, for being such a good friend and support to everyone. I’m really grateful that you took the time to understand where I was coming from. Josh is such a knowledgeable post-doc in so many areas. It was always enjoyable to get your input on random subjects but also with calculations and mercury chemistry. To the newest member of the group, Patrick, I wish you all the best.

Five years is a long time and the friendships that I have built with my peers in the chemistry department have made it pass by so seamlessly. Having such a strong friendships outside of the lab was so valuable, thanks for being an awesome group.

xix

I never would have gotten this far without the friendship and mentorship of my fabulous chemistry professors at Trinity College. Dr. Curran, Alison, Dr. Parr, Dr.

Moyer, and Dr. Mitzel you all played such a significant role in my career as a student and as a chemist. As a team, you taught me how to be inquisitive, how to design scientific experiments and how to present my work to different audiences. With your help and support, I was able to realize my dream of getting a Ph.D. in chemistry.

Most importantly, I’m so so grateful to my mom. In the beginning she told me to quit, perhaps I should have listened, but I wasn’t ready to give up on my dream. In the later years, when things were especially difficult, she stood with me to see this thing through. Thanks mom, you deserve this degree as much, and probably more, than I do.

For Ma

xxi

Chapter 1

Synthesis and Structural Characterization of Uncommon Trigonal Pyramidal

Lithium Tris(pyrazolyl)hydroborato [Tp] Complexes, Their Coordination

to Small Molecules, and a Study of Their Reactivity

Table of Contents

1.1 Introduction ...... 4

1.1.1 Objective ...... 4

1.1.2 The tris(pyrazolyl)hydroborato, [Tp], ligand ...... 5

t t 1.2 Synthesis of [TpBu ]Li and [TpBu ,Me]Li Complexes ...... 6

t t 1.3 [TpBu ]Li-L and [TpBu ,Me]Li-L Complexes ...... 16

t t 1.3.1 Synthesis and Molecular Structures of [TpBu ]Li-L and [TpBu ,Me]Li-L

Complexes ...... 16

t t 1.3.2 DFT Calculations of [TpBu ]Li-L and [TpBu ,Me]Li-L ...... 29

1.3.3 Equilibrium Studies of [Tp]Li and [Tp]Li-L Complexes ...... 32

1.4 Reactivity of [TpR,R]Li complexes with Cadmium Halide Salts ...... 43

1.5 Conclusion ...... 52

1.6 Experimental Section ...... 53

1.6.1 General Considerations ...... 53

1.6.2 X-ray Structure Determination...... 54

1.6.3 Computational Details ...... 54

t 1.6.4 Synthesis of [TpBu ]Li...... 54

t 1.6.5 Synthesis of [TpBu ,Me]Li ...... 55

t 1.6.6 Synthesis of [TpBu ]Li(NCMe) ...... 56

t 1.6.7 Synthesis of [TpBu ,Me]Li(NCMe) ...... 57

t t 1.6.8 Synthesis of [TpBu ]Li(pzBu H) ...... 59

t t t 1.6.9 Synthesis of [TpBu ,Me]Li(pzBu H)•(pzBu H) ...... 60

But,Me 1.6.10 Synthesis of [Tp ]Li(OH2) ...... 62

But 1.6.11 Synthesis of [Tp ]Li(OH2)•2(THF) ...... 62

But,Me 1.6.12 Synthesis of [Tp ]Li(OH2)•(pzH) ...... 62

t t 1.6.13 [TpBu ,R]Li and [TpBu ,R]LiL Equilibrium Studies ...... 63

t 1.6.14 Synthesis of [TpBu ,Me]CdCl ...... 63

t 1.6.15 Synthesis of [TpBu ,Me]CdBr ...... 64

t 1.6.16 Synthesis of [TpBu ,Me]CdI ...... 65

1.7 Crystallographic Data ...... 67

1.8 References and Notes ...... 73

Reproduced in part from:

Chakrabarti, N.; Sattler, W.; Parkin, G. Polyhedron 2013, 58, 235–246.

1.1 Introduction

1.1.1 Objective

Alkali metal tris(pyrazolyl)hydroborato [Tp] complexes (Figure 1) are used commonly used as transmetallation precursors to synthesize many of the [Tp]M compounds reported in the literature. 1-3,6,7 More specifically, [Tp]Li precursors have been used to obtain thallium,1 platinum2 and silver3 [Tp] complexes. Although [Tp]Li complexes have been widely used as precursors for these types of reactions, there are no structurally characterized 3-coordinate [Tp]Li complexes in the Cambridge

Structural Database (CSD).4 In fact, many alkali metal [Tp] complexes are not reported as simple three-coordinate species due to the coordination of additional molecules to the metal center.5

Figure 1. Structure of a metal tris(pyrazolyl)hydroborato complex, [TpR3,R5]M

In the following chapter, I discuss the first reported synthesis and structural

t characterization of two well-defined three-coordinate [TpBu ,R]Li (R = H or Me) complexes. The ability of these complexes to bind small molecules (acetonitrile,

4 pyrazole, and water) to form four-coordinate complexes was studied as well as their

t ability to act as transmetallating agents to access [TpBu ,Me]CdX (X = Cl, Br, and I) complexes.

1.1.2 The tris(pyrazolyl)hydroborato, [Tp], ligand

Following the synthesis of the first alkali metal tris(pyrazolyl)hydroborato, [Tp],

(Figure 1) complexes in 1967 by Swiatoslaw Trofimenko, there have been numerous reports and applications of various metal tris(pyrazolyl)hydroborato complexes in the literature.6 Such widespread use of the [Tp] ligand can be attributed to the variety of steric and electronic tuning that is achieved through substitution on the 3 and 5 positions of the pyrazole rings within the ligand.

Substitution at only the 3-position of the pyrazole ring adds steric bulk around the metal center and thus affects its coordination environment.7 The cone angles (Figure 2) for a number of substituted [TpR]Co complexes were measured and it was found that as the substituents increased in size from hydrogen to methyl to tert-butyl, the cone angle of the ligand also increased from 184˚ to 224˚ to 244˚ respectively.7 Furthermore, a bulky substituent at the 3-position, such as a tert-butyl or phenyl moiety, prevents the

7 formation of homoleptic sandwich complexes, [Tp]2M, for first row transition metals.

Conversely, if a less bulky proton or methyl moiety occupies the 3-position, [Tp]2M complexes are common.8

Figure 2. The cone angle () measured for [Tp]Co complexes

Substitution at the 5-position adds steric bulk around the boron atom in the ligand and can result in higher overall ligand stability by protecting the H-B bond.9

Remote substitution on the 5-position of the pyrazole ring has been found to affect the

t environment around the metal center as well. A study comparing [TpBu ]CuCl,

But But But,Me {[Tp ]Cu}2, and [Tp ]Tl with their 5-subsituted counterparts: [Tp ]CuCl,

But,Me But,Me {[Tp ]Cu}2, and [Tp ]Tl, showed that the methyl substitution skewed the pyrazole rings in order to increase the separation between these substituents. This ring- skewing effect results in a different coordination geometry around the metal.9

t t We are interested to see how the substitution in the [TpBu ]Li and [TpBu ,Me]Li complexes affects their coordination to small molecules.

t t 1.2 Synthesis of [TpBu ]Li and [TpBu ,Me]Li Complexes

t t To synthesize [TpBu ]Li and [TpBu ,Me]Li, four equivalents of the appropriate pyrazole was reacted with lithium borohydride in a melt (Scheme 1).

t t Scheme 1. Synthesis of [TpBu ]Li and [TpBu ,Me]Li

An excess of four equivalents of pyrazole was used to serve as both the reagent and the solvent in the reaction. The formation of the mono-, di-, and finally the tri- substituted borohydride was observed via measurement of hydrogen gas evolved from the reaction. The reaction was kept at high temperature until no hydrogen gas evolved and subsequently cooled to room temperature under a stream of nitrogen. For the

t reaction yielding [TpBu ]Li, the excess pyrazole was removed by washing with pentane,

t giving [TpBu ]Li as a clean white solid in high yield (88%). For the reaction yielding

t [TpBu ,Me]Li, the excess pyrazole was removed via sublimation. The remaining pink solid

t was washed with pentane giving [TpBu ,Me]Li in a 49% yield.

t t Crystals of both [TpBu ]Li and [TpBu ,Me]Li were obtained and the solid state structures are shown in Figure 3 and Figure 4. From a visual inspection of the

t t molecular structures of [TpBu ]Li and [TpBu ,Me]Li, the lithium atom adopts a pyramidal geometry (Figure 5).

t Figure 3. Molecular Structure of [TpBu ]Li

t Figure 4. Molecular Structure of [TpBu ,Me]Li

Figure 5. Trigonal pyramidal coordination geometry

To determine the most common coordination modes of lithium, a survey of lithium complexes reported in the CSD was completed. The results of this search are summarized in Table 1. Table 1 only includes compounds in which lithium adopted a single coordination mode (i.e. compounds in which lithium had more than one 8 coordination mode were excluded). In addition, compounds for which the CSD reported lithium as zero coordinate were also excluded because upon further examination, these compounds were not found to be truly zero coordinate.

Table 1. Summary of lithium coordination numbers in structurally characterized compounds listed in the Cambridge Structural Database

Coordination % Number 1 0.9

2 3.7

3 15.6

4 58.7

5 8.3

6 7.5

≥7 5.3

Table 1 indicates that lithium is mostly commonly 3- or 4- coordinate. Since our

t t [TpBu ]Li and [TpBu ,Me]Li complexes are 3-coordinate, we decided to further inspect the

3-coordinate compounds from the CSD. Within these 15.6% of compounds, lithium was found to adopt three distinct geometries: trigonal planar, T-shaped, and pyramidal. In order to objectively classify the lithium chelation environment within these 3-coordinate compounds, a series of requirements was defined for each geometry. Compounds were classified as planar if all three X-Li-X angles ranged from 115˚ – 125˚ and the sum of all

9 three X-Li-X angles was between 355˚ and 360˚. Compounds were considered T-shaped if one X-Li-X angle was ≥ 170˚ and the sum of all three X-Li-X angles was between 355˚ and 360˚. Pyramidal compounds were the 3-coordinate compounds remaining after the planar and T-shaped compounds had been identified. The distribution of 3-coordinate lithium complexes by geometry is provided in Table 2. Table 2 indicates that the majority of 3-coordinate lithium compounds adopt a pyramidal geometry.

Table 2. The geometric classification of 3-coordinate lithium complexes from the

Cambridge Structural Database

Geometry % of total lithium compounds

Planar 0.5

T-shaped 0.1

Pyramidal 15.1

t t The N-Li-N bond angle data for [TpBu ]Li and [TpBu ,Me]Li (Table 3) were used to quantitatively identify the lithium geometry. According to the bond angle criteria

t discussed previously, the lithium center was indeed pyramidal in both [TpBu ]Li and

t [TpBu ,Me]Li. Although a majority of 3-coordinate lithium centers are pyramidal (Table

2), it should be noted that this geometry is still considered uncommon as it accounts for only 15.1% of all reported lithium centers in the CSD.

t t Table 3. Selected bond angles for [TpBu ]Li and [TpBu ,Me]Li

Compound N12–Li–N22/˚ N12–Li–N32/˚ N22–Li–N32/˚

t [TpBu ]Li 98.06(13) 98.06(13) 96.41(16)

t [TpBu ,Me]Li 96.52(12) 97.42(12) 99.91(12)

t t In addition to characterization via X-ray crystallography, [TpBu ]Li and [TpBu ,Me]Li were characterized using 1H, 11B, 15N, and 7Li NMR spectroscopy. Interestingly, in the

t t 1H NMR spectrum of both [TpBu ]Li and [TpBu ,Me]Li complexes, the H-B resonance was a broad doublet (Figure 6); however, in theory, a 1:1:1:1 quartet is expected due to the proton-boron coupling, where boron is a quadrupolar nucleus with a spin (I) of 3/2.10

This proton peak broadening is a result of quadrupolar relaxation on the 11B nucleus and the effect of this relaxation can be clearly seen in variable temperature 1H NMR studies. Figure 6 shows that at low temperatures, the H-B resonance becomes a very broad singlet due to faster relaxation of the proton; conversely at higher temperatures, the relaxation is slower and the expected quartet begins to resolve.10,11

1 But,Me Figure 6. Variable temperature H NMR spectrum of the H-B bond in [Tp ]Li in d8- toluene. (* = impurity)

t t The 11B NMR of the [TpBu ]Li and [TpBu ,Me]Li showed the expected doublet with chemical shift resonances and H-B coupling constants within the range of values observed for other main group [Tp] complexes.5b,12 The chemical shifts and coupling constants of several main group [Tp] complexes are listed in Table 4 for comparison.

t t Table 4. 11B NMR data for [TpBu ]Li and [TpBu ,Me]Li and selected [TpR,R’]M compounds

Compound /ppm 1 Reference JB–H/Hz

t [TpBu ]Li –2.6 109 this work

t [TpBu ,Me]Li –8.5 93 this work

[Tp]K –1.3 105 5b

[TpMe2]K –5.7 -- 12

[TpMe2]Tl –8.0 94 12

Due to the inherently low natural abundance of the 15N nucleus a 2D

Heteronuclear Multiple Bond Correlation (HMBC) experiment observing 15N and 1H was completed in order to observe the nitrogen atoms in the [Tp] ligand.13 The chemical

t shift values for the two nitrogen atoms in the pyrazole ring of both [TpBu ]Li and

t [TpBu ,Me]Li and other main group [Tp] complexes are provided in Table 5.5,14,15

t t Table 5. 15N NMR data for [TpBu ]Li and [TpBu ,Me]Li and selected [TpR,R’]M compounds

Compound (N–B)/ppm (N–M)/ppm /ppma Reference

t [TpBu ]Li –149.1 –101.8 47.3 this work

t [TpBu ,Me]Li –155.1 –105.5 49.6 this work

[Tp]K –141.9 –68.8 73.1 5b

[TpCpr]Tl –150.1 –74.6 75.5 14

[TpCbu]Tl –150.8 –71.9 78.9 14

[TpMe2]K –151.7 –75.3 76.4 15

[TpMe2]Tl –154.6 –74.8 79.8 15 a  =  (N-M) – (N-B)

The chemical shifts for the nitrogen atoms attached to the boron center in

t t [TpBu ]Li and [TpBu ,Me]Li are –149.1 ppm and –155.1 ppm respectively, and are directly within the range of chemical shifts for the corresponding nitrogen atoms in other [Tp]M complexes. The chemical shift values for the nitrogen atoms attached to the metal

t t center are for [TpBu ]Li and [TpBu ,Me]Li are -101.8 ppm and -105.5 ppm respectively, and are further upfield in comparison with the corresponding nitrogen atoms in other

[Tp]M complexes. This shift difference was explained by the fact that these nitrogens are bound to different metals centers and thus have different chemical shift values. As a result of the N-M resonances being further upfield, the chemical shift difference ()

t t between the nitrogen atoms in [TpBu ]Li (47.3 ppm) and [TpBu ,Me]Li (49.6 ppm) was smaller than the  of other main group elements. 14

t t The 7Li NMR of [TpBu ]Li and [TpBu ,Me]Li showed the expected singlets for the

t t lithium atom in the complex. The chemical shift values for [TpBu ]Li and [TpBu ,Me]Li are provided in Table 6. There are no 7Li resonances reported for other [Tp]Li complexes; the values of selected other lithium compounds are listed in Table 6 for comparison.16,17

t t Table 6. 7Li NMR data for [TpBu ]Li and [TpBu ,Me]Li and other selected compounds

Compound /ppm Reference

t [TpBu ,Me]Li 3.2 this work

t [TpBu ]Li 2.7 this work

4 4.2 16a [ -C(SiMe2CH2PPh2)3]Li

– –1.8 16g {Li[(CF3SO2)N]2}

[Li(C211)]+b –1.0 16g

a,c –2.4 17 [Li(NCMe)4][BF4]

[4-Tptm]Li 7.2 17

t t The chemical shift values for the [TpBu ]Li and [TpBu ,Me]Li complexes are found to be in the range of values for other lithium-containing complexes. Obtaining these 7Li

t t data for the [TpBu ]Li and [TpBu ,Me]Li complexes was facile due to the high natural abundance of the 7Li nucleus and was an instrumental technique in our binding affinity studies described in section 1.3.2.

t t 1.3 [TpBu ]Li-L and [TpBu ,Me]Li-L Complexes

t t 1.3.1 Synthesis and Molecular Structures of [TpBu ]Li-L and [TpBu ,Me]Li-L Complexes

The data gleaned from the CSD and listed in Table 1, indicated that three coordinate lithium complexes (15.6%) were not as common as four coordinate complexes (58.7%). Therefore, it was our expectation that these three coordinate [Tp]Li complexes would be able to bind an additional ligand resulting in four coordinate

t t [Tp]Li-L complexes. The [TpBu ]Li and [TpBu ,Me]Li complexes were reacted with acetonitrile, tert-butyl pyrazole and water to form four coordinate complexes, [Tp]Li-L

(Scheme 2).

But But Scheme 2. Addition of small molecules (L = MeCN, Pz H, and H2O) to [Tp ]Li and

t [TpBu ,Me]Li to obtain the [Tp]Li-L adduct

Crystals of the acetonitrile, [Tp]Li(NCMe), adducts were obtained by slow

t t evaporation of solvent from an acetonitrile solution of [TpBu ]Li or [TpBu ,Me]Li

t t complexes. The molecular structures for [TpBu ]Li(NCMe) and [TpBu ,Me]Li(NCMe) are

t shown in Figure 7 and Figure 8. The molecular structures of [TpBu ]Li(NCMe) and

t [TpBu ,Me]Li(NCMe) show that the acetonitrile moiety binds to lithium in a linear fashion through the nitrogen atom.

t t t Crystals for the tert-butyl pyrazole adduct to [TpBu ]Li, [TpBu ]Li(pzBu H), were

t obtained from the slow evaporation of solvent from a solution of [TpBu ]Li and tert-butyl

t t pyrazole in benzene (Figure 9). The molecular structure of [TpBu ]Li(pzBu H) shows that the pyrazole moiety binds to lithium via a dative bonding interaction from the unprotonated nitrogen in the free pyrazole ring.

t Figure 7. Molecular Structure of [TpBu ]Li-NCMe

t Figure 8. Molecular Structure of [TpBu ,Me]Li-NCMe

t t Figure 9. Molecular structure of [TpBu ]Li(pzBu H)

But,Me But But Crystals of the tert-butyl pyrazole adduct, [Tp ]Li(pz H)•(pz H), were obtained from slow evaporation of solvent from a 1:2 pentane: benzene solution of

t [TpBu ,Me]Li and tert-butyl pyrazole (Figure 10). The molecular structure of

But,Me But But [Tp ]Li(pz H)•(pz H) shows that one tert-butyl pyrazole ring is datively bonded to the lithium center and a second tert-butyl pyrazole ring is hydrogen bonded to this pyrazole adduct. This additional hydrogen bonding pyrazolyl moiety is also observed

Me Me Me 18 But But in the [Tp 2]Li(pz 2H)•(pz 2H), however, it is not seen in the [Tp ]Li(pz H) complex, even in the presence of excess tert-butyl pyrazole during the crystallization process.

But,Me But But Figure 10. Molecular structure of [Tp ]Li(pz H)•(pz H)

t Crystals of the aquo adduct to [TpBu ]Li were obtained from slow evaporation of

t a solvent from a solution of [TpBu ]Li in THF containing adventitious water. Instead of

But obtaining the desired product [Tp ]Li(OC4H8), two crystallographically independent

But But molecules of [Tp ]Li(OH2)•2(THF) and [Tp ]Li(OH2) were observed in the asymmetric unit (Figure 11). There is an additional THF molecule hydrogen bonded to

But But water in [Tp ]Li(OH2)•2(THF) which is not observed in the [Tp ]Li(OH2) complex.

But But Figure 11. Molecular structures of [Tp ]Li(OH2)•2(THF) and [Tp ]Li(OH2). These two structures were obtained from the same unit cell (THF molecules which do not participate in hydrogen bonding have been omitted for clarity)

But,Me Crystals of the aquo adduct [Tp ]Li(OH2), were obtained from slow

t evaporation of solvent from a solution of [TpBu ,Me]Li in acetonitrile containing adventitious water (Figure 12).

But,Me Figure 12. Molecular structure of [Tp ]Li(OH2)

But,Me The crystals of another aquo adduct, [Tp ]Li(OH2)•(pzH) were obtained from

t the slow evaporation of solvent from a solution of [TpBu ,Me]Li and pyrazole in a 1:1

t mixture of wet benzene: pentane (Figure 13). Instead of the desired [TpBu ,Me]Li(pzH) product where the pyrazole ring is coordinated to lithium, the aquo adduct was obtained in which pyrazole hydrogen bonds to the water molecule.

But,Me Figure 13. Molecular structure of [Tp ]Li(OH2)•(pzH)

Further investigation of the molecular structures of these four-coordinate [Tp]Li-

L complexes, showed the lithium-nitrogen bond lengths (Table 7) and N-Li-N angles

(Table 8) within the [Tp]Li systems changed upon the addition of a fourth ligand on lithium.

Table 7. Li-N and Li-L bond lengths in the three coordinate [Tp]Li and four coordinate [Tp]Li-L complexes

Compound d(Li– d(Li–N22)/Å d(Li–N32)/Å d(Li–Navg)/Å d(Li–L)/Å N12)/Å

t [TpBu ]Li 1.982(4) 1.994(3) 1.994(3) 1.99 –

t [TpBu ,Me]Li 1.967(3) 1.977(3) 1.965(3) 1.97 –

t [TpBu ]Li(NCMe) 2.067(4) 2.080(4) 2.059(4) 2.07 2.048(5)

t [TpBu ,Me]Li(NCMe) 2.058(3) 2.078(3) 2.006(3) 2.05 2.029(3)

But But 2.137(4) 2.045(4) 2.126(4) 2.10 2.060(4)

24 [Tp ]Li(pz H)

But,Me But But 2.139(8) 2.140(8) 2.057(8) 2.11 2.059(8) [Tp ]Li(pz H)•(pz H)

But a 2.103(7) 2.076(7) 2.057(7) 2.08 1.948(6) [Tp ]Li(OH2)•2(THF)

2.083(7) 2.079(8) 2.093(7) 2.09 1.931(7)

But,Me 2.036(4) 2.061(4) 2.037(4) 2.05 1.975(3) [Tp ]Li(OH2)

But,Me 2.089(4) 2.062(4) 2.026(4) 2.06 1.941(4) [Tp ]Li(OH2)•(pzH)

But (a) two crystallographically independent molecules of [Tp ]Li(OH2) are present in the asymmetric unit, of which one hydrogen bonds to THF (second entry).

The values for the distinct Li-N bond lengths in each complex are provided in

Table 7. The average Li-N bond length value was calculated using only the three Li-N bonds between Li and the [Tp] ligand and does not include the Li-N bonds which are

t present in [Tp]Li(NCMe) or [Tp]Li(pzBu H). These Li-N bond length averages show that

But But,Me the three-coordinate [Tp ]Li and [Tp ]Li complexes have the smallest Li-N averages of 1.99 and 1.97 respectively, meaning the addition of a fourth ligand on lithium results in an elongation of the Li-N bonds within the [Tp]Li moiety. The binding of the tert-

But But But,Me But But butyl pyrazole ligands in [Tp ]Li(pz H) and [Tp ]Li(pz H)•(pz H) attribute to the highest degree of Li-N bond lengthening with a d of 2.10 and 2.11 respectively.

As previously discussed, the N-Li-N bond angles within the three coordinate

t t [TpBu ]Li and [TpBu ,Me]Li complexes show that the metal center adopts a trigonal pyramidal geometry. The distinct bond angles N-Li-N and L-Li-N are provided in

Table 8. These bond angle data was used to calculate the tau 4 (τ4) parameters for each

complex. The τ4 value allows for the determination of the geometry of four coordinate

complexes and is determined based on the equation: 4 = [360 – ( + )]/141, where  +  is the sum of the two largest angles, and allows for the qualitative identification of the

19 four-coordinate geometry. For tetrahedral complexes the 4 = 1 and for square planar

19 complexes the 4 = 0. These calculated values are provided in Table 9.

Table 8. N-Li-N and L-Li-N bond angles in the four coordinate [Tp]Li-L complexes

Compound N12–Li–N22/˚ N12–Li–N32/˚ N22–Li–N32/˚ L–Li–N12/˚ L–Li–N22/˚ L–Li–N32/˚

t [TpBu ]Li(NCMe) 97.34(18) 98.59(18) 93.21(18) 113.7(2) 129.0(2) 119.0(2)

t [TpBu ,Me]Li(NCMe) 98.70(12) 94.89(12) 96.79(12) 118.66(14) 112.90(14) 129.10(15)

t t [TpBu ]Li(pzBu H) 93.59(17) 101.86(14) 93.51(13) 114.26(16) 135.16(18) 112.68(16)

But,Me But But 98.1(3) 93.0(3) 93.1(3) 119.7(4) 114.8(3) 131.0(4) [Tp ]Li(pz H)•(pz H)

But a 96.2(3) 94.2(3) 94.9(3) 121.1(3) 122.1(3) 121.4(4) [Tp ]Li(OH2)•2(THF)

26 96.6(3) 94.7(3) 93.1(3) 121.8(4) 122.2(4) 121.4(4)

But,Me 96.7(2) 95.6(2) 95.6(2) 122.3(2) 114.8(2) 125.6(2) [Tp ]Li(OH2)

But,Me 94.75(16) 95.09(16) 95.17(17) 115.3(2) 126.7(2) 122.5(2) [Tp ]Li(OH2)•(pzH)

But (a) two crystallographically independent molecules of [Tp ]Li(OH2) are present in the asymmetric unit, of which one hydrogen bonds to THF (second entry)

Table 9. τ4 parameters as calculated from the bond angle information obtained from the molecular structures of the four coordinate [Tp]Li-L complexes

Compound L–Li–N range/˚ b 4

t [TpBu ]Li(NCMe) 15.3 0.79

t [TpBu ,Me]Li(NCMe) 16.2 0.80

t t [TpBu ]Li(pzBu H) 22.5 0.78

But,Me But But 16.2 0.76 [Tp ]Li(pz H)•(pz H)

But a 1.0 0.83 [Tp ]Li(OH2)•2(THF)

0.8 0.82

But,Me 11.1 0.79 [Tp ]Li(OH2)

But,Me 11.4 0.79 [Tp ]Li(OH2)•(pzH) a But two crystallographically independent molecules of [Tp ]Li(OH2) are present in the asymmetric unit, of which one hydrogen bonds to THF (second entry). b 19 4 = [360 – ( + )]/141, where  +  is the sum of the two largest angles.

The information in Table 9 shows that all of the four coordinate [Tp]Li-L

complexes significantly deviate from the tetrahedral geometry (4 = 1). The

But,Me But But [Tp ]Li(pz H)•(pz H) complex has a 4 of 0.76 and exhibits the greatest deviation from tetrahedral.

t In addition to characterization via X-ray diffraction, [TpBu ]Li(NCMe),

But,Me But But But,Me But But [Tp ]Li(NCMe), [Tp ]Li(pz H), and [Tp ]Li(pz H)•(pz H) were identified

using NMR spectroscopy. The 11B and 7Li chemical shift and coupling data are provided in Table 10 and Table 11.

t t Table 10. 11B NMR for [TpBu ]Li-L and [TpBu ,Me]Li-L compounds

Compound  (ppm) 1 JB-H (Hz)

t [TpBu ]Li(NCMe) -1.7 86

t [TpBu ,Me]Li(NCMe) -8.0 84

t t [TpBu ]Li(pzBu H) -1.7 108

But,Me But But -7.9 97 [Tp ]Li(pz H)•(pz H)

t t Table 11. 7Li NMR data for [TpBu ]Li –L and [TpBu ,Me]Li-L compounds

Compound  (ppm)

t [TpBu ]Li(NCMe) 2.35

t [TpBu ,Me]Li(NCMe) 2.71

t t [TpBu ]Li(pzBu H) 2.62

But,Me But But 2.93 [Tp ]Li(pz H)•(pz H)

But,Me 3.09 [Tp ]Li(OH2)

Table 10 shows that the 11B NMR chemical shifts and coupling constants for the selected [Tp]Li-L complexes are within the range of values (-1.3 ppm5b– -8.0 ppm12) reported in the literature for main group [Tp]M complexes (Table 4), and that the

t [TpBu ,Me]Li-L resonances are consistently further downfield than the corresponding

t [TpBu ]Li-L shifts. The 7Li chemical shift values for the selected [Tp]Li-L complexes are

quite similar to each other and the shift values (2.4 ppm17 – 7.2 ppm17) for other lithium compounds selected from the literature (Table 6).

t t 1.3.2 DFT Calculations of [TpBu ]Li-L and [TpBu ,Me]Li-L

In order to further probe the binding affinity between Li and L in [Tp]Li-L complexes and the effect of the substituents on the [Tp] ligand, density functional theory calculations were conducted (Table 12). These calculated values represent the mathematical difference in energy between the four coordinate [Tp]Li-L complexes and

t the respective [Tp]Li. For example, the -13.01 kcal/mol for [TpBu ]Li-(PzH) reported in

t t Table 12 is the difference in energies of [TpBu ]Li-(PzH) and [TpBu ]Li.

Table 12. DFT computed H energy changes (kcal mol-1) associated with coordination of a ligand to [Tp]Li

Me But But,Me Compound pzH pz 2H pz H pz H MeCN H2O

t [TpBu ]LiL –13.01 –11.39 –13.19 –11.26 –10.74 –17.95

t [TpBu ,Me]LiL –9.83 –8.76 –10.03 –8.71 –9.61 –15.46

[TpMe,H]LiL –17.85 –18.42 –18.15 –18.62 –13.62 –18.16

[TpMe2]LiL –17.68 –18.20 –17.65 –18.31 –13.33 –17.97

[TpH,H]LiL –18.55 –19.21 –18.95 –19.44 –13.67 –18.00

[TpH,Me]LiL –18.34 –18.95 –18.51 –19.24 –13.25 –17.70

Regarding trends within the [Tp]Li systems, the least substituted [TpH,H]Li-L complexes were the most favorable to form with the overall lowest energies. The addition of a methyl substituent in the [TpMe]Li-L, [TpH,Me]Li-L, and [TpMe2]Li-L complexes did not cause a significant change in their exothermicities compared to

[TpH,H]Li-L; however, substitution of a bulkier tert-butyl moiety on the 3 position in the

t t [TpBu ]Li-L and [TpBu ,Me]Li-L complexes decreases their favorability of formation due to increased steric interactions between the tert-butyl moiety and the L ligand.

Regarding the trends of coordination of the various pyrazoles, acetonitrile and

water to [Tp]Li, the formation of [Tp]Li-(OH2) complexes resulted in high exothermic values overall with little deviation. The calculated energies ranged from -18.00 to -15.46

-1 H,H But,Me kcal mol for [Tp ]Li(OH2) and [Tp ]Li(OH2) respectively. This small variation for the aquo complexes occurs due to the size of the water ligand and its ability to bind to the lithium center in a facile manner regardless of the substituents on the [Tp] ligand.

For pyrazole coordination to [Tp]Li, Table 12 shows similar exothermicities ranging from -17.65 kcal/mol-1 to -19.44 kcal mol-1 when any of the substituted pyrazoles are coordinated to specifically [TpMe,H]Li, [TpMe2]Li, [TpH,H]Li, and [TpH,Me]Li. It was interesting that the calculated values for the coordination of even the bulkiest pyrazoles,

t t pzBu H and pzBu ,MeH, to these [Tp]Li complexes were similar to those of the less substituted pyrazoles, PzH,H. The similarity in these values can be rationalized due to the fact that the bulky tert-butyl moiety in the coordinated pyrazole is positioned away from the [Tp] ligand and thus has little effect on the ability of the pyrazole to coordinate to lithium. A tert-butyl moiety on the [Tp] ligand, however, caused a significant drop in

t t favorability for the formation of [TpBu ]Li-(PzR,R’H) and [TpBu ,Me]Li-(PzR,R’H) due to steric interactions between the tert-butyl moiety on the [Tp] ligand and the coordinating

t pyrazole. For example, the exothermicities for [TpBu ]Li-(PzR,R’H) range from -11.26 kcal

t mol-1 to -13.19 kcal mol-1 and the values for [TpBu ]Li-(PzR,R’H) range from -8.71 kcal mol-

1 to -10.03 kcal mol-1, which are significantly higher than for the less substituted [Tp]Li-

(PzH) systems described above. The calculated exothermicities for the coordination of acetonitrile to [Tp]Li were higher overall, and thus less favorable, than coordination of

t water or pyrazole for all the substituted [Tp]Li systems except for [TpBu ,Me]Li. For

t [TpBu ,Me]Li, the coordination of acetonitrile was more favorable than the coordination of

t the 5-substituted pyrazoles, pzMe2H and PzBu ,MeH.

1.3.3 Equilibrium Studies of [Tp]Li and [Tp]Li-L Complexes

But In order to probe the strength of the Li-L (L = NCMe, pz H, OH2) interactions in

t t the [TpBu ]Li-L and [TpBu ,Me]Li-L complexes experimentally, titration studies were completed. Within these studies, aliquots of L were added to a solution of known

concentration of [Tp]Li in d6-benzene and monitored by NMR. Such use of NMR titration has commonly been used to measure binding constants in host-guest systems.20

7Li NMR spectroscopy proved useful in these studies for two reasons: first, the high natural abundance of the 7Li nucleus allowed for the detection of the [Tp]Li and [Tp]Li-

L complexes in a time-efficient manner. Second, previously discussed NMR data (Table

6 and Table 11) shows that a single lithium resonance was observed for the [Tp]Li and

[Tp]LiL species, allowing us to clearly track the chemical shift change from the three coordinate to four-coordinate complex as the concentration of L increased. The

observed chemical shift (obs) over the course of the titration experiment is the mole

weighted fraction of the chemical shifts of [Tp]Li and [Tp]Li-L complexes in solution

(Equation 1).

obs = Χ[Tp]Li[Tp]LiΧ[Tp]Li-L[Tp]Li-L (Equation 1)

The plots showing the 7Li chemical shift vs. the L concentration are provided in

Figure 14 through Figure 16.

[TpBut]Li + MeCN [TpBut]Li(NCMe) 3.5

7  Li 2.5 (ppm)

1.5 0 10 20 30 40 50 60 70 80

But [MeCN]tot/[[Tp ]Li]init

[TpBut,Me]Li + MeCN [TpBut,Me]Li(NCMe) 3.5

7Li 2.5 (ppm)

1.5 0 10 20 30 40 50 60 70 [MeCN] /[[TpBut,Me]Li] tot init

Figure 14. Plot of the 7Li NMR chemical shift versus concentration of acetonitrile in

But But,Me solutions of [Tp ]Li and [Tp ]Li in d6-benzene

[TpBut,Me]Li + PzButH [TpBut,Me]Li(PzButH) 3.5

3.4

3.3

3.2

3.1

3 0 5 10 15 20 25

But But,Me [Pz H]tot/[[Tp ]Li]init

t Figure 15. Plot of the 7Li NMR chemical shift versus concentration of PzBu H in a

But,Me solution of [Tp ]Li in d6-benzene 34

3.15 But,Me But,Me [Tp ]Li + H2O [Tp ]Li(OH2)

3.1

7Li 3.05 (ppm)

2.95 0 5 10 15 20 25 30 35

But,Me [H2O]tot/[[Tp ]Li]init

Figure 16. Plot of the 7Li NMR chemical shift versus concentration of water in a

But,Me solution of [Tp ]Li in d6-benzene

t Increasing the concentration of MeCN and PzBu H to solution of [Tp]Li complexes was relatively straightforward; the acetonitrile solvent was added with a syringe into

t the NMR sample and aliquots of pre-weighed pzBu H crystals were added directly to the

NMR solution of [Tp]Li in d6-benzene. To increase the water concentration,a saturated solution of water in benzene was prepared and added to a solution of [Tp]Li via syringe. The concentration of water in benzene was a known value of 0.03 M.21

In the case of a 1:1 host-guest complexes, the chemical shift data and the calculated concentrations of [Tp]Li and [L] in the solutions were related by two mathematical equations (Equations 2 and 3 ).20a,22

(Equation 2)

(Equation 3)

In these equations,  is the difference between the observed chemical shift and

the uncomplexed [Tp]Li species; Ka is the binding association constant; [L]0 is the

But known total concentration of L = MeCN, Pz H, H2O; max is the difference in chemical

20a shifts of [Tp]Li-L and [Tp]Li.

Using these equations, two sets of plots were prepared for each titration experiment: a double reciprocal plot for equation 2 and a y-reciprocal plot for equation

t 3. The double reciprocal and y-reciprocal plots for the addition of MeCN, pzBu H, and

H2O to [Tp]Li solutions are in Figure 17 through Figure 20.

Double Reciprocal Plot But But 0.95 [Tp ]Li + MeCN [Tp ]Li(NCMe)

0.9

0.85 R² = 0.9748 1/ -1 (ppm ) 0.8

0.75

0.7 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 1/[MeCN] (L/mol)

y-reciprocal Plot [TpBut]Li + MeCN [TpBut]Li(NCMe) 8

[MeCN]/ 5 R² = 0.9993 (mol/L*ppm) 4

2 2 3 4 5 6 7 8 9 10 11 [MeCN] (mol/L)

Figure 17. Double reciprocal (top) and y-reciprocal plots (bottom) for the addition of

t acetonitrile to [TpBu ]Li

Double Reciprocal Plot [TpBut,Me]Li + MeCN [TpBut,Me]Li(NCMe) 0.8

0.75

0.7 1/ R² = 0.9689 (ppm-1) 0.65

0.6

0.55 0.07 0.17 0.27 0.37 1/[MeCN] (L/mol)

y-reciprocal Plot [TpBut,Me]Li + MeCN [TpBut,Me]Li(NCMe)

7 6 5 [MeCN]/ 4 (mol/L*ppm) R² = 0.9993 3 2 1 2 3 4 5 6 7 8 9 10 11 [MeCN] (mol/L)

Figure 18. Double reciprocal (top) and y-reciprocal plots (bottom) for the addition of

t acetonitrile to [TpBu ,Me]Li

Double Reciprocal Plot [TpBut,Me]Li +PzButH [TpBut,Me]Li(PzButH)

4.3 4.0 R² = 0.9405 3.7 1/ (ppm-1) 3.4 3.1 2.8 2.5 0.2 0.3 0.4 0.5 0.6 1/[PzButH] (L/mol)

y-reciprocal Plot [TpBut,Me]Li +PzButH [TpBut,Me]Li(PzButH) 13 12 11 R² = 0.9491

[PzButH]/10 (mol/L*ppm) 9 8 7 6 1.5 2.0 2.5 3.0 3.5 4.0 4.5 [PzButH] (mol/L)

Figure 19. Double reciprocal (top) and y-reciprocal plots (bottom) for the addition of

t t PzBu H to [TpBu ,Me]Li

Double Reciprocal Plot But,Me But,Me [Tp ]Li + H2O [Tp ]Li(OH2) 14 13 12 11 1/ R² = 0.9765  10 (ppm-1) 9 8 7 6 50 60 70 80 90 100 110

1/[H2O] (L/mol)

y-reciprocal Plot But,Me But,Me [Tp ]Li + H2O [Tp ]Li(OH2) 0.16

0.15

0.14 R² = 0.9411 [H2O]/ 0.13 (mol/L*ppm) 0.12

0.11

0.1 0.008 0.01 0.012 0.014 0.016 0.018 0.02

[H2O]

Figure 20. Double reciprocal (top) and y-reciprocal plots (bottom) for the addition of

t water to [TpBu ,Me]Li

Figure 17 and Figure 18 show that the experimental data for the addition of

t t acetonitrile to solutions of [TpBu ]Li or [TpBu ,Me]Li is more linear, with a higher R2 value than the double reciprocal plot. Therefore, equation 3 was a better mathematical model for the data. The binding constants were calculated for these experiments and are provided in

Table 13.

But Table 13. Binding association, Ka, values for the addition of MeCN to [Tp ]Li and

t [TpBu ,Me]Li

Reaction -1 Binding constant, Ka (M )

t t 23 [TpBu ]Li + MeCN [TpBu ]Li(NCMe) 0.84

t t [TpBu ,Me]Li + MeCN [TpBu ,Me]Li(NCMe) 0.96

The Ka values for these reactions are close to 1, meaning that in solution, the dissociation of acetonitrile is facile and that the three species: [Tp]Li, L, and [Tp]Li-L are all present at equilibrium. As further proof of this facile dissociation, pumping on

t t crystals of the [TpBu ]Li-NCMe and [TpBu ,Me]Li-NCMe in vacuo at room temperature for 40 minutes resulted in the removal of acetonitrile as indicated by 1H NMR.

Using the experimentally determined Ka value for the addition of acetonitrile to the [Tp]Li complexes, the free energy value, G, was calculated for each reaction using equation 4. This equation mathematically relates the binding constant, K, with the free energy, G, where R is the gas constant and T is the temperature in Kelvin. The G values for the acetonitrile to the [Tp]Li are reported in Table 14.

G° = -RTlnK (Equation 4)

Table 14. Experimentally determined free energy values (G) for the addition of MeCN

t t to [TpBu ]Li and [TpBu ,Me]Li

Reaction G° (kcal/mol)

t t [TpBu ]Li + MeCN [TpBu ]Li(NCMe) 0.02

t t [TpBu ,Me]Li + MeCN [TpBu ,Me]Li(NCMe) 0.09

These values further show that [Tp]Li, L, and uncomplexed [Tp]Li-L are equally present and are at equilibrium in solution. The thermodynamic values, H, S, and G

t t for [TpBu ]Li-NCMe and [TpBu ,Me]Li-NCMe complexes were also calculated using DFT and are reported in Table 15. The calculated G values correlate with the experimentally determined free energies.

Table 15. DFT calculated thermodynamic values for the coordination of MeCN to

t t [TpBu ]Li and [TpBu ,Me]Li

H/kcal mol–1 S/cal K–1 mol–1 G/kcal mol–1 a

t [TpBu ]LiNCMe –10.92 –36.2 –0.11

t [TpBu ,Me]LiNCMe –8.14 –34.0 2.00

The values in Table 15 indicate that the coordination of acetonitrile to both of the

[Tp]Li complexes to form [Tp]Li-NCMe is enthalpically favored, however, the highly unfavorable entropy of formation of [Tp]Li-NCMe results in free energy values close to zero. These computed values confirm our experimental observations that the dissociation of acetonitrile from [Tp]Li is facile in solution.

t t The experimental data for the titration of pzBu H to a solution of [TpBu ,Me]Li exhibits non-linear character in both the double reciprocal and y-reciprocal plots. The

same non-linear behavior is seen in the plots for the titration of H2O to a solution of

t [TpBu ,Me]Li as well. Since neither equations 2 or 3 accurately model these processes, it was hypothesized that perhaps these compounds were not forming 1:1 host-guest

t t complexes in solution. The molecular structures of the [TpBu ,Me]Li(pzBu H),

But But,Me [Tp ]Li(OH2) and [Tp ]Li(OH2) in Figure 10, Figure 11, and Figure 13 show that these complexes do not form 1:1 complexes. In fact, the L moieties all have more complex interactions with other molecules through hydrogen bonding and form

But,Me But But But But,Me [Tp ]Li(pz H)•(pz H), [Tp ]Li-OH2•(THF) and [Tp ]Li-OH2•(pzH). These hydrogen bonds in the solid state give further indication that there could also be more complex binding in solution resulting in multiple equivalents of L complexing to [Tp]Li which are not modelled by equations 2 and 3.

1.4 Reactivity of [TpR,R]Li complexes with Cadmium Halide Salts

It was in our interest to investigate the reactivity of the newly synthesized [Tp]Li complexes and due to the widespread use of lithium as a transmetallation agent,1-3,6,7 we decided to synthesize a series of [Tp] cadmium halide complexes. In general, [Tp] cadmium complexes are of interest because they provide insight into the structure of

cadmium-substituted carbonic anhydrase. The [Tp] ligand is highly suited to model this enzyme because the three pyrazole rings are similar in structure to the tris-histidine motif at the active site24,25 and the ligand holds the metal center in a pseudotetrahedral geometry analogous to that in the enzyme.25,26 The 113Cd nucleus has also been shown to serve as an effective spectroscopic probe for the zinc carbonic anhydrase analogue which features a diamagnetic Zn2+ center.27

Cadmium halide complexes [Tp]CdX (X = Cl, Br, I) with various substitutions on

t the [Tp] ligand have been synthesized previously;28 however, [TpBu ,Me]CdX complexes have not been reported or characterized. These complexes were successfully

t synthesized via reaction of the appropriate cadmium halide salt and [TpBu ,Me]Li (Scheme

3).

t Scheme 3. Synthesis of [TpBu ,Me]CdX (X = Cl, Br, I)

Scheme 3 shows our synthesis omits the use of toxic [Tp]Tl, which is a common precursor to [Tp]CdX complexes reported in the literature.28e,f,g The molecular

t structures of [TpBu ,Me]CdX are provided in Figure 21 through Figure 23.

But,Me Figure 21. Molecular structure of [Tp ]CdCl●C6H6 (solvent is omitted for clarity)

t Figure 22. Molecular structure of [TpBu ,Me]CdBr (disordered atoms are omitted for clarity)

But,Me Figure 23. Molecular structure of [Tp ]CdI●C6H6 (solvent is omitted for clarity) 46

The solid state structures show that the cadmium center is four-coordinate in all the [Tp]CdX complexes. The N-Cd-N and X-Cd-N bond angles for the complexes are

listed in Table 16 and the 4 parameters were calculated from these bond angles. The 4

t values show that the cadmium metal in [TpBu ,Me]CdX adopts a distorted tetrahedral geometry.

Table 16. N-Cd-N and X-Cd-N bond angles in the four coordinate [Tp]CdX complexes

Compound N12–Li–N22/˚ N12–Li–N32/˚ N22–Li–N32/˚ L–Li–N12/˚ L–Li–N22/˚ L–Li–N32/˚

But,Me [Tp ]CdCl●C6H6 89.4(2) 90.1(2) 87.3(2) 126.12(16) 126.71(17) 125.23(16)

t [TpBu ,Me]CdBr 85.50(7) 90.40(7) 90.13(7) 125.73(5) 130.78(5) 122.08(5)

But,Me [Tp ]CdI●C6H6 86.45(6) 86.36(6) 90.54(6) 125.92(5) 128.51(4) 126.05(4)

Table 17. τ4 parameters as calculated from the bond angle information obtained from the molecular structures of the four coordinate [Tp]CdX complexes

Compound X-Cd-N range/° 4

But,Me 1.48 0.76 [Tp ]CdCl●C6H6

t [TpBu ,Me]CdBr 8.7 0.73

But,Me 2.59 0.75 [Tp ]CdI●C6H6

t The M-N bond lengths in the [TpBu ,Me]CdX complexes are significantly longer than the corresponding lengths in the [Tp]Li and [Tp]Li-L complexes (Table 7) by 0.2Å,

t with [TpBu ,Me]CdI having the longest M-N bonds with a M-N average of 2.254Å (Table

18). These elongated bond lengths do, however, correspond closely with the M-N lengths reported in other [Tp]CdX complexes which range from 2.22Å in [TpiPr2]CdBr28h

t to 2.25Å in [TpBu ]CdI.28e

Table 18. Cd-N and Cd-X bond lengths in the [Tp]CdX complexes

Compound d(Cd-N12)/Å d(Cd-N22)/Å d(Cd-N32)/Å d(Cd-N)avg/Å d(Cd-X)/Å Reference

t [TpBu ]CdCl 2.234 2.248 2.248 2.243 2.354 28d

t [TpBu ]CdI 2.233 2.256 2.256 2.248 2.674 28e

But,Me [Tp ]CdCl●C6H6 2.222(6) 2.248(7) 2.231(7) 2.234 2.3569(19) this work

t [TpBu ,Me]CdBr 2.2356(19) 2.2542(18) 2.2486(18) 2.246 2.4886(3) this work

But,Me [Tp ]CdI●C6H6 2.2557(18) 2.2554(17) 2.2494(17) 2.254 2.6740(2) this work

Table 18 also lists the Cd-X bond lengths for each complex, the Cd-X bond length

t t is longest in [TpBu ,Me]CdI complex out of the series of [TpBu ,Me]CdX complexes. The

t t same trend is seen when in a comparison of [TpBu ]CdCl28d and [TpBu ]CdI28e, in which the Cd-X bond length is longest for the cadmium iodide complex. Interestingly, a

t t comparison between [TpBu ]CdX and [TpBu ,Me]CdX shows no significant change in Cd-X bond lengths as a result of substitution.

t The [TpBu ,Me]CdX complexes were also characterized via NMR spectroscopy. The

11B NMR chemical shift resonances are listed in Table 19.

t Table 19. 11B NMR data for the [TpBu ,Me]CdX complexes

1 Compound /ppm JH-B/Hz

t [TpBu ,Me]CdCl -8.6 94

t [TpBu ,Me]CdBr -8.7 84

t [TpBu ,Me]CdI -8.5 80

11 1 But,Me The B NMR chemical shift data and JH-B coupling constants for the [Tp ]CdX complexes correlate closely with each other with the chemical shift data ranging from -

8.5 – -8.7 ppm and the coupling constants ranging from (80 - 102 Hz). This NMR

t chemical shift data also corresponds with the shifts for other [TpBu ,Me]M complexes

t t t including, [TpBu ,Me]Li (-8.5 ppm, Table 4) and [TpBu ,Me]Li-(NCMe) and [TpBu ,Me]Li-

But But 11 (Pz H)●(Pz H) which are -8.0 ppm and -7.9 ppm respectively (Table 10). The B 51

NMR data for other [Tp]CdX reported in the literature was not available for comparison.

t This investigation of the reactivity of [TpBu ,Me]Li shows that these complexes do indeed provide access to other [Tp]M complexes and can replace more toxic complexes, such as [Tp]Tl, as transmetallating agents.

1.5 Conclusion

The molecular structures of the first three-coordinate lithium [Tp] complexes,

t t [TpBu ]Li and [TpBu ,Me]Li, are reported and the lithium center is shown to adopt an unusual trigonal pyramidal geometry. Furthermore, experimental evidence and DFT calculations showed that these [Tp]Li complexes have the ability to favorably bind

But small molecules (MeCN, pz H, and H2O) to form four-coordinate [Tp]Li-L adducts.

Experimental studies and thermodynamic DFT calculations of the coordination of

t t MeCN to both [TpBu ]Li and [TpBu ,Me]Li showed that the MeCN moiety easily dissociates from the [Tp]Li complex in solution, resulting in the presence of [Tp]Li, L, and [Tp]Li-L

t t at equilibrium. Additionally, [TpBu ,Me]Li provides access to new [TpBu ,Me]CdX complexes, preventing the need to use the toxic [Tp]Tl complex as a precursor.

1.6 Experimental Section

1.6.1 General Considerations

NMR spectra were measured on Bruker 300 DRX, Bruker 400 DRX, and Bruker Avance

1 500 DMX spectrometers. H NMR spectra are reported in ppm relative to SiMe4 ( = 0) and were referenced internally with respect to the protio solvent impurity ( 7.16 for

29 13 C6D5H,  2.08 C7D7H). C NMR spectra are reported in ppm relative to SiMe4 ( = 0)

29 7 and were referenced internally with respect to the solvent ( 128.06 for C6D6). Li NMR

spectra are reported in ppm relative to a solution of 1 M LiCl in D2O ( = 0.0) as an

30 11 external standard. B NMR spectra are reported in ppm relative to BF3(OEt2) ( = 0.0) as an external standard.31 15N NMR chemicals shifts (obtained by 1H–15N HMBC

32a experiments) are reported in ppm relative to MeNO2 ( = 0.0) and were obtained by using the /100% value of 10.136767.32 Coupling constants are given in hertz. IR spectra were recorded as KBr pellets on a Nicolet Avatar 370DTGS and the data are reported in reciprocal centimeters (cm–1). Mass spectra were obtained on a JEOL JMS-

HX110HF tandem mass spectrometer using fast atom bombardment (FAB). Lithium borohydride (Strem), pyrazole (Aldrich), 3-tert-butyl-5-methylpyrazole (Richman

Chemical, Inc.) were obtained commercially. 3-Tert-butylpyrazole7 was synthesized according to literature methods. The cadmium halide salts cadmium chloride (Strem), cadmium bromide (Strem), and cadium iodide (Alfa Aesar) were also obtained 53

commercially.

1.6.2 X-ray Structure Determination

Single crystal X-ray diffraction data were collected on a Bruker Apex II diffractometer and crystal data, data collection and refinement parameters are summarized in Table 20.

The structures were solved using direct methods and standard difference map techniques, and were refined by full-matrix least-squares procedures on F2 with

SHELXTL (Version 6.12).33

1.6.3 Computational Details

Calculations were carried out using DFT as implemented in the Jaguar 7.5 (release 2007) suite of ab initio quantum chemistry programs.34 Geometry optimizations and frequency calculations were performed with the B3LYP density functional35 using the 6-

31G** (H, Li, B, C, N, Cl) and LAV3P (Br, I Cd) basis sets,36 that were also used for obtaining thermodynamic data for the calculation of G.

t 1.6.4 Synthesis of [TpBu ]Li

A mixture of 3-tert-butylpyrazole (30.05 g, 0.24 mol) and LiBH4 (1.38 g, 0.06 mol) was heated to 203 ˚C over 3 hours until no more dihydrogen was evolved. The reaction was allowed to cool under a nitrogen atmosphere, thereby forming a hard white solid, which was crushed in air, washed with pentane (100 mL) to remove excess 3-tert-

t butylpyrazole and dried in vacuo to give [TpBu ]Li as a white solid (20.11 g, 82%).

Crystals suitable for X-ray diffraction were obtained by slow evaporation of a solution in a mixture of pentane and benzene (1:1 by volume). Anal. calcd. for

HB{C3N2H2CMe3}3Li: C, 65.0%; H, 8.8%; N, 21.6%. Found: C, 64.4%; H, 8.6%; N, 21.5%.

1 H NMR (C6D6):  1.27 [s, 27H, HB{C3N2H2CMe3}3Li], 4.84 [br, 1H, HB{C3N2H2CMe3}3Li],

3 3 5.90 [d, 3H, JH-H = 2 Hz, HB{C3N2H2CMe3}3Li], 7.58 [d, 3H, JH-H = 2 Hz,

13 1 HB{C3N2H2CMe3}3Li]. C{ H} NMR (C6D6):  30.8 [s, 9C, HB{C3N2H2C(CH)3}3Li], 31.8 [s,

3C, HB{C3N2H2C(CH)3}3Li], 100.1 [s, 3C, HB{C3N2H2C(CH)3}3Li], 135.4 [s, 3C,

11 HB{C3N2H2C(CH)3}3Li], 161.5 [s, 3C, HB{C3N2H2C(CH)3}3Li]. B NMR (C6D6):  –2.63 [d,

1 7 15 JB-H = 109 Hz]. Li NMR (C6D6):  2.74 [s]. N NMR (C6D6):  –149.1 [s, B–N], –101.8 [s,

–1 Li–N]. IR data (KBr disk, cm ): 3568 (m), 3435 (m), 2961 (s), 2867 (w), 2426 (w) [B-H],

1618 (m), 1506 (m), 1461 (w), 1363 (m), 1255 (m), 1199 (s), 1160 (m), 1036 (s), 774 (w), 735

t (s) 720 (w). FAB MS: m/z = 387.3 [M]+, M = [TpBu ]Li.

t 1.6.5 Synthesis of [TpBu ,Me]Li

A mixture of 3-tert-butyl-5-methylpyrazole (5.02 g, 0.04 mol) and LiBH4 (0.20 g, 0.01 mol) was gradually heated to 212 ˚C over 2 hours until no more dihydrogen was evolved. The mixture was allowed to cool under a nitrogen atmosphere and the excess

3-tert-butyl-5-methylpyrazole was removed by sublimation. The off-white residue was

t washed with pentane (40 mL) and dried in vacuo to give [TpBu ,Me]Li as a light pink solid

(1.93 g, 49%). Colorless crystals suitable for X-ray diffraction were obtained by slow

evaporation from a solution in benzene. Anal. calcd. for HB{C3N2H(CH3)CMe3}3Li: C,

1 67.0%; H, 9.4%; N, 19.5%. Found: C, 66.9%; H, 9.2%; N, 19.5%. H NMR (C6D6)  1.31 [s,

27H, HB{C3N2H(CH3)CMe3}3Li], 2.32 [s, 9H, HB{C3N2H(CH3)CMe3}3Li], 4.96 [br, 1H,

13 1 HB{C3N2H(CH3)CMe3}3Li], 5.71 [s, 3H, HB{C3N2H(CH3)CMe3}3Li]. C{ H} NMR (C6D6) 

12.5 [s, 3C, HB{C2N2CH(CH3)C(Me)3}3Li], 30.8 [s, 9C, HB{C2N2CH(CH3)C(Me)3}3Li], 31.7

[s, 3C, HB{C2N2CH(CH3)C(Me)3}3Li], 100.8 [s, 3C, HB{C2N2CH(CH3)C(Me)3}3Li], 143.5 [s,

11 3C, HB{C2N2CH(CH3)C(Me)3}3Li], 160.0 [s, 3C, HB{C2N2CH(CH3)C(Me)3}3Li]. B NMR

1 7 15 (C6D6)  -8.52 [d, JB-H = 93 Hz]. Li NMR (C6D6):  3.21 [s]. N NMR (C6D6):  –155.1 [s,

–1 B–N], –105.5 [s, Li–N]. IR data (KBr disk, cm ): 2957 (s), 2860 (m), 2509 (m) [B-H], 1539

(s), 1484 (m), 1468 (m), 1441 (m), 1384 (m), 1356 (s), 1244 (m), 1181 (s), 1060 (s), 1026 (m),

974 (w), 775 (s), 762 (s), 647 (s), 520 (w).

t 1.6.6 Synthesis of [TpBu ]Li(NCMe)

t A solution of [TpBu ]Li (14.8mg, 0.03 mmol) in acetonitrile (0.7 mL) was allowed to

t evaporate overnight, thereby resulting in the formation of [TpBu ]Li(NCMe) as colorless

1 37 crystals (14 mg, 86%) that were suitable for X-ray diffraction. H NMR (C6D6):  1.17 [s,

29,38 3H, HB{C3N2H2CMe3}3Li(NCMe)], 1.39 [s, 27H, HB{C3N2H2CMe3}3Li(NCMe)], 4.97

3 [“d”, HB{C3N2H2CMe3}3Li(NCMe)], 6.00 [d, JH-H = 2 Hz, 3H,

3 1 HB{C3N2H2CMe3}3Li(NCMe)], 7.65 [d, JH-H = 2 Hz, 3H, HB{C3N2H2CMe3}3Li(NCMe)]. H

NMR (CD3CN):  1.33 [s, 27H, HB{C3N2H2CMe3}3Li(NCMe)], 4.47 [br, 1H,

3 HB{C3N2H2CMe3}3Li(NCMe)], 5.93 [d, 3H, JH-H = 2 Hz, HB{C3N2H2CMe3}3Li], 7.45 [d, 3H,

3 13 1 37 JH-H = 2 Hz, HB{C3N2H2CMe3}3Li]. C{ H} NMR (C6D6):  –0.27 [s, 1C,

HB{C3N2H2CMe3}3Li{NCMe}], 31.1 [s, 9C, HB{C3N2H2CMe3}3Li{NCMe}], 31.8 [s, 3C,

HB{C3N2H2CMe3}3Li{NCMe}], 100.2 [s, 3C, HB{C3N2H2CMe3}3Li{NCMe}], 117.8

[HB{C3N2H2CMe3}3Li{NCMe}], 134.9 [s, 3C, HB{C3N2H2CMe3}3Li{NCMe}], 162.0 [s, 3C,

11 37 1 7 HB{C3N2H2CMe3}3Li{NCMe}]. B NMR (C6D6):  -1.72 [d, JB-H = 86 Hz]. Li NMR

37 7 –1 (C6D6):  2.35 [s]. Li NMR (CD3CN):  1.57 [s]. IR data (KBr disk, cm ): 3211 (m), 3107

(w), 2962 (s), 2904 (w), 2869 (m), 2436 (m) [B-H], 2274 (m) [N-C], 1625 (w), 1507 (s), 1483

(m), 1462 (m), 1391 (w), 1365 (s), 1299 (w), 1255 (m), 1204 (s), 1164 (m), 1104 (m), 1050

(s), 1004 (m), 933 (m), 878 (w), 793 (m), 770 (s), 740 (s). The acetonitrile ligand can be

t t removed from [TpBu ]Li(NCMe), thereby regenerating [TpBu ]Li, by placing the sample in vacuo for 40 minutes.

t 1.6.7 Synthesis of [TpBu ,Me]Li(NCMe)

t A solution of [TpBu ,Me]Li (9 mg, 0.02 mmol) in acetonitrile (0.7 mL) was allowed to

t evaporate overnight, thereby resulting in the formation of [TpBu ,Me]Li(NCMe) as

colorless crystals (9.7 mg, 98%) that were suitable for X-ray diffraction. 1H NMR

37 (C6D6):  0.68 [s, 3H, HB{C3N2H(CH3)CMe3}3Li{NCCH3}], 1.39 [s, 27H,

HB{C3N2H(CH3)CMe3}3Li{NCCH3}], 2.35 [s, 9H, HB{C3N2H(CH3)CMe3}3Li{NCCH3}], 5.04

[“d”, 1H, HB{C3N2H(CH3)CMe3}3Li{NCCH3}], 5.77 [s, 3H,

1 HB{C3N2H(CH3)CMe3}3Li{NCCH3}]. H NMR (CD3CN):  1.29 [s, 27H,

HB{C3N2H(CH3)CMe3}3Li(NCMe)], 2.36 [s, 9H, HB{C3N2H(CH3)CMe3}3Li(NCMe)], 4.77

1 [d, 1H, JB-H= 126 Hz, HB{C3N2H(CH3)CMe3}3Li(NCMe)], 5.71 [s, 3H,

13 HB{C3N2H(CH3)CMe3}3Li(NCMe)]. C NMR (C6D6):  -0.33 [s, 1C,

HB{C3N2H(CH3)CMe3}3Li{NCCH3}], 12.6 [s, 3C, HB{C3N2H(CH3)CMe3}3Li{NCCH3}], 30.8

[s, 9C, HB{C3N2H(CH3)CMe3}3Li{NCCH3}], 31.6 [s, 3C,

HB{C3N2H(CH3)CMe3}3Li{NCCH3}], 100.9 [s, 3C, HB{C3N2H(CH3)CMe3}3Li{NCCH3}],

117.2 [s, 1C, HB{C3N2H(CH3)CMe3}3Li{NCCH3}], 142.9 [s, 3C,

HB{C3N2H(CH3)CMe3}3Li{NCCH3}], 160.1 [s, 3C, HB{C3N2H(CH3)CMe3}3Li{NCCH3}].

11 1 7 7 B NMR (C6D6):  - 8.04 [d, JB-H = 84 Hz] . Li NMR (C6D6):  2.71 [s]. Li NMR

–1 (CD3CN):  1.57 [s]. IR data (KBr disk, cm ): 3501 (w), 2957 (s), 2926 (m), 2903 (m), 2865

(w), 2516 (m) [B-H], 2276 (w) [N-C], 1538 (s), 1486 (m), 1467 (m), 1427 (m), 1362 (m), 1346

(s), 1243 (m), 1192 (s), 1176 (s), 1063 (s), 1023 (w), 1011(m), 980 (w), 851 (w), 775 (s), 650

t (m). The acetonitrile ligand can be removed from [TpBu ,Me]Li(NCMe) by in vacuo

t treatment for 40 minutes to yield [TpBu ,Me]Li as a white solid.

t t 1.6.8 Synthesis of [TpBu ]Li(pzBu H)

t A solution of [TpBu ]Li (24 mg, 0.06 mmol) in benzene (ca. 0.5 mL) was treated with 3- tert-butylpyrazole (9 mg, 0.07 mmol) and mixed with a pipette for 1 minute to give a

t t colorless solution. The mixture was lyophilized to give [TpBu ]Li(pzBu H) as a white solid

(30 mg, 94%). Crystals suitable for X-ray diffraction were obtained by slow evaporation from a solution in a mixture of pentane and benzene (1:1 by volume). 1H NMR

37,39 (C6D6):  1.18 [s, 9H, HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}], 1.31 [s, 27H,

HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}], 4.95 [“d”, 1H,

3 HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}], 5.95 [d, JH-H = 2 Hz, 1H,

3 HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}], 5.98 [d, JH-H = 2 Hz, 3H,

HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}], 7.31 [br, 1H,

3 HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}], 7.64 [d, JH-H = 2 Hz, 3H,

HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}], not observed

13 1 37 [HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}]. C{ H} NMR (C6D6):  30.2 [s, 3C,

HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}]. 30.9 [s, 1C,

HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}], 31.0 [s, 9C,

HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}], 31.8 [s, 3C,

HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}], 100.4 [s, 3C,

HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}], 101.2 [s, 2C,

HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}], not observed [s, 1C,

HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}], 135.4 [s, 3C,

HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}], 162.4 [s, 3C,

11 37 1 7 HB{C3N2H2CMe3}3Li{C3H2(CMe3)N2H}]. B NMR (C6D6):  -1.67 [d, JB-H = 108]. Li

37 But But NMR (C6D6):  2.62 [s]. Solutions of [Tp ]Li(pz H) convert over a period of ca. 1 hour to another species that is identified by a 7Li NMR chemical shift of –3.12 [s]. IR data (KBr disk, cm–1): 3506 (w), 3422 (w), 3186 (m), 3102 (m), 2963 (s), 2905 (m), 2868 (m),

2465 (w) [B-H], 1659 (w), 1572 (w), 1506 (m), 1468 (s), 1365 (s), 1302 (m), 1251 (s), 1204 (s),

1164 (m), 1106 (s), 1050 (s), 992 (s), 934 (s), 872 (w), 771 (s), 738 (m).

But,Me But But 1.6.9 Synthesis of [Tp ]Li(pz H)•(pz H)

t A solution of [TpBu ,Me]Li (20 mg, 0.05 mmol) in benzene (ca. 0.5 mL) was treated with 3- tert-butylpyrazole (6 mg, 0.05 mmol) and mixed with a pipette for 1 minute to give a

t t colorless solution. The mixture was lyophilized to give [TpBu ,Me]Li(pzBu H) as a white

1 37 solid (18 mg, 69%). H NMR (C6D6):  1.21 [s, 9H,

HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}], 1.32 [s, 27H,

HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}], 2.35 [s, 9H,

HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}], 5.03 [“d”,

HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}], 5.76 [s, 3H,

3 HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}], 5.98 [d, JH-H = 1 Hz, 1H,

HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}], 7.41 [br, 1H,

HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}], 11.62 [br, 1H,

13 1 37 HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}]. C{ H} NMR (C6D6):  12.7 [s, 3C,

HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}], 30.1 [s, 1C,

HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}],30.8 [s, 12C,

HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}], 31.6 [s, 3C,

HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}], 101.0 [s, 1C,

HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}], 101.1 [s,

HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}], not observed [s, 1C,

HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}], 143.1 [s, 3C,

HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}]. 160.4 [s, 3C,

11 37 1 HB{C3N2H(CH3)CMe3}3Li{C3H2(CMe3)N2H}]. B NMR (C6D6):  –7.93 [d, JH-H = 97 Hz].

7 –1 Li NMR (C6D6):  2.93 [s]. IR data (KBr disk, cm ): 3380 (m), 3197 (m), 3116 (m), 2961

(s), 2905 (w), 2867 (m), 2555 (w) [B-H], 1623 (w), 1540 (s), 1467 (s), 1426 (s), 1361 (s), 1342

(m), 1035 (w), 1245 (m), 1189 (s), 1102 (m), 1064 (s), 1011 (w), 982 (m), 933 m), 878 (w),

But,Me But But 842 (w), 774 (s), 714 (w), 647 (m). Crystals of composition [Tp ]Li(pz H)•(pz H) suitable for X-ray diffraction were obtained by slow evaporation from a solution in a mixture of pentane and benzene (1:2 by volume).

But,Me 1.6.10 Synthesis of [Tp ]Li(OH2)

t A solution of [TpBu ,Me]Li (16 mg, 0.04 mmol) was dissolved in acetonitrile (ca. 0.5 mL).

But,Me Crystals of [Tp ]Li(OH2) (14 mg, 86%) suitable for X-ray diffraction via reaction with adventitious water were obtained upon slow evaporation of the solvent.

But 1.6.11 Synthesis of [Tp ]Li(OH2)•2(THF)

t A solution of [TpBu ]Li (6 mg, 0.01 mmol) in THF (ca. 0.5 mL) was allowed to undergo

But slow evaporation, thereby depositing crystals of [Tp ]Li(OH2)•2(THF) (5 mg, 72%) suitable for X-ray diffraction via reaction with adventitious water.

But,Me 1.6.12 Synthesis of [Tp ]Li(OH2)•(pzH)

t A solution of [TpBu ,Me]Li (18 mg, 0.4 mmol) in 1:1 mixture of wet benzene/pentane (ca. 1

But,Me mL) was treated with pyrazole (4 mg, 0.06 mmol). Crystals of [Tp ]Li(OH2)•(pzH)

(21 mg, 97%) suitable for X-ray diffraction were obtained via slow evaporation of solvent.

t t 1.6.13 [TpBu ,R]Li and [TpBu ,R]LiL Equilibrium Studies

But,R But Solutions of [Tp ]Li in C6D6 were treated with aliquots of either MeCN, pz H, or a

21 7 saturated solution of H2O in C6D6 (0.036 M) and monitored by Li NMR spectroscopy, as illustrated in Figures Figure 14 – Figure 16. For situations in which there is a large

excess of MeCN such that [MeCN] ≈ [MeCN]tot (i.e. the total concentration of MeCN, whether coordinated or uncoordinated), the equilibrium constants for coordination of

MeCN may be obtained by using the relationship [MeCN]tot/ = 1/(Kmax) +

But,R [MeCN]tot/max, where (i)  = {[Tp ]Li(NCMe)} – obs, and (ii) max is the maximum

20a value of . Specifically, a plot of [MeCN]tot/ versus [MeCN]tot over a region in

But,R which [MeCN]tot > 10 [[Tp ]Li]init is linear and K = slope/intercept (Figures Figure 17 and Figure 18).

t 1.6.14 Synthesis of [TpBu ,Me]CdCl

To a clear, colorless solution of tris(3-tert-butyl-5-methyl-pyrazolyl)hydroborato lithium

(11 mg, 0.03 mmol) in benzene (ca. 0.5 mL), anhydrous cadmium chloride (27 mg, 0.15 mmol) was added. White precipitate formed immediately as the reaction was mixed.

After mixing for 3 days, the salt impurity and excess cadmium chloride was removed

t via filtration and the motherliquor was lyophilized to reveal [TpBu ,Me]CdCl as a white

But,Me solid (9 mg, 62%). Crystals of [Tp ]CdCl•C6D6 suitable for X-ray diffraction were

t obtained from slow evaporation of benzene. Anal. calcd. for [TpBu ,Me]CdCl: C, 51.57%;

1 H, 7.08%; N, 14.32%. Found: C, 51.55%; H, 7.26%; N, 14.26%. H NMR (C6D6): 1.47 [s,

1 27H, HB{C3N2H(CH3)CMe3}3CdCl], 2.12 [s, 9H, HB{C3N2H(CH3)CMe3}3CdCl], 4.97 [d, JB-

H = 137 Hz, 1H, HB{C3N2H(CH3)CMe3}3CdCl], 5.67 [s, 3H, HB{C3N2H(CH3)CMe3}3CdCl].

13 1 C{ H} NMR (C6D6): 12.8 [s, 3C, HB{C2N2CH(CH3)C(Me)3}3CdCl], 30.6 [s, 9C,

HB{C2N2CH(CH3)C(Me)3}3CdCl], 31.6 [s, 3C, HB{C2N2CH(CH3)C(Me)3}3CdCl], 103.0 [s,

3C, HB{C2N2CH(CH3)C(Me)3}3CdCl], 144.9 [s, 3C, HBC2N2CH(CH3)C(Me)3}3CdCl], 163.3

11 1 11 1 [s, 3C,HB{C2N2CH(CH3)C(Me)3}3CdCl]. B NMR(C6D6): -8.62 [d, JB-H = 95 Hz]. B{ H}

-1 NMR (C6D6): -8.73 [s, 1B]. IR Data (KBr disk, cm ): 2963 (s), 2939 (w), 2905 (w), 2865

(w), 2570 (w) [B-H], 1539 (m), 1471 (w), 1431 (m), 1365 (m), 1340 (w), 1243 (w), 1184 (s),

1072 (m), 1029 (w), 978 (w), 786 (w), 767 (w), 650 (w). FAB-MS: 571.3 m/z =

t [TpBu ,Me]CdCl.

t 1.6.15 Synthesis of [TpBu ,Me]CdBr

To a clear, colorless solution of tris(3-tert-butyl-5-methyl-pyrazolyl)hydroborato lithium

(17 mg, 0.04 mmol) in benzene (ca. 0.5 mL), cadmium bromide (58 mg, 0.21 mmol) was added. White precipitate formed immediately as the reaction was mixed. After mixing

for 6 days, the salt impurity and excess cadmium bromide was removed via filtration

t and the motherliquor was lyophilized to reveal [TpBu ,Me]CdBr as a white solid (18 mg,

74%). Crystals suitable X-ray diffraction were obtained from slow evaporation of

t benzene. Anal. calcd. for [TpBu ,Me]CdBr: C, 46.81%; H, 6.55%; N, 13.65%. Found: C,

1 46.83%; H, 6.81%; N, 13.79%. H NMR (C6D6): 1.48 [s, 27H,

1 HB{C3N2H(CH3)CMe3}3CdBr], 2.12 [s, 9H, HB{C3N2H(CH3)CMe3}3CdBr], 4.83 [d, JB-H =

13 1 138 Hz, HB{C3N2H(CH3)CMe3}3CdBr], 5.68 [s3H, HB{C3N2H(CH3)CMe3}3CdBr]. C{ H}

NMR (C6D6): 12.8 [s, 3C, HB{C2N2CH(CH3)C(Me)3}3CdBr], 30.9 [s, 9C,

HB{C2N2CH(CH3)C(Me)3}3CdBr], 31.7 [s, 3C, HB{C2N2CH(CH3)C(Me)3}3CdBr], 103.1 [s,

3C, HB{C2N2CH(CH3)C(Me)3}3CdBr], 144.9 [s, 3C, HBC2N2CH(CH3)C(Me)3}3CdBr], 163.4

11 1 11 1 [s, 3C, HB{C2N2CH(CH3)C(Me)3}3CdBr]. B NMR (C6D6): -8.59 [d, JB-H = 84 Hz]. B{ H}

-1 NMR (C6D6): -8.61 [s, 1B]. IR Data (KBr disk, cm ): 2962 (s), 2923 (w), 2905 (w), 2865 (w),

2567 (w) [νB-H], 1539 (s), 1472 (w), 1428 (m), 1364 (m), 1339 (w), 1243 (w), 1184 (s), 1073

t (m), 1014 (w), 992 (w), 797 (w), 769 (w), 650 (w). FAB-MS: 615.7 m/z = [TpBu ,Me]CdBr.

t 1.6.16 Synthesis of [TpBu ,Me]CdI

To a clear, colorless solution of tris(3-tert-butyl-5-methyl-pyrazolyl)hydroborato lithium

(30 mg, 0.070 mmol) in benzene (ca. 0.5 mL), cadmium iodide (79 mg, 0.22 mmol) was added. White precipitate formed immediately as the reaction was mixed. After mixing

for 7 days, the salt impurity and excess cadmium iodide was removed via filtration and

t the motherliquor was lyophilized to reveal [TpBu ,Me]CdI as a white solid (26 mg, 57%).

Crystals suitable for X-ray diffraction were obtained from slow evaporation of benzene.

t Anal. calcd. for [TpBu ,Me]CdI: C, 43.5 %; H, 6.1%; N, 12.7%. Found: C, 43.4%; H, 5.5%; N,

1 12.3%. H NMR (C6D6): 1.50 [s, 27H, HB{C3N2H(CH3)CMe3}3CdI], 2.13 [s, 9H,

1 HB{C3N2H(CH3)CMe3}3CdI], 4.84[ d, JB-H = 135 Hz, 1H, HB{C3N2H(CH3)CMe3}3CdI], 5.68

13 1 [s, 3H, HB{C3N2H(CH3)CMe3}3CdI]. C{ H} NMR (C6D6): 12.9 [s, 3C,

HB{C2N2CH(CH3)C(Me)3}3CdI], 31.7 [s, 9C, HB{C2N2CH(CH3)C(Me)3}3CdI], 31.9 [s, 3C,

HB{C2N2CH(CH3)C(Me)3}3CdI], 103.2 [s, 3C, HB{C2N2CH(CH3)C(Me)3}3CdI], 144.8 [s, 3C,

11 HBC2N2CH(CH3)C(Me)3}3CdI], 163.5 [s, 3C, HB{C2N2CH(CH3)C(Me)3}3CdI]. B NMR

1 11 1 -1 (C6D6): -8.54 [d, JB-H = 95 Hz]. B{ H} NMR (C6D6): -8.70 [s, 1B]. IR Data (KBr disk, cm ):

2961 (s), 2928 (m), 2894 (w), 2865 (w), 2570 (m) [νB-H], 1541 (s), 1528 (m), 1473 (w), 1423

(m), 1363 (m), 1337 (w), 1243 (w), 11186 (s), 1127 (w), 1073 (m), 1028 (w), 987 (w), 852

(w), 842 (w), 797 (m), 770 (m), 679 (w), 669 (w), 650 (m). FAB-MS: 662 m/z =

t [TpBu ,Me]CdI.

1.7 Crystallographic Data

Table 20. Crystal, intensity collection and refinement data

t t [TpBu ]Li [TpBu ,Me]Li

lattice Orthorhombic Monoclinic

formula C21H34BLiN6 C24H40BLiN6 formula weight 388.29 430.37

space group Pnma P21/n a/Å 14.170(8) 9.3989(8) b/Å 15.488(5) 30.425(3) c/Å 10.570(4) 9.5433(8) /˚ 90 90 /˚ 90 101.1130(10) /˚ 90 90 V/Å3 2319.8(17) 2677.8(4) Z 4 4 temperature (K) 150(2) 150(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 1.112 1.068  (Mo K), mm-1 0.067 0.064 max, deg. 30.78 30.56 no. of data collected 36141 43153 no. of data used 3718 8191 no. of parameters 153 305

R1 [I > 2(I)] 0.0525 0.0640

wR2 [I > 2(I)] 0.1255 0.1670

R1 [all data] 0.0930 0.0944

wR2 [all data] 0.1446 0.1878 GOF 1.040 1.041

Table 20. (cont’d) Crystal, intensity collection and refinement data

t t [TpBu ]Li(NCMe) [TpBu ,Me]Li(NCMe)

lattice Orthorhombic Monoclinic

formula C23H37BLiN7 C26H43BLiN7 formula weight 429.35 471.72 space group Pbcn Cc a/Å 28.392(15) 12.6668(10) b/Å 12.073(6) 20.9330(17) c/Å 15.628(9) 11.4680(9) /˚ 90 90 /˚ 90 106.3580(10) /˚ 90 90 V/Å3 5357(5) 2917.7(4) Z 8 4 temperature (K) 150(2) 130(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 1.065 1.073  (Mo K), mm-1 0.065 0.065 max, deg. 30.59 30.89 no. of data collected 81612 23571 no. of data used 8137 9103 no. of parameters 304 375

R1 [I > 2(I)] 0.0718 0.0511

wR2 [I > 2(I)] 0.1503 0.0930

R1 [all data] 0.1816 0.0856

wR2 [all data] 0.1973 0.1054 GOF 1.009 1.024

Table 20. (cont’d) Crystal, intensity collection and refinement data

But But But,Me But [Tp ]Li(pz H) [Tp ]Li(pz H)• t (pzBu H)

lattice Monoclinic Orthorhombic

formula C28H46BLiN8 C38H64BLiN10 formula weight 512.48 678.74

space group P21/c P212121 a/Å 15.974(19) 10.578(2) b/Å 10.390(12) 18.956(4) c/Å 20.44(2) 20.913(4) /˚ 90 90 /˚ 111.650(18) 90 /˚ 90 90 V/Å3 3153(6) 4193.5(15) Z 4 4 temperature (K) 200(2) 150(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 1.079 1.075  (Mo K), mm-1 0.066 0.065 max, deg. 29.57 26.37 no. of data collected 44080 53857 no. of data used 8819 9265 no. of parameters 391 475

R1 [I > 2(I)] 0.0545 0.0744

wR2 [I > 2(I)] 0.1052 0.1134

R1 [all data] 0.1340 0.1571

wR2 [all data] 0.1524 0.2137 GOF 1.000 0.985

Table 20. (cont’d) Crystal, intensity collection and refinement data But,Me But [Tp ]Li(OH2)•C6H6 [Tp ]Li(OH2)•2(THF)

lattice Monoclinic Triclinic

formula C33H51BLiN6O C29H52BLiN6O3 formula weight 565.55 550.52

space group C2/c P-1 a/Å 33.979(3) 10.5281(15) b/Å 11.2223(10) 10.5892(15) c/Å 19.0439(16) 30.611(4) /˚ 90 87.507(2) /˚ 108.0310(10) 82.518(2) /˚ 90 74.787(2) V/Å3 6905.3(10) 3264.9(8) Z 8 4 temperature (K) 130(2) 293(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 6905.3(10) 1.120  (Mo K), mm-1 0.066 0.072 max, deg. 30.58 27.10 no. of data collected 54889 39862 no. of data used 10575 13335 no. of parameters 345 746

R1 [I > 2(I)] 0.0743 0.0788

wR2 [I > 2(I)] 0.0911 0.1110

R1 [all data] 0.1940 0.2437

wR2 [all data] 0.1033 0.1453 GOF 1.141 1.090

Table 20. (cont’d) Crystal, intensity collection and refinement data

t But,Me Bu ,Me [Tp ]CdBr●C H [Tp ]Li(OH2)•(pzH) 6 6

lattice Orthorhombic Monoclinic

formula C27H46BLiN8O C24H40BBrCdN6 formula weight 516.47 615.74

space group Pbca P21/n a/Å 17.743(4) 10.3638(10) b/Å 18.128(5) 16.7365(17) c/Å 18.718(5) 16.1096(16) /˚ 90 90 /˚ 90 90.796(2) /˚ 90 90 V/Å3 6020(3) 2794.0(5) Z 8 4 temperature (K) 130(2) 150(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 1.140 1.464  (Mo K), mm-1 0.071 2.234 max, deg. 27.88 32.34 no. of data collected 76291 47876 no. of data used 7181 9773 no. of parameters 367 345

R1 [I > 2(I)] 0.0595 0.0378

wR2 [I > 2(I)] 0.1286 0.0749

R1 [all data] 0.1275 0.0681

wR2 [all data] 0.1623 0.0777 GOF 1.036 1.020

Table 20. (cont’d) Crystal, intensity collection and refinement data

But,Me But,Me [Tp ]CdCl●2C6H6 [Tp ]CdI●C6H6

lattice Orthorhombic Monoclinic

formula C27H43BCdClN6 C30H46BCdIN6 formula weight 610.33 740.84

space group P21212 P21/n a/Å 17.718(3) 9.6556(5) b/Å 17.999(3) 19.6394(10) c/Å 9.6959(15) 17.7611(9) /˚ 90 90 /˚ 90 95.5470(10) /˚ 90 90 V/Å3 3092.0(8) 3352.3(3) Z 4 4 temperature (K) 150(2) 130(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 1.311 1.468  (Mo K), mm-1 0.818 1.600 max, deg. 3055 32.60 no. of data collected 47739 58155 no. of data used 9426 11863 no. of parameters 325 344

R1 [I > 2(I)] 0.0773 0.0340

wR2 [I > 2(I)] 0.2227 0.0780

R1 [all data] 0.0824 0.0465

wR2 [all data] 0.2258 0.0850 GOF 1.103 1.011

1.8 References and Notes

(1) Janiak, C.; Braun, L.; Girgsdies, F. J. Chem. Soc. Dalt. Trans. 1999, 3, 3133–3136. (2) Kuchta, M. C.; Gemel, C.; Metzler-Nolte, N. J. Organomet. Chem. 2007, 692, 1310– 1314. (3) Dias, H. V. R.; Wang, X. Dalton Trans. 2005, 8, 2985–2987. (4) Cambridge Structural Database (Version 5.33). 3D Search and Research Using the

Cambridge Structural Database, Allen, F. H.; Kennard, O. Chemical Design Automation News 1993, 8 (1), pp 1 & 31-37. (5) a) Dowling, C. M.; Leslie, D.; Chisholm, M. H.; Parkin, G. Main Group Chemistry 1995, 1, 29-52. (b) Lopez, C.; Claramunt, R. M.; Sanz, D.; Foces Foces, C.; Cano, F. H.; Faure, E.; Cayon, E.; Elguero, J. Inorg. Chim. Acta 1990, 176, 195-204. (c) Lobbia, G. G.; Cecchi, P.; Spagna, R.; Colapietro, M.; Pifferi, A.; Pettinari, C. J.

Organomet. Chem. 1995, 485, 45-53. (d) Weis, K; Vahrenkamp, H. Inorg. Chem. 1997, 36, 5589-5591. (e) Dias H. V.R.; Kim, H.-J. Organometallics 1996, 15, 5374-5379. (f) Dias H. V. R.; Jin, W. C.; Kim, H. J.; Lu, H.-L. Inorg. Chem. 1996, 35, 2317-2328. (g) Dias H. V. R.; Lu, H.-L.; Ratcliff, R. E.; Bott, S. G. Inorg. Chem. 1995, 34, 1975- 1976. (h) Zagermann, J.; Merz, K.; Metzler-Nolte, N. Z. Anorg. Allg. Chem. 2011, 637,

1277-1279. (i) Joshi, H. K.; Arvin, M. E.; Durivage, J. C.; Gruhn, N. E.; Carducci, M. D.; Westcott, B. L.; Lichtenberger, D. L.; Enemark, J. H. Polyhedron 2004, 23, 429-438. (j) Dias, H. V. R.; Goh, T. Polyhedron 2004, 23, 273-282. (k) Olmo, C. P.; Bohmerle, K.; Steinfeld, G.; Vahrenkamp, H. Eur. J. Inorg. Chem. 2006, 3869-3877.

(l) Chisholm, M. H.; Gallucci, J. C.; Yaman, G. Inorg. Chem. 2007, 46, 8676-8683. (m) Batten, S. R.; Duriska, M. B.; Jensen, P.; Lu, J. Z. Aust. J. Chem. 2007, 60, 72- 74. (n) Chisholm, M. H.; Gallucci, J. C.; Yaman, G. Chem. Commun. 2006, 1872-1874. (o) Hu, Z. B.; Gorun, S. M. Inorg. Chem. 2001, 40, 667-671. (6) (a) Trofimenko, S. J. Am. Chem. Soc. 1967, 89, 3170–3177. (b) Trofimenko, S. J. Am. Chem. Soc. 1967, 89, 6288–6294.

(c) Trofimenko, S. Scorpionates – The Coordination Chemistry of Polypyrazolylborate Ligands , Imperial College Press, London, 1999. (7) Trofimenko, S.; Calabrese, J. C.; Thompson, J. S. Inorg. Chem. 1987, 26, 1507–1514. (8) (a) Kitano, T.; Sohrin, Y.; Hata, Y.; Wada, H.; Hori, T.; Ueda, K. Bull. Chem. Soc. Jpn. 2003, 76, 1365–1373. (b) Myers, W. K.; Duesler, E. N.; Tierney, D. L. Inorg. Chem. 2008, 47, 6701–6710. (9) Yoon, K.; Parkin, G. Polyhedron 1995, 14, 811–821.

(10) (a) Bacon, J.; Quail, J. W.; Gillespie, R. J. Can. J. Chem. 1963, 41, 3063-3069. (b) Suzuki, M.; Kubo, R. Mol. Phys. 1963, 7, 201-209. (c) Kofod, P. J. Magn. Reson. Ser. A 1996, 119, 219-224. (d) Gryff-Keller, A. Bull. Pol. Acad. Sci.-Chem. 1998, 46, 105-115. (11) Han, R.; Parkin, G. Inorg. Chem. 1992, 31, 983–988. (12) Sanz, D.; Claramunt, R. M.; Glaser, J.; Trofimenko, S.; Elguero, J. Magn. Reson. Chem. 1996, 34, 843-846.

(13) (a) Claramunt, R. M.; Sanz, D.; Santa Maria, M. D. Glaser, J. ; Trofimenko, S. Elguero, J. Magn. Reson. Chem. 1996, 34, 843. (b) Izod, K.; Stewart, J.; Clark, E.R.; McFarlane, W.; Allen, B.; Clegg, W;

Harrington, R.W. Organometallics 2009, 28, 3327.

(14) Claramunt, R. M.; Sanz, D.; Santa Maria, M. D.; Elguero, J.; Trofimenko, S. J. Organomet. Chem. 2004, 689, 463-470. (15) Alkorta, I.; Elguero, J.; Claramunt, R. M.; Lopez, C.; Sanz, D. Heterocycl. Commun. 2010, 16, 261-268. (16) (a) Avent, A. G.; Bonafoux, D.; Eaborn, C.; Hill, M. S.; Hitchcock, P. B.; Smith, J. D. J. Chem. Soc. Dalton Trans. 2000, 2183-2190. (b) Schmeisser, M.; Zahl, A.; Scheurer, A.; Puchta, R.; van Eldik, R. Z.

Naturforsch.(B) 2010, 65, 405-413. (c) Schmeisser, M.; Heinemann, F. W.; Illner, P.; Puchta, R.; Zahl, A.; van Eldik, R. Inorg. Chem. 2011, 50, 6685-6695. (d) Pasgreta, E.; Puchta, R.; Galle, M.; Hommes, N. V. E.; Zahl, A.; Van Eldik, R. J. Incl. Phenom. Macrocycl. Chem. 2007, 58, 81-88. (e) Pasgreta, E.; Puchta, R.; Zahl, A.; Van Eldik, R. Eur. J. Inorg. Chem. 2007, 1815-1822.

(f) Pasgreta, E.; Puchta, R.; Zahl, A.; Van Eldik, R. Eur. J. Inorg. Chem. 2007, 3067-3076. (g) Shirai, A.; Ikeda, Y. Inorg. Chem. 2011, 50, 1619-1627. (h) Kolonko, K. J.; Biddle, M. M.; Guzei, I. A.; Reich, H. J. J. Am. Chem. Soc. 2009, 131, 11525-11534. (i) Reich, H. J.; Green, D. P.; Medina, M. A.; Goldenberg, W. S.; Gudmundsson, B. O.; Dykstra, R. R.; Phillips, N. H. J. Am. Chem. Soc. 1998, 120, 7201-7210.

(17) Chakrabarti, N.; Sattler, W.; Parkin, G. Polyhedron 2013, 58, 235–246. (18) Hernandez, L.; Taboada, S.; d'Ornelas, L.; Gonzalez, T.; Atencio, R. Acta Crystallogr. Sect. E.-Struct Rep. Online 2004, 60, m979-m981.

(19) Yang, L.; Powell, D. R.; Houser, R. P. Dalton Trans. 2007, 955–964. (20) (a) Fielding, L. Tetrahedron 2000, 56, 6151–6170.

(b) Connors, K.A. Binding Constants, Wiley: New York, 1987. (c) Foster, R.; Fyfe, C.A.Prog. Nucl. Magn. Reson. Spectrosc. 1969, 4, 1-89. (d) Wang, T.; Bradshaw, J.S.; Izatt, R.M. J. Heterocycl. Chem. 1994, 31, 1097-1114. (e) Tsukube, H.; Furuta, H.; Odani, A.; Takeda, Y.; Kudo, Y.; Inoue, Y.; Liu, Y.; Sakamoto, H.; Kimua, K. Comprehensive Supramolecular Chemistry. Physical Methods in Supramolecular Chemistry, Davies, J.E.D.; Ripmeester, J.A.; Eds.; Elsevier: Oxford, 1996; Vol. 8, pp 425-483.

(f) Fielding, L. Prog. Nucl. Magn. Reson. Spectrosc. 2007, 51, 219–242. (21) Karlsson, R. J. Chem. Eng. Data 1973, 18, 290–292. (22) (a) Benesi, H.A.; Hildebrand, J.H. J. Amer. Chem. Soc. 1949, 71, 2703-2707. (b) Mathur, R.; Becker, E.D.; Bradley, R.B.; Li, N.C. J. Phys. Chem. 1963, 67, 2190. (c) Hanna, M.W.; Ashbaugh, A.L. J. Phys. Chem. 1964, 68, 811-816. (d) Scott, R.L. Rec. Trav. Chim. Pays-Bas. 1956, 51, 660-672.

-1 (23) A second titration experiment resulted in a Ka value of 0.77M .

(24) (a) Eriksson, E.; Jones, T.; Liljas, A. Proteins Struct. Funct. Genet. 1988, 4, 274–282. (b) Nair, S. K.; Christianson, D. W. J. Am. Chem. Soc. 1991, 113, 9455–9458. (25) (a) Looney, A. G.; Han, R.; Mcneill, K.; Parkin, G. J. Am. Chem. Soc. 1993, 115, 4690–4697. (b) Looney, A. G.; Saleh, A.; Zhang, Y.; Parkin, G. Inorg. Chem. 1994, 33, 1158– 1164. (c) Vahrenkamp, H. Acc. Chem. Res. 1999, 32, 589–596.

(26) (a) Gorrell, I. B.; Looney, A.; Parkin, G. J. Chem. Soc. Chem. Commun. 1990, 20, 220–222. (b) Han, R.; Gorrell, I. B.; Looney, A. G.; Parkin, G. J. Chem. Soc. Chem. Commun.

1991, 717–719.

(c) Trofimenko, S.; Calabrese, J. C.; Thompson, J. S. Inorg. Chem. 1987, 26, 1507– 1514. (d) Alsfasser, R.; Trofimenko, S.; Looney, A. G.; Parkin, G.; Vahrenkamp, H. A Inorg. Chem. 1991, 30, 4098. (27) For the use of 113Cd NMR to probe the nature of carbonic anhydrase see: (a) Looney, A. G.; Saleh, A.; Zhang, Y.; Parkin, G. Inorg. Chem. 1994, 33, 1158– 1164.

(b) Armitage, I. M.; Pajer, R. T.; Uiterkamp, A. J. M. S.; Chlebowski, J. F.; Coleman, J. E. J. Am. Chem. Soc. 1976, 98, 5710–5712. (c) Armitage, I. A. N. M.; Uiterkamp, A. J. M. S.; Chlebowski, J. A. N. F.; Coleman, J. E. J. Magn. Reson. 1978, 29, 375. (d) Sudmeier, J. L.; Bell, S. J. Am. Chem. Soc. 1972, 99, 4499–4500. (28) (a) Masciocchi, N.; Moret, M.; A., S.; S., B.; Cariati, F.; Pozzi, A.; Manfredini, T.; Menabue, L.; Pellacanit, G. C. Inorg. Chem. 1992, 31, 1401–1406.

(b) Rheingold, A. L.; White, C. B.; Trofimenko, S. Inorg. Chem. 1993, 32, 3471– 3477. (c) McWhinnie, W. R.; Monsef-Mirzai, Z.; Perry, M. C.; Shaikh, N.; Hamor, T. Polyhedron 1993, 12, 1193–1199. (d) Reger, D. L.; Mason, S. S.; Carolina, S.; Takats, J.; Zhang, X. W.; Rheingold, A. L.; Haggerty, B. S. Inorg. Chem. 1993, 32, 4345–4348. (e) Looney, A. G.; Saleh, A.; Zhang, Y.; Parkin, G. Inorg. Chem. 1994, 33, 1158–

1164. (f) Dowling, C. M.; Leslie, D.; Chisholm, M. H.; Parkin, G. Main Gr. Chem. 1995, 1, 29–52.

(g) Deng, Y.; Wang, R.; Ding, T.; Li, Y.; Sun, S.; Feng, Y.; Zhao, Y. Polyhedron 2001, 20, 291–295.

(h) Fujisawa, K.; Matsunaga, Y.; Ibi, N.; Amir, N.; Miyashita, Y.; Okamoto, K. Bull. Chem. Soc. Jpn. 2006, 79, 1894–1896. (29) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997, 62, 7512-7515. (30) Günther, H. Enc. Mag. Res. (2007) DOI: 10.1002/9780470034590.emrstm0273. (31) Smith, W. L. J. Chem. Educ. 1977, 54, 469-473. (32) (a) Harris, R. K.; Becker, E. D.; De Menezes, S. M. C.; Goodfellow, R.; Granger, P. Pure Appl. Chem. 2001, 73, 1795-1818.

(b) Harris, R. K.; Becker, E. D.; De Menezes, S. M. C.; Granger, P.; Hoffman, R. E.; Zilm, K. W. Pure Appl. Chem. 2008, 80, 59-84. (33) (a) Sheldrick, G. M. SHELXTL, An Integrated System for Solving, Refining and Displaying Crystal Structures from Diffraction Data; University of Göttingen, Göttingen, Federal Republic of Germany, 1981. (b) Sheldrick, G. M. Acta Cryst. 2008, A64, 112-122. (34) Jaguar 7.5, Schrödinger, LLC, New York, NY 2008.

(35) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652. (b) Becke, A. D. Phys. Rev. A 1988, 38, 3098-3100. (c) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B 1988, 37, 785-789. (d) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200-1211. (e) Slater, J. C. Quantum Theory of Molecules and Solids, Vol. 4: The Self-Consistent Field for Molecules and Solids; McGraw-Hill: New York, 1974. (36) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270-283.

(b) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284-298. (c) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299-310. (37) Note that, as described in the text, the NMR spectroscopic data are concentration

dependent.

(38) The 1H NMR chemical shift of MeCN in benzene has been reported as 1.55a and 0.58 ppm,b with the former being reported to be erroneous.b In this regard, we note that the 1H NMR chemical shift of MeCN in benzene is actually concentration dependent and increases from the value of 0.58 as the concentration increases. (a) see reference 22 (b) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.; Nudelman, A.;

Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I. Organometallics 2010, 29, 2176-2179. t t (39) The NMR spectroscopic data for [TpBu ]Li(pzBu H) are those for a freshly prepared solution because the sample degrades over a period of several hours at room temperature.

Chapter 2

Synthesis and Structural Characterization of Cadmium Complexes Supported by

i Nitrogen-Rich Ligands: [Tptm], [TitmMe], and [TitmPr Benz] and A Study of Their

Reactivity

Table of Contents

2.1 Introduction ...... 83

2.1.1 Objective ...... 83

2.1.2 The Ligand Systems ...... 84

2.2 Synthesis of [Tptm]CdX Compounds ...... 86

2.3 Synthesis of [TitmMe]CdX Compounds...... 95

i 2.4 Synthesis of [TitmPr Benz]CdX Complexes ...... 102

2.5 Discussion of [L]CdN(SiMe3)2 Complexes ...... 105

2.6 Discussion of [L]CdOSiR3 (R = Me, Ph) Complexes ...... 110

2.7 Discussion of [L]CdMe Complexes ...... 121

2.8 Discussion of [L]CdNCO Complexes ...... 131

2.9 Discussion of [L]CdO2CX (X = H, Me) Complexes ...... 139

2.10 Discussion of [L]CdX (X = Cl, Br, I) Complexes ...... 147

2.11 Conclusion ...... 155

2.12 Experimental Section ...... 156

2.12.1 General Considerations ...... 156

2.12.2 X-ray Structure Determination...... 157

2.12.3 Computational Details ...... 157

2.12.4 Synthesis of [Tptm]CdN(SiMe3)2 ...... 157

2.12.5 Synthesis of [Tptm]CdNCO ...... 158

2.12.6 Synthesis of [Tptm]CdOSiMe3 ...... 159

2.12.7 Synthesis of [Tptm]CdOSiPh3 ...... 160

2.12.8 Synthesis of [Tptm]CdCl ...... 161

2.12.9 Synthesis of [Tptm]CdBr ...... 162

2.12.10 Synthesis of [Tptm]CdOAc ...... 164

2.12.11 Synthesis of [Tptm]CdO2CH ...... 165

3 Me 2.12.12 Synthesis of [ -S2C-Titm ]CdMe ...... 166

Me 2.12.13 Synthesis of [Titm ]CdN(SiMe3)2 ...... 167

Me 2.12.14 Synthesis of [Titm ]CdOSiMe3 ...... 168

Me 2.12.15 Synthesis of [Titm ]CdOSiPh3...... 169

2.12.16 Synthesis of [TitmMe]CdNCO...... 170

2.12.17 Synthesis of [TitmMe]CdCl ...... 171

2.12.18 Synthesis of [TitmMe]CdBr ...... 171

2.12.19 Synthesis of [TitmMe]CdOAc ...... 172

2.12.20 Synthesis of [TitmMe]CdOPhMe ...... 173

3 PriBenz 2.12.21 Synthesis of [ -N2C-Titm ]CdMe ...... 174

4 PriBenz 2.12.22 Synthesis of [ - S3C-Titm ]CdMe ...... 176

PriBenz 2.12.23 Synthesis of [Titm ]CdN(SiMe3)2 ...... 177

PriBenz 2.12.24 Synthesis of [Titm ]CdOSiMe3 ...... 178

PriBenz 2.12.25 Synthesis of [Titm ]CdOSiPh3 ...... 180

i t 2.12.26 Synthesis of [TitmPr Benz]CdOPhBu ...... 181

PriBenz 2.12.27 Synthesis of [Titm ]CdO2CH ...... 183

2.12.28 Synthesis of [Tptm]CdI ...... 184

2.12.29 Synthesis of [TitmMe]CdI ...... 185

2.13 Crystallographic Data ...... 187

2.14 References and Notes ...... 197

2.1 Introduction

2.1.1 Objective

Cadmium complexes supported by nitrogen-rich ligands including porphyrin,1 tris(pyrazolyl)hydroborato, [Tp],2 and various pyridines3,4 are prevalent in the literature.

2a 2b 2b,d Most notably, [Tp]CdR complexes (R = NCS, OAc, NO3 ) are used as molecular models for carbonic anhydrase due to the resemblance between the ligand and the enzyme active site.5 Additionally, cadmium bipyridine complexes have shown catalytic activity for transesterification reactions.3a

Due to the potential applications of nitrogen-rich cadmium complexes, we turned our attention to three nitrogen-rich ligands: tris(pyridylthio)methane, [Tptm]H, tris(1-methylimidazolylthio)methane, [TitmMe]H, and tris(1-

i isopropylbenzimidazolylthio)methane, [TitmPr Benz]H (Figure 1).

Figure 1. The tris(pyridylthio)methane, [Tptm]H, tris(1-methylimidazolylthio)methane,

i [TitmMe]H, and tris(1-isopropylbenzimidazolylthio)methane, [TitmPr Benz]H ligands

These three ligands are in the nascent stages of development and thus allow for the synthesis of new cadmium complexes and investigation of their reactivities. Cadmium

silyl amide and siloxide complexes, [L]CdN(SiMe3)2,[L]CdOSiMe3, and [L]CdOSiPh3 ([L]

i = [Tptm], [TitmMe], and [TitmPr Benz]), were synthesized and provide access to a variety of

organometallic cadmium complexes, [L]CdR (R = Cl, Br, NCO, OAc, and O2CH). The cadmium acetate, formate complexes are of interest due to their potential to serve as models of biological systems, such as cadmium-substituted carbonic anhydrase.6

Additionally, cadmium methyl complexes, [L]CdMe were synthesized and structurally characterized.

2.1.2 The Ligand Systems

The [Tptm] ligand was first synthesized in 20027 and since then only a handful of transition metal complexes, including iron,8 copper,7,9 and nickel10 have been reported in the literature. Main group chemistry for [Tptm]M complexes is more developed, for example, the [Tptm]Li complex has been used as a transmetallating agent to obtain metal halide [Tptm] complexes.11 Also, a plethora of [Tptm] zinc complexes have been synthesized and characterized,12,13,14,15 perhaps most notably, the hydride species,

[Tptm]ZnH. The [Tptm]ZnH complex has shown catalytic activity that is applicable in two industrial processes: the release of hydrogen from the methanolysis and hydrolysis

13 of silanes and the hydrosilylation of aldehydes, ketones and CO2.

[TitmMe]H is a newer ligand and was first synthesized in 2009.16 This initial report observed isomerization of this ligand at elevated temperature and in the presence of

Lewis acids, resulting in the sulfur donor ligand shown in Figure 2.

Me Figure 2. Isomerized [S3-Titm ]H ligand

Me 16 A single transition metal complex, [Titm ]Ag(BF4), has been reported and efforts in the Parkin group have led to the characterization of a number of [TitmMe] zinc complexes.17 Characterization of these zinc complexes has shown that they are capable of serving as molecular models for nitrogen-rich enzyme active sites, such as carbonic anhydrase due to the structural similarity between the three imidazolyl rings in the ligand and the tris-histidine enzyme active site.17

i The [TitmPr Benz] ligand17 was designed by a colleague in the Parkin group to address the issues of low solubility of several zinc [TitmMe] complexes. As shown in

i Figure 1, two modifications were made to the [TitmMe] ligand to obtain [TitmPr Benz]: first, the annulation of the thioimidazole rings and second, the use of a bulkier R substituent on the thioimidazole rings. The goals of these modifications were twofold: to increase

i the solubility and to promote the crystallization of [TitmPr Benz] metal complexes. Since

i the relatively recent design of the ligand, several [TitmPr Benz] zinc complexes have been synthesized and characterized by our group and their reactivity has been investigated.17

2.2 Synthesis of [Tptm]CdX Compounds

i As previously mentioned, there are no reported [Tptm], [TitmMe], and [TitmPr Benz] cadmium complexes in the literature. The cadmium bis(trimethylsilylamide),

Cd[N(SiMe3)2]2 complex was used with the goal of accessing a variety of cadmium

complexes with these ligand systems. The Cd[N(SiMe3)2]2 reagent has proved to be a

very versatile in the literature: addition of Cd[N(SiMe3)2]2 to small organics produces

18,19,20 organo-cadmium starting materials, addition of Cd[N(SiMe3)2]2 to metal

21 compounds produces bimetallic complexes, and addition of Cd[N(SiMe3)2]2 to ligands

22 produces cadmium silylamide complexes, [L]CdN(SiMe3)2, or dimeric complexes,

23 {[L]Cd}2. The reactivity of the resulting cadmium silylamide complexes has not been widely studied; therefore, our goal was to access additional cadmium organometallic

complexes using these [L]CdN(SiMe3)2 cadmium silylamide complexes.

The [Tptm]CdN(SiMe3)2 complex was readily synthesized via addition of

Cd[N(SiMe3)2]2 to [Tptm]H, as shown in Scheme 1. The [Tptm]CdN(SiMe3)2 complex

86 was characterized via NMR spectroscopy and X-ray diffraction. The molecular

structure of [Tptm]CdN(SiMe3)2 was obtained and is provided in Figure 3.

Scheme 1. Synthesis of [Tptm] cadmium complexes

Figure 3. Molecular structure of [Tptm]CdN(SiMe3)2 (only one of two crystallographically independent molecules is shown)

Scheme 1 shows that the addition of CO2 to [Tptm]CdN(SiMe3)2 results in the

formation of the isocyanate complex, {[Tptm]Cd(-NCO)}2. The formation of the

isocyanate complex instead of the silylcarbamate from CO2 insertion into the Cd-

12 N(SiMe3)2 bond was expected due to the reported synthesis of [Tptm]ZnNCO. The mechanism of formation of the [Tptm]ZnNCO complex was thoroughly investigated, indicating that conversion to the isocyanate was a multi-step process (Scheme 2).12 The

1 H NMR spectra of the reaction of CO2 with [Tptm]CdN(SiMe3)2 shows the formation of trimethylsilylisocyanate and trimethylsilylcarbonate, which is observed in the formation of [Tptm]ZnNCO, and indicates that the cadmium analogue undergoes the same mechanism.

Scheme 2. Mechanism for the formation of [Tptm]ZnNCO from addition of CO2 to

[Tptm]ZnN(SiMe3)2 (reproduced from reference 12)

The molecular structure for the {[Tptm]Cd(-NCO)}2 complex is provided in

Figure 4.

Figure 4. Molecular structure of {[Tptm]Cd(-NCO)}2●C6H6 (solvent is omitted for clarity)

The conversion of [Tptm]CdN(SiMe3)2 to the trialkyl siloxides is achieved via

addition of trimethylsilanol or triphenylsilanol to form {[Tptm]Cd(-OSiMe3)}2 and

[Tptm]CdOSiPh3, respectively (Scheme 1). The loss of bis(trimethylsilyl)amine is observed by 1H NMR spectroscopy.

The conversion of metal bis(trimethylsilyl)amide complexes to trimethylsiloxide complexes has been observed in a number of other transition24,25 and main group12a,26,27,28,29 metal complexes; however, there are only two examples of cadmium

30 siloxide complexes, and they are the cubane molecules [CH3CdOSiMe3]4 and

31 [Cd4I4(OSiMe3)(NPEt3)3]. Only the latter of these two complexes has been

characterized by X-ray diffraction. {[Tptm]Cd(-OSiMe3)}2 and [Tptm]CdOSiPh3 were

90 both characterized via X-ray diffraction and their molecular structures are provided in

Figure 5 and Figure 6, respectively.

Figure 5. Molecular structure of {[Tptm]Cd(-OSiMe3)}2●2C6H6 (solvent is omitted for clarity)

Figure 6. Molecular structure of [Tptm]CdOSiPh3●C6H6 (solvent is omitted for clarity)

The reactivity of [Tptm]CdOSiMe3 is also shown in Scheme 1 and the

[Tptm]CdOSiMe3 complex provides access to a number of cadmium complexes. For example, the cadmium halide and acetate complexes were obtained from the addition

of Me3SiX reagents (X = Cl, Br, OAc) to [Tptm]CdOSiMe3. The molecular structures for

[Tptm]CdCl, [Tptm]CdBr, [Tptm]CdOAc are provided in Figure 7 through Figure 9.

Figure 7. Molecular structure of [Tptm]CdCl (disordered atoms are not shown)

Figure 8. Molecular structure of [Tptm]CdBr (disordered atoms are not shown)

Figure 9. Molecular structure of [Tptm]CdOAc

The formate complex, [Tptm]CdO2CH, was isolated after the addition of

1 phenylsilane and CO2 to [Tptm]CdOSiMe3. This compound was characterized by H

NMR spectroscopy and by X-ray crystallography, the molecular structure of the complex is provided in Figure 10.

Figure 10. Molecular structure of [Tptm]CdO2CH

2.3 Synthesis of [TitmMe]CdX Compounds

Scheme 3 shows the cadmium methyl complex supported by the [TitmMe] ligand

Me was readily synthesized via addition of CdMe2 to [Titm ]H. The molecular structure of

3 Me Me [ -S2C-Titm ]CdMe is provided in Figure 11. Additionally, [Titm ]CdN(SiMe3)2 was

Me readily obtained from the addition of Cd[N(SiMe3)2]2 to[Titm ]H. The

Me [Titm ]CdN(SiMe3)2 complex was characterized via NMR spectroscopy.

Scheme 3. Synthesis of [TitmMe] cadmium complexes

3 Me Figure 11. Molecular structure of [ -S2C-Titm ]CdMe

Me Scheme 3 shows that the [Titm ]CdN(SiMe3)2 complex provides access to four

new cadmium complexes. Similar to the [Tptm] system, the addition of HOSiMe3 to

Me [Titm ]CdN(SiMe3)2 provided access to the trimethylsiloxide complex,

Me [Titm ]CdOSiMe3, which was characterized by NMR spectroscopy. The addition of

Me Me HOSiPh3 to [Titm ]CdN(SiMe3)2 yielded [Titm ]CdOSiPh3. Crystals of the

Me [Titm ]CdOSiPh3 complex were obtained from slow evaporation of solvent from a benzene solution of the complex and the molecular structure of the complex is provided in Figure 12.

Me Figure 12. Molecular structure of [Titm ]CdOSiPh3

The isocyanate complex was obtained via addition of CO2 to

Me Me [Titm ]CdN(SiMe3)2. The molecular structure for the [Titm ]CdNCO complex is

provided in Figure 13. In contrast to the {[Tptm]Cd(-NCO)}2complex complex, the

[TitmMe] complex is monomeric with a terminal NCO moiety.

Me Figure 13. Molecular structure of [Titm ]CdNCO●2C6H6 (solvent is omitted for clarity)

Me The final compound that was obtained from the [Titm ]CdN(SiMe3)2 complex is

Me the [Titm ]CdOAc complex which was isolated after addition of Me3SiOAc to the cadmium amide complex as shown in Scheme 3. The solid state structure for the

[TitmMe]CdOAc complex is provided in Figure 14.

Figure 14. Molecular structure of [TitmMe]CdOAc

Me The reactivity of [Titm ]CdOSiPh3 with Me3SiX (X = Cl, Br) and p-tolOH was

also explored. As shown in Scheme 3, the addition of Me3SiCl or Me3SiBr to the cadmium siloxide formed [TitmMe]CdCl and [TitmMe]CdBr, respectively. The addition

Me of p-TolOH to [Titm ]CdOSiPh3 formed the aryloxide complex. These complexes were characterized by X-ray diffraction and the molecular structures of [TitmMe]CdCl,

[TitmMe]CdBr, and [TitmMe]Cd-p-Tol are shown in Figure 15 through Figure 17.

100

Me Figure 15. Molecular structure of [Titm ]CdCl●C6H6 (solvent omitted for clarity)

Figure 16. Molecular structure of [TitmMe]CdBr (there are two crystallographically independent molecules in the asymmetric unit)

101

Me Me Figure 17. Molecular structure of [Titm ]CdOPh ●p-TolOH

i 2.4 Synthesis of [TitmPr Benz]CdX Complexes

PriBenz The [Titm ]CdN(SiMe3)2 complex was readily synthesized via addition of

PriBenz Cd[N(SiMe3)2]2 to the protonated [Titm ]H ligand (Scheme 4). The

PriBenz [Titm ]CdN(SiMe3)2 complex provided access to the cadmium siloxide complexes,

PriBenz [Titm ]CdOSiR3 (R = Me or Ph), similar to the [Tptm]CdN(SiMe3)2 and

Me PriBenz [Titm ]CdN(SiMe3)2 complexes. These [Titm ]CdN(SiMe3)2 and

PriBenz [Titm ]CdOSiR3 complexes were characterized via NMR spectroscopy. Attempts to obtain crystals were unsuccessful.

102

i Scheme 4. Synthesis of [TitmPr Benz] cadmium complexes

PriBenz The reactivity of [Titm ]CdOSiMe3 was also investigated as shown in Scheme

Me But 4. Similar to the [Titm ]CdOSiMe3 complex, the addition of HOPh to

PriBenz [Titm ]CdOSiMe3 led to the formation of a cadmium phenoxide. Similar to the

PriBenz [Tptm]CdOSiMe3 complex, addition of CO2 to [Titm ]CdOSiMe3 treated with PhSiH3

PriBenz resulted in the formate complex, [Titm ]CdO2CH. Crystals suitable for X-ray

PriBenz But PriBenz diffraction of [Titm ]CdOPh and [Titm ]CdO2CH were not obtained, however both complexes were characterized via NMR spectroscopy.

The cadmium alkyl complexes were also obtained via addition of CdMe2 to

PriBenz [Titm ]H as shown in Scheme 5. Interestingly, the addition of CdMe2 to

PriBenz 3 PriBenz [Titm ]H the absence of heat results in the [ -N2C-Titm ]CdMe, in contrast, the

PriBenz addition of CdMe2 to [Titm ]H the presence of heat results in isomerization of the

4 PriBenz ligand to [ -S3C-Titm ]CdMe.

103

3 PriBenz 4 PriBenz Scheme 5. Synthesis of [ - N2C-Titm ]CdMe and [ -S3C-Titm ]CdMe

3 PriBenz 4 The molecular structures of the [ -N2C-Titm ]CdMe and [ -S3C -

i TitmPr Benz]CdMe complexes are provided in Figure 18 and Figure 19.

3 PriBenz Figure 18. Molecular structure of [ -N2C-Titm ]CdMe●2C6H6 (solvent atoms are omitted for clarity)

104

4 PriBenz Figure 19. Molecular structure of [ -S3C-Titm ]CdMe●C6H6 (solvent atoms are omitted for clarity)

2.5 Discussion of [L]CdN(SiMe3)2 Complexes

Me The synthesis of [Tptm]CdN(SiMe3)2, [Titm ]CdN(SiMe3)2, and

PriBenz [Titm ]CdN(SiMe3)2 is shown in Scheme 1, Scheme 3, and Scheme 4. Crystals of

[Tptm]CdN(SiMe3)2 were obtained and Figure 3 shows cadmium center in this complex is coordinated to the [Tptm] ligand in a 4 fashion. Selected bond angles and bond

length data from the structure of [Tptm]CdN(SiMe3)2 are listed in Table 1.

105

a Table 1. Selected bond lengths and angles in [Tptm]CdN(SiMe3)2

Bond Lengths (Å) Bond Angles (°)

Cd-N1 2.336(5), N1-Cd-N2 93.61(18),

2.328(5) 95.98(18)

Cd-N2 2.377(5), N2-Cd-N3 111.26(18),

2.382(5) 107.86(18)

Cd-N3 2.391(5), N1-Cd-N3 143.63(18),

2.404(5) 144.38(18)

Cd-C 2.332(6), N4-Cd-C 154.8(2),

2.343(6) 154.27(2)

Cd-N4 2.151(5),

2.155(5) a There are two crystallographically independent molecules in the asymmetric unit

From the bond angles in Table 1, the geometry could be quantifiably determined

32 using the 5 parameter, which is calculated by the equation ()/60. In this equation,  is the largest angle between the atoms in the equatorial plane and  is the

angle of the axial atoms. An ideal trigonal bipyramidal geometry has a 5 parameter of

32 1 and a square pyramidal geometry has a 5 parameter of 0. The calculated 5 parameters for the two crystallographically independent molecules of

106

[Tptm]CdN(SiMe3)2 in the asymmetric unit are 0.18 and 0.16, respectively. These 5

parameters indicate that the cadmium center in the [Tptm]CdN(SiMe3)2 complex sits in a distorted square pyramidal geometry.

There are only thirteen cadmium bis(trimethylsilyl)amide complexes that have been characterized by X-ray diffraction and reported in the Cambridge Structural

33 Database (CSD). Table 1 shows that our Cd-N(SiMe3)2 bonds are 2.151 Å and 2.155 Å for the two independent molecules in the unit cell, these bond lengths are within the

range of literature values for Cd-N bonds. The smallest Cd-N(SiMe3)2 bond is 2.102Å in a bipyridyl complex19b and the longest is 2.338Å in a Cp* complex (Table 2).22b

Table 2. Cd-N(SiMe3)2 bond lengths in select compounds

Compounds d[Cd-N(SiMe3)2]/Å Reference

Me a 2 2.104 22c [HC(pz )3]CdN(SiMe3)2

[(-OCH2CH3)CdN(SiMe3)2(py)]2 2.102 19b

b 2.257, 2.255 22b [(Cp*)Cd(-N(SiMe3)2)]2 2.323, 2.338 a There are two crystallographically independent molecules in the asymmetric unit b The Cd-N(SiMe3)2 moieties are bridging, resulting in four unique Cd-N bond lengths.

107

Me PriBenz The [Tptm]CdN(SiMe3)2, [Titm ]CdN(SiMe3)2, and [Titm ]CdN(SiMe3)2 compounds were characterized via NMR spectroscopy. The 1H NMR spectrum of the

[Tptm]CdN(SiMe3)2 complex shows no shift in the [Tptm] protons (Figure 20) upon cooling to -70°C, indicating that this complex is 4 in solution.

1 Figure 20. H NMR spectrum of the pyridylthio protons in [Tptm]CdN(SiMe3)2 at

various temperatures (* = d8- toluene)

1 The H NMR spectrum for [Tptm]Zn(SiMe3)2, in which there is one set of peaks for the [Tptm] protons at room temperature and two sets of peaks with an integrated

108 ratio of 2:1 at -10°C. This low temperature NMR experiment is evidence that one arm of

3 12a the [Tptm] ligand is uncoordinated in [ -Tptm]ZnN(SiMe3)2. The solid state

structure of the [Tptm]ZnN(SiMe3)2 complex was not available for comparison with our cadmium analogue.

1 Me The H NMR spectrum of the [Titm ]CdN(SiMe3)2 complex showed one set of peaks for the thioimidazolyl protons in the [TitmMe] ligand at 25°C and at -50°C, indicating the ligand is either 4 in solution or is fluxional and exchanging rapidly on the NMR timescale at low temperatures (Figure 21).

109

1 Me Figure 21. H NMR spectrum of the imidazolyl protons in [Titm ]CdN(SiMe3)2 at

various temperatures (* = d8-toluene; † = unknown impurity)

1 PriBenz The H NMR spectrum of the [Titm ]CdN(SiMe3)2 complex shows one set of broad peaks for the protons in the ligand and trimethylsilyl group at 25°C, however, at -

40°C, the broad peaks deconvolute to show two sets of resonances. This low

i temperature NMR experiment is evidence that one arm of the [TitmPr Benz] ligand is

3 PriBenz uncoordinated in [ -Titm ]CdN(SiMe3)2 and that the ligand is exchanging rapidly thus showing an average set of resonances for multiple coordination modes at higher temperatures.

2.6 Discussion of [L]CdOSiR3 (R = Me, Ph) Complexes

There are very few cadmium siloxide complexes reported in the literature,

Me therefore, we wanted to investigate the nature of the [Tptm]CdOSiR3, [Titm ]CdOSiR3,

PriBenz and [Titm ]CdOSiR3 (R = Me, Ph) complexes that we synthesized. The synthesis of

Me PriBenz [Tptm]CdOSiR3, [Titm ]CdOSiR3, and [Titm ]CdOSiR3 are shown in Scheme 1,

Scheme 3, and Scheme 4, respectively. These schemes show that the siloxide complexes

were obtained from treatment of [L]CdN(SiMe3)2 with R3SiOH. The molecular

Me structures of [Tptm]CdOSiMe3, [Tptm]CdOSiPh3, and [Titm ]CdSiOPh3 were obtained and are provided in Figure 5, Figure 6, and Figure 12, respectively.

110

Figure 5 shows that the {[Tptm]Cd(-OSiMe3)}2●2C6H6 complex is dimeric in the

solid state, and the oxygen atom in the OSiMe3 moiety bridges the two cadmium

centers. Selected bond lengths and angles in {[Tptm]Cd(-OSiMe3)}2●2C6H6 are listed in

Table 3.

a Table 3. Selected bond lengths and angles in {[Tptm]Cd(-OSiMe3)}2●2C6H6

Bond Lengths (Å) Bond Angles (°)

Cd-N1 2.330(4) N1-Cd-N2 133.64(12)

Cd-N2 2.339(3) N1-Cd-O2 114.52(12)

Cd-C 2.332(4) N2-Cd-O1 110.68(12)

Cd-O1 2.183(3) C-Cd-O2 152.97(12)

Cd-O2 2.271(3) Cd-O-Cd 98.32(11) aThe molecules are related by a plane of symmetry, only the unique bond length and angle data is listed.

Examples of the OSiR3 moiety bridging two or more metal centers is quite prevalent in the literature, M-O-M angles and M-O bond distances in other reported

dimeric main group MOSiMe3 complexes are listed in Table 4 for comparison with our

{[Tptm]Cd(-OSiMe3)}2●2C6H6.

Table 4. M-O-M angles and M-O bond lengths in dimeric main group [M(-OSiMe3)]2 complexes 111

Compounda M-O-M/° d(M-O)/Å d(Cd-O)/Å Reference

[(BDI-2)Zn(-OSiMe3)]2 96.03 1.978, 2.026 0.05 34

[(-Me3SiO)ZnC6F5(THF)]2 94.06, 1.963, 1.967, 0, 35

94.12 1.966, 1.966 0

[Li(THF)2][GaN(SiMe3)2(- 88.19, 1.872, 1.983, 0.11, 36 OSiMe ) Cl] 3 2 91.39 1.848, 1.902 0.05

b 96.13 1.860, 1.861 0 37 [(i-Bu)2Al(-OSiMe3)]2

[(CH2SiMe3)2In(- 100.36, 2.182, 2.163, 0.02, 38 OSiMe )] 3 2 100.30 2.180, 2.168 0.02

b 99.70 2.286, 2.251 0.04 39 [(BDI)Ca(-OSiMe3)]2 a List of abbreviations: BDI = -diiminate, i-Bu = isobutyl bA plane of symmetry relates the two molecules in the dimer, therefore, only the unique bond and angle data is listed

Table 4 shows that the Cd-O-Cd angle in {[Tptm]Cd(-OSiMe3)}2●2C6H6 is 98.32°,

which correlates well with the M-O-M angles in reported [M(-OSiMe3)]2 complexes

(Table 4). The Cd-O bond lengths in {[Tptm]Cd(-OSiMe3)}2●2C6H6 are 2.183 Å and

2.271 Å with a difference, d, between the distances of 0.09Å. Table 4 shows that within these reported complexes, the d between the M-O bonds ranging from 0Å to 0.11Å. In

comparison with these values, the Cd-O bond lengths in {[Tptm]Cd(-OSiMe3)}2●2C6H6 are within range of the literature. 112

Additionally, Figure 5 shows that the [Tptm] ligand in the {[Tptm]Cd(-

3 OSiMe3)}2●2C6H6 complex is coordinated in a  fashion to the cadmium center via two thiopyridine arms and the carbon center. To determine the geometry of the cadmium center, select bond angles were measured and are listed in Table 3. From the angle data

in Table 3, the 5 parameter is 0.32 for the {[Tptm]Cd(-OSiMe3)}2●2C6H6 indicating that cadmium center sits in a distorted square pyramidal geometry.

The zinc analogue of this complex, [Tptm]ZnOSiMe3 is a monomer in the solid state, as shown in Figure 22. The low quality of the structure prevents further discussion about bond lengths or angles.

Figure 22. The molecular structure of [Tptm]ZnOSiMe3 (reproduced from reference 12)

113

Density Functional Theory (DFT) geometry optimization calculations were

performed on the monomeric [Tptm]MOSiMe3 and dimeric {[Tptm]M(-OSiMe3)}2 (M =

Cd, Zn) complexes (Figure 23). The formation of the dimeric {[Tptm]M(-OSiMe3)}2 (M

= Cd, Zn) species from two monomers was calculated and compared with the energy

minima of the geometry optimized {[Tptm]M(-OSiMe3)}2 complexes. The energy difference, E, are listed in Table 5. The values in Table 5 show that formation of the

{[Tptm]Cd(-OSiMe3)}2 is more favorable than the formation of the {[Tptm]Zn(-

OSiMe3)}2, which supports our experimental observation that the molecular structure of

{[Tptm]Cd(-OSiMe3)}2 and [Tptm]ZnOSiMe3 were obtained.

Figure 23. Structures of the DFT geometry optimized of monomeric [Tptm]MOSiMe3

and dimeric {[Tptm]M(-OSiMe3)}2 (M = Cd, Zn) complexes

Table 5. DFT energy calculations of the formation of dimeric metal siloxide complexes

114

Compound E (kcal/mol)

{[Tptm]Cd(-OSiMe3)}2 -8.90

{[Tptm]Zn(-OSiMe3)}2 3.71

In contrast to {[Tptm]Cd(-OSiMe3)}2●2C6H6, the molecular structure of

4 [Tptm]CdOSiPh3 (Figure 5) is monomeric and the [Tptm] ligand coordinates in a  fashion to the cadmium center. Selected bond lengths and angles are listed in Table 6

and Table 7. From the bond angle data in Table 7, the 5 parameter was determined to

be 1.02, indicating [Tptm]CdOSiPh3 is in an ideal trigonal pyramidal geometry, in

which the C3 axis is comprised of the C-Cd-O atoms.

115

Table 6. Select bond lengths in [L]CdOSiPh3 complexes

d(Cd-N1)/Å d(Cd-N2)/Å d(Cd-N3)/Å d(Cd-C)/Å d(Cd-O)/Å

[Tptm]CdOSiPh3 2.283(6) 2.283(6) 2.283(6) 1.95(4) 2.198(8) Experimental

116 [Tptm]CdOSiPh3 2.366 2.366 2.366 2.446 2.117

Geometry optimized

Me 2.228(4) 2.234(4) 2.259(5) 2.558(5) 2.133(3) [Titm ]CdOSiPh3

Experimental

Me 2.321 2.325 2.327 2.669 2.117 [Titm ]CdOSiPh3

Geometry optimized

Table 7. Select bond angles in [L]CdOSiPh3 complexes

 N1-Cd-N2/° N2-Cd-N3/° N1-Cd-N3/° C-Cd-O/° Cd-O-Si/° 5

[Tptm]CdOSiPh3 118.30(8) 118.30(8) 118.30(8) 180.000(4) 180.000(1) 1.02

Experimental

[Tptm]CdOSiPh3 117.73 117.73 117.73 180.00 180.00 1.04

117 Geometry optimized

Me 111.15(17) 117.27(17) 120.94(18) 167.01(13) 138.9(2) 0.77 [Titm ]CdOSiPh3

Experimental

Me 112.71 115.99 117.25 174.49 159.09 0.95 [Titm ]CdOSiPh3

Geometry optimized

Select bond lengths in [Tptm]CdOSiPh3 are listed in Table 6. The Cd-O bond

length in [Tptm]CdOSiPh3 is 2.198Å, in comparison, the two Cd-O bond lengths in

{[Tptm]Cd(-OSiMe3)}2 are 2.183 Å and 2.271 Å. Since there are no other monomeric cadmium siloxide complexes in the literature, this Cd-O bond length was compared

with the M-O bond length in other monomeric metal complexes with terminal OSiPh3

moieties listed in the CSD. The shortest M-O bond length in these MOSiPh3 complexes

40 is 1.68Å in [Al(OSiPh3)2(acac)], and the longest M-O bond is 2.48Å in [Ba(OSiPh3)2(15-

41 crown-5)(THF)]. The Cd-O bond length of 2.198Å in [Tptm]CdOSiPh3 correlates well with this reported structural data.

A comparison with the molecular structure of the zinc analogue,

[Tptm]ZnOSiPh3, provided in Figure 24, shows that both of these complexes are monomeric and the metal center is in a five-coordinate trigonal bipyramidal geometry.

The low quality of the [Tptm]ZnOSiPh3 crystals preclude further discussion about bond lengths and angles in the complex.

118

Figure 24. Molecular structure of [Tptm]ZnOSiPh3

In the DFT geometry optimized calculations of [Tptm]CdOSiPh3, the cadmium

center maintained the an idealized trigonal bipyramidal geometry, with a calculated 5 parameter of 1.0. Selected bond lengths and angles in the geometry optimized structure are listed in Table 6 and Table 7, respectively.

Me Crystals of the [Titm ]CdOSiPh3 complex were obtained from slow evaporation of solvent from a benzene solution of the complex. The solid state structure is provided in Figure 12 and shows this complex is monomeric and the ligand is 4 coordinate to

cadmium, similar to the [Tptm]CdOSiPh3 analogue. Selected bond lengths and angles are listed in Table 6 and Table 7, respectively.

119

Me The calculated 5 parameter for the [Titm ]CdOSiPh3 complex is 0.77 (Table 7) and indicates that the cadmium center sits in a distorted trigonal bipyramidal geometry,

unlike the [Tptm]CdOSiPh3 complex which is an ideal trigonal bipyramid with a5 parameter of 1.02.

Me The Cd-O bond length in the [Titm ]CdOSiPh3 is 2.133Å which is 0.06Å shorter

Me than [Tptm]CdOSiPh3 (2.198 Å). The [Titm ]CdOSiPh3 Cd-O length is within the range

40 of M-O bond lengths in M-OSiPh3 complexes where the shortest M-O length is 1.68Å to 2.48Å,41 as discussed previously. A comparison of the Cd-O-Si angles in

Me Me [Tptm]CdOSiPh3 and [Titm ]CdOSiPh3 shows that the angle in [Titm ]CdOSiPh3,of

138.9°, is less linear than the 180.00° in [Tptm]CdOSiPh3, as shown in Table 7.

Me DFT geometry optimization calculations were performed on [Titm ]CdOSiPh3 and selected bond lengths and angles are listed in Table 6 and Table 7, respectively.

The values in Table 6 and Table 7 show the geometry optimized structure has a more

Me idealized trigonal bipyramidal geometry in the optimized [Titm ]CdOSiPh3 structure.

Specifically, the C-Cd-O angle became more linear, going from 167° in the experimental structure to 174° in the optimized structure. Additionally, the N-Cd-N angles are closer

to the ideal angles of 120° resulting in a 5 parameter of 0.95 for the optimized complex.

PriBenz Scheme 4 shows that the cadmium siloxide complexes, [Titm ]CdOSiR3 (R =

i Me or Ph) were successfully isolated. These [TitmPr Benz] cadmium siloxide complexes were characterized by NMR spectroscopy. 1H NMR experiments show one set of peaks

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for the thiobenzimidazolyl protons at room temperature and at -60°C for both

iPrBenz iPrBenz 4 [Titm ]CdOSiMe3 and [Titm ]CdOSiPh3, indicating that the ligand is either  coordinate or is fluxional and still rapidly exchanging at low temperatures. Efforts to

iPrBenz obtain crystals of [Titm ]CdOSiR3 were unsuccessful.

Just as the Cd[N(SiMe3)2]2 reagent has shown a broad range of reactivity in the literature, these nitrogen-supported cadmium alkyl silylamide complexes also show the ability to access numerous cadmium complexes.

2.7 Discussion of [L]CdMe Complexes

As previously discussed, the cadmium methyl complexes supported by the

Me PriBenz [Titm ] and [Titm ] ligands were readily synthesized via addition of CdMe2 to the

3 protonated ligands (Scheme 3 and Scheme 4). The molecular structures for [ -S2N-

Me 3 PriBenz 4 PriBenz Titm ]CdMe, [ -N3C-Titm ], and [ -S3C-Titm ] provided in Figure 11, Figure

18, and Figure 19, respectively. The [Tptm]CdMe complex was not synthesized,

multiple experiments showed that addition of CdMe2 to [Tptm]H yielded the decomposition product [Tptm]CdSpy.

3 Me The molecular structure of [ -S2N-Titm ]CdMe in Figure 11 shows two of the arms in the [TitmMe] ligand rearranged and are bound to the carbon center via nitrogen and to cadmium via sulfur. One arm remains bound to the carbon center by the sulfur atom and is not coordinated to the metal. A similar rearrangement of the [TitmMe] ligand has been observed in the literature.16 This conversion occurs in the presence of a 121

Me Lewis acid; for example, heating the protonated [S3-Titm ]H ligand in the presence of

Me 16 para-toluenesulfonic acid results in rearrangement to [N3-Titm ]H (Scheme 6).

Scheme 6. Isomerization of the [TitmMe]H ligand

3 Me In the reaction in which [ -S2N-Titm ]CdMe complex is formed, the CdMe2 reagent acts as the Lewis acid, resulting in the rearrangement of the two arms which coordinate to the metal center.

3 Me Selected bond lengths and angles in [ -S2N-Titm ]CdMe were measured to

identify the geometry of the cadmium center and are listed in Table 8. The 4 value of

0.31 indicates that the complex has a see-saw geometry.32b

Table 8. Selected bond lengths and angles in [TitmMe]CdMe

Bond lengths (Å) Bond Angles (°)

Cd-S1 2.6149(17) S1-Cd-Cligand 82.27(15)

Cd-S2 2.7334(16) S3-Cd-Cligand 77.19(15)

Cd-Cligand 2.298(6) S3-Cd-CH3 121.28(18)

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Cd-CH3 2.149(6) S1-Cd-CH3 111.18(19)

PriBenz Scheme 5 shows that addition of CdMe2 to [Titm ]H at room temperature

3 PriBenz results in the formation of [ -N2C-Titm ]CdMe (Figure 18). Heating, this reaction

4 PriBenz yields [ -S3C-Titm ]CdMe (Figure 19). The molecular structure in Figure 18 shows

3 PriBenz the third arm in the ligand in [ -N2C-Titm ]CdMe is not coordinated to the

4 cadmium center, which contrasts with the coordination of the ligand in [ -S3C-

i TitmPr Benz]CdMe.

3 Selected bond lengths and angles and 4 parameter for the [ -N2C-

PriBenz Titm ]CdMe complex are listed in Table 9. The 4 value of 0.31 indicates that the

four-coordinate cadmium center is in a see-saw geometry; the 4 value, and thus the

3 Me 3 PriBenz geometry, of both [ -S2C-Titm ]CdMe and [ -N2C-Titm ]CdMe complexes are the same.

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3 PriBenz Table 9. N-Cd-C and C-Cd-C bond angles and 4 parameter for [ -Titm ]CdMe

Bond lengths (Å) Bond Angles (°)

Cd-N11 2.2666(19) N11-Cd-Cligand 80.55(7)

Cd-N31 2.2773(19) N31-Cd-Cligand 81.06(7)

Cd-Cligand 2.370(2) N11-Cd-CH3 124.21(11)

Cd-CH3 2.142(3) N31-Cd-CH3 121.83(11)

4 PriBenz Selected bond lengths and angles for the [ -S3-Titm ]CdMe complex are

listed in Table 10 and show that this complex is trigonal bipyramidal with a 5 parameter of 0.97.

4 PriBenz Table 10. S-Cd-S and C-Cd-C bond angles and 5 parameter for [ -Titm ]CdMe

Bond lengths (Å) Bond Angles (°)

Cd-S1 2.7641(7) S1-Cd-S2 103.019(19)

Cd-S2 2.8051(6) S2-Cd-S3 115.613(18)

Cd-S3 2.8330(6) S1-Cd-S3 117.219(18)

Cd-Cligand 2.341(2) Cligand-Cd-CH3 175.53(9)

Cd-CH3 2.201(3)

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The Cligand-Cd-CH3 bond lengths in the three cadmium methyl complexes were measured (Table 11) and compared to see how the different coordination modes of the ligands affect these bond lengths. The Cd-Me bond lengths were also compared with other methyl cadmium complexes in the literature. Only three other cadmium alkyl complexes that contain an additional Cd-C bond have been structurally characterized,

and they are cadmium carbene complexes. The Cligand-Cd and Cd-Me bond lengths for these reported complexes are also listed in Table 11.

Table 11. Bond lengths in complexes containing a C-Cd-Me moiety

Compound d(Cligand-Cd)/Å d(Cd-Me)/Å Reference

3 Me 2.298(6) 2.149(6) this work [ -S2N-Titm ]CdMe

3 PriBenz 2.341(2) 2.201(3) this work [ -N3-Titm ]CdMe

4 PriBenz 2.370(2) 2.142(3) this work [ -S3-Titm ]CdMe

Ad 2 2.406 2.199, 2.185 42 [(im )CdMe2]

Mes 2 2.370 2.184, 2.185 42 [(im )CdMe2]

Mes 2 2.327 2.186, 2.181 42 [(im )CdMe2]●tol

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3 A comparison of the Cd-Cligand bond lengths in Table 11 show that the [ -S2C-

Me Titm ]CdMe complex has the shortest Cd-Cligand length of 2.298 Å, compared to the

3 PriBenz 4 PriBenz annulated [ -N2C -Titm ]CdMe and [ -S3C-Titm ]CdMe compounds which

3 have lengths of 2.341 Å and 2.370 Å, respectively. The longer Cd-Cligand bonds in the [ -

PriBenz 4 PriBenz N2C-Titm ]CdMe and [ -S3C-Titm ]CdMe complexes correlate well with the

literature values (Table 11). The Cd-Cligand bonds within all the complexes in Table 11 are longer than the Cd-Me bond lengths.

3 Me 3 PriBenz The Cd-Me bond lengths in the [ -S2C-Titm ]CdMe, [ -N2C-Titm ]CdMe,

4 PriBenz and [ -S3C-Titm ]CdMe complexes are 2.149 Å, 2.201 Å, and 2.142 Å, respectively.

These Cd-Me bond lengths are all within the literature values for complexes with terminal cadmium methyl moieties. The CSD reports that the average Cd-Me bond

43 length is 2.16Å in which the shortest Cd-Me bond is 2.07Å in a cubane complex and the longest is 2.28Å in the bimetallic complex.44

A CSD search for other cadmium alkyl compounds with a S2C or S3C binding

3 Me 4 PriBenz motif yielded no results making [ -S2C-Titm ]CdMe and [ -S3C-Titm ]CdMe the first structurally characterized cadmium alkyl complexes featuring this sulfur-rich coordination environment. This coordination environment is of special interest due to their similarity to biological systems. For example, the sulfur-rich [TmR] ligand is often used as a molecular mimic for the active sites of MerB45 and liver alcohol dehydrogenase.46 Furthermore, cadmium is often used as a substitute of zinc within

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these molecular models due to the ability of cadmium to act as a spectroscopic probe.47

3 Me 4 PriBenz Therefore, [ -S2C-Titm ]CdMe and [ -S3C-Titm ]CdMe can serve as similar

3 biological molecular models as they provide a sulfur rich environment. The [ -S2C-

Me 4 PriBenz Titm ] and [ -S3C-Titm ] ligands also are able to coordinate to metals via a C-M interaction, as we have seen. This additional bond is an interesting comparison to

[TmR]Cd and [BmR]Cd complexes which have boron as the central atom.

An investigation of the reactivity of the cadmium methyl bonds in all three [3-

Me 3 PriBenz 4 PriBenz S2C-Titm ]CdMe, [ -N2C-Titm ]CdMe, and [ -S3C-Titm ]CdMe complexes, could be of future interest. For example, previous studies of the reactivity of

t [TmBu ]CdMe in the Parkin group showed cadmium alkyls are able to access Cd-E (E =

48 But 49 O, S, Se, Te) complexes and the thiolate complex [Tm ]CdSCH2CONHPh.

3 Me 3 PriBenz 4 PriBenz The [ -S2C-Titm ]CdMe, [ -N2C-Titm ]CdMe, and [ -S3C-Titm ]CdMe complexes were also characterized via 1H NMR spectroscopy. The cadmium-methyl resonances for the complexes are listed in Table 12. Both 111Cd and 113Cd satellites in [3-

PriBenz 1 2 N2C-Titm ]CdMe were observed in the H NMR spectrum and two sets of JCd-H coupling values were measured and are listed in Table 12. Cadmium satellites were

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1 3 Me 4 PriBenz observed in the H NMR spectra of [ -S2C-Titm ]CdMe and [ -S3C-Titm ]CdMe but they were broad (Figure 25).

Table 12. 1H NMR data for terminal cadmium methyl complexes

Compound (Cd-CH )/ppm 2 2 Reference 3 J111Cd-H/Hz J113Cd-H/Hz

3 0.64 69 71 this work [ -N3- i TitmPr Benz]CdMe

t [TpBu ,Me]CdMe 0.56 71 74 2d

t [TmBu ]CdMe 0.37 67 70 48

Figure 25. 1H NMR spectrum of the Cd-Me resonance with cadmium satellites in [3-

Me S2C-Titm ]CdMe

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3 Table 12 shows that the Cd-Me chemical shifts and coupling values for [ -N2C-

i TitmPr Benz]CdMe are 69 Hz and 71 Hz for the 111Cd-H and 113Cd-H nuclei. These coupling constants fall within the range of observed literature values.2d,48

i Due to our observance of multiple coordination modes of the [TitmPr Benz] ligand in the cadium methyl complexes, DFT calculations comparing the energy minima for

3 PriBenz 4 PriBenz 3 PriBenz [ -N2C-Titm ]CdMe versus [ -N3C-Titm ]CdMe and [ -S2C-Titm ]CdMe

4 PriBenz versus [ -S3C-Titm ]CdMe were performed (Figure 26).

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3 PriBenz 4 PriBenz Figure 26. Structures of the [ -N2C-Titm ]CdMe versus [ -N3C-Titm ]CdMe

3 PriBenz 4 PriBenz (top) and [ -S2C-Titm ]CdMe versus [ -S3C-Titm ]CdMe (bottom)

3 3 Within Figure 26, the energies for the  coordinate species, [ -N2C-

PriBenz 3 PriBenz 4 Titm ]CdMe and [ -S2C-Titm ]CdMe, were set to zero, and the  coordinate

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energies are reported relative to these complexes. The DFT calculations show that the

3 PriBenz [ -N2C-Titm ]CdMe complex, which was observed in the solid state (Figure 18) has

4 PriBenz an energy difference of ~2 kcal/mol higher in energy than the [ -N3C-Titm ]CdMe

4 PriBenz complex. In contrast, the [ -S3C-Titm ]CdMe complex, which was observed in the solid state by X-ray diffraction (Figure 19), was significantly lower in energy than the

3 PriBenz [ -S2C-Titm ]CdMe complex by ~9 kcal/mol.

2.8 Discussion of [L]CdNCO Complexes

Me The {[Tptm]Cd(-NCO)}2 and [Titm ]CdNCO complexes were synthesized and their molecular structures are provided in previous sections in Figure 4 and Figure 13.

Figure 4 shows that the {[Tptm]Cd(-NCO)}2 complex is a dimer in the solid state.

However, unlike the dimeric {[Tptm]Cd(-OSiMe3)}2 complex, the [Tptm] ligand in the isocyanate complex is 4-coordinate to the cadmium center making the metal center

overall six coordinate. In addition, the bridging NCO moiety in {[Tptm]Cd(-NCO)}2 features an M-NCO-M coordination mode (Figure 27).50a The nitrogen and oxygen atoms in the bridging NCO moiety are assigned so that the refinement value is lowest, if these atom assignments are switched, the refinement parameter increases from 4.67% to 4.83% and the thermal parameter for the oxygen bound to carbon is disproportionately large.

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The M-NCO-M coordination mode is uncommon, and accounts for only 4% of the 370 total structurally characterized metal isocyanate compounds in the CSD,50 as shown in Table 13.

Figure 27. Coordination modes of NCO observed in structurally characterized metal complexes

Table 13. Percent of structurally characterized metal complexes containing an NCO moiety in CSD 1.1633

Coordination Mode (%)

N-terminal 80

Bridging M2-NCO 4

M-NCO-M 15

O-terminal 0.5

Bridging M2-OCN 0.8

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Selected bond angles and bond length data for our {[Tptm]Cd(-NCO)}2 complex are listed in Table 14 and this angle data shows that the complex is a distorted octahedron (Figure 28).

Table 14. Selected bond angles in {[Tptm]Cd(-NCO)}2

Bond lengths (Å) Bond Angles (°)

Cd-N1 2.319(3) N1-Cd-N2 99.07(11)

Cd-N2 2.303(4) N1-Cd-N3 103.31(11)

Cd-N3 2.322(3) N2-Cd-O 79.82(12)

Cd-C 2.345(4) N3-Cd-O 77.51(11)

Cd-N(CO) 2.219(4) C-Cd-O 174.38(14)

Cd-O(CN) 2.574(3) Cd-N-C(O) 145.96

Cd-O-C(N) 125.27

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Figure 28. Metal center in {[Tptm]Cd(-NCO)}2 showing a distorted octahedral geometry

There are only five other cadmium isocyanate complexes which have been characterized via X-ray diffraction and they all have terminal NCO moieties. The average Cd-N(CO) length in these reported complexes is 2.21Å, with the shortest Cd-

N(CO) bond of 2.171Å in a copper-cadmium bimetallic complex51d and the longest length of 2.245 Å in a tetrapyridine complex.51a Comparison with these reported

complexes shows that the Cd-N(CO) bond length of 2.22 Å in our {[Tptm]Cd(-NCO)}2 complex correlates well with these reported M-N(CO) bond lengths.

Of the other M-NCO-M bridging compounds in the CSD, the shortest M-N(CO) bond length is 1.88 Å in a copper diamine complex50c and the longest bond length is 2.63

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Å in a silver complex.50j The Cd-N(CO) bond length of 2.22 Å in our {[Tptm]Cd(-

NCO)}2 complex correlates well with these reported M-N(CO) bond lengths. Regarding the M-O(CN) bond lengths in reported M-NCO-M bridging compounds, the shortest

M-O(CN) bond is 1.93 Å in a copper dimer50a and the longest bond is 2.59 Å in a copper nitrogen-rich cryptand complex. 50b The Cd-O(CN) bond length of 2.57 Å in our

{[Tptm]Cd(-NCO)}2 correlate well with these literature values.

In comparison, the zinc analogue, [Tptm]ZnNCO, is a monomer, as shown in

Figure 29.

Figure 29. Molecular structure of [Tptm]ZnNCO●0.5C6H6 (reproduced from reference

12)

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Density Functional Theory (DFT) geometry optimization calculations were

performed on the monomeric [Tptm]MNCO and dimeric {[Tptm]M(-NCO)}2 (M = Cd,

Zn) complexes. The formation of the dimeric {[Tptm]M(-OSiMe3)}2 (M = Cd, Zn) species from two monomers was calculated and compared with the energy minima of

the geometry optimized {[Tptm]M(-NCO)}2 complexes. The energy difference, E, are listed in Table 15. The values in Table 15 show that formation of the {[Tptm]Cd(-

NCO)}2 is more favorable than the formation of the {[Tptm]Zn(-NCO)}2, which

supports our experimental observation that the molecular structure of {[Tptm]Cd(-

NCO)}2 and [Tptm]ZnNCO were obtained.

Table 15. DFT energy calculations of monomeric and dimeric metal isocyanate complexes

Compound E (kcal/mol)

{[Tptm]Cd(-NCO)}2 -12.89

{[Tptm]Zn(-NCO)}2 -6.37

The molecular structure for the [TitmMe]CdNCO complex is provided in Figure

Me 13. In contrast to the {[Tptm]Cd(-NCO)}2complex complex, the [Titm ]CdNCO complex is monomeric with a terminal NCO moiety. Selected bond lengths and angles

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for the complex are listed in Table 16 and Table 17, respectively. The 5 value of 0.94 shows the cadmium center sits in a distorted trigonal bipyramidal geometry.

The Cd-NCO bond length is 2.175(4)Å (Table 16) and the Cd-NCO bond angle is

130.5(4)° (Table 17) in [TitmMe]CdNCO. In comparison with the [Tptm] analogue, the

Cd-NCO length is shorter by 0.04Å and the Cd-NCO angle is significantly smaller in

[TitmMe]CdNCO. Even though the in [TitmMe]CdNCO complex is a monomer in the solid state, the Cd-N-C bond angle, in the NCO moiety, corresponds more closely to the angles in dimeric M-NCO complexes which feature smaller M-N-C angles.

DFT geometry optimization calculations were performed on [TitmMe]CdNCO and selected bond lengths and angles for the optimized complex are listed in Table 16 and Table 17, respectively. The geometry optimized structure is an ideal trigonal

bipyramid, with a 5 parameter of 0.99. Additionally, this structure has a Cd-NCO angle of 127.60° which is even smaller than that in the experimentally determined molecular structure.

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Table 16. Select bond lengths in the X-ray and the DFT optimized structures of [TitmMe]CdNCO

d(Cd-N11)/Å d(Cd-N21)/Å d(Cd-N31)/Å d(Cd-C)/Å d(Cd-NCO)/Å

Experimental 2.226(4) 2.230(4) 2.233(4) 2.514(5) 2.175(4)

Geometry optimized 2.226 2.230 2.233 2.514 2.175

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Table 17. Select angles in the X-ray and the DFT geometry optimized structures of [TitmMe]CdNCO

N11-Cd-N21/° N21-Cd-N31/° N11-Cd-N31/° C-Cd-NCO/° Cd-N-CO/° 5

Experimental 111.37(14) 119.69(14) 120.26(14) 176.92(17) 130.5(4) 0.94

Geometry optimized 109.58 117.64 117.95 177.44 127.60 0.99

a There are two independent molecules in the asymmetric unit.

2.9 Discussion of [L]CdO2CX (X = H, Me) Complexes

As shown in Scheme 1, [Tptm]CdOAc was obtained from the reaction of

Me3SiOAc with the [Tptm]CdOSiMe3. The molecular structure in Figure 9 shows that

4 the [Tptm] ligand is coordinated in a  manner to the cadmium center and that both oxygen atoms in the acetate moiety are coordinated to cadmium. Selected bond lengths and angles in [Tptm]CdOAc are listed in Table 18 and Table 19, respectively.

The bond lengths Table 18 show that the acetate moiety coordinated in an asymmetric bidentate manner to cadmium. The Cd-O lengths in [Tptm]CdOAc are

2.289 Å and 2.507 Å having a d of 0.218Å. The Cd-O bond lengths are within the range of bond lengths reported in the literature for bidentate cadmium acetate complexes.

The average Cd-O bond length is 2.39 Å, with a range of 2.20 Å in a cadmium diacetate hydrate complex,52 with the longest Cd-O bond of 2.78 Å, in a sulfur-rich cadmium diacetate complex.53 The cadmium center in [Tptm]CdOAc is six-coordinate overall.

The most common six-coordinate geometries are octahedral or trigonal prismatic.54 The measurement of the dihedral angle (Figure 30) looking down the three-fold axis of a six- coordinate complex can be used to distinguish between the two geometries.

Specifically, a dihedral angle of 60° is indicative of an ideal octahedron and an angle of

0° is observed in a trigonal prism.55

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Table 18. Selected bond lengths in cadmium acetate and formate complexes

Compound Cd-N1/Å Cd-N2/Å Cd-N3/Å Cd-C/Å Cd-O1/Å Cd-O2/Å d(Cd-O)

[Tptm]CdOAc 2.2327(6) 2.297(6) 2.336(6) 2.383(7) 2.289(5) 2.507(5) 0.218

[Tptm]CdO2CH 2.307(7) 2.338(5) 2.346(9) 2.380(8) 2.299(9) 2.522(8) 0.223

Me [Titm ]CdOAc 2.227(8) 2.237(8) 2.238(9) 2.615(10) 2.261(8) 2.274(7) 0.013

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Table 19. Selected dihedral bond angles in cadmium acetate complexes

Compound N2-Cd-O1/° C-Cd-N3/° N1-Cd-O2/°

[Tptm]CdOAc 18.87 1..13 22.54

[Tptm]CdO2CH 24.01 3.78 21.77

[TitmMe]CdOAc 8.82 8.90 34.98

Figure 30. A view down the three-fold axis in an octahedron and trigonal prism

The dihedral angles in [Tptm]CdOAc 18.87°, 1.13°, and with the largest of 22.54°

(Table 19) indicating that the metal adopts a distorted trigonal prismatic geometry

(Figure 31). As shown in Figure 31, two Cd-N and one Cd-C bond from the [Tptm] ligand comprises one hemisphere and both Cd-O bonds from the acetate and one Cd-N bond comprises the other hemisphere.

Figure 31. Atoms coordinating to cadmium in [Tptm]CdOAc showing a distorted trigonal antiprismatic geometry

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The molecular structure of [Tptm]CdO2CH in Figure 10 shows the [Tptm] ligand

4 is coordinated in a  manner to the cadmium center. The Cd-O bond lengths in

[Tptm]CdO2CH (Table 18) show there is one shorter Cd-O bond length of 2.289Å and a longer Cd-O interaction of 2.522Å. with a d of 0.223 Å. For comparison between the

Cd-O bond lengths in our [Tptm]CdO2CH complex, a list of Cd-O bond lengths in other cadmium formate complexes reported in the CSD are listed in Table 20.

Table 20. Cd-O bond distances in cadmium formate complexes

Compounda d(Cd-O1)/Å d(Cd-O2)/Å d(Cd-O)/Å Reference

a,b [(NioxH2)2Cd(O2CH)2] 2.265 3.610 1.345 56a

b [(py)2Cd(H2O)2(O2CH)2] 2.284 3.520 1.236 56b

a,b [Cd(Niox)(O2CH)2H2O(bpy)]2 2.221, 2.224 3.424, 3.475 1.203, 56c

[(py-CONH2)2Cd(O2CH)2] 2.286, 2.250 3.032, 3.166 0.746, 0.916 56d

a,b [(NioxH2)2Cd(O2CH)2] 2.214 3.521 1.307 56e a Niox = 1,2-cyclohexanedionedioxime b The molecule is related by a plane of symmetry, only the unique Cd-O atom distances are listed

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Table 20 shows that the cadmium formate complexes reported in the literature also exhibit one short Cd-O bond and one longer interaction and the d values range

56d 56a from the smallest of 0.746 Å in a pyridine complex to the 1.345 Å. The d within our

[Tptm]CdO2CH complex is significantly smaller (0.223 Å) than the corresponding values in the reported cadmium acetates and is similar to the d value of [Tptm]CdOAc,

which is 0.218 Å. The cadmium center in [Tptm]CdO2CH is considered six coordinate with dihedral angles of 24.01°, 3.78°, and 21.77° (Table 19). These dihedral angles indicate that the complex is distorted trigonal prismatic, since they are closer to 0° than

60°, in which O1, O2 and N3 comprise one hemisphere and N1, N2, and C comprise the other (Figure 32).

Figure 32. Atoms coordinating to cadmium in [Tptm]CdO2CH showing a distorted trigonal antiprismatic geometry

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The isolation of [Tptm]CdO2CH was significant for two reasons: first, there are not many cadmium formate complexes which have been isolated and structurally characterized. Second, this complex is evidence that a cadmium hydride complex forms

in situ, followed by CO2 insertion into the Cd-H bond. This mechanism has been

13 observed for the [Tptm]ZnO2H complex.

This evidence of an in situ cadmium hydride is significant because terminal cadmium hydrides are scarce within the literature and only two complexes have been characterized via X-ray diffraction: a terphenyl cadmium hydride57 and a bridging terphenyl cadmium hydride.58 The interest in cadmium hydride complexes stems from the difficulty in synthesizing group 12 complexes with M-M bonds. The homolytic cleavage of the M-H bond in a cadmium hydride complex allows the facile synthesis of complexes containing Cd-Cd bonds.57,58 Additionally, as previously discussed the

[Tptm]ZnH complex synthesized in the Parkin group was found to have high catalytic activity,12 it would be interesting to probe the reactivity of a cadmium hydride complex.

Unfortunately, the numerous attempts to isolate [Tptm]CdH were unsuccessful.

The molecular structure of [TitmMe]CdOAc in Figure 14 shows the [TitmMe] ligand is 4 to the metal. The selected bond lengths and angles in the complex are listed in Table 18 and Table 19, respectively. The two Cd-O bond lengths in Table 18 indicate

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the acetate ligand is coordinated in a symmetric manner, and have a d of only 0.01Å.

The similarity in the Cd-O bonds indicates that both of the oxygen atoms in the acetate moiety are bound to cadmium, making the metal six-coordinate overall. The dihedral angles in the complex are 8.82°, 8.90°, and with the largest angle of 34.98°, indicating that the complex adopts a distorted trigonal prismatic geometry, as shown in Figure 33.

The coordinate environment of cadmium in Figure 33 shows that both Cd-O bonds in the acetate and one Cd-N bond from the [TitmMe] ligand comprises one hemisphere, and two Cd-N bonds and one Cd-C bond from the [TitmMe] ligand comprises the other.

Figure 33. The cadmium center in [TitmMe]CdOAc showing the cadmium in a distorted trigonal prismatic geometry

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The cadmium acetate and formate complexes are of interest because of their structural similarity to the metal carboxylate intermediate formed during the catalytic

59 mechanism of the hydration of CO2 by carbonic anhydrase (CA) (Scheme 7).

Scheme 7. Catalytic mechanism of the hydration of carbon dioxide by zinc CA

(reproduced from reference 59b)

Although the zinc analogue for carbonic anhydrase is more prevalent in the literature and in nature, the metal is spectroscopically inert, therefore, cadmium is often substituted into CA molecular models to serve as a spectroscopic probe.47 In addition, naturally occurring cadmium substituted carbonic anhydrase enzyme was found within

marine diatoms. The enzyme undergoes the same mechanism for hydration of CO2 as zinc CA.60 As shown in Scheme 7, a key intermediate in the CA catalytic mechanism is the formation of a metal bicarbonate species. There is only one cadmium bicarbonate complex that has been structurally characterized, a cyclic amine complex.61 As such, the

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synthesis of cadmium carboxyl complexes and investigation of their structure can provide insight into the metal bicarbonate intermediate in CA.

2.10 Discussion of [L]CdX (X = Cl, Br, I) Complexes

The cadmium chloride and bromide complexes supported by the [Tptm] and

[TitmMe] ligands were synthesized as outlined in Scheme 1 and Scheme 3. The cadmium iodide complexes were synthesized through a different route than the chloride and bromide complexes, as shown in Scheme 8.

Scheme 8. Synthesis of [L]CdI (L = [Tptm], [TitmMe])

The molecular structures of the [Tptm]CdI and [TitmMe]CdI complexes are provided in Figure 34 and Figure 35, respectively.

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Figure 34. Molecular structure of [Tptm]CdI (disordered atoms are not shown)

Figure 35. Molecular structure of [TitmMe]CdI

The molecular structures of [Tptm]CdX complexes (X = Cl, Br, I) in Figure 7,

Figure 8, and Figure 34 show the [Tptm] ligand is 4 coordinate to the metal center.

Similarly, the molecular structures of [TitmMe]CdX (X = Cl, Br, I) in Figure 15, Figure 16,

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and Figure 35 show that the [TitmMe] ligand is also 4 coordinate to cadmium. To determine the exact cadmium geometry, the bond lengths and angles for these complexes are listed in Table 21 and Table 22, respectively.

Table 21. Select bond lengths in [Tptm]CdX and [TitmMe]CdX

Compound d(Cd-N1)/Å d(Cd-N2)/Å d(Cd-N3)/Å d(Cd-C)/Å d(Cd-X)/Å

[Tptm]CdCl 2.307(3) 2.322(3) 2.329(4) 2.4842(14) 2.383(5)

[Tptm]CdBra 2.301(3) 2.307(4) 2.318(4) 2.375(5) 2.5848(6)

[Tptm]CdI 2.325(10) 2.337(11) 2.347(11) 2.361(13) 2.7741(15)

[TitmMe]CdCla 2.227(6) 2.231(6) 2.234(6) 2.510(7) 2.5318(17)

[TitmMe]CdBra 2.256(12), 2.241(12), 2.253(13), 2.496(16), 2.618(2), 2.237(12) 2.256(12) 2.338(13) 2.481(18) 2.593(2)

[TitmMe]CdI 2.217(6) 2.232(7) 2.238(7) 2.631(7) 2.8295(13)

Table 22. Select bond angles in [Tptm]CdX and [TitmMe]CdX Complexes

Compound N1-Cd-N2/° N2-Cd-N3/° N1-Cd-N3/° C-Cd-X/° 5

[Tptm]CdCl 107.15(12) 114.25(12) 133.31(13) 177.33(12) 0.73

[Tptm]CdBra 114.1(2) 115.8(2) 121.6(2) 177.65(14) 0.72

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[Tptm]CdI 109.6(4) 118.4(4) 125.1(4) 177.0(3) 0.87

[TitmMe]CdCl 114.1(2) 115.8(2) 121.6(2) 177.86(15) 0.94

[TitmMe]CdBra 112.3(4), 117.8(5), 119.8(5), 177.0(4), 0.95,

112.4(5) 118.3(4) 123.3(5) 177.3(4) 0.90

[TitmMe]CdI 107.2(2) 115.9(2) 124.1(2) 175.86(16) 0.86

Me The 5 parameters of the [Tptm]CdX and [Titm ]CdX complexes in Table 21 show that the metal center in these [Tptm] cadmium halide complexes adopt a distorted

Me trigonal bipyramidal geometry. The 5 parameters in the [Titm ]CdCl and

Me [Titm ]CdBr complexes are noticeably much higher than the 5 parameters in

[Tptm]CdCl or [Tptm]CdBr, indicated that the [TitmMe]CdX complexes are closer to an ideal trigonal bipyramidal geometry.

In a comparison between the bond lengths in [Tptm]CdCl and [TitmMe]CdCl, Cd-

Cl bond in the [TitmMe]CdCl complex (2.532Å) is significantly longer than that in the

[Tptm]CdCl complex (2.383Å). In comparison with terminal cadmium chloride complexes reported in the CSD, the average Cd-Cl bond length is 2.48Å. The range of

Cd-Cl bond lengths spans 2.05 Å in a phenanthroline complex62a to 2.88Å in a tetraamine complex.59b The Cd-Cl bond length in the [Tptm]CdCl complex is 2.383Å

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and in [TitmMe]CdCl is 2.53Å which are within the range of these literature values. In structurally characterized cadmium complexes which contain a C-Cd-Cl moiety, the C-

Cd bond lengths range from 1.80 Å in an aryl complex 63b to 2.78 Å in a porphyrin complex.63a The C-Cd bond length in [TitmMe]CdCl is 2.510Å, which is longer than the corresponding bond length in [Tptm]CdCl of 2.484Å. Both of these C-Cd bond lengths are within range of these literature values.

DFT geometry optimization of the calculations of the [Tptm]CdCl and

[TitmMe]CdCl complexes were performed. The bond lengths and angles within the

optimized complexes are listed in Table 23 and Table 24, respectively. The 5 parameters of 1.02 and 1.07 (Table 23) the optimized [Tptm]CdCl and [TitmMe]CdCl complexes are ideal trigonal bipyramidal.

A comparison of the Cd-Cl bond lengths between the optimized [Tptm]CdCl and

[TitmMe]CdCl structures shows that the Cd-Cl bond in Tptm is 2.506 Å which is longer than that in [TitmMe]CdCl (2.492 Å), which contrasts with the experimental data in with

[TitmMe]CdCl has a longer Cd-Cl bond, as discussed previously. The C-Cd bonds in the optimized structures are 2.450 Å in [Tptm]CdCl and 2.723 Å in [TitmMe]CdCl, which correlates with the experimental data in which the [TitmMe]CdCl complex has a longer

C-Cd bond.

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Table 23. Select bond lengths in DFT optimized [Tptm]CdX and [TitmMe]CdX

Compound d(Cd-N1)/Å d(Cd-N2)/Å d(Cd-N3)/Å d(Cd-C)/Å d(Cd-X)/Å

[Tptm]CdCl 2.364 2.365 2.366 2.450 2.506

[Tptm]CdBra 2.372 2.373 2.374 2.449 2.689

[Tptm]CdI 2.388 2.388 2.389 2.446 2.877

[TitmMe]CdCla 2.310 2.313 2.315 2.723 2.492

[TitmMe]CdBra 2.312 2.314 2.315 2.771 2.672

[TitmMe]CdI 2.315 2.317 2.318 2.707 2.861

Table 24. Select bond angles in DFT optimized [Tptm]CdX and [TitmMe]CdX

Compound N1-Cd-N2/° N2-Cd-N3/° N1-Cd-N3/° C-Cd-X/° 5

[Tptm]CdCl 115.82 118.548 118.69 179.86 1.02

[Tptm]CdBra 115.59 118.32 118.96 179.92 1.02

[Tptm]CdI 114.32 118.57 119.62 179.78 1.00

[TitmMe]CdCl 114.24 114.62 115.57 179.65 1.07

[TitmMe]CdBra 113.71 114.36 116.68 179.83 1.05

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[TitmMe]CdI 113.97 115.19 115.56 179.81 1.07

Table 21 shows the Cd-Br bond lengths in [TitmMe]CdBr (2.618 Å and 2.593 Å) are slightly longer than those in in [Tptm]CdBr (2.585 Å). They are also within the range of terminal Cd-Br bond lengths reported in the CSD. The average length of for terminal

Cd-Br bond in the CSD is 2.591Å, with the shortest length of 2.393Å in a terpyridine

64a 64b complex and the longest length of 3.026Å in a tetrabenzimidazole complex. The C-

Cd bond length in [Tptm]CdBr is 2.375Å, and those in [TitmMe]CdBr, are 2.481Å and

2.496Å, showing that the C-Cd bond in [TitmMe]CdBr is longer than that in [Tptm]CdBr, similar to the chloride complexes.

DFT geometry optimization of the calculations of the [Tptm]CdBr and

[TitmMe]CdBr complexes were performed. The bond lengths and angles within the

optimized complexes are listed in Table 23 and Table 24, respectively. The 5 parameters of 1.02 and 1.05 (Table 23) the optimized [Tptm]CdBr and [TitmMe]CdBr complexes are ideal trigonal bipyramidal.

The Cd-Br bond lengths in the optimized [Tptm]CdBr and [TitmMe]CdBr structures are 2.689 Å and 2.672 Å, respectively, indicating that the [Tptm]CdBr complex has slighter longer Cd-Br bond than [TitmMe]CdBr, which contrasts with the experimental data in which [TitmMe]CdBr has slightly longer Cd-Br bonds (2.618 Å and

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2.593 Å) than [Tptm]CdBr (2.585 Å). The Cd-C bonds in the optimized [Tptm]CdBr and

[TitmMe]CdBr structures are 2.449 Å and 2.771 Å, respectively. These calculated bond lengths match the experimental data, in which [TitmMe]CdBr (2.481Å and 2.496Å) has a longer Cd-C bond than [Tptm]CdBr (2.375 Å).

Table 21 shows Cd-I bond in [TitmMe]CdI is 2.83 Å, which is 0.06Å longer than the corresponding bond length in [Tptm]CdI of 2.77 Å. According the CSD, the average

Cd-I length for terminal iodides is 2.75Å, where the shortest Cd-I bond is 2.623Å in a nitrogen-rich tripodal cadmium complex2d and the longest is 3.452Å in a propane diamine complex.65 In comparison with these Cd-I lengths in the literature, both Cd-I bond lengths in [TitmMe]CdI and [Tptm]CdI are within this range of literature values.

The C-Cd bond length in [TitmMe]CdI is 2.63Å, which is significantly longer than that in

[Tptm]CdI (2.36Å). These lengths are in accord with the trend seen in the chloride and bromide complexes where the [TitmMe]CdX complexes have longer C-Cd bonds.

DFT geometry optimization of the calculations of the [Tptm]CdI and [TitmMe]CdI complexes were performed. The bond lengths and angles within the optimized

complexes are listed in Table 23 and Table 24, respectively. The 5 parameters of 1.00 and 1.07 (Table 23) the optimized [Tptm]CdI and [TitmMe]CdI complexes are ideal trigonal bipyramidal.

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The Cd-I bond lengths in the optimized [Tptm]CdI and [TitmMe]CdI structures are 2.689 Å and 2.672 Å, respectively, indicating that the [TitmMe]CdI complex has slighter longer Cd-I bond than [Tptm]CdI. The calculated bond data correlates with the experimental data in which the Cd-I bond in [TitmMe]CdI (2.830 Å) is longer than that in

[Tptm]CdI (2.774 Å). The Cd-C bonds in the optimized [Tptm]CdI and [TitmMe]CdI structures are 2.446 Å and 2.707 Å, respectively. These calculated bond lengths match the experimental data, in which [TitmMe]CdI (2.631 Å) has a longer Cd-C bond than

[Tptm]CdI (2.361 Å).

2.11 Conclusion

The reactivity of cadmium bis(silylamide) and siloxide complexes supported by

i the nitrogen-rich [Tptm], [TitmMe] and [TitmPr Benz] ligands was investigated. Reactions

with [Tptm]CdN(SiMe3)2 and [Tptm]CdOSiMe3 complexes yielded [Tptm]CdX

Me complexes (X = OSiPh3, NCO, Cl, Br, OAc, O2CH). Reactions with [Titm ]CdN(SiMe3)2

Me Me and [Titm ]CdOSiPh3 yielded [Titm ]CdX complexes (X = OSiPh3, NCO, Cl, Br, OAc,

Me PriBenz PriBenz OPh ), and reactions with [Titm ]CdN(SiMe3)2 and [Titm ]CdOSiMe3 yielded

PriBenz But [Titm ]CdX (X = OSiPh3, OPh , O2CH). The cadmium acetate and formate complexes are of particular interest due to their structural similarity to cadmium

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bicarbonate carbonic anhydrase intermediate, a key intermediate produced by cadmium carbonic anhydrase. In addition, the synthesis of the cadmium methyl

3 Me 4 PriBenz complexes, [ -S2N-Titm ]CdMe and [ -S3-Titm ]CdMe, is reported and have the potential to serve as molecular models for sulfur-rich biological systems.

2.12 Experimental Section

2.12.1 General Considerations

All manipulations were performed using a combination of glovebox, high vacuum, and

Schlenk techniques under a nitrogen atmosphere.66 Solvents were purified and degassed by standard procedures. NMR spectra were measured on Bruker 300 DRX,

Bruker 400 DRX, and Bruker Avance 500 DMX spectrometers. 1H NMR spectra are

reported in ppm relative to SiMe4 ( = 0) and were referenced internally with respect to

67 13 the protio solvent impurity ( 7.16 for C6D5H,  2.08 C7D7H). C NMR spectra are

reported in ppm relative to SiMe4 ( = 0) and were referenced internally with respect to

67 the solvent ( 128.06 for C6D6). Coupling constants are given in hertz. IR spectra were recorded as KBr pellets on a Nicolet Avatar 370DTGS or ATR-IR spectra were obtained on a Perkin Elmer UATR Two and the data are reported in reciprocal centimeters (cm–1).

Mass spectra were obtained on a JEOL JMS-HX110HF tandem mass spectrometer using

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fast atom bombardment (FAB). All chemicals were obtained from Aldrich, with the

68 69 Me 70 exception of phenylsilane (Alfa Aesar). [CdN(SiMe3)2]2, [Tptm]Li, and [Titm ]Li were synthesized according to the literature.

2.12.2 X-ray Structure Determination

Single crystal X-ray diffraction data were collected on a Bruker Apex II diffractometer and crystal data, data collection and refinement parameters are summarized in Table 25.

The structures were solved using direct methods and standard difference map techniques, and were refined by full-matrix least-squares procedures on F2 with

SHELXTL (Version 6.12).71

2.12.3 Computational Details

Calculations were carried out using DFT as implemented in the Jaguar 7.5 (release 2007) suite of ab initio quantum chemistry programs.72 Geometry optimizations and frequency calculations were performed with the B3LYP density functional73 using the 6-

31G** (H, S, B, C, N, O, Si) basis set, the LACBP (Cl, Br) basis set and the LAV3P (Cd, I) basis set.74

2.12.4 Synthesis of [Tptm]CdN(SiMe3)2

A light yellow solution of [Tptm]H (79 mg, 0.23 mmol) in benzene (ca. 0.5 mL) was

treated with Cd[N(SiMe3)2]2 (130 mg, 0.30 mmol) via pipette. The reaction mixture

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became brighter yellow. The reaction mixture was allowed to stand for 10 minutes at

4 room temperature and was lyophilized to give [κ -Tptm]CdN(SiMe3)2 as a beige solid

(131 mg, 93%) Crystals suitable for X-ray were obtained via slow evaporation of

1 pentane into benzene. H NMR (C6D6): 0.37 [s, 18H, [(H3C)3Si]2NCdC(SC5H4N)3], 6.32

[m, 3H, [(H3C)3Si]2NCdC(SC5H4N)3], 6.56 [m, 6H, [(H3C)3Si]2NCdC(SC5H4N)3], 8.70 [d,

3 13 1 JH-H = 4 Hz, 3H, [(H3C)3Si]2NCdC(SC5H4N)3]. C{ H} NMR (C6D6): 6.9 [s, 6C,

[(H3C)3Si]2NCdC(SC5H4N)3], not observed [[(H3C)3Si]2NCdC(SC5H4N)3], 119.5 [s, 3C,

[(H3C)3Si]2NCdC(SC5H4N)3]. 121.9 [s, 3C, [(H3C)3Si]2NCdC(SC5H4N)3], 137.4 [s, 3C,

[(H3C)3Si]2NCdC(SC5H4N)3], 149.2 [s, 3C, [(H3C)3Si]2NCdC(SC5H4N)3]. IR Data (KBr disk, cm-1): 3070 (w), 3052 (w), 2994 (w), 2923 (w), 1585 (s), 1556 (m), 1456 (m), 1414 (s),

1282 (w), 1124 (m), 1088 (w), 1042 (w), 1003 (w), 756 (m), 720 (w), 680 (w), 636 (w). FAB-

MS: m/z = 455.9 [M]+, M = [κ3-Tptm]Cd.

2.12.5 Synthesis of [Tptm]CdNCO

3 A solution of [κ -Tptm]CdN(SiMe3)2 (36 mg, 0.06 mmol) in C6D6 (ca. 0.5 mL) in a NMR

tube equipped with a J. Young valve was treated with CO2 (1 atm). The reaction mixture was allowed to sit for 16 hours at room temperature. Monitoring by 1H NMR spectroscopy showed full conversion to [κ 4-Tptm]CdNCO after this time. The reaction mixture was lyophilized and [κ 4-Tptm]CdNCO (23 mg, 78%) was obtained as a light

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4 yellow solid. Crystals of [κ -Tptm]CdNCO•C6D6 suitable for X-ray diffraction were obtained via vapor diffusion of pentane into benzene. Anal. Calcd. for [κ 4-

Tptm]CdNCO: C, 41.1%; H, 2.4%; N, 11.3%. Found: C, 41.3%; H, 2.4%; N, 11.1%. 1H

NMR (C6D6): 6.18 [m, 3H, OCNCdC(SC5H4N)3], 6.50[m, 6H, OCNCdC(SC5H4N)3], 8.67

13 1 [m, 3H. OCNCdC(SC5H4N)3]. C{ H] NMR (C6D6): not observed [OCNCdC(SC5H4N)3],

119.7 [s, 3C, OCNCdC(SC5H4N)3], 120.7 [s, 3C, OCNCdC(SC5H4N)3], 128.1 [s, 1C,

OCNCdC(SC5H4N)3], 137.9 [s, 3C, OCNCdC(SC5H4N)3], 148.2 [s, 3C,

-1 OCNCdC(SC5H4N)3], 160.0 [s, 3C, OCNCdC(SC5H4N)3]. ]. IR Data (KBr disk, cm ): 3074

(w), 3050 (w), 2957 (w), 2927 (w), 2903 (w), 2878 (w), 2846 (w), 2191 (s) [asym (NCO)],

1589 (s), 1557 (m), 1457 (m), 1415 (s), 1287 (w), 1123 (m), 1083 (w), 1039 (w), 1014 (w),

757 (m). FAB-MS m/z = 496.9 [M]+, M = [κ 4-Tptm]CdNCO.

2.12.6 Synthesis of [Tptm]CdOSiMe3

4 A light yellow solution of [κ -Tptm]CdN(SiMe3)2 (122 mg, 0.20 mmol) in benzene (ca. 0.5 mL) was treated with TMSOH (39 mg, 0.43 mmol). The reaction was mixed over a period of 10 minutes at room temperature at which point colorless crystals crashed out of solution. The crystals were collected, washed with pentane (3 mL), and dried to give

4 [κ -Tptm]CdOSiMe3 as an off-white solid (80 mg, 74%). Crystals of {[Tptm]Cd(-

OSiMe3)}2 suitable for X-ray diffraction were obtained directly from the reaction

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4 mixture. Anal. Calcd. for [κ -Tptm]CdOSiMe3: C, 41.9%; H, 3.9%; N, 7.7%. Found C,

1 41.1%; H, 3.9%; N, 7.3%. H NMR (C6D6): 0.70 [s, 9H, (H3C)3SiOCdC(SC5H4N)3], 6.27 [br,

3 3H, (H3C)3SiOCdC(SC5H4N)3], 6.51 [br, 6H, (H3C)3SiOCdC(SC5H4N)3], 8.91 [d, JH-H = 5

13 Hz, 3H, (H3C)3SiOCdC(SC5H4N)3]. C NMR (C6D6): 5.68 [s, 3C,

(H3C)3SiOCdC(SC5H4N)3], not observed (H3C)3SiOCdC(SC5H4N)3], 119.1 [s, 3C,

(H3C)3SiOCdC(SC5H4N)3], 121.5 [s, 3C, (H3C)3SiOCdC(SC5H4N)3], 137.0 [s, 3C,

(H3C)3SiOCdC(SC5H4N)3], 148.8 [s, 3C, (H3C)3SiOCdC(SC5H4N)3], 160.6 [s, 3C,

-1 (H3C)3SiOCdC(SC5H4N)3]. IR Data (KBr disk, cm ): 3070 (w), 3043 (w), 3003 (w), 2950

(w), 1585 (s), 1556 (s), 1455 (s), 1414 (s), 1281 (m), 1241 (w), 1126 (s), 1090 (w), 1043 (m),

1002 (m), 913 (m), 841 (w), 757 (s), 721 (m), 635 (m), 483 (m). FAB-MS: m/z = 455.9 [M]+,

M = [κ3-Tptm]Cd.

2.12.7 Synthesis of [Tptm]CdOSiPh3

3 A solution of [κ -Tptm]CdN(SiMe3)2 (131 mg, 0.22 mmol) in benzene (ca. 0.5 mL) was

treated with Ph3SiOH (60 mg, 0.22 mmol). The reaction was allowed to sit for 30 minutes at room temperature. The reaction was then lyophilized to giving a beige solid which was washed with pentane (ca. 5 mL). The solid was dried giving [κ 4-

4 Tptm]CdOSiPh3 as a beige solid (126 mg, 81%). Crystals of [κ -Tptm]CdOSiPh3•C6D6 suitable for X-ray diffraction were obtained via slow evaporation of benzene. Anal.

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4 Calcd. for [κ -Tptm]CdOSiPh3: C, 55.9%; H, 3.7%; N, 5.6%. Found C, 56.0%; H, 3.9%; N,

1 5.5%. H NMR (C6D6): 6.04 [m, 3H, Ph3SiOCdC(SC5H4N)3], 6.48 [m, 6H,

3 Ph3SiOCdC(SC5H4N)3], 7.30 [m, 9H, Ph3SiOCdC(SC5H4N)3], 8.12 [d of d, JH-H = 2Hz and

3 13 1 8 Ph3SiOCdC(SC5H4N)3], 8.72 [d, JH-H = 5 Hz, 3H, Ph3SiOCdC(SC5H4N)3]. C{ H} NMR

(C6D6): not observed [Ph3SiOCdC(SC5H4N)3], 119.2 [s, 3C, Ph3SiOCdC(SC5H4N)3], 120.4

[s, 3C, Ph3SiOCdC(SC5H4N)3], 127.6 [s, 3C, Ph3SiOCdC(SC5H4N)3], 128.4 [s, 3C,

Ph3SiOCdC(SC5H4N)3], 135.5 [s, 6C, Ph3SiOCdC(SC5H4N)3], 137.6 [s, 3C,

Ph3SiOCdC(SC5H4N)3], 134.2 [s, 3C, Ph3SiOCdC(SC5H4N)3], 148.9 [s, 3C,

-1 Ph3SiOCdC(SC5H4N)3], 160.0 [s, 3C, Ph3SiOCdC(SC5H4N)3]. IR Data (KBr disk, cm ):

3059 (w), 3008 (w), 1586 (s), 1557 (m), 1456 (m), 1414 (s), 1286 (w), 1122 (m), 1105 (m),

1040 (m), 1019 9 (m), 1004 (m), 756 (m), 703 (s), 667 (w), 636 (w), 516 (s). FAB-MS: m/z =

455.9 [M]+, M = [κ4-Tptm]Cd.

2.12.8 Synthesis of [Tptm]CdCl

3 A cloudy beige solution of [κ -Tptm]CdOSiMe3 (7 mg, 0.01 mmol) in benzene (ca.0.5 mL) was treated with TMSCl (10 L, 0.08 mmol). The reaction mixture remained a cloudy beige solution. After 3 minutes of mixing, the reaction was lyophilized to give

[κ 4-Tptm]CdCl and a small amount of [Tptm]H as an off-white solid. The solid was washed with acetonitrile (3 mL) and dried to give [κ 4-Tptm]CdCl (6 mg, 92%) as an off-

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white solid. Crystals suitable for X-ray diffraction were obtained via slow evaporation

4 from benzene. Anal. Calcd. for [κ -Tptm]CdCl•0.15(C6D6): C, 40.4%; H, 2.6%; N, 8.4%.

1 Found: C, 40.4%; H, 2.0%; N, 7.7%. H NMR (C6D6): 6.19 [m, 3H, ClCdC(SC5H4N)3], 6.48

3 13 1 [m, 6h, ClCdC(SC5H4N)3], 9.13 [d, JH-H = 5 Hz, 3H, ClCdC(SC5H4N)3]. C{ H} NMR

(C6D6): not observed [ClCdC(SC5H4N)3], 119.3 [s, 3C, ClCdC(SC5H4N)3], 137.8 [s, 3C,

ClCdC(SC5H4N)3], 148.7 [s, 3C,ClCdC(SC5H4N)3], 159.9 [s, 3C, ClCdC(SC5H4N)3]. IR

Data (KBr disk, cm-1): 3052 (w), 3003 (w), 2920 (w), 2851 (w), 1579 (s), 1556 (s), 1455 (s),

1413 (s), 1282 (m), 1152 (w), 1122 (s), 1089 (w), 1042 (m), 1004 (m), 878 (w), 800 (w), 760

(s), 719 (m), 698 (w), 636 (w), 3609 (w), 485 (w). FAB-MS m/z = 490.4 [M]+, M = [κ 4-

Tptm]CdCl.

4 4 Reaction of [κ -Tptm]CdOSiPh3 with TMSCl: Formation of [κ -Tptm]CdCl

4 A solution of [κ -Tptm]CdOSiPh3 (10 mg, 0.01 mmol) in C6D6 (ca. 0.5 mL) in an NMR

tube equipped with a J. Young valve, was treated with excess TMSCl over CaH2 via vapor transfer. The reaction was monitored by 1H NMR spectroscopy, the data indicated conversion to [κ 4-Tptm]CdCl after 5 minutes at room temperature.

2.12.9 Synthesis of [Tptm]CdBr

3 A cloudy beige solution of [κ -Tptm]CdOSiMe3 (4 mg, 0.01 mmol) in benzene (ca. 0.5 mL) was treated with TMSBr (10 L, 0.08 mmol). A white precipitate formed in the

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reaction mixture. Immediately upon addition, the reaction mixture was lyophilized to a white solid. The solid was washed with acetonitrile (3 mL) and dried to give [κ 4-

Tptm]CdBr (4 mg, 99%). Crystals suitable for X-ray diffraction were obtained via slow

4 evaporation from benzene. Anal. Calcd. for [κ -Tptm]CdBr•0.5(C6D6): C, 39.8%; H,

1 2.6%; N, 7.3%. Found: C, 39.1%; H, 2.7%; N, 7.0%. H NMR (C6D6): 6.18 [m, 3H,

BrCdC(SC5H4N)3], 6.47 [m, 6H, BrCdC(SC5H4N)3], 9.18 [m, 3H, BrCdC(SC5H4N)3].

13 1 C{ H} NMR (C6D6): not observed 9 [BrCdC(SC5H4N)3], 119.3 [s, 3C, BrCdC(SC5H4N)3],

120.5 [s, 3C, BrCdC(SC5H4N)3], 137.8 [s, 3C, BrCdC(SC5H4N)3], 148.7 [s, 3C,

-1 BrCdC(SC5H4N)3], 159.8 [s, 3C, BrCdC(SC5H4N)3]. IR Data (KBr disk, cm ): 3070 (w),

3048 (w), 2999 (w), 1588 (s), 1556 (s), 1455 (s), 1412 (s), 1282 (m), 1156 (w), 1122 (s), 1089

(m), 1043 (m), 1003 (m)/,874 (w), 760 (s), 719 (m), 631 (m), 609 (w), 489 (w). FAB-MS m/z

= 534.8 [M]+, M = [κ 4-Tptm]CdBr.

4 4 Reaction of [κ -Tptm]CdOSiPh3 with TMSBr: Formation of [κ -Tptm]CdBr

4 A solution of [κ -Tptm]CdOSiPh3 (10 mg, 0.01 mmol) in C6D6 (ca. 0.5 mL) in an NMR

tube equipped with a J. Young valve, was treated with excess TMSBr over CaH2 via vapor transfer. The reaction was monitored by 1H NMR spectroscopy, the data indicated conversion to [κ 4-Tptm]CdBr after 5 minutes at room temperature.

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2.12.10 Synthesis of [Tptm]CdOAc

3 A cloudy beige solution of [κ -Tptm]CdOSiMe3 (15 mg, 0.03 mmol) in benzene (ca. 0.5 mL) was treated with TMSOAc (20 L, 0.13 mmol). The reaction mixture turned yellow and became clear. Monitoring by 1H NMR confirmed full conversion to [κ 4-

Tptm]CdOAc after sitting for 15 minutes at room temperature. The volatile components were removed in vacuo resulting in an off-white solid which was then washed with pentane to give [κ 4-Tptm]CdOAc (14 mg, 98%). Crystals suitable for X- ray diffraction were obtained from diffusion of pentane into toluene at 0˚C. 1H NMR

(C6D6): 2.57 [s, 3H, H3CC(O)CdC(SC5H4N)3], 6.23 [ br, 3H, H3CC(O)CdC(SC5H4N)3], 6.50

13 1 [m, 6H, H3CC(O)CdC(SC5H4N)3], 8.88 [br, 3H, H3CC(O)CdC(SC5H4N)3]. C{ H] NMR

(C6D6): 22.2 [s, 1C, Me(O)COCdCS(C5H4N)3], not observed [AcOCdC(SC5H4N)3], 119.2 [s,

3C, AcOCdCS(C5H4N)3], 120.8 [s, 3C, AcOCdCS(C5H4N)3], 137.4 [s, 3C,

AcOCdCS(C5H4N)3], 149.6 [s, 3C, AcOCdCS(C5H4N)3], 160.4 [s, 3C, AcOCdCS(C5H4N)3],

-1 179.2 [s, 1C, Me(O)COCdCS(C5H4N)3]. IR Data (KBr disk, cm ): 3061 (w), 3048 (w), 3012

(w), 2954 (w), 2954 (w), 2918 (w), 1586 (s), 1557 (m), 1457 (m), 1414 (s), 1349 (w)

[ν(OAc)], 1284 (m), 1124 (m), 1086 (w), 1044 (m), 1003 (m), 933 (w), 842 (w), 757 (m), 720

(w), 673 (m), 637 (w), 608 (w). FAB-MS: m/z = 455.9 [M]+, M = [κ4-Tptm]Cd.

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4 4 Reaction of [κ -Tptm]CdOSiPh3 with TMSOAc: Formation of [κ -Tptm]CdOAc

4 A solution of [κ Tptm]CdOSiPh3 (10 mg, 0.01 mmol) in C6D6 (ca. 0.5 mL) in an NMR tube equipped with a J. Young valve, was treated with TMSOAc (20 L, 0.13 mmol).

The reaction was monitored by 1H NMR spectroscopy indicating the conversion to [κ4-

Tptm]CdOAc and a small amount of H[Tptm] over 10 minutes at room temperature.

The sample was lyophilized to a tan solid which was then washed with diethyl ether (ca

4 2 mL) giving [κ -Tptm]CdOAc as an off-white solid.

2.12.11 Synthesis of [Tptm]CdO2CH

A solution of TptmCdOSiMe3 (23 mg, 0.04 mmol) in C6D6 (ca. 0.5 mL) in an NMR tube

equipped with a J. Young valve, was treated with PhSiH3 (10 mg, 0.09 mmol) and CO2

(~1 atm). The reaction turned from cloudy and beige to brown upon mixing for 1 minute. Monitoring by 1H NMR spectroscopy showed the conversion to [κ 4-

Tptm]CdOC(O)H and a small amount of decomposition. The reaction mixture was lyophilized yielding a light brown solid which was washed with pentane (5 mL) and dried giving [κ 4-Tptm]CdOC(O)H (11 mg, 53%). Crystals suitable for X-ray diffraction were obtained from slow evaporation of benzene . Anal. Calcd. for [κ 4-

Tptm]CdOC(O)H•0.1(C6H6) : C, 41.6%; H, 2.7%; N, .8.3%. Found: C, 41.4%; H, 2.4%; N

1 3 8.2%. H NMR (C6D6): 6.22 [m, 3H, H(O)COCdC(SC5H4N)3], 6.52 [d, JH-H = 4 Hz, 6H,

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3 H(O)COCdC(SC5H4N)3], 8.81 [d, JH-H = 4 Hz, 3H, H(O)COCdC(SC5H4N)3], 9.50 [s,

13 1 1H(O)COCdC(SC5H4N)3]. C{ H} NMR (C6D6): not observed [H(O)COZnC(SC5H4N)3],

119.3 [s, 3C, H(O)COZnC(SC5H4N)3], 120.8 [s, 3C, H(O)COZnC(SC5H4N)3], 137.5 [s, 3C,

H(O)COZnC(SC5H4N)3], 149.3 [s, 3C, H(O)COZnC(SC5H4N)3], 160.3 [s, 3C,

-1 H(O)COZnC(SC5H4N)3], 169.2 [s, 1C, H(O)COZnC(SC5H4N)3]. IR Data (KBr disk, cm ):

3079 (w), 3048 (w), 2999 (w), 2954 (w), 2803 (w), 1631 (m) [νasym(CO2)], 1585 (s), 1554 (m),

1454 (m), 1413 (s), 1349 (w), 1281 (w), 1252 (w), 1124 (s), 1087 (m), 1041 (m), 1001 (m),

843 (s), 756 (s), 728 (m), 694 (w), 633 (w), 611 (w). FAB-MS: m/z = 455.9 [M]+, M = [κ4-

Tptm]Cd.

3 Me 2.12.12 Synthesis of [ -S2C-Titm ]CdMe

An amber solution of [TitmMe]H (23 mg, 0.07 mmol) in benzene (0.5 mL) in a NMR tube

equipped with a J.Young valve, was treated with CdMe2 (5 L, 0.07 mmol). The reaction mixture sat for 72 hours. The isomerization reaction was monitored by 1H

NMR spectroscopy until completion, the methane gas byproduct, excess CdMe2 reagent and solvent were removed in vacuo giving [TitmMe]CdMe (16 mg, 49%) as a brown solid.

Crystals suitable for X-ray diffraction were obtained from slow evaporation of benzene.

1 H NMR (C6D6): 0.39 [s, 3H, {SC3H2N2(CH3)}3CCdCH3], 2.69 [s, 9H,

{SC3H2N2(CH3)}3CCdCH3], 5.60 [s, 2H, {SC3H2N2(CH3)}3CCdCH3], 6.24 [s, 1H,

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{SC3H2N2(CH3)}3CCdCH3] 7.12 [s, 1H, {SC3H2N2(CH3)}3CCdCH3], 7.81 [s, 2H,

13 1 {SC3H2N2(CH3)}3CCdCH3]. C{ H} NMR (C6D6): -10.8 [s, 1C, {SC3H2N2(CH3)}3CCdCH3],

32.7 [s, 1C, {SC3H2N2(CH3)}3CCdCH3],34.6 [s, 2C, {SC3H2N2(CH3)}3CCdCH3],119.1 [s, 2C,

{SC3H2N2(CH3)}3CCdCH3], 123.0 [s, 2C, {SC3H2N2(CH3)}3CCdCH3], 127.9 [s, 1C,

{SC3H2N2(CH3)}3CCdCH3], 129.5 [s, 1C, {SC3H2N2(CH3)}3CCdCH3], 140.2 [s, 1C,

{SC3H2N2(CH3)}3CCdCH3], 162.1 [s, 2C, {SC3H2N2(CH3)}3CCdCH3], not observed [1C,

-1 {SC3H2N2(CH3)}3CCdCH3],. ATR-IR (cm ): 3214 (w), 3161 (w), 3000 (w), 2957 (w), 1578

(w), 1457 (m), 1393 (s), 1319 (m), 1299 (m), 1216 (m), 1158 (m), 1142 (w), 1115 (w), 1071

(w), 1000 (w), 927 (w), 828 (w), 790 (w), 744 (m), 720 (m), 675 (m), 650 (w), 540 (w), 508

(m), 457 (w), 436 (w). FAB-MS: 464 m/z = [TitmMe]Cd+.

Me 2.12.13 Synthesis of [Titm ]CdN(SiMe3)2

A solution of H[TitmMe] (71 mg, 0.20 mmol) in benzene (ca. 1 mL) was treated with

Cd[N(TMS)2]2 (91 mg, .21 mmol) was added. The solution became slightly cloudier with yellow precipitate. The reaction mixture was mixed for 15 minutes and was

Me subsequently lyophilized to give [Titm ]CdN(SiMe3)2 as a beige solid (91 mg, 72%).

1 H NMR (C6D6): 0.57 [s, 18H, {SC3H2N2(CH3)}3CCdN{Si(CH3)3}2], 2.38 [s, 9m,

{SC3H2N2(CH3)}3CCdN{Si(CH3)3}2], 5.99 [s, 3m, {SC3H2N2(CH3)}3CCdN{Si(CH3)3}2], 7.29

13 1 [s, 3m, {SC3H2N2(CH3)}3CCdN{Si(CH3)3}2]. C{ H} NMR (C6D6): 2.65 [s, HN(SiMe3)2

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impurity], 6.64 [s, 6C, {SC3H2N2(CH3)}3CCdN{Si(CH3)3}2], 31.2 [s, 3C,

{SC3H2N2(CH3)}3CCdN{Si(CH3)3}2], 122.1 [s, 3C, {SC3H2N2(CH3)}3CCdN{Si(CH3)3}2], 127.6

[s, 3C, {SC3H2N2(CH3)}3CCdN{Si(CH3)3}2], 148.4 [s, 3C,

{SC3H2N2(CH3)}3CCdN{Si(CH3)3}2], not observed [1C, {SC3H2N2(CH3)}3CCdN{Si(CH3)3}2].

ATR-IR (cm-1): 3135 (w), 2966 (w), 1470 (s), 1388 (s), 1354 (w), 1280 (s), 1270 (w), 1202

(w), 1147 (m), 1131 (w), 1087 (w), 1059 (w), 937 (s), 910 (w), 847 (m), 741 (s), 701 (m), 685

(s), 510 (w). FAB-MS: 464 m/z = [TitmMe]Cd+.

Me 2.12.14 Synthesis of [Titm ]CdOSiMe3

Me A clear amber solution of [Titm ]CdN(SiMe3)2 (72 mg, 0.12 mmol) in benzene (ca. 0.5 mL) was treated with TMSOH (18 mg, 0.20 mmol). The reaction was allowed to stand for 5 minutes, after this time the reaction mixture was lyophilized giving a tan solid

Me which was crude [Titm ]CdOSiMe3. The tan solid was washed with pentane to give

Me 1 [Titm ]CdOSiMe2 as an off-white solid (49 mg, 77%). H NMR (C6D6): 0.61 [s, 9H,

{SC3H2N2(CH3)}3CCdOSi(CH3)3], 2.34 [s, 9H, {SC3H2N2(CH3)}3CCdOSi(CH3)3], 5.90 [s, 3H,

13 1 {SC3H2N2(CH3)}3CCdOSi(CH3)3], 7.47 [s, 3H, {SC3H2N2(CH3)}3CCdOSi(CH3)3]. C{ H}

NMR (C6D6): 5.3 [s, 3C, {SC3H2N2(CH3)}3CCdOSi(CH3)3], 31.1 [s, 3C,

{SC3H2N2(CH3)}3CCdOSi(CH3)3], 122.4 [s, 3C, {SC3H2N2(CH3)}3CCdOSi(CH3)3], 149.01 [s,

3C, {SC3H2N2(CH3)}3CCdOSi(CH3)3], not observed 1C, {SC3H2N2(CH3)}3CCdOSi(CH3)3].

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ATR-IR (cm-1): 2990 (w), 1624 (m), 1467 (w), 1445 (m), 1422 (w), 1359 (w), 1327 (m), 1288

(m), 1270 (w), 1187 (m), 1173 (m), 1148 (w), 1126 (w), 1067 (m), 1042 (w), 907 (w), 854

(w), 797 (w), 743 (s), 714 (w), 708 (w), 637 (w), 567 (w), 556 (w), 496 (w), 441 (w), 431 (w).

Me FAB-MS: 353 m/z = [Titm ]CdOSiMe3.

Me 2.12.15 Synthesis of [Titm ]CdOSiPh3

Me A clear amber solution of [Titm ]CdN(SiMe3)2 (13 mg, 0.02 mmol) in benzene (ca. 0.5

mL) was treated with Ph3SiOH (6 mg, 0.02 mmol).. After sitting for 10 minutes at room temperature, the reaction mixture was lyophilized resulting in a tan powdery solid.

This solid was washed with pentane (5 mL) and then dried in vacuo giving [κ4-

Me Titm ]CdOSiPh3 as a tan solid (8 mg, 53%). Crystals suitable for X-ray diffraction were

1 obtained from slow evaporation of benzene. H NMR (C6D6): 2.31 [s, 9H,

{SC3H2N2(CH3)}3CCdOSi(C6H5)3], 5.79 [s, 3H, {SC3H2N2(CH3)}3CCdOSI(C6H5)3], 7.02 [s,

3H, {SC3H2N2(CH3)}3CCdOSi(C6H5)3], 7.24 [s, 9H, {SC3H2N2(CH3)}3CCdOSi(C6H5)3], 7.99

13 1 [s, 6H, {SC3H2N2(CH3)}3CCdOSi(C6H5)3]. C{ H} NMR (C6D6): 30.8 [s, 3C,

{SC3H2N2(CH3)}3CCdOSi(C6H5)3], 122.3 [s, 3C, {SC3H2N2(CH3)}3CCdOSi(C6H5)3], 127.5 [s,

3C, {SC3H2N2(CH3)}3CCdOSi(C6H5)3], 128.7 [s, 3C, {SC3H2N2(CH3)}3CCdOSi(C6H5)3], 135.6

[s, 12C, {SC3H2N2(CH3)}3CCdOSi(C6H5)3], 141.0 [s, 3C, {SC3H2N2(CH3)}3CCdOSi(C6H5)3],

148.7 [s, 3C, {SC3H2N2(CH3)}3CCdOSi(C6H5)3], not observed [1C,

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-1 {SC3H2N2(CH3)}3CCdOSi(C6H5)3]. ATR-IR (cm ): 3182 (w), 3000 (w), 2970 (w), 1636 (w),

1591 (w), 1465 (m), 1450 (m), 1395 (s), 1330 (w), 1285 (m), 1230 (m), 1155 (w), 1119 (m),

1067 (w), 1000 (w), 972 (w), 743 (m), 706 (s), 692 (m), 515 (s), 456 (m). FAB-MS: 739 m/z =

Me Titm ]CdOSiPh3.

2.12.16 Synthesis of [TitmMe]CdNCO

Me A clear amber solution of [Titm ]CdN(SiMe3)2 (6 mg, 0.01 mmol) in benzene (ca. 0.5

mL) in an NMR tube equipped with a J. Young valve, was treated with CO2 (1 atm). A yellow precipitate immediately formed in the reaction mixture. The reaction was allowed to stand at room temperature for 12 hours and was lyophilized after this time.

1H NMR spectroscopy showed full conversion to [κ4-TitmMe]CdNCO (3 mg, 67%) as an

Me off-white solid. Crystals of [Ttim ]CdNCO●2C6H6 suitable for X-ray diffraction were

1 obtained from slow evaporation of benzene. H NMR (C6D6): 2.27 [s, 9H,

{SC3H2N2(CH3)}3CCdNCO], 5.79 [s, 3H, {SC3H2N2(CH3)}3CCdNCO], 7.27 [s, 3H,

13 1 {SC3H2N2(CH3)}3CCdNCO]. C{ H} NMR (C6D6): 30.8 [s, 3C,

{SC3H2N2(CH3)}3CCdNCO], 122.6 [s, 3C, {SC3H2N2(CH3)}3CCdNCO], 127.0 [s, 3C,

{SC3H2N2(CH3)}3CCdNCO], 148.6 [s, 3C, {SC3H2N2(CH3)}3CCdNCO], not observed [1C,

- {SC3H2N2(CH3)}3CCdNCO], not observed [1C, {SC3H2N2(CH3)}3CCdNCO]. ATR-IR (cm

1): 3143 (w), 2979 (w), 2198 (w), 1529 (w), 1469 (m), 1384 (m), 1355 (w), 1278 (s), 1264 (w),

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1141 (s), 1116 (w), 1071 (w), 939 (m), 850 (w), 737 (s), 740 (s), 733 (s), 593 (w), 454 (w).

FAB-MS: 464 m/z = [TitmMe]Cd+.

2.12.17 Synthesis of [TitmMe]CdCl

Me A yellow solution of [Titm ]CdOSiPh3 (20 mg, 0.03 mmol) in C6D6 (0.5 mL) was treated with TMSCl (ca. 5 L). The solution was lyophilized after 3 minutes resulting in a beige solid which was washed with pentane (2 mL). The beige solid was dried in vacuo giving

[TitmMe]CdCl as an off-white solid (10 mg, 74%). Crystals suitable for X-ray diffraction were obtained from slow evaporation of solvent from a filtered solution of

Me 1 [Titm ]CdCl in benzene. H NMR (C6D6): 2.28 [s, 9H, {SC3H2N2(CH3)}3CCdCl], 5.80 [s,

13 1 3H, {SC3H2N2(CH3)}3CCdCl], 7.51 [s, 3H, {SC3H2N2(CH3)}3CCdCl]. C{ H} NMR (C6D6):

31.3 [s, 3C, {SC3H2N2(CH3)}3CCdCl], 122.8 [s, 3C, {SC3H2N2(CH3)}3CCdCl], 127.34 [s, 3C,

{SC3H2N2(CH3)}3CCdCl], 148.9 [s, 3C, {SC3H2N2(CH3)}3CCdCl], not observed [s, 1C,

-1 {SC3H2N2(CH3)}3CCdCl]. ATR-IR Data (cm ): 3136 (w), 3972 (w), 2964 (w), 1526 (m),

1464 (s), 1448 (s), 1356 (w), 1282 (s), 1258 (w), 1146 (s), 1118 (m), 1068 (w), 950 (m), 764

(s), 690 (s), 660 (w), 630 (w), 510 (m), 490 (w), 454 (w). FAB-MS: 499 m/z = [TitmMe]CdCl.

2.12.18 Synthesis of [TitmMe]CdBr

Me A yellow solution of [Titm ]CdOSiPh3 (25 mg, 0.03 mmol) in C6D6 (0.5 mL) was treated with TMSBr (ca. 5 L). The solution was lyophilized after 3 minutes resulting in a beige

171

solid which was washed with pentane (2 mL). The beige solid was dried in vacuo giving

[TitmMe]CdBr as an off-white solid (16mg, 88%). Crystals suitable for X-ray diffraction were obtained from slow evaporation of solvent from a filtered solution of

Me 1 [Titm ]CdBr in benzene. H NMR (C6D6): 2.28 [s, 9H, {SC3H2N2(CH3)}3CCdBr], 5.80 [d,

3 3 JH-H = 1 Hz, 3H, {SC3H2N2(CH3)}3CCdBr], 7.53 [d, JH-H = Hz, {SC3H2N2(CH3)}3CCdBr].

13 1 C{ H} NMR (C6D6): 30.6 [s, 3C, {SC3H2N2(CH3)}3CCdBr], 122.2 [s, 3C,

{SC3H2N2(CH3)}3CCdBr], 127.3 [s, 3C, {SC3H2N2(CH3)}3CCdBr], 148.6 [s, 3C,

- {SC3H2N2(CH3)}3CCdBr], not observed, 1C, {SC3H2N2(CH3)}3CCdBr]. ATR-IR Data (cm

1): 3132 (w), 2964 (w), 2902 (w), 1588 (w), 1530 (w), 1518 (w), 1470 (s), 1392 (s), 1354 (w),

1282 (s), 1252 (m), 1148 (s), 1134 (m), 1088 (m), 1052 (w), 948 (m), 938 (w), 750 (s), 700 (s),

684 (s), 638 (w), 550 (w), 508 (m), 464 (m), 442 (w). FAB-MS: 544 m/z = [TitmMe]CdBr.

2.12.19 Synthesis of [TitmMe]CdOAc

Me A clear yellow solution of [Titm ]CdN(SiMe3)2 (5 mg, 0.01 mmol) in benzene (0.5 mL) was treated with excess TMSOAc (ca. 5 L) was added. Upon mixing, the reaction mixture became less soluble in the benzene solvent. The reaction mixture was lyophilized and the remaining brown solid was washed with benzene and dried in vacuo to give [TitmMe]CdOAc as a beige solid (3mg, 64%). Crystals suitable for X-ray diffraction were obtained from slow evaporation of solvent from a solution of

172

Me 1 [Titm ]CdOAc in benzene. H NMR (C6D6): 2.35 [s, 9H,

{SC3H2N2(CH3)}3CCd(CO)CH3], 2.64 [s, 3H, {SC3H2N2(CH3)}3CCd(CO)CH3], 5.89 [s, 3H,

13 1 {SC3H2N2(CH3)}3CCd(CO)CH3], 7.50 [s, 3H, {SC3H2N2(CH3)}3CCd(CO)CH3]. C{ H}

NMR (CDCl3): 22.5 [1C, {SC3H2N2(CH3)}3CCd(CO)CH3], 32.3 [s, 3C,

{SC3H2N2(CH3)}3CCd(CO)CH3], 122.7 [s, 3C, {SC3H2N2(CH3)}3CCd(CO)CH3], 127.7 [s,

3C, {SC3H2N2(CH3)}3CCd(CO)CH3], 148.7 [s, 3C, {SC3H2N2(CH3)}3CCd(CO)CH3], not

observed [1C, {SC3H2N2(CH3)}3CCd(CO)CH3], not observed [1C,

-1 {SC3H2N2(CH3)}3CCd(CO)CH3]. ATR-IR Data (cm ): 3146 (w), 2965 (w), 1531 (w), 1475

(s), 1445 (m), 1397 (s), 1352 (m), 1335 (s), 1282 (w), 1228 (w), 1149 (m), 1112 (w), 1000 (w),

939 (s), 910 (w), 855 (s), 743 (s), 726 (s), 658 (w), 624 (s), 570 (w), 518 (w). FAB-MS: 523 m/z = [TitmMe]CdOAc.

2.12.20 Synthesis of [TitmMe]CdOPhMe

Me A yellow solution of [Titm ]CdOSiPh3 (17 mg, 0.02 mmol) in C6D6 (0.5 mL) was treated with para-cresol (3 mg, 0.03 mmol) was added. The reaction mixture became more opaque as tan solid precipitated from the solution. The sample was filtered and the motherliquor was lyophilized giving [4-TitmMe]CdOPhMe as a tan solid (10 mg, 76%).

Crystals suitable for X-ray diffraction were obtained from slow evaporation of benzene

Me Me 1 from a solution of [Titm ]CdOPh . H NMR (C6D6): 2.19 [s, 3H,

173

{SC3H2N2(CH3)}3CCdOC6H4(CH3)], 2.28 [S, 9h, {SC3H2N2(CH3)}3CCdOC6H4(CH3)], 5.78

3 [S, 3H, {SC3H2N2(CH3)}3CCdOC6H4(CH3)], 6.99 [d, JH-H = 7 Hz, 3H,

{SC3H2N2(CH3)}3CCdOC6H4(CH3)], 7.20 [m, 2H, {SC3H2N2(CH3)}3CCdOC6H4(CH3)], 7.89

13 [m, 2H, {SC3H2N2(CH3)}3CCdOC6H4(CH3)]. C NMR (C6D6): 20.8 [s, 1C,

{SC3H2N2(CH3)}3CCdOC6H4(CH3)], 31.1 [s, 3C, {SC3H2N2(CH3)}3CCdOC6H4(CH3)], 118.1

[s, 1C, {SC3H2N2(CH3)}3CCdOC6H4(CH3)], 122.7 [s, 3C,

{SC3H2N2(CH3)}3CCdOC6H4(CH3)], 129.4 [s, 2C, {SC3H2N2(CH3)}3CCdOC6H4(CH3)], 130.3

[s, 3C, {SC3H2N2(CH3)}3CCdOC6H4(CH3)], 135.8 [s, 2C,

{SC3H2N2(CH3)}3CCdOC6H4(CH3)], 139.4 [s, 1C, {SC3H2N2(CH3)}3CCdOC6H4(CH3)], 148.9

[s, 3C, {SC3H2N2(CH3)}3CCdOC6H4(CH3)], 160.8 [s, 3C,

-1 {SC3H2N2(CH3)}3CCdOC6H4(CH3)]. ATR-IR (cm ): 3180 (w), 3072(w), 2978 (w), 2924

(w), 1614 (m), 1504 (m), 1502 (m), 1458 (m), 1272 (m), 1148 (m), 10442 (s), 962 (m), 824

(m), 810 (m), 724 (m), 482 (s). ). FAB-MS: 572 m/z = [TitmMe]CdOPhMe.

3 PriBenz 2.12.21 Synthesis of [ -N2C-Titm ]CdMe

i A cloudy white slurry of [ 4-TitmBenz Pr]H (38 mg, 0.07 mmol) in benzene (0.5 mL) was

treated with CdMe2 (5 L, 0.07 mmol) causing the reaction to turn clear and yellow. The

mixture was allowed to react for 1 hour and then the solvent and excess CdMe2 reagent

174

3 BenziPr was removed in vacuo resulting in [ – N2C–Titm ]CdMe as a beige solid (32 mg,

66%). Crystals suitable for X-ray diffraction were obtained from. Anal. calcd. [ 3–

BenziPr Titm ]CdMe •0.5 C6H6: C, 55.9%; H, 5.2%; N, 11.1%. Found: C, 55.2%; H, 5.2%; N,

1 11.3%. H NMR (C6D6): 0.64 [s, 3H, {SC3N2CH(CH3)2C4H4}3CCd-CH3], 0.92 [br, 18H,

{SC3N2CH(CH3)2C4H4}3CCd-CH3], 4.18 [m, 3H, {SC3N2CH(CH3)2C4H4}3CCd-CH3], 6.96

3 [br, 6H, {SC3N2CH(CH3)2C4H4}3CCd-CH3], 7.10 [t, JH-H = 7 Hz , 3H,

13 {SC3N2CH(CH3)2C4H4}3CCd-CH3], 7.99[ br, 3H, {SC3N2CH(CH3)2C4H4}3CCd-CH3]. C

NMR (C6D6): 14.9 [s, 1C, SC3N2CH(CH3)2C4H4}3CCd-CH3], 20.4 [s, 6C,

{SC3N2CH(CH3)2C4H4}3CCd-CH3], 49.0 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-CH3], 111.4 [s,

3C, {SC3N2CH(CH3)2C4H4}3CCd-CH3], 117.9 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-CH3],

119.7 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-CH3], 121.6 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-

CH3], 122.3 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-CH3], 135.9 [s, 3C,

{SC3N2CH(CH3)2C4H4}3CCd-CH3], 143.4 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-CH3], not

observed {1C, SC3N2CH(CH3)2C4H4}3CCd-CH3], not observed [3C,

-1 {SC3N2CH(CH3)2C4H4}3CCd-CH3]. ATR-IR (cm ): 2987 (w), 2968 (w), 1464 (m), 1437 (m),

1424 (m), 1393 (w), 1352 (m), 13358 (m), 1302 (m), 1290 (m), 1289 (m), 1225 (w), 1184 (w),

1175 (w), 1137 (w), 1106 (w), 1067 (w), 1017 (w), 927 (w), 891 (w), 833 (w), 741 (s), 704

(w), 6446 (w), 586 (w), 541 (w), 503 (w), 492 (w), 532 (w).

175

4 PriBenz 2.12.22 Synthesis of [ - S3C-Titm ]CdMe

i A cloudy white slurry of [ 4-TitmBenz Pr]H (32mg, 0.06 mmol) in benzene (0.5 mL) was

treated with CdMe2 (5 L, 0.07 mmol), causing the reaction turned clear and yellow.

The reaction was heated at 60˚C for 18 hours, after which monitoring by 1H NMR

spectroscopy confirmed that the reaction was complete. The solvent and excess CdMe2

4 BenziPr reagent was removed in vacuo resulting in [ - S3C–Titm ]CdMe as a tan solid (24 mg, 59%). Anal. calcd.: C, 54.9%; H, 5.8%; N, 11.3%. Found: C, 54.8%; H, 4.8%; N,

1 2 11.2%. H NMR (C6D6): 0.52 [s, JCd-H = 71 Hz, 3H, {SC3N2CH(CH3)2C4H4}3CCd-CH3],

3 1.12 [d, JH-H = 7 Hz, 18H, {SC3N2CH(CH3)2C4H4}3CCd-CH3], 5.60 [br, 3H,

3 {SC3N2CH(CH3)2C4H4}3CCd-CH3], 6.39 [d, JH-H = 8 Hz, 3H, {SC3N2CH(CH3)2C4H4}3CCd-

3 3 CH3], 6.52 [t, JH-H = 8 Hz,3H, {SC3N2CH(CH3)2C4H4}3CCd-CH3], 6.75 [t, JH-H = 8 Hz,3H,

3 {SC3N2CH(CH3)2C4H4}3CCd-CH3], 6.99 [t, JH-H = 8 Hz,3H, {SC3N2CH(CH3)2C4H4}3CCd-

13 CH3]. C NMR (C6D6): -3.4 [s, 1C, SC3N2CH(CH3)2C4H4}3CCd-CH3], 19.3 [s, 6C,

{SC3N2CH(CH3)2C4H4}3CCd-CH3], 50.3 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-CH3], 111.3 [s,

3C, {SC3N2CH(CH3)2C4H4}3CCd-CH3], 111.8 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-CH3],

122.9 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-CH3], 123.1 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-

CH3], 130.8 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-CH3], 133.6 [s, 3C,

{SC3N2CH(CH3)2C4H4}3CCd-CH3], 169.9 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-CH3]. ATR-

176

IR (cm-1): 3143 (w), 2989 (w), 2988 (w), 2203 (w), 1473 (m), 1411 (m), 1373 (s), 1348 (s),

1322 (s), 1261 (w), 1141 (m), 1136 (m), 1072 (w), 937 (w), 882 (w), 739 (s), 751 (w), 724

(w), 658 (w), 646 (w), 609 (w), 600 (w), 545 (w), 421 (m). FAB-MS: 730 m/z =

i [TitmPr Benz]Cd+.

PriBenz 2.12.23 Synthesis of [Titm ]CdN(SiMe3)2

i In benzene (0.5 mL), [TitmBenz Pr]H (41 mg, 0.07 mmol) was dissolved, making a cloudy

white slurry. Upon addition of Cd[N(SiMe3)2]2 (5 mg, 0.01 mmol), a yellow liquid, the reaction turned yellow and became less opaque after mixing for 5 minutes. The reaction

BenziPr was lyophilized to remove the HN(SiMe3)2 byproduct to give [Titm ]CdN(SiMe3)2 as a yellow solid (53 mg, 88%). Crystals suitable for X-ray diffraction were obtained via

1 slow evaporation of pentane into benzene. . H NMR (C6D6, 300K): 0.55 [s, 18H,

{SC3N2CH(CH3)2C4H4}3CCd-N{(Si(CH3)3}2], 0.88 [br, 18H, {SC3N2CH(CH3)2C4H4}3CCd-

N{(Si(CH3)3}2], 4.22 [br, 3H, {SC3N2CH(CH3)2C4H4}3CCd-N{(Si(CH3)3}2], 6.92 [br, 6H,

{SC3N2CH(CH3)2C4H4}3CCd-N{(Si(CH3)3}2], 7.11 [m, 3H, {SC3N2CH(CH3)2C4H4}3CCd-

13 1 N{(Si(CH3)3}2], 8.10 [br, 3H, {SC3N2CH(CH3)2C4H4}3CCd-N{(Si(CH3)3}2]. C{ H} NMR

(C6D6): 6.8 [6C, {SC3N2CH(CH3)2C4H4}3CCd-N{(Si(CH3)3}2], 19.3 [2C,

{SC3N2CH(CH3)2C4H4}3CCd-N{(Si(CH3)3}2], 20.5 [4C, {SC3N2CH(CH3)2C4H4}3CCd-

N{(Si(CH3)3}2], 49.1 [3C, {SC3N2CH(CH3)2C4H4}3CCd-N{(Si(CH3)3}2], 111.1 [3C,

177

{SC3N2CH(CH3)2C4H4}3CCd-N{(Si(CH3)3}2], 120.8 [3C, {SC3N2CH(CH3)2C4H4}3CCd-

N{(Si(CH3)3}2], 122.2 [3C, {SC3N2CH(CH3)2C4H4}3CCd-N{(Si(CH3)3}2], 122.2 [3C,

{SC3N2CH(CH3)2C4H4}3CCd-N{(Si(CH3)3}2], 136.2 [3C, {SC3N2CH(CH3)2C4H4}3CCd-

N{(Si(CH3)3}2], 142.7 [3C, {SC3N2CH(CH3)2C4H4}3CCd-N{(Si(CH3)3}2], 153.5 [s,

{SC3N2CH(CH3)2C4H4}3CCd-N{(Si(CH3)3}2],[not observed, {SC3N2CH(CH3)2C4H4}3CCd-

-1 N{(Si(CH3)3}2]. ATR-IR (cm ): 2992 (w), 2984 (w), 2924 (w), 1452 (m), 1430 (m), 1356 (m),

1288 (m), 1250 (m), 1184 (w), 1174 (w), 1138 (w), 1026 (m), 932 (w), 880 (w), 826 (s), 740

(s), 720 (w), 666 (w), 654 (w), 624 (w), 556 (w), 500 (w), 420 (w).

PriBenz 2.12.24 Synthesis of [Titm ]CdOSiMe3

BenziPr A clear yellow solution of [Titm ]CdN(SiMe3)2 (10 mg, 0.01 mmol) in benzene (0.5 ml) was treated with trimethyl silanol (1 mg, 0.01 mmol). The reaction lost its yellow color, after mixing for 10 minutes and small crystals formed in the reaction solution.

BenziPr The byproduct HN(SiMe3)2 was removed in vacuo resulting in [Titm ]CdOSiMe3 (7 mg, 84%) as a white solid. Anal. calcd.: C, 51.8%; H, 5.4%; N, 10.7%. Found: C, 51.4%;

1 H, 4.9%; N, 9.6%. H NMR (C6D6): 0.70 [br, 9H, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3],

15.20 [s, 18H, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 4.21 [m, 3H,

{SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 6.90 [m, 6H, {SC3N2CH(CH3)2C4H4}3CCd-

3 3 O(Si(CH3)3], 7.33 [t, JH-H = 8 Hz, 3H, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 9.22 [d, JH-

178

1 H = 8 Hz, 3H, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3]. H NMR (CDCl3): 0.29 [s, 9H,

3 {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 1.60 [t, JH-H = 7 Hz, 18H,

{SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3],4.59 [m, 3H, {SC3N2CH(CH3)2C4H4}3CCd-

3 3 O(Si(CH3)3], 7.16 [t, JH-H = 7 Hz, 3H, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 2.27 [t, JH-H

3 = 7 Hz, 3H, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 7.38 [d, JH-H= 8 Hz, 3H,

3 {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 8.53 [d, JH-H= 8 Hz, 3H,

13 1 {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3]. C{ H} NMR (CDCl3): 2.60 [s, 1C,

{SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 5.44 [s, 2C, {SC3N2CH(CH3)2C4H4}3CCd-

O(Si(CH3)3], 21.0 [s, 2C, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 21.1 [s, 4C,

{SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 48.4 [s, 2C, {SC3N2CH(CH3)2C4H4}3CCd-

O(Si(CH3)3], 48.6 [s, 1C, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 110.8 [s, 3C,

{SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 119.7 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-

O(Si(CH3)3], 122.0 [s, 2C, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 122.0 [s, 2C, ,

{SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 122.2 [s, 1C, {SC3N2CH(CH3)2C4H4}3CCd-

O(Si(CH3)3], 122.8 [s, 1C, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 135.6 [s, 2C,

{SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 135.7 [s, 1C, {SC3N2CH(CH3)2C4H4}3CCd-

O(Si(CH3)3], 142.1 [s, 1C, 142.1 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 155.72 [s,

1C, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3], 156.0 [s, 2C, {SC3N2CH(CH3)2C4H4}3CCd-

179

-1 O(Si(CH3)3], [not observed, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(CH3)3]. ATR-IR (cm ):

2962 (w), 1448 (m), 1452 (m), 1408 (m), 1292 (m), 1252 (m), 1220 (w), 1174 (w), 1034 (w),

910 (s), 888 (s), 746 (s), 760 (w), 724 (w), 558 (w), 448 (m).

PriBenz 2.12.25 Synthesis of [Titm ]CdOSiPh3

BenziPr A yellow slurry of [Titm ]CdN(SiMe3)2 (11 mg, 0.01 mmol) in benzene (0.5 ml), was

treated with Ph3SiOH (3 mg, 0.01 mmol). The reaction lost its yellow color as the

reagents were mixed. The byproduct HN(SiMe3)2 was removed in vacuo resulting in a white powder as the crude product which was washed with pentane (2 mL) giving

BenziPr [Titm ]CdOSiPh3 (7 mg, 84%) as a white solid. Anal. calcd.

BenziPr [Titm ]CdOSiPh3•C6H6: C, 62.8%; H, 5.2%; N, 8.0%. Found: C, 62.3 %; H, 4.7%; N,

1 3 7.1%. H NMR (C6D6): 0.96 [d, JH-H = 8 Hz, 18H, {SC3N2CH(CH3)2C4H4}3CCd-

O(Si(C6H5)3], 4.24 [m, 3H, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(C6H5)3], 6.77 [m, 3H,

3 {SC3N2CH(CH3)2C4H4}3CCd-O(Si(C6H5)3], 6.81 [d, JH-H = 4 Hz, 6H,

{SC3N2CH(CH3)2C4H4}3CCd-O(Si(C6H5)3], 7.22 [m, 9H, {SC3N2CH(CH3)2C4H4}3CCd-

3 O(Si(C6H5)3], 8.38 [d, JH-H = 6 Hz, 6H, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(C6H5)3], 8.97 [d,

13 1 JH-H = 8 Hz, 3H, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(C6H5)3]. C{ H} NMR (C6D6): 20.3 [s,

6C, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(C6H5)3], 48.3 [s, 3C, {SCN2CH(CH3)2C4H4}3CCd-

180

O(Si(C6H5)3], 110.53 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(C6H5)3], 121.0 [s, 3C,

{SC3N2CH(CH3)2C4H4}3CCd-O(Si(C6H5)3], 122.3 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-

O(Si(C6H5)3], 122.7 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(C6H5)3], 127.7 [s, 3C,

{SC3N2CH(CH3)2C4H4}3CCd-O(Si(C6H5)3], 128.6 [s, 12C, {SC3N2CH(CH3)2C4H4}3CCd-

O(Si(C6H5)3], 135.6 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(C6H5)3], 136.5 [s, 3C,

{SC3N2CH(CH3)2C4H4}3CCd-O(Si(C6H5)3], 142.4 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-

O(Si(C6H5)3], 156.2 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-O(Si(C6H5)3], not observed [1C,

-1 {SC3N2CH(CH3)2C4H4}3CCd-O(Si(C6H5)3]. ATR-IR (cm ): 3080 (w), 2996(w), 2990 (w),

1462 (w), 1446 (m), 1424 (m), 1356 (m), 1340 (w), 1290 (m), 1188 (w), 1178 (w), 1138 (w),

1106 (m), 1066 (w), 1036 (w), 1018 (m), 930 (w), 906 (w), 850 (w), 744 (s), 704 (s), 644 (m),

521 (s), 436 (w).

i t 2.12.26 Synthesis of [TitmPr Benz]CdOPhBu

BenziPr A yellow slurry of [Titm ]CdOSiMe3 (12 mg, 0.02 mmol) in benzene (0.5 ml), was was treated with 4-t-butyl phenol (3 mg, 0.02 mmol). The reaction became more soluble

in the solvent. The byproduct HOSiMe3 was removed in vacuo giving

BenziPr But [Titm ]CdOPh as a beige powder (11 mg, 85%). Anal. calcd.

BenziPr But But [Titm ]CdOPh •HOPh • 0.5 C6H6: C, 62.1%; H, 6.1%; N, 8.2%. Found: C, 62.7%; H,

1 3 7.0%; N, 8.6%. H NMR (C6D6): 0. 95 [d, JH-H = 7 Hz, 18H, {SC3N2CH(CH3)2C4H4}3CCd-

181

OC6H4C(CH3)3],1.41 [s, 9H, {SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3],4.24 [m, 3H,

{SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3],6.83 [m, 6H, {SC3N2CH(CH3)2C4H4}3CCd-

3 OC6H4C(CH3)3], 7.06 [t, JH-H = 7 Hz, 3H, {SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3],7.38

3 3 [d, JH-H = 7 Hz, 2H, {SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3], 7.52 [d, JH-H = 7 Hz, 2H,

3 {SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3], 8.93 [d, JH-H = 8 Hz, 3H,

13 1 {SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3]. C{ H} NMR (C6D6): 20.3 [s, 6C,

{SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3], 32.4 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-

OC6H4C(CH3)3], 34.0 [s, 1C, {SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3], 48.4 [s, 3C,

{SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3], 110.6 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-

OC6H4C(CH3)3],120.7 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3], 120.8 [s, 2C,

{SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3], 122.4 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-

OC6H4C(CH3)3], 123.3 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3], 126.8 [s, 2C,

{SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3], 135.0 [s, 1C, {SC3N2CH(CH3)2C4H4}3CCd-

OC6H4C(CH3)3], 135.8 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3], 142.3 [s, 3C,

{SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3], 155.9 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-

OC6H4C(CH3)3], 168.5 [s, 1C, {SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3], not observed

-1 [1C, {SC3N2CH(CH3)2C4H4}3CCd-OC6H4C(CH3)3]. ATR-IR (cm ): 3116 (w), 2988 (w),

2928 (w), 1608 (w), 1506 (m), 1500 (w), 1448 (m), 1448 (m), 1356 (m), 1290 (s), 1182 (w),

182

1170 (w), 1142 (w), 1108 (w), 1068 (w), 1022 (w), 928 (w), 832 (m), 744 (s), 702 (w), 680

(w), 642 (w), 556 (w).

PriBenz 2.12.27 Synthesis of [Titm ]CdO2CH

i A solution of [TitmBenz Pr]CdOTMS (8 mg, 0.01 mmol) in benzene (0.5 mL) in a NMR

tube equipped with a J.Young valve was treated with PhSiH3 (ca. 3L) and CO2 (ca. 1

i atm). The benzene solvent was removed in vacuo resulting in [TitmBenz Pr]CdO(CO)H (6

1 3 mg, 80%) as a brown solid. H NMR (CDCl3): 1.56 [d, JH-H = 7 Hz, 18H,

{SC3N2CH(CH3)2C4H4}3CCd-O(CO)H], 4.56 [m, 3H, {SC3N2CH(CH3)2C4H4}3CCd-

3 3 O(CO)H], 7.11 [t, JH-H = 8 Hz, 3H, {SC3N2CH(CH3)2C4H4}3CCd-O(CO)H], 7.23 11 [t, JH-H =

3 8 Hz, 3H, {SC3N2CH(CH3)2C4H4}3CCd-O(CO)H], 7.35 [d, JH-H = 8 Hz,

3 {SC3N2CH(CH3)2C4H4}3CCd-O(CO)H], 8.11 [d, JH-H = 8 Hz, 3H,

{SC3N2CH(CH3)2C4H4}3CCd-O(CO)H], 9.03 [s, 1H, {SC3N2CH(CH3)2C4H4}3CCd-O(CO)H].

13 C NMR (CDCl3): 21.1 [s, 6C, {SC3N2CH(CH3)2C4H4}3CCd-O(CO)H ], 48.6 [s, 3C,

{SC3N2CH(CH3)2C4H4}3CCd-O(CO)H], 111.0 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-

O(CO)H], 118.5 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-O(CO)H ], 122.2 [s, 3C,

{SC3N2CH(CH3)2C4H4}3CCd-O(CO)H ], 122.6 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-

O(CO)H], 135.7 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-O(CO)H ], 141.8 [s, 3C,

183

{SC3N2CH(CH3)2C4H4}3CCd-O(CO)H ], 156.1 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-

O(CO)H], 170.4 [s, 3C, {SC3N2CH(CH3)2C4H4}3CCd-O(CO)H ], not observed {1C,

-1 SC3N2CH(CH3)2C4H4}3CCd- O(CO)H]. ATR-IR (cm ): 3000 (w), 2988 (w), 2967 (w), 1610

(m), 1465 (m), 1444 (m), 1410 (m), 1356 (m), 1326 (m), 1288 (s), 1185 (w), 1160 (m), 1153

(w), 1126 (w), 1069 (m), 1021 (m), 926 (m), 891 (w), 8966 (w), 849 (w), 796 (w), 744 (s), 703

(m), 642 (w), 643 (w), 568 (w), 554 (w), 496 (w), 438 (w).

2.12.28 Synthesis of [Tptm]CdI

A solution of [Tptm]Li (17 mg, 0.05 mmol) in THF (3 mL) was treated with CdI2 (22 mg,

0.06 mmol) was added. The cloudy white slurry was stirred overnight at room temperature. The THF solvent was removed in vacuo and the solid was dissolved in

benzene (3 mL). Excess CdI2 was removed via filtration and the motherliquor was lyophilized giving a white solid. This solid was washed with acetonitrile (3 mL) and dried giving [κ 4-Tptm]CdI as a white solid (27 mg, 94%). Crystals suitable for X-ray diffraction were obtained via slow evaporation from benzene. Anal. Calcd. for [κ 4-

1 Tptm]CdI•0.3(C6D6): C, 32.3%; H, 2.3%; N, 6.9%. Found: C, 34.6%; H, 2.7%; N, 6.8%. H

3 NMR (C6D6): 6.20 [m, 3H, ICdC(SC5H4N)3], 6.48 [m, 6H, ICdC(SC5H4N)3], 9.20 [d, JH-H = 4

13 1 Hz, ICdC(SC5H4N)3]. C{ H} NMR (C6D6): not observed [ICdC(SC5H4N)3], 119.6 [s, 3C,

ICdC(SC5H4N)3], 121.1 [s, 3C, ICdC(SC5H4N)3], 138.3 [s, 3C, ICdC(SC5H4N)3], 149.2 [s,

184

-1 3C, ICdC(SC5H4N)3], 160.2 [s, 3C, ICdC(SC5H4N)3]. IR Data (KBr disk, cm ): 2958 (w),

2923 (m), 2853 (w), 1586 (s), 1556 (m), 1458 (m), 1414 (s). 1277 (w), 1261 (w), 1123 (m),

1091 (m), 1045 (m), 996 (m), 800 (w), 760 (m), 716 (w), 489 (w). FAB-MS: m/z = 582 [M]+,

M = [κ 4-Tptm]CdI.

2.12.29 Synthesis of [TitmMe]CdI

Me [Titm ]Li (17 mg, 0.05 mmol) and CdI2 (32 mg, 0.09 mmol) were allowed to react under nitrogen at room temperature in tetrohydrofuran (3 mL). After stirring for 16 hours, the volatile components were removed in vacuo and the remaining solid was dissolved

in benzene (ca. 2 mL) and filtered to remove excess CdI2. The motherliquor was lyophilized to give [κ4-TitmMe]CdI (21 mg, 93%) as an off-white solid. Crystals suitable

1 for X-ray diffraction were obtained from slow evaporation of benzene. H NMR (C6D6):

3 2.29 [s, 9H, {SC3H2N2(CH3)}3CCdI], 5.81 [d, JH-H = 1 Hz, {SC3H2N2(CH3)}3CCdI], 7.56 [d,

3 13 1 JH-H = 1 Hz, {SC3H2N2(CH3)}3CCdI]. C{ H} NMR (C6D6): 31.2 [s, 3C,

{SC3H2N2(CH3)}3CCdI], 122.4 [s, 3C, {SC3H2N2(CH3)}3CCdI], 127.3 [s, 3C,

{SC3H2N2(CH3)}3CCdI], not observed [3C, {SC3H2N2(CH3)}3CCdI], not observed [1C,

-1 {SC3H2N2(CH3)}3CCdI]. ATR-IR Data (cm ): 2964 (w), 2920 (w), 2850 (s), 1638 (w), 1514

(w), 1465 (m), 1407 (w), 1384 (w), 1334 (w), 1278 (w), 1261 ()w, 1142 (m), 1081 (w), 1025

185

(w), 944 (m), 802 (m), 736 (s), 697 (s), 678 (w), 543 (w), 501 (w). FAB-MS: 464 m/z =

[TitmMe]Cd+.

186

2.13 Crystallographic Data

Table 25. Crystal, intensity collection and refinement data

[Tptm]CdN(SiMe3)2 {[Tptm]CdNCO}2●C6

lattice Triclinic Monoclinic

formula C22H30CdN4S3Si2 C40H30Cd2N8O2S6 formula weight 615.26 1071.88 space group P-1 C2/c a/Å 13.4871(14) 31.790(8) b/Å 14.3560(15) 10.148(3) c/Å 15.1815(16) 13.907(4) /˚ 74.481(2) 90 /˚ 73.363(2) 111.394(4) /˚ 87.447(2) 90 V/Å3 2712.1(5) 4177.1(19) Z 4 4 temperature (K) 293(2) 150(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 1.507 1.704  (Mo K), mm-1 1.142 1.365 max, deg. 25.27 39.49 no. of data collected 14593 32928 no. of data used 5788 6476 no. of parameters 589 247

R1 [I > 2(I)] 0.0622 0.0467

wR2 [I > 2(I)] 0.0721 0.1160

R1 [all data] 0.1017 0.0743

wR2 [all data] 0.2001 0.1309 GOF 0.901 1.029

187

Table 25. (cont’d) Crystal, intensity collection and refinement data

{[Tptm]CdOSiMe3}2 [Tptm]CdOSiPh3●C6H6

lattice Triclinic Trigonal

formula C62H66Cd2N6S6Si2O2 C40H33CdN3OS3Si formula weight 1400.55 808.36

space group P-1 P31c a/Å 9.780(4) 12.88767(14) b/Å 11.925(5) 12.8867(14) c/Å 16.401(6) 12.3936(16) /˚ 69.745(13) 90 /˚ 74.755(9) 90 /˚ 67.968(10) 120 V/Å3 1643.9(11) 1782.4(4) Z 1 2 temperature (K) 150(2) 150(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 1.415 1.506  (Mo K), mm-1 0.919 0.859 max, deg. 30.61 30.03 no. of data collected 26431 27787 no. of data used 9978 3647 no. of parameters 364 143

R1 [I > 2(I)] 0.0607 0.0626

wR2 [I > 2(I)] 0.1441 0.1970

R1 [all data] 0.0908 0.0730

wR2 [all data] 0.1139 0.2048 GOF 0.935 1.111

188

Table 25. (cont’d) Crystal, intensity collection and refinement data

[Tptm]CdOAc [Tptm]CdCl

lattice Monoclinic Monoclinic

formula C18H15CdN3O2S3 C14H11CdC1N3S3 formula weight 513.91 464.54

space group P21/n Cc a/Å 8.801(3) 15.429(3) b/Å 15.225(6) 9.2620(18) c/Å 14.604(6) 14.154(3) /˚ 90 90 /˚ 99.722(7) 117.813(4) /˚ 90 90 V/Å3 1928.7(13) 1789.0(6) Z 4 4 temperature (K) 150(2) 150(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 1.770 1.725  (Mo K), mm-1 1.476 1.717 max, deg. 20.84 30.94 no. of data collected 7377 14075 no. of data used 5901 5561 no. of parameters 246 267

R1 [I > 2(I)] 0.0759 0.0362

wR2 [I > 2(I)] 0.1060 0.0458

R1 [all data] 0.1357 0.0831

wR2 [all data] 0.1857 0.0883 GOF 1.010 1.004

189

Table 25. (cont’d) Crystal, intensity collection and refinement data

[Tptm]CdBr [Tptm]CdO2CH

lattice Monoclinic Monoclinic

formula C14H11BrCdN3S3 C20H15CdN3O2S3 formula weight 509.00 613.15 space group Ia Cc a/Å 14.080(4) 15.9718(15) b/Å 9.2860(15) 9.0439(8) c/Å 15.366(3) 14.831(2) /˚ 90 90 /˚ 116.239(2) 120.2053(12) /˚ 90 90 V/Å3 1802.1(6) 1851.5(4) Z 4 3 temperature (K) 150(2) 150(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 1.876 1.650  (Mo K), mm-1 3.773 1.525 max, deg. 30.63 30.56 no. of data collected 14085 14220 no. of data used 5512 5617 no. of parameters 267 273

R1 [I > 2(I)] 0.0355 0.0543

wR2 [I > 2(I)] 0.0772 0.1456

R1 [all data] 0.0523 0.0802

wR2 [all data] 0.0836 0.1690 GOF 1.007 0.996

190

Table 25. (cont’d) Crystal, intensity collection and refinement data

[Tptm]CdI [TitmMe]CdMe

lattice Monoclinic Orthorhombic

formula C16H12CdIN3S3 C14H18CdN6S3 formula weight 581.77 478.92

space group P21/n Pbca a/Å 9.21(3) 16.149(4) b/Å 14.243(5) 11.769(3) c/Å 14.330(5) 19.414(5) /˚ 90 90 /˚ 92.782(5) 90 /˚ 90 90 V/Å3 1879(11) 3689.7(16) Z 4 8 temperature (K) 150(2) 150(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 2.056 1.724  (Mo K), mm-1 3.141 1.532 max, deg. 31.22 26.81 no. of data collected 17127 43268 no. of data used 2977 3919 no. of parameters 218 221

R1 [I > 2(I)] 0.1139 0.0470

wR2 [I > 2(I)] 0.1214 0.0844

R1 [all data] 0.3957 0.1087

wR2 [all data] 0.4063 0.1065 GOF 1.077 1.001

191

Table 25. (cont’d) Crystal, intensity collection and refinement data

Me Me [Titm ]CdNCO●2C [Titm ]CdOAc

6H6

lattice Triclinic Monoclinic

formula C20H21CdN7OS3 C15H18CdN6O2S3 formula weight 584.02 522.93

space group P-1 P21/c a/Å 9.563(4) 9.190(4) b/Å 9.669(4) 10.897(5) c/Å 13.853(6) 19.478(8) /˚ 106.563(6) 90 /˚ 102.037(6) 90.478(7) /˚ 96.314(6) 90 V/Å3 1181.0(9) 1950.5(15) Z 2 4 temperature (K) 150(2) 150(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 1.642 1.781  (Mo K), mm-1 1.217 1.465 max, deg. 26.94 30.52 no. of data collected 18855 20261 no. of data used 7255 3982 no. of parameters 281 248

R1 [I > 2(I)] 0.0562 0.0776

wR2 [I > 2(I)] 0.0827 0.1832

R1 [all data] 0.0711 0.1542

wR2 [all data] 0.1247 0.2194 GOF 1.078 1.001

192

Table 25. (cont’d) Crystal, intensity collection and refinement data

Me Me Me [Titm ]CdOSiPh3 [Titm ]CdOPh ●H OPhMe

lattice Monoclinic Trinclinic

formula C31H30CdN6OS3Si C27H30CdN6O2S3 formula weight 739.28 679.15

space group P21/c P-1 a/Å 8.6827(17) 10.052(4) b/Å 15.633(3) 11.308(4) c/Å 24.026(5) 13.536(5) /˚ 90 88.194(6) /˚ 95.662(4) 76.122(7) /˚ 90 78.094(8) V/Å3 3245.3(11) 1461.3(9) Z 4 2 temperature (K) 150(2) 150(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 1.513 1.543  (Mo K), mm-1 0.938 0.997 max, deg. 26.96 22.36 no. of data collected 37917 23690 no. of data used 6640 8853 no. of parameters 391 357

R1 [I > 2(I)] 0.521 0.0737

wR2 [I > 2(I)] 0.1024 0.1054

R1 [all data] 0.0993 0.0825

wR2 [all data] 0.1161 0.1922 GOF 1.037 0.992

193

Table 25. (cont’d) Crystal, intensity collection and refinement data

Me [Titm]CdCl●C6H6 [Titm ]CdBr

lattice Monoclinic Monoclinic

formula C13H16CdIN6S3 C13H15BrCdN6S3 formula weight 591.80 543.80

space group P21/n P21/n a/Å 9.838(5) 15.263(4) b/Å 12.961(6) 16.129(4) c/Å 15.209(8) 16.310(4) /˚ 90 90 /˚ 99.308(13) 107.545(3) /˚ 90 90 V/Å3 1913.7(17) 3828.5(15) Z 4 8 temperature (K) 150(2) 150(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 2.054 1.887  (Mo K), mm-1 3.090 3.563 max, deg. 30.58 20.78 no. of data collected 28848 38176 no. of data used 5785 6301 no. of parameters 220 384

R1 [I > 2(I)] 0.0605 0.0823

wR2 [I > 2(I)] 0.1419 0.1780

R1 [all data] 0.1271 0.2206

wR2 [all data] 0.1819 0.1774 GOF 1.002 1.021

194

Table 25. (cont’d) Crystal, intensity collection and refinement data

Me PriBenz [Titm ]CdI [3-Titm ]CdMe

●C6H6

lattice Monoclinic Monoclinic

formula C13H16CdIN6S3 C50H55CdN6S3 formula weight 591.80 948.58

space group P21/n P21/n a/Å 9.838(5) 10.1520(15) b/Å 12.961(6) 16.171(2) c/Å 15.209(8) 28.833(4) /˚ 90 90 /˚ 99.308(13) 97.900(2) /˚ 90 90 V/Å3 1913.7(17) 4688.5(12) Z 4 4 temperature (K) 150(2) 130(2) radiation (, Å) 0.71073 0.71073  (calcd.), g cm-3 2.054 1.344  (Mo K), mm-1 3.090 0.640 max, deg. 29.09 30.62 no. of data collected 28848 75885 no. of data used 5785 14473 no. of parameters 220 548

R1 [I > 2(I)] 0.0605 0.0450

wR2 [I > 2(I)] 0.1419 0.1078

R1 [all data] 0.1271 0.0683

wR2 [all data] 0.1819 0.1219 GOF 1.002 1.002

195

Table 25. (cont’d) Crystal, intensity collection and refinement data

PriBenz [4-Titm ]CdMe ●C6H6

lattice Triclinic

formula C41H45CdN6S3 formula weight 830.41 space group P-1 a/Å 11.3350(11) b/Å 11.5552(11) c/Å 15.6384(15) /˚ 71.6720(10) /˚ 81.6230(10) /˚ 88.2290(10) V/Å3 1923.4(3) Z 2 temperature (K) 130(2) radiation (, Å) 0.71073  (calcd.), g cm-3 1.434  (Mo K), mm-1 0.769 max, deg. 31.97 no. of data collected 33582 no. of data used 13205 no. of parameters 413

R1 [I > 2(I)] 0.0420

wR2 [I > 2(I)] 0.0984

R1 [all data] 0.0606

wR2 [all data] 0.1056 GOF 0.993

196

2.14 References and Notes

(1) (a) Givaja, G.; Blake, A. J.; Wilson, C.; Schröder, M.; Love, J. B. Chem. Commun.

2005, 9380, 4423–4425.

(b) Chen, K.-T.; Tsai, M. Y.; Chen, J.-H.; Wang, S.-S.; Tung, J.-Y. Inorg. Chem.

Commun. 2010, 13, 506–510.

(2) Select examples of cadmium [Tp] complexes:

(a) Reger, D. L.; Wright, T. D.; Smith, M. D.; Rheingold, A. L.; Kassel, S.;

Concolino, T.; Rhagitan, B. Polyhedron 2002, 21, 1795–1807.

(b) Deng, Y.; Wang, R.; Ding, T.; Li, Y.; Sun, S.; Feng, Y.; Zhao, Y. Polyhedron

2001, 20, 291–295.

Haggerty, B. S.; Ellis, P. D. Inorg. Chem. 1995, 34, 4996–5002.

(d) Looney, A. G.; Saleh, A.; Zhang, Y.; Parkin, G. Inorg. Chem. 1994, 33, 1158–

1164.

(3) Select examples of cadmium bipyridine complexes:

(a) Park, H. M.; Hwang, I. H.; Bae, J. M.; Jo, Y. D.; Kim, C.; Kim, H.; Kim, Y.; Kim,

S. Bull. Korean Chem. Soc. 2012, 33, 1517–1522.

(b) Casanova, I.; Sousa-Pedrares, A.; Viqueira, J.; Durán, M. L.; Romero, J.;

Sousa, A.; García-Vázquez, J. A. New J. Chem. 2013, 37, 2303.

197

2012, 68, m1428.

(d) Li, X.-P.; Fang, W.; Mei, Z.-M.; Jin, X.-J.; Qi, W.-L. Acta Crystallogr. Sect. E.

Struct. Rep. Online 2009, 65, m1069–70.

(d) Subramanian, R.; Govindaswamy, N.; Santos, R. A.; Koch, S. A.; Harbison, G.

S Inorg. Chem. 1998, 37, 4929–4933.

(4) Select examples of cadmium terpyridine complexes

(a) Díaz de Vivar, M. E.; Harvey, M. A.; Garland, M. T.; Baggio, S.; Baggio, R.

Acta Crystallogr. C. 2005, 61, m240–244.

(b) Hannon, M. J.; Painting, C. L.; Errington, W. Chem. Commun. 1997, 2, 307–

308.

(5) (a) Eriksson, E.; Jones, T.; Liljas, A. Proteins Struct. Funct. Genet. 1988, 4, 274–282.

(b) Nair, S. K.; Christianson, D. W. II. J. Am. Chem. Soc. 1991, 113, 9455–9458.

(d) Looney, A. G.; Han, R.; McNeill, K.; Parkin, G. J. Am. Chem. Soc. 1993, 115,

4690–4697.

(e) Vahrenkamp, H. Acc. Chem. Res. 1999, 32, 589–596.

(6) (a) Poole, J. H.; Tyack, P. L.; Stoeger-Horwath, A. S.; Watwood, S. Nature 2005,

434, 455–456.

(b) Lane, T. W.; Morel, F. M. Proc. Natl. Acad. Sci. U. S. A. 2000, 97, 4627–4631.

198

(7) Kinoshita, I.; Wright, L. J.; Kubo, S.; Kimura, K.; Sakata, A.; Yano, T.; Miyamoto,

R.; Isobe, K. Dalt. Trans. 2003, 1993–2003.

(8) Kuwamura, N.; Kato, R.; Kitano, K.; Hirotsu, M.; Nishioka, T.; Hashimoto, H.;

Kinoshita, I. Dalt. Trans. 2010, 39, 9988–9993.

(9) Kinoshita, I.; Hashimoto, H.; Nishioka, T.; Miyamoto, R.; Kuwamura, N.;

Yoshida, Y. Photosynth. Res. 2008, 95, 363–371.

(10) Vieira, F. T.; de Lima, G. M.; Wardell, J. L.; Wardell, S. M. S. V.; Krambrock, K.;

Alcântara, A. F. D. C. J. Organomet. Chem. 2008, 693, 1986–1990.

(11) Sattler, Wesley. Graduate Thesis, 2012., Columbia University, NY.

(12) Sattler, W.; Parkin, G. J. Am. Chem. Soc. 2011, 133, 9708–9711.

(13) Sattler, W.; Parkin, G. J. Am. Chem. Soc. 2012, 134, 17462–17465.

(14) Sattler, W.; Ruccolo, S.; Parkin, G. J. Am. Chem. Soc. 2013, 135, 18714–18717.

(15) Kitano, K.; Kuwamura, N.; Tanaka, R.; Santo, R.; Nishioka, T.; Ichimura, A.;

Kinoshita, I. Chem. Commun. 2008, 1314–1316.

(16) Gwengo, C.; Silva, R. M.; Smith, M. D.; Lindeman, S. V.; Gardinier, J. R.

Inorganica Chim. Acta 2009, 362, 4127–4136.

(17) Ruccolo, S.; Parkin, G. unpublished results

(18) Barr, D.; Edwards, A. J.; Raithby, P. R.; Rennie, M.; Verhorevoott, K.; Wright, D.

S. Chem. Commun. 1994, 147, 1627–1628.

(19) (a) Boulmaaz, S.; Papiernik, R.; Hubert-Pfalzgraf, L. G. Polyhedron 1992, 11,

1331–1336.

199

(b) Boyle, T. J.; Bunge, S. D.; Alam, T. M.; Holland, G. P.; Headley, T. J.;

Avilucea, G. Inorg. Chem. 2005, 44, 1309–1318.

Chem. 1999, 38, 1356–1359.

(d) Darensbourg, D. J.; Niezgoda, S. A.; Reibenspies, J. H.; Draper, J. D. Inorg.

Chem. 1997, 36, 5686–5688.

(e) Darensbourg, D. J.; Rainey, P.; Larkins, D. L.; Reibenspies, J. H. Inorg. Chem.

2000, 473–479.

(f) Darensbourg, D. J.; Wildeson, J. R.; Lewis, S. J.; Yarbrough, J. C. J. Am. Chem.

Soc. 2002, 124, 7075–7083.

(g) Goel, S. C.; Chiang, M. Y.; Buhro, W. E. J. Am. Chem. Soc. 1990, 112, 6724–

6725.

(20) Matchett, M. A.; Chiang, M. Y.; Buhro, W. E. Inorg. Chem. 2004, 33, 1109–1114.

(21) (a) Bashall, A.; Beswick, M. A.; Harmer, C. N.; McPartlin, M.; Paver, M. A.;

Wright, D. S. Dalt. Trans. 1998, 61, 517–518.

(b) Beswick, M. A.; Cromhout, N. L.; Harmer, C. N.; Palmer, J. S.; Raithby, P. R.;

Steiner, A.; Verhorevoott, K.; Wright, D. S Chem. Commun. 1997, 501, 583–584.

(d) Edwards, A. J.; Fallaize, A.; Raithby, P. R.; Rennie, M.; Steiner, A.;

Verhorevoott, K.; Wright, D. S. Dalt. Trans. 1996, 133–137.

200

(e) Bochmann, V. M.; Coleman, A. P.; Webb, K. J.; Hursthouse, M. B. Angew.

Chem. Int. Ed. Engl. 2006, 103, 975–976.

(22) (a) Bailey, P. J.; Mitchell, L. A.; Raithby, P. R.; Rennie, M.; Verhorevoott, K.;

Wright, D. S Chem. Commun. 1996, 58, 1351–1352.

(b) Cummins, C. C.; Schrock, R. .; Davis, W. M. Organometallics 1991, 10, 3781–

3785.

ndez, I.; Breher, F.;

Mountford, P. Organometallics 2010, 29, 1174–1190.

(23) For a list of cadmium sandwich complexes:

(a) Bochmann, M.; Bwemby, G. C.; Hursthouse, M. B.; Coles, S. J. Dalt. Trans.

1995, 2813–2817.

(b) Johnson, A. L.; Hollingsworth, N.; Kociok-Köhn, G.; Molloy, K. C.

Organocadmium Aminoalcoholates: Inorg. Chem. 2008, 47, 9706–9715.

(d) Park, H. S.; Mokhtari, M.; Roesky, H. W. Vap. Depos. 1996, 135–139.

(24) Finke, A. D.; Moore, J. S. Lewis Acid Activation of Molybdenum Nitrides for

Alkyne Metathesis. Chem. Commun. (Camb). 2010, 46, 7939–7941.

(25) (a) Hubert-Pfalzgraf, L. G.; Touati, N.; Pasko, S. V.; Vaissermann, J.; Abrutis, A.

Polyhedron 2005, 24, 3066–3073.

(b) Andersen, A. J. Organomet. Chem. 1980, 192, 189–193.

201

(26) Lee, H. H.; Go, M. J.; Park, K. H.; Kim, Y.; Lee, J. Acta Crystallogr. Sect. E. Struct.

Rep. Online 2012, 68, m87.

(27) (a) Fortier, S.; Kaltsoyannis, N.; Wu, G.; Hayton, T. W. J. Am. Chem. Soc. 2011,

133, 14224–14227.

(b) Arnold, P. L.; Patel, D.; Wilson, C.; Love, J. B. Nature 2008, 451, 315–317.

Love, J. B. Nat. Chem. 2012, 4, 221–227.

(28) Bibal, C.; Gornitzka, H.; Couret, C.; Sabatier, P. Organometallics 2002, 40, 2940–

2943.

(29) Bremer, M.; Linti, G.; Noth, H.; Thomann-Albach, M.; Wagner, G. E. W. J.

Zeitschrift Anorg. und Allg. Chemie 2005, 631, 683–697.

(30) Schindler, F.; Schmidbaur, H.; Kruger, U. Angew. Chem. 1965, 77, 865.

(31) Harms, K.; Merle, J.; Massa, W.; Krieger, M. Inorg. Chem. 1998, 1669, 1099–1104.

(32) (a) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rign, J.; Verschoor, Gerrit, C.

Dalt. Trans. 1984, 1349–1356.

(b) Yang, L.; Powell, D. R.; Houser, R. P. Dalt. Trans. 2007, 955–964.

(33) Cambridge Structural Database (Version 5.35). “Chemical Design Automation

News” 8, pp. 1, 31-37.

(34) Moore, D. R.; Cheng, M.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2003,

125, 11911–11924.

202

(35) Driess, M.; Merz, K.; Schoenen, R.; Bochum, D Organometallics 2007, 26, 2133–

2136.

(36) Barry, S. T.; Richeson, D. S. Chem. Mater. 1994, 9, 2220–2221.

(37) Rennekamp, C.; Wessel, H.; Roesky, H. W.; Mu, P.; Schmidt, H.; Noltemeyer, M.;

Uso, I.; Barron, A. R.; Alf, M. Inorg. Chem. 1999, 38, 5235–5240.

(38) Dembowski, U.; Pape, T.; Herbst-Irmer, R.; Pohl, E.; Roesky, H. W.; Sheldrick, G.

M. Acta Crystallogr. Sect. C Cryst. Struct. Commun. 1993, 49, 1309–1311.

(39) Avent, A. G.; Crimmin, M. R.; Hill, M. S.; Hitchcock, P. B. J. Organomet. Chem.

2006, 691, 1242–1250.

(40) Garbauskas, M. F.; Wengrovius, J. H.; Going, R. C.; Kasper, J. S Acta Crystallogr.

Sect. C Cryst. Struct. Commun. 1984, C40, 1536.

(41) Wojtczak, W. A.; Hampden-smith, M. J.; Duesler, E. N.; Sime, N. Inorg. Chem. 1996,

35, 6638–6639.

(42) Arduengo, A. J.; Goerlicha, J. R.; Davidsonb, F.; Marshall, W. J. Z. Naturforsch, B

Chem. Sci. 1999, 54, 1350–1357.

(43) Lulin, S.; Madura, I.; Serwatowski, J.; Zachara, J. Inorg. Chem. 1999, 38, 4937–4941.

(44) Tang, H.; Parvez, M.; Richey, H. G. Organometallics 1996, 15, 5281–5283.

(45) Melnick, J. G.; Parkin, G. Science 2007, 317, 225–227.

(46) Lipscomb, W. N.; Sträter, N. Chem. Rev. 1996, 96, 2375–2434.

(47) For the use of 113Cd NMR spectroscopy to probe the nature of carbonic

anhydrase see:

203

(a) See reference 2d

(b) Armitage, I. M.; Pajer, R. T.; Uiterkamp, A. J. M. S.; Chlebowski, J. F.;

Coleman, J. E. J. Am. Chem. Soc. 1976, 98, 5710–5712.

Coleman, J. E. . J. Magn. Reson. 1978, 29, 375.

(d) Sudmeier, J. L.; Bell, S. Cadmium-1 13 Nuclear Magnetic Resonance Studies

of 113Cd(II)-Substituted Human Carbonic Anhydrase B. J. Am. Chem. Soc. 1972,

99, 4499–4500.

(48) Melnick, J. G.; Parkin, G. Dalt. Trans. 2006, 4207–4210.

(49) Melnick, J. G.; Zhu, G.; Buccella, D.; Parkin, G. J. Inorg. Biochem. 2006, 100, 1147–

1154.

(50) For cadmium isocyanate compounds containing a M-NCO-M bridging moiety:

- a, M.; Peñalba, E.; Solans, X.; Vicente, R. Inorganica

Chim. Acta 1999, 286, 189–196.

(b) Derossi, S.; Farrell, D. T.; Harding, C. J.; McKee, V.; Nelson, J. Dalt. Trans.

2007, 1762–1772.

Martins, F. R.; Tarrasqui, L. H. R. Transit. Met. Chem. 2004, 29, 893–899.

(d) Meyer, F.; Kaifer, E.; Kircher, P.; Heinze, K.; Pritzkow, H. Chem. Eur. J. 1999,

5, 1617–1630.

204

(e) Buchler, S.; Meyer, F.; Kaifer, E.; Pritzkow, H. Inorganica Chim. Acta 2002, 337,

371–386.

(f) Mahendrasinh, Z.; Ankita, S.; Kumar, S. B.; Escuer, A.; Suresh, E. Inorganica

Chim. Acta 2011, 375, 333–337.

- a, M.

Mechanism for the Nickel Pseudohalide System T. Dalt. Trans. 1996, 21, 1013–

1019.

(h) Meyer, F.; Kaifer, E.; Kircher, P.; Heinze, K.; Pritzkow, H. Chem. - A Eur. J.

1999, 5, 1617–1630.

(i) Harding, C. J.; Mabbs, F. E.; MacInnes, E. J. L.; McKee, V.; Nelson, J. J. Chem.

Soc. Dalt. Trans. 1996, 3227.

(h) Duggan, D. M.; Hendrickson, D. N. Inorg. Chem. 1974, 13, 2056–2062.

(j) Effendy, C.; Di Nicola, C.; Fianchini, M.; Pettinari, C.; Skelton, B. W.; Somers,

N.; White, A. H. Inorganica Chim. Acta 2005, 358, 763–795.

(51) For a list of cadium isocyanate complexes, see:

(a) Wang, Y.; Gu, B.; Wang, C.; Ma, C.; Ma, Y.; Liao D. Nankai Daxue Xuebao,Ziran

Kexueban(Chin.)(Acta Scient.Nat.Univ.Nankaiensis) 2011, 44, 20-21.

(b) Das, L. K.; Drew, M. G. B.; Ghosh, A. Inorganica Chim. Acta 2013, 394, 247–

254.

K. J. Mol. Struct. 2011, 994, 306–312.

205

(d) Das, L. K.; Biswas, A.; Frontera, A.; Ghosh, A. Polyhedron 2013, 52, 1416–

1424.

(e) Ukraintseva, E.A.; Soldatov, D.V. Zh. Strukt. Khim. 2005, 46, S171.

(52) Fang, H.; Ng, S. W. Acta Crystallogr. Sect. E Struct. Reports Online 2007, 63, m1523– m1524. (53) Mahmood, R.; Ghulam Hussain, S.; Fettouhi, M.; Isab, A.; Ahmad, S. Acta

Crystallogr. Sect. E. Struct. Rep. Online 2012, 68, m1352–3. (54) Lippard, S. J.; Russ, B. J. Inorg. Chem. 1968, 7, 1686–1688. (55) Kang, S. O.; Begum, R. A.; Bowman-James, K. Angew. Chem. Int. Ed. Engl. 2006, 45, 7882–7894. (56) For a list of cadmium formate complexes which in the CSD: (a) Croitor, L.; Coropceanu, E. B.; Siminel, A. V.; Masunov, A. E.; Fonari, M. S. Polyhedron 2013, 60, 140–150.

(b) Antsyshkina, A.S.; Porai-Koshits, M.A.; Khandlovich, M.; Ostrikova, V.N. Koord. Khim. Russ. 1981, 7, 461. (c) Croitor, L.; Coropceanu, E. B.; Jeanneau, E.; Dementiev, I. V.; Goglidze, T. I.; Chumakov, Y. M.; Fonari, M. S. Cryst. Growth Des. 2009, 9, 5233–5243. (d) Batsanov, A.S.; Matsaberidze, M.I.; Struchkov, Y.T.; Tsintsadze, G.V.; Tsivtsivadze, T.I.; Gverdtsiteli, L.V. Koord. Khim. Russ. 1986, 12, 1555. (e) Coropceanu, E. B.; Croitor, L.; Fonari, M. S. Polyhedron 2012, 38, 68–74

(57) Zhu, Z.; Fettinger, J. C.; Olmstead, M. M.; Power, P. P. Organometallics 2009, 28, 2091–2095. (58) Zhu, Z.; Brynda, M.; Wright, R. J.; Fischer, R. C.; Merrill, W. A.; Rivard, E.; Wolf, R.; Fettinger, J. C.; Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 2007, 129, 10847–10857.

206

(59) (a) Lindskog, S. Structure and Mechanism of Carbonic Anhydrase. Pharmacol.

Ther. 1997, 74, 1–20.

(b) Parkin, G. Chem. Commun. 2000, 1971–1985.

(60) (a) Lane, T. W.; Morel, F. M. A Biological Function for Cadmium in Marine

Diatoms. Proc. Natl. Acad. Sci. U. S. A. 2000, 97, 4627–4631.

(b) Coleman, J. E. Metal Ion Dependent Binding of Sulphonamide to Carbonic

Anhydrase. Nature 1967, 214, 193–194.

(61) Ito, H.; Ito, T. Acta Crystallogr. Sect. C Cryst. Struct. Commun. 1985, 41, 1598–

1602.

(62) (a) Chen, Y.; Peng, J.; Yu, H.; Han, Z.; Gu, X.; Shi, Z.; Wang, E.; Hu, N. A

Inorganica Chim. Acta 2005, 358, 403–408.

(b) Ciani, G.; Masciocchi, N.; Sironi, A.; Menabue, L.; Bruni, S.; Cariati, F.; A, P.;

Forti, L.; Manfredini, T. C Inorganica Chim. Acta 1991, 189, 13–18.

(63) (a) Chang, G.-F.; Wang, C.-H.; Lu, H.-C.; Kan, L.-S.; Chao, I.; Chen, W. H.;

Kumar, A.; Lo, L.; de la Rosa, M. A. C.; Hung, C.-H. Chemistry 2011, 17, 11332–

11343.

(b) Dey, S. K.; Shit, S.; Dey, S. P.; Mitra, S.; Malik, K. M. A. Chem. Lett. 2011, 40,

810–812.

(64) (a) Zhou, F.-X.; Zheng, Z.; Zhou, H.-P.; Ke, W.-Z.; Wang, J.-Q.; Yu, Z.-P.; Jin, F.;

Yang, J.-X.; Wu, J.-Y.; Tian, Y.-P. CrystEngComm 2012, 14, 5613.

(b) Jian, F.; Sun, P.; Xiao, H.; Zhao, P. Struct. Chem. 2005, 16, 561–565.

207

(65) Masciocchi, N.; Moret, M.; A., S.; S., B.; Cariati, F.; Pozzi, A.; Manfredini, T.;

Menabue, L.; Pellacanit, G. C. Inorg. Chem. 1992, 31, 1401–1406.

(66) (a) McNally, J. P.; Leong, V. S.; Cooper, N. J. in Experimental Organometallic

Chemistry, Wayda, A. L.; Darensbourg, M. Y., Eds.; American Chemical Society:

Washington, DC, 1987; Chapter 2, pp 6-23.

(b) Burger, B. J.; Bercaw, J. E. in Experimental Organometallic Chemistry; Wayda, A.

L.; Darensbourg, M. Y., Eds.; American Chemical Society: Washington, DC, 1987;

Chapter 4, pp 79-98.

2nd Edition; Wiley-Interscience: New York, 1986.

(67) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997, 62, 7512-7515.

(68) Bochmann, M.; Bwembya, G.; Webb, K.J.; Malik, M.A.; Walsh, J.R.; O’Brien, P.

Inorg. Synth. 1997, 31, 19-24.

(69) Chakrabarti, N.; Sattler, W.; Parkin, G. Polyhedron 2013, 58, 235–246.

(70) Ruccolo, S.; Parkin, G. unpublished results.

(71) (a) Sheldrick, G. M. SHELXTL, An Integrated System for Solving, Refining and

Displaying Crystal Structures from Diffraction Data; University of Göttingen,

Göttingen, Federal Republic of Germany, 1981.

(b) Sheldrick, G. M. Acta Cryst. 2008, A64, 112-122.

(72) Jaguar 7.5, Schrödinger, LLC, New York, NY 2008.

208

(73) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652.

(b) Becke, A. D. Phys. Rev. A 1988, 38, 3098-3100.

(d) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200-1211.

(e) Slater, J. C. Quantum Theory of Molecules and Solids, Vol. 4: The Self-Consistent

Field for Molecules and Solids; McGraw-Hill: New York, 1974.

(74) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270-283.

(b) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284-298.

209 Chapter 3

Synthesis and Characterization of Bis(2-mercapto-1-benzimidazolyl) hydroborato,

[BmRBenz] (R = Me, But), Compounds of Sodium, Potassium and Calcium

Table of Contents

3.1 Introduction ...... 212

3.1.1 Objective ...... 212

3.1.2 The tris(mercaptoimidazolyl)hydroborato, [Tm] and

bis(mercaptoimidazolyl)hydroborato, [Bm] class of ligands...... 213

t 3.2 [BmBu Benz]M (M = Na, K) Compounds ...... 215

RBenz t 3.3 Synthesis and Molecular Structure of [Bm ]2Ca(THF)2 (R = Me, Bu ) ...... 218

MeBenz 3.4 [Bm ]2Ca(THF)2 as a Transmetallating Agent ...... 235

3.5 Conclusion ...... 236

3.6 Experimental Section ...... 236

3.6.1 General Considerations ...... 236

3.6.2 X-ray Structure Determination...... 237

3.6.3 Computational Details ...... 237

t 3.6.4 Synthesis of [BmBu Benz]Na ...... 238

210

t 3.6.5 Synthesis of [BmBu Benz]K ...... 240

MeBenz 3.6.6 Synthesis of [Bm ]2Ca(THF)2 ...... 242

ButBenz 3.6.7 Synthesis of [Bm ]2Ca(THF)2 ...... 244

MeBenz 3.6.8 Reaction with [Bm ]2Ca(THF)2 and ClHgMe ...... 245

MeBenz 3.6.9 Reaction with [Bm ]2Ca(THF)2 and ClHgEt ...... 246

3.7 Crystallographic Data ...... 247

3.8 References and Notes ...... 248

211

3.1 Introduction

3.1.1 Objective

The tris- and bis(mercaptoimidazolyl)hydroborato, [TmR]1 and [BmR],2 ligands

(Figure 1) have experienced wide synthetic use with main group and transition metals since their introduction in 1996 and 2000, respectively.3 Recently, the benzannulated versions of these ligands, [TmRBenz] (R = Me, But)and [BmMeBenz], (Figure 1) were synthesized by the Parkin group.4

Figure 1. The [TmR] and [BmR] class of ligands

In a comparison between [TmR] and [TmRBenz], benzannulation of the ligand promoted 3 coordination of the ligand to the metal center.4 It was in our interest to compare the [BmRBenz] ligand with [BmR] to see how benzannulation of this ligand would affect the structure and reactivity of the metal center. To this end, I synthesized

212

t group 1 and 2 complexes, [BmBu Benz]M (M = Na, K, Ca). These are the first complexes featuring the benzannulated ligand with the tert-butyl R–group. In addition, I

MeBenz synthesized [Bm ]2Ca(THF)2, which is the first structurally characterized complex of calcium coordinated to the [Bm] or [Tm] class of ligands.

3.1.2 The tris(mercaptoimidazolyl)hydroborato, [Tm] and

bis(mercaptoimidazolyl)hydroborato, [Bm] class of ligands

The tris(mercaptoimidazolyl)hydroborato, [TmR], ligand (Figure 1) was designed

1 by Reglinski and Spicer in 1996 to serve as a softer [S3] donor version of the [N3] donor tris(pyrazolyl)hydroborato, [Tp], ligand (Figure 2) developed by Trofimenko in 1967.5

Figure 2. The tris(pyrazolyl)hydroborato, [TpR,R’], ligand

Since the introduction of the [TmR] ligand, it has found use in a variety of biologically relevant applications. These include serving as a molecular mimic for protein active sites such as alcohol liver dehydrogenase (ALAD), the Ada DNA repair

213 protein, and MerB.3 There are over 250 main group and transition metal complexes with a variety of substitutions on the [Tm] ligand which have been structurally characterized and reported in the Cambridge Structural Database (CSD).6 Similarly, the

R 2 S2-donor[Bm ] ligand, reported by the Parkin group, has found widespread use as a biological molecular mimic as well.3,7,8

The benzannulated versions of these ligands, [TmRBenz] and [BmMeBenz], (R = Me,

But) were introduced by the Parkin group4 and coordinated to main group and transition metals. DFT (Density Functional Theory) calculations and experimentally determined molecular structures of [TmRBenz]Na versus [TmR]Na complexes showed that benzannulation of [TmRBenz] promoted 3 coordination of the ligand to the metal center.4a,9 The molecular structure of [BmR]Na complexes have not been reported,10

MeBenz however, the molecular structure of the {[Bm ]Na(THF)2}2 complex has two

[BmMeBenz] ligands coordinated to two sodium centers (Figure 3).

214

MeBenz Figure 3. {[Bm ]Na(THF)2}2 complex (reproduced from reference 4a)

t I synthesized [BmBu Benz]M complexes in order to compare their molecular structures with [BmMeBenz]M and [BmR]M complexes to see how the benzannulation and bulky tert-butyl group affects the coordination and reactivity of the metal center. In the

t following chapter, I discuss the syntheses of [BmBu Benz] sodium, potassium, and calcium complexes. I also will discuss the synthesis of the methyl analogue,

MeBenz [Bm ]2Ca(THF)2, which is the first structurally characterized calcium [Bm] complex.

Me 11 To date, there is only one other reported calcium complex, [Tm ]2Ca(H2O)6, in which the [Tm] ligands are uncoordinated anions.

t 3.2 [BmBu Benz]M (M = Na, K) Compounds

t The [BmBu Benz]M (M = Na, K) complexes were synthesized by adding 2 equivalents of benzimidazolethione to the appropriate metal borohydride and heating at 130°C for 18 hours (Scheme 1).

215

t Scheme 1. Synthesis of [BmBu Benz]M (M = Na, K)

t Upon heating, the [BmBu Benz]M (M = Na, K) products precipitated out of solution

t as an amorphous solid. Due to the very low solubilities of both [BmBu Benz]M (M = Na, K) complexes, crystals suitable for molecular structure determination of these complexes

t were not obtained. [BmBu Benz]M (M = Na, K) were characterized via 1H and 13C NMR and IR spectroscopy. A boron resonance for these complexes was not observed by 11B

NMR spectroscopy. The 1H NMR spectrum was collected in DMSO for both

t t [BmBu Benz]Na and [BmBu Benz]K and, as expected, showed the protons in the thiobenzimidazole ring in the aromatic region of the spectrum, and the t-butyl protons further upfield at 2.02 ppm for both compounds.

t t The B-H stretching frequencies in the IR spectra of [BmBu Benz]Na and [BmBu Benz]K appeared as weak, broad absorption bands in the characteristic region at 2428 cm-1 and

2452 cm-1, respectively (Table 1).12 The corresponding IR stretches in

MeBenz 4a R 10 [Bm ]Na}2(THF)2 and the [Bm ] sodium compounds are listed in Table 1 for

ButBenz comparison. Table 1 shows that the B-H stretching frequencies for [Bm ]M are

216 similar for M = Na and K, and correlate with the B-H stretches for other group 1 [Bm] complexes.

Table 1. B-H stretching frequencies in the IR spectra in [BmR]M (M = Na, K) compounds

-1 Compound B-H/cm Reference

t [BmBu Benz]Na 2428 this work

t [BmBu Benz]K 2452 this work

MeBenz {[Bm ]Na}2(THF)2 2444 4a

[BmMe]Na 2415 10

t [BmBu ]Na 2397 10

[BmMe]Li 2399 2

Group 1 metal complexes are often used as transmetallating agents, the

t t [BmBu Benz]M (M = Na,K) complexes also show this capability as the [BmBu Benz]Na

t complex was reacted with alkyl mercury chloride reagents to obtain [BmBu Benz]HgR (R =

Me, Et). The synthesis and characterization of these mercury alkyl compounds are discussed in Chapter 4.

217

RBenz t 3.3 Synthesis and Molecular Structure of [Bm ]2Ca(THF)2 (R = Me, Bu )

RBenz The synthesis of [Bm ]2Ca(THF)2 is outlined in Scheme 2. Four equivalents of

the appropriate benzimidazolethione were added to Ca(BH4)2 in tetrahydrofuran. The reaction mixture was heated to 130 °C for 18 hours in a thick-walled ampoule.

RBenz t Scheme 2. Synthesis of [Bm ]2Ca(THF)2 (R = Me, Bu )

RBenz The [Bm ]2Ca(THF)2 complexes were obtained in modest yields and were characterized via 1H and 13C NMR spectroscopy. Similar to many group 1 and 2 [Bm]M complexes, a boron resonance for these calcium complexes was not observed by 11B

NMR spectroscopy. IR spectroscopy on the complexes showed the characteristic B-H

-1 -1 MeBenz stretching frequencies at 2429 cm and 2420 cm for [Bm ]2Ca(THF)2 and

218

ButBenz [Bm ]2Ca(THF)2, respectively. As shown by the listed values in Table 1, these H-B frequencies are within range of other main group [Bm] complexes.10

MeBenz [Bm ]2Ca(THF)2 was characterized via X-ray diffraction and the molecular structure of the compound is provided in Figure 4.

MeBenz Figure 4. Molecular structure of [Bm ]2Ca(THF)2

Figure 4 shows that the calcium center is eight coordinate with both sulfurs from each of the two [BmMeBenz] ligands coordinating to the metal, as well as two THF molecules. In addition, these bonding interactions are supported by two secondary

… MeBenz BH Ca interactions. The bond lengths and angles in [Bm ]2Ca(THF)2 are listed in

Table 2.

219

MeBenz Table 2. Selected bond lengths in [Bm ]2Ca(THF)2

d(Ca-S1)/ d(Ca-S2)/ d(Ca-S3)/ d(Ca-S4)/ d(Ca-O1)/ d(Ca-O2)/ d(Ca…H1)/ d(Ca…H2)/

Å Å Å Å Å Å Å Å

Experimental 2.8460(11) 2.8900(12) 2.8822(12) 2.8850(12) 2.414(2) 2.441(2) 2.520 2.630

Geometry 3.538 3.061 3.007 3.048 2.536 2.521 2.469 2.465 optimized

MeBenz Table 3. Selected bond angles in [Bm ]2Ca(THF)2

220

S1-Ca-H1 H1-Ca-H2 H2-Ca-S4 S1-Ca-S4 S2-Ca-O1 O1-Ca-O2 S4-Ca-O2 S2-Ca-S3

/° /° /° /° /° /° /° /°

Experimental 66.65 64.89 65.28 163.30(4) 74.72(6) 75.69(8) 75.74(6) 134.76(3)

Geometry 64.00 73.39 64.25 158.95 149.36 77.63 145.18 135.54 optimized

MeBenz The Ca-S bond lengths within [Bm ]2Ca(THF)2 range from 2.846 Å to 2.890 Å.

A CSD search for compounds having Ca-S bonds yielded only 23 results. Within these complexes the Ca-S bond lengths ranged from 2.746 Å in a calcium diiron complex13 to

3.147 Å in a calcium calixarene complex14 with an average Ca-S length of 2.940 Å. The

MeBenz Ca-S bond lengths in our [Bm ]2Ca(THF)2 complex correlate well with these reported Ca-S bonds.

In contrast to the relatively low number of Ca-S bonds in the CSD, there are over

1000 complexes containing Ca-O bonds. The Ca-O bond lengths reported in the CSD vary widely from 1.934 Å in a calcium sandwich complex15 to 4.490 Å in a calcium pyrazolyl complex16 with an average length of 2.410Å. In a search of Ca-O bonds specifically between calcium and the THF ligand, there are 360 complexes, in which the lengths of the Ca-O bonds range from 2.295 Å in trimetallic calcium complex17 to 2.619

Å in a nitrogen-rich bidentate calcium complex18 with an average bond length of 2.386

MeBenz Å. The corresponding lengths in [Bm ]2Ca(THF)2 correlate closely with these reported Ca-O bond lengths.

The bond angles Table 2 indicate that the eight-coordinate calcium center adopts a trigonal dodecahedral geometry.19 A clear characteristic of this geometry is to identify

the C2v symmetry element in which four of the coordinated atoms are within one plane and the other four coordinated atoms are in a perpendicular plane. A view of the two sets of planar atoms is shown in Figure 5.

221

Figure 5. The two sets of planar atoms in a trigonal dodecahedron (image modified from reference 19b)

MeBenz Within the [Bm ]2Ca(THF)2 structure, the S1, H1, H2 and S4 atoms from the

[BmMeBenz] ligand are in one plane and the O1 and O2 atoms from the THF solvent and

S2 and S3 from the ligand thioimidazolyl rings are in another plane (Figure 6).

MeBenz Figure 6. The two sets of planar atoms in [Bm ]2Ca(THF)2

The sum of bond angles between S1, H1, H2, and S4 is 360.91° and the sum of the bond angles between O1, O2, S2, and S3 is 360.11° which quantitatively shows these sets of atoms are planar.

222

MeBenz This molecular structure of [Bm ]2Ca(THF)2 represents the first structure of calcium coordinated to the [Bm] ligand class. As mentioned previously, there is a

Me structurally characterized [Tm ]2Ca(H2O)6 complex, that was synthesized by addition

Me 11 Me of Ca(NO3)2 to [Tm ]Na. In the molecular structure of this complex, the [Tm ] ligand is an uncoordinated anion.

The number of calcium complexes reported in the CSD were tabulated based on their coordination modes and are provided in Table 4. From the values in Table 4, six- coordinate calcium is the most common coordination mode, followed by eight- coordinate calcium.

Table 4. Summary of calcium coordination numbers in structurally characterized compounds listed in the CSD

Coordination %

Number

1 0.00

2 0.22

3 1.35

4 6.59

5 8.91

6 33.38

223

7 15.34

8 22.83

9 4.72

10 2.10

+11 4.56

The most common geometries for eight-coordinate complexes are triangular dodecahedron and square antiprism.20 A visual inspection of the eight-coordinate calcium complexes showed that 17% of the reported complexes adopted a trigonal dodecahedral geometry, the remaining complexes adopt a square antiprismatic geometry or are distorted square antiprisms. These relatively uncommon calcium trigonal dodecahedral geometries can be forced to have two planar sets of atoms from chelation of the metal to two planar tetradentate ligands. Examples of a forced dodecahedral calcium geometry can be seen in a bis(triamine) aquo complex,21a a modified bis(phenanthroline) complex,21b and a tetradentate ligand with a pyrrole backbone.21c There are a number of calcium centers which adopt a dodecahedral geometry and are coordinated to more flexible ligands. Complexes which show this type of calcium coordination include a calcium cyclic ether complex,22a and a hydroxyketone complex,22b and a sulfur-oxygen cryptand complex.22c Our

224

MeBenz MeBenz [Bm ]2Ca(THF)2 complex fits into this category of complexes as [Bm ] is not a planar ligand.

MeBenz The Ca-HB atom distances in [Bm ]2Ca(THF)2 are listed in Table 2 are 2.520Å and 2.630Å. The average calcium-hydrogen atom distances in other calcium borohydride complexes reported in the CSD is 2.417Å with the shortest Ca…H distance of 1.951 Å in a terphenyl calcium complex23 and the longest distance of 2.970 Å in a

24 … MeBenz calcium imidazolyl complex The Ca H atom distances in [Bm ]2Ca(THF)2 correspond with this range of literature values.

The significance of these Ca…HB interactions can be quantitatively assessed using a distance (d) measurement which is the difference of the Ca-B atom distance and the shortest Ca-S bond length.25 The Ca…B distances and the shortest M-S bond length are listed in Table 5 along with the corresponding values for other [BmMeBenz]M complexes and main group [BmMe]M complexes reported in the literature.

225

… MeBenz Table 5. Selected M-S bond and M B atom distances in [Bm ]2Ca(THF)2 and reported compounds

… Compound d(M-S)short/Å d(M B)/Å d/Å Reference

MeBenz 2.8460 3.467, 0.62, this work [Bm ]2Ca(THF)2 a experimental 3.484 0.64

MeBenz 3.007 3.528, 0.52, this work [Bm ]2Ca(THF)2 a geometry optimized 3.538 0.53

a 2.443 3.385, 0.94, 26 [Bp]2Ca(THF)2 3.268 0.83

iPr2 b 2.478 3.369 0.89 26 [Bp ]2Ca(THF)2

MeBenz 2.802 b 0.72 4a {-[Bm ]Na(THF)2}2 3.521

Me 2.267 2.818 0.55 2 [Bm ]ZnNO3

MeBenz 2.287 2.750 0.46 4a [Bm ]2CuPMe3

Me 2.487 3.208 0.72 27 {[Bm ]Cd-SPh}2

[BmMe]ZnMe 2.342 2.883 0.54 2

[BmMe]ZnI 2.288 2.941 0.65 28 a There are two Ca…B atom distances within the molecule b Only one value is listed as the second half of the molecule is related by a plane of symmetry

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… MeBenz The d values for the two Ca HB interactions within [Bm ]2Ca(THF)2 are 0.62

Å and 0.64 Å. In comparison with other [BmMeBenz]M complexes reported in the

… MeBenz literature, the Ca HB interactions are less significant than those in [Bm ]2CuPMe3, which has a d of 0.46 Å,4a and are more significant than the Na…HB interactions in the

MeBenz 4a main group bridging complex (-[Bm ]Na(THF)2)2 which has a d of 0.72 Å.

Of other main group [BmMe]M complexes reported in the literature, the smallest

d value is 0.54 Å in [BmMe]ZnMe2 and the largest d value is 0.65 Å in [BmMe]ZnI.28 The

MeBenz d value for [Bm ]2Ca(THF)2 is within this range of literature values.

MeBenz The calcium coordination in our [Bm ]2Ca(THF)2 complex and [Bp]2Ca(THF)2

iPr2 and [Bp ]2Ca(THF)2, reported in the literature, is the same. For example, in the

R,R [Bp ]2Ca(THF)2 complexes, the calcium center is coordinated to two [Bp] ligands and two THF molecules. However, as shown in Table 5, the Ca…HB interactions are much

R,R less significant in the [Bp ]2Ca(THF)2 complexes, with d values for [Bp]2Ca(THF)2 of

iPr2 26 0.94 Å and 0.83 Å and the d value for [Bp ]2Ca(THF)2 of 0.89 Å.

Density Functional Theory (DFT) geometry optimization calculations were

MeBenz performed on [Bm ]2Ca(THF)2 (Figure 7) and selected bond lengths and angles are listed in Table 2 and Table 3, respectively and Ca…B atom distances are listed in Table 5.

227

MeBenz Figure 7. DFT optimized structure of [Bm ]2Ca(THF)2

MeBenz Table 2 shows the calcium center in the geometry optimized [Bm ]2Ca(THF)2 structure adopts a trigonal dodecahedron geometry. One set of planar atoms is S1, H1,

H2, and S4 with a bond angle sum of 360.59°. The second set of planar atoms is O1, O2,

S2, and S3 with a bond angle sum of 364.0°. The geometry in the optimized structure is slightly more distorted than the trigonal dodecahedral geometry of the experimentally determined structure. This distortion can be seen in the sum of the bond angles of the second set of planar atoms which is 364.0° which is deviated by 4° from the ideal planar bond angle of 360°. Upon visual inspection of the coordinates of the optimized

228

structure it can be seen that the oxygen from one THF ligand is slightly displaced from the plane of the other oxygen, S2 and S3 atoms.

MeBenz The d value for the optimized [Bm ]2Ca(THF)2 structure was calculated and determined to be 0.52 Å and 0.53 Å for the two Ca…HB interactions present in the molecule (Table 5). In comparison with the d values of the experimentally determined

MeBenz molecular structure of [Bm ]2Ca(THF)2 (0.62 Å and 0.64 Å) in Table 5, the d values in the optimized structure are 0.1 Å smaller, indicating that the Ca…HB interactions in this structure were made more significant within the optimized structure.

The oxygen analogue of the [Bm] ligand class is the bis(2-oxo-1- methylimidazolyl) hydroborato ligand, [BoMe], (Figure 8) which was previously synthesized by a colleague in the Parkin group.25 The benzannulated version of this ligand, [BoMeBenz]M, has been synthesized as well (Figure 8).25

Figure 8. [BoR]M and [BoRBenz]M complexes

229

The synthesis and comparison of the molecular structures of [BoMe] and [BoMeBenz] calcium complexes would be of future interest because calcium is known to bind strongly to oxygen in biological systems such as in -lactalbumin (-LA), 29 and in the serine proteases, trypsin30 and subtilisin.30

The enzyme -LA catalyzes the final step in the synthesis of lactose in mammals.

In -LA, calcium is featured in two different binding sites, a distorted pentagonal bipyramidal geometry in which calcium coordinates to the oxygen atoms in three aspartic acid residues and the backbone carbonyl of two residues.29 In the second binding site, calcium is tetrahedral and coordinates to the oxygen atoms in threonine, glutamine, aspartic acid and the backbone carbonyl of leucine.29 Calcium binding in -

LA is not involved in the catalysis but prevents denaturation of the enzyme at high pressures.31

Trypsin is digestive enzyme which catalyzes the hydrolysis of peptide bonds and features two different calcium binding sites. In one site, calcium is in an octahedral geometry and coordinates to the oxygen atoms in the side chains of two glutamic acid residues and one aspartic acid. Additionally, the backbone carbonyls of two other residues and two water molecules bind to calcium. The second binding site is relatively unknown and has not been structurally characterized.30 Calcium does not play a catalytic role in trypsin, but is necessary for the stability and activation of the enzyme.32

230

Figure 9. One of two binding sites featuring seven-coordinate calcium in subtilisin

BPN’ (image reproduced from reference 30)

Subtilisin is also a digestive enzyme and it has two seven-coordinate calcium binding sites which are conserved across the family of proteins. Specifically in one binding site in substilisin BPN’, calcium coordinates to the backbone carbonyl oxygen atoms of leucine, isoleucine, and valine and the side chain oxygen atoms in asparagine, glutamine and aspartic acid (Figure 9).30,33 In the second binding site, calcium coordinates to the backbone carbonyl oxygen atoms in glycine, tyrosine, valine and glutamic acid, as well as to one oxygen in aspartic acid and two water molecules.30

Calcium binding within subtilisin maintains structural stability so the enzyme does not unfold.34 Coordination of calcium to smaller, oxygen-rich molecules would be of use in understanding the chemistry in these larger biological systems.

231

Calcium complexes with the tris(2-oxo-benzimidazolyl) hydroborato ligand,

[ToRBenz] (R = Ad, But) (Figure 10) have been synthesized by colleagues in the Parkin

RBenz 35 group by addition of CaI2●4(THF) to [To ]Tl.

Figure 10. Structure of the [ToRBenz]M complex (R = Ad, But)

AdBenz ButBenz The molecular structures of [To ]2Ca and [To ]2Ca●3(C6H6) were also obtained and are reproduced in Figure 11 and Figure 12. The calcium centers within these complexes are six-coordinate with distorted octahedral geometries and have two

[ToRBenz] ligands coordinated to the calcium center.35

232

AdBenz Figure 11. Molecular structure of [To ]2Ca (reproduced from reference 35)

233

ButBenz Figure 12. Molecular structure of [To ]2Ca●3(C6H6) (benzene omitted for clarity)

(reproduced from reference 35)

In the analysis of the 34% of six-coordinate calcium complexes listed in the CSD

(Table 4), a search for octahedral complexes was completed by adding constraints on the angles of the complexes so that one angle was between 165°-180° and two angles were 85°-95°. Of the six-coordination calcium complexes in the CSD, half of them matched this set of criteria for an octahedral geometry, indicating that six-coordinate, octahedral calcium centers are quite prevalent.

234

RBenz The coordination modes in the [To ]2Ca complexes have the potential to serve as molecular models for biological systems, such as the octahedral binding site in

RBenz trypsin. In this vein, [Bo ]nCa (n = 1, 2) complexes could potentially model lower coordinate calcium binding sites, such as the four-coordinate site in -LA.

MeBenz 3.4 [Bm ]2Ca(THF)2 as a Transmetallating Agent

Group 1 and 2 metal compounds are often used as transmetallating agents.36

MeBenz To see if the [Bm ]2Ca(THF)2 complex could be used in this manner, mercury alkyl

MeBenz chloride was added to [Bm ]2Ca(THF)2.

MeBenz Scheme 3. Addition of RHgCl (R = Me, Et) to [Bm ]2Ca(THF)2

MeBenz As shown in Scheme 3, the [Bm ]2Ca(THF)2 complex can be used to obtain

[BmMeBenz]HgMe and [BmMeBenz]HgEt, which are known complexes and are discussed in 235

Chapter 4. Evidence of formation of [BmMeBenz]HgMe and [BmMeBenz]HgEt were confirmed by 1H NMR spectroscopy.

3.5 Conclusion

t The synthesis and spectroscopic characterization of group 1 and 2 [BmBu Benz]M

(M = Na, K, Ca) complexes has been discussed. Evidence of the synthesis of these complexes was shown through 1H and 13C NMR spectroscopy as well as via characteristic H-B stretching frequencies in infrared spectroscopy. In addition, the molecular structure of the first calcium [Bm] complex has been reported, specifically

MeBenz MeBenz [Bm ]2Ca(THF)2. The calcium center in [Bm ]2Ca(THF)2 has a trigonal dodecahedral geometry and is supported by two secondary Ca…HB interactions from

t the [Bm] ligand. These group 1 and 2 [BmBu Benz]M complexes are key in accessing other main group and transition metal complexes with this ligand class.

3.6 Experimental Section

3.6.1 General Considerations

NMR spectra were measured on Bruker 300 DRX, Bruker 400 DRX, and Bruker Avance

1 500 DMX spectrometers. H NMR spectra are reported in ppm relative to SiMe4 ( = 0) and were referenced internally with respect to the protio solvent impurity ( 2.50 for

37 13 DMSO). C NMR spectra are reported in ppm relative to SiMe4 ( = 0) and were

236

referenced internally with respect to the solvent ( 39.52 for DMSO). Coupling constants are given in hertz. ATR-IR spectra were recorded Perkin Elmer UATR Two and Nicolet iS10 Instrument and the data are reported in reciprocal centimeters (cm–1).

Mass spectra were obtained on a JEOL JMS-HX110HF tandem mass spectrometer using fast atom bombardment (FAB). Sodium borohydride (Aldrich), potassium borohydride

(Strem), calcium borohydride (Strem), and 1-methyl-2-benzimidazole-2-thione (Aldrich) were obtained commercially and 1-t-butyl-2-benzimidazole-2-thione was synthesized according to literature methods.38

3.6.2 X-ray Structure Determination

Single crystal X-ray diffraction data were collected on a Bruker Apex II diffractometer and crystal data, data collection and refinement parameters are summarized in Table 6.

The structures were solved using direct methods and standard difference map techniques, and were refined by full-matrix least-squares procedures on F2 with

SHELXTL (Version 6.12).39

3.6.3 Computational Details

Calculations were carried out using DFT as implemented in the Jaguar 7.5 (release 2007) suite of ab initio quantum chemistry programs.40 Geometry optimizations and

237

frequency calculations were performed with the B3LYP density functional41 using the 6-

31G** (H, B, C, N, S) basis set and the LACVP (Ca) basis set.42

t 3.6.4 Synthesis of [BmBu Benz]Na

A mixture of 1-t-butyl-2-benzimidazole-2-thione (317 mg, 1.5 mmol) and NaBH4 (29 mg,

0.8 mmol) were added to a thick-walled ampoule and treated with THF (ca. 2 mL). The ampoule was heated at 100˚C overnight, during which time a white precipitate formed.

The mixture was allowed to cool to room temperature and the motherliquor was removed via filtration, the white precipitate was collected and dried in vacuo to give

t [BmBu Benz]Na as a white solid (169 mg, 35 %). 1H NMR (DMSO): 2.01 [s, 18H,

H2B{(C4H4)C2N2(CCH3)2CS}2Na], 5.33 [br, 2H, H2B{(C4H4)C2N2(CCH3)2CS}2Na], 6.62 [br,

2H, H2B{(C4H4)C2N2(CCH3)2CS}2Na], 6.79 [m, 4H, H2B{(C4H4)C2N2(CCH3)2CS}2Na], 7.50

3 3 [d, JH-H = 8 Hz, 2H, H2B{(C4H4)C2N2(CCH3)2CS}2Na],7.58 [d, JH-H = 8 Hz, 2H,

3 H2B{(C4H4)C2N2(CCH3)2CS}2Na], 8.13 [d, JH-H = 8 Hz, 2H,

13 1 H2B{(C4H4)C2N2(CCH3)2CS}2Na]. C{ H} NMR (DMSO): 25.2 [s, 2C, THF], 30.0 [s, 6C,

H2B{(C4H4)C2N2(CCH3)3CS}2Na], 67.1 [s, 2C, THF], 111.61 [s, 2C,

H2B{(C4H4)C2N2(CCH3)3CS}2Na], 111.7 [s, 2C, H2B{(C4H4)C2N2(CCH3)3CS}2Na], 114.9 [s,

2C, H2B{(C4H4)C2N2(CCH3)3CS}2Na], 133.4 [s, 3C, H2B{(C4H4)C2N2(CCH3)3CS}2Na], 133.9

238

[s, 2C, H2B{(C4H4)C2N2(CCH3)3CS}2Na], 137.7 [s, 2C, H2B{(C4H4)C2N2(CCH3)3CS}2Na],

-1 172.4 [s, 2C, H2B{(C4H4)C2N2(CCH3)3CS}2Na]. IR (ATR, cm ): 3028 (w), 2986 (w), 2960

(w), 2924 (w), 2428 [H-B] (br), 2324 (w), 2290 (w), 1606 (w), 1478 (m), 1324 (s), 1264 (w),

1192 (m), 1120 (m), 1102 (w), 1034 (m), 1022 (w), 960 (w), 918 (w), 828 (w), 828 (w), 742

(s), 640 (w), 632 (w), 584 (w), 416 (m). 11B NMR not observed. FAB-MS: 446 m/z =

t [BmBu Benz]Na.

t Figure 13. Experimentally obtained mass spectrum for [BmBu Benz]Na

239

t Figure 14. Predicted isotope pattern for the parent ion in [BmBu Benz]Na43

t 3.6.5 Synthesis of [BmBu Benz]K

A mixture of 1-t-butyl-2-benzimidazole-2-thione (511 mg, 2.5 mmol) and KBH4 (68 mg,

1.2 mmol) were added to a thick-walled ampoule and treated with THF (ca. 2 mL). The ampoule was heated at 100 ˚C overnight, during which time a white precipitate formed.

The mixture was allowed to cool to room temperature and the motherliquor was

t removed via filtration, the precipitate was collected dried in vacuo to give [BmBu Benz]K as a white solid (305 mg, 55%). 1H NMR (DMSO): 2.01 [s, 18H,

H2B{(C4H4)C2N2(CCH3)2CS}2K], 3.78 [br, 2H, H2B{(C4H4)C2N2(CCH3)3CS}2K], 6.63 [br, 2H,

3 H2B{(C4H4)C2N2(CCH3)3CS}2K], 6.77 [m, 4H, H2B{(C4H4)C2N2(CCH3)3CS}2K], 7.51 [d, JH-H

3 = 8 Hz, 1H, H2B{(C4H4)C2N2(CCH3)3CS}2K], 7.58 [d, JH-H = 8 Hz, 2H,

240

3 H2B{(C4H4)C2N2(CCH3)3CS}2K], 8.14 [d, JH-H = 8 Hz, 1H, H2B{(C4H4)C2N2(CCH3)3CS}2K].

13 1 C{ H} NMR (DMSO): 25.2 [s, 2C, THF], 30.0 [s, 6C, H2B{(C4H4)C2N2(CCH3)3CS}2K], 67.1

[s, 2C, THF], 111.6 [s, 2C, H2B{(C4H4)C2N2(CCH3)3CS}2K], 111.8 [s, 2C,

H2B{(C4H4)C2N2(CCH3)3CS}2K], 114.9 [s, 2C, H2B{(C4H4)C2N2(CCH3)3CS}2K], 133.4 [s, 2C,

H2B{(C4H4)C2N2(CCH3)3CS}2K], 133.8 [s, 2C, H2B{(C4H4)C2N2(CCH3)3CS}2K], 137.8 [s, 2C,

11 H2B{(C4H4)C2N2(CCH3)3CS}2K], 172.4 [s, 2C, H2B{(C4H4)C2N2(CCH3)3CS}2K]. B NMR

-1 not observed. IR (ATR, cm ): 3076 (w), 2996 (w), 2978 (w), 2930 (w), 2452 [H-B] (br),

2320 (w), 1480 (w), 1330 (s), 1264 (w), 1192 (w), 1120 (m), 1104 (m), 1020 (w), 958 (w), 874

t (w), 832 (w), 744 (s), 642 (w), 628 (w), 582 (w), 416 (m). FAB-MS: 462 m/z = [BmBu Benz]K.

t Figure 15. Experimentally obtained mass spectrum for [BmBu Benz]K 241

t Figure 16. Predicted isotope pattern for the parent ion in [BmBu Benz]K43

MeBenz 3.6.6 Synthesis of [Bm ]2Ca(THF)2

A mixture of 1-methyl -2-benzimidazole-2-thione (83 mg, 0.51 mmol) and

Ca(BH4)2●(THF)2 (36 mg, 0.17 mmol) were added to a thick-walled ampoule and was treated with THF (ca. 2 mL). The ampoule was heated at 120˚C overnight, then the clear reaction mixture was allowed to cool to room temperature. The reaction was filtered

MeBenz and large colorless crystals of [Bm ]2Ca(THF)2 (34 mg, 23%) grew from the motherliquor. These crystals were suitable for X-ray diffraction. Anal. calc. C, 55.7%;

1 H, 5.6%; N, 13.0%. Found: C, 55.5%; H 5.6%; N, 12.8%. H NMR (C6D6): 1.36 [m, 8H,

242

[H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 3.03 [s, 12H,

[H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 3.79 [m, 8H,

[H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 4.47 [s, 4H,

3 H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 6.48 [d, JH-H = 7 Hz, 4H,

[H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 6.87 [m, 8H,

3 [H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 7.61 [d, JH-H = 7 Hz, 4H,

13 1 [H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2]. C{ H} NMR (C6D6): 25.6 [s, 4C,

[H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 30.5 [s, 4C,

[H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 68.7 [s, 4C,

[H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 108.9 [s, 4C,

[H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 113.5 [s, 4C,

[H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 121.9 [s, 4C,

[H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 122.6 [s, 4C,

[H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 134.4 [s, 4C,

[H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 137.4 [s, 4C,

[H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2], 170.3 [s, 4C,

11 -1 [H2B{C4H4C2N2(CH3)CS}2]2Ca(C4H8O)2]. B NMR (C6D6): not observed. IR (ATR, cm ):

3065 (w), 2970 (w), 2879 (w), 2429 [H-B] (w), 2394 (w), 2237 [B-H-M] (w), 1483 (m), 1435

243

(m), 1398 (m), 1373 (m), 1348 (s), 1315 (m), 1297 (w), 1240 (w), 1193 (w), 1181 (w), 1153

(w), 1122 (s), 1096 (m), 1035 (m), 1016 (w), 977 (w), 615 (w), 876 (w), 810 (w), 796 (w), 777

(w), 744 (s), 738 (s).

ButBenz 3.6.7 Synthesis of [Bm ]2Ca(THF)2

A mixture of 1-t-butyl-2-benzimidazole-2-thione (132 mg, 0.64 mmol) and

Ca(BH4)2●(THF)2 (34 mg, 0.16 mmol) were added to a thick-walled ampoule and treated with THF (ca. 2 mL). The ampoule was heated at 100 ˚C overnight, during which time a white precipitate formed. The mixture was allowed to cool to room temperature and the motherliquor was removed via filtration, the precipitate was collected dried in vacuo

ButBenz to give [Bm ]2Ca(THF)2 (45 mg, 35%) as a white solid. Anal. calc. C, 60.8 %; H,

1 7.0%; N, 10.9%. Found: C, 58.0%; H, 6.8%; N, 10.9 %. H NMR (C6D6): 2.01 [s, 36H,

[H2B{C4H4C2N2C(CH3)3CS}2]2Ca(C4H8O)2], 3.81 [br, 2H,

[H2B{C4H4C2N2C(CH3)3CS}2]2Ca(C4H8O)2], 6.79 [m, 8H,

3 [H2B{C4H4C2N2C(CH3)3CS}2]2Ca(C4H8O)2], 7.50 [d, JH-H = 8Hz, 4H,

3 [H2B{C4H4C2N2C(CH3)3CS}2]2Ca(C4H8O)2], 8.14 [d, JH-H = 8Hz, 4H,

13 1 [H2B{C4H4C2N2C(CH3)3CS}2]2Ca(C4H8O)2]. C{ H} NMR (C6D6): 30.0 [s, 12C,

[H2B{C4H4C2N2C(CH3)3CS}2]2Ca(C4H8O)2], 60.9 [s, 4C,

244

[H2B{C4H4C2N2C(CH3)3CS}2]2Ca(C4H8O)2], 111.6 [s, 4C,

[H2B{C4H4C2N2C(CH3)3CS}2]2Ca(C4H8O)2], 114.9 [s, 4C,

[H2B{C4H4C2N2C(CH3)3CS}2]2Ca(C4H8O)2], 119.7 [s, 4C,

[H2B{C4H4C2N2C(CH3)3CS}2]2Ca(C4H8O)2], 119.9 [s, 4C,

[H2B{C4H4C2N2C(CH3)3CS}2]2Ca(C4H8O)2], 133.4 [s, 4C,

[H2B{C4H4C2N2C(CH3)3CS}2]2Ca(C4H8O)2], 137.8 [s, 4C,

[H2B{C4H4C2N2C(CH3)3CS}2]2Ca(C4H8O)2], 172.5 [s, 4C,

11 - [H2B{C4H4C2N2C(CH3)3CS}2]2Ca(C4H8O)2]. B NMR (C6D6): not observed. IR (ATR, cm

1 ): 2.964 (w), 2926(w), 2420 (w) [H-B], 2375 (w), 1473 (w), 1439 (w), 1375 (m), 1329 (s),

1271 (w), 1218 (w), 1183 9m), 1122 (m), 1030 (m), 999 (w), 957 (w), 887 (w), 818 (w), 734

(s), 679 (m).

MeBenz 3.6.8 Reaction with [Bm ]2Ca(THF)2 and ClHgMe

MeBenz To a slurry of [Bm ]2Ca(THF)2 (3 mg, 0.01 mmol) in THF (0.5 mL), MeHgCl (3 mg,

1 MeBenz 0.01 mmol) was added. H NMR spectroscopy showed all the [Bm ]2Ca(THF)2 had converted to [BmMeBenz]HgMe.

245

MeBenz 3.6.9 Reaction with [Bm ]2Ca(THF)2 and ClHgEt

MeBenz To a slurry of [Bm ]2Ca(THF)2 (3 mg, 0.01 mmol) in THF (0.5 mL), EtHgCl (3 mg,

1 MeBenz 0.01 mmol) was added. H NMR spectroscopy showed all the [Bm ]2Ca(THF)2 had converted to [BmMeBenz]HgEt.

246

3.7 Crystallographic Data

Table 6. Crystal, intensity collection and refinement data

MeBenz [Bm ]2Ca(thf)2

lattice Orthorhombic

formula C40H48B2CaN8O2S4 formula weight 862.80

space group P212121 a/Å 9.4345(15) b/Å 9.4345(15) c/Å 24.635(4) /˚ 90 /˚ 90 /˚ 90 V/Å3 4239.4(12) Z 4 temperature (K) 130(2) radiation (, Å) 0.71073  (calcd.), g cm-3 1.352  (Mo K), mm-1 0.391 max, deg. 30.64 no. of data collected 69824 no. of data used 13038 no. of parameters 517

R1 [I > 2(I)] 0.0592

wR2 [I > 2(I)] 0.1099

R1 [all data] 0.1206

wR2 [all data] 0.1310 GOF 1.027

247

3.8 References and Notes

(1) (a) Garner, M.; Reglinski, J.; Cassidy, I.; Spicer, M. D.; Kennedy, A. R. Chem. Commun. 1996, 1975–1976. (b) Reglinski, J.; Garner, M.; Cassidy, I. D.; Slavin, P. A.; Spicer, M. D.; Armstrong, D. R. J. Chem. Soc. Dalt. Trans. 1999, 2119–2126. (2) Kimblin, C.; Bridgewater, B. M.; Hascall, T.; Parkin, G. J. Chem. Soc. Dalt. Trans.

2000, 891–897. (3) (a) Parkin, G. New J. Chem. 2007, 31, 1996–2014. (b) Warren, M.J.; Cooper, J.B.; Wood, S.P.; Shoolingin- Jordan, P.M. Trends Biochem. Sci. 1998, 23, 217–221. (c) Jaffe, E.K.; Martins, J. ; Li, J. ; Kervinen, J.; Dunbrack, R.L. J. Biol. Chem. 2001, 276, 1531–1537. (d) Shoolingin-Jordan, P.M.; Spencer, P.; Sarwar, M.; Erskine, P.E.; Cheung,

K.M.; Cooper, J.B.; Norton, E.B. Biochem. Soc. Trans. 2002, 30, 584–590. (e) Melnick, J.G.; Zhu, G.; Buccella, D.; Parkin, G. J. Inorg. Biochem. 2006, 100, 1147–1154. (f) Morlok, M.M; Janak, K.E.; Zhu, G.; Quarless, D.A.L; Parkin, G. J. Am. Chem. Soc. 2005, 127, 14039–14050. (g) Melnick, J. G.; Parkin, G. Science 2007, 317, 225–227. (4) (a) Al-Harbi, A.; Rong, Y.; Parkin, G. Dalt. Trans. 2013, 42, 11117–11127.

(b) Rong, Y.; Palmer, J. H.; Parkin, G. Dalt. Trans. 2014, 43, 1397–1407. (5) (a) Trofimenko, S. J. Am. Chem. Soc. 1967, 89, 6288–6294. (b) Trofimenko, S. J. Am. Chem. Soc. 1967, 89, 3170–3177. (c) Trofimenko, S.; Calabrese, J. C.; Thompson, J. S. Inorg. Chem. 1987, 26, 1507– 1514.

248

(6) Cambridge Structural Database (Version 5.35). 3D Search and Resarch Using the Cambridge Structural Database: Allen, F.H., and Kennard O. (1993) 3D search and research using the Cambridge Structural Database. “Chemical Design Automation News” 8, pp. 1, 31-37. (7) (a) Philson, L.; Alyounes, D. M.; Zakharov, L. N.; Rheingold, A. L.; Rabinovich, D. Polyhedron 2003, 22, 3461–3466. (b) Seebacher, J.; Shu, M.H.; Vahrenkamp, H. Chem. Commun. 2001, 1026–1027.

(c) Shu, M.H.; Walz, R.; Wu, B.; J. Seebacher, J.; Vahrenkamp, H. Eur. J. Inorg. Chem. 2003, 2502–2511. (d) Ibrahim, M.M.; He, G.; Seebacher, J.; Benkmil, B.; Vahrenkamp, H. Eur. J. Inorg. Chem. 2005, 4070–4077. (8) Alvarez, H. M.; Krawiec, M.; Donovan-Merkert, B. T.; Fouzi, M.; Rabinovich, D. Inorg. Chem. 2001, 40, 5736–5737. (9) Biernat, A.; Schwalbe, M.; Wallace, D.; Reglinski, J.; Spicer, M. D. Dalt. Trans.

2007, 2242–2244. (10) Alvarez, H. M.; Tran, T. B.; Richter, M. A; Alyounes, D. M.; Rabinovich, D.; Tanski, J. M.; Krawiec, M. Inorg. Chem. 2003, 42, 2149–2156. (11) Cetin, A.; Ziegler, C. J. Dalt. Trans. 2006, 1006–1008. (12) Nakamoto, K. Handbook of Vibrational Spectroscopy; Sons, J. W. &, Ed.; 2006; pp. 1872–1892. (13) Ogienko, M. a.; Naumov, D. Y.; Konchenko, S. N. Acta Crystallogr. Sect. E Struct.

Reports Online 2012, 68, m1559–m1560. (14) Bilyk, A.; Dunlop, J. W.; Fuller, R. O.; Hall, A. K.; Harrowfield, J. M.; Hosseini, M. W.; Koutsantonis, G. A.; Murray, I. W.; Skelton, B. W.; Stamps, R. L.; White, A.L.

Eur. J. Inorg. Chem. 2010, 2106–2126. (15) Chaney, M. O.; Tones, N. D.; Debono, M. J. Antibiot. (Tokyo). 1976, 424–427.

249

(16) Teng, W.; Guino-O, M.; Hitzbleck, J.; Englich, U.; Ruhlandt-Senge, K. Inorg. Chem. 2006, 45, 9531–9539. (17) He, X.; Noll, B. C.; Beatty, A.; Mulvey, R. E.; Henderson, K. W. J. Am. Chem. Soc. 2004, 126, 7444–7445. (18) Fedushkin, I. L.; Skatova, A. A.; Chudakova, V. A.; Fukin, G. K.; Dechert, S.; Schumann, H. Eur. J. Inorg. Chem. 2003, 2003, 3336–3346. (19) (a) Hoard, J. L.; Silverton, J. V. . Inorg. Chem. 1963, 2, 235–242.

(b) Hawthorne, S. L.; Bruder, A. H.; Fay, R. C. Inorg. Chem. 1983, 22, 3368–3375. (20) Lippard, S. J.; Russ, B. J.Inorg. Chem. 1968, 7, 1686–1688. (21) (a) Waters, A. F.; White, A. H. Aust. J. Chem. 1996, 49, 87–98. (b) Raymond, T. G.; Williams, N. J.; Reibenspies, J. H.; Sousa, A. S. De; Hancock, R. D. Inorg. Chem. 2008, 47, 10342–10348. (c) Clarke, E. T.; Squattrito, P. J.; Rudolf, P. R.; Motekaitis, R. Z.; Martell, A. E.; Clearfield, A. Inorganica Chim. Acta 1989, 166, 221–231.

(22) (a) Itoh, S.; Kumei, H.; Nagatomo, S.; Kitagawa, T.; Fukuzumi, S. J. Am. Chem. Soc. 2001, 123, 2165–2175. (b) Hauser, M. R.; Doxsee, K. M.; Hope, H. Inorg. Chem. 2009, 48, 10780–10788. (c) Farina, P.; Levason, W.; Reid, G. Dalton Trans. 2013, 42, 89–99. (23) Krieck, S.; Görls, H.; Westerhausen, M. Inorg. Chem. Commun. 2010, 13, 1466– 1469. (24) Arrowsmith, M.; Hill, M. S.; Kociok-Kohn, G. Organometallics 2009, 28, 1730–

1738. (25) Al-Harbi, A.; Rong, Y.; Parkin, G. Inorg. Chem. 2013, 52, 10226–10228. (26) Saly, M. J.; Heeg, M. J.; Winter, C. H. Polyhedron 2011, 30, 1330–1338.

(27) Philson, L.A.; Alyounes, D. M.; Zakharov, L. N.; Rheingold, A. L.; Rabinovich, D. Polyhedron 2003, 22, 3461–3466.

250

(28) Kimblin, C.; Hascall, T.; Parkin, G. Inorg. Chem. 1997, 1669, 5680–5681. (29) Permyakov, E. A; Berliner, L. J. FEBS Lett. 2000, 473, 269–274. (30) Gilliland, G. L.; Teplyakov, A. Handb. Met. 2006, 1–13. (31) Dzwolak, W.; Kato, M.; Shimizu, A.; Taniguchi, Y. Biochim. Biophys. Acta 1999, 1433, 45–55. (32) (a) Martin, R.B.; Siegel, H. Metal Ions in Biological Systems , Vol 17. Marcel Dekker, New York, 1984, pp 1-49.

(b) Northrop, J.H.; Kunitz, M.; Herriot, R.M. Crystalline Enzymes, 2nd Ed. Columbia University Press, New York, 1948. (33) Botts, R.; Ultsch, M.; Kossiakoff, A.; Graycar, T.; Katz, B.; Power, S. J. Biol. Chem. 1988, 263, 7895–7906. (34) Voordouw, C.; Milo, C.; Roche, R. S Biochemistry 1976, 15, 3716–3724. (35) Palmer, J.H.; Rong, Y.; Parkin, G. unpublished results (36) (a) Janiak, C.; Braun, L.; Girgsdies, F. J. Chem. Soc. Dalt. Trans. 1999, 3, 3133–3136.

(b) Kuchta, M. C.; Gemel, C.; Metzler-Nolte, N. J. Organomet. Chem. 2007, 692, 1310–1314. (c) Dias, H. V. R.; Wang, X. ." Dalton Trans. 2005, 8, 2985–2987. (37) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997, 62, 7512-7515. (38) Ellsworth, E. L.; Domagala, J.; Vara Prasad, J. V. N.; Hagen, S.; Ferguson, D.; Holler, T.; Hupe, D.; Graham, N.; Nouhan, C.; Tummino, P. J.; Zeikus, G.; Lunney, E.A. Bioorg. Med. Chem. Lett. 1999, 9, 2019–2024.

(39) (a) Sheldrick, G. M. SHELXTL, An Integrated System for Solving, Refining and Displaying Crystal Structures from Diffraction Data; University of Göttingen, Göttingen, Federal Republic of Germany, 1981.

(b) Sheldrick, G. M. Acta Cryst. 2008, A64, 112-122. (40) Jaguar 7.5, Schrödinger, LLC, New York, NY 2008.

251

(41) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652. (b) Becke, A. D. Phys. Rev. A 1988, 38, 3098-3100. (c) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B 1988, 37, 785-789. (d) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200-1211. (e) Slater, J. C. Quantum Theory of Molecules and Solids, Vol. 4: The Self-Consistent Field for Molecules and Solids; McGraw-Hill: New York, 1974. (42) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270-283.

(b) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284-298. (c) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299-310. (43) Predicted isotope patterns were calculated using: Winter, Mark. University of Sheffield, England.

252

Chapter 4

Synthesis and Structural Characterization of Mercury Methyl and Ethyl Complexes

Supported by Sulfur-Rich tris- and bis(2-mercapto-1-imidazolyl),

[Tm] and [Bm], Ligands

Table of Contents

4.1 Introduction ...... 256

4.1.1 Objective ...... 256

4.1.2 Rationalization for the [Tm] ligand ...... 257

4.2 [Tm]HgR (R = Me, Et) Complexes ...... 260

4.2.1 Synthesis and Molecular Structures of [TmMe]HgR ...... 260

t 4.2.2 Synthesis and Molecular Structures of [TmMeBenz]HgR and [TmBu Benz]HgR 269

4.3 [Bm]HgR (R = Me, Et) Complexes ...... 277

t 4.3.1 Synthesis and Molecular Structures of [BmMe]HgR and [BmBu ]HgEt ...... 277

t 4.3.2 Synthesis and Molecular Structures of [BmMeBenz]HgR and [BmBu Benz]HgR 286

4.4 NMR Characterization of Mercury Alkyl Complexes ...... 288

4.4.1 NMR Characterization of [L]HgMe Complexes ...... 288

4.4.2 NMR Characterization of [L]HgEt Complexes ...... 293 253

4.5 Hg-C Bond Cleavage with Benzenethiol ...... 296

4.5.1 Reactions with [TmMe]HgEt and [TmMeBenz]HgEt ...... 296

t t 4.5.2 Reactions with [TmBu ]HgEt and [TmBu Benz]HgEt ...... 297

4.6 Conclusion ...... 298

4.7 Experimental Section ...... 298

4.7.1 General Considerations ...... 298

4.7.2 X-ray Structure Determination...... 299

4.7.3 Computational Details ...... 300

4.7.4 Synthesis of [TmMe]HgMe ...... 300

4.7.5 Synthesis of [TmMe]HgEt ...... 301

4.7.6 Synthesis of [TmMeBenz]HgMe ...... 302

4.7.7 Synthesis of [TmMeBenz]HgEt ...... 304

t 4.7.8 Synthesis of [TmBu Benz]HgMe ...... 305

4.7.10 Synthesis of [BmMe]HgMe ...... 308

4.7.11 Synthesis of [BmMe]HgEt ...... 309

t 4.7.12 Synthesis of [BmBu ]HgEt ...... 311

4.7.13 Synthesis of [BmMeBenz]HgMe ...... 312

4.7.14 Synthesis of [BmMeBenz]HgEt ...... 313

254

t 4.7.15 Synthesis of [BmBu Benz]HgMe ...... 315

t 4.7.16 Synthesis of [BmBu Benz]HgEt ...... 316

4.7.17 Addition of Benzenethiol to [TmMe]HgEt and [TmMeBenz]HgEt ...... 318

t t 4.7.18 Addition of Benzenethiol to [TmBu ]HgEt and [TmBu Benz]HgEt ...... 320

4.8 Crystallographic Data ...... 322

4.9 References and Notes ...... 327

255

4.1 Introduction

4.1.1 Objective

The study of the reactivity of mercury complexes has long been of biological interest due to the high toxicity of these compounds.1,2 Mercury is known to disrupt biological environments by binding readily to thiol groups within metalloproteins and displacing metals, such as zinc, which are vital for protein function.3 Exposure to mercury alkyls, which are potent neurotoxins, is known to be biologically harmful and even fatal,1,4 therefore, detoxification of these species from biological systems is of the utmost importance. Two enzymes known for detoxifying mercury alkyls are sulfur-rich

MerB and MerA; MerB promotes cleavage of the Hg-C bond and MerA reduces the toxic

Hg2+ species to the less toxic Hg0 species.1,2,5,6 This biological mechanism indicates the cleavage of the Hg-C bond is a key step in the detoxification process.

I synthesized a series of mercury alkyl complexes with a variety of coordination modes to sulfur to expand our knowledge about Hg-C bond cleavage. Within this chapter, I will discuss the synthesis and structural characterization of new mercury methyl and ethyl complexes that are supported by the bis- and tris(mercaptoimidazolyl)hydroborato, [BmR] and [TmR], class of ligands and their benzannulated counterparts bis- and tris(mercaptobenzimidazolyl)hydroborato

[BmRBenz] and [TmRBenz] (where R = Me or But) (Figure 1).

256

Figure 1. The [Tm] and [Bm] class of ligands (R = Me, or But)

4.1.2 Rationalization for the [Tm] ligand

Previously, the Parkin group studied the cleavage of the Hg-C bond within

t t [TmBu ]HgMe and [TmBu ]HgEt (Figure 2) in order to elucidate the mercury detoxification mechanism enzyme MerB employs.7

t Figure 2. [TmBu ]HgR complexes (R = Me and Et)

The sulfur-rich environment provided by the [Tm] ligand is quite similar to that within the active site of MerB extracted from E. coli.8 The crystal structure of MerB shows that there are two cysteine residues in the active site that coordinate to the

257 mercury substrate. The mechanism for the detoxification process indicates that after coordination of mercury alkyl to the cysteine residues, an aspartic acid residue acts as a proton donor in the protonolysis of the Hg-C bond.8

t The [TmBu ]Hg alkyl complexes were considered appropriate molecular models of mercury binding to MerB due to structural similarity of the ligand to the enzyme; thus, the subsequent Hg-C bond cleavage studies of the [Tm]HgR complexes were considered a direct parallel to the biological detoxification process.7 Upon addition of

t t benzenethiol to [TmBu ]HgMe or [TmBu ]HgEt (Scheme 1), cleavage of the Hg-C bond was observed by the evolution of methane or ethane gas, respectively, within the 1H

t NMR spectrum. The formation of the [TmBu ]HgSPh complex was also observed by 1H

NMR spectroscopy.7

t Scheme 1. Cleavage of the Hg-C bond in [TmBu ]HgR (R = Me or Et) via reaction with benzenethiol

258

It is known that two coordinate X-Hg-C species are not susceptible to protolytic

t cleavage,9 therefore, it was interesting that the Hg-C bond in [TmBu ]HgR was cleaved in a facile manner at room temperature, even though the molecular structure of the complexes shows a 1 coordinate mercury alkyl moiety. NMR experiments completed

t by the Parkin group showed that in solution, the [TmBu ] ligand was flexible and able to adopt more coordination modes. Specifically, variable temperature 1H and a 2D exchange experiments showed an increase in the coordination sphere of the mercury

t center from the two coordinate, linear [1-TmBu ]HgR species to the four coordinate [3-

t t TmBu ]HgR species through a proposed three coordinate [2-TmBu ]HgR intermediate

(Figure 3). This increase from 1 to 3 coordination makes the Hg-C bond more susceptible to protolytic cleavage, thus showing the relation between the mercury coordination sphere and Hg-C bond cleavage.

t Figure 3. Interconversion from 1 (left) to 3 (right) coordination modes in [TmBu ]HgR complexes (R = Me or Et)

259

The flexibility and multiple coordination modes of the [Tm] ligand to mercury could be compared to the concerted coordination of the two cysteine residues within

MerB.5,8 Due to the importance of the coordination of mercury to the [Tm] ligand, we wanted to synthesize mercury alkyl complexes with variety of coordination modes with this class of ligand.

4.2 [Tm]HgR (R = Me, Et) Complexes

4.2.1 Synthesis and Molecular Structures of [TmMe]HgR

Mercury alkyl complexes were readily synthesized via addition of methyl- or ethylmercury chloride to [TmMe]K10 (Scheme 2).

Scheme 2. Synthesis of [TmMe]HgR (R = Me, Et)

The molecular structures of [TmMe]HgMe and [TmMe]HgEt are provided in

Me Figures 4 and 5. A crystal of the solvated [Tm ]HgMe•C6H6 was also obtained, however, it is not shown as the structure is similar to that in Figure 4.

260

Figure 4. Molecular structure of [TmMe]HgMe

Figure 5. Molecular structure of [TmMe]HgEt

261

Figures 4 and 5 show that the mercury atoms in [TmMe]HgR are coordinated to

t one sulfur atom in a 1 fashion, similar to the mercury in [TmBu ]HgR.7 Select bond length and atom distance data in [TmMe]HgMe and [TmMe]HgEt are listed in Table 1.

The figures also show that another sulfur (S3) on an uncoordinated imidazolyl ring and the hydrogen on the H-B moiety are oriented toward the mercury center. To determine whether these sulfur and hydrogen atoms have an interaction with the mercury center, the S…Hg and B-H…Hg atom distances were measured (Table 1) and compared with mercury complexes in the literature. The range of S-Hg bond length values are 2.118Å –

2.403 Å, as reported in the Cambridge Structural Database (CSD).11 The S3…Hg atom distances in Table 1 are on average 1 Å longer than these reported lengths, indicating there is no bond between S3 and mercury.

Table 1. Selected bond lengths and atom distances in [TmMe]HgR (R = Me or Et)

Compound d(S1-Hg)/Å d(S2…Hg)/Å d(S3…Hg)/Å d(Hg-C1)/Å d(Hg…H)/Å

[TmMe]HgMe 2.3620(12) 5.410 3.435 2.072(5) 2.873

Me 2.3796(15) 5.338 3.312 2.074(6) 2.891 [Tm ]HgMe•C6H6

[TmMe]HgEt 2.366(2) 5.967 3.627 2.099(10) 3.247

262

A distance, d, measurement of the HB…Hg atom distances relative to the shortest Hg-S distance was used to determine the significance of the B-H…Hg interactions in the [TmMe]HgR complexes (Equation 1).12

… d = d(B Hg) – d(M-Sshort) (Equation 1)

Table 2. Selected atom distances in 1-S mercury alkyl complexes

… Compound d(Sshort-Hg)/Å d(Hg B)/Å d/Å Reference

[TmMe]HgMe 2.362 3.684 1.32 this work

Me 2.3796 3.684 1.31 this work [Tm ]HgMe•C6H6

[TmMe]HgEt 2.366 3.957 1.59 this work

t [TmBu ]HgMe 2.396 3.371 0.98 7

t [TmBu ]HgEt 2.401 3.395 0.99 7

Table 2 shows that the d values for our [TmMe]HgR complexes in comparison

t with the [TmBu ]HgR complexes reported in the literature. The d values indicate that the BH moiety is significantly farther, and thus less significant, (0.3Å – 0.6 Å) in our

t [TmMe]HgR complexes than in [TmBu ]HgR.

Select bond angles in the [TmMe]HgMe and [TmMe]HgEt complexes, summarized in Table 3, show an S-Hg-C bond angle of 175.54° and 176.07°, respectively. The S-Hg-C

263

t bond angles in [TmMe]HgMe and [TmMe]HgEt are similar to those in [TmBu ]HgMe and

t [TmBu ]HgEt which are both 176°.7

Table 3. S-Hg-C bond angles in mercury alkyl complexes

Compound S-Hg-C/° Reference

[TmMe]HgMe 175.54(13) this work

Me 176.07(16) this work [Tm ]HgMe•C6H6

[TmMe]HgEt 176.5(3) this work

t [TmBu ]HgMe 176.11 7

t [TmBu ]HgEt 176.49 7

[(MeHg)([9]aneS3)](BF4) 168 14

[EtHg{Ph2(PC6H4S)2}] 179 16

Such linear X-Hg-C angles are also observed in other two-coordinate mercury alkyl complexes reported in the CSD (Table 3).13 For example, a search within the CSD for two coordinate terminal mercury alkyl complexes, X-Hg-C, where X could be any atom, showed complexes with X-Hg-C bond angles ranging from 168° for a thioether complex14 to 180° for a thiazole mercury methyl complex15 with an average angle of

174°. A search for specifically two coordinate mercury alkyl S-Hg-C species had a range of S-Hg-C angles between 168° for a thioether14 complex and 179° for a phosphinothiol

264 mercury ethyl complex16 with the average S-Hg-C angle value of 173°. The S-Hg-C bond angles in [TmMe]HgMe and [TmMe]HgEt are well within these literature values.

Me Me Me The Hg-C bond lengths in [Tm ]HgMe, [Tm ]HgMe•C6H6 and [Tm ]HgEt are

2.072Å, 2.074 Å and 2.099Å respectively (Table 1). These values indicate that the Hg-C bond in [TmMe]HgEt is 0.02Å longer than that in the mercury methyl analogues. The

t Hg-C bond lengths in the reported [TmBu ]HgR complexes also show this trend in which

t t [TmBu ]HgEt has a Hg-C length of 2.093Å and the corresponding length in [TmBu ]HgMe is 2.072Å.7

Density Functional Theory (DFT) geometry optimization calculations on the

[TmMe]HgR molecular structures were performed. The calculated bond lengths and

t atom distances in [TmMe]HgR and [TmBu ]HgR, for comparison, are summarized in

Table 4. The optimized [TmMe]HgR structures have two equivalent S-Hg bond distances and one long S-Hg atom distance indicating that the mercury is interacting with two imidazolyl rings and not just one as the molecular structure suggests. Additionally, the

d values for the BH…Hg distances in the optimized [TmMe]HgR complexes are significantly smaller in comparison with the corresponding d values in the crystal structures. The d values for the optimized structures of [TmMe]HgMe and [TmMe]HgEt are 0.55Å and 0.58Å, respectively, indicating there is a more significant BH…Hg secondary interaction. The same differences are seen between the crystal structure and 265

t optimized [TmBu ]HgR complexes in which there are two equivalent Hg-S bond distances, indicating the mercury center is coordinated to two thioimidazole rings, and smaller d values increasing the significance of the interaction between the BH moiety and mercury.

DFT calculations on the different coordination modes of the [TmR] ligand to mercury were also performed. Specifically, the energy differences between [1-

TmR]HgMe vs. [3-TmR]HgMe and [1-TmR]HgEt vs. [3-TmR]HgEt (R = Me, But) were calculated and are summarized in Figure 6. The energies of the mercury complexes in

Figure 6 show that the [3-TmMe] coordinate complexes are slightly lower in energy than

t t the [1-TmMe] by ~3 kcal mol-1. Figure 6 shows that the [1-TmBu ] and [3-TmBu ] are about the same energy. These energy values show that the observance of 1 and 3 coordinate [TmR] mercury alkyl complexes experimentally, via X-ray diffraction and

NMR spectroscopy,7 are energetically reasonable.

266

t Table 4. Calculated bond lengths and atom distances from DFT geometry optimizations of [TmMe]HgR and [TmBu ]HgR

Compound d(S1-Hg)/Å d(S2…Hg)/Å d(S3…Hg)/Å d(Hg-C1)/Å d(Hg…B)/Å d/Å Reference

[TmMe]HgMe 2.810 4.593 2.838 2.250 3.362 0.55 this work

[TmMe]HgEt 2.792 4.581 2.891 3.354 3.373 0.58 this work

t [TmBu ]HgMe 2.809 4.519 2.848 2.252 3.312 0.50 7

t [TmBu ]HgEt 2.790 4.556 2.895 2.275 3.335 0.55 7

267

Figure 6. Relative energies between [1-TmR]HgMe vs. [3-TmR]HgMe and [1-

TmR]HgEt vs. [3-TmR]HgEt (R = Me and But)

268

t 4.2.2 Synthesis and Molecular Structures of [TmMeBenz]HgR and [TmBu Benz]HgR

[TmRBenz]HgMe and [TmRBenz]HgEt (R = Me, But) were synthesized by addition of methyl- or ethylmercury chloride to [TmRBenz]Na (R = Me, But)17,18 (Scheme 3). The molecular structures of [TmRBenz]HgMe and [TmRBenz]HgEt are provided in Figure 7 through 10.

Scheme 3. Synthesis of [TmRBenz]HgR’ (R = Me, But; R’ = Me, Et)

269

MeBenz Figure 7. Molecular structure of [Tm ]HgMe•HgCl2 (co-crystallized HgCl2 is omitted for clarity)

MeBenz Figure 8. Molecular structure of [Tm ]HgEt•EtHgBr (co-crystallized EtHgBr is omitted for clarity)

270

t Figure 9. Molecular structure of [TmBu Benz]HgMe

t Figure 10. Molecular structure of [TmBu Benz]HgEt (disordered atoms are not shown)

271

t Table 5. Select bond lengths in [TmMeBenz]HgR (R = Me, Et) and [TmBu Benz]HgMe

Compound d(Hg-S1)/Å d(Hg-S2)/Å d(Hg-S3)/Å d(Hg-S)avg/Å d(Hg-C1)/Å

[TmMeBenz]HgMe 2.5011(18) 2.7998(18) 2.8448(18) 2.715 2.116(7)

[TmMeBenz]HgEt 2.865(2) 2.923(2) 2.44(2) 2.745 2.149(8)

t [TmBu Benz]HgMe 2.484(3) 2.777(3) 2.801(2) 2.687 2.111(11)

272 t Table 6. Select bond angles in TmMeBenz]HgR (R = Me, Et) and [TmBu Benz]HgMe

Compound S1-Hg-S2/° S2-Hg-S3/° S1-Hg-S3/° S1-Hg-C1/° S2-Hg-C1/° S3-Hg-C1/° B-Hg-C1/°

[TmMeBenz]HgMe 90.42(5) 90.95(6) 94.59(5) 108.0(2) 110.1(2) 148.2(3) 154.70

[TmMeBenz]HgEt 89.57(6) 92.08(5) 94.34(6) 100.8(2) 105.6(3) 156.2(3) 146.14

t [TmBu Benz]HgMe 93.04(7) 93.11(8) 97.76(7) 103.5(3) 107.9(4) 148.9(3) 152.31

Selected bond lengths and angles obtained from the molecular structures of

t [TmMeBenz]HgR (R = Me, Et) and [TmBu Benz]HgMe are listed in Table 5 and Table 6.

t Severe disorder of the mercury and ethyl moiety in [TmBu Benz]HgEt precludes a detailed discussion of the structure.

Table 5 shows that the Hg-C bonds within the methyl complexes,

t [TmMeBenz]HgMe and [TmBu Benz]HgMe, are the same with values of 2.116 Å and 2.111 Å respectively. The [TmMeBenz]HgEt complex has a Hg-C bond length of 2.149 Å. The longer Hg-Et bond is in accord with the trend seen in the non-benzannulated [Tm]HgEt complexes which have Hg-C bonds 0.02 Å longer than the [Tm]HgMe complexes.

Additionally, the Hg-C bonds in the annulated [TmRBenz] mercury alkyl complexes are

0.05 Å longer than the Hg-C bonds in [TmR] mercury complexes (Table 1). Thus the increase in coordination from 1 in [TmR] to 3 in [TmRBenz] corresponds with the increase in length of the Hg-C bond.

The calculated average Hg-S lengths are similar for [TmMeBenz]HgMe,

t [TmMeBenz]HgEt and [TmBu Benz]HgMe with values of 2.72 Å, 2.75 Å, and 2.69 Å

MeBenz respectively. The Hg-Savg value in [Tm ]HgEt is slightly longer at 2.75 Å, indicating that the Hg-S bond lengths in the benzannulated [TmRBenz]Hg alkyl complexes are longer when larger alkyl groups are coordinated to the mercury center.

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The bond angles for the [TmRBenz]Hg alkyl complexes are listed in Table 6. These

angles were used to calculate a 4 parameter using the equation 4 = [360 - ()]/141 in which  +  is the sum of the two largest angles.19 This parameter allowed us to quantitatively determine the geometry of the mercury center in [TmMeBenz]HgR (R = Me,

ButBenz Et) and [Tm ]HgMe. For an ideal tetrahedron the 4 parameter is 1 and for a square

MeBenz planar complex the 4 parameter is 0. The 4 parameters for [Tm ]HgR (R = Me., Et)

t and [TmBu Benz]HgMe, listed in Table 7, indicate that the mercury sits in a distorted tetrahedral geometry in all three complexes. The bond angles of the B-Hg-C1 atoms,

MeBenz ButBenz which comprise the C3 axis in [Tm ]HgR (R = Me, Et) and [Tm ]HgMe (Table 6) are 154.70°, 146.14°, and 152.31°, respectively and are also indicative of this distorted tetrahedral geometry, as these angles deviate from 180°.

3 Table 7. 4 parameters for  -S mercury alkyl complexes

Compound S–Hg–C range/˚ 4 Reference

[TmMeBenz]HgMe 40.2 0.72 this work

[TmMeBenz]HgEt 56.4 0.70 this work

t [TmBu Benz]HgMe 45.4 0.73 this work

But 8.77 0.79 7 [Tm ]CH2CN

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a 15.3, 0.64, 14 [MeHg([9]andS3)](BF4) 9.9 0.64

{PhHg[S2CN(CH2)4]}2 76.2 0.51 20 a There are two crystallographically independent molecules in the unit cell

There are only three other mercury alkyl complexes that have this 3-S-Hg

But 7 binding motif in the CSD, these include [Tm ]HgCH2CN, a crown ether complex

14 20 [MeHg([9]andS3)](BF4), and a dimer, {PhHg[S2CN(CH2)4]}2. For comparison, the 4

But values for these complexes are listed in Table 7. The [Tm ]HgCH2CN complex,

7 reported by the Parkin group, has a 4 value of 0.79 which indicates this complex has a similarly distorted tetrahedral geometry as our annulated [TmRBenz] complexes. The

[MeHg([9]andS3)](BF4) thioether and {PhHg[S2CN(CH2)4]}2 dimer have lower 4 values of

0.64 and 0.51 respectively, meaning these complexes adopt a different see-saw geometry.14,19,20

3 RBenz The κ coordination in the molecular structures of [Tm ]HgMe and

RBenz 1 [Tm ]HgEt complexes is in contrast to the κ coordination in the molecular structures of the non-annulated [TmR]HgMe and [TmR]HgEt complexes. To address the differences in coordination between [TmMe] and [TmMeBenz], the Parkin group previously compared the solid state structures of [TmMe]Na complexes with [TmMeBenz]Na.17 Out of

Me 21 3 the two [Tm ]Na solvate complexes in the CSD, neither one exhibits κ -S3 coordination of [Tm] to the sodium, whereas the benzannulated [TmMeBenz]Na has this κ3 coordination.17 DFT calculations on the [TmMe]- and [TmMeBenz]- anions in the gas phase

275

show the promotion of the κ3-S coordination mode by benzannulation. It was found that the specific conformation of the ligand required for κ3-S coordination, in which the three sulfur atoms point away from the B-H group, was more stable for the benzannulated ligand anion than for [TmMe]-.17

DFT calculations of the energy differences between 1 coordinate and 3 coordinate [TmRBenz] mercury alkyl complexes were performed (Table 8). The relative energies of [3-TmRBenz]Hg alkyl (R = Me, But) complexes were compared to the [1-

TmRBenz]Hg alkyl, which were set as the reference energy. The calculated energies show that the 3 coordinate complexes are the significantly lower in energy than the 1 coordinate complexes. The promotion of 3 coordination observed in the sodium complexes17,21 is also seen in the mercury alkyl complexes.

Table 8. Relative energies calculated by DFT of [3-TmRBenz]HgMe and Et complexes with [1-TmRBenz]HgMe and Et set as the reference point

Compound Relative Energy (kcal mol-1)

[3-TmMeBenz]HgMe -23.26

[3-TmMeBenz]HgEt -22.73

t [3-TmBu Benz]HgMe -22.29

t [3-TmBu Benz]HgEt -21.89

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The molecular structure and DFT calculations for the [TmMe]HgR, [TmMeBenz]HgR,

t and [TmBu Benz]HgR (R = Me, Et) indicate that the benzannulation of the [Tm] ligand does indeed promote 3 coordination. In addition, the Hg-Me and Hg-Et bonds are elongated in the benzannulated complexes showing a relation between the increase in coordination to the mercury center and the susceptibility of the Hg-C bond toward protolytic cleavage.

4.3 [Bm]HgR (R = Me, Et) Complexes

t 4.3.1 Synthesis and Molecular Structures of [BmMe]HgR and [BmBu ]HgEt

[BmMe]HgR (R = Me, Et) was synthesized by adding methyl- or ethylmercury chloride to [BmMe]Na22 (Scheme 4).

Scheme 4. Synthesis of [BmMe]HgR (R = Me, Et)

t [BmBu ]HgEt was readily synthesized by a colleague in the Parkin group23 by

t adding ethylmercury chloride to [BmBu ]Na22 (and Scheme 5). Attempts to synthesize

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But But 22 [Bm ]HgMe were unsuccessful as only the known [Bm ]2Hg complex was formed in solution, this product was also confirmed by X-ray diffraction.

t Scheme 5. Synthesis of [BmBu ]HgEt

t The molecular structures of [BmMe]HgR (R = Me, Et) and [BmBu ]HgEt are provided in Figure 11 through Figure 13.

Figure 11. Molecular structure of [BmMe]HgMe

278

Figure 12. Molecular structure of [BmMe]HgEt

t Figure 13. Molecular structure of [BmBu ]HgEt

279

The solid state structures in Figure 11 through Figure 13 shows that the mercury center in the [BmR] mercury alkyl complexes is coordinated to both sulfur atoms in the

[BmR] ligand. Select bond lengths and atom distances in [BmMe]HgMe, [BmMe]HgEt, and

t [BmBu ]HgEt are listed in Table 9.

Table 9. Hg-S and Hg-C bond lengths in [BmMe]HgMe and [BmR]HgEt (R = Me or But)

Compound d(Hg-S1)/Å d(Hg-S2)/Å d(Hg-C1)/Å d(Hg…H)/Å

[BmMe]HgMe 2.420(7) 2.876(8) 2.091(3) 2.457

[BmMe]HgEt 2.438(9) 2.8437(2) 2.103(4) 2.551

t [BmBu ]HgEta 2.428(7), 2.777(6), 2.11(3), 2.516, 2.396(6)) 2.826(6) 2.07(3) 2.543 a There are two crystallographically independent molecules present

Table 9 shows that there is one long Hg-S interaction and one short Hg-S interaction within each [Bm]HgR complex. The Hg-C bonds in [BmMe]HgMe,

t [BmMe]HgEt, and [BmBu ]HgEt are all quite similar, ranging from 2.07Å to 2.11 Å. In comparison with the [Tm] mercury alkyls, the Hg-C bonds in the [TmR]HgMe complexes (R = Me, But) are 2.072 Å and the Hg-C bonds in [TmR]HgEt are 2.099 Å

(Table 1)7 which are slightly shorter than the Hg-C bonds in the [BmR] complexes.

Whereas, the Hg-C bonds in [TmRBenz]HgMe and [TmRBenz]HgEt range from 2.111-2.149

Å which are slightly longer than the [BmR] complexes (Table 5). This structural data

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shows that the Hg-C bond length increases as the coordination to the metal center increases from 1 in [TmR] to 2 in [BmR] to 3 in [TmRBenz].

A study into the BH and Hg distances in the molecular structures in Figure 11 through Figure 13 indicated that there is a three-center two-electron interaction between the hydrogen and mercury atoms. Similar to the [TmMe] mercury alkyl complexes, the significance of such an interaction was quantitatively assessed using the d measurement.12 This d was calculated for each [BmR] complex by taking the difference between the B…Hg distance and the average S-Hg bond length (Table 10).

… … R Table 10. H2B Hg and Hg Sshort distances in select [Bm ]M complexes

… Compound d(M-S)avg/Å d(B Hg)/Å d/Å Reference

[BmMe]HgMe 2.648 3.284 0.64 this work

[BmMe]HgEt 2.641 3.300 0.66 this work

t [BmBu ]HgEta 2.602, 3.324, 0.72, this work 2.611 3.290 0.68

[BmMe]ZnMe 2.36 2.88 0.52 24

But a 2.55, 3.59, 1.03, 22 [Bm ]2Hg 2.57 4.35 1.79

But a 2.35, 3.23, 0.87, 22 [Bm ]2Zn 2.37 3.45 1.09

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Me 2.34 3.78 1.44 24 [Bm ]2Zn a There are two crystallographically independent molecules present.

The d values for our [BmR]Hg alkyl complexes in Table 10 have a small range between 0.64 Å to 0.72Å, with [BmMe]HgMe having the smallest d value of 0.64 Å.

Table 10 also lists the d values of other [BmR]M complexes reported in the literature.

The [BmMe]ZnMe complex has the lowest d value of 0.52,24 indicating the BH…Hg secondary interaction in this complex is much more significant than the longer d

R 22,24 values in the homoleptic [Bm ]2M complexes. In a comparison, the d values in our

[BmR]Hg alkyl complexes are quite similar to that in the [BmMe]ZnMe complex, which is of no surprise as it is also a terminal metal alkyl complex.

The existence of a H…Hg interaction within [BmR] metal alkyl complexes and not

R in the [Bm ]2M complexes is from the pseudo “boat-like” configuration that is observed in the [BmR]Hg alkyls which positions the H and Hg atoms in closer proximity to each other. This configuration is in contrast with the “chair-like” 8-membered ring that is

But present in [Bm ]2Hg (Figure 14).

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Figure 14. Coordination motifs of the “boat” configuration in [BmR]Hg alkyl complexes

But (left) versus the “chair” configuration in [Bm ]2Hg (right)

This “boat-like” conformation in the terminal alkyl complexes positions the B-H moiety closer to the mercury center and thus promotes a H-Hg interaction. A parallel example of this “boat-like” vs “chair-like” conformation is seen in the [BmR]ZnMe and

Me 22,24 R [Bm ]2Zn complexes. The effect of substitution on the [Bm ] ligand is more

R predominant in the examples of [Bm ]2Zn as well. For example, Table 10 shows that the

t … Me Bu 22,24 BH Zn distance is significantly longer in [Bm ]2Zn than that in [Bm ]2Zn.

Select bond angles from the molecular structures of the [BmR] mercury alkyl complexes were measured and are listed in Table 11.

Table 11. Selected bond angles in [BmR]HgMe and [BmR]HgEt (R = Me or But)

Compound S1-Hg-S2/° S1-Hg-C1/° S2-Hg-C1/° S-Hg-C/°

[BmMe]HgMe 94.62(2) 107.25 (10) 157.00 (10) 358.87

[BmMe]HgEt 94.15 (3) 102.82 (10) 161.59(11) 358.56

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t [BmBu ]HgEt 95.16(19), 107.9(9), 156.5(8), 359.56, 95.2(2) 110.8(16) 153.1(14) 359.10

The angle data in Table 11 shows that the mercury centers, S1, S2, C1 atoms in

[BmMe]HgMe and [BmR]HgEt (R = Me or But) are planar and adopt a distorted T-shaped geometry. The largest angle in these complexes are 157° in [BmMe]HgMe, 162° in

t [BmMe]HgEt, and 157° and 153° in the two molecules in [BmBu ]HgEt. Of the structurally characterized three-coordinate terminal mercury alkyl complexes reported in the CSD,

90% of them possess this geometry.16,25 The largest X-Hg-C angles in these reported complexes range from 165° in a mercury imine complex25a to 178° in a sandwich complex.16

DFT calculations on the molecular structures of the [BmR]Hg alkyl complexes were completed. The bond lengths and angles from the geometry optimized [BmR] mercury alkyl complexes are listed in Table 12 and Table 13.

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t Table 12. DFT calculated bond lengths in the optimized [BmMe]HgR and [BmBu ]HgEt structures

… Compound d(Hg-S1)/ d(Hg-S2)/ d(Hg-S)avg/ d(Hg-C1)/ d(Hg B)/ d/

Å Å Å Å Å Å

[BmMe]HgMe 2.717 2.834 2.776 2.255 3.360 0.58

[BmMe]HgEt 2.721 2.862 2.792 2.278 3.383 0.59

t [BmBu ]HgEta 2.716 2.868 2.79 2.279 3.352 0.56

t Table 13. DFT calculated bond angles in the optimized [BmMe]HgR and [BmBu ]HgEt structures

Compound S1-Hg-S2/° S1-Hg-C1/° S2-Hg-C1/° S-Hg-C/°

[BmMe]HgMe 96.34 124.76 137.70 358.80

[BmMe]HgEt 96.21 122.39 141.00 359.60

t [BmBu ]HgEt 96.72 122.48 140.08 359.28

Table 12 shows that there are two long Hg-S interactions (2.717Å, 2.721 Å, 2.716

Å and 2.834 Å, 2.862 Å, 2.868 Å) in the geometry optimized structure, whereas, in the molecular structures, there was one short Hg-S interaction (2.420 Å, 2.348 Å, 2.428 Å,

2.396 Å) and one long one (2.876 Å, 2.843 Å, 2.777 Å, 2.826 Å) (Table 9). The Hg-C bond 285

lengths in the [BmR] mercury alkyl complexes are also significantly longer by 0.2 Å in the optimized structures than the corresponding bonds in the crystal structures (Table

9). These changes in bond length in the optimized structures resulted in d values which are ~0.1 Å less than the corresponding values in the molecular structures (Table

10), making the secondary BH…Hg interaction more significant in the optimized structure, similar to [Tm]HgR.

The bond angles in the optimized structures which are listed in Table 13 are significantly different than the corresponding angles in the molecular structures of the

[BmR]Hg alkyls (Table 11). The angles in the optimized structures suggest a distorted trigonal planar geometry around the mercury center, rather than the distorted T-shape in the crystal structures in Figure 11 through Figure 13.

t 4.3.2 Synthesis and Molecular Structures of [BmMeBenz]HgR and [BmBu Benz]HgR

[BmRBenz]HgMe and [BmRBenz]HgEt (R = Me or But) were readily synthesized by

t adding methyl- or ethylmercury chloride to [BmMeBenz]Na or [BmBu Benz]K (Scheme 6 and

Scheme 7).

286

Scheme 6. Synthesis of [BmMeBenz]HgR (R = Me, Et)

t Scheme 7. Synthesis of [BmBu Benz]HgR (R = Me, Et)

Attempts to obtain crystal structures of these complexes were unsuccessful, because [BmRBenz]HgMe and [BmRBenz]HgEt converted to [TmRBenz]HgMe and

[TmRBenz]HgEt, repectively, during crystallization. Similar conversion has been seen in other systems studied within the Parkin group including: [BmRBenz]ZnI, [BmRBenz]CdI,

i and [Bse PrBenz]HgMe.26 These [BmRBenz]Hg alkyl complexes were characterized via NMR spectroscopy as detailed in the next section.

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4.4 NMR Characterization of Mercury Alkyl Complexes

4.4.1 NMR Characterization of [L]HgMe Complexes

The [Tm] and [Bm] mercury methyl complexes were characterized by 1H and 11B

NMR spectroscopy. The 1H NMR spectra of the mercury methyl complexes showed

199Hg satellites (17.0% abundance) (Figure 15).

Figure 15. 199Hg satellites in the 1H NMR spectrum of [TmMe]HgMe

The 1H NMR data for these complexes is listed in Table 14 and shows that for the

[Tm] and [TmRBenz] mercury methyl complexes there is a correlation between the substitution on the [Tm] ligand and the chemical shift of the Hg-Me resonance. For

288

t example, the mercury methyl chemical shifts in the reported [TmBu ]HgMe7 and our

t [TmBu Benz]HgMe are 1.11 ppm and 1.24 ppm respectively. These values are further downfield from the mercury methyl resonances in [TmMe]HgMe and [TmMeBenz]HgMe which are 0.69 ppm and 0.55 ppm respectively. The same trend is seen with the

t [Bm]HgMe complexes, specifically, the mercury methyl resonance in [BmBu Benz]HgMe is

0.85 ppm which is further downfield than the corresponding shifts in [BmMe]HgMe (0.71 ppm) and [BmMeBenz]HgMe (0.80 ppm).

2 The JH-Hg coupling constants in our mercury methyl complexes are similar to

2 each other and within the range of 200 Hz to 213 Hz. In addition, the JH-Hg coupling constants are within the literature values for mercury methyl complexes which are also provided in Table 14 for comparison. The coupling values in various  1 to  3 mercury methyl complexes range from 163 Hz in  1-PhS]HgMe27 to 237 Hz in [3-

14 MeHg([9]andS3)](BF4).

289

Table 14. 1H NMR data for mercury methyl complexes

Compound /ppm 2 Reference JH-Hg /Hz

[1-TmMe]HgMe 0.69 203 this work

[3-TmMeBenz]HgMe 0.55 212 this work

t [3-TmBu Benz]HgMe 1.24 213 this work

[2-BmMe]HgMe 0.71 200 this work

[2-BmMeBenz]HgMe 0.80 206 this work

t [2-BmBu Benz]HgMe 0.85 207 this work

t [1-TmBu ]HgMe 1.11 200 7

1 1.11 224 14 [ -MeHg([12]aneS3)](BF4)

1 1.16 231 14 [ - (MeHg)2([14]aneS4)](BF4)2

 1-PhS]HgMe 0.19 163 27

3 1.09 237 14 [ -MeHg([9]andS3)](BF4)

Additionally, the 1H NMR spectra for [TmMe]HgMe shows only one set of resonances for the three imidazolyl rings indicating that they are fluxional at room temperature. Thus the coordination of the [TmMe] ligand to mercury in solution

290

contrasts with the solid state structure in which the ligand is clearly coordinated to mercury in a 1 fashion.

The 11B NMR data for the [Tm] and [Bm] mercury methyl complexes is listed in

Table 15. The range of chemical shift values is from -2.70 ppm for [TmMe]HgMe to -

12.25 ppm for [BmMeBenz]HgMe. The [TmRBenz]HgMe complexes have similar boron chemical shift values of -4.69 ppm (R = Me) and -4.70 ppm (R = But). These shift values are 2 ppm upfield from the boron shift in [TmMe]HgMe, which could be a result of the benzannulation of the ligand. This trend is not seen within the [Bm] and [BmRBenz] complexes, instead the methyl substituted [BmMe] and [BmMeBenz] complexes are

t t significantly more upfield than [BmBu ] or [BmBu Benz]. Specifically, [BmMe]HgMe has a boron shift of -9.13 ppm and [BmMeBenz]HgMe has a shift of -12.25 ppm, compared to

t [BmBu Benz]HgMe which has a shift of -4.76 ppm.

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Table 15. 11B NMR data for mercury methyl complexes

Compound /ppm 1 Reference JH-B/Hz

[TmMe]HgMe -2.70 111 this work

[TmMeBenz]HgMe -4.69 101 this work

t [TmBu Benz]HgMe -4.70 94 this work

[BmMe]HgMe -9.13 107 this work

[BmMeBenz]HgMe -12.25 --a this work

t a [BmBu Benz]HgMe -4.76 -- this work

t [TmBu ]HgMe not observed -- 7

t [TpBu ]Li –2.6 109 28

t [TpBu ,Me]Li –8.5 93 28

[Tp]K –1.3 105 29

Me [Tp 2]Tl –8.0 94 29

a 1 The boron resonance was broad, the JH-B coupling value could not be determined

1 The JH-B coupling values for the mercury methyl complexes are within a range of

t 94 Hz for [TmBu Benz]HgMe and 111 Hz for [TmMe]HgMe. No 11B NMR data for other

292

[TmR]HgX or [TmR]M compounds were reported in the literature; however, the 11B

NMR data for metal tris(pyrazolyl)hydroborato, [Tp]M, complexes are listed in Table 15

1 for comparison. The JH-B coupling values for our mercury methyl complexes correlate with the corresponding values in the reported [Tp]M complexes.7,28,29

4.4.2 NMR Characterization of [L]HgEt Complexes

The [Tm] and [Bm] mercury ethyl complexes were also characterized by 1H and

11B NMR spectroscopy. The 1H NMR data for these complexes is listed in Table 15.

Table 16. 1H NMR data for mercury ethyl complexes

Compound (CH )/ppm (CH )/ppm 2 3 Reference 2 3 JHg-H/Hz JHg-H/Hz

[TmMe]HgEt 1.55 1.36 170 322 this work

[TmMeBenz]HgEt 1.68 1.34 207 296 this work

t a a [TmBu Benz]HgEt 1.50 1.38 -- -- this work

[BmMe]HgEt 1.58 1.29 201 --a this work

t a [BmBu ]HgEt 1.56 1.30 -- 271 this work

[BmMeBenz]HgEt 1.71 1.28 194 286 this work

t a a [BmBu Benz]HgEt 1.56 1.32 -- -- this work

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t [TmBu ]HgEt not observed not observed -- -- 7

CO [(Ar 2)SHgEt]Na 1.65 1.26 173 249 27

PhSHgEt 0.95 0.75 162 228 27

CO H (Ar 2 )SHgEt 1.89 1.35 168 252 30

EtHgNO3 0 -0.65 233 311 31 aThe 199Hg-H satellites were obscured by other resonances or by THF solvent, thus the 2 3 JHg-H and JHg-H coupling constants could not be determined.

The 1H NMR data in Table 15 shows that the chemical shift values for the methyl and methylene protons in the mercury-ethyl moiety are similar in all our mercury ethyl complexes with values ranging from 1.55 ppm to 1.71 ppm for the methylene protons in

[TmMe]HgEt and [BmMeBenz]HgEt, respectively. The range of shift values for the methyl protons are within a similarly small window and range from 1.28 ppm to 1.36 ppm in

[BmMe]HgEt and [TmMe]HgEt, respectively. These chemical shift values for the ethyl moiety correlate well with the shifts in other mercury ethyl complexes reported in the literature (Table 15).

2 3 2 The JHg-H and JHg-H coupling values reported in Table 15 shows that the JHg-H

3 coupling values are consistently smaller than the JHg-H value. This trend is consistently observed in mercury ethyl complexes in the literature.7,27,30,31

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The 1H NMR for [TmMe]HgEt shows only one set of resonances for the [TmMe] ligand at room temperature, similar to [TmMe]HgMe as previously discussed, showing the ligand is fluxional at this temperature.

The 11B NMR data for the mercury ethyl complexes is listed in Table 17.

Table 17. 11B NMR data for mercury ethyl complexes

Compound /ppm 1 JH-B/Hz

[TmMe]HgEt -2.59 110

[TmMeBenz]HgEt -4.77 91

t a [TmBu Benz]HgEt -4.70 --

[BmMe]HgEt -9.04 85

t [BmBu ]HgEt -8.77 96

[BmMeBenz]HgEt -12.21 --a

t a [BmBu Benz]HgEt -4.60 -- a 11 1 The B resonance was broad even at elevated temperatures. A JH-B coupling constant could not be determined.

The boron chemical shifts for the ethyl complexes correspond closely with the shifts in the mercury methyl complexes (Table 15). For example, the range of chemical 295

shift values is -2.59 ppm for [TmMe]HgEt to -12.21 ppm for [BmMeBenz]HgEt. As previously discussed, [TmMe]HgMe also had the most downfield boron shift of -2.70 ppm and [BmMeBenz]HgMe had the most upfield chemical shift of -12.25 ppm.

Additionally, the same trend in which the benzannulated [TmRBenz]HgEt complexes are

2 ppm upfield from the [TmMe]HgEt is observed in Table 17.

t The boron chemical shifts for [BmMe]HgEt (-9.04 ppm), [BmBu ]HgEt (-8.77 ppm), and [BmMeBenz]HgEt (-12.21 ppm) are significantly more upfield than the [Tm]HgEt complexes. These upfield values correlate well with the [Bm]HgMe shift values. For example, [BmMe]HgMe had a shift of -9.13 ppm and [BmMeBenz]HgMe had a shift of -12.25

t ppm. The boron shift for the [BmBu Benz]HgEt complex was appeared at -4.60 ppm;

t which corresponds well with [BmBu Benz]HgMe which had a boron shift at -4.76 ppm.

4.5 Hg-C Bond Cleavage with Benzenethiol

Following the synthesis of this library of [TmR] and [TmRBenz] mercury alkyls, we were interested in studying the cleavage of the Hg-C bonds in these complexes and to see how the kapticity of the [Tm] ligand affected Hg-C bond cleavage. These reactions were carried out by a colleague within the Parkin group.32

4.5.1 Reactions with [TmMe]HgEt and [TmMeBenz]HgEt

A solution of [TmMe]HgEt and [TmMeBenz]HgEt was prepared with an internal mesitylene standard. Subsequently, aliquots of benzenethiol were added to the mixed 296

sample and the consumption of [TmMe]HgEt and [TmMeBenz]HgEt compounds was measured via 1H NMR spectroscopy. The NMR spectra showed that as benzenethiol as added to the mixture, [TmMeBenz]HgEt decreased more rapidly than [TmMe]HgEt and ethane gas was released. The overall loss of [TmMeBenz]HgEt was 56%, compared with only a 11% loss of [TmMe]HgEt, indicating that benzenethiol reacted preferentially with the Hg-C bond in [TmMeBenz]HgEt over [TmMe]HgEt.

t t 4.5.2 Reactions with [TmBu ]HgEt and [TmBu Benz]HgEt

t t A similar experiment involving a solution of [TmBu ]HgEt and [TmBu Benz]HgEt was prepared. Aliquots of benzenethiol were added to this sample and the

t t disappearance of [TmBu ]HgEt and [TmBu Benz]HgEt was monitored by 1H NMR. The

t t NMR spectrum of the reaction of benzenethiol with [TmBu ]HgEt and [TmBu Benz]HgEt

t showed that [TmBu ]HgEt decreased more rapidly as ethane gas was evolved. Overall,

t t [TmBu ]HgEt experienced a loss of 74%, whereas [TmBu Benz]HgEt lost 53%. This trend is opposite to that seen within the reaction of benzenethiol with [TmMeBenz]HgEt and

t [TmMe]HgEt. The presence of a bulky t-butyl moiety in [TmBu Benz]HgEt may block access to the Hg-C bond in the mercury ethyl moiety, whereas the non-benzannulated [Tm] ligand is more flexible and thus may provide greater access to the Hg-C bond.

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4.6 Conclusion

In summary, six new [TmMe] and [TmRBenz] mercury alkyl complexes were

t synthesized, which provide a good comparison to the [TmBu ] mercury alkyls in the

RBenz 3 literature. Furthermore, the [Tm ]Hg alkyl complexes confirmed the trend that  coordination is promoted upon benzannulation of the imidazolyl rings in the [Tm] ligand system. Additionally, the first [BmR] and [BmBenzR] mercury alkyl complexes were synthesized and characterized via NMR spectroscopy and X-ray diffraction.

Addition of benzenethiol to a mixture of [TmMeBenz]HgEt and [TmMe]HgEt resulted in the preferential Hg-C bond cleavage in [TmMeBenz]HgEt over [TmMe]HgEt. Conversely,

t t the addition of benzenethiol to a mixture of [TmBu Benz]HgEt and [TmBu ]HgEt resulted in

t t preferential Hg-C cleavage in [TmBu ]HgEt over [TmBu Benz]HgEt. It is expected that further study of Hg-C bond cleavage in these new mercury alkyl complexes can provide further insight into the enzymatic detoxification of mercury alkyl species.

4.7 Experimental Section

4.7.1 General Considerations

All manipulations were performed using a combination of glovebox, high vacuum, and schlenck techniques. NMR spectra were measured on Bruker 300 DRX, Bruker 400

DRX, and Bruker Avance 500 DMX spectrometers. 1H NMR spectra are reported in

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ppm relative to SiMe4 ( = 0) and were referenced internally with respect to the protio

33 13 solvent impurity ( 7.16 for C6D5H and  1.72 for C4D3HO). C NMR spectra are

reported in ppm relative to SiMe4 ( = 0) and were referenced internally with respect to

33 11 the solvent ( 128.06 for C6D6 and  67.2 for C4D4O ). B NMR spectra are reported in

34 ppm relative to BF3(OEt2) ( = 0.0) as an external standard. The temperatures of spectra obtained within the range of 300 – 370K are referenced according to ethylene glycol and spectra obtained in the range of 250 – 320K are referenced according to methanol.35 Coupling constants are given in hertz. ATR-IR spectra were obtained on a

Perkin Elmer UATR Two and the data are reported in reciprocal centimeters (cm–1).

Ethyl mercury chloride (Alfa Aesar), and methyl mercury chloride (Aldrich) were

t obtained commercially. [TmMe]K,36 [TmMe Benz]Na,17 [TmBu Benz]Na,18 [BmMe]Na,22

t [BmBut]Na,22 [BmMeBenz]Na,17 and [BmBu Benz]K37 were synthesized according to literature methods.

4.7.2 X-ray Structure Determination

Single crystal X-ray diffraction data were collected on a Bruker Apex II diffractometer and crystal data, data collection and refinement parameters are summarized in Table 20.

The structures were solved using direct methods and standard difference map

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techniques, and were refined by full-matrix least-squares procedures on F2 with

SHELXTL (Version 2008/4).38

4.7.3 Computational Details

Calculations were carried out using DFT as implemented in the Jaguar 7.5 (release 207) suite of ab initio quantum chemistry programs.39 Geometry optimizations were performed with the B3LYP density functional40 using the 6-31G** (H, B, C, N, S) basis set and the LAV3P (Hg) basis set.41

4.7.4 Synthesis of [TmMe]HgMe

A cloudy white solution of [TmMe]K (42 mg, 0.11 mmol) in methanol (0.5 mL) was reacted with a solution of MeHgCl (25 mg, 0.10 mmol) in MeOH (0.5 mL). Upon stirring the solutions, the reaction mixture became less opaque. After mixing for 5 minutes, the reaction was filtered and the motherliquor collected. The MeOH solvent was removed via slow evaporation in a well-ventilated hood leaving large pink block crystals of [TmMe]HgMe (46 mg, 75 %). These crystals were suitable for X-ray diffraction. Analysis calcd. [TmMe]HgMe: C, 27.5 %; H, 3.4 %; N, 14.8 %. Found: C, 27.3

1 1 %, H, 3.4 %, 14.6 %. H NMR (d-THF): 0.69 [s, 3H, JHg-C = 102 Hz,

1 = HB{C3N2H2(CH3)S}3HgMe], 3.53 [s, 9H, HB{C3N2H2(CH3)S}3HgMe], 5.01 [d, 1H, JB-H

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129 Hz, HB{C3N2H2(CH3)S}3HgMe], 6.87 [s, 3H, HB{C3N2H2(CH3)S}3HgMe], 6.94 [s, 3H,

13 HB{C3N2H2(CH3)S}3HgMe]. C NMR (d-THF): 7.9 [s, 1C, HB{C3N2H2(CH3)S}3HgMe],

34.6 [s, 3C, HB{C3N2H2(CH3)S}3HgMe], 119.4 [s, 3C, HB{C3N2H2(CH3)S}3HgMe], 123.5 [s,

11 3C, HB{C3N2H2(CH3)S}3HgMe], 160.7 [s, 3C, HB{C3N2H2(CH3)S}3HgMe]. B NMR (d-

1 -1 THF): -2.70 [d, JH-B = 111 Hz, HB{C3N2H2(CH3)S}3HgMe]. IR data (ATR, cm ): 3134 (w),

3076 (w), 2917 (w), 2450 (w), 1562 (m), 1470 (w), 1446 (m), 1367 (s), 1285 (s), 1194 (s),

1087 (s), 995 (w), 733 (s), 698 (s), 676 (s), 525 (m), 444 (m).

4.7.5 Synthesis of [TmMe]HgEt

A cloudy white solution of [TmMe]K (28 mg, 0.07 mmol) in methanol (0.5 mL) was reacted with a solution of MeHgCl (17 mg, 0.06 mmol) in MeOH (0.5 mL). Upon stirring the solutions, the reaction mixture became less opaque. After mixing for 5 minutes, the reaction was filtered and the motherliquor collected. The MeOH solvent was removed via slow evaporation in a well-ventilated hood giving [TmMe]HgEt (34 mg,

90%) as a crystalline solid. Crystals suitable for X-ray diffraction were obtained directly from the motherliquor. Analysis calcd. [TmMe]HgEt: C, 28.9 %; H, 3.6 %; N, 14.5 %.

1 3 Found: C, 28.4 %, H, 3.5 %, 13.9 %. H NMR (d-THF): 1.34 [t, 3H, JH-H = 7 Hz,

3 HB{C3N2H2(CH3)S}3HgCH2CH3], 1.57 [q, 2H, JH-H = 7 Hz,

HB{C3N2H2(CH3)S}3HgCH2CH3], 3.53 [s, 9H, HB{C3N2H2(CH3)S}3HgCH2CH3], 5.12 [br,

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3 1H, HB{C3N2H2(CH3)S}3HgCH2CH3], 6.87 [d, 3H, JH-H = 2 Hz,

3 HB{C3N2H2(CH3)S}3HgCH2CH3], 6.91[d, 3H, JH-H = 2 Hz,

13 HB{C3N2H2(CH3)S}3HgCH2CH3]. C NMR (d-THF): 15.5 [s, 1C,

HB{C3N2H2(CH3)S}3HgCH2CH3], ~25 [obscured by THF solvent , 1C,

HB{C3N2H2(CH3)S}3HgCH2CH3], 34.6 [s, 3C, HB{C3N2H2(CH3)S}3HgCH2CH3], 119.5 [s,

3C, HB{C3N2H2(CH3)S}3HgCH2CH3], 123.3 [s, 3C, HB{C3N2H2(CH3)S}3HgCH2CH3],

11 1 160.84 [s, 3C, HB{C3N2H2(CH3)S}3HgCH2CH3]. B NMR (d-THF): - 2.59 [d, 1B, JH-B =

-1 110 Hz, HB{C3N2H2(CH3)S}3HgCH2CH3]. IR data (ATR, cm ): 3156 (w), 3140 (w), 2952

(w), 2910 (w), 1564 (m), 1470 (m), 1440 (w), 1374 (s), 1356 (m), 1200 (s), 1182 (m), 1100 (s),

1044 (m), 1018 (w), 978 (w), 846 (w), 736 (s), 684 (s), 634 (w), 522 (m), 468 (w), 444 (w).

4.7.6 Synthesis of [TmMeBenz]HgMe

To THF (0.5 mL), Na[TmMeBenz] (20 mg, 0.030 mmol) and MeHgCl (11 mg, 0.04 mmol) were added, resulting in a cloudy white solution. Upon mixing the sample turned slightly yellow and after sitting for 3 hours, the reaction mixture was filtered and the motherliquor collected. The THF solvent was removed via slow evaporation in a well ventilated hood. Crystals of [TmMeBenz]HgMe (16 mg, 69%) grew from the motherliquor

MeBenz and were suitable for X-ray diffraction. Analysis calcd. [Tm ]HgMe•0.1

ClHgMe•0.25 HgCl2: C, 37.2 %; H, 3.2 %; N, 10.4 %. Found: C, 37.7 %, H, 3.0 %, N 9.7%.

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1 H NMR (d-THF): 0.55 [s, 3H, HB{(C4H4)C2N2(CH3)CS}3HgMe], 3.72 [s, 9H,

HB{(C4H4)C2N2(CH3)CS}3HgMe], 5.96 [br, 1H, HB{(C4H4)C2N2(CH3)CS}3HgMe], 7.09 [t,

3 3 3H, JH-H = 7 Hz, HB{(C4H4)C2N2(CH3)CS}3HgMe], 7.19 [t, 3H, JH-H = 7 Hz,

3 HB{(C4H4)C2N2(CH3)CS}3HgMe], 7.32 [t, 6H, JH-H = 8 Hz,

13 HB{(C4H4)C2N2(CH3)CS}3HgMe]. C NMR (d-THF): 4.68 [s, 1C,

HB{(C4H4)C2N2(CH3)CS}3HgMe], 30.9 [s, 3C, HB{(C4H4)C2N2(CH3)CS}3HgMe], 110.0 [s,

3C, HB{(C4H4)C2N2(CH3)CS}3HgMe], 113.6 [s, 3C, HB{(C4H4)C2N2(CH3)CS}3HgMe],

123.5 [s, 3C, HB{(C4H4)C2N2(CH3)CS}3HgMe], 123.6 [s, 3C,

HB{(C4H4)C2N2(CH3)CS}3HgMe], 134.9 [s, 3C, HB{(C4H4)C2N2(CH3)CS}3HgMe], 137.2

[s, 3C, HB{(C4H4)C2N2(CH3)CS}3HgMe], 168.4 [s, 3C, HB{(C4H4)C2N2(CH3)C S}3HgMe].

11 11 B NMR (d-THF, 300K): 5.68 [br, 1B, HB{(C4H4)C2N2(CH3)CS}3HgMe]. B NMR (d-THF,

1 -1 330K): - 4.69 [d, JH-B = 101 Hz, 1B, HB{(C4H4)C2N2(CH3)CS}3HgMe]. IR data (ATR, cm ):

3116 (w), 2986 (w), 2904 (w), 1484 (m), 1440 (m), 1404 (m), 1346 (s), 1300 (m), 1238 (w),

1194 (w), 1158 (w), 1136 (w), 1018 (w), 1016 (w), 858 (w), 814 (w), 744 (s), 622 (m), 560

(m), 442 (w), 420 (m).

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4.7.7 Synthesis of [TmMeBenz]HgEt

To THF (0.5 mL), Na[TmMeBenz] (8 mg, 0.01 mmol) and EtHgCl (3 mg, 0.01 mmol) were added, resulting in a cloudy white solution. Upon mixing, the sample turned slightly yellow and after sitting for 3 hours, the reaction mixture was filtered and the motherliquor collected. The THF solvent was removed via slow evaporation in a well ventilated hood. Crystals of [TmMeBenz]HgMe (7 mg, 76%) grew from the motherliquor

MeBenz after 48 hours and were suitable for X-ray diffraction. Analysis calcd. [Tm ]HgEt •

0.75 ClHgEt • 0.5 HgCl2: C, 31.0 %; H, 2.9 %; N, 7.9 %. Found: C, 31.5%, H, 3.1%, N

1 3 7.2%. H NMR (d-THF): 1.34 [t, JH-H = 8 Hz, 3H, HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3],

3 1.66 [q, JH-H = 8 Hz, 2H, HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3], 3.72 [s, 9H,

HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3], 5.98 [br, 1H,

3 HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3], 7.08 [t, JH-H = 7 Hz, 3H,

3 HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3], 7.18 [t, JH-H = 7 Hz, 3H,

3 HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3], 7.31 [t, JH-H = 7 Hz, 6H,

13 HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3]. C NMR (d-THF): 15.1 [s, 1C,

HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3], ~25 [obscured by THF solvent, 1C,

HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3], 30.9 [s, 3C, HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3],

109.9 [s, 3C, HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3], 113.6 [s, 3C,

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HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3], 123.4 [s, 3C,

HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3], 123.5 [s, 3C,

HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3], 135.0 [s, 3C,

HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3], 137.3 [s, 3C,

HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3], 168.7 [s, 3C,

11 1 HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3]. B NMR (d-THF): - 4.69 [d, JH-B = 91 Hz, 1B,

-1 HB{(C4H4)C2N2(CH3)CS}3HgCH2CH3]. IR data (ATR, cm ): 2982 (w), 2960 (w), 2866 (w),

1486 (m), 1436 (m), 1398 (m), 1344 (s), 1300 (m), 1238 (w), 1196 (m), 1152 (m), 1136 (w),

1098 (w), 1016 (w), 1014 (w), 974 (w), 860 (w), 816 (w), 756 (m), 744 (s), 692 (w), 622 (m),

560 (m), 488 (w), 442 (w), 420 (s).

t 4.7.8 Synthesis of [TmBu Benz]HgMe

t To THF (0.5 mL), Na[TmBu Benz] (12 mg, 0.02 mmol) and MeHgCl (5 mg, 0.02 mmol) were added, resulting in a cloudy white solution. The reagents were mixed for 3 hours and then the reaction was filtered and the motherliquor was collected. Crystals suitable for X-ray were grown from a mixture of THF and toluene. The THF solvent was

t removed under vacuum giving [TmBu Benz]HgMe (14 mg, 87%) as an off-white solid.

t Analysis calcd. [TmBu Benz]HgMe: C, 48.4 %; H, 5.1 %; N, 10.0 %. Found: C, 49.2%, H,

1 5.4%, N 9.8%. H NMR (d-THF): 0.62 [s, 3H, HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 2.03 [s,

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27H, HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 5.88 [br, 1H,

HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 7.03 [br, 6H, HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 7.19

3 3 [d, JH-H = 7 Hz, 3H, HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 7.84 [d, JH-H = 7 Hz, 3H,

1 HB{(C4H4)C2N2C(CH3)3CS}3HgMe]. H NMR (C6D6): 1.24 [s, 3H,

HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 1.80 [s, 27H, HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 6.36

[br, 1H, HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 6.89 [m, 6H,

HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 7.45 [m, 3H, HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 7.56

13 [m, 3H, HB{(C4H4)C2N2C(CH3)3CS}3HgMe]. C NMR (C6D6): 5.9 [s, 1C,

HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 30.8 [s, 9C, HB{(C4H4)C2N2C(CH3)3CS}3HgMe],

63.1[s, 3C, HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 113.8 [s, 3C,

HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 114.2 [s, 3C, HB{(C4H4)C2N2C(CH3)3CS}3HgMe],

122.5 [s, 3C, HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 134.5 [s, 3C,

HB{(C4H4)C2N2C(CH3)3CS}3HgMe], 137.5 [s, 3C, HB{(C4H4)C2N2C(CH3)3CS}3HgMe],

11 168.9 [s, 3C, HB{(C4H4)C2N2C(CH3)3CS}3HgMe]. B NMR (d-THF, 300K): - 4.77 [br, 1B,

11 1 HB{(C4H4)C2N2C(CH3)3CS}3HgMe]. B NMR (d-THF, 330K): - 4.65 [d, JH-B = 94 Hz, 1B,

-1 HB{(C4H4)C2N2C(CH3)3CS}3HgMe]. IR data (ATR, cm ): 2976 (w), 2916 (w), 2852 (w),

1472 (w), 1399 (w), 1379 (m), 1367 (m), 1323 (s), 1276 (w), 1222 (w), 1176 (s), 1154 (s),

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1124 (m), 1036 (w), 964 (w), 936 (w), 862 (w), 826 (w), 790 (w), 739 (s), 686 (w), 666 (w),

634 (m), 580 (w), 556 (w), 480 (w).

t 4.7.9 Synthesis of [TmBu Benz]HgEt

t To THF (0.5 mL), Na[TmBu Benz] (4 mg, 0.01 mmol) and MeHgCl (2 mg,0.01 mmol) were added, resulting in a cloudy white solution. The reagents were mixed for 3 hours and then the reaction was filtered and the motherliquor was collected. Crystals suitable for

X-ray were obtained from slow evaporation of THF. The THF solvent was removed

t under vacuum giving [TmBu Benz]HgEt (3 mg, 57%) as an off-white solid. Analysis calcd.

t [TmBu Benz]HgEt: C, 49.0 %; H, 5.3 %; N, 9.8 %. Found: C, 48.8%, H, 5.0%, N 9.5%. 1H

3 NMR (d-THF): 1.38 [t, 3H, JH-H = 8 Hz, HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 1.60 [br,

2H, HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 2.05 [s, 27H,

HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 5.90 [br, 1H,

HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 7.06 [m, 6H

3 HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 7.21 [d, JH-H = 8 Hz, 3H,

3 HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 7.88 [d, JH-H = 8 Hz,

13 HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3]. C NMR (d-THF): 16.9 [s, 1C,

HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 23.0 [s, 1C,

HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 31.2 [s, 9C,

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HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 63.1[s, 3C,

HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 114.0 [s, 3C,

HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 114.6 [s, 3C,

HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 122.6 [s, 3C,

HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 122.9 [s, 3C,

HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 135.0 [s, 3C,

HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 138.0 [s, 3C,

HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3], 169.3 [s, 3C,

11 HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3]. B NMR (d-THF, 300K): - 4.70 [br, 1B,

11 HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3]. B NMR (d-THF, 330K): -4.62 [br, 1B.

-1 HB{(C4H4)C2N2C(CH3)3CS}3HgCH2CH3]. IR data (ATR, cm ): 2971 (w), 2920 (w), 2875

(w), 1442 (w), 1473 (w), 1383 (m), 1365 (m), 1325 (s), 1278 (w), 1219 (w), 1177 (m), 1156

(m), 1123 (w), 1034 (m), 966 (w), 932 (w), 853 (w), 823 (w), 790 (w), 734 (s), 714 (w), 633

(m), 580 (w), 555 (w), 537 (w), 503 (w), 410 (m).

4.7.10 Synthesis of [BmMe]HgMe

[BmMe]Na (22 mg, 0.08 mmol) was added to THF (0.5 mL) resulting in a clear colorless solution. MeHgCl (17 mg, 0.07 mmol) was then added to the solution and mixed for 1 hour. A very fine precipitate formed and was removed via filtration. The THF solvent

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was removed via slow evaporation to give [BmMe]HgMe (16 mg, 58%) as an off-white solid. Crystals suitable for X-ray diffraction were obtained from methanol. Anal. calcd.

C, 23.8 %; H, 3.3 %; N, 2.4%. Found C, 23.9%; H, 3.2%; N, 12.2%. 1H NMR (d-THF): 0.71

[s, 3H, H2B{C3N2H2(CH3)S}2HgMe], 3.50 [s, 6H, H2B{C3N2H2(CH3)S}2HgMe], 3.83 [br, 2H,

H2B{C3N2H2(CH3)S}2HgMe], 6.67 [br, 2H, H2B{C3N2H2(CH3)S}2HgMe], 6.85 [br, 2H,

13 H2B{C3N2H2(CH3)S}2HgMe]. C NMR (d-THF): 6.2 [s, 1C, H2B{C3N2H2(CH3)S}2HgMe],

34.8 [s, 2C, H2B{C3N2H2(CH3)S}2HgMe], 119.2 [s, 2C, H2B{C3N2H2(CH3)S}2HgMe], 123.4

11 [s, 2C, H2B{C3N2H2(CH3)S}2HgMe], 160.6 [s, 2C, H2B{C3N2H2(CH3)S}2HgMe]. B NMR

1 -1 (d-THF): -9.13 [t, JH-B = 107 Hz, 1B, H2B{C3N2H2(CH3)S}2HgMe]. IR data (ATR, cm ):

3164 (w), 3126 (w), 3124 (w), 2384 (m), 1566 (w), 1464 (m), 1448 (w), 1380 (s), 1356 (m),

1204 (s), 1168(m), 1122 (s), 1102 (m), 1090 (w), 1046 (w), 1016 (w), 972 (w), 874 (w), 738

(m), 696 (m), 678 (m), 646 (w), 522 (m), 508 (m), 464 (m).

4.7.11 Synthesis of [BmMe]HgEt

[BmMe]Na (18 mg, 0.07 mmol) was added to THF (0.5 mL) resulting in a clear colorless solution. EtHgCl (14 mg, 0.05 mmol) was then added to the solution and mixed for 1 hour. A very fine precipitate formed and was removed via filtration. The THF solvent was removed via slow evaporation from the filtrate to give [BmMe]HgEt (18 mg, 57%) as an off-white solid. Crystals suitable for X-ray diffraction were obtained from slow

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evaporation of methanol. Anal. calcd. C, 25.6%; H, 3.7%; N, 12.0%. Found C, 25.4%; H,

1 3 3.8 %; N, 11.7%. H NMR (d-THF): 1.29 [t, JH-H = 7 Hz, 3H,

1 H2B{C3N2H2(CH3)S}2HgCH2CH3], 1.58 [q, JH-H = 7 Hz, 2H,

H2B{C3N2H2(CH3)S}2HgCH2CH3], 3.50 [s, 6H, H2B{C3N2H2(CH3)S}2HgCH2CH3], 4.00 [br,

3 2H, H2B{C3N2H2(CH3)S}2HgCH2CH3], 6.67 [d, JH-H = 2 Hz, 2H,

3 H2B{C3N2H2(CH3)S}2HgCH2CH3], 6.84 [d, JH-H = 2 Hz, 2H,

13 H2B{C3N2H2(CH3)S}2HgCH2CH3]. C NMR (d-THF): 15.3 [s, 1C,

H2B{C3N2H2(CH3)S}2HgCH2CH3], 23.0 [s, 1C, H2B{C3N2H2(CH3)S}2HgCH2CH3], 34.8 [s,

2C, H2B{C3N2H2(CH3)S}2HgCH2CH3], 119.2 [s, 2C, H2B{C3N2H2(CH3)S}2HgCH2CH3],

123.4 [s, 2C, H2B{C3N2H2(CH3)S}2HgCH2CH3], 160.5 [s, 2C,

11 1 H2B{C3N2H2(CH3)S}2HgCH2CH3]. B NMR (d-THF): - 9.04 [t, JH-B = 85 Hz, 1B,

-1 H2B{C3N2H2(CH3)S}2HgCH2CH3]. IR data (ATR, cm ): 3144 (w), 2954 (w), 2914 (w), 2428

(m), 1556 (m), 1470 (m), 1440 (w), 1382 (M), 1360 (w), 1380 (s), 1334 (w), 1308 (w), 1194

(s), 1172 (s), 1128 (s), 1102 (w), 1080 (w), 1054 (w), 1032 (w), 968 (w), 892 (w), 730 (s), 688

(s), 624 (w), 518 (m), 458 (m).

310

t 4.7.12 Synthesis of [BmBu ]HgEt

t [BmBu ]Na (33 mg, 0.14 mmol) was dissolved in THF (0.5 mL) resulting in a clear solution to which EtHgCl (35 mg, 0.13 mmol) was added. Fine precipitate formed upon mixing for 1 hour. The precipitate was removed via filtration and the motherliquor collected. The THF solvent was removed via slow evaporation resulting

t in [BmBu ]HgMe (39 mg, 63%) as an off-white solid. Crystals suitable for X-ray

1 3 diffraction were obtained from slow evaporation of THF. H NMR (d-THF): 1.30 [t, JH-

3 H = 8 Hz, 3H, H2B{C3N2H2C(CH3)3S}2HgCH2CH3], 1.56 [q, JH-H = 8 Hz, 2H,

H2B{C3N2H2C(CH3)3S}2HgCH2CH3], 1.75 [s, 6H, H2B{C3N2H2C(CH3)3S}2HgCH2CH3], 3.89

3 [br, 2H, H2B{C3N2H2C(CH3)3S}2HgCH2CH3], 6.63 [d, JH-H = 2 Hz, 2H,

3 H2B{C3N2H2C(CH3)3S}2HgCH2CH3], 7.00 [d, JH-H = 2 Hz, 2H,

13 H2B{C3N2H2C(CH3)3S}2HgCH2CH3]. C NMR (d-THF): 15.4 [s, 1C,

H2B{C3N2H2C(CH3)3S}2HgCH2CH3], 22.6 [s, 1C, H2B{C3N2H2C(CH3)3S}2HgCH2CH3], 29.0

[s, 6C, H2B{C3N2H2C(CH3)3S}2HgCH2CH3], 58.8 [s, 2C,

H2B{C3N2H2C(CH3)3S}2HgCH2CH3], 116.0 [s, 2C, H2B{C3N2H2C(CH3)3S}2HgCH2CH3],

122.7 [s, 2C, H2B{C3N2H2C(CH3)3S}2HgCH2CH3], 158.9 [s, 2C,

11 H2B{C3N2H2C(CH3)3S}2HgCH2CH3]. B NMR (d-THF, 300K): -8.92 [br, 1B,

311

11 1 H2B{C3N2H2C(CH3)3S}2HgCH2CH3]. B NMR (d-THF, 330K): - 8.77 [t, JH-H = 96 Hz, 1B,

-1 H2B{C3N2H2C(CH3)3S}2HgCH2CH3]. IR data (ATR, cm ): 3202 (w), 3178 (w), 2984 (w),

2964 (w), 2904 (w), 2424 (w), 1574 (w), 1430 (m), 1364 (s), 1342 (w), 1264 (w), 1202 (w),

1172 (s), 1142 (m), 1066 (w), 1042 (w), 948 (w), 890 (w), 838 (w), 726 (m), 686 (s), 642 (w),

594 (w), 550 (w), 488 (w).

4.7.13 Synthesis of [BmMeBenz]HgMe

[BmMeBenz]Na (14 mg, 0.04 mmol) and MeHgCl (9 mg, 0.04 mmol) were reacted in THF

(0.5 mL) for 6 hours. During this time, precipitate formed and was removed via filtration. The mother liquor was collected and the THF solvent was removed via slow evaporation resulting in [BmMeBenz]HgMe (12 mg, 49%) as an off-white solid. Crystals suitable for X-ray were obtained from THF, but were of the rearranged product

MeBenz MeBenz [Tm ]HgMe. Anal. calcd. [Bm ]HgMe • 0.2 HgCl2 • 0.5 THF: C, 35.4%; H, 3.6%;

N, 8.6%. Found C, 35.5%; H, 3.7%; N, 8.1%. 1H NMR (d-THF): 0.80 [s, 3H,

H2B{(C4H4)C2N2(CH3)CS}2HgMe], 3.76, [s, 6H, H2B{(C4H4)C2N2(CH3)CS}2HgMe] , 4.81

[br, 2H, H2B{(C4H4)C2N2(CH3)CS}2HgMe], 7.13 [m, 4H,

3 H2B{(C4H4)C2N2(CH3)CS}2HgMe], 7.31 [d, JH-H = 8Hz, 2H,

3 H2B{(C4H4)C2N2(CH3)CS}2HgMe], 7.48 [d, JH-H = 8Hz, 2H,

312

1 H2B{(C4H4)C2N2(CH3)CS}2HgMe]. H NMR (C6D6): 0.66 [s, 3H,

H2B{(C4H4)C2N2(CH3)CS}2HgMe], 2.97 [s, 6H, H2B{(C4H4)C2N2(CH3)CS}2HgMe], 5.38 [br,

3 2H, H2B{(C4H4)C2N2(CH3)CS}2HgMe], 6.46 [d, JH-H = 8 Hz, 2H,

H2B{(C4H4)C2N2(CH3)CS}2HgMe], 6.91 [m, 4H, H2B{(C4H4)C2N2(CH3)CS}2HgMe], 7.76 [d,

3 13 JH-H = 8 Hz, 2H, H2B{(C4H4)C2N2(CH3)CS}2HgMe]. C NMR (d-THF): 5.1 [s, 1C,

H2B{(C4H4)C2N2(CH3)CS}2HgMe], 31.5 [s, 2C, H2B{(C4H4)C2N2(CH3)CS}2HgMe], 110.2 [s,

2C, H2B{(C4H4)C2N2(CH3)CS}2HgMe], 114.2 [s, 2C, H2B{(C4H4)C2N2(CH3)CS}2HgMe],

123.3 [s, 2C, H2B{(C4H4)C2N2(CH3)CS}2HgMe], 123.7 [s, 2C,

H2B{(C4H4)C2N2(CH3)CS}2HgMe], 135.0 [s, 2C, H2B{(C4H4)C2N2(CH3)CS}2HgMe], 137.6 [s,

11 2C, H2B{(C4H4)C2N2(CH3)CS}2HgMe], 167.5 [s, 2C, H2B{(C4H4)C2N2(CH3)CS}2HgMe]. B

-1 NMR (d-THF): -12.3 [br, 1B, H2B{(C4H4)C2N2(CH3)CS}2HgMe]. IR data (ATR, cm ): 3169

(w), 3000 (w), 1593 (w), 1472(w), 1448 (w), 1393 (m), 1328 (w), 1283 (m), 1232 (w), 1148

(w), 1120 (w), 1099 (w), 949 (w), 772 (w), 701 (s), 692 (s), 514 (s), 475 (w).

4.7.14 Synthesis of [BmMeBenz]HgEt

[BmMeBenz]Na (12 mg, 0.03 mmol) and EtHgCl (8 mg, 0.03 mmol) were reacted in THF

313

suitable for X-ray were obtained from methanol and were determined to be the

MeBenz MeBenz rearranged product [Tm ]HgEt . Anal. calcd. [Bm ]HgEt • 0.5 HgCl2: C, 30.7%;

1 3 H, 3.0%; N, 8.0%. Found C, 31.4%; H, 3.0%; N, 7.7%. H NMR (d-THF): 1.28 [t, JH-H = 8

3 Hz, 3H, H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 1.71 [q, JH-H = 8 Hz, 2H,

H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 3.76 [s, 6H,

H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 4.88 [br, 2H,

H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 7.12 [m, 4H,

3 H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 7.31 [d, JH-H = 8 Hz, 2 H,

3 H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 7.48 [d, JH-H = 8 Hz, 2 H,

1 3 H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3]. H NMR (C6D6): 1.19, [t, JH-H = 8 Hz, 3H,

3 H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 1.55 [q, JH-H = 8 Hz, 2H,

H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 3.03 [s, 6H,

H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 5.55 [br, 2H,

3 H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 6.49 [d, JH-H = 8 Hz, 2H,

H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 6.89 [m, 4H, H2B{(C4H4)C2N2(CH3)CS}2HgCH-

3 13 2CH3], 7.77 [d, JH-H = 8 Hz, 2H, H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3]. C NMR (d-

THF): 15.1 [s, 1C, H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 23.5 [s, 1C,

H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 31.5 [s, 2C,

314

H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 110.2 [s, 2C,

H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 114.1 [s, 2C,

H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 123.3 [s, 2C,

H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 123.6 [s, 2C,

H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 135.0 [s, 2C,

H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3], 137.6 [s, 2C, H2B{(C4H4)C2N2(CH3)CS}2HgCH-

11 2CH3], 167.7 [s, 2C, H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3]. B NMR (d-THF): -12.2 [br,

-1 1B, H2B{(C4H4)C2N2(CH3)CS}2HgCH2CH3]. IR data (ATR, cm ): 3146 (w), 3000 (w), 2987

(w), 1470 (m), 1448 (w), 1392 (s), 1350 (m), 1282 (s), 1232 (m), 1147 (m), 1119 (m), 1052

(w), 999 (w), 946 (w), 917 (w), 741 (s), 706 (s), 711 (s), 516 (s), 477 (w), 453 (w).

t 4.7.15 Synthesis of [BmBu Benz]HgMe

t [BmBu Benz]K (15 mg, 0.04 mmol) was dissolved in THF (0.5 mL) making a white slurry.

Upon addition of MeHgCl (10 mg, 0.04 mmol), more white precipitate formed. The reaction was allowed to sit for 1 hour, then the white precipitate was removed via filtration. The THF solvent was removed from the motherliquor in vacuo giving

t [BmBu Benz]HgMe (16, 70%) as an off-white solid. Crystals of the rearranged

t [TmBu Benz]HgMe were obtained from slow evaporation of solvent. Anal. calcd.

ButBenz [Bm ]HgMe•2 THF: C, 41.3%; H, 4.4%; N, 8.4%. Found C, 41.3%; H, 4.6%; N,

315

1 7.9%. H NMR (d-THF): 0.85 [s, 3H, H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3], 2.00 [s, 18H,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3], 7.03 [m, 4H, H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3],

3 5.83 [br, 2H, H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3], 7.18 [d, JH-H = 8 Hz, 2H,

3 H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3], 7.84 [d, JH-H = 8 Hz, 2H,

13 H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3]. C NMR (d-THF): 3.7 [s, 1C,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3], 31.11 [s, 6C, H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3],

63.7 [s, 2C, H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3], 113.9 [s, 2C,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3], 114.6 [s, 2C, H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3],

122.7 [s, 2C, H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3], 123.0 [s, 2C,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3], 135.0 [s, 2C, H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3],

137.8 [s, 2C, H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3], 169.0 [s, 2C,

11 H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3]. B NMR (d-THF): -4.76 [br, 1B,

-1 H2B{(C4H4)C2N2C(CH3)3CS}2HgCH3]. IR data (ATR, cm ): 3000 (w), 2965 (w), 1507 (w),

1478 (w), 1402 (m), 1329 (s), 1179 (m), 1176 (m), 1130 (w), 1040 (w), 982 (w), 864 (w), 796

(w), 742 (s), 688 (w), 635 (m), 594 (w), 593 (w), 561 (w), 557 (w).

t 4.7.16 Synthesis of [BmBu Benz]HgEt

t [BmBu Benz]K (14 mg, 0.04 mmol) was dissolved in THF (0.5 mL) making a white slurry.

Upon addition of EtHgCl (11 mg, 0.04 mmol), more white precipitate formed. The

316

reaction was allowed to sit for 1 hour, then the white precipitate was removed via filtration. The THF solvent was removed from the motherliquor in vacuo giving a

t [BmBu Benz]HgEt (11 mg, 51%) as a white solid. Colorless crystals were seen on the walls of the reaction vessel, X-ray diffraction confirmed these were of the rearranged

t [TmBu Benz]HgEt product. 1H NMR (d-THF): 1.32 [m, 3H,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 1.56 [m, 2H,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 2.01 [s, 27H,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 5.41 [br, 2H,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 7.03 [m, 4H,

1 3 H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 7.19 [d of d, JC-H = 1 Hz, JH-H = 7 Hz, 2H,

3 H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 7.83 [d, JH-H = 7 Hz, 2H,

13 H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3]. C NMR (d-THF): 14.8 [s, 1C,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 16.9 [s, 1C,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 31.1 [s, 6C,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 63.6 [s, 2C,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 113.8 [s, 2C,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 114.5 [s, 2C,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 122.7 [s, 2C,

317

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 122.8 [s, 2C,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 134.9 [s, 2C,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 137.8 [s, 2C,

H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3], 169.2 [s, 2C,

11 H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3]. B NMR (d-THF): -4.60 [br, 1B,

-1 H2B{(C4H4)C2N2C(CH3)3CS}2HgCH2CH3]. IR data (ATR, cm ): 3000 (w), 2970 (w), 2911

(w), 1478 (w), 1405 (w), 1374 (w), 1332 (w), 1295 (w), 1237 (w), 1185 (w), 1169 (w), 1040

(w), 977 (w), 956 (w), 741 (s), 684 (m), 638 (m), 612 (w), 600 (w), 566 (w), 558 (w).

4.7.17 Addition of Benzenethiol to [TmMe]HgEt and [TmMeBenz]HgEt

A solution of [TmMe]HgEt (0.03 mmol) in benzene (0.5 mL) with a mesitylene internal standard (2 L) and [TmMeBenz]HgEt (0.03 mmol) is benzene (0.5 mL) with a mesitylene internal standard (2 L) were mixed. Aliquots of benzenethiol were added to this mixture and the reaction was monitored by 1H NMR. The disappearance of

[TmMe]HgEt and [TmMeBenz]HgEt was measured by taking the integral of the methyl protons on the [Tm] ligands and comparing the ratios with the mesitylene internal standard. The results of the experiment are provided in Table 18.

318

Table 18. 1H NMR data for the addition of benzenethiol to [TmMe]HgEt and

[TmMeBenz]HgEt

∫ ∫ MeBenz CH3 CH3 [Tm ]/ Eq. PhSH [TmMeBenz] [TmMe] [TmMe]

0 1.09 1.72 0.634

0.017 0.45 0.76 0.592

0.100 0.46 0.78 0.590

0.250 0.41 0.70 0.586

0.400 0.40 0.69 0.580

0.4 (90 minutes later) 0.41 0.74 0.554

0.4 (one day later) 0.33 0.72 0.458

0.550 0.33 0.71 0.465

0.55 (one day later) 0.21 0.70 0.300

0.700 0.20 0.68 0.294

% Loss 56 11

319

t t 4.7.18 Addition of Benzenethiol to [TmBu ]HgEt and [TmBu Benz]HgEt

t A solution of [TmBu ]HgEt (0.03 mmol) in benzene (0.5 mL) with a mesitylene

t internal standard (2 L) and [TmBu Benz]HgEt (0.02 mmol) is benzene (0.5 mL) with a mesitylene internal standard (2 L) were mixed. Aliquots of benzenethiol were added to this mixture and the reaction was monitored by 1H NMR. The disappearance of

t t [TmBu ]HgEt and [TmBu Benz]HgEt was measured by taking the integral of the methyl protons on the [Tm] ligands and comparing the ratios with the mesitylene internal standard. The results of the experiment are provided in Table 19.

t Table 19. 1H NMR data for the addition of benzenethiol to [TmBu ]HgEt and

t [TmBu Benz]HgEt

∫ ∫ ButBenz CH3 CH3 [Tm ]/ Eq. PhSH t t t [TmBu Benz] [TmBu ] [TmBu ]

0 1.58 10.87 0.145

0.017 0.77 2.14 0.360

0.100 0.81 2.17 0.373

0.250 0.74 1.98 0.374

0.400 --a

320

0.4 (90 minutes later) 0.71 1.38 0.514

0.4 (one day later) 0.67 1.26 0.532

0.550 0.59 1.00 0.590

0.55 (one day later) 0.36 0.55 0.655

0.700 0.20 0.68 0.294

% Loss 53 74 a Data could not be obtained due to overlap of the t-butyl proton resonances.

321

4.8 Crystallographic Data

Table 20. Crystal, intensity collection and refinement data

Me Me [Tm ]HgMe [Tm ]HgMe●C6H6

lattice Monoclinic Triclinic

formula C13H19BHgN6S3 C28H35BHgN6S3 formula weight 566.92 763.20

space group P21/n P-1 a/Å 10.1768(12) 10.4649(14) b/Å 12.8965(15) 12.1518(14) c/Å 15.3221(18) 13.1238(16) /˚ 90 107.3487(19) /˚ 108.956(2) 91.7178(19) /˚ 90 101.0545(13)

V/Å3 1901.9(4) 1556.7(3) Z 4 2 temperature (K) 296(2) 130(2) radiation (, Å) 0.71073 0.71073

 (calcd.), g cm-3 1.980 1.628  (Mo K), mm-1 8.430 5.173 max, deg. 30.66 27.36 no. of data collected 5849 9441 no. of data used 4703 6391 no. of parameters 221 356

R1 [I > 2(I)] 0.0343 0.0504

wR2 [I > 2(I)] 0.0738 0.0875

R1 [all data] 0.488 0.0916

wR2 [all data] 0.0795 0.1006 GOF 1.031 1.002

322

Table 20. (cont’d) Crystal, intensity collection and refinement data

Me MeBenz [Tm ]HgEt [Tm ]HgMe●HgCl2

lattice Monoclinic Monoclinic

formula C14H21BHgN6S3 C50H50B2C12Hg3N12S6 formula weight 580.95 1705.67

space group P21/n P2/c a/Å 11.019(2) 11.6469(16) b/Å 13.117(3) 11.2923(15) c/Å 14.344(3) 22.179(3) /˚ 90 90 /˚ 111.629(3) 103.623(2) /˚ 90 90

V/Å3 1927.3(6) 2834.9(7) Z 4 2 temperature (K) 296(2) 130(2) radiation (, Å) 0.71073 0.71073

 (calcd.), g cm-3 2.002 1.998  (Mo K), mm-1 8.321 8.466 max, deg. 30.78 30.778 no. of data collected 6008 8821 no. of data used 3440 5234 no. of parameters 229 344

R1 [I > 2(I)] 0.0568 0.0523

wR2 [I > 2(I)] 0.1127 0.1083

R1 [all data] 0.1247 0.1106

wR2 [all data] 0.1381 0.1310 GOF 1.001 0.994

323

Table 20. (cont’d) Crystal, intensity collection and refinement data

MeBenz ButBenz [Tm ]HgEt● [Tm ]HgMe BrHgEt

lattice Monoclinic Triclinic

formula C54H59B2BrC10Hg3N12S6 C41H51BHgN6S3 formula weight 1171.79 935.46 space group P2/c P-1 a/Å 11.6945(14) 11.754(3) b/Å 11.3810(14) 12.267(3) c/Å 22.305(3) 15.901(4) /˚ 90 103.592(4) /˚ 102.836(2) 109.395(4) /˚ 90 95.476(4)

V/Å3 2894.5(6) 2064.3(9) Z 2 2 temperature (K) 130(2) 150(2) radiation (, Å) 0.71073 0.71073

 (calcd.), g cm-3 2.033 1.505  (Mo K), mm-1 8.893 3.917 max, deg. 30.79 31.19 no. of data collected 46007 12806 no. of data used 9030 4370 no. of parameters 360 410

R1 [I > 2(I)] 0.0574 0.0730

wR2 [I > 2(I)] 0.1023 0.1399

R1 [all data] 0.1278 0.1899

wR2 [all data] 0.1243 0.1562 GOF 1.003 0.999

324

Table 20. (cont’d) Crystal, intensity collection and refinement data

t Me [TmBu Benz]HgEt [Bm ]HgMe

lattice Trigonal Monoclinic

formula C35H45BHgN6S3 C9H15BHgN4S2 formula weight 846.66 454.77

space group R-3 P21/c a/Å 17.971(3) 7.6880(7) b/Å 17.971(3) 13.5311(13) c/Å 20.140(3) 13.4340(12) /˚ 90 90 /˚ 90 101.4270(10) /˚ 120 90

V/Å3 5633(2) 1369.8(2) Z 6 4 temperature (K) 130(2) 296(2) radiation (, Å) 0.71073 0.71073

 (calcd.), g cm-3 1.498 2.205  (Mo K), mm-1 4.279 11.523 max, deg. 30.472 32.54 no. of data collected 24760 22878 no. of data used 3759 4823 no. of parameters 169 157

R1 [I > 2(I)] 0.0400 0.0226

wR2 [I > 2(I)] 0.0780 0.0515

R1 [all data] 0.0946 0.306

wR2 [all data] 0.0891 0.0541 GOF 0.999 0.996

325

Table 20. (cont’d) Crystal, intensity collection and refinement data

Me t [Bm ]HgEt [BmBu ]HgEt

lattice Monoclinic Monoclinic

formula C10H17BHgN4S2 C16H29BHgN4S2 formula weight 468.80 552.95

space group P21/n P21/c a/Å 11.3707(11) 14.272(3) b/Å 10.2100(10) 9.8893(17) c/Å 13.4415(13) 29.663(5) /˚ 90 90 /˚ 112.1300(10) 92.493(3) /˚ 90 90

V/Å3 1445.5(2) 4182.7(13) Z 4 8 temperature (K) 296(2) 296(2) radiation (, Å) 0.71073 0.71073

 (calcd.), g cm-3 2.154 1.756  (Mo K), mm-1 10.923 7.565 max, deg. 32.46 24.10 no. of data collected 24371 6641 no. of data used 5084 4603 no. of parameters 165 446

R1 [I > 2(I)] 0.0275 0.1030

wR2 [I > 2(I)] 0.0602 0.2732

R1 [all data] 0.0381 0.1398

wR2 [all data] 0.0643 0.2944 GOF 0.998 1.106

326

4.9 References and Notes

(1) Clarkson, T. W.; Magos, L. Crit. Rev. Toxicol. 2006, 36, 609– 662.

(2) Moore, M. J.; Distefano, M. D.; Zydowsky, L. D.; Cummings, R. T.; Walsh, C. T.

Acc. Chem. Res. 1990, 23, 301–308.

(3) (a) Tai, H.-C.; Lim, C. J. Phys. Chem. A 2006, 110, 452– 462.

(b) Hartwig, A.; Asmuss, M.; Blessing, H.; Hoffmann, S.; Jahnke, G.;

Khandelwal, S.; Pelzer, A.; Bürkle, A. Food Chem. Toxicol. 2002, 40, 1179–1184.

(4) (a) Clarkson, T. W. Crit. Rev. Clin. Lab. Sci. 1997, 34, 369–403.

(b) Langford, N.; Ferner, R. J. Hum. Hypertens. 1999, 13, 651– 656.

(5) Pitts, K. E.; Summers, A. O. Biochemistry 2002, 41, 10287–10296.

(6) Walsh, C. T.; Distefano; Moore, M. J.; Shewchuk, L. M.; Verdine, G. L. FASEB

1988, 2, 124–130.

(7) Melnick, J. G.; Parkin, G. Science 2007, 317, 225–227.

(8) Lafrance-Vanasse, J.; Lefebvre, M.; Di Lello, P.; Sygusch, J.; Omichinski, J. G. J.

Biol. Chem. 2009, 284, 938– 944.

(9) (a) Maurice, B. Y. J. Am. Chem. Soc. 1957, 79, 5927–5930.

(b) Strasdeit, H.; von Döllen A; Saak, W.; Wilhelm, M. Angew. Chem. Int. Ed.

Engl. 2000, 39, 784–786.

327

(10) Soares, L.F.; Silva R.M.; Doriguetto, A.C.; Ellena, J.; Mascarenhas, Y.P.;

Castellano, E.E. J. Braz. Chem. Soc. 2004, 15, 695-700.

(11) Cambridge Structural Database (Version 5.35). 3D Search and Resarch Using the

Cambridge Structural Database: Allen, F.H., and Kennard O. (1993) 3D search

and research using the Cambridge Structural Database. “Chemical Design

Automation News” 8, pp. 1, 31-37.

(12) Al-Harbi, A.; Rong, Y.; Parkin, G. Inorg. Chem. 2013, 52, 10226– 10228.

(13) (a) Casas, ; arc a-Tasende, M.; Sordo, J. Coord. Chem. Rev. 1999, 193-195,

283–359.

(b) Milan, M.; Holloway, C. E. J. Organomet. Chem. 1995, 495, 1–31.

(14) Wilhelm, M.; Deeken, S.; Berssen, E.; Saak, W.; Lützen, A.; Koch, R.; Strasdeit, H.

Eur. J. Inorg. Chem. 2004, 2301–2312.

(15) Liu, L.; Lam, Y.-W.; Wong, W.-Y J. Organomet. Chem. 2006, 691, 1092–1100.

(16) Fernández, P.; Sousa-Pedrares, A. ; Romero, J.; García-Vázquez, J. A.; Sousa, A.;

Perez-Lourido, P. Inorganic Chemistry, 2008, 47, 2121–2132.

(17) Al-Harbi, A.; Rong, Y.; Parkin, G. Dalton Trans. 2013, 11117– 11127.

(18) Rong, Y.; Palmer, J. H.; Parkin, G. Dalton Trans. 2014, 1397– 1407.

(19) Yang, L.; Powell, D. R.; Houser, R. P. Dalton Trans. 2007, 955– 964.

(20) Lai, C. S.; Tiekink, E. R. T. Acta Crystallogr. Sect. E Struct. Reports Online 2002, 58,

m674–m675. 328

(21) Biernat, A.; Schwalbe, M.; Wallace, D.; Reglinski, J.; Spicer, M. D. Dalton Trans.

2007, 2242– 2244.

(22) Alvarez, H. M.; Tran, T. B.; Richter, M. A; Alyounes, D. M.; Rabinovich, D.;

Tanski, J. M.; Krawiec, M. Inorg. Chem. 2003, 42, 2149–2156.

(23) Chakrabarti, N; Yurkerwich, K.; Parkin, G. unpublished results.

(24) Kimblin, C.; Bridgewater, B. M.; Hascall, T.; Parkin, G. Dalton Trans. 2000, 1267–

1274.

(25) For a list of T-shaped mercury alkyl complexes:

(a) López-Torres, E.; Mendiola, M. A. J. Organomet. Chem. 2013, 725, 28–33.

(b) Canty, A. J.; Chaichit, N.; Gatehouse, B. M.; George, E. E.; Hayhurst, G. Inorg.

Chem. 1981, 20, 2414–2422.

748.

(d) Bach, R. D.; Vardhan, H. B.; Rahman, A. F. M. M.; Oliver, J. P.

Organometallics 1985, 4, 846–852.

(e) Kresinski, R. A.; Fackler Jr., J. P. Acta Crystallogr. Sect. C Cryst. Struct.

Commun. 1993, 49, 1059–1061.

(f) Falvello, L R ; Fornie, ; Mart , A ; Navarro, R ; Sicilia, V ; Villarroya, P

Inorg. Chem. 1997, 36, 6166–6171.

329

(g) Schumann, H.; Freitag, S.; Girgsdies, F.; Hemling, H.; Kociok-Köhn, G. Eur. J.

Inorg. Chem. 1998, 1998, 245–252.

(h) Barbaro, P.; Ghilardi, C. A.; Midollini, S.; Orlandini, A. J. Organomet. Chem.

1998, 555, 255–262.

(i) Forniés, J.; Martín, A.; Sicilia, V.; Villarroya, P. Organometallics 2000, 19, 1107–

1114.

(j) Bebout, D. C.; Bush, J. F.; Crahan, K. K.; Bowers, E. V; Butcher, R. J. Inorg.

Chem. 2002, 41, 2529–2536.

(k) Canty, A. J.; Devereux, J. W.; Skelton, B. W.; White, A. H. Can. J. Chem. 2006,

84, 77–80.

(l) Khan, M. A K.; Asaduzzaman, A. M.; Schreckenbach, G.; Wang, F. Dalt.

Trans. 2009, 5766–5772.

(m) Liu, Q.-X.; Li, H.-L.; Zhao, X.-J.; Ge, S.-S.; Shi, M.-C.; Shen, G.; Zang, Y.;

Wang, X.-G. Inorganica Chim. Acta 2011, 376, 437–445.

(n) Zheng, A.-X.; Li, H.-X.; Hou, K.-P.; Shi, J.; Wang, H.-F.; Ren, Z.-G.; Lang, J.-P.

Dalton Trans. 2012, 41, 2699–2706.

(26) Palmer, J. H.; Parkin, G. Manuscript in progress.

(27) Melnick, J. G.; Yurkerwich, K.; Buccella, D.; Sattler, W.; Parkin, G. Inorg. Chem.

2008, 47, 6421–6426.

(28) Chakrabarti, N.; Sattler, W.; Parkin, G. Polyhedron 2013, 58, 235–246. 330

(29) Sanz, D.; Claramunt, R. M.; Glaser, J.; Trofimenko, S.; Elguero, J. Magn. Reson.

Chem. 1996, 34, 843-846.

(30) Sattler, W.; Yurkerwich, K.; Parkin, G Dalton Trans. 2009, 4327– 4333.

(31) Petrosyan, V. S.; Reutov, O. A. J. Organomet. Chem. 1974, 76, 123–169.

(32) Palmer, J.H.; Chakrabarti, N.; Parkin, G. unpublished results.

(33) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997, 62, 7512-7515.

(34) Smith, W. L. J. Chem. Educ. 1977, 54, 469-473.

(35) Cavanagh, J.; Fairbrother, W.; Palmer, A.; Skelton, N.; Rance, M. Protein

Spectroscopy, 2nd Ed.: Principles and Practice; Academic Press, New York, 1996.

(36) Soares, L.F.; Silva R.M.; Doriguetto, A.C.; Ellena, J.; Mascarenhas, Y.P.;

Castellano, E.E. J. Braz. Chem. Soc. 2004, 15, 695-700.

(37) Chakrabarti, N.; Parkin, G. Unpublished results.

(38) (a) Sheldrick, G. M. SHELXTL, An Integrated System for Solving, Refining and

Displaying Crystal Structures from Diffraction Data; University of Göttingen,

Göttingen, Federal Republic of Germany, 1981.

(b) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112-122.

(39) Jaguar 7.5, Schrödinger, LLC, New York, NY 2008.

(40) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652.

(b) Becke, A. D. Phys. Rev. A 1988, 38, 3098-3100.

331

(d) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200-1211.

(e) Slater, J. C. Quantum Theory of Molecules and Solids, Vol. 4: The Self-Consistent

Field for Molecules and Solids; McGraw-Hill: New York, 1974.

(41) (a) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 270-283.

(b) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985, 82, 284-298.

332