Hydrogen Bonding in Silanols and Their Adducts

Home , Silyl ether

Hydrogen Bonding in Silanols and their Adducts

A Thesis presented by

Lisa Dawn Cother

In partial fulfilment of the requirements for the award of the degrees of

Doctor of Philosophy of the University of London and Diploma of Imperial College

Department of Chemistry Imperial College

London SW7 2AY June 1998 Abstract

ABSTRACT

The work described in this thesis concentrates mainly on the formation of hydrogen bonded adducts of silanols with nitrogen and oxygen containing molecules. Hydrogen bonded adducts of triphenylsilanol, Ph3SiOH, and tetraphenyldisiloxane-1,3-diol, (HOPh2Si)20, with a range of amines, azacrowns, alcohols, ethers and crown ethers have been prepared and characterised by infrared (IR), multinuclear solution NMR and solid state 29Si CPMAS NMR spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The adducts [(Me3S03CSiPh2OH}2.TMEDA, (HOPh2Si)20. { {}10Ph2SiOSiPh20} [Et3N11] } , [(HOPh2Si)20]4.(Et2NH)2, (HOPh2S i)2 0 . dioxane, Ph3SiOH.tris(2-aminoethyl)amine, (Ph3SiOH)2.piperazine, (Ph3SiOH)2.TMEDA and (Ph3SiOH)2.18-crown-6.(H20)2 have also been characterised by X-ray crystallography which reveals a range of hydrogen bonded arrangements. Attempts were also made at preparing, and characterising by X-ray crystallography, unusual or interesting silanols The X-ray structure of tBu2Si(H)OH, a rare example of a stable hydridosilane, is reported. In infrared spectroscopy, the shift in OH streching frequency, AD, between a 'free' SiOH and one involved in hydrogen bonding to a suitable base is proportional to the enthalpy of hydrogen bonding, AH. This relationship was used to assess the relative hydrogen bonding capabilities of a variety of silanols towards bases in solution before adduct formation in the solid state was,attempted. By this method the hydrogen bonding interactions of Ph3SiOH with relatively weak hydrogen bond acceptor molecules such as silyl ethers, siloxanes and alkenes were studied since these species are important in industrial reaction mixtures. The low temperature X-ray structure of the cyclic siloxane (Me2SiO)5 was also determined and the relationship previously proposed between Si-O-Si bond angle and basicity further investigated. Variable temperature infrared spectroscopic studies also enabled the equilibrium constants and enthalpy of hydrogen bonding to be determined quantitatively for Ph3SiOH with a series of ethers. The application of 170 NMR spectroscopy to the study of organosilicon compounds is reviewed and 170 NMR studies carried out on a variety of silanols. The occurance of significant exchange between the OH groups in Ph3SiOH and 170 labelled water was also revealed.

2 Dedication

To My Parents

3 Acknowledgements

ACKNOWLEDGEMENTS

Firstly, I would like to thank my supervisor, Dr. Paul Lickiss, for all his help, encouragement and advice throughout the course of this work. I would also like to thank my industrial supervisors, Dr. Sian Rees and Dr. Richard Taylor (Dow Corning Corporation), for their advice and support, and donations of samples. Thanks must also go to the following people for their help and invaluable services: Paul Hammerton for his time and patience setting up the 170 NMR experiment, as well as helpful discussions and advice on other NMR aspects of this work, also Simeon Bones for setting up the 170 NMR experiment at Dow Corning, Dr. Abil Aliev (University College, London) for the solid state 29Si CPMAS NMR spectra, Prof. David Williams, Dr. Andrew White and Dr. Ian Baxter (Imperial College), and Prof. Mary Mc Partlin and Dr. Nick Choi (University of North London) for X-ray crystallographic studies, Dr. Simon Parsons (Edinburgh University) for low temperature X-ray crystallographic studies, Simon Turner for the loan of many items of equipment, John Barton and Geoff Tucker for mass spectrometry, Hilary O'Callaghan for microanalyses, Dr. Alan Bailey for Raman spectra, and Izoldi Bezougli and Phil Blakeman for themogravimetric analyses. I would like to give a big thanks to the past and present members of the Lickiss research group for providing help, friendship and lots of entertainment over the years: Dipti Shah, Colin Smith, Mark Bronstrup, Phindile Masangane, Guilaine Veneziani and Chris Yates. These thanks are also extended to Carole Dupuy for preliminary research into this project before I started and for her generous hospitality whilst attending the XIth International Symposium on Organosilicon Chemistry in Montpellier. I would also like to thank everyone on the sixth floor for making it an enjoyable and fun place to work. In particular, thanks go to Brent, Nige, Big Steve, Mine and Colin (GBY group), and Phil Dyer, Little Steve, Crispin and Phil B. (DMPM group). Additional thanks go to Phil Dyer for many helpful discussions and practical advice. Many thanks are also due to Edie for brightening up the mornings and her endless kindness and generosity. Thanks go to everyone I met in R & D at Dow Corning, Barry, for their help and for making my time spent there very enjoyable, including the Doonans for their warm hospitality and excellent food. Outside college, I would especially like to thank Sarah Lancaster for being a great friend and flatmate over the last three years and for providing me with such luxurious accomodation. These thanks are also extended to her parents, Mike and Gill, and her sister, Karen, for everything that they have done for me, and for the fun I had. I would also like to thank Roxy, Betty, Alex and Laura for many entertaining evenings out and

4 Acknowledgements dim sum lunches, and Andy for all his patience and encouragement, especially whilst writing up. The EPSRC and Dow Corning Corporation are thanked for financial support via the CASE sheme. Last, but not least, I would like to thank my parents for their continuous support and encouragement throughout my studies.

5 Contents

CONTENTS

Title Page 1 Abstract 2 Dedication 3 Acknowledgements 4 Contents 6 List of Figures 11 List of Tables 15 List of Schemes 17 List of Abbreviations 18

Chapter 1 Introduction 1.1 General introduction 22 1.1.1 The silanol group in nature 22 1.1.2 The silanol group in industry 24 1.1.3 The degradation of polydimethylsiloxanes (silicones) to silanols in the environment 25 1.2 Synthesis of silanols 27 1.3 Acidity and basicity of silanols 29 1.3.1 Acidity 29 1.3.2 Basicity 30 1.4 Hydrogen bonding interactions of silanols 31 1.4.1 The hydrogen bond 31 1.4.2 Infrared spectroscopy in the study of hydrogen bonding 32 1.4.2.1 Correlation between Aus and the enthalpy of hydrogen bond formation, AH 34 1.4.3 Infrared spectroscopic studies of the hydrogen bonding interactions of silanols in solution 35 1.4.4 X-ray crystallographic studies of the hydrogen bonded structures formed by silanols in the solid state 39 1.4.4.1 Compounds containing one SiOH group, silanols 39 1.4.4.2 Compounds containing an Si(OH)2 group, silanediols, or two Si-OH groups, oc,co-siloxanediols 42 1.4.4.3 Compounds containing an Si(OH)3 group, silanetriols 43 1.4.4.4 Compounds containing both Si-OH and other functional groups 44

6 Contents

1.4.5 Hydrogen bonded adducts of silanols with other molecules in the 48 solid state and their X-ray structures

Chapter 2 Infrared spectroscopic studies of the hydrogen bonding interactions of silanols in solution 2.1 Introduction 57 2.2 The relative propensity of a series of silanols towards hydrogen bonding interactions with suitable bases 58 2.3 Infrared spectroscopic studies of the hydrogen bonding interactions between mixtures of silanols in solution 64 2.4 Qualitative infrared spectroscopic studies of the hydrogen bonding interactions between Ph3SiOH and other suitable molecules 65 2.4.1 With silyl ethers and siloxanes 65 2.4.1.1 Low temperature crystal structure of D5 72 2.4.2 With alkenes 75 2.5 Determination of thermodynamic data for hydrogen bonded adducts of Ph3SiOH by infrared spectroscopy 78 2.5.1 Method 78 2.5.2 Thermodynamic data for hydrogen bonded adducts of Ph3SiOH with ethers 82 2.5.3 Thermodynamic data for hydrogen bonded adducts of Ph3SiOH with amines 87

Chapter 3 Hydrogen bonded adducts of silanols 3.1 Introduction 89 3.2 General methods for the preparation of adducts of silanols 90 3.3 Identification and characterisation of adducts of silanols 92 3.4 Adducts of (HOPh2S020 97 3.4.1 With amines 98 3.4.1.1 Primary amines 98 3.4.1.2 Secondary amines 99 3.4.1.2.1 Crystal structure of RHOPh2Si)2014.(Et2NH)2 104 3.4.1.3 Tertiary amines 107 3.4.1.3.1 Crystal structure of (HOPh2S020. ( [HOPh2SiOSiPh20][Et3N11] } 113 3.4.1.4 With nitrogen heterocycles 115 3.4.2 With alcohols 118 3.4.3 With ethers 119 Contents

3.4.3.1 Crystal structure of (HOPh2Si)20.1,4-dioxane 120 3.4.4 With crown ethers 123 3.4.5 With amino acids 123 3.4.6 With mixtures of amines and oxygen containing molecules 124 3.4.7 With phosphines 125 3.5 Adducts of Ph3SiOH 126 3.5.1 With amines 126 3.5.1.1 Primary amines 126 3.5.1.1.1 Crystal structure of Ph3SiOH.tris(2- aminoethyl)amine 127 3.5.1.2 Secondary amines 129 3.5.1.2.1 Crystal structure of (Ph3SiOH)2.piperazine 130 3.5.1.3 Tertiary amines 130 3.5.1.3.1 Crystal structure of (Ph3SiOH)2.TMEDA 135 3.5.1.4 With nitrogen heterocycles 135 3.5.2 With azacrowns 135 3.5.3 With crown ethers 140 3.5.3.1 Crystal structure of (Ph3SiOH)2.18-crown-6.(H20)2 146 3.5.4 With azacrown ethers 149 3.5.5 With amine hydrochlorides 151 3.5.6 With carboxylic acids 152 3.5.7 With phosphines 152 3.6 Adducts of other silanols 153 3.6.1 Adducts of Ph2Si(OH)2 153 3.6.2 Adducts of HO(SiPh2O)3H 154 3.6.3 Adducts of meso-(HOMePhSi)20 and (HOMe2Si)20 156 3.6.4 Adducts of the bulky silanols TsiSiPh2OH and TsiSi(OH)3 156 3.6.4.1 Crystal structure of (TsiSiPh2OH)2.TMEDA 158 3.6.5 Adducts of (-)MePhNaphthSiOH 160 3.6.6 Adducts of tBuMe2SiOH 161 3.6.7 Adducts of cis-cis-cis-[(HO)PhSiO]4 162 3.7 Co-crystallisation of mixtures of silanols 163 3.8 Summary of hydrogen bond lengths and angles found in silanol adducts 164 3.9 Thermal analyses of silanol adducts 167

Chapter 4 Synthesis and structures of miscellaneous silanols 4.1 Introduction 179 4.2 Compounds containing one Si-OH group, silanols 179 4.2.1 Crystal structure of tBu2SiH(OH) 180

8 Contents

4.3 Compounds containing an Si(OH)2 group, silanediols, or two Si-OH groups, oc,co-siloxanediols 184 4.4 Compounds containing an Si(OH)3 group, silanetriols 188 4.5 Compounds containing four Si-OH groups 194

Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts 5.1 Introduction 197 5.2 Solid state 29Si NMR studies 198 5.3 170 NMR 204 5.3.1 Experimental considerations 205 5.3.2 170 NMR studies on organosilicon compounds 207 5.3.3 170 NMR studies of silanols 212 5.3.3.1 170 NMR chemical shifts of silanols 212 5.3.3.2 Effect of hydrogen bonding on the 170 NMR chemical shift 218 5.3.4 170 exchange reactions 221

Chapter 6 Experimental 6.1 Preparation of silanols and their adducts in the solid state 227 6.1.1 General techniques 227 6.1.2 Instrumentation 227 6.1.3 Solvents 228 6.1.4 Starting materials 229 6.1.5 Preparation of compounds containing one Si-OH group, silanols 229 6.1.5.1 Preparation of (-)methylphenylnaphthylsilanol 229 6.1.5.2 Preparation of tert-butyldimethylsilanol 230 6.1.6 Preparation of compounds containing an Si(OH)2 group, 230 silanediols, or two Si-OH groups, a,co-siloxanediols 6.1.6.1 Preparation of dimethylsilanediol, tetramethyldisiloxane-1,3-diol, hexamethyltrisiloxane- 1,5-diol and octamethyltetrasiloxane-1,7-diol 230 6.1.6.2 Preparation of methylphenylsilanediol 231 6.1.6.3 Preparation of 1,3-dimethy1-1,3-diphenyldisiloxanediol 232 6.1.6.4 Preparation of tetraphenyldisiloxane-1,3-diol 234 6.1.6.5 Preparation of hexaphenyltrisiloxane-1,5-diol 235 6.1.7 Compounds containing an Si(OH)3 group, silanetriols 236 6.1.7.1 Preparation of phenylsilanetriol 236

9 Contents

6.1.7.2 Attempted preparation of CH3O(CH2CH2O)2(CH2)3Si(OH)3 236 6.1.7.3 Attempted preparation of CH3O(CH2CH2O)3(CH2)3Si(OH)3 239 6.1.8 Preparation of compounds containing four Si-OH groups 241 6.1.8.1 Preparation of cis-cis-cis-2,4,6,8-tetraphenylcyclotetrasiloxanetetrol 241 6.1.9 Preparation of hydrogen bonded adducts of silanols 242 6.1.9.1 Adducts of (HOPh2Si)20 243 6.1.9.2 Adducts of Ph3SiOH 248 6.1.9.3 Attempted preparation of adducts of Ph2Si(OH)2 257 6.1.9.4 Attempted preparation of adducts of HO(SiPh2O)3H 257 6.1.9.5 Attempted preparation of adducts of meso- (HOMePhSi)20 and (HOMe2Si)20 257 6.1.9.6 Preparation of adducts of the bulky silanols TsiSi(OH)3 and TsiSiPh2OH 257 6.1.9.7 Attempted preparation of adducts of (-)MePhNaphthSiOH 258 6.1.9.8 Attempted preparation of adducts of tBuMe2SiOH 259 6.1.9.9 Attempted preparation of adducts of

cis, cis, cis- RHO)PhS i0i 4 259 6.1.10 Attempted co-crystallisation of mixtures of silanols 260 6.2 Infrared spectroscopic studies 260 6.2.1 Materials 260 6.2.2 Qualitative studies of the hydrogen bonding interactions of silanols with suitable bases and themselves 261 6.2.3 Determination of thermodynamic data for hydrogen bonded adducts of Ph3SiOH 261 6.3 170 NMR studies 262 6.3.1 Instrumentation 262 6.3.2 Solvents 263 6.3.3 Silanols 263 6.3.4 Exchange reactions between Ph3SiOH and 10% 170 enriched H2O 264

References 266 Appendix 287

10 List of Figures

LIST OF FIGURES

Figure 1.1 A schematic representation of a silica surface 23 Figure 1.2 (a) ORTEP plot of [(cyclohexyl)7Si7O9(OH)3]. (b) ORTEP plot of an idealised portion of /3-cristobalite. (c) ORTEP plot of an idealised portion of /3-tridymite. 23

Figure 1.3 Major pathways by which PDMS enters the environment 26

Figure 1.4 Synthesis of silanols from silanes 28 Figure 1.5 Infrared spectrum of 'um of Ph3SiOH upon hydrogen bonding to

dioxane 33 Figure 1.6 Structural units found in silanols with two hydrogen bonding

sites 40 Figure 1.7 The flattened tetrahedral structure of Ph3SiOH, with hydrogen

atoms omitted for clarity 41 Figure 1.8 The hydrogen bonded hexameric unit that builds up the columnar

structure of Ph2Si(OH)2, with hydrogen atoms omitted for clarity 41 Figure 1.9 A view parallel to the double-sheet hydrogen bonded structure formed by tBuSi(OH)3, showing the hydrophilic interior and the

hydrophobic exterior of the sheet 43 Figure 1.10 The hydrogen bonded structure of (2- morpholinoethyl)diphenylsilanol , with the hydrogen atoms

omitted for clarity 44 Figure 1.11 The hydrogen bonded structure of an intramolecularly hydrogen

bonded disiloxanediol 45

Figure 1.12 The hydrogen bonded dimer formed by

(Me3Si)3CSiPh(OMe)OH 46

Figure 1.13 The tetrameric hydrogen bonded structure of TsiSi(OH)202CCF3 47 Figure 1.14 Crystal structure of (decamethy1-7-oxahexasilanorbornane)2.(1,4-

dihydroxydecamethylcyclohexasilane) 47 Figure 1.15 The hydrogen bonded chain structure formed by

(HOPh2Si)20.TMEDA 48

Figure 1.16 Structure of the adduct [(HOPh2Si)20]3.(C4H4N2)2 49

Figure 1.17 Structure of the adduct (HOPh2Si)20.C5H5N.HC1 49 Figure 1.18 A portion of the hydrogen bonded chain formed by the 1:2 complex between 1,1,5,5-tetrapheny1-3,3,7,7-

tetrahydroxycyclotetrasiloxane and pyridine 50 Figure 1.19 The 1:2 host-guest complex (1-naphthyl)3SiOH.(p-xylene)2 with

hydrogen atoms omitted 52

11 List of Figures

Figure 1.20 A view along the c-axis showing the hydrogen bonding in (tBuMe2SiOH)2.H20 52 Figure 1.21 The hydrogen bonded structure of (Me3Si)3CSiF(OH)2, showing the hexameric unit containing two water molecules, [(Me3S03CSiF(OH)2162F120, with hydrogen atoms and methyl groups omitted for clarity 53 Figure 1.22 The structure of cis-bis(2,2'-bipyridine)dihydroxysilicondiiodidedihydrate 53 Figure 1.23 The hexagonal prism formed by [tBu2Si(OH)(ONa)THF]6 54 Figure 1.24 The structure of Ru(CF3CO2)(PPh2CH2SiMe2OH).Et20 54 Figure 2.1 Infrared spectra showing the hydrogen bonding interactions of (HOPh2S020 with the bases mesitylene, diethyl ether, THF, DMSO and pyridine 61 Figure 2.2 Infrared spectra showing the hydrogen bonding interactions of Ph3SiOH with D4and D4MeVi 68 Figure 2.3 Two views of the X-ray crystal structure of D5, hydrogen atoms are removed from the upper view for clarity 73 Figure 2.4 Infrared spectrum showing the hydrogen bonding interactions between Ph3SiOH and allyl ether 77 Figure 2.5 Calculated geometric layout of the 1:1 hydrogen bonded adducts formed by Ph3SiOH with ethers 83 Figure 2.6 Plots of (A0 - A)/A against [B0] for the hydrogen bonding interaction of Ph3SiOH with 1,4-dioxane at different temperatures ranging from 25 - 60 °C. 85 Figure 2.7 The linear least squares plot of lnK against 1/T for the hydrogen bonding interaction of Ph3SiOH with dioxane in CC14 between 25 and 60 °C (R2 = 0.998) 85 Figure 2.8 Plot of All against 10H for the hydrogen bonding interactions of Ph3SiOH with some ethers 86 Figure 3.1 Absorption spectra in the infrared region of (a) Ph3SiOH and its 1:1 hydrogen bonded adducts with (b) 4-NO2C5H4NO, (c) C5H5NO, (d) 4-MeC5H4NO, and (e) 4-Me0C5H4 93 Figure 3.2 A typical endotherm associated with the guest-release reaction of a hydrogen bonded adduct 96 Figure 3.3 IR spectrum of [(HOPh2Si)20]4.(Et2NH)2 in the OH stretching region (KBr disc) 101 Figure 3.4 Infrared spectrum of (HOPh2Si)20.piperazine (KBr disc) 103 Figure 3.5 Proposed structure of (HOPh2S020.piperazine 103

12 List of Figures

Figure 3.6 View of the hydrogen bonding in [(HOPh2Si)20]4.(Et2NH)2 with the phenyl rings removed 105 Figure 3.7 Alternative view of the hydrogen bonding in [(HOPh2Si)20]4.(Et2NH)2 106

Figure 3.8 Molecular structure of [K{O(Ph2Si0)2SiPh2OH}]2•C6H6 109 Figure 3.9 The structures of the strong hindered amine bases (a) DABCO and (b) DBU 109 Figure 3.10 The infinite chain structure formed by (HOPh2Si)20.HMTA 112 Figure 3.11 View of the hydrogen bonded adduct (HOPh2Si)20.{[HOPh2SiOSiPh20][Et3NH]) 114 Figure 3.12 The hydrogen bonded chain formed by (HOPh2Si)20.pyridine 116 Figure 3.13 The hydrogen bonded structure of [(HOPh2Si)20]2.pyrazine 116 Figure 3.14 The hydrogen bonded chain stucture of (HOPh2Si)20.2,2'- bipyridyl 117 Figure 3.15 Stuctures of (a) imidazole, (b) 2-methylimidazole and (c) 1,2- dimethylimidazole 117 Figure 3.16 View of the hydrogen bonded chain formed by (HOPh2Si)20.1,4-dioxane 122 Figure 3.17 View of the hydrogen bonded adduct Ph3SiOH.tris(2- aminoethyl)amine 128 Figure 3.18 View of the hydrogen bonded adduct (Ph3SiOH)2.piperazine 131 Figure 3.19 Positions of the heavy atoms in the X-ray crystal structure of the hydrogen bonded adduct (Ph3SiOH)4.DABCO 134 Figure 3.20 View of the hydrogen bonded adduct (Ph3SiOH)2.TMEDA 136 Figure 3.21 Azacrowns employed in adduct formation 137 Figure 3.21 Structure of (Ph3SiOH)2.18-crown-6.(H20)2 141 Figure 3.22 Infrared spectrum of (Ph3SiOH)2.18-crown-6.(H20)2 (KBr disc) 142 Figure 3.23 Raman spectrum of (Ph3SiOH)2.18-crown-6.(H20)2 in the solid state 143 Figure 3.24 View of the hydrogen bonding in the ternary complex

(Ph3SiOH)2.18-crown-6.(H20)2 147 Figure 3.25 View of the macrocyclic ring in 18-crown-6 showing the positions of the water molecules 148 Figure 3.26 Structure of (Ph3SiOH)2.1-aza-18-crown-6.H20 149 Figure 3.27 Proposed structure of (Ph3SiOH)2.7,16-diaza-18-crown-6 149 Figure 3.28 Structures of (a) 1-aza-12-crown-4 and (b) 1-aza-15-crown-5 149 Figure 3.29 Proposed structure of (Ph3SiOH)2.1-aza-15-crown-5 151 Figure 3.30 The discrete hydrogen bonded adduct [HO(SiPh2O)3H]2.(pyridine)3 155

13 List of Figures

Figure 3.31 The hydrogen bonded arrangement found in [HO(SiPh20)311]4•Pyrazine 155 Figure 3.32 View of the hydrogen bonded adduct (TsiSiPh2OH)2.TMEDA 159 Figure 3.33 TGA and DSC curves for (HOPh2Si)20 168 Figure 3.34 TGA and DSC curves for Ph3SiOH 168 Figure 3.35 TGA and DSC curves for (HOPh2Si)20.DABCO 172 Figure 3.36 TGA and DSC curves for (HOPh2S020.{[HOPh2SiOSiPh20][Et3NH] 172 Figure 3.37 TGA and DSC curves for (Ph3SiOH)2.18-crown-6.(H20)2 174 Figure 3.38 TGA and DSC curves for (Ph3SiOH)4.(DABCO)3 176 Figure 3.39 TGA and DSC curves for (Ph3SiOH)4.DABCO 177 Figure 4.1 Molecular structure of tBu2SiH(OH) 181 Figure 4.2 The tetrameric hydrogen bonded structure of tBu2SiH(OH) 182 Figure 4.3 A view along the c axis showing the stacking arrangement of the cyclic tetramers in tBu2SiH(OH) 183 Figure 4.4 The two isomeric forms of (HOMePhSi)20 186 Figure 4.5 Possible configuration of CH3O(CH2CH2O)3(CH2)3Si(OH)3 189 Figure 4.6 Ab Initio, 3-21G(*), structure calculated for CH3O(CH2CH2O)2(CH2)3Si(OH)3 193 Figure 4.7 Ab Initio, 3-21G(*), structure calculated for CH3O(CH2CH2O)3(CH2)3Si(OH)3 193 Figure 4.8 Hydrogen bonded structure of the ether solvate of cis, cis, cis- [(HO)PhSiO] 4 195 Figure 5.1 29Si CPMAS NMR spectra of (a) Ph3SiOH and (b) (Ph3SiOH)2.12-crown-4 200 Figure 5.2 29Si CPMAS NMR spectra of (Ph3SiOH)2.TMEDA (a) after 434 scans, 36 minutes and (b) after 2000 scans, 167 minutes 200 Figure 5.3 29Si CPMAS NMR spectra of (a) (HOPh2S 020, (b) (HOPh2Si)20.TMEDA, (c) [(HOPh2S020]4.(Et2NH)2 and (d) (HOPh2Si)20.( (HOPh2SiOSiPh20][Et3NH] 203 Figure 5.4 170 NMR spectrum of tBuMe2SiOH, neat, at 65 °C 216 Figure 5.5 170 Chemical shifts of Ph3SiOH, ppm, in a range of solvents versus Gutmann's donor number 221 Figure 5.6 170 NMR spectrum of 0.44 M Ph3SiOH and 6.17 M 10 % 170 enriched H2O in dioxane 222 Figure 5.7 Calculated and experimental isotope patterns for the molecular ion of Ph3SiOH 225

14 List of Tables

LIST OF TABLES

Table 1.1 Vibrational modes of a hydrogen bonded complex, A-H • • • B 32 Table 1.2 Infrared spectroscopic data for silanols and their hydrogen bonded complexes with bases in CC14 solution 36 Table 1.3 Infrared spectroscopic data for hydrogen bonded complexes of phenol with silanols 37 Table 2.1 Band shifts (cm-1) of the OH stretching frequency, Ap0H, of a variety of silanols due to hydrogen bonding with a range of bases 59 Table 2.2 Au0H (cm-1) of the SiOH group in Ph3SiOH due to hydrogen bonding to silyl ethers and some simple ethers for comparison. ADOH (cm-1) for the analogous interactions of the OH group of phenol are also included for comparison 67 Table 2.3 AbOH (cm-1) of the SiOH group in Ph3SiOH due to hydrogen bonding to siloxanes compared with MOH (cm-1) for the analagous interactions of the OH group of phenol 68 Table 2.4 Average Si-O-Si angles for the cyclic siloxanes, Dr, (where n = 3, 4, 5) and (Me3Si)20 for comparison 71 Table 2.5 Selected bond lengths and anges for D5 determined by X-ray crystallography 74 Table 2.6 M (cm-1) of the SiOH group in Ph3SiOH due to hydrogen bonding to alkenyl groups 77 Table 2.7 Infrared spectroscopic and thermodynamic parameters for the hydrogen bonding interactions of Ph3SiOH with a series of ethers in CC14 84 Table 3.1 Selected bond lengths and angles in the crystal structure of [(HOPh2S 020] 4.(Et2NH)2 107 Table 3.2 Selected bond lengths and angles in the crystal structure of (HOPh2Si)20. { [HOPh2SiOSiPh20][Et3NH] } 115 Table 3.3 Selected bond lengths and angles in the crystal structure of (HOPh2Si)20.1,4-dioxane 121 Table 3.4 Observed Raman wavenumbers (cm-1) and vibrational assignments for (Ph3SiOH)2.18-crown-6.(H20)2, Ph3SiOH and 18-crown-6 144 Table 3.5 Selected bond lengths and angles in the crystal structure of (Ph3SiOH)2.18-crown-6.(H20)2 148 Table 3.6 Summary of structural data for selected hydrogen bonded adducts of silanols 165 Table 3.7 Thermal analyses of some adducts of (HOPh2Si)2O and Ph3SiOH 169

15 List of Tables

Table 4.1 Selected bond lengths and angles in tBu2SiH(OH) 181 Table 5.1 29Si CPMAS NMR chemical shift values, ppm, for (HOPh2Si)20 and Ph3SiOH and their adducts. Solution 29Si NMR chemical shift values are included for comparison 199 Table 5.2 Properties of the 170 isotope 205 Table 5.3 170 Chemical shift values, ppm, for some silanols calculated from Riihlmann's increment system (this work) 214 Table 5.4 170 Chemical shift values, ppm, for some silanols at natural abundance 215 Table 5.5 Influence of solvent on 170 chemical shift of Ph3SiOH compared with Gutmann's donor number 220

16 List of Schemes

LIST OF SCHEMES

Scheme 1.1 Hydrolysis of alkoxysilanes 24

Scheme 1.2 Hydrolysis of chlorosilanes 25 Scheme 4.1 Proposed reaction scheme for the preparation of silanetriols of

the formula CH30(CH2CH20)n(CH2)3 (n = 2, 3) 190

17 List of Abbreviations

LIST OF ABBREVIATIONS

3-21G(*) A basis set in which each inner-shell atomic orbital is written in terms of three Gaussian functions, and each valence-shell atomic orbital is split into two parts, written in terms of two and one Gaussians, respectively. Second row and heavier main group elements are also supplemented with a set of six d-type Gaussian functions. 6-31G(*) A basis set in which each inner-shell atomic orbital is written in terms of six Gaussian functions, and each valence-shell atomic orbital is split into two parts, written in terms of three and one Gaussians, respectively. Non- hydrogen atoms are also supplemented with a set of six d-type Gaussian functions. 8 chemical shift (in ppm) OH enthalpy of hydrogen bond formation AG Gibbs free energy AS entropy 6,1)0H difference in the O-H stretching frequency between a 'free' OH and one involved in hydrogen bonding to a suitable base 1)0H OH stretching frequency a molar extinction coefficient A absorbance AH hydrogen bond donor B hydrogen bond acceptor A-H • • • B hydrogen bonded adduct acac acetylacetonate AM1 Austin Method 1. A semi-empirical molecular orbital method. bipy 2,2'-bipyridine b.p. boiling point iBu iso-butyl nBu n-butyl ±sBu sec-butyl tBu tert-butyl c concentration CI Chemical Ionisation cm-1 wavenumbers CNDO/2 Complete Neglect of Differential Overlap CP Cross-Polarization Calcd calculated 12-crown-4 1,4,7,10-tetraoxacyclododecane

18 List of Abbreviations

15-crown-5 1,4,7,10,13-pentaoxacyclopentadecane 18-crown-6 1,4,7,10,13,16-hexaoxacyclooctadecane cyclam 1,4,8,11-tetraazacyclotetradecane cyclen 1,4,7,10-tetraazacyclododecane Dn (Me2SiO)n DnRR' (RR'SiO)n DABCO 1,4-diazabicyclo[2.2.2]octane DBU 1,8-diazabicyclo[5.4.0Jundec-7-ene dec. decomposes DMF dimethylformamide DMSO dimethylsulfoxide DSC Differential Scanning Microscopy EI Electron Ionisation ESR Electron Spin Resonance equiv. equivalent(s) Et ethyl FAB Fast Atom Bombardment FT Fourier Transform furyl 1-oxacyclopenta-2,4-dienyl HMTA hexamethylenetetramine Hz Hertz IR Infrared s strong m medium w weak br broad J modulus of the coupling constant K equilibrium constant LUMO Lowest Unoccupied Molecular Orbital MAS Magic Angle Spinning m/z mass / charge ratio Me methyl MIBK methylisobutylketone m.p. melting point Naphth naphthyl NMR Nuclear Magnetic Resonance s singlet d doublet t triplet m multiplet 19 List of Abbreviations

OMCTS octamethylcyclotetrasiloxane ORTEP Oak Ridge Thermal Ellipsoid Plot PDMS polydimethylsiloxanes Ph phenyl PM3 Parameterization Method 3. A semi-empirical molecular orbital method. ppm parts per million iPr iso-propyl npr n-propyl Ton onset temperature TGA Thermogravimetric Analysis THE tetrahydrofuran TMEDA N,N,N',N'-tetramethylethylenediamine TMS tetramethylsilane Tsi (Me3Si)3C UV Ultra Violet Vi vinyl

20 CHAPTER 1 Introduction Chapter 1 Introduction

CHAPTER 1 Introduction

1.1 General introduction

Silanols are the silicon analogues of alcohols but, unlike alcohols, all three species from simple silanols of the type R3SiOH to silanediols, R2Si(OH)2, and silanetriols, RSi(OH)3 are well known. Silanols are finding increasing use in organic synthesis, for example, triphenylsilanol as a water surrogate for regioselective palladium catalysed allylations, and triisopropylsilanol as a versatile solid-liquid phase transfer catalyst in the dehydrohalogenation of haloalkanes.1'2 Silanols containing one, two or three Si-OH groups have also received much attention recently as precursors for the preparation of metallosiloxanes, compounds with M-O-Si frameworks, which have many possible applications in both chemistry and materials science due to their thermal stability and catalytic properties.3'4 The silanol group is also important in the chemistry of silica surfaces, in several major industrial processes and is formed in the environment from the breakdown of silicones. These areas are described briefly below.

1.1.1 The silanol group in nature Although organosilanols themselves do not occur naturally in the environment the silanol group is ubiquitous in nature, in particular on the surface of silicate rocks and as dissolved silicic acid, Si(OH)4 which is present in low concentrations in water. The many varieties of silica, Si02, and aluminosilicates (zeolites) also have surface hydroxyl groups (Figure 1.1) at which significant surface chemistry can occur. The simple organosilanols Ph3SiOH and (HOPh2Si)20 have been used previously as models for the surface sites on silicate rocks, (HOPh2Si)20 being a model for adjacent surface sites." The incompletely condensed silsesquioxanes [R7Si7O9(OH)3] (where R = cyclo-pentyl, -hexyl or -heptyl) have also been used as more realistic molecular models for the silanol groups on a silica surface, since the silanol groups are geometrically comparable to the idealised surfaces of /3-tridymite and j3-crystobalite (Figure 1.2).7

Chapter 1 Introduction

OH OH OH OH I I I I Si Si Si Si -07 1 No- -07 I NO" -07 NO- -07 NO- 0- 0- 0- 0-

Figure 1.1. A schematic representation of a silica surface.

(a) (b)

(c)

Figure 1.2. (a) ORTEP plot of [(cyclohexy1)7Si709(OH)3]. For clarity, only C attached to Si are shown. (b) ORTEP plot of an idealised portion of /3-cristobalite. (c) ORTEP plot of an idealised portion of /3-tridymite. The three upper-most hydroxyl groups in parts (b) and (c) are located on J3-cristabolite (111) and /3-tridymite (0001), respectively. Parts

(a)-(c) are plotted on the same scale. Silicon atoms are large cross-hatched circles, carbon atoms are small shaded circles, and oxygen atoms are open circles.?

Chapter 1 Introduction

1.1.2 The silanol group in industry

Industrially, the silanol group plays a number of very important roles, the main ones are described briefly below.

i) Sol-Gel Processes The production of colloidal silica and optical glasses by the sol-gel process in which alkoxysilanes undergo hydrolytic polycondensation reactions forms reactive silanols as the intermediates (Scheme 1.1). A more detailed discussion of the sol-gel process can be found in the literature, for example, see ref. 8.

hydrolysis_ (RO)4Si + H2O (RO)3SiOH + ROH etc. alcoholysis

(RO)3SiOH + (RO)4Si (RO)3SiOSi(OR)3 + ROH

condensation with alcohol formation

2(RO)3SiOH r= (RO)3SiOSi(OR)3 + H2O

condensation with water formation

Scheme 1.1. Hydrolysis of alkoxysilanes.

ii) Silica Surfaces

Silane coupling reactions, in which compounds are tethered to silanol groups at a surface by covalent bonding to give surface modified materials, rely on the hydrolysis of an alkoxysilane to give a silanol which then reacts with a surface hydroxy group with the elimination of water to form a strong siloxane linkage. The uses and preparations of silane coupling agents have been reviewed extensively.9'1°

Chapter 1 Introduction iii) Polysiloxanes Low molecular weight silanols and a,w-siloxanediols, HO(SiR2O)mH are also vital intermediates in the formation of polysiloxanes from chlorosilanes by hydrolysis (Scheme 1.2).

R2 S iC12 21-120 R2Si(OH)2 + 2HC1

-H20 R2Si(OH)2 (R2SiO)n + HO(SiR20)11H

cyclic oligomers linear oligomers

Scheme 1.2. Hydrolysis of chlorosilanes.

There is a vast amount of literature available on the subject of polysiloxanes due to the wide range of functional groups which may be attached to the siloxane backbone, the wide range of molecular weights, viscosity, etc. and, thus, the wide range of applications they have found.11"14

1.1.3 The degradation of polydimethylsiloxanes (silicones) to silanols in the environment

Polydimethylsiloxanes, silicones, possess many unique and desirable properties such as exceptional thermal and chemical stability, low surface tension, hydrophobicity, high dielectric constant and presumed biological inertness. They have, therefore, found a number of diverse applications, for example, in lubricants, polishes, cosmetics and hair- care products, medical implants and antifoams. Since World War II the use of silicones has become widespread and the rapidly increasing production and associated rate of release into the environment of silicones has led to concern over their environmental impact. The most widely used polydimethylsiloxanes which enter the environment on a significant scale are liquids with the long chain structure CH3-[Si(CH3)20]„-Si(CH3)3

(PDMS). They are introduced into the environment via wastewater treatment plants

25 Chapter 1 Introduction where, due to their hydrophobic nature, they partition into the sewage sludge and pass through without being broken down.15 Sewage sludge may be disposed of by a number of pathways which are represented in Figure 1.3.

PDMS

Wastewater Industrial and Refuse into Treatment Urban Landfill Plant Effluent Sites SEWAGE SLUDGE Landfill Sea, Sites Rivers Agricultural II Incineratio SOIL Fertilizer SEDIMENT

AMORPHOUS SILICA SOIL + CO2 + H2O

Figure 1.3. Major pathways by which PDMS enters the environment.

The most attractive method of disposal is to use the sewage sludge as crop fertiliser by which PDMS is introduced into the soil. Research into the environmental fate of silicones has thus concentrated on the ecological effect of PDMS itself and its degradation on soi1.16-25 A number of studies on the degradation of silicones on the soil have shown that PDMS undergoes a clay catalysed degradation to the low moleular weight silanediol, Me2Si(OH)2 (m.p. 96-101 °C).18-22,24 Therefore, the fate of silicones may depend on the fate of Me2Si(OH)2. Recent studies suggest that a major route of loss of Me2Si(OH)2 from soil will be volatilization.26 Once in the air Me2Si(OH)2 should undergo CH3 oxidation by reaction with sunlight-induced hydroxyl radicals in the air or, if it is washed out of the air in rainfall, it may be oxidised in water by a similar reaction with hydroxyl radicals.27-30 The only other silicone which is produced on a significant scale is octamethylcyclotetrasiloxane, D4 (OMCTS). Although 90 % of it is used at the site of

26 Chapter 1 Introduction manufacture in the synthesis of PDMS materials, the remainder (- 4.5 million kg/year) is used in skin and hair products, antiperspirants and automobile polishes/protectants, etc.31 Since the release of OMCTS by industry is strictly controlled, the major source of OMCTS in the environment is from consumer products.31 The relatively high volatility of OMCTS (vapour pressure32 0.681 mm Hg, 20 °C) means that it predominantly enters the atmosphere either directly or indirectly where it is oxidised by the hydroxyl radical and ultimately undergoes mineralisation.33

1.2 Synthesis of silanols

Silanols have a tendency to undergo self-condensation to form a siloxane particularly in acidic or alkaline conditions and upon heating. These reactions have been discussed in Section 1.1.2 for their industrial uses. Their isolation can, therefore, only be achieved by careful choice of reaction conditions such as low concentration (since the condensation reactions are bimolecular in silanol), low temperature and neutral pH. The size and shape of the substituents attached to silicon also affects the propensity of the silanol to undergo condensation eg. the presence of bulky substituents such as tBu or (Me3Si)3C (Tsi) on silicon considerably reduces condensation reactions and the precautions mentioned above can often be relaxed. Also compounds containing more than one silanol function such as Si(OH)2 or Si(OH)3 are more susceptible to condensation reactions.

The most common ways of preparing and isolating silanols have been summarised below. A more detailed discussion of preparative routes can be found in ref. 34. i) From silicon halides This is the most widely used method for the production of silanols and disiloxanediols, and the commercially available chlorosilanes show particularly useful reactivity. Silicon halides may be hydrolysed under a variety of conditions but fluorosilanes require alkaline hydrolysis conditions. The hydrolysis of halosilanes results in the formation of strong acids, HX (X = Cl, Br or I), which must be removed by the addition of a base eg. triethylamine or aniline to form the corresponding hydrochloride, or

27 Chapter 1 Introduction neutralised by adding KOH or NaOH to the reaction solution. These reactions are generally carried out at low temperatures using dilute solutions. ii) From Si-H groups Silanols may be prepared from compounds containing the Si-H group, usually by oxidation or hydrolysis. This often avoids the presence of acidic or basic species and can be used for the preparation of sensitive compounds. Examples of these reactions are given in Figure 1.4.

AgNO3 or AgNO2

PhCO3H

02 for n = 3 or 02 hv, or (PhCH2O)2 R4_,SiHn R4_„Si(OH)„ n = 1, 2, or 3 KMnO4

dioxiranes

aqueous acid or base._

[Ph3PCuH]6

Figure 1.4. Synthesis of silanols from silanes.34

iii) From Si-O and Si-S functions The hydrolysis of alkoxysilanes has been widely researched due to its application in sol-gel processes and for silane coupling reagent reactions. Since no acids or bases are formed during the reaction, only alcohols, this method may be used for preparing sensitive silanols and disiloxanediols, eg.:

R4_nSi(OR')n + n H2O R4_,,Si(OH)n + nR'OH

28 Chapter 1 Introduction

Although acetates, triflates, perchlorates and sulfates may also be hydrolysed the production of strong acids is a disadvantage, as discussed earlier.

R3SiSH and (R3Si)2S species may also be readily hydrolysed.34 iv) From Si-N functions

Compounds containing a Si-N bond eg. silylamides, may be readily hydrolysed to give silanols. A basic by-product such as ammonia or an amine is also generated and must be neutralised, for example, by dilute HC1.34 v) From Si-C bonds

If a compound contains a carbon centred substituent that can act as a relatively good leaving group, eg. allyl or pentahalophenyl, then the Si-C bond may be hydrolysed.34

1.3 Acidity and basicity of silanols

1.3.1 Acidity

The high acidity and reactivity of silanols was first noticed in 1946 when Sommer et al. found that Et3SiOH reacted rapidly with sodium in xylene and that Me3SiOH was rapidly converted to its sodium salt in 12 M NaOH.35 The relatively high acidity of silanols in comparison with carbinols was subsequently established, predominantly by acid/base titration and IR spectroscopic studies.34 Badger and Bauer have shown that in spectroscopic studies the difference in the O-H stretching frequency between a 'free' OH and one involved in hydrogen bonding to a suitable base, Au, is approximately proportional to AH.36'37 Such measurements have been used for many years to give an estimate of the strength and relative acidity of the OH groups in a wide variety of silanols and alcohols. These studies have shown that the strength of the hydrogen bonding interaction for silanols is nearly twice as large as that for carbinols.38 For example, the shift in frequency on going from 'free' Ph3SiOH to Ph3SiOH hydrogen bonded to acetone is 226 cm-1 whereas the corresponding change from 'free' Ph3COH to the acetone complex is only 120 cm-1.

29 Chapter 1 Introduction

West studied the OH frequency shifts for a series of silanols and alcohols upon hydrogen bonding to the bases ether and mesitylene and, thus, established the order of relative acidities: arylsilanols > alkylsilanols > arylcarbinols > alkylcarbinols.3 8 The presence of phenyl groups bonded to the central atom was found to increase the acidity of both silanols and carbinols.

1.3.2 Basicity The relative basicities of a series of alcohols and silanols were also studied by West by measuring the shift of the OH band of phenol on hydrogen bonding to the hydroxyl compound.38 The order of basicity was found to be alkylcarbinols > alkylsilanols > arylcarbinols arylsilanols. The values for the alkyl substituted carbinols were only about 20% larger than for the silanols, implying that despite their enhanced acidity, silanols are nearly as basic as alcohols (in alcohols there is an inverse relationship between acidity and basicity).

For a number of years the relative basicity (in comparison to alcohols) and high acidity of the silanol group was explained by invoking (p - d)n bonding between silicon and oxygen.38'39 This involves an overlap between one of the oxygen lone pairs and the vacant silicon 3d orbitals allowing the negative charge of an R3Si0- ion to be delocalised, thus giving an enhanced acidity. The remaining lone pairs on the oxygen atom would allow silanols to be still almost as basic as carbinols, despite the high acidity of the SiOH group. Although this appears superficially reasonable, it has now been discredited since calculations have shown that d orbital contribution is relatively unimportant in the Si-O bond and that the high ionic character of the bond is much more significant.40-45

30 Chapter 1 Introduction

1.4 Hydrogen bonding interactions of silanols

The high acidity and the relatively high basicity of silanols means that silanols are capable of interacting via hydrogen bonding both with themselves and with other suitable species. These interactions are of particular interest since there are a number of molecules which co-exist in industrial reactions or that are present in the environment with which the silanol group is capable of hydrogen bonding.

1.4.1 The hydrogen bond

Hydrogen bonding is the term given to the interaction between a hydrogen atom bound to a more electronegative atom, A—H, and any a or IT electron donor site (Lewis base), B:

5— 5+ A—H • • • B where A = 0, N, F, S, C etc. B = 0, N, F etc.

The strengths of hydrogen bonds range from around 3 Id mol-1 for weak hydrogen bonds such as O-H • • • It, to 155 kJ mo1-1 (HF2-) for the strongest when the proton is approximately equidistant between A and B. The majority of hydrogen bonds, however, are in the range 10 - 40 kJ mo1-1.

Since the recognition of hydrogen bonding in 192046 there has been an overwhelming volume of literature produced on the subject. In particular, more detailed discussions of hydrogen bonding may be found in several reviews on the subject,47-52 a full discussion is beyond the scope of this work.

A variety of spectroscopic and other techniques have been used to detect and study hydrogen bonding including NMR, IR, Raman, ESR and UV-Visible spectroscopy, and X-ray and neutron diffraction.48•51,53

Chapter 1 Introduction

1.4.2 Infrared spectroscopy in the study of hydrogen bonding

One of the most widely used techniques for identifying the presence of a hydrogen bond is infrared spectroscopy since the vibrational modes are particularly sensitive to such interactions. The vibrational modes of a hydrogen bonded complex are given in Table 1.1.51

Table 1.1. Vibrational modes of a hydrogen bonded complex, A-H • • . B.51

Region Description

-41E- --30.- --).- us A—H Stretch 3500 - 2500 cm-1 A — H B

t 1700 - 1000 cm-1 A —H- - - -B 1)13 A—H In-plane bend i'

+ 900 - 300 cm-1 A —H B Ut A—H Out-of-plane benda

-40- -4.- 250 - 100 cm-1 A— H B 'pa H- - -B Stretch

t Below 200 cm-1 A— H B 113, uy H- - -B Bendb i'

a ± Indicates vibrational movement perpendicular to the A-H • • • B plane. b up = in- plane hydrogen bond bending mode; o -= out-of-plane hydrogen bond bending mode.

Chapter 1 Introduction

Upon the formation of a hydrogen bond the most significant spectral changes are:

i) a decrease in the A-H stretching frequency, vs

ii) an increase in the band width and band intensity of the A-H stretching frequency, us

iii) an increase in the A-H bending frequency, -013, and lk

In addition to displaying a smaller shift in frequency than vs upon hydrogen

bonding, the bending frequencies, vb and vt, are located in the fingerprint region and vb is often coupled with other vibrational modes.54 The A-H stretching frequency, us, is

therefore most commonly chosen to study hydrogen bonds due to its sensitivity and ease of measurement. For example, the differences in frequency, &o, band width and band intensity of DOH for Ph3SiOH upon hydrogen bonding to dioxane in CC14 solution are

shown in Figure 1.5.

% loos T r 90' a n 80' S m 70. 'free' OH 1 t 60. t 50. a n hydrogen bonded OH 40. C e I 3850 3600 3350 3100 Wavenumbers

Figure 1.5. Infrared spectrum of um of Ph3SiOH upon hydrogen bonding to dioxane.

(0.01 M Ph3SiOH + 0.05 M dioxane in CCI4).

33 Chapter 1 Introduction

There have been a number of important relationships found between Aus and the physical properties of the hydrogen bonded system. The first and most important was proposed by Badger and Bauer in 1937.36,37

1.4.2.1 Correlation between Aus and the enthalpy of hydrogen bond formation, All Badger and Bauer proposed a linear relationship between the difference, Avs, in the O—H stretching frequency between a 'free' OH and one involved in hydrogen bonding to a suitable base and the enthalpy of hydrogen bond formation, AH.36'37

Although this relationship was subsequently challenged and found to be non- universa1,55'56 the validity of this relationship when considering the hydrogen bonding interactions of one hydrogen bond donor with a series of relatively similar hydrogen bond acceptors has been proved and the following relationship postulated:57-69

-AH = a.ku + b (1.1) where a and b are functions of the nature of the hydrogen bond donor. As a rule, the coefficient a decreases and b increases on going to another type of hydrogen bond acceptor series with a higher average All value.58

Later, in the 1970's, Orville-Thomas and co-workers7°-72 used AH and DOH values for phenols and alcohols with various bases to propose a universal non-linear relationship for AD against AH formed by O—H groups based on the charge transfer

model of hydrogen bonds:

-AH = 0002 _ u2)1/2 + d (1.2)

where vo and D are the wavenumbers of the 'free' and hydrogen bonded O-H bands and c

and d are coefficients derived from the theory.

34 Chapter 1 Introduction

Using the same experimental data Iogansen73 also proposed an empirical relationship which described the data more effectively:

-AH = 75.24 Au / (AD + 720) (1.3) where AH is in Id mol-1 and Au is in cm-1. The value 75.24 kJ mol-1 corresponds to the

'proton transfer' limit for hydrogen bonding. The coefficient 720 is a constant derived from fitting the data.

Relationships (1.2) and (1.3) were derived from Au values obtained from solutions in CC14 and can only be applied to these experimental conditions.

Other correlations which have been prOpOSed48'51'74'75 include:

AvAH and A • • • B bond distance (solid state) AvAH and A-H bond length (solid state)

ADAH and the band width, 1)1/2, Of DAH (solution) AUAH and the relative integrated intensity AB of umi (solution)

The last correlation is often difficult to assess since the intensity of um{ is strongly temperature dependent.

1.4.3 Infrared spectroscopic studies of the hydrogen bonding interactions of silanols in solution

Values for the 'free' O-H infrared stretching frequency and the frequency shift, AvOH, upon self-association of a number of silanols in CC14 solution have been obtained.

These have been summarised in a recent review.34 For the silanols R3SiOH (R = Me, Et and Ph) the intensity and frequency shift of

1)0H upon hydrogen bonding to a series of bases has been studied to compare their relative acidities.38'76-82 A selection of these results have been summarised in Table 1.2. Full details of these and other studies may also be found in ref. 34. It can be seen from

Table 1.2 that, for a given silanol, as the base strength is increased there is a

Chapter 1 Introduction

corresponding increase in Amoif. The values of Auce for Ph3SiOH are also much greater

than the values for the trialkylsilanols upon hydrogen bonding to the same base, thus reflecting the enhanced acidity provided by phenyl substituents at the silicon.

Table 1.2. Infrared spectroscopic data for silanols and their hydrogen bonded complexes

with bases in CC14 solution. Data taken from ref. 34.

Silanol Base Free O-H stretch iSx0H OH (cm-1) (cm-1) (kJ mol-1) Me3SiOH 3702 Me3SiOH 189 Mesitylene 71 dioxane 220 Et20 238 THF 265 Et3SiOH 3685 Et3SiOH 185 Mesitylene 62 dioxane 212 Et20 230 Ph3SiOH 3681 Ph3SiOH 206 Mesitylene 79 MeC(0)CH2Ph 185 11.3 MeC(0)Ph 192 11.4 MeC(0)Et 195 15.1 MeC(0)C6H11 222 20.1 (cyclopropy1)2C0 223 17.6 dioxane 283 Et20 319 nBu20 319.5 THF 333

Chapter 1 Introduction

Infrared spectroscopic studies of the hydrogen bonding interactions between phenol and various silanols have also been carried out to give a measure of the relative basicities of silanols (Table 1.3).38'83-85 Full details of these studies may also be found in ref. 34. It can be seen that Ph3SiOH is less basic than the corresponding trialkylsilanols and the addition of siloxane linkages also increase the relative basicities of the silanols.

Table 1.3. Infrared spectroscopic data for hydrogen bonded complexes of phenol with silanols. Data taken from ref. 34.

Silanol ADOH of phenol 6,11

(cm-1) (Id mol-1)

Me3SiOH 216

E 3SiOH 228

Ph3SiOH 175

1Bu2Si(OH)2 208 16.72

(PhCH2)2Si(OH)2 169 13.79

(HOMe2Si)20 268 20.48

HO(Me2SiO)3H 291 22.15

(HOPh2Si)20 190 15.47

HO(Ph2SiO)3H 243 18.81

Infrared spectroscopic studies of silanols with varying concentrations of base also enable equilibrium constants, K, to be derived (Section 2.5.1).48'51 Although equilibrium constant values occasionally appear in the literature, the temperature at which they were obtained, or the units used are not often given. Equilibrium constants, however, calculated for the formation of hydrogen bonds between Ph3SiOH and anisole, substituted anisoles, nitrobenzene and 4-nitrotoluene vary from 0.36 dm3 mol-1 (2-fluoroanisole) to 1.12 dm3 mot-1 (2,6-dimethylanisole) at 25 °C.86 Those calculated for the formation of

Chapter 1 Introduction hydrogen bonds between Ph3SiOH and a series of ketones range from 3.92 dm3 mold for acetophenone to 5.66 dm3 mo1-1 for methylcyclohexylketone at 20 °C.81 Although the temperature is slightly different in each case, the greater degree of association of the complexes with ketones is clearly demonstrated. The equilibrium constants for the formation of hydrogen bonds between the analogous Ph3COH and ketones at 20 °C are in the range 1.31 to 1.88 dm3 mold, also demonstrating the greater degree of association found in hydrogen bonded complexes of silanols in comparison to alcohols.81 From the temperature dependence of the equilibrium constants the enthalpy of hydrogen bond formation, AH, can be calculated (Section 2.5.1).48'51 There is, however, very little thermodynamic data available for hydrogen bonding to silanols. The enthalpies of hydrogen bond formation, AH, for Ph3SiOH with a series of ketones have been obtained spectroscopically and are included in Table 1.2.34,81 Likewise, AH values obtained for the formation of hydrogen bonded complexes of phenol with silanols are included in Table 1.3.34,84 These values, however, were calculated using the relationship postulated in Equation 1.1 (Section 1.4.2.1) where a = 0.016 and b = 0.63 for the hydrogen bonding interactions of pheno1.57 For the interactions of Ph3SiOH with ketones the following linear correlation between AH and Au OH was proposed:81

-AH (kJmo1-1) = (0.272 ± 0.055)Au - (39.1 ± 11.1) r = 0.94 (1.4)

The empirical relationship between OH and AD°H proposed by Iogansen73 for 0-H groups (Section 1.4.2.1) does not appear to correlate satisfactorily with the results obtained.

Chapter 1 Introduction

1.4.4 X-ray crystallographic studies of the hydrogen bonded structures formed by

silanols in the solid state Silanols form a wide range of hydrogen bonded structures in the solid state. These range from simple dimers to infinite chains, infinite layers and three dimensional networks and cages. This is due to the variety of functional groups that are available to

silicon, SiOH, Si(OH)2, Si(OH)3 and siloxanediol, etc., not all of which are common in carbon chemistry. For example, a selection of the hydrogen bonded structures formed by

silanols with two hydrogen bonding sites, e.g. silanediols and disiloxanediols are shown in Figure 1.6, along with some examples. In general, chains [Figure 1.6(e), (f), (g)], sheets and three dimensional networks are favoured by increasing the number of SiOH groups present and by reducing the size of the other substituents in the molecule.

Although few silanols have the simple structure, Figure 1.6(a), those with large substituents tend to form the discrete units (c) and (d). Compounds containing both a

single SiOH group and a COH, C=0 or nitrogen function mostly form simple chains as in Figure 1.6(b). An extensive discussion of the hydrogen bonded structures formed by silanols is provided in ref. 34 and only those structures with particular relevance to this work have been described below.

1.4.4.1 Compounds containing one SiOH group, silanols

Compounds containing one Si-OH group and no other functional groups are the most widely studied by X-ray crystallography due to their relative stability in comparison to silanediols and silanetriols. The structures are often monomeric or dimeric in nature. Triphenylsilanol, however, is one of a small number of silanols that form a hydrogen bonded tetramer with the four oxygen atoms occupying the vertices of a slightly flattened tetrahedron (Figure 1.7).87'88 Two sets of two of these independent tetrameric hydrogen bonded units make up the unit cell and the O • • • 0 distances vary from 2.637 to

2.684 A. The analogous group 14 compounds of carbon and germanium also have comparable structures.89'9°

Chapter 1 Introduction

0 Si\ Sim Si Si X / or or HO OH OH OH OH

X = COH, C=0, NR2 etc.

0 0

(a) (b)

R2Si(OH)2 ---- 9 9 R = iPr,93 (e) tB11,94'95 c-C6Hii,96 o-tolyl 97

/\ /\ r/\,..\ 0 0 ,0 • 10 • 1'. ,...... , • • , • • • I • , • , % •, • , . • • s • •• • • • • • • • • s • • . , . I • , • (HOR2Si)20 • • • • • • • • • • I (f) t • % • •I • • • • • • • , R = iPr,98 0\ / 0 0 0 0 0 c-05H999 \/ \/

(g) (HOR2Si)20 R = me,100,101 Et,102 npr,103 ph104,105

Figure 1.6. Structural units found in silanols with two hydrogen bonding sites

40 Chapter 1 Introduction

Figure 1.7. The flattened tetrahedral structure of Ph3SiOH, with hydrogen atoms omitted for clarity.88

2.698 A 2.670 A — i' , "..\' \ s' •o/ , , \ • '. / , • , < i c....44 2.688 A 44001r11) -

2.691 A

2.709 A r - 2.745 A

Figure 1.8. The hydrogen bonded hexameric unit that builds up the columnar structure of

Ph2Si(OH)2, with hydrogen atoms omitted for clarity.88

41 Chapter 1 Introduction

1.4.4.2 Compounds containing an Si(OH)2 group, silanediols, or two Si-OH groups, a,,co-siloxanediols

The discovery that iBu2Si(OH)2 forms a discotic liquid crystalline phase106'107 and that the disiloxanediols (HOR2Si)20 (where R = Et, nPr or nBu), Figure 1.6(g), also form unusual thermotropic liquid crystalline phases 101, 108-110 has led to an increased interest in the structures of other simple silanediols and disiloxanediols. Unfortunately, crystals of iBu2Si(OH)2 suitable for X-ray analysis have so far proved impossible to obtain.

Until recently, only relatively stable silanediols had been characterised by X-ray crystallography due to the difficulties associated with their isolation. A variety of arrangements have been found, including ladder chains, hexamers, tetramers and dimers

(Figure 1.6). For example, the simple diols R2Si(OH)2 (where R = iPr,93 tBu,94'95 c- C6H11 96and o-toly197) form ladder chains as shown in Figure 1.6(e). The structure of Ph2Si(OH)2, however, is more complicated (Figure 1.8).88,111,112 A centrosymmetric hydrogen bonded hexameric unit is formed with a chair-like ring of oxygen atoms with alternate short, medium and long O • • • 0 distances (2.670, 2.688 and 2.698 A). These hexameric units are further linked to others, above and below, to form a column. The OH groups point towards the centre of the column and the phenyl groups point away so as to preclude any hydrogen bonding between the columns. A variety of disiloxanediols have been structurally characterised and examples of the hydrogen bonding arrangements formed are given in Figures 1.6(f) and (g) It can be seen that the structures of (HOMe2S020100,101 a n d

(HOPh2Si)20104'105 comprise siloxane molecules hydrogen bonded to form double chains [Figure 1.6(g)]. The structure of (HOPh2Si)20, in fact, contains three crystallographically independent molecules with Si-O-Si bond angles of 147.8(3), 157.0(3) and 162.5(3) .105 The molecules are hydrogen bonded into helical chains with each silanol group acting as both a hydrogen bond donor and acceptor.

42 Chapter 1 Introduction

The related trisiloxanediol, HO(SiPh2SiO)3H, forms discrete hydrogen bonded dimers comprising both intra- (2.74 A) and intermolecular (2.72 A) 0 • • • 0 hydrogen bonds.113

1.4.4.3 Compounds containing an Si(OH)3 group, silanetriols The propensity of silanetriols towards condensation means that relatively few have been isolated and even fewer structurally characterised. The first crystal structure of a silanetriol was that of c-C6H11Si(OH)3 which has a sheet structure consisting of double layers of molecules joined so as to give a hydrophobic outer surface, thus preventing further interaction between the sheets.114 Tert-butylsilanetriol also comprises sheets, with alternating tBu groups above and below the sheet which prevent interactions between the sheets (Figure 1.9).115 All three acceptor and three donor hydrogen bonding sites are used in the interaction with four other molecules. The highly bulky silanetriols, (Me3Si)3CSi(OH)3 and (Me3Si)3SiSi(OH)3, have 117 also been structurally characterised and both comprise hexameric cages.116'

Figure 1.9. A view parallel to the double-sheet hydrogen bonded structure formed by tBuSi(OH)3, showing the hydrophilic interior and the hydrophobic exterior of the sheet.

Hydrogen atoms are omitted for clarity.34

43 Chapter 1 Introduction

1.4.4.4 Compounds containing both Si-OH and other functional groups

There are also a number of silanols which also contain oxygen, nitrogen, halogen or 7C functional groups which form inter- or intra-molecular hydrogen bonds to the silanol group. These have also been reviewed extensively in ref. 34.

In particular, the series of sila drugs, silicon analogues of drugs, provide a wealth of examples of intra- and intermolecular Si-OH • • • N hydrogen bonding.118-126 For example, Figure 1.10 shows the infinite chain structure of (2- morpholinoethyl)diphenylsilanol which is formed by intermolecular O-H • • • N hydrogen bonds [0-H • • • N distance 2.776(8) A, O-H • • • N angle 168(3) °J.118

Recently the structure of 3-(cyclohexylamino)propyldimethylsilanol was reported to show a similar chain structure comprising intermolecular O-H • • • N hydrogen bonds.127

Figure 1.10. The hydrogen bonded structure of (2-morpholinoethyl)diphenylsilanol, with the hydrogen atoms omitted for clarity. 34

44 Introduction Chapter 1

CI"

NMe2 Me2HN+ CI-

Figure 1.11. The hydrogen bonded structure of an intramolecularly hydrogen bonded

disiloxanedio1.34

Unlike the disiloxanediols discussed in Section 1.4.4.2, the disiloxanediol shown

in Figure 1.11 only contains intramolecular 0-H • • • N hydrogen bonds (0 • • • N distance

2.644 A).128 The Si-O-Si linkage is linear, as in the adducts of (HOPh2Si)20 with the

amines pyridazine6 and TMEDA129 (Section 1.4.5) and in [(H0)2tBuSi]20.130

The trisiloxane HOtBu2SiOSiMe20SitBu2NH2 forms an intramolecular

O-H • • • N hydrogen bond [0 • • • N distance 2.859(4) A, O-H • • • N angle 151.5(27)1.131

In this case, intermolecular hydrogen bonding appears to be prevented by the bulky tBu

groups.

Another common interaction found in the solid state, particularly for sterically hindered silanols, is OH • • • it bonding to phenyl rings. This is exemplified by the

structures of the related silanols (PhMe2Si)3CSiMeR(OH) (where R = H132 or Me133)

and by (PhMe2Si)3CSiH2(OH)134 which solely contain intramolecular OH • • • it

interactions with a phenyl ring.

45 Chapter 1 Introduction

Tsi(Me0)Si - H \ • .0 SiPh(OMe)Tsi 0—H --

Figure 1.12. The hydrogen bonded dimer formed by (Me3Si)3CSiPh(OMe)OH.

In the dimeric structure of (Me3Si)3CSiPh(OMe)OH, an alkoxysilanol, both an intermolecular O-H • • • OH and an 0-H • • • TC interaction are present but no OH • • • OMe interactions.(Figure 1.12).91'133

The structure of the cc,w-silanediol HO(SiPh2)70H also contains a combination of 135 intermolecular 0-H • • • 0 and intramolecular 0-H • • • TC interactions.

The bulky silanediol TsiSi(OH)2O2CCF3 forms a hydrogen bonded tetramer via a combination of O-H • • • 0 and 0-H • • • O=C interactions (Figure 1.13), the fluorine playing no part in the hydrogen bonding interactions.136 Likewise, the racemic acetylsilanol tBu(Me2SiCH2)Si(OH)C(0)CH3, contains O-H • • • O=C hydrogen bonds linking the molecules to form simple chains.137

An example of a OH • • • X interaction is provided by

[OsCl(CO)(PPh3)2Si(OH)2]20 which contains a weak intramolecular OH • • • Cl interaction (0 • • • Cl distance 3.17 A) and possibly OH • • • it interactions.138

Although silanol to siloxane hydrogen bonding interactions in the solid state are relatively rare,139- 141 a particularly interesting example of silanol to siloxane hydrogen- bonding is shown in Figure 1.14 between two molecules of decamethyl-7- oxahexasilanorbornane and one molecule of 1,4-dihydroxydecamethylcyclohexasilane.I39

In the solid state silanols usually preferentially bond to other more basic sites but in this case the silanol groups sterically do not have much choice. Intermolecular silanol to siloxane hydrogen bonding has also been reported in the structure of

HOMe2SiCHSiMe2OSiMe2OSiMe2 1 4 0 and its nitrogen analogue 1 HOMe2SiNSiMe20SiMe20SiMe2,141 even in the presence of a more basic amine site.

46 Chapter 1 Introduction

C(SiMe3)3 Si 0// \O

H/ H I, CR . ,,/H-"O' . 0 .. H -- OS \ (Me3Si)3CSict\---°-19 - ° 0=R—o /S i C (S i M e 3 )3 O, H R ---;.,o' . 0" ...H .% II ,' CR H H \ 0 p R = CF3 \// Si C(SiMe3)3 Figure 1.13. The tetrameric hydrogen bonded structure of TsiSi(OH)202CCF3.34

• Si 3 Cts • Si4 Sia

C tr Si 7 CSi~Si 31 "elf C11 • CS Sia 11/ C to C12 C13

Figure 1.14. Crystal structure of (decamethy1-7-oxahexasilanorbornane)2.(1,4- dihydroxydecamethylcyclohexasilane).139

47 Chapter I Introduction

1.4.5 Hydrogen bonded adducts of silanols with other molecules in the solid state and their X-ray structures The isolation of hydrogen bonded adducts of silanols with other molecules in the solid state was first reported by Prescott and Selin in 1965.142 They reported that the disiloxanediol (HOPh2Si)20 formed solid 1:1 adducts with pyridine, Et3N, Et2NH, PhNH2 and TMEDA and that the trisiloxanediol HO(Ph2SiO)3H formed a 1:1 adduct with pyridine.142 Selin also prepared 1:1 adducts of the unsymmetrical disiloxanediol HOPh2SiOSiMePhOH with pyridine and with Bu3N.143 Subsequently, structural characterisation of the 1:1 adduct formed by (HOPh2Si)20 with TMEDA revealed that the adduct comprises an infinite chain of alternate disiloxanediol and TMEDA molecules (Figure 1.15) linked by O • • • N hydrogen bonds (O • • • N distance 2.74 A).129 The Si-0- Si angle is linear, which is significantly different from the usual value of around 140 ° found in disiloxanediols.

Figure 1.15. The hydrogen bonded chain structure formed by (HOPh2Si)20.TMEDA129

The adduct [(HOPh2Si)20]3.(C4H4N2)2 has also been prepared and structurally characterised, containing both OH • • • OH and OH • • • N hydrogen bonds (Figure 1.16).6 It can be seen that the central siloxane molecule in this adduct also has a linear Si-O-Si angle whereas the other two siloxane molecules have a more common value of 144.5°.

Chapter 1 Introduction

Ph2 0 SiPh2 / 0N1I ,.....I .._ Hc ,H0

SrSiPh2 Osliph2i

-L-... .."-\.... /OH' ' N I Ph2Si ill 1 • 0 • `SiPh2 34 Figure 1.16. Structure of the adduct [(1-10Ph2Si)20]3-(C4114N2)2.

A pyridinium hydrochloride adduct (HOPh2Si)20.C5H5N.HC1, has been isolated

from a reaction mixture of the disiloxanediol and TiC14 in the presence of pyridine

(Figure 1.17).144 This is particularly interesting given that amine hydrochlorides are very common by-products in the synthesis of silanols and there is a general lack of such adducts reported in the literature.

Ph2Si'° -- SiPh2 I I 0 0 1 I HH, (I \—H)C1-

Figure 1.17. Structure of the adduct (HOPh2Si)20.C5H5N.HC1.34

Like the a,co-siloxanediols reported by Selin,142,143 1,1,5,5-tetrapheny1-3,3,7,7-

tetrahydroxycycloterasiloxane also forms a hydrogen bonded adduct with pyridine

(Figure 1.18).145 The stoichiometry is 1:2 with the two pyridine molecules trans to each

49 Chapter 1 Introduction other across the siloxane ring. Intermolecular O-H • • • 0 hydrogen bonds also link the silanols to form an infinite chain.

Figure 1.18. A portion of the hydrogen bonded chain formed by the 1:2 complex between 1,1,5,5-tetrapheny1-3,3,7,7-tetrahydroxycyclotetrasiloxane and pyridine. Hydrogen atoms have been omitted for clarity.34

Triphenylsilanol has been found to be selective in its adduct formation and will form an adduct with ethanol, [Ph3Si01-1]4.Et0H, in the presence of water, methanol or propano1.146 The tetrameric structure of Ph3SiOH (Figure 1.7) is retained in this adduct, which has a cyclic network of hydrogen bonds with 0 • • • 0 distances ranging from 2.60 to 2.79 A. Triphenylsilanol also forms a simple centrosymmetric 2:1 adduct with 12- crown-4 ether5 (0 • • • 0 distance 2.76 and O-H • • - 0 1.91 A) and a 4:1 adduct with dioxane.147 In (Ph3SiOH)4.dioxane two pairs of hydrogen bonded Ph3SiOH molecules are joined via further hydrogen bonds to the oxygen atoms in the dioxane molecule.147 Triphenylsilanol forms 1:1 adducts with a series of substituted pyridine N-oxides, 148,149 XC5H4NO (where X= 4-MeO, 4-Me, 2-Me, 3-Me, H, 4-Cl and 4-NO2). Although no crystal structures have been reported, the OH stretching frequencies of the adducts range from 2870 cm-1 for 4-Me0C5H4NO to 3160 cm-1 for 4-NO2C5H4NO

50 Chapter 1 Introduction reflecting the decreasing hydrogen bond acceptor properties of the pyridine N-oxides with 148 149 decreasing electron donating ability of the substituent on the pyridine ring. '

A 1:1 adduct of tBu2FSiOH and pyridine N-oxide has also been reported in which the molecules are held together by an O-H • • • 0 interaction.15° The Si-0 bond is considerably shorter than in other hydrogen bonded silanols due to the electron- withdrawing fluoro substituent.

Tri(1-naphthyl)silanol forms 1:1 adducts with toluene and o-xylene in which the arene molecules lie in channels (having regular constrictions) in the lattice of the silanol molecules.151 The 1:1 adduct with m-xylene is similar, with narrow channels connecting cavities in which the arene guest molecules are found.151 A 1:2 adduct is formed with p- xylene.151 This shows a very different structure containing three crystallographically distinct guest molecules lying in intersecting channels in the lattice, Figure 1.19. It is interesting because no OH • • • 0 hydrogen bonds are present, only OH • • • rt interactions are observed. Tri(1-naphthyl)silanol also forms a discrete 1:1 host guest complex with dioxane in which there is a single OH • • • 0 hydrogen bond leaving the second dioxane oxygen free from hydrogen bonds.147

Anhydrous tBuMe2SiOH is a liquid but on exposure to moisture it rapidly forms a solid hemihydrate, (tBuMe2SiOH)2.H20.152'153 This forms hydrogen bonded chains with the water molecules acting as linkages down the chain (Figure 1.20). The related silanols iPrMe2SiOH, t-hexylMe2SiOH and Ph2tBuSiOH,153 howeVer, do not form simple hydrates but the carbinol tBuMe2COH does.154'155

A hydrogen bonded adduct with water is also formed by the bulky silanol

TsiSiF(OH)2, [TsiSiF(OH)2]6.2H2O, in which two sets of three hydrogen bonded silanediol molecules, related by an inversion centre, are hydrogen bonded together via two water molecules (Figure 1.21).156 Interactions of the type OH • • • F are also present.

The structure of cis-bis(2,2'-bipyridine)dihydroxysilicondiiodidedihydrate (Figure

1.22), synthesised by the hydrolysis of SiI4.2bipy, provides a further example of silanol groups hydrogen bonded to water molecules.157

51 Chapter 1 Introduction

Figure 1.19. The 1:2 host-guest complex (1-naphthy1)3SiOH.(p-xylene)2 with hydrogen atoms omitted. The p-xylene molecules are shown drawn with solid lines.34

r . . . ..cr:

. , . Si

Figure 1.20. A view along the c-axis showing the hydrogen bonding in

(tBuMe2SiOH)2.H20. All hydrogen atoms have been omitted.34

52 Chapter 1 Introduction

Si(2b)

Sil6a) Si(9c)

C(21c)

Sioc d, CH3c)

\\ 20017b) 0(7a*:

0(5b) Siab Sat)) 013b1 $44, * S 171D) CI21b) Si(Sb) F(3b1 Sil9b) Sibb Si61D) 0(4b) Si2c)

Figure 1.21. The hydrogen bonded structure of (Me3Si)3CSiF(OH)2, showing the hexameric unit containing two water molecules, [(Me3Si)3CSiF(OH)2]6.2H20, with hydrogen atoms and methyl groups omitted for clarity.34

I H- - -0H2 2I N I -.0 —H- - - OH2

Figure 1.22. The structure of cis-bis(2,2'-bipyridine)dihydroxysilicondiiodidedihydrate.34

Chapter 1 Introduction

There are also some examples of silanols which crystallise out as solvates,

forming hydrogen bonded adducts with solvent molecules such as THF, Et20 or EtOH.

For example, Nu2Si(OH)(0Li).THFL forms a tetramer held together by Si-O-Li

interactions, with the silanol groups involved in 0-H • • • 0 interactions with

the THF molecules (OH • • • 0 distances 2.64 - 2.78 A).158 The sodium analogue,

[tBu2Si(OH)(0Na).THF]6, forms a hexagonal prism of alternating Na and 0 atoms, with

the silanol groups again involved in O-H • • • 0 interactions with the THF molecules

(Figure 1.23).159 ,thf 0 t • UgU 2 ,• thf. Si ,0 / / 0 Na t b...... SiBU 2 si Na 1 I\0_.. „---- °, But e‹..\0— I NaGf thf thf.s .....Na— —0 s \ N t '0 -.'0 Na SiBu 2 Z But2Si Na 0 'thf \ \ t ,0 SiBu 2 0 r thf 34 Figure 1.23. The hexagonal prism formed by [tBu2Si(OH)(ONa).THF]6.

The ruthenium silanol complex shown in Figure 1.24 forms OH • • • 0 hydrogen

bonds with an ether of crystallisation and the highly sterically hindered disiloxane [(2,6-

Et2C6H3)(2,6-Et2-4-t-BuC6H2)(OH)S 20 forms an ethanol adduct in which two

disiloxane molecules are linked via two ethanol molecules to form a cyclic arrangement of hydrogen bonds. 160-162 Et20 Mee Si O

(CF3CO2)2R) Ph 2 OC CO

Figure 1.24. The structure of Ru(CF3CO2)2(C0)2(PPh2CH2SiMe2OH).Et20.34

54 Chapter 1 Introduction

The ability of silanols to form hydrogen bonds with other molecules containing potential hydrogen bonding sites has a variety of implications and applications. As described previously the silanol group is ubiquitous in nature, e.g. on the surface of silicate rocks, is important in several major industrial processes and is formed in the environment from the breakdown of silicones. There are many molecules containing, for example, oxygen or nitrogen sites such as water, amines, alcohols and ethers in the natural environment and in industrial process mixtures with which these silanol groups may interact. It is also clear that silanols, e.g. Ph3SiOH, are highly selective in adduct formation which may be used to effect chemical separations. The hydrogen bonded adduct may then be broken down by heating for example, or dehydration as in the case of (tBuMe2SiOH)2.H20,153 and the silanol recovered and recycled.

Recently, Ab initio studies of the hydrogen bonding interactions of silanols acting as proton donors to water have been carried out.163 The calculations revealed that the basicity of the silanol oxygen is strongly enhanced when the silanol group is involved in a hydrogen bond as a proton donor, - 54 - 113 kJ mol-1 more basic than the free silanol group. Thus, hydrogen bonded adducts of this type should show enhanced reactivity in condensation reactions of silanols. It has also been shown that the acidity of silanol groups involved in hydrogen bonds as proton acceptors in hydrated silica gel is greatly enhanced.164

Thus, the wide variety of situations in which silanol groups play a significant role, together with their interesting physical properties and structures described above make them an important class of compounds on which to obtain more detailed information. In particular, despite the industrial importance of the silanol group in condensation reactions, relatively little is known about the thermodynamic aspects of the hydrogen bonds to silanols. Also, the factors governing the extent and type of hydrogen bonded structures formed by silanols are little understood, and a better understanding might lead to the design of hydrogen bonded adducts with particular structures and useful properties. The work described in the following Chapters thus addresses both the thermodynamic and the structural features of hydrogen bonding to silanols.

55 CHAPTER 2

Infrared spectroscopic studies of the hydrogen bonding interactions of silanols in solution Chapter 2 Infrared spectroscopic studies

CHAPTER 2 Infrared spectroscopic studies of the hydrogen bonding interactions of silanols in solution

2.1 Introduction

As discussed in Section 1.4 infrared spectroscopic studies of silanols in solution have enabled an estimate to be made of the strength and relative acidity of the OH group in silanols compared with the analogous alcohols. Badger and Bauer proposed that the difference in the OH stretching frequency, AvoH, between a 'free' OH and one involved in hydrogen bonding to a suitable base is approximately proportional to the enthalpy of hydrogen bond formation, AH (Section 1.4.2.1).36'37 Although other more universal relationships have been proposed,70-73 the validity of this linear relationship has been proved when considering the hydrogen bonding interactions within a series of relatively similar hydrogen bond acceptors or donors57-69 and is, therefore, widely used for such studies (Sections 1.3 and 1.4). In this chapter infrared spectroscopic studies of the hydrogen bonding interactions of silanols in solution have been used for a variety of purposes. Studies of the interactions of different silanols with a variety of bases in solution have been used as a preliminary assessment of their relative hydrogen bonding capabilities prior to attempting the preparation of hydrogen bonded adducts in the solid state (Chapter 3).

Previous infrared spectroscopic studies of silanols have concentrated on their hydrogen bonding interactions with hydrogen bond acceptors such as ethers, ketones and DMSO. In this work the range of hydrogen bond acceptors has been extended to silyl ethers and the much less basic siloxanes, both of which co-exist with silanols in industrial reactions, and with other weak bases such as alkenes. Variable temperature infrared spectroscopy has also been employed to extend the limited amount of thermodynamic data available for the hydrogen bonding interactions of silanols with other suitable organic species.

57 Chapter 2 Infrared spectroscopic studies

2.2 The relative propensity of a series of silanols towards hydrogen bonding interactions with suitable bases

Before attempting the preparation of hydrogen bonded adducts of silanols with other suitable molecules in the solid state (Chapter 3) it has been useful to estimate their relative hydrogen bonding ability in solution, in comparison with silanols such as Ph3SiOH and (HOPh2Si)20, which are known to form hydrogen bonded adducts in the solid state (Section 1.4.5).5,6,129,142,144,146-149 It is not, however, possible to determine which adducts will be formed in the solid state, since other factors, especially steric, appear to come into play in the solid state.

Infrared spectroscopic studies of a variety of alkyl and aryl silanols, disiloxanediols and a silanetriol were carried out with a range of bases in CC14 solution (Table 2.1). The Avori values for the interactions of TsiSiPh2OH and TsiSi(OH)3 were obtained from a previous study.165 Although at a concentration of 0.02 M the amount of intermolecular hydrogen bonding was negligible for TsiSiPh2OH, it was significant for TsiSi(OH)3. The concentration of TsiSi(OH)3 had to be reduced to 0.001 M in order for the amount of intermolecular hydrogen bonding to be negligible, perhaps due to the presence of extensively hydrogen bonded aggregates, such as the hexameric units found in the solid state.116 Subsequent spectra recorded for the interaction of 0.001 M TsiSi(OH)3 with the bases were of very poor quality, presumably due to the very low concentration of the silanol and the unavailability of a cell with pathlength greater than 6 mm. With the exception of mesitylene, however, the hydrogen bonding interactions of TsiSi(OH)3 with the bases studied are of larger 6,v0H than that for self-association of the silanetriol and, due to the excess of base employed may, therefore, be considered as wholly due to hydrogen bonding interactions with the base alone. Studies of HO(Ph2SiO)3H and Ph2Si(OH)2 were not carried out as previous infrared spectroscopic studies have shown that their hydrogen bonding acidity is of a similar magnitude to that of (HOPh2Si)20 and is unaffected by the extent of the siloxane chain.79'85 HO(Ph2SiO)3H has also been shown to be capable of adduct formation with pyridine in the solid state (Section 1.4.5).142

Chapter 2 Infrared spectroscopic studies

Table 2.1. Band shifts (cm-1) of the OH stretching frequency, Alki, of a variety of

silanols due to hydrogen bonding with a range of bases.

Silanol 'Free' LDOH A'001-1 ADOH LDOH Al.) OH ADOH OH Self- Mesitylene Diethyl THE DMSO Pyridine association ether (HOPh2Si)20 3680a 280 110 329e 356 388 —540 0.01 M 121b Ph3SiOHb 3681d 233d 80e 319d 334f 411d —540 0.01 M MePhNaphthSiOH 3683 222 90 303 328 400 —540 0.01 M 110b Meso- 3684a 318 —85 296 315 378 483 (HOMePhSi)20 116b 0.005 M TsiSiPh2OH 3670g 72g 280g 290g 395g 521g 0.02 M tB uMe2SiOH 3694 192 52 284 352 447 0.005 M (HOMe2Si)2O 3694a 389 273e 287 321 458 0.005 M TsiSi(OH)3 3685g 267g 277g 279g 317g 537g 0.02 M

a In agreement with ref. 166. b Values due to OH • • • it interaction with phenyl rings. a In

agreement with ref. 85. d This work. Literature values vary.34,38,82,83,167-170e In agreement with ref. 38. f In agreement with refs. 82 and 83. g Ref. 165. The infrared spectra of the silanols were recorded in CC14 at silanol concentrations at which the degree of self-association was negligible [except for TsiSi(OH)3, refer to text for further details], these concentrations are given in column 1, underneath the silanol. The bases were used at concentrations of 0.05 M. Values due to self-association were recorded at a silanol concentration of 0.03 M. 'Free' OH values are ± 1 cm-1. LDOH values are ± 2 cm-1

except for those due to OH • • • TE interactions which are ± 4 cm-1.

59 Chapter 2 Infrared spectroscopic studies

Discrepancies are possible when relating acidity solely to hydrogen bonding ability. For example, Ph3SiOH and Ph3SiSiPh2OH give similar Au°H values upon hydrogen bonding to DMSO, 411 and 401 cm-1 respectively, yet the acidity of Ph3SiSiPh2OH has been measured by acid/base titration to be about 2.67 pKa units lower than that of Ph3SiOH.169 The enhanced acidity of Ph3SiSiPh2OH has been attributed to interaction of an oxygen lone pair with the LUMO of the Si-Si system.169 The AOOH values for the selected silanols, upon hydrogen bonding to a series of hydrogen bond acceptors of increasing basicity, are given in Table 2.1. It can be seen from Table 2.1 that all the silanols show the expected increase in AvoH as the strength of the base increases from mesitylene to pyridine. A typical series of spectra for (HOPh2Si)20 can be seen in Figure 2.1.

The shift in the frequency caused by the interaction of silanols with mesitylene is always somewhat smaller than that observed for the other bases. This is because the intermolecular interaction is OH • • • rc rather than OH • • • 0. In the case of (HOMe2Si)20 this shift could not be observed, presumably the interaction is so weak that it is obscured by the base of the 'free' OH band, and for meso-(HOMePhSi)20 this shift was seen as a shoulder on the 'free' OH band. The shift in frequency observed for hydrogen bonding between the silanols (HOPh2Si)2O, Ph3SiOH and MePhNaphthSiOH and pyridine is given as an approximation since the shift is so large that it overlaps with the C-H stretching region of the phenyl rings. Deuteration of the silanols may enable the AD op value upon hydrogen bonding to pyridine to be observed more readily.

Unfortunately, deuteration of (HOPh2Si)20 by recrystallisation of the disiloxanediol from

D20 or Me0D only went halfway to completion and was not pursued further due to the qualitative nature of these studies. As mentioned previously, the order of acidity is not always reflected in the &Doll values upon hydrogen bonding and Table 2.1 shows a number of discrepancies. For example, although (HOPh2Si)2O shows a greater AI) 0 H than Ph3SiOH or

MePhNaphthSiOH upon hydrogen bonding to mesitylene, ether and THF, a smaller Aucgi is observed upon hydrogen bonding to DMSO. Likewise, TsiSi(OH)3 shows a

60 %

T mesitylene r a n s m i diethyl ether t t a n c e

. . 3500 3400 3300 3200 3100 Wavenumbers

Figure 2.1 Infrared spectra showing the hydrogen bonding interactions of (HOPh2Si)20 with the bases mesitylene, diethyl ether, THF, DMSO and pyridine. Chapter 2 Infrared spectroscopic studies much greater Auce upon hydrogen bonding to pyridine than would be expected. These discrepencies may be due to steric interactions.

The 'free' OH stretching frequencies come within the 3660 - 3700 cm-1 region expected for silanols.34 This is higher than the 'free' OH stretching region for carbinols which is usually around 3605 - 3645 cm-1.34 This has been attributed to a number of factors including enhancement of the 0-H bond force constant by the electropositive silicon atom171 and the larger Si-O-H bond angle.38 The 'free' OH bands of the disiloxanediols are in fact slightly asymmetric and consist of two or more overlapping absorptions which may be observed at higher resolution. A detailed explanation of these absorptions in terms of rotational isomerisation is given in ref. 166. Within the series of disiloxanediols, the shift in frequencies of the OH bands due to self-association in solution increase in the order (HOPh2Si)20 < meso-(HOMePhSi)20 < (HOMe2Si)20 showing that the intermolecular hydrogen bonding is greater in the disiloxanediols with methyl substituents. This is borne out by the greater degree of association (relative intensities of 'free' and hydrogen bonded bands) observed in the spectra of the methyl containing disiloxanediols at a given concentration and suggests that steric factors are the most important in determining the degree of intermolecular association.

The silanols which show weaker hydrogen bond donating capabilities towards other molecules in solution often show stronger hydrogen bonding interactions due to self-association at a given concentration (Table 2.1). The relative strength of the hydrogen bonding interactions due to self-association in solution may also be another factor controlling adduct formation. The spectra of 0.03M (HOPh2Si)20, MePhNaphthSiOH and of meso- (HOMePhSi)20, from which the intermolecular hydrogen bonding frequencies were ascertained, also have a weak intermolecular band at 3559, 3573 and 3568 cm-1 respectively. Harris also observed the band for (HOPh2Si)20 and similar bands in 0.03M solutions of hexaphenyltrisiloxane-1,5-diol, 1,3,5-trimethy1-1,3,5-triphenyltrisiloxanediol and the racemic form of 1,3-dimethyl-1,3-diphenyldisiloxanediol as a shoulder on the

62 Chapter 2 Infrared spectroscopic studies hydogen bonded hydroxy peak.172 These peaks are due to interactions with the phenyl rings resulting in an intermolecular OH • • • IT bond. This accounts for the smaller shift in frequency from the 'free' OH band than for an OH • • • 0 band because of the relatively low basicity of the aryl ring. Upon dilution of these solutions the bands disappear, confirming that these interactions are intermolecular and not intramolecular in origin.

Intramolecular OH • • • it interactions have been observed previously for the siloxanols

(PhCH2Me2Si0)3SiOH and Me3_„(PhMe2SiOSi)„ SiOH (n = 1 - 3)173 , the poly(diphenylsilane)diols HO-(SiPh2)n-OH (n = 4, 5, 7)170 and the sterically hindered silanols (PhMe2Si)3CSi(OH)3 and (PhMe2S03CSiH2OH165 in dilute CC14 solution.

From the values in Table 2.1 it can be seen that on going from (HOPh2Si)20 to TsiSi(OH)3 there is an average decrease in UGH for a given base of between

50 - 70 cm-1, although a number of anomalies exist. The order of hydrogen bond acidity, therefore, based on AD0H values is:

(HOPh2Si)20 > Ph3SiOH > MePhNaphthSiOH > (HOMePhSi)20 > TsiSiPh2OH > tBuMe2SiOH > (HOMe2Si)20 = TsiSi(OH)3

The values for the self-association of the silanols do not vary so consistently. Although tBuMe2SiOH shows significantly smaller AD oH values than

(HOPh2Si)20 upon hydrogen bonding to the series of bases, tBuMe2SiOH is known to form a hydrogen bonded adduct with water, (tBuMe2SiOH)2.H20, in the solid

State.152'153 It, therefore, seems reasonable that the hydrogen bonding acidity of all the silanols studied is suitably high for the formation of hydrogen bonded adducts in the solid state. The discrepencies observed also stress the role that steric factors play in addition to acidity/basicity in adduct formation and the difficulties involved in predicting such interactions.

63 Chapter 2 Infrared spectroscopic studies

2.3 Infrared spectroscopic studies of the hydrogen bonding interactions between mixtures of silanols in solution

Attempts at co-crystallising mixtures of different silanols were unsuccessful

(Section 3.7). It was, therefore, of interest to study whether hydrogen bonding interactions would occur between mixtures of different silanols and disiloxanediols in solution.

Infrared spectroscopic studies of the hydrogen bonding interactions between the following mixtures of silanols and disiloxanediols were considered:

Ph3SiOH and (HOMe2Si)20

Ph3SiOH and (HOPh2Si)20

(HOPh2Si)20 and (HOMe2Si)20

The intended hydrogen bonding studies between Ph2Si(OH)2 and other silanols/disiloxanediols were not carried out as Ph2Si(OH)2 was found to have a very limited solubility in CC14.

Two different approaches were taken to these infrared spectroscopic studies. The first involved treatment of the two silanols as for the studies of silanol base hydrogen bonding interactions. The OH region of the infrared spectrum of one silanol, at a concentration at which the degree of intermolecular hydrogen bonding was negligible

(-0.005 - 0.01 M), was studied upon addition of an excess of the other silanol (0.05 M).

Unlike the non self-associating bases studied previously, however, at 0.05 M the silanols show strong self-association. The roles of the two silanols were then exchanged and the experiment repeated. Although it appears that slight hydrogen bonding interactions are occurring, since a small decrease in the intensity of the 'free' OH band is observed, the spectra have a high noise level in the hydrogen bonded OH region and no MOH values can be obtained.

The other approach taken was to study the OH region of the infrared spectrum of both silanols, in turn, at concentrations at which individually they displayed a negligible degree of intermolecular hydrogen bonding but on combination would be at a concentration at which hydrogen bonding interactions usually occur. Very weak

64 Chapter 2 Infrared spectroscopic studies hydrogen bonded bands appear to be present but they are too weak to assign AU0H values.

Since the hydrogen bonding interactions for both approaches are weak and the spectra of poor quality, no 6,10H values were able to be obtained and it is difficult to say precisely whether the silanols are bonding to like silanol molecules or to different silanol molecules.

2.4 Qualitative infrared spectroscopic studies of the hydrogen bonding interactions between Ph3SiOH and other suitable molecules

The most commonly used silanol in infrared spectroscopic studies is Ph3SiOH due to its relatively high acidity and stability to condensation reactions provided by the phenyl groups. Previous potentiometric studies have shown that the acid strength of Ph3SiOH is of the same order of magnitude as phenol, the strongly acidic alcohol.174 Infrared spectroscopic studies have also confirmed that Ph3SiOH (and other aryl silanols) are of comparable hydrogen bond acidity to phenol, which is used extensively in the study of hydrogen bonding interactions.38 The presence of one silanol group simplifies the hydrogen bonding possibilities available and comparisons may, therefore, be made both with phenol and, where available, the carbon analogue Ph3COH. Although a number of groups have carried out qualitative studies on the hydrogen bonding. interactions of

Ph3SiOH with bases by infrared spectroscopy, the range of bases has been limited to mesitylene, DMSO and a series of ethers and ketones (Section 1.4.3).34,38,82,83,167-170

2.4.1 With silyl ethers and siloxanes The hydrogen bonding interactions of Ph3SiOH with a series of silyl ethers and siloxanes have been studied by infrared spectroscopy in order to establish the relative basicities of the oxygen atoms in such compounds towards the silanol group. These interactions are of interest since both silanols, and silyl ethers or linear and cyclic siloxanes co-exist in industrial polymerisation reactions. There appears to be only one previous example of such a study in the literature, on the hydrogen bonding interactions

65 Chapter 2 Infrared spectroscopic studies between Me3SiOH and D4 [AuOH 91 curl] and Ph3SiOH and D4 (AD0H 149 cm-1).175

The exact details of this study, however, are unclear, as a translated version of the Chinese paper is not available. Due to the expected low basicity of these groups the concentration of the silyl ether or siloxane used was relatively high, 0.5 M and 1 M respectively, in comparison to 0.05 M employed in the studies with stronger bases. At higher concentrations of siloxane, the silanol was not soluble. The concentration of Ph3SiOH was 0.01 M, at which the degree of self-association was negligible. The results for the hydrogen bonding interactions of Ph3SiOH with silyl ethers can be seen in Table 2.2 and with siloxanes in Table 2.3. Previous infrared spectroscopic studies have established the relative basicities of a selection of silyl ethers and siloxanes towards 1-18176 phenol, pyrrole177'178'182 and deuterochloroform.183 Where applicable, the results of the relative basicities towards the OH hydrogen bond donor phenol have been included in Tables 2.2 and 2.3 for comparison. In Table 2.2, Avoli values for the interaction of

Ph3SiOH with some simple ethers have also been included for comparison. The spectra for the hydrogen bonding interactions of Ph3SiOH with silyl ethers with phenyl substituents also show very small bands due to OH • • . IC bonding to the phenyl rings. These bands are only sufficiently large enough to assign a MOH value for Ph2Si(OEt)2 and Ph3SiOEt and are given in Table 2.2. It can also be seen from Table 2.2 that OH • • • it interactions have also been observed between phenol and Ph3Si0Et.177,180

In Table 2.3 the siloxanes are referred to by their common abbreviation Dn where D refers to the structural unit (-Me2SiO-). Where the methyl groups have been substituted for other groups these are referred to in superscripts. The LIDOH values from the spectra showing the hydrogen bonding interactions between Ph3SiOH and D4Mevi and (ViSiMe2)20 are not included in Table 2.3. These spectra show a shoulder on the 'free' OH peak which merges with the very weak hydrogen bonded band due to hydrogen bonding with the siloxane group, making it difficult to assign a 600H value. The spectrum showing the hydrogen bonding interactions between Ph3SiOH and D4MeVi is shown in Figure 2.2 along with the spectra of Ph3SiOH and D4 for comparison.

Chapter 2 Infrared spectroscopic studies

Table 2.2. AU0H (cm-1) of the SiOH group in Ph3SiOH due to hydrogen bonding to silyl ethers and some simple ethers for comparison. duOH (cm-1) for the analogous interactions of the OH group of phenol are also included for comparison.

Compound .A.uoli Ph3SiOH (cm-1) ADoll Phenol (cm-1)

Si(OMe)4 244 202,181 206179

PhSi(OMe)3 248 210179

MeSi(OMe)3 270 226181

Me2Si(OMe)2 297 252181 269181 Me3SiOMe 319 278,176

Si(OEt)4 260 219177

PhSi(OEt)3 257 221179

MeSi(OEt)3 278 237177

ViSi(OEt)3 263 225179

Ph2Si(OEt)2 272 (63a)

Me2Si(OEt)2 297 257177

MeHS40Et)2 272 233180

MeViSi(OEt)2 283 250179

MePhSi(0E02 279 251179

Ph3SiOEt 258 (58a) 222 (52a),177 219 (51a) 180

Me3SiOEt 319 271,177 280180

Vi3SiOEt 280

Et20 319 282177

Prn0Pri 326.582 aAu (cm-1) due to OH • • • m interactions with phenyl rings. A•uoli values are ±2 cm-1.

Chapter 2 Infrared spectroscopic studies

Table 2.3. MOH (cm-1) of the SiOH group in Ph3SiOH due to hydrogen bonding to siloxanes compared with Avoll (cm-1) for the analagous interactions of the OH group of phenol.

Siloxane Avoii Ph3SiOH (cm-1) Aum Phenol (cm-1)

(Me3Si)20 164 169,177 170184

D3 189 166177

D3MeVi 168

D4 156 (149)175 144177

D4MeH 125 101177

D5 162 147177 AUOR values are ±4 cm-1.

T r a n s m i t t a n c e

3600 3400 Wavenumbers

Figure 2.2. Infrared spectra showing the hydrogen bonding interactions of Ph3SiOH with

D4 and D4mevi.

68 Chapter 2 Infrared spectroscopic studies

These shoulders are presumably due to OH • • • IC bonding between the silanol and the vinyl groups of the siloxane. Hydrogen bonding to the vinyl groups in silyl ethers was not observed, possibly due to the position and magnitude of the hydrogen bonded bands to the alkoxy groups. The strength of hydrogen bonding interaction between silanols and alkenes has also been studied further in this work and is described in the following section (Section 2.4.2).

From Tables 2.2 and 2.3 it can be seen that the order of basicity upon hydrogen bonding to Ph3SiOH is as expected:

ether silyl ether >> siloxane

This agrees with the results from previous qualitative infrared spectroscopic studies using other proton donors and also with those obtained from quantitative thermodynamic studies with pheno1.185

It is not, however, possible to compare directly the values between ethers and silyl ethers since these are two different species and the linear relationship between Aucm and

AH proposed by Badger and Bauer (Section 1.4.2.1)36'37 is not valid outside each series. It can be seen clearly from Tables 2.2 and 2.3 that the AvoH values for Ph3SiOH are significantly larger than those for the strong acid phenol, although the same trend is followed. This demonstrates the high acidity of silanols towards hydrogen bonding interactions with such species, suggesting that interactions such as these may play a significant part in industrial reaction mixtures.

The hydrogen bonded hydroxyl bands of Ph3SiOH with siloxanes are weaker and have much lower values of LDOH (Table 2.3) compared to the hydrogen bonded bands with silyl ethers (Table 2.2). This difference in basicity has previously been explained by do - pit bonding39'177'185 but more detailed explanations consider the interactions with the HOMO on silicon to be important.43'44 It has been suggested previously that the weak band at 3620 cm-1, AvoH 60 cm-1 in the spectrum of octaphenyltetrasiloxane-1,7-diol in dilute CC14 solution is due to

69 Chapter 2 Infrared spectroscopic studies intramolecular SiOH • • • siloxane hydrogen bonding.186 The magnitude of the difference in OH stretching frequency, however, suggests that the interaction is due to OH • • • it interactions with a phenyl ring as discussed in Section 2.2, as these studies have shown that Au oii for silanols upon hydrogen bonding to siloxanes is still larger than that for interactions with phenyl rings. Within the series of silyl ethers the following order of basicity applies:

R3SiOR' > R2Si(OR)2 > RSi(OR')3

It has been concluded previously that the ApoH values of ethers are mainly affected by the inductive influence of the oxygen atom and not by hyperconjugative or steric effects.187,188 The factors controlling the relative basicities of silyl ethers and hexaorganodisiloxanes have been the subject of much literature, a detailed review of which may be found in ref. 189. Although the relative basicities have been ascribed to a function of several parameters including the MOM' (M = C, Si; M' = Si) valence angle, the lone electron pair ionisation potential and the mutual polarisability of the M-O bonds,189 linear correlations have suggested that the relative basicities of silyl ethers and hexaorganodisiloxanes are also determined predominantly by the total inductive effect of the substituents.178,180,190 It can be seen from Table 2.2 that as the number of alkoxy groups on silicon increase the basicity of the silyl ether decreases. This may be due to the opposing inductive effect of the additional oxygen bonded to the silicon. Also, the relative basicities of, for example, the series R1R2Si(OEt)2 are in the order expected for the inductive effects of the substituents Rn.

The basicity of siloxanes, however, has also been found to be strongly affected by the Si-O-Si angle.185,189 The basicities of (Me3Si)20 and D3 are greater than the other polydimethyl cyclic siloxanes (Table 2.3). For example the ApoH value of Ph3SiOH upon hydrogen bonding to D3 is 189 cm-1 (169 cm-1 for phenol), in comparison to that of 156 cm-1 upon hydrogen bonding to D4 (144 cm-1 for phenol). For (Me3Si)20 this may also be due to the fact that it contains an oxygen atom bonded to two trimethylsilyl

70 Chapter 2 Infrared spectroscopic studies groups. In the case of D3 and D3Mevi the increased basicity may be caused by bond strain.

The low temperature crystal structures of D3 and D4 have been determined previously.191-194 It was, thus, of interest to determine the structure of D5 in order to compare the Si-O-Si angles. The crystal structure of D5 is discussed in more detail in

Section 2.4.1.1. The average Si-O-Si bond angles for Dn (where n = 3, 4, 5) and (Me3Si)20 are given in Table 2.4 for comparison.

Table 2.4 Average Si-O-Si angles for the cyclic siloxanes, Dn (where n = 3, 4, 5) and (Me3Si)20 for comparison.

Siloxane Average Si-O-Si angle

(Me3Si)20 148.8(2) '195

D3 131.9 '191

D4 142.5 .192'193

D5 148.01 °

It can be seen from Table 2.4 that the average Si-O-Si angle increases with increasing ring size. Although solid state X-ray data may not be the same as that in solution, a similar trend is expected. For D3, the average Si-O-Si angle is considerably lower than for D4 or D5 which may explain the increase in basicity. Upon going from D4 to D5, however, the 6:00H values do not decrease in relation to increasing Si-O-Si angle. In fact the AuoH values are very similar and actually show a slight increase. For example, the AvoH value of Ph3SiOH upon hydrogen bonding to D4 is 156 cm-1

(144 cm-1 for phenol), in comparison to that of 162 cm-1 upon hydrogen bonding to D5 (147 cm-1 for phenol). For larger siloxanes the Si-O-Si angles may be similar to each other and may not be an important factor in determining basicity, the basicity not changing much in unstrained rings. Since the Si-O-Si angle in (Me3Si)20 is similar to that in D5, the increased basicity of (Me3Si)20, which is more prominant for the

71 Chapter 2 Infrared spectroscopic studies hydrogen bonding interaction with phenol than Ph3SiOH (Table 2.3), may be attributed to the presence of two Me3Si groups.

Although silanol to siloxane hydrogen bonding may be observed by infrared spectroscopy in solution, crystallographic studies indicate that such interactions are very rare in the solid state (Section 1.4.5.4).139-141 An example of silanol to siloxane hydrogen bonding occuring between two molecules of decamethyl-7- oxahexasilanorbornane and one molecule of 1,4-dihydroxydecamethylcyclohexasilane is shown in Figure 1.13, Section 1.4.5.4.

Despite the greater basicity of silyl ethers in comparison to siloxanes, there appear to be no examples reported in the literature of silanol to silyl ether hydrogen bonding in the solid state. For example, in the dimeric structure of the alkoxysilanol (Me3Si)3SiPh(OMe)OH both intermolecular O-H • • • 0 and O-H • • • It interactions are present, but no O-H • • • OMe (Figure 1.11, Section 1.4.5.4). The lack of such examples in more common unhindered environments may be due to the reaction of silanols with silyl ethers to form siloxanes, see ref. 196 for example:

E Si- OH + E Si- OR = Si- 0- Si E + ROH

2.4.1.1 Low temperature crystal structure of D5 The low temperature crystal structure of the cyclic siloxane D5 was determined at -163 °C. The crystal structure is shown in Figure 2.3 and selected bond lengths and angles are given in Table 2.5. Further crystallographic data, including the method by which the crystal was obtained, may be found in the Appendix. D5 adopts a boat conformation (Figure 2.3) in which the average Si-0 bond length is 1.628 A and the average Si-O-Si angle is 148.01 ° (Table 2.5). The range of Si-O-Si bond angles is large from 138.64(14) ° to 156.8(2) ° (Table 2.5). The Si-C bond lengths are unexceptional.

Chapter 2 Infrared spectroscopic studies

C22

C42

C21 C41

Figure 2.3. Two views of the X-ray crystal structure of D5, hydrogen atoms are removed

from the upper view for clarity.

Chapter 2 Infrared spectroscopic studies

Table 2.5. Selected bond lengths and angles for D5 determined by X-ray crystallography.

Si(1) - 0(1) 1.619(2) A 0(1) - Si(2) 1.627(2) A Si(2) - 0(2) 1.630(2) A Si(1) - 0(1) - Si(2) 156.8(2) ° 0(2) - Si(3) 1.628(2) A Si(3) - 0(2) - Si(2) 144.2(2) ° Si(3) - 0(3) 1.621(2) A Si(3) - 0(3) - Si(4) 155.5(2) ° 0(3) - Si(4) 1.624(2) A Si(5) - 0(4) - Si(4) 138.64(14) ° Si(4) - 0(4) 1.637(2) A Si(1) - 0(5) - Si(5) 144.91(15)° 0(4) - Si(5) 1.632(2) A Si(5) - 0(5) 1.631(2) A 0(5) - Si(1) 1.628(2) A

The low temperature crystal structures of D3 and D4 have been determined previously.191-194 The original structural determination of D3 by Peyrone1191 was shown to be inaccurate and was redetermined by Pomes.192'193 The Si-0 distances were found to be 1.61±0.01 A and the Si-O-Si angles 131.9±1.8 °. The ring is not planar, as had previously been determined,191 but the silicon and oxygen atoms are located in different planes, the distance between the planes being 0.19 A.192'193 In the crystal structure of D4 the molecules are located at centres of symmetry and the ring adopts a "twist-chair" conformation of C2h symmetry.194 The Si-0 bond lengths are 1.65 A (1.64 - 1.66 A) and the Si-O-Si angles are 142.5 ° (141.5 - 143.5 °). The small Si-O-Si bond angle in D3 results in considerable bond strain. It can be seen that on going from D3 to D4 to D5 the average Si-O-Si bond angle increases in accordance with the expected reduction in ring strain.

A number of vibrational spectroscopic studies have been carried out in the solid, liquid and gas phases by various authors on the cyclic siloxanes from D3 to D12 and interpreted in terms of the conformational preferences.197-203 For D5, however, the

74 Chapter 2 Infrared spectroscopic studies spectra could not be interpreted as being due to any single conformation.202 It has also been suggested that for Dn where n 5 several conformations may coexist in the crystal lattice.204

Gas phase electron diffraction studies have also been carried out for Dri where n = 3 _ 6.205-207 D3 was found to be nearly planar, the best agreement for D4 was obtained with a model of S4 symmetry and the larger rings were not found to possess a well- defined conformation due to large amplitude vibrations.207 Grigoras and Lane found from Ab Initio computations that the most stable conformation of D4 has S4 symmetry.208'209 This is in agreement with the experimentally determined gas phase structure.207 They found that the most stable conformation is determined by the steric repulsion of methyl groups. No theoretical calculations, however, have been carried out for D5 in the literature. PM3 semiempirical calculations (Mac Spartan Plus software, Wavefunction Inc.

California) were, therefore, carried out on D5 but the calculated Si-O-Si bond angles were much smaller than expected and in the narrow range of 133 to 136 0, and the Si-O bond lengths were large, all at approximately 1.66 A. Calculations at the more reliable Ab Initio level, however, appeared to be too slow on the computer available.

2.4.2 With alkenes

There are very few crystal structures in the literature which show hydrogen bonding between hydroxy groups and C-C multiple bonds210 and no examples are available for silanols. There are some infrared spectroscopic studies on the OH • • • it hydrogen bonding interactions between alcohols and C-C multiple bonds211-213 but no work has been carried out on the interaction of silanols with such groups. Whilst investigating rotational isomerism in poly(diorganosiloxane)-cc, cu-diols, Harris166 observed that the asymmetric 'free' OH bands in the infrared spectra of MeViSi(OH)2 and (HOMeViSi)20 at high resolution comprised two absorptions at 3693 and 3684 cm-1, the latter of much greater intensity, assigned to the anti- and gauche- conformations respectively. The high population of the gauche conformation was ascribed to

75 Chapter 2 Infrared spectroscopic studies stabilisation by a weak intramolecular OH • • • ic interaction between the silanol and vinyl groups, a phenomenon which was also observed in the spectra of allyl alcohol.166 In the spectrum of HO(MeViSiO)3H the absorption at 3684 cm-1 due to the gauche isomer was much higher than in the lower members of the series and an additional strong absorption, also ascribed to an OH • • • TC interaction with the vinyl groups, was present at 3673 cm-1.166

In HO(MeViSiO)3H, therefore, the OH • • TE interaction is sufficient to cause a shift in the OH stretching frequency, whereas in MeViSi(OH)2 and (HOMeViSi)2O the interaction only causes an increase in the intensity of the gauche absorption. This present work has already shown that significant intermolecular OH • • • TC interactions are possible between silanol and vinyl groups in the intermolecular hydrogen bonding interactions of Ph3SiOH with vinyl containing siloxanes (Section 2.4.1). Further hydrogen bonding studies were therefore carried out to establish the relative hydrogen bonding acidity of Ph3SiOH towards a range of common alkenes. Since these interactions were expected to be relatively weak, the highly acidic Ph3SiOH was chosen for the studies and the concentration of alkene was high, 1M. The concentration of Ph3SiOH was 0.01 M. The results can be seen in Table 2.6. The infrared spectrum of the hydrogen bonding interactions between Ph3SiOH and allyl ether is shown in Figure 2.4 . Both the allyl and ether groups can clearly be seen to participate in hydrogen bonding to the silanol group. The magnitude of the Aucal values and strength of the bands due to hydrogen bonding to alkenyl groups are similar to those obtained for hydrogen bonding to aromatic groups, for example upon hydrogen bonding to mesitylene in Table 2.1. Silanols, therefore, seem to be sufficiciently acidic to form hydrogen bonding interactions with a range of weak bases and such interactions should not be ignored.

Chapter 2 Infrared spectroscopic studies

Table 2.6. LuOH (cm-1) of the SiOH group in Ph3SiOH due to hydrogen bonding to alkenyl groups.

Alkene A-uoll Ph3SiOH (cm-1)

1,5-Cyclooctadiene 94

1,4-Cyclohexadiene 93

Allyl ether 120 (2919

2,5-Norbornadiene 85

2,3-Dimethy1-1,3-butadiene 95

Cyclohexene 115 a AD (cm-1) due to OH • • • 0 hydrogen-bonding to the ether group. Auoli values are ±4 cm-1.

T r Rio- a hydrogenI bonding n to ally! group s m i 95. t 'free' 011 t a n hydrogen bonding c to ether group ....4. e 80-

3800 3600 3400 3200 Wavenumbers

Figure 2.4. Infrared spectrum showing the hydrogen bonding interactions between

Ph3SiOH and ally! ether.

77 Chapter 2 Infrared spectroscopic studies

2.5 Determination of thermodynamic data for hydrogen bonded adducts of Ph3SiOH by infrared spectroscopy

As discussed in the introduction (Section 1.4.3), there is a paucity of thermodynamic data available for the hydrogen bonding interactions of silanols in solution. Only experimentally determined values for the enthalpy of hydrogen bond formation, -AH, between Ph3SiOH and a series of ketones in CC14 solution are available

(Section 1.4.3).81

2.5.1 Method The enthalpy of hydrogen bond formation, AH, and the related thermodynamic functions, entropy, AS, and Gibbs free energy, AG, are derived from the temperature dependence of the equilibrium constant, K.48'51 A number of different experimental approaches may be used in the determination of the equilibrium constant, K, but they all involve the quantification of concentration or pressure values from the changes observed in the spectrum of the equilibrium mixture when compared to the spectrum of the acid or base.48'51 These values are then used to determine K.

The following method48'51,214 may be applied to study 1:1 complexes between hydrogen bond donors (AH) and acceptors (B) in media of 'inert' solvents (low dielectric constant, low dipole moment, low polarizabiliy and lack of specific Lewis acid-base sites), e.g. CC14 and cyclohexane.

The concentration of the hydrogen bond donor, AH, is chosen such that only the 'free' hydrogen bond donor, AH, is present in solution, as shown by a single sharp AH stretch in the infrared spectrum. This avoids competitive hydrogen bonding interactions due to self-association or the formation of adducts with stoichiometries other than 1:1 (Equations 2.1 and 2.2):

nAH (AH)n (2.1)

(AH)n + B ---"" (AH)n "• • B (2.2)

Chapter 2 Infrared spectroscopic studies

Thus, the equilibrium given in Equation 2.3 is assumed to occur rapidly to give the 1:1

adduct AH • • • B: K, DH AH + B AH • • • B (2.3)

where K is the equilibrium constant and AH is the enthalpy of hydrogen bond

formation.

The equilibrium constant expression for this reaction is (Equation 2.4):

[AH . • . B] K = (mo1-1 dm3) (2.4) [AH][B]

where [AH], [B] and [AH • • • B] are the equilibrium concentrations of the

hydrogen bond donor, AH, the hydrogen bond acceptor, B, and the hydrogen

bonded adduct, AH • • • B, respectively.

This may be rewritten as (Equation 2.5):

[AH0] - [AH] K = (m01-1 dm3) (2.5) [AH]{O3o] - ([AH.] - [AH])}

where [AH0] and [Bo] are the initial concentrations of the proton donor, AH, and

the hydrogen bond acceptor, B, respectively.

When the initial concentration of the hydrogen bond acceptor, [Bo] is much greater than

the equilibrium concentration of the complex, ([A110] - [AH]), then Equation 2.6 may be written:

K = [AHo] - [AH] (mol-1 dm3) (2.6) [Ali][Bo]

79 Chapter 2 Infrared spectroscopic studies

The concentration of the hydrogen bond donor, [AH], is directly proportional to the absorbance of the 'free' AH stretch, A if:

i) Beer's Law (Equation 2.7) is valid for the employed concentration of hydrogen bond donor, AH.

A = ecl (2.7)

where A is the absorbance, 6, the molar extinction coefficient, c, the concentration

and, 1, the pathlength.

ii) the absorbance band of the hydrogen bonded adduct, AH • • • B does not overlap with the absorbance due to the 'free' AH.

iii) there is no effect of the hydrogen bond acceptor concentration on the extinction coefficient of the 'free' AH band.

Therefore, if these criteria are met, the equilibrium constant may be represented as in Equation 2.8:

A. - A K = (mol-1 dm3) (2.8) A[B0]

where Ao and A correspond to the absorbance of 'free' AH in the absence of hydrogen bond acceptor and in the presence of hydrogen bond acceptor, B respectively, and [B0] is the initial concentration of hydrogen bond acceptor, B.

The absorbance of the 'free' AH band, A, is measured for a series of different initial concentrations of base, [Bo], at a specific temperature. If (A0 - A)/A is plotted against [Bo] then the slope gives the equilibrium constant, K, directly for that temperature (Equation 2.8).

80 Chapter 2 Infrared spectroscopic studies

The enthalpy of hydrogen bond formation, AH, is related to the equilibrium constant, K, by Equation 2.9.

d In K/dT = AH/RT2 (2.9)

where T is the temperature in Kelvin and R is the gas constant (8.314 J K-1 mol-1)

Hence:

ln K = A - AH/RT (2.10)

Thus, the determination of K at a range of different temperatures allows AH to be calculated from the slope of a plot of In K against 1/T. A linear least squares plot is the most generally used.

Also, the Gibbs free energy , AG, is related to the equilibrium constant, K, by Equation

2.11: AG = -RT ln K (2.11)

The entropy, AS, of hydrogen bond formation may then also be calculated from:

AS = (AH — AG)/T (2.12)

The method described above may be used to determine the enthalpy of hydrogen bond formation of Ph3SiOH with hydrogen bond acceptors such as ethers, ketones or amines. Carbon tetrachloride is the most commonly used solvent for these studies. With hydrogen bond acceptors such as amines, however, a saturated hydrocarbon like cyclohexane should be used as the 'inert' solvent, since CC14 is known to interact with amines.215-217

81 Chapter 2 Infrared spectroscopic studies

With weak hydrogen bond acceptors such as it donors or siloxanes, however, it is more difficult to determine the equilibrium constant since the interaction becomes measureable only when very large concentrations of hydrogen bond acceptor in 'inert' solvent or even solutions of the hydrogen bond donor in pure acceptor are used. This increase in hydrogen bond acceptor concentration can affect the extinction coefficient of the 'free' OH group, thus invalidating Beer's law (Equation 2.7).218,219 Also, the weak hydrogen bonding is accompanied by a small shift in 'OH' stretching frequency, often resulting in an overlapping of the 'free' and 'hydrogen bonded' OH bands, again affecting the relationship between concentration and absorbance of the 'free' OH stretch.82,220 The evaluation of All by measuring the temperature dependence of the equilibrium constant, therefore, is not an easy task for such systems. The value of specific interaction enthalpy due to hydrogen bonding, where the degree of complexation of the hydrogen bond donor is taken into consideration is better suited to such systems.219 Since thermodynamic studies of silanols with weak hydrogen bond acceptors have not been attempted in this work, the various approaches involved in the determination of specific interaction enthalpy will not be discussed further. A full discussion may be found in ref. 219.

2.5.2 Thermodynamic data for hydrogen bonded adducts of Ph3SiOH with ethers Although the frequency shifts for Ph3SiOH interacting with a series of ethers have been recorded previously and correlations made between MOH and the nucleophilicity parameters of the ethers, only a few association constants, Kass, are available.82 The temperature, units and method by which these were obtained is not given. AM1 semiempirical quantum chemical calculations, however, have been performed for the hydrogen bonding interactions between Ph3SiOH and Ph3COH and ethers.221 These calculations yielded the most stable conformations, the molecular electrostatic potentials at the 0 and H atoms of the silanol/carbinol and on the oxygen atoms of the ether, and the enthalpies of hydrogen bond formation. The geometric layout calculated for the hydrogen bonded complexes with ether is shown in Figure 2.5.

82 Chapter 2 Infrared spectroscopic studies

117. H- 0- 0 \ 2.09 A I R Si I Ph Ph Ph

Figure 2.5. Calculated geometric layout of the 1:1 hydrogen bonded adducts formed by Ph3SiOH with ethers.

In the same paper, calculations were also made for complexes of Ph3COH, Me3COH,

Ph3SiOH and Me3SiOH with ketones.221 These calculations give rise to a number of discrepancies. Although the enthalpies of hydrogen bond formation for the carbinols with ketones were less than those of the silanols, as may be expected, the values for the two silanols are almost identical, the values for Me3SiOH actually being slightly higher than those for Ph3SiOH. For example, with acetophenone -AHph3SiOH = 13.64 kJ mol-1 and

-AHMe3SiOH = 13.69 kJmo1-1, and with methylcyclohexylketone -AHph3SiOH = 13.71 kJ mol-1 and -AHme3SiOH = 13.87 kJmol-1. The expected higher acidity towards hydrogen bonding interactions of Ph3SiOH in comparison to Me3SiOH has been borne out previously by the higher AvoH values obtained for hydrogen bonding interactions with the ethers dioxane, Et20 and THE (Section 1.4.3).76-78'82 In addition, the experimentally determined enthalpy values for the interaction of Ph3SiOH with acetophenone and methylcyclohexylketone are -11.4 ± 1.9 and -20.1 ±1.8 kJmo1-1 respectively which are not in good agreement with the calculated values of -13.64 and -13.71 kJmo1-1. These results suggest that the calculations employed may not be appropriate for such systems and that they may give unreliable results.

Experimental values for the enthalpy of hydrogen bond formation of Ph3SiOH with a series of ethers were, therefore, obtained. The method discussed previously in Section 2.5.1 was used and full experimental details may be found in Section 6.2.3. The thermodynamic parameters determined from infrared spectroscopic studies are given in Table 2.7, along with the frequency shift, Av0H, for the hydrogen bonding interactions.

Chapter 2 Infrared spectroscopic studies

For example, the plots used in the calculation of the thermodynamic parameters for the hydrogen bonding interaction of Ph3SiOH with 1,4-dioxane are given in Figures 2.6 and 2.7.

Table 2.7. Infrared spectroscopic and thermodynamic parameters for the hydrogen bonding interactions of Ph3SiOH with a series of ethers in CC14.

Ether Au K298a -fib -zG298 -AS298 cm-1 dm3mol-1 kimol-1 kJmo1-1 Jmol-1

Diethyl ether 319 3.41 ± 0.07 10.80 3.03 26.0

Di-n-butyl 322 2.64 ± 0.07 10.94 2.40 28.6 ether

1,4-Dioxane 282 6.02 ± 0.03 8.45 4.44 13.4

THF 334 6.97 ± 0.06 13.97 4.81 30.7

Aucni values are ±2 cm-1. a Standard errors obtained from curve fit. bThe correlation coefficients, R2, obtained from the least squares plot of lnK against 1/T are 0.99.

The frequency shifts are in good agreement with the literature values of 319,

319.5, 283 and 333 cm-1 for diethyl ether, di-n-butyl ether, 1,4-dioxane and THF respectively,82 and the enthalpies of hydrogen bond formation, -OH, show an increase with increasing Au, as may be expected. From the plot of OH against AUOH in Figure 2.8 it can be seen that a satisfactory linear correlation for these ethers was not found. More data points are required, however, to see if a reasonable correlation exists. Correlations with other parameters such as pka, Gutmann Donor Number, nucleophilicity factors, etc. may also be possible with a larger data set.

84 Chapter 2 Infrared spectroscopic studies

1111 4 11111111 1111 I 1111 1111 3.5 O 25 C IS1 30 C 3 o 35 C 40C ✓ 2.5 I 45 C 50 C (Ao - A)/A 2 A I:I 55 C 60 C 1.5 x 1 0.5

1111 1 1 1 1 - 0 11 1111 1111 1111 0 0.1 0.2 0.3 0.4 0.5 0.6 [Bo]

Figure 2.6. Plots of (A0 - A)/A against [B 0] for the hydrogen bonding interaction of Ph3SiOH with 1,4-dioxane at different temperatures ranging from 25 - 60 °C. The slope of the line gives the equilibrium constant K.

1.9

1.8

1.7 lnK 1.6

1.5

1.4

1.3 2.9 3 3.1 3.2 3.3 3.4

irr x 103

Figure 2.7. The linear least squares plot of lnK against 1/T for the hydrogen bonding interaction of Ph3SiOH with dioxane in CC14 between 25 and 60 °C (R2 = 0.998). Values for K were obtained from the plot in Figure 2.6.

85 Chapter 2 Infrared spectroscopic studies

-8 -9 -10 -11 AH -12 -13 -14 -15 280 290 300 310 320 330 340

A1)0H Figure 2.8. Plot of AH against AD0H for the hydrogen bonding interactions of Ph3SiOH with some ethers.

For the interactions of Ph3SiOH with ketones the following correlation between AH and At 01-1 was proposed:221

-AH (kJmo1-1) = (0.272 ± 0.055)A1) - (39.1 ± 11.1) r = 0.94

The largest enthalpy of hydrogen bond formation determined is for the interaction of Ph3SiOH with THF. This may be due to the planarity and, thus, lower steric hindrance in this molecule in comparison with the aliphatic ethers and dioxane. There is very little difference in the enthalpy values determined for diethyl ether and di-n-butyl ether which suggests that the chain length has very little effect on the strength of the hydrogen bonding interaction and that steric factors may also predominate. The lowest AH and AS values were obtained for the interaction with dioxane which may also be due to a combination of steric and electronic effects, for example, unlike planar THF, dioxane

86 Chapter 2 Infrared spectroscopic studies adopts either a boat or chair-like conformation. Under the conditions studied 1:1 Ph3SiOH:1,4-dioxane rather than 2:1 hydrogen bonding interactions should be occurring. The calculated values for the enthalpy of hydrogen bond formation of Ph3SiOH with ethers appear to be in poor agreement with those calculated by AM1 semiempirical methods,221 e.g. the calculated values for Ph3SiOH with diethyl ether and dioxane are 12.92 and 11.91 kJmo1-1 respectively, in comparison with the experimentally determined values of 10.80 and 8.45 kJmo1-1. The values for THF, however, are close, -Al-lcalc. 13.73 khno1-1 and -AHexpt. 13.97 kJmol-1. As described previously, for the interactions with ketones, the calculated values do not effectively model the interactions occurring in solution.

The enthalpy values for the interactions between Ph3SiOH and ethers are of a similar order of magnitude to those obtained for the interactions with ketones,221 although the Au values are substantially less for the interactions with ketones. This again emphasises that the linear relationship between 6,1) and zH proposed by Badger and

Bauer is only valid when comparing the hydrogen bonding interactions within a series of similar hydrogen bond acceptors or donors.

Comparative data for the interactions of the analogous carbinol, Ph3COH, with ethers are not available in the literature.

2.5.3 Thermodynamic data for hydrogen bonded adducts of Ph3SiOH with amines Since the preparation of hydrogen bonded adducts of silanols with a range of amines was successful in the solid state, it was attempted to obtain thermodynamic data for the analogous interactions in solution. The method described in Section 2.5.1 was employed, using cyclohexane as the solvent to avoid any additional interactions between CC14 and the amines.215-217 With pyridine and Et3N, however, the relative intensities of the 'free' OH bands were very weak in comparison to the hydrogen bonded bands when using a similar concentration range of amine as used for the studies wth ethers, and upon heating, the spectra became very noisy. Time did not permit the conditions required for these studies to be optimised, although the concentration of the amine needs to be reduced substantially.

87 CHAPTER 3 Hydrogen bonded adducts of silanols Chapter 3 Hydrogen bonded adducts of silanols

CHAPTER 3 Hydrogen bonded adducts of silanols

3.1 Introduction

Silanols have been found to form a wide range of hydrogen bonded structures in the solid state (Section 1.4.4).34 For silanols containing nitrogen functions (e.g. the siladrugs) or a variety of other functional groups both intra- and intermolecular hydrogen bonding between the silanol goup and these functions has also been observed (Section 1.4.4.4). Although infrared spectroscopic studies have shown the high acidity of silanols towards hydrogen bonding interactions in solution there is, comparitively, a lack of literature on simple adducts of silanols with other suitable molecules in the solid state (Section 1.4.5).34 The majority of hydrogen bonded adducts of organic molecules containing hydroxy groups, in the solid state, have been reported for highly acidic species such as carboxylic acids and phenols. Adducts of the less acidic alcohols, the carbon analogues of silanols, have received less attention and will be mentioned, for comparative purposes, in the relevant sections. Supramolecular chemistry (chemistry beyond the molecule) is a field which has 222-225 rapidly evolved over the last ten years and there are several reviews on the subject. Supramolecular chemistry may be described as 'the designed chemistry of the intermolecular bond',223 the hydrogen bond being the most extensively used due to its relativly high strength and directionality. The selective binding of a substrate by a molecular receptor to form a supermolecule involves molecular recognition which rests on the molecular information stored in the interacting molecules. This requires the design of receptors possessing steric and electronic features complementary to those of the substrate to be bound and a balance between rigidity and flexibility suitable for the function to be formed. Ideally, simply mixing the component molecules should result in the specific and spontaneous self-assembly of the desired supramolecular structure. The exploitation of intermolecular forces, particularly hydrogen bonding, in this manner is the

89 Chapter 3 Hydrogen bonded adducts of silanols basis for crystal engineering.226-228 From a detailed study of existing crystal structures Etter developed the concept of graph sets to classify hydrogen bonding patterns and delineated definite rules to predict hydrogen bonding arrangements in single- and two- component crystals.229 The Etter type of analysis has not been used in this work, for reasons described below, but a detailed description can be found in ref. 230. Although there is now a vast amount of literature on the formation of such hydrogen bonded complexes it is very difficult to transfer these design strategies to the preparation of hydrogen bonded adducts of silanols and am-siloxanediols for a number of reasons. Although silanols have a relatively high acidity they also retain their basicity and so. the SiOH group may act both as a Lewis acid or base. This results in silanols possessing a strong tendency to hydrogen bond to themselves to the exclusion of other molecules. The propensity of the silanol group towards condensation reactions in the presence of molecules containing acidic or basic functionalities has to be taken into consideration as another possible reaction pathway. Also, the low energy barrier to bending and therefore, flexibility of the siloxane linkage in am—siloxanediols of the general formula HO(R2SiO)nH means that they do not have sufficient rigidity to allow reliable structural predictions to be made. Different conformations and thus hydrogen bonded arrangements may be adopted by the same a,co—siloxanediol.

Since the study of hydrogen bonded adducts of silanols is still in its early stages a range of molecules with oxygen or nitrogen functions were employed in the attempted preparation of adducts.

3.2 General methods for the preparation of adducts of silanols

When attempting to prepare hydrogen bonded adducts the role of solvent cannot be ignored since it may act as a competitive hydrogen bond acceptor and/or donor or be included as guest molecules. In general the preparation of adducts was carried out by one of the following two methods which use toluene or ether as the solvents, both of which are weaker hydrogen bond acceptors than the molecules with which hydrogen bond formation was being attempted.

90 Chapter 3 Hydrogen bonded adducts of silanols

Method 1

The hydrogen bond acceptor molecule (1 equivalent) was added to a solution of the silanol (1 equivalent) in hot toluene with vigorous stirring. After stirring for between 2-5 minutes the solution was allowed to cool to room temperature and enough hexane added to initiate crystallisation. If crystals did not form the solvent was allowed to evaporate. Any solid product was then collected by vacuum filtration.

Method 2

The hydrogen bond acceptor molecule (1 equivalent) was added to a solution of the silanol (1 equivalent) in ether and the solution stirred for between 1-5 hours. Under reduced pressure the solvent was then evaporated to dryness if the hydrogen bond acceptor was a low boiling point liquid or until crystals started to form if the hydrogen bond acceptor was a solid or high boiling point liquid.

As discussed in Section 1.2, condensation reactions of silanols are catalysed by heat and/or traces of acid or base. Silanols with bulky groups and/or one SiOH group such as Ph3SiOH are less sensitive to such conditions and so fewer precautions need to be taken when attempting the preparations of adducts. In some cases the adduct may also be prepared by slow evaporation of a solution of the silanol dissolved in an excess of the hydrogen bond acceptor as solvent.

Since silanols can be sensitive to small changes in temperature, acidity or basicity the reactions were repeated at least three or four times to confirm the results obtained. Elucidation of the hydogen bond arrangements formed by adducts is important in an attempt to understand the factors controlling hydrogen bond formation with silanols. When attempting to grow crystals suitable for X-ray crystallography care had to be taken not to leave adducts of the more sensitive silanols in solution for prolonged periods of time as this encouraged condensation reactions. In some cases dissociation of the hydrogen bonded adduct occurred upon recrystallisation.

91 Chapter 3 Hydrogen bonded adducts of silanols

3.3 Identification and characterisation of adducts of silanols

NMR spectroscopy Initial identification of the isolated product was carried out by 1H NMR spectroscopy since this gives a fast and reliable indication of whether the product is unreacted silanol, a possible hydrogen bonded adduct or a condensation product. In the case of a possible hydrogen bonded adduct if the hydrogen bond acceptor molecule is a liquid then the solid product has to be a hydrogen bonded adduct and the stoichiometry was determined by integration of the 111 NMR spectrum. Characterisation of the adducts was also carried out by 13C and 29Si NMR spectroscopy. In the solution 29Si NMR spectra, however, only one silicon resonance was observed for all the adducts even though the presence of up to four different silicon centres may have been determined by X-ray crystallography . This suggests that in solution either rapid exchange processes occur or that the solid state structures are not retained in solution due to dissociation. Due to the concentration dependance of hydrogen bonded systems the position of the Si resonance in the 29Si NMR spectra carries very little information about the strength or extent of hydrogen bonding. Likewise, the 13C NMR spectra show only one set of signals for the molecules present, even if several different sets are seen in the X-ray structure. As no correlations could be made between solution NMR and the solid state structures the solid state 29Si NMR spectra of some samples were recorded. These are discussed in more detail in Section 5.2.

Infrared spectroscopy The solid state infrared spectrum is the most important spectroscopic tool in the characterisation of a hydrogen bonded adduct. Differences in the v(OH) region (3500 - 2600 cm-1) and also in the v(SiO) region (950 - 830 cm-1) of the hydrogen bonded adduct from the infrared spectrum of the self-associated silanol are very apparent. The silanols which have been most extensively used in this study are Ph3SiOH and (HOPh2Si)20.

92 Me0C5H4N0. bonded adductswith(b) 4-NO2C5H4NO,(c)C5H5NO,(d)4-MeC5H4NO, and(e)4- Figure 3.1.Absorptionspectraintheinfraredregion of(a)Ph3SiOHandits1:1hydrogen the OHbandoftenoverlapswithCHstretchingregion. oxides alsoincreasesresultinginalargershiftOHfrequency.Itcanbeseenthat seen inFigure3.1.Itcanbethatastheelectrondonatingabilityofsubstituenton substituent onthehydrogenbondingpropertiesofadductswasstudiedindetailby the pyridineringincreaseshydrogenbondacceptorpropertiesofN- infrared spectroscopy.TheOHstretchingfrequenciesoftheadductsare3160,3000, X= 4-NO2,4-C1,H,3-Me,4-Me,2-Meand4-Me0). In thesolidstatespectrumbandsduetoSi-Ostretchareat855and835cm 3683 cm 2990, 2940,2930,2910and2870cm adducts inthesolidstatewithaseriesofsubstitutedpyridineN-oxidesXC5H4NO(where are ofstrongintensity.AsdescribedpreviouslyinSection1.4.5,Ph3SiOHforms1:1 around 3250cm Chapter 3 The 'free'OHinfraredstretchingfrequencyofPh3SiOHindiluteCC14solutionis -1

butinthesolidstate(KBrdisc)OHstretchingbandisbroadandcentred 148 4000 ABSO RBANCE -1

duetointermolecularhydrogenbondingbetweenPh3SiOHmolecules.

-1 respectively.Aselectionofthesespectramaybe 93 3000

Hydrogen bondedadductsofsilanols 148,149 Theinfluenceofthe 2000 -1 and Chapter 3 Hydrogen bonded adducts of silanols

Similarly, the 'free' OH stretching frequency of (HOPh2Si)20 in dilute CC14 solution is 3681 cm-1 but in the solid state (KBr disc) the OH stretching band is broad and centred around 3197 cm-1. The Si-O stretches in the solid state are both of strong intensity at 887 and 848 cm-1. When the hydrogen bond acceptor was a solid, infrared spectroscopy was instrumental in determining whether the product was genuinely an adduct or just a mixture of starting materials. If upon comparison of the infrared spectrum of the product with the infrared spectrum of a mixture of the starting materials in the same stoichiometric ratio (prepared by carefully grinding the starting materials together), negligible differences could be observed then it was concluded that no adduct had been formed. Infrared spectra were recorded of the samples as KBr discs to avoid interference from the C-H stretching vibrations associated with the use of Nujol mulls. Spectra for each adduct were obtained from at least three different sample preparations since small variations in the grinding technique have been associated with spectral variations of hydrogen bonded molecules.48 The preparation of adducts of silanols with a range of amines, in particular, has been attempted. The NH2 and NH stretching bands of primary and secondary amines appear in the same region as OH stretching bands (3450 - 3250 and 3500 - 3300 cm-1 respectively), although they are generally weaker.231,232 Upon hydrogen bonding the N-H or NH2 stretching band shows similar trends to those of the OH stretching band, it decreases in frequency, broadens, and increases in intensity and the NH2 bending frequency increases. Aliphatic secondary amines also exhibit a strong broad IR band in the 785 - 720 cm-1 region that is attributed to the NH wagging vibration. Tertiary amines are characterised only by skeletal vibrations involving nitrogen atoms and by modified CH3-(N) and CH2-(N) group vibrations. Secondary amine salts, R2NH2+, and tertiary amine salts, R3NH+, exhibit a broad multiband absorption in the 2700 - 2250 cm-1 region of medium to strong intensity.

94 Chapter 3 Hydrogen bonded adducts of silanols

Raman spectroscopy In Raman spectroscopy the OH stretching band of a molecule upon hydrogen bonding, although less broad, shows similarities to that in the infrared as far as frequency, band-width and structure are concerned. The intensity of the OH stretching fundamental, however, which is very strong in the infrared spectrum is quite weak in the Raman. Raman spectroscopic studies of Ph3SiOH have also shown that the '0 (SiO) vibration which is strong in the infrared spectrum is absent in the Raman spectrum.233 Therefore, Raman spectroscopy has not been used in general for the characterisation of adducts. Since Raman transitions require a polarizability change, however, the spectra can sometimes be useful for conformational studies and identifying complexes with centres of symmetry.

Mass spectrometry Mass spectrometry was not found to be useful in the characterisation of hydrogen bonded adducts since even the more gentle technique of FAB caused the hydrogen bonded adduct to be broken up into its constituent parts and no molecular ion peak was seen.

Thermal analysis Thermal analysis is the examination of the temperature dependent properties of materials and the basic principles and applications of thermoanalytical techniques have been reviewed recently.234 One of the commonest applications of thermoanalysis is in the examination of high molecular weight polymers such as polysiloxanes. However, the techniques of TGA (thermogravimetric analysis) and DSC (differential scanning calorimetry) have also been applied to the study of hydrogen bonded adducts of low molecular weight silanols.146,147,151 TGA measurements study the change in weight of a sample as a function of temperature and/or time. They can be used, therefore, to confirm host to guest stoichiometries in adducts formed by silanols and to determine whether the guest is lost in a single or multiple step. DSC allows the study of the enthalpy changes occurring during the heating process and also whether a reaction (i.e. a phase change or

95 Chapter 3 Hydrogen bonded adducts of silanols melting point) or chemical change (irreversible decomposition) is occurring. For example, Bourne et a/.146 have shown that in (Ph3SiOH)4.EtOH the ethanol is removed in two distinct steps with the formation of a new phase. A typical endotherm associated with the guest-release reaction of a hydrogen bonded adduct is shown in Figure 3.2. The thermal stability of the adduct can be assessed from the temperature characterising the start of the endothermic guest-release reaction, the extrapolated peak-onset temperature, Ton.151 This temperature is defined as the intersection of the tangent to the ascending peak slope and the linearly extrapolated initial base line.234 It is almost independent of the heating rate and sample quantity and is easier to determine than the initial peak temperature, Ti. The accuracy of temperature measurements are within 0.5 °C.

interpolated final base line ....-- base line initial

• Ton Tp Tc Tf Temperature

Figure 3.2. A typical endotherm asociated with the guest-release reaction of a hydrogen bonded adduct. Ti, initial peak temperature; Ton, extrapolated peak-onset temperature;

Tp, maximum peak temperature; Tc, extrapolated peak-offset temperature and Tf, final peak temperature.

For inclusion compounds which contain a host with different guests the onset temperatures are also a function of both the host-guest nonbonding interactions and the intrinsic physical properties of the guest itself.147 In particular, Bourne et al.151 have suggested that the normal boiling point, Tb, of the guest compound is important and that

96 Chapter 3 Hydrogen bonded adducts of silanols

Ton - Tb may be used as a measure of the relative stabilities of inclusion compounds. For example, the following order of stability was found for tris(1-naphthyl)silanol inclusion compounds, T" - Tb values are given in brackets: (1-naphthy1)3SiOH.toluene (-22.6 K) > (1-naphthyl)3SiOH.o-xylene (-42.9 K) > (1-naphthyl)3SiOH.m-xylene (-62.1 K) > (1-naphthy1)3SiOH.(p-xylene)2 (-66.9 K). The enthalpy of the guest release reaction may be obtained by integration of the peak, the base line usually being constructed by a linear interpolation and with an accuracy within several percent.

3.4 Adducts of (HOPh2Si)20

After the first adducts of (HOPh2Si)20 with amines were reported in 1965142 no further literature appears on the subject until in the late 1980's when crystal structures of a pyridazine adduct, RHOPh2S02013.(C4H4N2)26 and a pyridinium hydrochloride adduct (HOPh2Si)20.C5H5N.HC1144 were published (Section 1.4.5). This disiloxanediol is particularly suitable for hydrogen bonding studies since the it has an enhanced acidity compared to the analogous tetraalkyldisiloxanediols due to the presence of electron withdrawing phenyl groups, the bulk of which also make it less prone to condensation reactions. It also contains two Si-OH groups for hydrogen bonding, one at either end of the molecule which is ideal for the formation of infinite chain structures as in (HOPh2Si)20.TMEDA129 (Figure 1.15, Section 1.4.5). As discussed previously the SiOH groups are connected by a flexible siloxane linkage which is capable of adopting a range of Si-O-Si angles, e.g. in [(HOPh2Si)20]3.(C4H4N2)2 one Si-O-Si angle is linear while the other two have a more typical value of 144.5° (Figure 1.16, Section 1.4.5).6 It is, therefore, difficult to predict which molecules (HOPh2Si)20 will form an adduct with by geometry alone, since there appears to be little geometrical constraint on the disiloxanediol. Despite the bulky phenyl groups, (HOPh2Si)20 may still undergo condensation reactions to form higher linear or cyclic oligomers in the presence of acidic or basic molecules as described in Section 1.2.

97 Chapter 3 Hydrogen bonded adducts of silanols

Although no direct carbon analogue of (HOPh2Si)20 seems to be known, diols of the general formula (HOPh2C)2X where X represents a spacer group of limited flexibility such as o-, m- or p -C6H4, C.C, furyl, 1,1'-diphenyl or ferrocenyl, have been found to form hydrogen bonded adducts with a wide range of molecules such as acetone, DMSO, 1,4-dioxane and pyridine.235-238 Adducts of diols with a flexible spacer group, X, do not appear to have been reported.

Attempted preparation of the adducts was generally carried out by Method 1. The same results were obtained when a representative sample were attempted by Method 2.

3.4.1 With amines

Since (HOPh2Si)20 had been shown previously to have a propensity towards hydrogen bonded adduct formation with the amines Et2NH,142 Et3N,142 PhNH2,142

TmEDA,129,142 pyridine142 and pyridazine,6 attempts were made to prepare adducts of (HOPh2Si)20 with a wider range of amines. The reactions were generally carried out by Method 1. Enough hexane was added to the solutions to initiate crystallisation since prolonged periods of time in solution was found to encourage condensation reactions. Slow evaporation of a solution of (HOPh2Si)20 in an excess of liquid amine is not a viable method for adduct formation since this generally results in the formation of condensation products, e.g. with Et2NH or Et3N a viscous solid/liquid is formed which analysis by 1H NMR spectroscopy shows to be a mixture of oligomers and amine.

3.4.1.1 Primary amines

The NH2 group in primary amines has two hydrogen bond donors and one acceptor which is complementary to the OH group which has one hydrogen bond donor and two acceptors.

With the primary amines RNH2 where R = Me, Et, ripr, riBu, tBu, ±sBu, tpentyl or benzyl no adducts could be isolated. The 1H NMR spectra of the products revealed that no amine was present and that small quantities of condensation product were often formed. The reactions were carried out by Method 1 except for with MeNH2 and EtNH2

98 Chapter 3 Hydrogen bonded adducts of silanols which were purchased as anhydrous solutions in THF and, therefore, the reactions were carried out under nitrogen by Method 2 using THF as the solvent. With 1PrNH2, a white sticky solid was repeatedly formed by both methods and identified by 1H NMR spectroscopy as a mixture of condensation products and amine. In some cases, however, adduct formation appeared to take place by Method 1 and a white solid was isolated. Integration of the 1H NMR spectra suggested the formation of an adduct with either 2:1 or 3:1 stoichiometry and the infrared spectra were significantly different from the spectrum of the disiloxanediol. The irreproducibility of the results did not enable further analysis to be carried out or a conclusion to be made.

The common diaminoalkanes with terminal NH2 groups separated by a (CH2)n backbone where n = 3, 4 , 5, or 8 also failed to form adducts with (HOPh2Si)20 by Method 1.

There are a number of molecules containing two or three pendant NH2 groups attached to di- or triethylene arms which potentially provide both flexibility and multiple nitrogen donor sites for the preparation of interesting supramolecular hydrogen bonded structures. Although Ph3SiOH, surprisingly, forms a 1:1 adduct with tris(2- aminoethypamine (Section 3.5), the results with (HOPh2Si)20 were not so reproducible. With tris(2-aminoethyl)amine, a 2:1 adduct appeared to be formed from integration of the

1H NMR spectrum, although the additional formation of condensation products did not allow isolation and further characterisation of the adduct. No adduct could be isolated with N-(3-aminopropy1)-1,3-propanediamine.

3.4.1.2 Secondary amines

With the secondary amines R2NH where R = Me, iPr, nBu, 1Bu or pentyl no adduct could be isolated.

With Et2NH, however, an adduct was readily isolated by Method 1. Although integration of the 1H NMR spectrum suggested a 2:1 adduct, X-ray crystallography revealed that the stoichiometry in the solid state was, in fact, 4:2 (Section 3.4.1.2.1). The structure, shown in Figures 3.6 and 3.7, comprises two pairs of hydrogen bonded disiloxanediol molecules linked by a diethylamine molecule via Si-OH • • • N and

99 Chapter 3 Hydrogen bonded adducts of silanols

N-H • • • 0 hydrogen bonds. Instead of forming an infinite chain in this manner, however, the second pair of disiloxanediol molecules are hydrogen bonded to a second diethylamine molecule which terminates the hydrogen bonded network by a NH • • • it interaction with a phenyl ring (Figure 3.7). There appear to be no other structures of hydrogen bonded adducts with Et2NH reported in the literature (Cambridge Crystallographic Database search). The preparation was carried out using 1:1 molar equivalents of disiloxanediol and Et2NH but the 1:1 adduct reported to form by a similar method (using toluene and hexane) by Prescott and Selin142 could not be isolated. Prescott and Selin inferred the stoichiometry of their adduct from microanaltytical data. The theoretical elemental composition for a 1:1 adduct is C 69.1, H 6.6, Si 11.5 %. They found C 67.3, H 6.8, Si 12.55 %, i.e. the values are in poor agreement with those calculated. The theoretical composition of a 2:1 adduct is C 69.31, H 6.04, Si 12.43 %. The C and H percentages found by Prescott and Selin are still in poor agreement with these calculations but the Si percent is in reasonable agreement. The melting point of their adduct was 104-109 ° which is similar to that reported in this work for the 2:1 adduct, 102-104 °C. It may be concluded that the stoichiometry of the adduct prepared by Prescott and Selin was actually 2:1 but the unavailability of techniques such as 1H NMR spectroscopy and poor microanalytical data made identification difficult. Although the adduct is formed readily it must be noted that, if left in solution long before the addition of hexane to initiate crystallisation, condensation occurs to give the cyclic trisiloxane,

(Ph2SiO)3 as shown by 1H NMR and IR spectroscopy and melting point. In the infrared spectrum of [(HOPh2Si)20]4.(Et2NH)2 (Figure 3.3) there is a broad band in the OH stretching region corresponding to a hydrogen bonded silanol group. The centre of this band, however, is obscured by a relatively broad peak at 3230 cm-1 characteristic of a hydrogen bonded NH group. These stretches are in agreement with the hydrogen bonding arrangement observed in the X-ray structure, although a band corresponding to the NH • • • it interaction cannot be observed and is presumably obscured by the OH band. There is only one peak in the Si-O stretching region and this is

100 Chapter 3 Hydrogen bonded adducts of silanols reasonably broad and centred at 908 cm-1. The N-H deformation band is too weak to be detected in the Et2NH.

% 75-

T r a 6 n

m 5.5 t t a n. 45-

e . . . 3400 3000 2600 Wavenumbers

Figure 3.3. JR spectrum of [(HOPh2Si)20]4.(Et2NH)2 in the OH stretching region (KBr disc).

Since (HOPh2Si)20 formed an adduct with Et2NH it was attempted to see if an adduct would be formed if one of the ethyl groups was substituted for another group. However, no adduct was formed with either MeEtNH or nBuEtNH. Piperazine is a potentially useful amine for the formation of hydrogen bonded adducts since it contains two N-H groups which can act as hydrogen bond acceptors and /or donors and it has structural flexibility. The ring may adopt a variety of conformations and the N-H bonds may occupy either axial or equatorial sites. There has been, however, a paucity of hydrogen bonded adducts of piperazine in the literature until recently.236,239-

243 For example, Glidewell et c11.242 have prepared adducts of the rigid bisphenols X(C6H40 H )2 (X = 0, S, SO2, CO, CMe2) with piperazine in which the bisphenol:piperazine stoichiometries are either 1:1 (X = 0, S, CO) or 2:1 (X = SO2, CO, CMe2). The crystal structure of the 1:1 4,4'thiodiphenol (X = S) adduct with piperazine

101 Chapter 3 Hydrogen bonded adducts of silanols was found to contain chains of alternating bisphenol and piperazine units linked by 0-H • • • N hydrogen bonds.242 The N-H bonds are axial and are involved in N-H • • • n interactions with the phenyl rings in adjacent chains, thus acting as crosslinkers. Glidewell et al.239 have also prepared a 1:1 adduct of the diol ferrocene-1,1'- diylbis(diphenylmethanol) with piperazine in which the piperazine adopts a chair conformation with one axial and one equatorial N-H bond. The adduct is held together only by O-H • • • N hydrogen bonds. Ph3SiOH was also found to form a discrete centrosymmetric 2:1 adduct with piperazine by Method 1 (Section 3.5.1.2). Upon addition of either one or half an equivalent of piperazine to (HOPh2Si)20 dissolved in hot toluene, a white powdery solid was observed to precipitate rapidly from the clear solution initially obtained. The solid was filtered off to give a 1:1 adduct, (HOPh2Si)20.piperazine, as shown by integration of the 1H NMR spectrum. The adduct was repeatedly formed as a white powder which was sparingly soluble in toluene or ether. Attempts at recrystallising the adduct by slow evaporation of an acetone solution or from acetone/hexane failed to produce material suitable for X-ray crystallography.

The infrared spectrum of piperazine shows one strong N-H stretch at 3225 cm-1, as may be expected. In the adduct (HOPh2Si)20.piperazine, however, there are two sharp

N-H stretches of medium intensity at the higher frequencies of 3293 and 3270 cm-1 which suggest the presence of two inequivalent N-H groups (Figure 3.4). The relatively high frequency and narrow band width of these stretches suggest that the N-H groups are not participating in any hydrogen bonding interactions with the oxygen atoms of the silanol groups. The O-H stretching band of the disiloxanediol is broad and has shifted into the

CH region, although the centre of the band appears to be around 2738 cm-1. This is consistent with the formation of a very strong hydrogen bond, in this case OH • • • N, with the possibility of some proton transfer. The .u(Si-0) region of this adduct is more difficult to interpret since the N-H wagging modes of piperazine also occur in this region, although the v(Si-0) bands at 887 and 848 cm-1 have disappeared.

102 Chapter 3 Hydrogen bonded adducts of silanols

T r a

t t n

3500 3200 2800 2400 Wavenumbers

Figure 3.4. Infrared spectrum of (HOPh2Si)20.piperazine (KBr disc).

Apart from the presence of two N-H stretching bands instead of one, the infrared spectrum in the 3500 - 2600 cm-1 region is very similar to the spectrum of (Ph3SiOH)2.piperazine which X-ray crystallographic studies show to be a centrosymmetric adduct with each Ph3SiOH molecule hydrogen bonded to one of the nitrogen atoms of the piperazine via OH • • • N interactions (Section 3.5.1.2). The structure of (HOPh2Si)20.piperazine may, therefore, be an extension of this structure, comprising an infinite chain of alternating disiloxanediol and piperazine molecules (Figure 3.5), but with either non centrosymmetric piperazine molecules or two crystallographically independent centrosymmetric piperazine molecules as in the arrangement found in (HOPh2Si)20.dioxane (Section 4.3.1).

Ph Ph Ph / Ph,„ / i —0 Ff - - - rSi—OH /S L0 O I I N - - - - -HO —Si-. 2,N - - - - -HO — Si-.Sm i H / Ph H Ph Ph Ph

Figure 3.5. Proposed structure of (HOPh2Si)20.piperazine.

103 Chapter 3 Hydrogen bonded adducts of silanols

3.4.1.2.1 Crystal structure of RHOPh2Si)204(Et2N11)2

Needle-like crystals of [(110Ph2S020]4.(Et2N1-1)2 suitable for a structure determination were obtained from toluene/hexane. Data were collected at room temperature and the hydrogen atoms were not located. The acidic and N-H protons are fixed at 0.90 A. Selected bond lengths and angles are provided in Table 3.1 and further crystallographic data, including full bond lengths and angles, may be found in the Appendix.

The asymmetric unit (Figures 3.6 and 3.7) contains four crystallographically independent siloxanediol molecules of similar conformations, hydrogen bonded together to form two pairs. Each disiloxanediol molecule has a pseudo gauche relationship between its hydroxyl groups with respect to the associated Si—Si vector (torsion angles 0- Si—Si-0 ranging between 37 and 59°). The two pairs of hydrogen bonded siloxanediols are connected by one Et2NH acting as a bridge (0 • • • N 2.82 A, N • • • 0 3.14 A). The second Et2NH, rather than acting as a bridge to a further pair of disiloxanediol molecules, prevents any further chain formation by interacting with a phenyl group. The distance of the N atom of the NH group from the nearest carbon (ipso carbon), C(63), is 3.59 A and that from the plane of the ring is 3.50 A. The NH bond makes an angle of 79.1° with the plane of the ring. The 4:2 complexes in the crystal, therefore, exist as discrete hydrogen bonded units. The siloxane Si-O-Si angles are in the narrow range between 140.5(4) and 145.5(4) ° and their Si-O distances range between 1.608(6) and 1.649(5) A; the Si-OH distances range between 1.587(6) and 1.636(6) A. The Si-C and aromatic C-C bond lengths are unexceptional.

For comparison of hydrogen bond distances and angles in related silanol adducts see Table 3.6, Section 3.8.

104 C(22)

C(99)

C1204)

C(200)

C(33)

Figure 3.6. View of the hydrogen bonding in [(HOPh2Si)20]4.(Et2NH)2 with the phenyl rings removed. Hydrogen bonds are represented by

dashed lines and hydrogen atoms attached to the carbons in Et2NH are omitted for clarity. Figure 3.7. Alternative view of the hydrogen bonding in [(HOPh2Si)20]4.(Et2NH)2. The phenyl rings are included to demonstrate the terminal

N-H • • • It interaction with a phenyl ring. Silicon atoms are large textured circles, carbon atoms are open circles, oxygen atoms are shaded circles, nitrogen atoms are hatched circles and hydrogen atoms are small open circles.

Chapter 3 Hydrogen bonded adducts of silanols

Table 3.1. Selected bond lengths and angles in the crystal structure of

RHOPh2Si)2014.(Et2N11)2.-

0(1) • • • 0(30) 2.66 A

0(1) • • • 0(32) 2.58 A

o(i) • • • N(202) 2.82 A

0(3) • • • 0(32) 2.74 A Si(1) - 0(2) - Si(3) 142.3(4)°

0(92) • • • 0(62) 2.69 A Si(30) - 0(31) - Si(32) 145.5(4)°

0(92) • • • 0(60) 2.56 A Si(92) - 0(91) - Si(90) 143.9(4)°

0(92) • • • N(302) 2.70 A Si(62) - 0(61) - Si(60) 140.5(4)°

0(90) • • • 0(60) 2.75 A N(302)-H • • • C(63) 151.2°

N(202) • • • 0(90) 3.14 A

N(302) • • • C(63) 3.59 A

3.4.1.3 Tertiary amines

Tetraphenyldisiloxanediol has been reported to form a 1:1 adduct with Et3N142 and the unsymmetrical disiloxanediol HOPh2SiOSiMePhOH has been reported to form a

1:1 adduct with Bu3N.143 Attempts at preparing adducts of (HOPh2Si)20 with nPr3N or nBu3N, however, failed by Method 1. The 1H NMR spectra of the products showed peaks due to the disiloxanediol only.

A 2:1 adduct of (HOPh2Si)20 with Et3N, as determined by 1H NMR spectroscopy, was found to form readily by Method 1. The 1:1 adduct reported by

Prescott and Selin142 could not be isolated even though the reaction was repeatedly carried out using a 1:1 stoichiometric ratio of disiloxanediol and triethylamine. The melting point of the 2:1 adduct is 85-88 °C which is in a similar range to that obtained by

107 Chapter 3 Hydrogen bonded adducts of silanols

Prescott and Selin of 90-95 'C.142 The stoichiometry of the 1:1 adduct was inferred from microanalytical data, although the actual data was not published. It is possible that, as in the case of RHOPh2S02014-(Et2NH)2 (Section 3.4.1.2), the microanalytical data obtained was inconclusive and the unavailability of 1H NMR spectroscopic analysis, for example, precluded an accurate determination of the stoichiometry. The 2:1 stoichiometry of the adduct formed in this work was also confirmed by X- ray crystallography (Section 3.4.1.3.1). The structure, however, is particularly interesting since proton transfer from one of the silanol groups occurs to form a siloxy anion and Et3NH+ (Figure 3.11).

The infrared spectrum of the adduct shows a broad band of medium intensity centred around 3280 cm-1 which is consistent with the formation of hydrogen bonds between the disiloxanediol molecules, which make up the largest part of the structure. The region between 3000 and 2250 cm-1, however, is very broad making it difficult to assign the NH stretch of the Et3NI-1+ moiety. Therefore, without crystallographic evidence, it is unlikely that the presence of proton transfer would have been discovered. As in the adduct of (HOPh2Si)20 with Et2NH, Section 3.4.1.2, there is only one peak in the Si-O stretching region which is relatively broad and centred at 912 cm-1. The presence of both a silanol group and a siloxy anion in the same siloxanediol molecule is unusual. In fact, early last year Sullivan et al.244 presented the first structurally characterised example of a monometallated derivative of an a,w-siloxanediol,

[K{O(Ph2Si0)2SiPh2OH}12.C6H6 (Figure 3.8). This structure may represent the associated product of the first step in the ring-opening polymerisation of (Ph2SiO)3.

It may be postulated that the adduct (HOPh2Si)20. { [HOPh2SiOSiPh20][Et3N11]} represents the first stage in the base catalysed condensation of oc,0-siloxanediols. The siloxy anion thus produced may proceed to attack a silicon atom in another disiloxanediol molecule with the release of OH- which combines with the H+ ion on the protonated amine to regenerate the Et3N and the process is repeated. The monometallated derivatives of some diorganosilanediols such as [tBu2Si(OH)(OLi).THF]4158 and Nu2Si(OH)(0Na).THF)6159 have also been structurally characterised (Section 1.4.5).

108

Chapter 3 Hydrogen bonded adducts of silanols

O(2a) C(13a)

Si(2a) O(3a) C(26) C(3 I a)

Si(3a)

C(25a)

C(13)

Figure 3.8. Molecular structure of [K{O(Ph2Si0)2SiPh2OH}12.C6116244

The strong hindered amine bases 1,4-diazabicyclo[2.2.2.]octane (DABCO) [Figure 3.9(a)] and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) [Figure 3.9(b)] are commonly used as dehydrohalogenating agents and are effective catalysts for a range of organic reactions. Since the strong base Et3N was found to form an adduct with (HOPh2Si)20 in which proton transfer occurred from one of the silanol groups to the Et3N molecule, it was of interest to find out whether (HOPh2Si)20 would form an adduct with other strong bases without condensation and, if so, whether proton transfer would also occur.

00,4 ‘1:1\

1,4-Diazabicyclo[2.2.2]octane 1,8-Diazabicyclo[5.4.0]undec-7-ene (DABCO) (DBU)

(a) (b) Figure 3.9. The structures of the strong hindered amine bases (a) DABCO and (b) DBU.

109 Chapter 3 Hydrogen bonded adducts of silanols

Previous work has shown that DABCO forms a discrete 2:1 adduct with phenol and a 1:1 adduct with the diol hydroquinone of infinite chain structure.245 In both cases the molecules are linked by O-H • • • N hydrogen bonds. A 1:1 adduct of the diol ferrocene-1,1'-diylbis(diphenylmethanol), [Fe(C5H4CPh2OH)2] with DABCO has also been reported although no structural data was obtained.237

Recently, the bisphenols of the type X(C6H4OH)2 (X = Me2C, 0, S or CO) have been found to form 1:1 adducts with DABC0.246 In the case where X = S, a 2:1 adduct was also isolated. The crystal structures of the 1:1 adducts where X = Me2C, 0, S were determined and found to comprise infinite chains of alternating biphenol and DABCO molecules linked by 0-H • • • N hydrogen bonds. Where X = 0 or S, additional CH • • • X interactions cross-linked pairs of parallel chains to form ladders. In the crystal structure of [S(C6H4OH)2]2.DABCO one OH group of the bisphenol acts as a hydrogen bond donor to the nitrogen of the DABCO molecule and also as a hydrogen bond acceptor from an OH group of another bisphenol molecule resulting in an infinite sheet like chain.

With the trisphenol, 1,1,1 -tris(4-hydroxyphenypethane, CH3C(C6H4OH)3, however, a more complicated ternary complex CH3( C6H4OH)3.DABCO.H20 was isolated which exhibited partial proton transfer.243 Structural characterisation of the adduct showed that one trisphenol and one DABCO molecule were linked by a water molecule which acts as a hydrogen bond donor to one nitrogen of the DABCO molecule and to one oxygen of the trisphenol molecule. Partial transfer, however, of one of the hydroxyl hydrogen atoms of the next bisphenol molecule to the other nitrogen atom in the

DABCO molecule links the trisphenol and DABCO unit by a mixture of N-H • • • 0

(major occupancy) and O-H • • • N (minor occupancy) hydrogen bonds.

In the adduct formed between 1,3,5-benzenetricarboxylic acid and DABCO a single but complete proton transfer occurs to give C6H13N2-F.C9H506-.247 An infinite two-dimensional sheet structure is formed by a combination of OH • • • 0, OH • • • H and

N-H • • • 0 hydrogen bonds.

When one molar equivalent of DABCO was added to a solution of (HOPh2Si)20 in hot toluene as in Method 1, the solution initially became colourless but then a white

110 Chapter 3 Hydrogen bonded adducts of silanols powdery solid rapidly precipitated. Integration of the 1H NMR spectrum of a CDC13 solution of the solid indicated a 1:1 stoichiometry. Recrystallisation of the adduct from toluene/hexane and by slow evaporation of an ether solution failed to give crystals suitable for X-ray crystallography.

The infrared spectrum of (HOPh2Si)20.DABCO shows a broad band of medium intensity centred around 2730 cm-1 consistent with the presence of a strong hydrogen bond, or even some proton transfer, as may be expected with the strong base, DABCO.

The spectrum is almost identical in the 3500 to 2600 cm-1 region to the infrared spectrum of (HOPh2Si)20.piperazine (Figure 3.4) except for the absence of the NH stretching vibrations. The Si-O stretching region is difficult to interpret as DABCO also exhibits bands in this region. The spectrum is also almost identical to that recorded for the Ph3SiOH adduct with DABCO of 4:3 stoichiometry (Section 3.5.1.3), an X-ray structure of which also could not be obtained. It may be postulated, therefore, that the structure is similar to that proposed for (HOPh2Si)20.piperazine (Figure 3.5) with infinite chains of alternating (HOPh2Si)20 and DABCO molecules. This would also be similar to the 1:1 biphenol [X(C6H4OH)2] : DABCO adducts where X = Me2C, 0, S.246 When half a molar equivalent of DABCO was used the same observations as above were made. The stoichiometry of the adduct was found to be 2:1 by 1H NMR spectroscopy and the infrared spectrum was significantly different to that of the starting materials. Attempts at recrystallising the adduct from similar solvents to those described above also failed.

In the infrared spectrum of [(HOPh2Si)20]2.DABCO, a broad band of medium intensity centred around 3293 cm-1 indicates the presence of hydrogen bonded OH groups, although of much weaker strength than in the 1:1 adduct above. The v(Si-0) bands at 887 and 848 cm-1 in the spectrum of the disiloxanediol have been replaced by a broader band at 914 cm-1, although as mentioned earlier, DABCO also exhibits bands in the Si-O stretching region. In the absence of crystallographic data it is very difficult to suggest a structure for this adduct. The frequency of the OH stretching band in the infrared spectrum, however, provides conclusive evidence that proton transfer has not

111

Chapter 3 Hydrogen bonded adducts of silanols

occurred. Its relatively high frequency (compared with 3197 cm-1 in the disiloxanediol) suggests that a structure containing weaker OH • • • 0 hydrogen bonds between disiloxanediol molecules in addition to OH • • • N hydrogen bonds to the DABCO molecule may be present. For example, the chain structure formed by

RHOPh2S02012.pyrazine (Section 3.4.1.4, Figure 3.13) is just one possibility. When either one or half a molar equivalent of DBU was added to a solution of (HOPh2Si)2O in hot toluene a white powdery solid was rapidly precipitated. This solid, however, was identified by 1H NMR spectroscopy as the disiloxanediol only. Upon standing the solid dissolved to give a colourless solution which, when the solvent evaporated, left a white sticky solid, identified by 1H NMR spectroscopy as a mixture of condensation products and amine. The absence of adduct formation for this amine may be due to steric factors. There appears to be no literature on adduct formation with DBU. Hexamethylenetetramine, HMTA, has been found to form a variety of hydrogen bonded adducts with phenols and substituted phenols and also with ferrocene- 1,11diylbis(diphenylmethanol).237,248-254 During the course of these studies Spalding et al.255 isolated and structurally characterised the adduct (HOPh2Si)20.HMTA which forms hydrogen bonded chains of alternate disiloxanediol and HMTA molecules (Figure 3.10). Only two of the available four nitrogen atoms of the HMTA molecule are involved in hydrogen bonding interactions. Similarly with phenols and substituted phenols,

HMTA acts only as a mono- or bis- acceptor of hydrogen bonds. 249-252 Only with pheno1248 itself and tris(4-hydroxy-3,5-dimethyl-benzyl)amine253 does HMTA act as a triple acceptor and there appear to be no examples of HMTA acting as a quadruple hydrogen bond acceptor.

N.. N N.. N N N N . v •, • H H H H • Ph2 Ph2 / Ph2 Ph2 / 0 —SiN ,Si 0 NO S i—O iN VS 0 0

Figure 3.10. The infinite chain structure formed by (HOPh2Si)20.HMTA.255

112 Chapter 3 Hydrogen bonded adducts of silanols

3.4.1.3.1 Crystal structure of (HOPh2Si)20.{[HOPh2SiOSiPh20][Et3MI]}

Crystals of (HOPh2Si)20. [HOPh2SiOSiPh20][Et3N1-1] } suitable for X-ray crystallography were obtained from toluene/hexane. X-ray data were collected at 223(2) K and the acidic hydrogens were located. Pertinent bond lengths and angles are summarised in Table 3.2 and further crystallographic data may be found in the Appendix. The X-ray structure determination (Figure 3.11) establishes that the amine has been protonated to give a cation [Et3NH]+ and that the siloxy anion, thus formed, is hydrogen bonded to both protons of the second disiloxanediol [0(1A) • • • H-0(1B) 1.840, O(1A) • • • H-0(2B) 1.695 A], the link between the two disiloxane species being reinforced by a third hydrogen bond [O(2A)-H • • • O(1B) 1.871 A]. The cation [Et3NH-1 is linked via a strong hydrogen bond [N(1)-H • • • O(1A) 1.717 A] to the siloxy anion resulting in approximately tetrahedral coordination at O(1A). The two Si-O-Si bond angles, Si(2B)-0(3B)-Si( 1B) and Si(2A)-O(3A)-Si(1A) of 144.6(4) and 139.1(4) ° respectively, are smaller than those found in the hydrogen bonded double chains of (HOPh2S020 alone [147.8(3) - 162.5(3) 1,105 although comparable to those in the structure of [(HOPh2Si)20}4.(Et2NH)2 [140.5(4) - 145.5(4) °] (Section 3.4.1.2.1). The Si- C and aromatic C-C bond lengths are typical.

113 C(24A1 CC23A) 034B)

LI43A)

M5A1

Figure 3.11. View of the hydrogen bonded adduct (HOPh2S020.([1-10Ph2SiOSiPh20][Et3NH]l. Hydrogen bonds are represented by dashed

lines and hydrogen atoms attached to carbon are omitted for clarity.

Chapter 3 Hydrogen bonded adducts of silanols

Table 3.2. Selected bond lengths and angles in the crystal structure of

(HOPh2Si)20. { [HOPh2SiOSiPh20][Et3N1-1]1

0(2A)-H • • • 0(1B) 1.871 A

0(1B)-H • • • 0(1A) 1.840 A

O(2B)-H • • • 0(1A) 1.695 A

N(1)-H • • • O(1A) 1.717 A O(2A)-H • • • 0(1B) 168.9 °

O(2A) • • • 0(1B) 2.750 A 0(1B)-H • • • 0(1A) 159.6°

0(1B) • • • 0(1A) 2.547 A O(2B)-H • • • O(1A) 164.8 °

0(2B) • • • 0(1A) 2.660 A N(1)-H • • • O(1A) 159.4 °

N(1) • • • 0(1A) 2.861 A Si(2B)-O(3B)-Si(1B) 144.6(4) °

O(2A)-H 0.89(8) A Si(2A)-O(3A)-Si(1A) 139.1(4) °

O(1B)-H 0.74(7) A

O(2B)-H 0.99(10) A

N(1)-H 1.189(9) A

3.4.1.4 With nitrogen heterocycles

A 1:1 adduct of (HOPh2Si)20 with pyridine was isolated in agreement with that prepared by Prescott and Selin.142 This was structurally characterised by Spalding et al.255 who also prepared and structurally characterised adducts with other nitrogen heterocycles over the time period of these studies. The adduct (HOPh2Si)20.pyridine

(Figure 3.12) comprises an infinite chain of alternate disiloxanediol and pyridine molecules in which each silanol group acts both as a hydrogen bond donor towards the nitrogen atom of the pyridine and as a hydrogen bond acceptor from the silanol group of the next disiloxanediol molecule. The Si-O-Si angle in the disiloxanediol appears to be linear, as found in (HOPh2Si)20.TMEDA129 and one of the disiloxanediol molecules in

RHOPh2S02013.(C4H4N2)26 (Section 1.4.5).

115 Chapter 3 Hydrogen bonded adducts of silanols

„,... -...... /, ri,

H ... I '0-..,_ •.....-- 0. Ph2 Ph2 '-9---si-o-si-..... O H Ph2 Ph2 N

Figure 3.12. The hydrogen bonded chain formed by (HOPh2Si)20.pyridine.255

A 2:1 adduct of (HOPh2Si)20 with pyrazine and a 1:1 adduct with 2,2'-bipyridyl were also structurally characterised by Spalding et al.255 (Figures 3.13 and 3.14). In the structure of [(HOPh2Si)20]2.pyrazine (Figure 3.13) two disiloxanediol molecules are hydrogen bonded to each other via OH • • • 0 interactions to form a ring and then one silanol group on each disiloxanediol is involved in a further hydrogen bond to a nitrogen atom of the pyrazine molecule. In this manner an infinite chain structure is formed. The adduct (HOPh2Si)20.2,2'bipyridyl forms an infinite chain structure of alternate disiloxanediol and bipyridyl molecules (Figure 3.14), as may be expected.

--- Ph2....,°••••.„. Ph2 ....0 Si Si —0 Hs , .. ,.N ...... „..z,„,.., s, *0 i...... _ .....,.S0.,.H `H Ph2 -0- Ph2

Figure 3.13. The hydrogen bonded structure of [(HOPh2Si)20]2.pyrazine.255

116

Chapter 3 Hydrogen bonded adducts of silanols

H'O—SiPh2 SiPh2

H" H" Ph2S1-0 .../ Ph2Si-0

Figure 3.14. The hydrogen bonded chain structure of (HOPh2Si)20.2,2'-bipyridy1.255

Attempts were made at preparing adducts of imidazole and the substituted imidazoles shown below in Figure 3.15. These are representative of fragments present in biological systems.

CH3 CH3 H H CH3

(a) (b) (c) Figure 3.15. Structures of (a) imidazole, (b) 2-methylimidazole and (c) 1,2-dimethylimidazole.

Addition of one equivalent of imidazole to (HOPh2Si)20 by Method 1 resulted in the formation of fine white crystals upon the addition of hexane. It was difficult to determine the stoichiometry from 1H NMR spectroscopy as the two peaks due to the CH groups of imidazole coincide with the phenyl region of (HOPh2Si)20. Careful analysis of the spectra obtained, however, suggests that a 1:1 adduct is formed but recrystallisation of the adduct from toluene/hexane or slow evaporation of an ether solution did not produce crystals suitable for X-ray analysis. The infrared spectrum of the white crystals (KBr disc) is significantly different from the spectra of either 1:1 or 1:2 molar ratios of the starting materials ground together. The OH and NH stretching region, however, is difficult to interpret due to the large number of CH peaks between 3159 and 2870 cm-1 which appear to obscure the OH and

117 Chapter 3 Hydrogen bonded adducts of silanols

NH bands. The band at 3159 cm-1, however, may be due to a hydrogen bonded NH group as it is relatively broad compared with the other peaks, but not broad enough to be an OH band. The Si-O stretching frequencies, though, have shifted from 887 and 848 cm-1 to 878 and 828 cm-1. Addition of hexane to an equimolar solution of 2-methylimidazole and (HOPh2Si)20 in toluene resulted in the formation of a white powder. Integration of the

1H NMR spectrum suggests the formation of a 2:3 adduct but attempts at recrystallisation by the same methods as above repeatedly resulted in the formation of powder. Again, the infrared spectrum confirms the formation of a hydrogen bonded adduct with 2-methylimidazole but interpretation of the infrared spectrum is difficult due to a number of CH peaks which obscure the OH and NH region. Although a peak occurs at 3197 cm-1 which is identical in wavenumber to that of the OH band in (HOPh2S020 alone, the peak is much narrower, possibly due to the NH stretch of a NH group involved in hydrogen bonding interactions with a silanol oxygen. There is only one stretch in the

Si-O stretching region which is relatively broad and centred at 902 cm-1. It is not possible to suggest a hydrogen bonded structure for this adduct due to the unusual stoichiometry and lack of related examples. With a molar equivalent of 1,2-dimethylimidazole and (HOPh2Si)20, colourless needles were formed upon addition of hexane and integration of the 1H NMR spectrum revealed a 1:1 stoichiometry. Recrystallisation of the adduct was also attempted by the methods mentioned previously but suitable crystals for X-ray analysis were not obtained. The infrared spectrum of the 1,2-dimethylimidazole adduct displays a broad OH band centred around 3260 cm-1 compared with 3197 cm-1 in the spectrum of the disiloxanediol. The 1)(Si-0) region contains one relatively broad band at 910 cm-1. A possible structure for this adduct is also difficult to suggest.

3.4.2 With alcohols

Triphenylsilanol has been shown to form a 4:1 adduct with ethanol in the presence of methanol, isopropanol and water l 46 and [(2,6-Et2C 6H 3)(2,6-Et2-4- tBuC6H2)(OH)Si)20 crystallises as a hydrogen bonded adduct with ethanol161,162

118 Chapter 3 Hydrogen bonded adducts of silanols

(Section 1.4.5). It was, therefore, of interest to determine whether (HOPh2Si)20 would also form an adduct with a simple alcohol. The rigid diol, 2,2'-bis- (diphenylhydroxymethyl)-1,11-diphenyl is also known to form 1:1 adducts with Me0H and EtOH.235

Slow evaporation of solutions of (HOPh2Si)20 in methanol, ethanol or isopropanol gave colourless crystals which were identified by 1H NMR spectroscopy as unreacted disiloxanediol.

As (HOPh2Si)20 is insoluble in water alone, an acetone solution of the disiloxanediol and water was left so that the solvent could evaporate slowly. The white powder produced was identified as the disiloxanediol by 1H NMR and infrared spectroscopy.

The structure of pentaerythritol, C(CH2OH)4, with four OH groups appears to be suited to the preparation of interesting supramolecular hydrogen bonded structures, although no examples could be found in the literature. It is, however, a high melting point solid which is insoluble in most organic solvents. It was found to be slightly soluble in methanol and so it was attempted to isolate an adduct of (HOPh2Si)20 with pentaerythritol by carrying out the reactions in methanol by a modification of Method 2. The resulting product, however, appeared to be just a mixture of the starting materials, as shown by infrared and 1H NMR spectroscopy.

3.4.3 With ethers

Tetraphenyldisiloxanediol may be recrystallised from Et20 or THE without hydrogen bonded adduct formation. Such adduct formation is exemplified by cis-cis-cis- [(HO)PhSi0]4 which crystallises from ether as a hydrogen bonded dimer of tetrasilanol units with one molecule of ether per tetrasilanol (Section 4.5).256 The ether, as may be expected, is only loosely associated and is rapidly lost in vacuo to leave the tetrasilanol as a white powder.

1,4-Dioxane is a widely used solvent and is frequently used in the condensation reactions of organosilanol species. In fact, the monofunctional silanols Ph3SiOH and (1-naphthyl)3SiOH have both been reported to form adducts with 1,4-dioxane (Section

119 Chapter 3 Hydrogen bonded adducts of silanols

1.4.5).147 Therefore, it was of interest to see whether the difunctional (HOPh2Si)20 would also form an adduct with 1,4-dioxane. 1H NMR spectroscopy indicated that a 1:1 adduct of (HOPh2Si)20 with 1,4-dioxane was isolated from both Method 1 and slow evaporation of a solution of the disiloxanediol in 1,4-dioxane. X-ray crystallographic studies revealed that the structure consists of an infinite chain of hydrogen bonded disiloxanediol and 1,4-dioxane molecules, as may have been expected (Figure 3.16, Section 3.4.3.1). The infrared spectrum of (HOPh2Si)20.1,4-dioxane shows a strong broad OH stretch centred at 3357 cm-1 consistent with the formation of SiOH • • • 0 interactions. The Si-O stretches are shifted to 862 and 889 cm-1 but still retain their strong intensity. Weber and co-workers have previously designed a series of singly bridged triarylmethanol host compounds as receptors or sequestering agents for the formation of crystalline inclusion complexes with 1,4-dioxane in order to facilitate safe handling, storage and sensing of the toxic solvent.257-260 A variety of organic inclusion compounds with 1,4-dioxane as the guest have also been isolated261-270 e.g. with substituted fluoren- 9-ol hosts.269 The related 1,3,5-trioxane, (CH2O)3, is a solid. Attempts at isolating an adduct of (HOPh2Si)20 with trioxane by Method 1 failed and only the disiloxanediol precipitated out of solution upon addition of hexane, as shown by 1H NMR spectroscopy.

3.4.3.1 Crystal structure of (HOPh2Si)20.1,4-dioxane Crystals suitable for X-ray crystallography were grown from toluene/hexane. Data were collected at 198(2) K and the hydrogen atoms were located. Further crystallographic details may be found in the Appendix. Selected bond lengths and angles are given in Table 3.3. In the crystal structure of (HOPh2Si)20.1,4-dioxane the disiloxanediol is linked via OH • • • 0 interactions to the two oxygen donors of the two crystallographically independent centrosymmetric dioxane molecules [0(1)-H• • • 0(5) 1.920, 0(2)-H • • • 0(4) 1.911 A] to form an infinite polymeric chain of alternate (HOPh2Si)20 and 1,4-dioxane molecules , as shown in Figure 3.16. There are no hydrogen bonding interactions

120 Chapter 3 Hydrogen bonded adducts of silanols between the chains. The 0-H • • • 0 hydrogen bond angles of 168.7 and 164.8 ° are close to those found in the related 1,4-dioxane adducts (Ph3SiOH)4.1,4-dioxane (164.7 and

165.6 0)147 and (1-naphthyl)3SiOH.1,4-dioxane (169.7 0).147 The OH groups of the siloxane unit are arranged in a transoid configuration in order for the molecules to link up in a linear polymeric fashion. This is in contrast to the cisoid arrangement found in (HOPh2Si)20.{ [HOPh2SiOSiPh20][Et3N11]} in which a discrete 2:1 adduct is formed (Section 3.4.1.3.1). The Si-O-Si angle of the siloxane unit at 166.0(2)° is similar to that found in (HOPh2Si)20105 itself and near the mid range of the reported values for

[(HOPh2Si)20]3-(C4H4N2)2 6 but somewhat greater than that found in (HOPh2S020.1 (110Ph2SiOSiPh20][Et3N11]} or [(HOPh2Si)20]4.(Et2NH)2. The Si-C and C-C bonds of the disiloxanediol molecule are unexceptional. Each six-membered

1,4-dioxane molecule has an inversion centre in the middle of the ring, and the ring atoms are arranged in a chair conformation with the maximum deviations from best mean plane defined by the ring atoms of 0.23 and 0.22 A for C(1) and C(3) respectively. In the 1,4- dioxane molecules the C-0 bond lengths vary from 1.390(5) to 1.448(6) A and the C-C bond lengths vary from 1.465(7) to 1.473(7) A and are typical.

Table 3.3. Selected bond lengths and angles in the crystal structure of (HOPh2Si)20.1,4-dioxane.

0(1)-1-1 • • • 0(5) 1.920 A 0(2)-H • • • 0(4) 1.911 A Si(2)-0(3)-Si(l) 166.0(2) 0 0(1) • • • 0(5) 2.714 A 0(1)-H • • • 0(5) 168.7 ° 0(2) • • • 0(4) 2.836 A 0(2)-H • • • 0(4) 164.8 ° 0(1)-H 0.80(4) A 0(2)-H 0.92(4) A

121 C(13) CI14)

cns) C(12)

C(16)

C(3)

C(33)

Figure 3.16. View of the hydrogen bonded chain formed by (HOPh2Si)20.1,4-dioxane. Hydrogen bonds are represented by dashed lines and

hydrogen atoms attached to carbon are omitted for clarity. Chapter 3 Hydrogen bonded adducts of silanols

3.4.4 With crown ethers

Triphenylsilanol forms a simple centrosymmetric 2:1 adduct with 12-crown-4.5 With (HOPh2Si)20 it was, therefore, considered that this discrete hydrogen bonded arrangement may be extended to form an infinite chain of alternate disiloxanediol and crown ether molecules. Unlike the simple 12-crown-4 adduct, Ph3SiOH forms a ternary complex, (Ph3SiOH)2.18-crown-6.(H20)2, with 18-crown-6 (Section 3.5.3). The formation of ternary complexes of 18-crown-6 with neutral molecules is common (Section 3.5.3) and has been observed for the diol complex, (4,4'-biphenyldiol)2.18- crown-6.(H20)2 which forms an infinite chain of diol and crown ether molecules linked by water molecules.271 It was anticipated that (HOPh2Si)20 would form a similar complex with 18-crown-6.

When one or two molar equivalents of (HOPh2Si)20 were used in the attempted preparation of adducts, with either 12-crown-4 or 18-crown-6, by Method 1, no crystals could be isolated upon addition of hexane. When the toluene/hexane was left to evaporate a colourless viscous liquid remained which appeared by infrared spectroscopy to be a mixture of the disiloxanediol and crown. When three or four equivalents of

(HOPh2Si)20 were employed 1H NMR spectroscopy showed that only the disiloxanediol crystallised out. There appears to be no simple explanation for these results since solution studies have shown that (HOPh2Si)20 is generally a stronger hydrogen bond donor than Ph3SiOH towards molecules in solution (Section 2.2). An assessment of the relative hydrogen bonding abilities of (HOPh2Si)20 towards crown ethers in solution in comparison to Ph3SiOH was not carried out since only solution cells with NaC1 or KBr plates were available.

3.4.5 With amino acids

Since amino acids contain both a basic amine function and an acidic carboxylic acid function, which are both capable of hydrogen bonding interactions with silanol groups (Section 1.4.5), attempts were made to prepare adducts of (HOPh2Si)20 with amino acids. Since amino acids exist as zwitterions they form particularly strong crystal

123 Chapter 3 Hydrogen bonded adducts of silanols lattices and are, therefore, insoluble in most solvents. Anthranilic acid, 2- (H2N)C6H4CO2H, however, was found to be soluble in ether and the attempted preparation of an adduct was carried out by Method 2. The resulting solid proved to be just a mixture of the two starting materials and not an adduct as shown by infrared and 1H NMR spectroscopy. The adducts of silanols prepared so far, both in this thesis and in the literature, have been with non self-associating molecules. The preparation of adducts with amino acids may therefore be prevented by the strength of their self-association, as well as by the pH dependence of the form in which the amino acid exists. More research into the viability of hydrogen bonding to amino acids, therefore, is needed before further experimental work is carried out.

3.4.6 With mixtures of amines and oxygen containing molecules Having successfully prepared a number of adducts of (HOPh2Si)20 with amines, experiments were carried out to determine how selective the disiloxanediol was in adduct formation and whether, having two silanol groups available for hydrogen bonding, the formation of ternary complexes with two different amines/oxygen containing molecules was possible. The reactions were carried out by Method 1 using two slightly different approaches. The first one involved the use of a molar ratio of (HOPh2Si)20 and a mixture of two amines, or an amine and dioxane, such that there was insufficient disiloxanediol to form an adduct with each of the amines/dioxane separately. Under these conditions the adduct (HOPh2Si)20.TMEDA was formed in high yield exclusively over the adducts with Et2NH or Et3N. The adduct (HOPh2Si)20.pyridine, however, was formed exclusively over (HOPh2Si)20.TMEDA. As may be expected, adducts with either TMEDA, pyridine, Et2NH or Et3N were found to precipitate out of solution in preference to the adduct with dioxane.

The second approach involved using sufficient (HOPh2Si)20 to form the respective adducts of both amines or amine/dioxane. With TMEDA and pyridine, a 1:1 mixture of (HOPh2Si)20.TMEDA and (HOPh2Si)20.pyridine was formed as shown by

124 Chapter 3 Hydrogen bonded adducts of silanols

1 H NMR and infrared spectroscopy. With TMEDA and Et2N H , [(HOPh2Si)20]4.(Et2NH)2 was formed almost exclusively. This is the opposite result to that obtained by the first approach. Again, when an amine (either Et2NH, Et3N, TMEDA or pyridine) and dioxane were employed, the amine adduct was formed in preference to the dioxane adduct. These results suggest that, as may be expected, the formation of adducts with the more basic amines is preferred over oxygen containing molecules but within the series of amines used the preference for adduct formation is less predictable. The preparation of ternary disiloxanediol complexes with two different amines/oxygen donors appears to be difficult. This observation, therefore, suggests that silanols are so highly selective in adduct formation that they may be very useful in carrying out separations even from solutions containing two or more known hydrogen bond acceptor species.

3.4.7 With phosphines Phosphine ligands play a major role in transition metal chemistry and the properties of phosphines and their complexes depend on both steric (cone angle, 0) and electronic effects (basicity, pKa). Preliminary attempts, therefore, at preparing adducts of (HOPh2Si)20 with phosphines were made due to their relatively high basicity. The common phosphine, PPh3 was chosen and also the related substituted triphenyl phosphine P(p-MeC6H4)3 to provide an easier NMR interpretation due to the methyl groups present.

The reactions were carried out by Method 1 using both one and half an equivalent of phosphine but with either phosphine only (HOPh2Si)20 precipitated out of solution upon addition of hexane. Attempts at adduct preparation were not made with alkylphosphines which may have attacked the silicon atom causing Si-O bond cleavage due to their high nucleophilicity and reduced steric hindrance.

125 Chapter 3 Hydrogen bonded adducts of silanols

3.5 Adducts of Ph3SiOH

Triphenylsilanol has been reported previously to form 4:1, 4:1 and 2:1 adducts with the oxygen donors EtOH, dioxane and 12-crown-4 respectively.5,146,147 The presence of three phenyl groups enhances the acidity of this silanol and, combined with the presence of only one SiOH group, stabilises it against polycondensation reactions. The analogous alcohol (carbinol) triphenylmethanol, Ph3COH, has been found to be highly specific in adduct formation.272 It forms 1:1 complexes with methanol, piperidine, N-methylpiperazine, morpholine, dioxane and CC14, and 2:1 complexes with acetone and DMSO.272 The complexes Ph3COH.MeOH and (Ph3COH)2.DMSO are isolated exclusively from solvent mixtures of methanol or DMSO and solvent mixtures containing one or more of a variety of alcohol or amine solvents.272

3.5.1 With amines

There have been no reports of adducts of Ph3SiOH with amines in the literature, although its less acidic carbon analogue has been reported to form adducts with amines as mentioned above.272 Since Ph3SiOH is less sensitive to the presence of base than (HOPh2Si)20 it appears superficially that it may be better suited to the formation of adducts with amines.

3.5.1.1 Primary amines

The suitability of primary amines for hydrogen bonding has been discussed in Section 3.4.1.1.

No adducts could be isolated with the primary amines RNH2 where R = Me, Et, npr, ipr, nBu, tBu or ±sBu. In all cases only Ph3SiOH was isolated from solution by Method 1 even after all the solvent had evaporated. The attempted preparation of adducts of MeNH2and EtNH2 were carried out by Method 2 in anhydrous THF, as discussed previously for (HOPh2Si)O. Preparation of an adduct with allylamine was also attempted as infrared spectroscopy (Section 2.4.2) has shown that the ally! group is also a potential hydrogen bonding site for Ph3SiOH. Again, only Ph3SiOH was isolated.

126 Chapter 3 Hydrogen bonded adducts of silanols

With the amine, tris(2-aminoethyl)amine which has three pendant (CH2)2 arms with terminal NH2 groups, surprisingly a 1:1 adduct was isolated, as determined by 1H NMR spectroscopy. X-ray crystallography (Section 3.5.1.1.1) confirmed that this was indeed a discrete 1:1 adduct containing only one Si-OH • • • NH2 hydrogen bond, the remaining nitrogen atoms not participating in any further hydrogen bonding interactions.

111 NMR spectroscopy also shows that the stoichiometry of the adduct isolated remains 1:1 even when 2 or 3 molar equivalents of Ph3SiOH are employed. In the infrared spectrum of Ph3SiOH.tris(2-aminoethylamine) the OH stretching band is strong and broad at 3299 cm-1 and the Si-O stretching mode is observable at 898 cm-1. Two relatively weak and narrow peaks at 3363 and 3343 cm-1 are consistent with the presence of non hydrogen bond donating NH2 groups.

3.5.1.1.1 Crystal structure of Ph3SiOH.tris(2-aminoethyl)amine Needle-like crystals of Ph3SiOH.tris(2-aminoethyl)amine suitable for X-ray crystallographic studies were obtained by careful agitation of a toluene/hexane solution until crystals just began to form and then leaving the crystals to crystallise slowly. Data were collected at 198(2) K and the acidic protons were located. Further crystallographic data may be found in the Appendix. In the crystal structure (Figure 3.17) one molecule each of Ph3SiOH and tris(2- aminoethylamine) are hydrogen bonded to each other via the proton of the OH group and one nitrogen donor [0(1) • • • N(3a) 2.680 A, 0(1)-H • • • N(3a) 1.847 M. Surprisingly, the remaining potential nitrogen donors of the tris(2-aminoethylamine) molecule play no significant part in hydrogen bonding interactions, and the closest approach of neighbouring acceptors to these 'vacant' donors is relatively long, with an N • • • H contact of 2.398 A (N • • • N 3.172 A) between centrosymmetrically related amine groups. The Si-O, Si-C and C-C bond lengths are as expected.

127 C124) C125)

Ct13) CHO

COM C(16) cnc)

MCI

Figure 3.17. View of the hydrogen bonded adduct Ph3SiOH.tris(2-aminoethyl)amine. The hydrogen bond is represented by a dashed line and

hydrogen atoms attached to carbon are omitted for clarity. Chapter 3 Hydrogen bonded adducts of silanols

3.5.1.2 Secondary amines No adduct could be isolated with Et2NH, despite the ready formation of an adduct between the related disiloxanediol, (HOPh2S020 and Et2NH (Section 3.4.1.2). Adducts could not be isolated either with the secondary amines R2NH where R = Me, iPr, nBu, tBu or cyclohexyl. In all cases only Ph3SiOH was isolated. Piperazine is a particularly versatile hydrogen bond donor as discussed previously in Section 3.4.1.2. It forms a 1:1 adduct with (HOPh2Si)20 (Section 3.4.1.2) and, as anticipated, with Ph3SiOH a 2:1 adduct was formed by Method 1. The X-ray crystal structure of (Ph3SiOH)2.piperazine (Section 3.5.1.2.1) shows that the adduct is discrete and centrosymmetric, each Ph3SiOH molecule hydrogen bonded to each of the nitrogen atoms of the piperazine. The N-H bonds do not take part in any hydrogen bonding interactions. A 2:1 adduct of phenol with piperazine has also been reported but with a very different hydrogen bonded structure.24° In the structure of (C6H5OH)2.piperazine two phenols hydrogen bond to each nitrogen atom, one acting as a proton donor and the other as an acceptor for the amine hydrogen. Each phenol then forms a second hydrogen bond with the next piperazine ring, thus forming an infinite chain of piperazine molecules linked by phenol molecules in hydrogen bonded rings. The amine hydrogens are in axial orientations. The infrared spectrum of (Ph3SiOH)2.piperazine shows a relatively sharp peak of medium intensity at 3306 cm-1 (compared to 3225 cm-1 in piperazine itself). This is consistent with the presence of two identical N-H groups not participating in hydrogen bonding interactions with the oxygen atom in the silanol. The OH stretching band is very broad and shows a large frequency shift into the CH stretching region, centered around 2730 cm* consistent with the formation of a strong hydrogen bond. The Si-O stretches and N-H wagging vibrations occur in the same region so it is difficult to assign them.

129 Chapter 3 Hydrogen bonded adducts of silanols

3.5.1.2.1 Crystal structure of (Ph3SiOH)2.piperazine

Crystals suitable for X-ray crystallography were obtained from toluene/hexane. Data were collected at room temperature, 293(2) K. The acidic hydrogen atoms were not located and are fixed at 0.90 A from the 0 or N atom. Full details may be found in the Appendix. The crystal structure of (Ph3SiOH)2.piperazine consists of two Ph3SiOH molecules held together by hydrogen bonds involving the protons of the silanol groups and the nitrogen atoms of the piperazine molecule [OH • • • N 1.83, 0 • • • N 2.72 A], Figure 3.18. The 0 • • • N distances are similar to those found in 4,4'- thiophenol.piperazine [2.725(3)A] but, as may be expected, less than those in ferrocene-

1,1'-diylbis(diphenylmethanol) [2.821(3) and 2.867(3) Al. In the phenol adduct the O-H • • • N and N-H • • • 0 distances lie between 2.682(3) and 3.075(4) A. The O-H • • • N bond angle in (Ph3SiOH)2.piperazine is 169 ° which is similar to the value of 168 ° present in the 4,4'thiophenol.piperazine adduct. The N-H bonds play no part in the hydrogen bonding interactions. The piperazine molecule lies on an inversion centre and adopts a chair conformation. The N-H bonds are both equatorial and the nitrogen lone pairs are axial.

3.5.1.3 Tertiary amines No adducts could be isolated with the tertiary amines R3N where R = Et, nPr or nBu despite the ready formation previously observed of an adduct between (HOPh2Si)20 and Et3N (Section 3.4.1.3). Again, in all cases only Ph3SiOH was recovered from the solution. A 2:1 adduct was isolated between Ph3SiOH and TMEDA by both Method 1 and Method 2. The adduct did not crystallise very readily upon the addition of hexane in Method 1 and so Method 2 was the preferred synthetic route. The X-ray crystallographic structure showed that the adduct was discrete, consisting of a centrosymmetric TMEDA molecule with one Ph3SiOH molecule hydrogen bonded to each nitrogen atom (Figure 3.20). The structure is similar to that obtained for the TMEDA adduct of the bulky

130 C(5) C(11')

C(1)

C(1')

C(5')

C(11)

Figure 3.18. View of the hydrogen bonded adduct (Ph3SiOH)2.piperazine. Hydrogen bonds are represented by dashed lines and hydrogen atoms

attached to carbon are omitted for clarity. Chapter 3 Hydrogen bonded adducts of silanols silanol TsiSiPh2OH, (TsiSiPh2OH)2.TMEDA (Section 3.6.4), and resembles one fragment of the chain structure determined for (HOPh2Si)20.TMEDA (Figure 1.14, Section 1.4.5).

The OH stretching band of (Ph3SiOH)2.TMEDA, although broader, is centred at 3247 cm-1 which is almost identical to that found in Ph3SiOH in the solid state at 3250 cm-1. The Si-O stretching region contains three peaks at 890, 854 and 833 cm-1, the latter two similar to those found in Ph3SiOH alone, although of significantly reduced intensity.

The strong hindered base DABCO forms adducts with a range of acids and also forms both 1:1 and 2:1 adducts with (HOPh2Si)20 by Method 1 (see Section 3.4.1.3). Upon addition of 1 equivalent of DABCO to Ph3SiOH by Method 1, colourless hexagonal crystals were formed after addition of hexane, which had a stoichiometry of 4:3 determined by integration of the 1H NMR spectrum. Crystals of (Ph3SiOH)4.(DABCO)3 suitable for X-ray crystallography could not be obtained by slow evaporation of benzene, acetone, ether or chloroform solutions of the adduct or from ether/hexane. Although colourless hexagonal crystals were obtained from toluene/hexane they were repeatedly thin and twinned. The infrared spectrum of (Ph3SiOH)4.(DABCO)3 shows a broad band of medium intensity centred around 2732 cm-1 consistent with the presence of a strong hydrogen bond, or even some proton transfer. The spectrum is almost identical to that recorded for (HOPh2Si)2O.DABCO for which no X-ray structure was obtained either (Section 3.4.1.3). Peaks due to DABCO in the Si-O stretching region make the assignment of v(Si-O) difficult. Due to the unusual stoichiometry of this adduct and no similar adducts being available for comparison, it is difficult to predict the hydrogen bonding arrangement present. Upon addition of half an equivalent of DABCO to Ph3SiOH by the same method, needle-like crystals were formed after the addition of hexane which had a stoichiometry of 4:1 as determined by integration of the 1H NMR spectrum. Crystals suitable for X-ray crystallography were obtained from toluene/hexane. Although the heavy atom positions were located, the number of molecules in the unit cell was ambiguous, and a complete 132 Chapter 3 Hydrogen bonded adducts of silanols

X-ray structural determination indicating the hydrogen bonding network was not possible.

The relative positions of the Ph3SiOH and DABCO molecules are shown in Figure 3.19. It is clear from the orientations of the molecules that both silanol to silanol and silanol to amine hydrogen bonds are present. This is in agreement with the infrared spectrum which displays a broad band of medium intensity centred around 3301 cm-1 consistent with the formation of weaker OH • • • 0 hydrogen bonds in addition to OH • • • N hydrogen bonds. The Si-O stretches appear to have shifted to 900 and 854 cm-1, although it is not clear due to bands from DABCO also occuring in this region. The hydrogen bonding arrangement may be similar to that found in (Ph3SiOH)4.dioxane which has a similar geometrical arrangement of molecules.147

When either one or half an equivalent of the strong base DBU was added to Ph3SiOH by Method 1 only the silanol crystallised out upon addition of hexane, as for (HOPh2Si)20 (Section 3.4.1.3).

With hexamethylethylenetetramine, HMTA, which forms a 1:1 adduct with (HOPh2Si)20 (Figure 3.10, Section 3.4.1.3), preliminary results using either one or half an equivalent of HMTA by Method 1 suggested that adduct formation took place as the infrared spectra of the small crystals obtained were very different in the OH and Si-O stretching regions to infrared spectra of the starting materials ground together in various proportions. The 1H NMR spectra of the crystals, however, were not consistent upon repetition of the experiment, suggesting stoichiometries intermediate between 2:1 and 1:1, or 1:1 and 3:2, irrespective of whether one or half an equivalent of HMTA was employed in the preparation. Microanalytical data was also inconclusive. X-ray structural analysis of the adducts formed were therefore sought to elucidate both the stoichiometries and the hydrogen bonding arrangement formed. No crystals suitable for X-ray crystallography, however, were formed from toluene/hexane, ether/hexane or slow evaporation of ether, acetone or chloroform solutions of the adducts.

Further work is required with HMTA, as it is possible that a range of adducts with Ph3SiOH of different stoichiometries and hydrogen bonding arrangements may genuinely be formed due to the availability of four nitrogen atoms as hydrogen bond acceptors.

133 Figure 3.19. Positions of the heavy atoms in the X-ray crystal structure of the hydrogen bonded adduct (Ph3SiOH)4.DABCO Chapter 3 Hydrogen bonded adducts of silanols

3.5.1.3.1 Crystal structure of (Ph3SiOH)2.TMEDA Crystals of (Ph3SiOH)2.TMEDA suitable for X-ray structural analysis were obtained by slow evaporation of an ether solution of the adduct. The data were collected at 213(2) K and the acidic protons were located. Further data is given in the Appendix. In the crystal structure of (Ph3SiOH)2.TMEDA (Figure 3.20), the TMEDA molecule forms a hydrogen bonded bridge unit between the two Ph3SiOH molecules. The hydrogen bonds are relatively strong, 1.968 A and nearly linear, 171.9 °. There is an inversion centre in the middle of the TMEDA molecule dictating that the nitrogen groups are arranged in an anti configuration (torsion angle of N-C(3)-C(3')-N' 180.0°). The arrangement of the substituents around the unique silicon atom is best described as a slightly distorted tetrahedron with angles ranging from 107.00(9) to 110.73(8)°. The shortest bond to the silicon is from the oxygen atom, the Si(1)-0(1) bond being 1.628(2) A, and the Si(1)-C bonds range from 1.868(2) to 1.872(2) A. Both the Si-O and Si-C bond lengths and angles are typical of this type of molecule.

3.5.1.4 With nitrogen heterocycles Although (HOPh2Si)20 readily forms a 1:1 adduct with pyridine (Section 3.4.1.4), no adduct could be isolated with Ph3SiOH by Method 1 or 2. Only the unreacted silanol was found to crystallise out. There are no reports of an adduct formed between the analogous carbinol and pyridine.

3.5.2 With azacrowns Azacrowns are the nitrogen analogues of crown ethers. There is, however, a lack of literature available on complexes of azacrowns with neutral molecules. Since only Ph3SiOH shows a propensity towards adduct formation with crown ethers (Section 3.5.3) this silanol was chosen for the attempted preparation of adducts with azacrowns (Figure 3.21). The preparation of these complexes were carried out from toluene under anhydrous conditions since the azacrowns are very hygroscopic (Section 6.1.9.2). One equivalent of Ph3SiOH for each nitrogen atom present was added and any unreacted silanol filtered off.

135 C(341

CI21

Figure 3.20. View of the hydrogen bonded adduct (Ph3SiOH)2.TMEDA. Hydrogen bonds are represented by dashed lines and hydrogen atoms attached to carbon are omitted for clarity. Chapter 3 Hydrogen bonded adducts of silanols

/-1 HN NH HN NH c, NJ N,) H H 1,4,7-Triazacyclononane 1,5,9-Triazacyclododecane

r-\ CNH HN NH FINk ) J NH HN NH HN \...__/ c) 1,4,7,10-Tetraazacyclododecane 1,4,8,11-Tetraazacyclotetradecane (cyclen) (cyclam)

/- NH HN -\

\- NH HN --/ \__/ 1,4,8,12-Tetraazacyclopentadecane

Figure 3.21. Azacrowns employed in adduct formation

The addition of pentane to a toluene solution of three equivalents Ph3SiOH and one equivalent of 1,4,7-triazacyclononane resulted in the formation of small rectangular crystals. Surprisingly, 1H NMR spectroscopy revealed that the crystals had a stoichiometry of 4:1 silanol:azacrown which also best fitted the microanalytical data.

The infrared spectrum of (Ph3SiOH)4.1,4,7-triazacyclononane displays a sharp peak at 3370 cm-1 consistent with the presence of NH groups not involved in hydrogen bonding interactions as proton donors. The OH stretching region shows a broad band of medium intensity centred around 3256 cm-1. In the Si-O stretching region, however, there are four peaks of medium intensity at 894, 882, 859 and 835 cm-1. As described previously in the infrared spectrum of (Ph3SiOH)2.TMEDA, the OH band is at

3247 cm-1, similar to that in Ph3SiOH itself (3250 cm-1) and two of the three peaks in the

137 Chapter 3 Hydrogen bonded adducts of silanols

Si-O stretching region at 854 and 833 cm-1 are also similar to those found in Ph3SiOH itself (Section 3.5.1.3). Only X-ray crystallography, however, provides conclusive evidence that a hydrogen bonded adduct is formed between Ph3SiOH and TMEDA. It is not clear, therefore, without crystallographic evidence, whether a genuine 4:1 adduct is formed between Ph3SiOH and 1,4,7-triazacyclononane. The stretches at 894 and 882 cm-1 may be due to the azacrown which also absorbs in this region. Further work on this adduct is required, and in particular X-ray structural analysis. Recrystallisation of the adduct from toluene/pentane, toluene/hexane, or slow evaporation of an ether or acetone solution of the adduct, however, failed to produce crystals suitable for X-ray crystallography.

Addition of three equivalents Ph3SiOH to one equivalent of 1,5,9- triazacyclododecane resulted in small colourless crystals which upon integration of their 1H NMR spectrum revealed a 1:1 stoichiometry. Microanalytical data, although slightly low, were also consistent with a 1:1 stoichiometry. Recrystallisation of the adduct from the same solvents as above also failed to produce crystals suitable for X-ray structural analysis.

The OH stretching region of the infrared spectrum of Ph3SiOH.1,5,9- triazacyclododecane shows a broad band of medium intensity centred around 3413 cm-1. The Si-O stretches have shifted to 927 (medium) and 881 (weak) cm-1. The NH stretching frequency for 1,5,9-triazacyclododecane is at 3337.6 cm-1 (gas phase). In the adduct, however, two NH stretching frequencies are apparent at 3291 (relatively sharp, strong) and 3180 (broader, weak) cm-1. These suggest the presence of two different sorts of NH groups, the higher frequency band corresponding to NH groups not involved in hydrogen bonding interactions as hydrogen bond donors and the lower frequency band corresponding to NH groups acting as hydrogen bond donors. Since both the OH group of the silanol and NH group(s) of the azacrown appear to be participating in hydrogen bonding interactions as hydrogen bond donors , it is difficult to propose a structure. When four equivalents of Ph3SiOH were treated with one equivalent of 1,4,7,10- tetraazacyclododecane, cyclen, in toluene colourless rectangular crystals were formed

138 Chapter 3 Hydrogen bonded adducts of silanols upon the addition of pentane. These were shown to be a 4:1 adduct, as expected, by integration of the 11-1 NMR spectrum. Recrystallisation of the adduct from toluene/pentane, toluene/hexane and by slow evaporation of an ether solution of the adduct failed to produce crystals suitable for X-ray crystallography. In the infrared spectrum of (Ph3SiOH)4.cyclen, there are a number of NH and CH peaks in the OH stretching region which appear to obscure the OH band. Two relatively sharp peaks of medium intensity at 3311 and 3241 cm-1 suggest the presence of NH groups acting solely as hydrogen bond acceptors. There are also very weak peaks at 3384 and 3268 cm-1 which may also be due to NH stretches. This would suggest the presence of four different NH groups. Although bands due to the azacrown also occur in the Si-O stretching region, peaks at 854 and 836 cm-1 are present, similar to those in the spectrum of Ph3SiOH alone, but much weaker in intensity. The structure may comprise one

Ph3SiOH molecule hydrogen bonded via OH • • • N interactions to each of the four N atoms of the ring, the conformation of the ring dictating inequivalency of the NH groups.

The structure of 1,4,7,10-tetraazacyclododecane trihydrate has been published previously273 and found to comprise one water molecule hydrogen bonded to each nitrogen atom of the ring, two via OH • • • N interactions and two via NH • • • 0 interactions, each of the latter hydrogen bonded to one further water molecule. The cyclen molecule exhibits crystallographic twofold rotation symmetry and a [3333] quadrangular conformation with C atoms occupying corner positions. The reaction of one equivalent of 1,4,8,11-tetraazacyclotetradecane (cyclam) with four equivalents of Ph3SiOH in toluene gave long, thick, colourless, needle-like crystals.

Integration of the 1H NMR spectrum revealed the compound to be a 2:1 adduct. The presence of the (CH2)3 linkages may provide too much steric hindrance for four Ph3SiOH molecules to coordinate. Crystals suitable for X-ray crystallography, however, could not be obtained from toluene/pentane, toluene/hexane or by slow evaporation of an ether solution of the adduct.

The infrared spectrum of (Ph3SiOH)2.cyclam, like the spectrum of cyclam alone, displays two peaks in the NH stretching region. These are at 3288 (medium) and

139 Chapter 3 Hydrogen bonded adducts of silanols

3249 (medium) cm-1 compared with 3270 and 3185 cm-1 in cyclam. This suggests that the NH groups, if participating in hydrogen bonding interactions, are acting as hydrogen bond acceptors only. The OH stretching band is very broad and has shifted into the CH stretching region, its centre is around 2700 cm-1, consistent with the formation of strong OH • • • N bonds with the possibility of some proton transfer. The u(Si-0) bands are at

881 and 925 cm-1. As this adduct was prepared in larger quantities than the others, it was possible to obtain a Raman spectrum of the crystals. Peaks due to vibrations of Ph3SiOH in the adduct (Table 3.4, Section 3.5.3), however, are very strong and dominate the spectrum, whereas peaks due to the azacrown are much weaker and often indistinguishable above the baseline. A weak peak at 3289 cm-1 due to an N-H stretching mode may be observed, though, which is coincident with one of the NH stretches at 3288 cm-1 in the infrared spectrum. A number of overlapping peaks in the CH region around 2800 cm-1 may also be observed and a weak peak at 1473 cm-1 due to the CH2 scissor mode. Unfortunately, there was no cyclam remaining to obtain a Raman spectrum of the uncomplexed azacrown for comparison and a literature spectrum was not available. The simplicity of the Raman spectrum suggests that the complexed azacrown may have high symmetry. It may be postulated, therefore, that the adduct is centrosymmetric and held together by OH • • • N interactions only. From the previous results with cyclen and cyclam it was predicted that upon reaction of Ph3SiOH with 1,4,8,12-tetraazacyclopentadecane a 1:1 adduct would be formed due to the presence of three propylene groups. Unfortunately time did not permit the experiment to be carried out.

3.5.3 With crown ethers A simple 2:1 adduct of Ph3SiOH with 12-crown-4 has been isolated previously by others, from a hot toluene solution.5 Attempts were therefore made to prepare adducts with other simple crown ethers from toluene/hexane. No adduct could be isolated with 15-crown-5 when either one or two molar equivalents of Ph3SiOH were employed. In

140

Chapter 3 Hydrogen bonded adducts of silanols

both cases, and repeatedly, a white sticky solid was isolated which 1H NMR spectroscopy suggested to be the silanol together with a small and varying amount of 15-crown-5. A 2:1 adduct of Ph3SiOH with 18-crown-6 was isolated using either one or two

equivalents of Ph3SiOH, as shown by 1H NMR spectroscopy. X-ray crystallography, however, revealed that this was not a simple adduct but a ternary complex consisting of

two Ph3SiOH molecules bound to one molecule of 18-crown-6 via two bridging water molecules (Figure 3.21).

i----"\ ...... H.... (7.0 0...=\. 0 1- s H \ Ph3SiO—H--- -0\ )0 /0- -- -H—OSiPh3 H-- rj.,- -H ...=-2'0\__/0

Figure 3.21. Structure of (Ph3SiOH)2.18-crown-6.(H20)2

This arrangement has been observed previously for hydrogen bonded complexes of 18-

crown-6 with neutral molecules such as 3-nitropheno1,274 p-nitrobenzaldehyde oxime,274 2,4-dinitropheno1,275 oxalic acid,276 maleic acid277, dichloropicric acid278, acetic acid,279 cyanoacetic acid280 and 4,4'-biphenyldio1.271 The mediation of water molecules is of interest, particularly in the study of surface silanol groups on silicate rocks as the role of water as an integral component of molecular recognition has not been widely studied. Also, Ph3SiOH does not form an adduct with water on its own, and water has not been included in any other adducts of Ph3SiOH, even though in most cases no

precautions were taken to exclude it. Recent work by Brisdon et al. 281 shows that in the absence of water, Ph3SiOH forms a 3:1 aduct with 18-crown-6 which is formed as a very hygroscopic white powder. The proposed structure comprises Ph3SiOH molecules hydrogen bonded to alternate oxygen atoms of the crown.

The O-H streching region of the infrared spectrum of (Ph3SiOH)2.18-crown- 6.(H20)2 in the solid state exhibits three bands (Figure 3.22). Two medium and relatively

sharp bands at 3550 and 3500 cm-1 can be attributed to the weak hydrogen bonds between

the water molecules and 18-crown-6.276 A broad band of medium intensity centred

141 Chapter 3 Hydrogen bonded adducts of silanols around 3232 cm-1 is consistent with the stronger hydrogen bond formed between the

Ph3SiOH molecules and the water molecules. A sharp peak of medium intensity at

1629 cm-1 may be attributed to the bending mode of water. In the Si-O stretching region there are two peaks at 900 and 840 cm-1. The peak at 840 cm-1, however, is broad with an unresolved shoulder on the high wavenumber side. Previous studies have shown that this band is due to the C-C stretching mode of 18-crown-6 in which D3d symmetry is adopted.276 ,280 The CH2 rocking band at 962 cm-1 is also consistent with D3d symmetry in the crown.28°

T r a n s m i t t a n c e 3400 Wavenumbers

Figure 3.22. Infrared spectrum of (Ph3SiOH)2.18-crown-6.(H20)2 (KBr disc).

The bands in the Raman spectrum of (Ph3SiOH)2.18-crown-6.(H20)2 (Figure 3.23) due to the vibrations of the 18-crown-6 molecule (Table 3.4) are very similar to those of other complexes in which the ether is known to have the regular crown geometry of D3d symmetry.276,277,279 In particular, the bands at 1472, 1246 and 864 cm-1 are exclusive to D3d symmetry.

142 8.0 _

77 _

4_ Egy

N FO I VJ

00 JLL,I0 i 1 1 4000.0 3000 2000 1500 1000 500 100.0 Raman Shift / cm-1

Figure 3.23. Raman spectrum of (Ph3SiOH)2.18-crown-6.(H20)2. The bands at 1472, 1246 and 864 cm-1 are exclusive to Dad symmetry in the 18-crown-6 molecule.

Chapter 3 Hydrogen bonded adducts of silanols

Table 3.4. Observed Raman wavenumbers (cm-1) and vibrational assignments for

(Ph3SiOH)2.18-crown-6.(H20)2, Ph3SiOH and 18-crown-6.

(Ph3SiOH)2. Ph3SiOH 18-crown-6 Assignmenta Conformation of 18-crown-6.(H20)2 18-crown-6b

3175 (vw) 3176 (vw) u(CH) 3134 (vw) 3135 (vw) v(CH) 3044 (s) 3050 (m) v(CH) 2958 (vw) 2960 (vw) v(CH) 2950 (vw) 2950 (m) u(CH) D3d, Ci 2908 (w) v(CH) D3d, Ci 2896 (s) u(CH) D3d, Ci 2888 (w) p(CH) D3d, Ci 2875 (s) v(CH) Ci 2841 (w) 2843 (m) v(CH) D3d, Ci 2806 (vw) 2811 (m) .0(CH) D3d, Ci 1589 (m) 1590 (m) v(CC) 1567 (w) 1568 (w) 'u(CC) 1492 (w) CH2 scissor Ci 1476 (w) CH2 scissor Ci 1472 (vw) CH2 scissor D3d(eg) 1294 (w) CH2 twist D3d(aig), Ci 1275 (vw) 1277 (w) CH2 twist D3d(eg), Ci 1260 (w) CH2 twist Ci 1246 (vw) CH2 twist D3d(eg) 1238 (vw) CH2 twist Ci 1184 (w) 1191 (w) 5(CH) 1159 (w) 1158 (w) 5(CH) 1136 (w) u(C0)/CH2 rock D3d(eg), Ci 1109 (w) 1110 (w) p(CSi)

1028 (w) 1030 (w) 6(CH)

1000 (s) 1000 (s) p(CC) or 5(CCC) 988 (vw) '0(C0)/CH2 rock Ci

(continues)

144

Chapter 3 Hydrogen bonded adducts of silanols

Table 3.4. Observed Raman wavenumbers (cm-1) and vibrational assignments for (Ph3SiOH)2.18-crown-6.(H20)2, Ph3SiOH and 18-crown-6 (continued).

(Ph3SiOH)2. Ph3SiOH 18-crown-6 Assignmenta Conformation of 18-crown-6.(H20)2 18-crown-6b

892 (w) p(C0)/CH2 rock Ci 238 (w) 237 (w) 8a(CSi) & 85(CSi) 864 (vw) v(CO) D3d(aig) 834 (vw) v(C0)/CH2 rock D3d(eg), Ci 824 (w) CH2 rock Ci 674 (w) 675 (w) y(CH) 620 (w) 620 (w) y(CCC) 367 (vw) 376 (vw) y(CCC) 238 (w) 237 (w) 8a(CSi) & Ss(CSi)

Approximate relative intensities: s, strong; m, medium; w, weak; vw, very weak. a Refs.

233 and 282. b Ref. 282. Assignments: v, stretch; 6a, asymmetric deformation; Ss, symmetric deformation; y, skeletal vibrations. Symmetry species for the Dad form below

1600 cm-1 are shown in brackets.

The uncomplexed 18-crown-6 assumes a shape of symmetry Ci with three different kinds of -O-CH2CH2-O- units.283 This low symmetry is reflected in the Raman spectrum which is appreciably more complicated as can be seen from Table 3.4. The Raman spectrum of Ph3SiOH has also been included in Table 3.4 for comparison. The bands in the 4000 - 3000 cm-1 region associated with the OH stretches of the silanol or water molecules and the band at - 1635 cm-1 due to the bending mode of water are too weak to be observed in the Raman. As mentioned previously (Section 3.3), the Si-O stretches are not observed in the Raman.233

The presence of water in the structure, and also the OH protons, were not detected by 1H NMR spectroscopy since they were so broad that they were barely observable above the baseline, as is often the case for hydroxyl protons.

145 Chapter 3 Hydrogen bonded adducts of silanols

3.5.3.1 Crystal structure of (Ph3SiOH)2.18-crown-6.(H20)2 Large rectangular crystals of (Ph3SiOH)2.18-crown-6.(H20)2 suitable for X-ray structural determination were grown slowly from toluene/hexane. Data were collected at 223(2) K and the acidic hydrogens were located. Selected bond lengths and angles are reported in Table 3.5. Additional crystallographic data is included in the Appendix. In the crystal structure of (Ph3SiOH)2.18-crown-6.(H20)2 (Figure 3.24) the asymmetric unit consists of one Ph3SiOH, one water molecule and half of an 18-crown-6 macrocycle, since the macrocycle lies on an inversion the ratio of the adduct is therefore equal to 2:2:1. The molecules are held together by hydrogen bonding interactions between the proton of the OH group of the Ph3SiOH molecule and the oxygen of the water molecule which in turn is linking to the oxygen atoms of the 18-crown-6 via two hydrogen bonds. The water molecules are situated above and below the inner great ring of the macrocycle, which have atoms alternately above and below the best mean plane defined by the ring atoms (maximum deviation from mean plane 0.39 A for C(4)). This can be observed more easily in Figure 3.25. The structure is analogous to that found in the 2:1 diaquo complexes of the neutral molecules 3-nitropheno1,274 p-nitrobenzaldehyde oxime,274 2,4-dinitropheno1,275 oxalic acid,276 maleic acid277, dichloropicric acid278, acetic acid,279 cyanoacetic acid280 with 18-crown-6 and one fragment of the hydrogen bonded infinite chain structure of (4,4.- biphenyldio1)2.18-crown-6 .(H20)2.271

146 C(14)

Figure 3.24. View of the hydrogen bonding in the ternary complex (Ph3SiOH)2.18-crown-6.(H20)2. Hydrogen bonds are represented by dashed

lines and hydrogen atoms attached to carbon are omitted for clarity.

Chapter 3 Hydrogen bonded adducts of silanols

Table 3.5. Selected bond lengths and angles in the crystal structure of

(Ph3SiOH)2.18-crown-6.(H20)2

0(4) • • •H-0(1W) 2.110 A

0(3) • • •H-0(1W) 2.233 A 0(1)-H • •• 0(1W) 173.7 ° 0(1)-H • • • 0(1W) 1.945 A 0(4) . . . 0(1W) 3.015 A 0(3) . . . 0(1W) 2.940 A 0(1) . . . 0(1W) 2.724 A 0(1)-H 0.78(3) A

MAI Ct6A)

Figure 3.25. View of the macrocyclic ring in 18-crown-6 showing the positions of the water molecules.

148

Chapter 3 Hydrogen bonded adducts of silanols

3.5.4 With azacrown ethers

The adducts (Ph3SiOH)2.1-aza-18-crown-6.H20 and (Ph3SiOH)2.7,16-diaza-18- crown-6 were isolated by Brisdon et a/.281 at the same time as these studies. In the adduct (Ph3SiOH)2.1-aza-18-crown-6.H20, X-ray crystallography has shown that one Ph3SiOH molecule is hydrogen bonded to the crown via a direct OH • • - NH interaction and the other Ph3SiOH via a coordinated water linkage (Figure 3.26).281

i''' \ O

CC) 1.. -1-1...... Ph3SiO H- - - -NH 0 0- - - H—OSiPh3 ) H/ C— 0 0 r=- - - - \___/

Figure 3.26. Structure of (Ph3SiOH)2.1-aza-18-crown-6.H20.281

Infrared spectroscopy suggests that in (Ph3SiOH)2.7,16-diaza-18-crown-6 the

Ph3SiOH molecules are hydrogen bonded via OH • • •NH interactions as shown in Figure

3.27.281 1—\

Ph3SiO—H- - - -NH HN- - - - H—OSiPh3

--.0 0-1

Figure 3.27. Proposed structure of (Ph3SiOH)2.7,16-diaza-18-crown-6.281

Attempts were therefore made to prepare adducts of Ph3SiOH with the commercially available monoazacrowns, 1-aza-12-crown-4 and 1-aza-15-crown-5 (Figure 3.28).

1-aza-12-crown-4 1-aza-15-crown-5

(a) (b) Figure 3.28. Structures of (a) 1-aza-12-crown-4 and (b) 1-aza-15-crown-5.

149 Chapter 3 Hydrogen bonded adducts of silanols

Since a 2:1 adduct of Ph3SiOH with 12-crown-4 has been reported previously and a 4:1 adduct of Ph3SiOH was isolated with the analagous azacrown, cyclen, (Section 3.5.2) it was thought that Ph3SiOH would form an adduct with 1-aza-12-crown-4. Upon addition of four equivalents of Ph3SiOH to one equivalent of 1-aza-12-crown-4 in toluene small colourless crystals were formed. Integration of the 1H NMR spectrum suggested the formation of a 3:1 adduct. Attempts at recrystallising the adduct from toluene/pentane, toluene/hexane and slow evaporation of an acetone solution failed to produce crystals suitable for X-ray crystallography. X-ray structural analysis was attempted on crystals grown by slow evaporation of an ether solution of the adduct but the crystals proved too small and the data set too large.

The infrared spectrum of (Ph3SiOH)3.1-aza-12-crown-4 shows a broad band centred around 3343 cm-1 consistent with the OH stretching frequency of a hydrogen bonded adduct. There are no bands in the 3450-3550 cm-1 region which suggests that there are no water molecules involved in the hydrogen bonding between the Ph3SiOH molecules and the azacrown. A sharp peak at 3266 cm-1 corresponds to the stretching frequency of an NH group acting solely as a hydrogen bond acceptor. The Si-O stretches are at 885 (medium) and 838 (medium) cm-1. The Raman spectra resembles the spectrum of Ph3SiOH itself (Table 3.4, Section 3.5.3), except for extra unresolved peaks in the CH2 region, and it is not possible to distinguish any other peaks due to the azacrown. The structure of the adduct may comprise one Ph3SiOH molecule hydrogen bonded to the nitrogen atom and one to each of the two oxygen atoms adjacent to the NH group, but without X-ray structural analysis it is difficult to predict the structure in more detail.

It has not been possible to isolate an adduct of Ph3SiOH with 15-crown-5 by Method 1. It was, however, thought that the presence of an aza group in the ring would encourage adduct formation. Upon addition of five equivalents of Ph3SiOH to one equivalent of 1-aza-15-crown-5 in toluene long white needle like crystals were formed upon addition of pentane. Integration of the 1H NMR spectrum suggested that a 2:1 adduct had been formed. Attempts at recrystallisng the adduct from toluene/hexane and

150 Chapter 3 Hydrogen bonded adducts of silanols from slow evaporation of an ether solution failed to produce crystals suitable for X-ray crystallography. In all cases a white powder was formed.

In the infrared spectrum the OH stretching frequency of (Ph3SiOH)2.1-aza-15- crown-5 appears as a broad band centred around 3361 cm-1. Like the adduct with 1-aza- 12-crown-4 there are no bands in the 3450-3550 cm-1 region associated with hydrogen bonded water molecules. A sharp band at 3278 cm-1 is indicative of the stretching frequency of an NH group acting solely as a hydrogen bond acceptor. There are three peaks in the Si-O stretching region at 842 (weak), 875 (medium) and 892 (medium) cm-1. Again, peaks due to the azacrown, other than in the CH stretching region, were not visible in the Raman spectrum so no conformational analysis of the crown was possible. The structure of the adduct may be as proposed in Figure 3.29 with one Ph3SiOH molecule hydrogen bonded to a nitrogen atom and one to an alternate oxygen atom on the ring.

Ph3Si0— ('o 'NH -•-• 0- - -H—OSiPh3 ( 0

Figure 3.29. Proposed structure of (Ph3SiOH)2.1-aza-15-crown-5

3.5.5 With amine hydrochlorides

A pyridinium hydrochloride adduct, (HOPh2Si)20.C5H5N.HC1 has been reported to crystallise from a reaction mixture of the silanol and TiC14 in the presence of pyridine

(Section 1.4.5).144 The exact experimental conditions, however, are not given. The hydrolysis of chlorosilanes results in the formation of HC1 which is usually removed by the addition of an amine (e.g. Et3N, pyridine or aniline) to form the corresponding hydrochloride which precipitates from the solution. There is, therefore, a surprising lack of such adducts reported in the literature given that amine hydrochlorides are very common by-products in the synthesis of silanols.

151 Chapter 3 Hydrogen bonded adducts of silanols

It was therefore of interest to study the interactions of silanols with amine hydrochlorides. The insolubility of amine hydrochlorides in organic solvents meant that infrared spectroscopic studies could not be carried out and the attempts at preparing adducts in the solid state had to be carried out from heterogeneous reaction mixtures. Attempts at preparing adducts of Ph3SiOH with diethylamine hydrochloride, ethylamine hydrochloride and aniline hydrochloride by a modification of Method 1 failed.

3.5.6 With carboxylic acids

Since silanols have a relatively high basicity it was of interest to see if Ph3SiOH would form adducts with simple acids. Ph3SiOH was chosen for these studies as it is much more stable to the presence of acid than (HOPh2Si)20.

With one equivalent of benzoic acid, by Method 1, Ph3SiOH initially precipitated out upon addition of hexane, and benzoic acid was recovered from the filtrate, as shown by 1H NMR spectroscopy. Similarly, with acetic acid only Ph3SiOH precipitated out. Slow evaporation of a solution of Ph3SiOH dissolved in excess acetic acid, and of Ph3SiOH and acetic acid dissolved in toluene or ether, resulted only in the recovery of Ph3SiOH.

3.5.7 With phosphines

Attempts at preparing adducts of Ph3SiOH with PPh3 and P(p-MeC6H4)3 were made by Method 1. With either one or half an equivalent of either phosphine only

Ph3SiOH precipitated out of solution upon addition of hexane, as shown by 111 NMR spectroscopy. These results are identical to those obtained with (HOPh2Si)20 (Section 3.4.7).

152 Chapter 3 Hydrogen bonded adducts of silanols

3.6 Adducts of other silanols

This work has primarily concentrated on the formation of adducts with (HOPh2Si)20 and Ph3SiOH in order to obtain a better understanding of the factors which control adduct formation via a systematic approach with one or two silanols. A number of ideas for adducts with other silanols arose during the course of these studies and this section represents the preliminary results obtained. Of course, for each silanol, a more detailed study of their hydrogen bonding interactions in the solid state is required before any conclusions can be made.

3.6.1 Adducts of Ph2Si(OH)2

Having studied the ability of (HOPh2Si)20 and Ph3SiOH to form adducts with a range of organic molecules it was of interest to see whether the related silanediol, Ph2Si(OH)2, which is commercially available and which has biological activity (anticonvulsant), would also form adducts with other molecules in the solid state. There have been no previous reports of adducts of Ph2Si(OH)2 in the literature and the presence of two OH groups on the same silicon increases the propensity of this silanol towards condensation reactions. The solubility of Ph2Si(OH)2 was found to be very low in hot toluene and therefore the reactions were carried out from ether by Method 2. The reactions were left stirring for 2 hours to try to minimise condensation reactions but with the amines Et2NH, TMEDA, Et3N and pyridine (all known to form adducts with the related disiloxanediol) a sticky residue was produced which was shown by 1H NMR spectroscopy and mass spectrometry to be a mixture of silanediol, the condensation product (Ph2SiO)3 and amine. With dioxane, both by this method and by slow evaporation of a solution in excess dioxane only the silanediol was recovered, as shown by 1H NMR spectroscopy.

Attempts were also made to prepare adducts of Ph2Si(OH)2 with the crown ethers, 18-crown-6 and 12-crown-4 by a modification of Method 1. The silanediol was added to a solution of crown ether in hot toluene (reversal of the normal order) in anticipation that the crown ether would solubilise the silanediol as is common in crown ether chemistry.

153 Chapter 3 Hydrogen bonded adducts of silanols

The silanediol, however, did not dissolve and was recovered unchanged from the reaction mixture, as shown by 1H NMR spectroscopy.

3.6.2 Adducts of HO(SiPh20)3H

During the course of these studies Spalding et al.255 prepared and structurally characterised adducts of HO(SiPh2O)3H with the nitrogen heterocycles pyridine and pyrazine with stoichiometries of 2:3 and 4:1 respectively (Figures 3.30 and 3.31). Unlike the corresponding adducts with the disiloxanediol (Section 3.4.1.4) these adducts are discrete and contain very different hydrogen bonding networks. In [HO(SiPh2O)3H]2.(pyridine)3 (Figure 3.30) two trisiloxanediol molecules are hydrogen bonded to each other, with the OH group accepting the hydrogen bond from the other trisiloxanediol molecule also involved in an OH • • • N hydrogen bond to a pyridine molecule. Instead of extending the hydrogen bonded structure into a infinite chain the remaining silanol group on each trisiloxanediol terminates the structure in an OH • • • N interaction with a pyridine molecule only. In the structure of EHO(SiPh20)3HL.pyrazine two pairs of hydrogen bonded trisiloxanediol molecules are linked via OH • • • N hydrogen bonds to the pyrazine molecule (Figure 3.31). The stoichiometry of the adduct formed between HO(Ph2SiO)3H and pyridine is different to the 1:1 stoichiometry reported by Prescott and Selin. This may be due to the unavailability of NMR instrumentation when this adduct was first isolated, as discussed previously for the adducts of (HOPh2Si)20 with amines in Section 3.4.1. It was, therefore, of interest to see whether the trisiloxanediol would also form adducts with the other amines that form adducts with the related disiloxanediol. Hexaphenyltrisiloxanediol was prepared via the sodium diolate salt by a modified method of Selin.284 With Et2NH, Et3N, and TMEDA, however 1H NMR spectroscopy showed that polycondensation reactions occurred by both Methods 1 and 2. This suggests that the trisiloxanediol has a higher tendency towards condensation reactions than the disiloxanediol, as may be expected from the greater flexibility of the structure.

154

Chapter 3 Hydrogen bonded adducts of silanols

..''.

I r‘i -,..„....ri 7 I Ph2 Ph2 Ph2 H H Si Si Si ,o o :)' N °--... / o1 / °°7. \.0 [1- \Si Sii Si Ph2 Ph2 Ph2 )i, --/ -I I .%/

Figure 3.30. The discrete hydrogen bonded adduct [HO(SiPh20)3H]2.(pyridine)3.255

Ph2 Ph2 Ph2 Si Si ri 12 Si...... r \ / ..•.....,..... Si 0 0 9 u 0 I I o / SiPh2 Ph2Si\ H H 0, „'OOH.. / \ ... ••• '6 I-I . -H" HN ' • -0-H- - -N N- - - H- 0” 0 \ ‘ e \ / S' SiPh2 Ph2Si Siph Ph2 `•-• 0 1 1 0 2 ./0 0 / Si Si Ph2 Ph2

Figure 3.31. The hydrogen bonded arrangement found in [HO(SiPh2O)3H]4.pyrazine.255

155 Chapter 3 Hydrogen bonded adducts of silanols

3.6.3 Adducts of meso-(HOMePhSi)20 and (HOMe2Si)20 The unsymmetrical disiloxanediol HOMePhSiOSiPh2OH forms an adduct of 1:1 stoichiometry with Bu3N143 but there appear to be no reports in the literature of the less acidic disiloxanediols (HOMe2Si)20 and (HOMePhSi)20 forming adducts.

The preparation of these disiloxanediols is described in Section 4.3. The attempted preparation of adducts was carried out by Method 1 using pentane instead of hexane. Adducts of (HOMe2Si)20 and meso-(HOMePhSi)20 with Bu3N, Et3N, Et2NH, TMEDA or pyridine could not be isolated. In all cases, except for with pyridine, a white sticky solid was formed which 1H NMR spectroscopy identified as a mixture of disiloxanediol and varying amounts of condensation product. With pyridine, only the disiloxanediol precipitated out in both cases.

There are, however, a large number of other less basic amines or oxygen containing molecules with which these disiloxanediols may form adducts.

3.6.4 Adducts of the bulky silanols TsiSiPh2OH and TsiSi(OH)3 The adducts of silanols and siloxanediols reported in the literature have generally been of relatively sterically unhindered silanols, although as described previously in Section 1.4.5, the sterically hindered silanediol TsiSiF(OH)2 crystallises out as a hexameric unit containing two water molecules.156 It was, therefore, thought to be of interest to try and prepare adducts of some sterically bulky silanols to see if they would form discrete hydrogen bonded units, rather than the extended structures often formed by adducts. The silanols chosen were TsiSi(OH)3 and TsiSiPh2OH. From Section 2.2 it can be seen that their relative acidities towards hydrogen bonding interactions are much less than for Ph3SiOH or (HOPh2Si)20. There are also no previous reports of adducts of silanetriols in the literature, presumably due to their propensity to undergo condensation reactions. The silanetriol, TsiSi(OH)3, however, is very stable to such condensation reactions.285

The attempted isolation of adducts of TsiSi(OH)3 and TsiSiPh2OH was carried out by Method 2. Adducts of neither silanol with Et2NH, Et3N, pyridine and 'PrNH2

156 Chapter 3 Hydrogen bonded adducts of silanols could be isolated. The white solids produced were shown to be the silanol only by 1H NMR and infrared spectroscopy. As may be expected, no condensation reactions occurred and the silanols could be left stirring in amine solution for 24 hours with no sign of condensation. Slow evaporation of the solvent from solutions of TsiSi(OH)3 or

TsiSiPh2OH in an excess of dioxane also failed to produce adducts. TsiSi(OH)3 and TsiSiPh2OH, however, did form adducts with TMEDA by

Method 1, with stoichiometries of 4:3 and 2:1 respectively, as indicated by 1H NMR spectroscopy. Both adducts were crystalline and, therefore, attempts were made to produce crystals suitable for X-ray crystallography. The adducts were recrystallised by slow evaporation of solvent from both ether and acetone solutions and by the liquid diffusion method from toluene-hexane and toluene-cyclohexane solvent systems. No crystals of [TsiSi(OH)3]4.(TMEDA)3 of sufficient quality for X-ray crystallography could be obtained by any of the above methods.

Crystals of (TsiSiPh2OH)2.TMEDA suitable for X-ray crystallography, however, were obtained by slow evaporation of solvent from an ether solution of the adduct and the crystal structure is shown in Figure 3.32. The structure, as may be expected, is discrete comprising a centrosymmetric TMEDA molecule with one TsiSiPh2OH molecule hydrogen bonded to each nitrogen atom. This arrangement is almost identical to that found in (Ph3SiOH)2.TMEDA (Figure 3.20, Section 3.5.1.3) and resembles one fragment of the (HOPh2Si)20.TMEDA chain structure (Figure 1.15, Section 1.4.5). The infrared spectrum of (TsiSiPh2OH)2.TMEDA is very different to that of the original silanol in the OH stretching region. In TsiSiPh2OH there is a narrow peak of medium intensity at 3639 cm-1, corresponding to a 'free' OH group, a weak peak at 3598 cm-1 and a broad band of medium intensity centred at 3442 cm-1 corresponding to a hydrogen bonded OH. In the adduct (TsiSiPh2OH)2.TMEDA there is only one OH band which is very broad and coincides with the CH stretching region of the silanol and TMEDA (3074 - 2787 cm-1) indicating a relatively strong hydrogen bond. It is, therefore, difficult to assign the centre of this band. The Si-O stretching region of the adduct,

157 Chapter 3 Hydrogen bonded adducts of silanols however, is similar to that of the original silanol. Both spectra show stretches at 853 and

834 cm-1, although for the adduct an additional peak at 894 cm-1 is observed. The infrared spectrum of [TsiSi(OH)3]4.(TMEDA)3 is also very different to that of the original silanetriol in the OH stretching region. In the spectrum of TsiSi(OH)3 there is a weak band at 3662 cm-1 in addition to a broad band of medium intensity centred around 3426 cm-1. In [TsiSi(OH)3]4.(TMEDA)3 there is also a OH band of medium intensity but it is very broad and centred around 3206 cm-1. In the Si-O stretching region of both spectra, three strong overlapping bands are present. These are at 870, 855 and

835 cm-1 for TsiSi(OH)3 itself whereas in the adduct they have shifted to 878, 864 and 837 cm-1. Due to the unusual stoichiometry of this adduct and the availability of three OH groups for hydrogen bonding, it is not possible to suggest a plausible hydrogen bonding arrangement.

3.6.4.1 Crystal structure of (TsiSiPh2OH)2.TMEDA Needle-like crystals of (TsiSiPh2OH)2.TMEDA suitable for a structure determination were obtained from toluene/hexane. Data were collected at room temperature and the hydrogen atoms were not located but are fixed at 0.90 A from their parent atoms. Further crystallographic data, including full bond lengths and angles, may be found in the Appendix. The structure is disordered and, therefore, the structure which applies to 80 % of the molecules will be discussed only (Figure 3.32). The remaining 20 % of molecules differ by rotation about the central Si - C bonds of the Tsi groups.

The adduct consists of discrete centrosymmetric units comprising two silanol molecules held together by one molecule of TMEDA. The 0 • • • N distances are 2.75 A which are similar to the hydrogen bond lengths in (HOPh2Si)20.TMEDA129 and (Ph3SiOH)2.TMEDA (Section 3.5.1.3.1). The 0-H • • • N bond angle is 158°. The various Si - C bonds within the Tsi groups are as expected. The structure resembles one fragment of the chain structure of (HOPh2Si)20.TMEDA (Figure 1.15, Section 1.4.5).

158 Figure 3.32. View of the hydrogen bonded adduct (TsiSiPh2OH)2.TMEDA. Hydrogen bonds are represented by dashed lines and hydrogen

atoms attached to carbons are omitted for clarity. Chapter 3 Hydrogen bonded adducts of silanols

3.6.5 Adducts of (-)MePhNaphthSiOH The possibility of separating mixtures of enantiomers by adduct formation with a chiral silanol was considered. There are, however, very few chiral silanols, although (-)MePhNaphthSiOH appears to be a good candidate since both the related silanols, Ph3SiOH and tris(1-naphthyl)silanol form adducts with a number of molecules. Solution studies (Section 2.2) also showed that the relative hydrogen bonding ability of

(-)MePhNaphthsilanol is of a similar magnitude to Ph3SiOH. The stereospecific and direct conversion of MePhNaphthSiH into MePhNaphthSiOH by 0 atom insertion into the Si-H bond by dimethyldioxirane has been reported in the literature.286 The preparation of dimethyldioxirane, however, is a time consuming procedure but oxidation of a variety of substrates has been achieved by dioxiranes prepared 'in situ' from OXONE® (potassium peroxymonosulfate) and acetone.287-289 The viability of this method for the conversion of (-)MePhNaphthSiH into (-)MePhNaphthSiOH was therefore tested but no oxidation took place under the 'in situ' reaction conditions. For comparison, the oxidation of other bulky silanes was also attempted 'in situ' but although Ph3Sill was rapidly oxidised to Ph3SiOH within half an hour, this method did not work for the more sterically hindered TsiSiPh2H, TsiSiH3 or TsiSiMe2H even after two days. Lickiss and Lucas have reported the oxidation of sterically hindered silanes using potassium permanganate.290 The conversion of (-)MePhNaphthSiH into (-)MePhNaphthSiOH was successful using this method. As both Ph3SiOH and (1-naphthy1)3SiOH are known to form 4:1 and 1:1 adducts respectively with dioxane,147 the isolation of adducts with (-)MePhNaphthSiOH was first attempted with dioxane. Slow evaporation of a chloroform solution of the silanol and excess dioxane, however, did not produce any crystals. The preparation of adducts of (-)MePhNaphthSiOH with TMEDA and pyridine (which form adducts readily with a number of silanols) were attempted by Method 2 but in both cases no adducts were isolated. Then the racemic amine (±)-sec-butylamine was chosen to see if (-)MePhNaphthSiOH would form an adduct with either or both of the

160 Chapter 3 Hydrogen bonded adducts of silanols enantiomers but no adduct could be isolated. The amine, (±)-sec-butylamine, however, did not form adducts with (HOPh2Si)20 or Ph3SiOH either (Sections 3.4.1.1 and 3.5.1.1).

Further work is needed to establish whether (-)MePhNaphthSiOH is capable of adduct formation in the solid state, and if so, attempting adduct preparation with a range of suitable chiral organic species.

3.6.6 Adducts of tBuMe2SiOH

The use of a liquid silanol was considered as a potential way of overcoming the difficulties of preparing adducts of silanols with compounds which are insoluble in organic solvents. The liquid silanol tBuMe2SiOH was chosen as this is already known to form an adduct, a solid hemihydrate [tBuMe2SiOH]2.H20, on exposure to moisture88'153

(Figure 1.20, Section 1.4.5) and also, the bulky tBu group makes the silanol very resistant to condensation. The analogous carbinol, tBuMe2COH, also forms a hemihydrate.155

The hemihydrate [ButMe2SiOH]2.H20 was prepared by the method of Sommer and Tyler152 and dehydrated by dissolving it in anhydrous carbon tetrachloride, drying over magnesium sulfate and removing the solvent under vacuum to give tBuMe2SiOH as a colourless liquid.

The trialkylsilanol, tBuMe2SiOH is, as expected, substantially less acidic than the arylsilanols (HOPh2Si)20 and Ph3SiOH as shown by infrared spectroscopic studies in

Section 2.2. The attempted preparation of adducts with the insoluble solid amino acid

N-glycylglycine, H2NCH2CONHCH2CO2H, and with pentaerythritol, C(CH2OH)4, were carried out under nitrogen by addition of the solid to an excess of tBuMe2SiOH and stirring for a three days. The mixture remained heterogeneous in both cases and no adducts could be isolated.

The preparation of adducts of tBuMe2SiOH with amines was also attempted by stirring an excess of amine with tBuMe2SiOH under nitrogen for two days and removing the excess amine under vacuum. No solid adduct could be isolated with TMEDA, pyridine or aniline.

161 Chapter 3 Hydrogen bonded adducts of silanols

3.6.7 Adducts of cis-cis-cis-[(HO)PhSiO]4 The cyclic silanol cis-cis-cis-[(HO)PhSiO]4, was prepared by the method of Brown291 and recrystallised from ether/hexane to give a white powdery solid (Section 4.5). The proposed structure of cis-cis-cis-[(HO)PhSiO]4, with four OH groups pointing upwards from one face of the ring appears to be particularly suitable for hydrogen bonding to crown-ethers and during the course of these studies the cis-cis-cis structure was confirmed in an ether solvate (Section 4.5).256 Attempted preparation of adducts of cis-cis-cis-[(HO)PhSiO]4 with 12-crown-4 and 15-crown-5 were carried out by Method 2, except that the solutions were only stirred for between 2 and 10 minutes before hexane was added to encourage precipitation. The tetrol was not left in solution for long periods of time due to its high propensity towards polycondensation reactions. With both crown ethers a 'soft' white solid precipitated. The 1H NMR spectra of the solids suggest that adduct formation may have taken place as there are peaks attributable to both cis-cis-cis-[(HO)PhSi0]4 and the crown ether. The integration of the peaks, however, did not remain consistent on repetition of the experiment.

The infrared spectra show shifts in the OH stretching frequency from 3230 cm-1 in cis-cis-cis-[(-10)PhSi0]4, alone to around 3322 cm-1 with 12-crown-4 and around 3369 cm-1 with 15-crown-5. It is difficult to observe changes in the D(Si-O) region as peaks due to the crown ethers also occur in this region. The melting points of the white solids obtained in all attempts were also depressed from 156 - 161 °C irr pure cis-cis-cis- [(110)PhSiO]4 to between 120 - 130 °C. Although it appears that adduct formation has taken place with both the crown ethers, the stoichiometry of the adducts is unclear and further work is needed for clarification.

The high propensity of this silanol to undergo condensation reactions does not allow the preparation of adducts with amines. Whether cis-cis-cis-[(HO)PhSiO]4 could interact with barium, as in the complexation of metal ions by crown ethers, was also of interest since Ba(OH)2.8H20 is used as an industrial catalyst in siloxane polymerisation reactions. This proved difficult

162 Chapter 3 Hydrogen bonded adducts of silanols experimentally due to the insolubility of Ba(OH)2.8H20 and other barium salts such as BaC12.2H20 in organic solvents and the unsuitability of water as a solvent for cis-cis-cis-

[(HO)PhSiO]4. The reactions were therefore carried out using a similar principle to those for the complexation of metal salts by crown ethers.292 Due to the instability of cis-cis- cist(HO)PhSi0J4 in solution for long periods, the reactions were carried out over a shorter period of time. For example, a suspension of BaC12.2H20 in methanol was added to a solution of cis-cis-cis-[(HO)PhSiO]4 in methanol and stirred vigorously for 3 hours. The solution, which had remained cloudy, was then filtered and the filtrate concentrated on the rotary evaporator until white crystals started to come out of solution. Analysis of these crystals by infrared spectroscopy was inconclusive as to whether they just contained a mixture of the two starting materials, whether any complexation had occurred or whether an alternative reaction had occurred.

3.7. Co-crystallisation of mixtures of silanols

Attempts at co-crystallising (HOPh2Si)20 and (HOMe2Si)20 in a 1:1 molar ratio, (HOPh2Si)20 and Ph3SiOH in both a 2:1 and 1:1 molar ratio and, (HOMe2Si)20 and Ph3SiOH in a 2:1 molar ratio by both Spalding's method and from toluene/hexane failed. The products were analysed by melting point and by 1H NMR and FTIR spectroscopy and the results compared to those obtained from analyses of the original silanol mixtures. The melting points and FTIR spectra of the products were the same as those of the corresponding mixtures of silanols which showed that in all cases they were just mixtures of the two silanols and not new stoichiometric adducts.

163 Chapter 3 Hydrogen bonded adducts of silanols

3.7 Summary of hydrogen bond lengths and angles found in silanol adducts

Table 3.6 provides a summary of the structural data obtained for the hydrogen bonded adducts of silanols prepared in this Chapter. Literature data, where available, for related silanol adducts have also been included for comparison. It can be seen from Table 3.6 that these silanols are capable of forming a wide variety of structures. Some of these structures may be anticipated whilst it is unclear why others are formed.

The 0 • • • 0 distances for silanol to silanol interactions in these adducts fall in the wide range of 2.547 - 2.789(2) A, whilst 0 • • • 0 distances for silanol to dioxane or crown ether interactions are in the much narrower range of 2.714 - 2.836(A). The 0 • • • N distances also fall in the narrow range of 2.70 - 2.774 A. All these distances fall in the range usually associated with medium strength hydrogen bonds.48'74 The shorter 0 • • • 0 distances often found for silanol to silanol hydrogen bonding interactions, however, reflect the relatively high strength of such interactions in comparison to hydrogen bonding interactions between silanol groups and other molecules. The

O-H • • • X (X = 0 or N) angles range from 159.6 - 176.1 0, which may be classified as linear.

Correlations between the AH stretching frequency in the solid state infrared spectra of hydrogen bonded adducts, A-H • • • B, and A • • • B bond distance, and A-H bond length have been proposed previously.48,50,74,75 For the silanol adducts in Table 3.6, however, it is not possible to study the relationship between the OH stretching frequency and 0 • • • X (X = 0 or N) bond distances or OH bond lengths for a number of reasons. Firstly, although many different OH • • • X hydrogen bonds may exist in the crystal structure, only one broad OH band is observed in the infrared spectrum. In many cases the centre of this OH band is obscured by the CH stretching region. Apart from these more complicated cases, there are relatively few simple adducts to give sufficient data for detailed studies to be carried out.

164 Table 3.6. Summary of structural data for selected hydrogen bonded adducts of silanols.

Complex OH • - • Xa 0 • • • Xa 0-H 0-H • • • Xa Structural summary (A) (A) (A) (a) [(HOPh2Si)20]4.(Et2NH)2 2.56 - 2.75 Discrete 4:2 adduct. 2.70b OH • • • OH, OH • • • N, 2.82b NH • • • 0 and NH • • • n 3.14e interactions 3.59d (HOPh2Si20).1[HOPh2SiOSiPh20] 1.695 - 1.871 2.547 - 2.750 0.740(7)- 159.6 - 168.9 Discrete 2:1 adduct. [Et3NH] } 1.717e 2.861e 0.987(10) 159.4e OH • • • OH and NH • • • 0 1.189(9)f interactions (HOPh2Si)2O.TMEDA129 2.74b Chain [(HOPh2S020]3.(C4114N2)26 2.71(1) Discrete 3:2 adduct. 2.75(1)b 0 H • • • OH and OH • • • N 2.75(2)b interactions (HOPh2Si)20.C5H5N.HC1144 2.28g Simple, discrete 1:1 adduct. 2.42g OH • • • Cl interactions (HOPh2Si)20.1,4-dioxane 1.911 2.714 0.80(4) 168.7 Chains 1.920 2.836 0.92(4) 164.8 Ph3SiOH.tris(2-aminoethyl)amine 1.847b 2.680b 0.83(3) 176.1b Simple, discrete 1:1 adduct (Ph3SiOH)2.piperazine 2.72b 169b Simple, discrete 2:1 adduct

(continues) Table 3.6. Summary of structural data for selected hydrogen bonded adducts of silanols (continued).

Complex OH • • • Xa 0 • • • Xa O-H 0-H • • • Xa Structural summary (A) (A) (A) (°) (Ph3SiOH)2.TMEDA 1.968b 2.774b 0.81(3) 171.9b Simple, discrete 2:1 adduct (Ph3SiOH)2.18-crown-6.(H20)2 1.945 2.724 0.78(3) 173.1 Discrete ternary adduct. 2.110h 3.015h OH • • • OH2 and 2.333h 2.940h OH(H20) • • • 0 (crown) interactions. (Ph3SiOH)2.12-crown-45 1.91(2) 2.76 Simple, discrete 2:1 adduct (Ph3SiOH)4.Et0H146 2.60 - 2.79 4:1 clathrate (Ph3SiOH)4.1,4-dioxane147 2.789(2) 0.94(3) 164.7(42) 4:1 host-guest complex. 2.703(2) 0.92(3) 165.6(26) OH • • OH and OH • • • 0 (dioxane) bonds [(1-naphthy1)3SiOH].1,4-dioxane147 2.736(3) 169.7(23) Simple, discrete 1:1 adduct (TsiSiPh2OH)2.TMEDA 2.75b 158b Simple, discrete 2:1 adduct

a X = oxygen unless otherwise stated. bX.N. eN•••0. dN•••ic. eNH•••0. fNH. g X = Cl. hOH (H2O) • • • 0 (18-crown-6) Chapter 3 Hydrogen bonded adducts of silanols

3.8 Thermal analyses of silanol adducts

TGA (thermogravimetric analysis) and DSC (differential scanning calorimetry) studies were carried out on a range of the adducts prepared. The results are summarised in Table 3.7. For comparison, TGA and DSC studies were also carried out on the corresponding silanols, (HOPh2Si)20 and Ph3SiOH (Figures 3.33 and 3.34). The melting point of (HOPh2Si)20 was 110-112 °C in air. This is in agreement with the DSC curve which shows a sharp endotherm centred at 111.49 (Ton 105.7 °C, -17.32 mcal/mg), due to the melting point of the compound (Figure 3.33). The TGA curve shows a gradual region of weight loss between 160 - 300 °C and a steeper region of weight loss between 300 - 450 °C giving a final residue of 6.60 % at 600 °C (Figure 3.33).

The DSC curve for Ph3SiOH shows a sharp endotherm centred at 155.0 °C (Ton 140.0 °C, -24.67 mcal/mg) corresponding to the melting point of the silanol (Figure 3.34). This is in good agreement with the value of 155-156 °C obtained in air. The TGA curve shows a steep region of weight loss between 190 - 330 and a less steep region between 330 - 500 °C to give a final residue of 0.60 % at 600 °C (Figure 3.34). The first steep region of weight loss is accompanied by a broad endotherm in the DSC curve centred at around 330 °C.

The behaviour of the silanols upon thermolysis is complicated, the regions of weight loss corresponding to the formation of condensation products with loss of water. In the case of (HOPh2Si)20, an independent thermolysis experiment suggested that the first region of weight loss between 160 - 300 °C was due to the formation of some of the cyclic trisiloxane (Ph2SiO)3. The sample of (HOPh2Si)20 was placed in a quartz test tube and heated slowly to 300 °C under a stream of nitrogen, using a graphite bath to keep the temperature distribution even. A colourless liquid remained in the sample tube which rapidly turned into an opaque solid on cooling to room temperature. The solid was analysed by 1H NMR and 29Si NMR spectroscopy and by CI mass spectrometry which identified the solid as a mixture of (HOPh2Si)20 and the cyclic (Ph2SiO)3.

167

Chapter 3 Hydrogen bonded adducts of silanols

120 .14

-12

100 -10

.8 BO- .6 ) I ) t .4 /sec 60- l Ca rcen

e -2 (p (m

ht 0 ig 40 Flew t We

-2 Hea

-‘6

--B 1 100 200 33D 400 500 600 temperature (0)

Figure 3.33. TGA ( — ) and DSC ( - - -) curves for (HOPh2Si)20.

120 -10

B I 100 6 —

-4 80 --- [ )

-0 l/sec 50 Ca -2 (m w --4

CO Flo t a --5' He

--B 20

100 200 300 400 500 600 Temperature

Figure 3.34. TGA ( —) and DSC ( - - - ) curves for Ph3SiOH.

168 Table 3.7. Thermal analyses of some adducts of (HOPh2Si)20 and Ph3SiOH.

TG weight loss due to m.p./b.p. release of Endotherms in the DSC curve Adduct of amine/oxygen donor amine/oxygen Calc. Obs. Ton Centre of Energy of Ton - Tb donor (%) (%) (°C) endotherm endotherm (°C) (°C) (°C) (mcal/mg) [(HOPh2Si)20]4.(Et2NH)2 b.p. 55 8.1 10.0 101.8 114.9 41.56 47 (HOPh2Si)20.piperazine m.p. 108-110 17.2 19.1 122.0 128.4 55.48 -23 b.p.145-146 (HOPh2Si)20.{ [HOPh2SiOSiPh20] b.p. 88.8 10.9 12.9 78.7 85.4 13.31 -3 [Et3NH]1 115.4 (HOPh2Si)20.DABCO m.p. 158-160 21.2 23.5 145.2 153.8 59.89 -29 b.p. 174 (HOPh2Si)20.dioxane b.p. 100-102 17.5 19.4 79.1 90.9 21.02 -21 (Ph3SiOH)2.piperazine m.p. 108-110 127.6 132.6 25.43 -17 b.p.145-146 (Ph3SiOH)2.TMEDA b.p. 120-122 76.1 81.7 18.67 -44

(continues) Table 3.7. Thermal analyses of some adducts of (HOPh2Si)20 and Ph3SiOH (continued).

TG weight loss due to m.p./b.p. release of Endotherms in the DSC curve Adduct of amine/oxygen donor amine/oxygen Calc. Obs. Ton Centre of Energy of Ton - Tb donor (%) (%) (°C) endotherm endotherm (°C) (°C) (°C) (mcal/mg) (Ph3SiOH)4.(DABCO)3 m.p. 158-160 118.8 126.1 18.52 -55 b.p. 174 142.0 149.8 5.34 (Ph3SiOH)4.DABCO m.p.158-160 124.7 128.5 3.68 -49 b.p. 174 149.1 153.8 22.87 (Ph3SiOH)2.1,4,8,11- m.p. 184-186 137.3 143.1 27.15 tetraazacyclotetradecane (Ph3SiOH)2.18-crown-6.(H20)2 m.p. 42-45 4.2 (H2O) 3.7 66.43 (Ph3SiOH)3.1-aza-12-crown-4 m.p. 56-58 66.1 71.9 7.23 b.p. 58-62 /0.005 mm (Ph3SiOH)2.1-aza-15-crown-5 m.p. 35-37 57.2 61.7 17.25 Chapter 3 Hydrogen bonded adducts of silanols

In the case of Ph3SiOH, a white solid sublimed on the TGA apparatus, which was identified by EI mass spectrometry and melting point as the disiloxane (Ph3Si)20 (m.p. 224-225 °C).

One region of weight loss between 25 to 200 °C was observed for all the adducts of (HOPh2Si)O. The weight loss values observed, however, are consistently around 2 % higher than those calculated for the loss of amine/dioxane and this is due to a slight overlap of the weight loss region with the beginning of the weight loss region for (HOPh2Si)20 itself (Figure 3.33). The observed total weight losses, therefore, are in good agreement with the calculated values for the loss of amine/dioxane and confirm the disiloxanediol to amine/dioxane stoichiometric ratios (Table 3.7). The regions of weight loss in all the adducts of (HOPh2Si)2O, except for

(HOPh2Si)20.{ [HOPh2SiOSiPh20][Et3N1-1]1, are accompanied by a single endotherm in the DSC curve which suggests release of the amine or dioxane with concomitant dissolution of the disiloxanediol (Table 3.7). For example, the TGA and DSC curves for (HOPh2Si)2 0.DABCO are shown in Figure 3.35. In (HOPh2Si)20. [HOPh2SiOSiPh20][Et3NH]1, however, the endotherm due to release of the amine, centred at 85.4 °C, is followed by a second endotherm centred at 115.4 °C due to the melting point of the disiloxanediol. The onset temperatures, Ton, of the endotherms are in good agreement with the observed melting (decomposition) points of the adducts in the Experimental (Section 6.1.9). It can be seen from Table 3.7 that for the adducts of (HOPh2Si)20 with the low boiling point amines Et2NH and Et3N, the onset temperatures, Ton, of the endotherms due to release of the amine are above and similar respectively to the normal boiling points of the amines. With the high melting/boiling point solid amines piperazine and DABCO, and with dioxane, the onset temperatures, Ton, of the endotherms due to release of the amine/dioxane are below the normal boiling points of the amines. For (HOPh2Si)20.DABCO the onset temperature of the endotherm even occurs just before the melting point of the amine (although DABCO is known to sublime readily at room temperature293). These variations are to be expected since the amine/dioxane no longer

171

Chapter 3 Hydrogen bonded adducts of silanols

120-

100- -5

BO- -4

\ • E

••.;,„ -0

20-

--4 I i I 0 50 100 n0 200 250 300 7e-::vature ICI

Figure 3.35. TGA ( — ) and DSC ( - - - ) curves for (HOPh2Si)20.DABCO.

120- •12

.10 100-

60- ----1 1

-4 ) ec .; l/s 60 • al Ca Irn oa 40- now \ t a

I He 1 20-

--8

I I 50 ipo 10 200 250 300 le,,pe,ature IC)

Figure 3.36. TGA ( —) and DSC ( - - - ) curves for

(HOPh2Si)20. { [HOPh25i0SiPh20][Et3N11]}-

172 Chapter 3 Hydrogen bonded adducts of silanols has the same bulk properties when incorporated within a matrix of silanol molecules. This also occurs for the corresponding adducts with Ph3SiOH.

As discussed earlier the first region of weight loss in the TGA of Ph3SiOH starts at 190 °C. Unfortunately for all the adducts of Ph3SiOH reported in Table 3.7, except for (Ph3SiOH)2.18-crown-6.(H20)2, the regions of weight loss associated with the loss of amine form a continuum with the weight loss region of Ph3SiOH itself and, therefore, weight loss percentages may not be observed to confirm the stoichiometries. As may be expected, the start of the weight loss region in the TGA of

(Ph3SiOH)2.TMEDA is accompanied by a single endotherm, with onset temperature at 76.1 °C, corresponding to the release of the amine with concomitant dissolution of the silanol. This agrees with the observed decomposition (Section 6.1.9).

The TGA and DSC curves for (Ph3SiOH)2.piperazine are similar to those obtained for the related (HOPh2Si)20 adduct in that the start of the weight loss region is accompanied by a single endotherm in the DSC trace with onset temperature of 127.6 °C, below the normal boiling point of piperazine (b.p. 145-146). This endotherm may, therefore also be due to release of the amine with concomitant dissolution of the silanol. Likewise, the DSC curve for (Ph3SiOH)2.1,4,8,11-tetraazacyclotetradecane displays a single endotherm with Ton 137.3 °C accompanying the start of the weight loss region in the TGA curve, far below even the melting point of 1,4,8,11- tetraazacyclotetradecane itself (184-186 °C) (Table 3.7). In the TGA curve of (Ph3SiOH)2.18-crown-6.(H20)2 (Figure 3.37) it is possible to observe a small region of weight loss associated with the water molecules and the observed weight loss is in good agreement with the value calculated (Table 3.7). This region of weight loss is accompanied by a broad endotherm in the DSC curve (Figure 3.37) which appears to comprise two broad overlapping endotherms which are not fully resolved for values of Ton and energy to be meaningful. Since there are no further endotherms in the DSC curve, these endotherms appear to correspond to loss of water rapidly followed by melting of the 18-crown-6 and concomitant dissolution of the silanol.

173 Chapter 3 Hydrogen bonded adducts of silanols

120- -10

-5

BO- ) l/sec 60- -2 Ca a (m w z 0 flo

AO- t

--2 Hea

20 --a

T i i 50 100 150 200 250 300 Tenerature IC)

Figure 3.37. TGA ( ) and DSC ( - - - ) curves for (Ph3SiOH)2.18-crown-6.(H20)2.

As discussed previously in Section 3.5.3, a number of neutral molecules form 2:1 diaquo complexes with 18-crown-6.271274- 280 There is, however, a paucity of thermal analytical data available for these adducts, largely because of their low melting points.278 Thermal studies have only been carried out on the 2:1:2 dichloropicric acid: 18-crown-6: water adduct278 which has as identical hydrogen bonding arrangement to that found in (Ph3SiOH)2.18-crown-6.(H20)2. For the dichloropicric acid adduct there are two broad endotherms in the DSC curve centred at 86 and 111.5 °C. These correspond to loss of water and fusion respectively. The region of weight loss in the TGA, however, starts at 66 °C, some 7 °C lower than that of the onset temperature of the first endotherm, for which no explanation could be found. The weight loss corresponds to the loss of only one water molecule to give a 2:1:1 dichloropicric acid:18-crown-6:water complex of undetermined crystal structure. It was found that this complex could be rehydrated on exposure to water vapour at 25 °C to reform the original 2:1:2 adduct. This is in contrast to (Ph3SiOH)2.18-crown-6.(H20)2 which loses both water molecules upon heating. More detailed studies on the thermal behaviour of (Ph3SiOH)2.18-crown-6.(H20)2, including whether it can be rehydrated, are required. Unfortunately time did not permit these studies to be carried out.

174 Chapter 3 Hydrogen bonded adducts of silanols

For the adducts of Ph3SiOH with the azacrowns 1-aza-12-crown-4 and 1-aza-15- crown-5, the TGA curves show no weight loss until around 120 and 140 °C respectively. The DSC curves, however, show single endotherms with onset temperatures of 66.1 and

57.2 °C respectively which, therefore, must correspond to the decomposition points of the adducts without volatization of the azacrown i.e. the azacrown-silanol hydrogen bonds are broken, accompanied by the melting of the azacrown with concomitant dissolution of the silanol (Table 3.7). These results are in agreement with the observed melting (decomposition) points of the adducts in air (Section 6.1.9.2). The DSC curves of the 4:3 and 4:1 adducts of Ph3SiOH with DABCO are more complicated (Figures 3.38 and 3.39). In air the observed melting point of (Ph3SiOH)4.(DABCO)3 is 124-125 °C. The region of weight loss in the TGA curve, however, is accompanied by two endotherms, a large endotherm with onset temperature of 118.8 °C and a smaller endotherm with onset temperature 142.0 °C (Figure 3.38). As in the case of (HOPh2Si)20.DABCO the onset temperatures of the endotherms associated with weight loss are lower than the melting point of DABCO itself. The first endotherm may correspond to release of the amine, followed by a second endotherm due to the melting point of Ph3SiOH. Although the adduct (Ph3SiOH)4.DABCO was observed to soften at around 127 °C, rapid melting did not occur until 150-155 °C. This is in agreement with the DSC curve which shows a small endotherm, Ton 124.7 °C, followed by a large sharp endotherm with Ton 149.1 °C (Figure 3.39). These endotherms accompany the region of weight loss in the TGA. Again, the first endotherm may also correspond to release of the amine and the second to the melting poiint of Ph3SiOH, but as the 4:1 adduct is significantly richer in silanol than the 4:3 adduct, the endotherm due to the release of the amine is smaller and the endotherm due to the melting point of Ph3SiOH much larger and sharper. Although energies have been included in Table 3.7, no conclusions may be drawn from these values since many different bonds are being broken and several processes are often occurring simultaneously. As discussed previously in Section 3.3, however, the

175 Chapter 3 Hydrogen bonded adducts of silanols thermal stabilities of adducts can be assessed from the temperature characterising the start of the endothermic guest-release reaction.151 It has been suggested that the functions Ton - Tb (where Tb = normal boiling point of guest molecule) may be useful parameters of complex stability (Section 3.3).151 Ton Tb values have been included in Table 3.7, where appropriate, for comparison. It can be seen that for the adducts of (HOPh2Si)20 the order of thermal stability suggested by Ton - Tb values is:

[(HOPh2Si)20]4.(Et2NH)2 > (HOPh2Si)20.{ [HOPh2SiOSiPh20][Et31\11-1]1 > (HOPh2Si)20.1,4-dioxane > (HOPh2Si)20.piperazine > (HOPh2Si)20.DABCO

For the adducts of Ph3SiOH, the order of thermal stability suggested is:

(Ph3SiOH)2.piperazine > (Ph3SiOH)2.TMEDA > (Ph3SiOH)4.DABCO > (Ph3SiOH)4.(DABCO)3

For both silanols, the adducts containing the strong base DABCO appear to be the least thermally stable.

120- -4

-3 10D-

80-

60-

a, —1

40- Flow t

--2 Hea

20^

0 50 100 150 200 250 300 Temperature (C)

Figure 3.38. TGA ( — ) and DSC ( - - -) curves for (Ph3SiOH)4.(DABC0)3-

176

Chapter 3 Hydrogen bonded adducts of silanols

120- -7

-6

100- -5

-4 00-

) -2 t n 60^ erce (p

' ht Flow ig 40- t We

It --2 Hea

20- --3 --4

--5

50 100 150 200 250 300 Temperature (C)

Figure 3.39. TGA ( — ) and DSC ( - - -) curves for (Ph3SiOH)4.DABCO.

177 CHAPTER 4 Synthesis and structures of miscellaneous silanols Chapter 4 Synthesis and structures of miscellaneous silanols

CHAPTER 4 Synthesis and structures of miscellaneous silanols

4.1 Introduction

The wide variety of hydrogen bonded structures formed by silanols has been discussed in Section 1.4.4. Although more than one hundred structures for silanols are now known, the hydrogen bonding arrangement is often difficult to predict since chemically very similar compounds may have very different structures, e.g. Et2Si(OH)2 (infinite sheets)294 and iPr2Si(OH)2 (infinite chains).93 Although this this work has concentrated on the less well studied interactions of silanols with other molecules it was thought of interest to try to obtain structures of, and elucidate the hydrogen bonding arrangements found in, some of the more interesting or unusual silanols.

4.2 Compounds containing one Si-OH group, silanols

The structures of about fifty compounds with one SiOH group have been reported since they are in general less susceptible to condensation reactions when compared to silanediols and silanetriols. In particular a number of silanols containing tBu groups have been synthesised and structurally characterised, the steric hindrance provided by tBu groups greatly enhancing their stability in comparison with silanols containing other simple alkyl groups.

Upon exposure to moisture the liquid silanol tBuMe2SiOH forms a solid hemihydrate (tBuMe2SiOH)2.H20 whose structure has been described previously (Section 1.4.6).152,153 Tert-butyldimethylsilanol is unusual in the fact that it is liquid whereas almost all other simple silanols exist as solids. The gas phase structure of the anhydrous silanol has been determined previously and, like structure of the hemihydrate in the gas phase, comprises free silanol molecules only.295 It was, therefore, of interest to determine the hydrogen bonded arrangement formed by the anhydrous silanol which was

179 Chapter 4 Synthesis and structures of miscellaneous silanols attempted by low temperature X-ray crystallography. [tBuMe2SiOH]2.H20 was prepared by the hydrolysis of tBuMe2SiCl with KOH/H20/Me0H/Et20152 and dehydrated by dissolving in anhydrous carbon tetrachloride, drying over magnesium sulfate and removing the solvent under vacuum to give tBuMe2SiOH as a colourless liquid. The anhydrous silanol was sealed into an oven-dried thin-walled, glass capillary tube, with all manipulations carried out in a glove box. Unfortunately the silanol went glassy upon cooling to low temperature and no crystal structure could be obtained by Dr. S. Parsons at Edinburgh University.

The bulky silanol tBu2SiH(OH), prepared by hydrolysis of tBu2SiHC1 with NaOH/H20/Et20,296 is the precursor to the radical anion of di-t-butylsilanone, tB u2Si=0 —, which was the first silanone species to be spectroscopically characterised,297'298 and is a rare example of a stable hydridosilane, i.e. it has an H and an OH substituent on the same silicon. It may even be sublimed without decomposition. Determination of the structure of tBu2SiH(OH) by X-ray crystallography revealed that it forms a terameric hydrogen bonded structure with a cyclic arrangement of molecules (Section 4.2.1). This arrangement is also found in the crystal structure of the related silanol tBu2SiF(OH) in which the flourine, surprisingly, plays no part in the hydrogen bonding.299 A similar tetramer is formed by the silanoate, [tBu2Si(OH)OLi.THF]4, in which Si-O-Li interactions hold the tetrameric structure together and the silanol groups are hydrogen bonded to molecules of THE from the solvent (Section 1.4.5).158 The structure of the related silanediol, tBu2Si(OH)2, for comparison, comprises ladder chains in which pairs of molecules are linked to form dimers and then further hydrogen bonds link the dimers to form chains [Section 1.4.4.2, Figure 1.6(e)].94'95

4.2.1 Crystal structure of tBu2SiH(OH) Crystals of tBu2SiH(OH) suitable for X-ray crystallography were donated by Dr. R. G. Taylor (Dow Corning Corporation). Data were collected at room temperature and the hydrogen atoms were not located but are fixed at 0.90 A from their parent atoms.

180 Chapter 4 Synthesis and structures of miscellaneous silanols

Further crystallographic details may be found in the Appendix. Selected bond lengths and angles are given in Table 4.1.

In the molecular structure of tBu2SiH(OH) (Figure 4.1), the Si-O and Si-C bond lengths and angles are normal except for the C(2)-Si-C(1) angle which is 117.6(2) °. This angle has opened up from the normal value of 109.3 ° due to the steric repulsion between the tBu groups.

Table 4.1. Selected bond lengths and angles in tBu2SiH(OH).

Si-O 1.655(3) A O-Si-C(1) 108.9(2) ° Si-C(1) 1.882(6) A O-Si-C(2) 110.0(2) ° Si-C(2) 1.876(5) A C(2)-Si-C(1) 117.6(2) ° o • • • 0 2.7A 0-H • • • 0 147° O-H • • • 0 1.9A

C(22)

Figure 4.1. Molecular structure of tBu2SiH(OH).

181 Chapter 4 Synthesis and structures of miscellaneous silanols

The silanol group in each tBu2SiH(OH) molecule acts both as a hydrogen bond donor and acceptor which results in a tetrameric hydrogen bonded structure with a cyclic arrangement of molecules (Figure 4.2). The 0 • • • 0 and O-H • • • 0 distances are 2.7 A and 1.9 A respectively and the 0-H • • • 0 angle is 147 0. The hydrogen bond distances are comparable to those found in the hydrogen bonded tetramer formed by tBu2SiF(OH), with 0 • • • 0 distances of 2.756(9) A.299 The cyclic tetramers are stacked on top of each other, Figure 4.3, and the repeat distance along the c axis is 9.1 A.

Figure 4.2. The tetrameric hydrogen bonded structure of tBu2SiH(OH).

182 Chapter 4 Synthesis and structures of miscellaneous silanols

Figure 4.3. A view along the c axis showing the stacking arrangement of the cyclic tetramers in tBu2SiH(OH).

183 Chapter 4 Synthesis and structures of miscellaneous silanols

4.3 Compounds containing an Si(OH)2 group, silanediols, or two Si-OH groups, am—siloxanediols

The crystal structure of the disiloxanediol (HOMe2Si)20 [Section 1.4.4.2, Figure 1.6(g)] has been reported previously by two groups100'101 but no crystal data is available for the lower member of the series, Me2Si(OH)2, and the higher members of the series HO(Me2SiO)nH where n 3 which are liquids. These compounds are important intermediates in the production of silicones by hydrolysis (Section 1.1.2) and are also formed by the degradation of silicones in the environment, particularly Me2Si(OH)2 (Section 1.1.3). Dimethylsilanediol is extremely sensitive to the catalytic effect of traces of acid or base which condense it to polysiloxanes. Therefore without proper precautions, especially against the hydrogen chloride produced in the hydrolysis reaction, a successful preparation cannot be expected. Even glass contains sufficient alkali to cause slow condensation.300

The preparation of Me2Si(OH)2 was first reported from the corresponding dimethoxy- or diethoxysilanes.300-302 Takiguchi then found that Me2Si(OH)2 could be successfully prepared by hydrolysis of Me2SiC12 using aniline as an acceptor for the hydrogen chloride.303 Although this method produces Me2Si(OH)2 in good yield (71 %), trace amounts of residual aniline, immiscible with the pentane used in the washing step, often cause condensation reactions to occur upon storage. This method was later modified by Cella and Carpenter who used Et3N as the acid acceptor which is volatile and soluble in pentane.304 This was found to be the easiest and most reliable method for the preparation of Me2Si(OH)2 which crystallised as white plates. It's 1H NMR and IR spectra agreed with those given in the literature301304 and the 29Si, 13C NMR and CI mass spectrum were consistent with that expected for Me2Si(OH)2 (,Section 6.1.6.1). The microanalytical data, however, was low on hydrogen content and the melting point was 75 °C which was significantly lower than literature melting points which range from 96-101 oc.282,300,301,303-305 Although the preparation was repeated several times no improvement on the melting point occurred. It is not clear why the melting point is lower

184 Chapter 4 Synthesis and structures of miscellaneous silanols than expected, as all other data is in good agreement and no impurities were detected by spectroscopic analysis. The Me2Si(OH)2 thus produced was stored in polythene containers in the freezer as a precaution against condensation. Dimethylsilanediol was recrystallised from ether/pentane, acetone/pentane and slow evaporation of benzene, ether or acetone solutions of Me2Si(OH)2.

Dimethylsilanediol consistently crystallised as plates which were not of sufficient thickness for X-ray crystallography. No improvement was observed in the melting point either. The a,co-siloxanediols, HO(Me2SiO)3H and HO(Me2SiO)4H were also prepared from the corresponding chlorosiloxanes by the method of Cella and Carpenter.304 Since they are viscous oils, residual Et3N from their preparation, which may encourage condensation reactions, was removed by dissolving the siloxanediol in CH2C12 and rapidly removing the solvent under vacuum three times to leave the siloxanediol as a colourless viscous liquid. The siloxanediols thus produced were stored in the freezer as a precaution against condensation reations which often occur when the liquids are left at room temperture for prolonged periods. Small amounts of the siloxanediols were sealed into oven dried thin-walled glass capillary tubes taking care not to expose the samples to heat or moisture. Unfortunately, both compounds went glassy upon cooling and no crystal structures could be obtained by Dr. S. Parsons at Edinburgh University.

The discovery that the silanediol iBu2Si(OH)2 and the disiloxanediols (HOR2Si)20 (where R = Et, nPr or nBu) form unusual liquid crystal phases101'106-110 has led to an increased interest in the structures of other simple silanediols and disiloxanediols.

Methylphenylsilanediol was isolated as plate-like crystals,s‘ instead of meso- (HOMePhSi)20 from the hydrolysis of MePhSiC12 in neutral medium.3" It was identified by its melting point, 75-76 °C (lit.3°6307 74-75 °C, 73-75 °C), and characterised by it's 1H, 13C and 29Si NMR and IR spectra and by CI mass spectrometry and microanalytical data (Section 6.1.6.2). Due to the presence of a bulky phenyl group it

185 Chapter 4 Synthesis and structures of miscellaneous silanols was considered not to be as sensitive to self-condensation as Me2Si(OH)2 and was stored in a glass sample vial in the refrigerator. After a month, however, condensation had started to occur and 29Si NMR spectroscopy and CI mass spectrometry showed that although MePhSi(OH)2 was still the major constituent, (HOMePhSi)20, (MePhSiO)3 and HO(MePhSiO)3H were also present. Recrystallisation of MePhSi(OH)2 from ether/petroleum ether 40/60 and ether/pentane by the vapour diffusion method produced plates which were too thin for X- ray analysis, although the plates obtained from ether/petroleum ether 40/60 were slightly thicker. No crystals of MePhSi(OH)2 were obtained by the vapour diffusion method from acetone/petroleum ether 40/60 or acetone/pentane solvent systems. Slow evaporation of a solution of MePhSi(OH)2 dissolved in acetone produced no crystals and slow evaporation of an ether solution of MePhSi(OH)2 resulted in a powdery solid. The X-ray structure of the related disiloxanediol, (HOMePhSi)20, was also sought since almost all the structures of disiloxanediols reported in the literature are of compounds containing the same four R substituents. The disiloxanediol (HOMePhSi)20 has two isomeric forms which are shown in Figure 4.4.

Me Ph Ph 'Me Me, Ph /OH ‘`, # s, i , Si Si Si Si / \ / \ / " / % Me HO 0 OH HO O 'ph

Racemic diol meso-diol

Figure 4.4. The two isomeric forms of (HOMePhSi)20.

Daudt and Hyde308 were the first to report their preparation and assigned the compound with m.p. 110-111 °C as the meso-form on symmetry grounds and the compound with m.p. 82-84 °C as the racemic isomer. Jarvie et al.,309'310 however, on repeating the experiment assigned the meso-disiloxanediol as having a melting point of 110 °C and the racemic disiloxanediol a melting point of 100 °C by cyclisation experiments. The material with m.p. 82-84 °C was found to be a mixture of

186 Chapter 4 Synthesis and structures of miscellaneous silanols approximately 40% meso and 60% racemic diol. They also prepared another form of the meso diol with m.p. 114.5 °C which differs in its solid state IR and thermal analysis. A diol with m.p. 112-113 °C has also been prepared.306 The preparation of meso-(HOMePhSi)20 was first attempted by the method of

Jarvie et a/.310 but no crystals could be isolated. Methylphenyldichlorosilane was hydrolysed in ether employing (NH4)2CO3 as the acid acceptor. A white viscous oil was produced which gave several methyl and phenyl peaks in the 1H NMR spectrum. Polymerisation was probably attributable to the difficulty in maintaining the pH of the solution around 7 throughout the reaction. This method was repeated but the same problem was encountered. Since (HOMe2Si)20 is more sensitive to condensation than (HOMePhSi)20 a method for the preparation of (HOMe2Si)20 from Me2Si(OEt)2 was followed using the corresponding methylphenyl analogue which was prepared by refluxing MePhSiC12 in excess ethano1.302 This reaction proceeded via acid hydrolysis and condensation of MePhSi(OEt)2 with 1 x 10-4 N H2SO4 in a solution of ether and benzene. This method was successful and gave (HOMePhSi)20 as white crystals, m.p. 110-111 °C which corresponded to that of the meso diol. The 1H, 13C and 29Si NMR and IR spectra and microanalysis were as expected (Section 6.1.6.3). This reaction, however, took 72 hours and gave a very low yield. A more convenient method, therefore, was sought. Attempted hydrolysis of MePhSiC12 in alkaline medium,306 using an aqueous solution of NaOH in ether, led to the formation of polysiloxanes. The hydrolysis of MePhSiC12 in a neutral medium306 by simultaneous addition of an ether solution of

MePhSiC12 and 1 M NaOH to ether at a rate so as to keep the pH of the solution at 7, however, produced (HOMePhSi)20 as white needles, mp 109-111 °C which corresponded to the meso form. The 1H, 13C and 29Si NMR and IR spectra were identical to those obtained above, although the microanalytical data was slightly low. There appears to be no reasonable explanation for this as spectroscopic data revealed no impurities or condensation products. This proved to be the most convenient and highest yielding preparation of meso-(HOMePhSi)20.

187 Chapter 4 Synthesis and structures of miscellaneous silanols

Meso-(HOMePhSi)20 was recrystallised by the vapour diffusion method from ether/petroleum ether 40/60 and ether/pentane to give needles which were too thin for X- ray crystallography. The crystals from the ether/petroleum ether 40/60 solvent system, however, were slightly thicker. Slow evaporation of an ether or acetone solution of meso- (HOMePhSi)20 also failed to produce crystals suitable for X-ray analysis and so no structural data could be obtained.

4.4 Compounds containing an Si(OH)3 group, silanetriols

There are very few crystal structures of silanetriols available due to their propensity towards condensation as discussed in Section 1.4.4.3.

PhSi(OH)3 was the first example of a silanetriol to be isolated311 and is the intermediate in the preparation of phenyl silsesquioxanes, which generally have either cage or ladder structures, by the hydrolytic condensation of PhSiC13. The structures of the related silanol, Ph3SiOH,87'88 and the silanediol, Ph2Si(OH)2,88'111,112 are shown in Figures 1.7 and 1.8 respectively in Section 1.4.4. Phenylsilanetriol, as may be expected, is not very stable and is sensitive to the catalytic effect of acid and base and decomposes on heating. On standing in sealed containers some samples have been observed to resinify gradually with loss of water.311 The preparation of PhSi(OH)3 was first attempted by the method of Takiguchi303 which involved the hydrolysis of PhSiC13 in ether. Triethylamine was used as the acid acceptor instead of aniline but polymerisation occurred. Phenylsilanetriol was successfully prepared as a microcrystalline powder, mp 127- 130 °C (lit.303'311 128-130 °C), by the hydrolysis of PhSi(OMe)3, catalysed by a small amount of acetic acid.311 It was characterised by 1H, 13C and 29Si NMR spectroscopy and CI mass spectrometry (Section 6.1.7.1) and it's IR spectrum was in good agreement with literature.311 Microanalytical data was also in agreement, although slightly low. The PhSi(OH)3 thus produced was stored in a polythene container in the refrigerator as a precaution against condensation.

188 Chapter 4 Synthesis and structures of miscellaneous silanols

Phenylsilanetriol is also known to be unstable in solution and Tyler found that all attempts to purify the compound by recrystallisation led to complete loss of the material due to condensation or resulted in a product with a lower melting point and a more pronounced tendency to decompose on standing.311 Since the crystal structure of PhSi(OH)3 would be interesting to determine it was necessary to try and recrystallise it. Rapid recrystallisation of PhSi(OH)3 was attempted by concentration of a solution of PhSi(OH)3 in methyl acetate and 2-butanone under vacuum3°3 and from ether/hexane, methyl acetate/petroleum ether 40/60 and acetone/petroleum ether 40/60. In no case did crystals come out of the solution. Slow evaporation of solutions containing PhSi(OH)3 was not considered a viable method due to the instability of the silanetriol in solution.

The preparation of more stable silanetriols by a careful choice of steric and electronic factors which would stabilise the silanetriol and not lead to its self condensation has been attempted by Roesky et al.312 who successfully prepared a series of stable N-bonded (silylamino)silanetriols containing ortho disubstituted anilines. Instead of stabilising silanetriols by the use of bulky substituents, attempts were made to prepare stable silanetriols by the use of intramolecular hydrogen bonding. In 1977 Birchall et a/.313 prepared a series of silanetriols of the general formula

CH30(CH2CH20)n(CF12)3Si(OH)3 (n = 1, 2, 3, 6, 7) which displayed outstanding stability in aqueous solution. Their stability was attributed to intramolecular hydrogen bonding between the silanol groups and the ether oxygen atoms, a possible configuration of which is shown in Figure 4.5.

0 OH 0 Si— OH

OH °

Figure 4.5. Possible configuration of CH30(CH20120)3(CH2)3Si(01)3• 313

189

Chapter 4 Synthesis and structures of miscellaneous silanols

Since no further work was published on these silanetriols it was of interest to investigate their hydrogen bonding properties further, especially in the light of more recent knowledge available about the ready formation of adducts between silanols and organic molecules. As discussed previously in Section 1.4.4.4, there are a number of silanols which demonstrate intramolecular hydrogen bonding to other functional groups.119,131-134,138 No experimental methods for their preparation were given by Birchall et al.313 so the general reaction scheme below was proposed (Scheme 4.1):

1) Base CH30(CH2CH20),111 > CH30(CH2CH20),ICH2CHCH2 2) CH2CHCH2Br

Catalyst, HSiC13

H2O CH30(CH2CH20)n(CH2)3SKOH)3 CH30(CH2CH20)n(CH2)3SiC13

Scheme 4.1. Proposed reaction scheme for the preparation of silanetriols of the formula

CH30(CH2CH20)n(CH2)3Si(OH)3 (n = 2, 3).

The first step involves the conversion of the ethylene glycol derivatives into their monoallyl ethers. The most recent method involves the use of potassium•hydroxide as the base, avoiding the use of sodium metal used in earlier methods.314 This method was attempted for the ethylene glycol derivatives with n = 2 and 3 but in both cases the reaction did not go to completion, even when slight excesses of potassium hydroxide and allyl bromide were employed. Separation of the monoallyl ethers from their ethylene glycol derivatives by fractional distillation proved impossible and so another method was attempted. Conversion of CH30(CH2CH20)nH where n = 2 and 3 into their monoallyl ethers was successfully achieved by a method similar to that of Pittman et al.315 which involved the use of sodium hydride as the base. The conversion went to completion in both cases and the products were purified by fractional distillation.

190 Chapter 4 Synthesis and structures of miscellaneous silanols

The monoallyl ethers were then successfully hydrosilylated using HSiC13 and chloroplatinic acid, Speier's catalyst, in a THE solution. Pittman et al.315 have previously used tert-butyl perbenzoate as the catalyst for the hydrosilylation of monoallyl ethers of ethylene glycols where n = 2 and 12. The trichlorosilanes produced were then purified by fractional distillation.

Hydrolysis of the trichlorosilanes, CH30(CH2CH20)n(CH2)3SiC13 (n = 2, 3) was attempted from ether solutions at -5 °C using triethylamine as the HC1 acceptor, by a method similar to Cella and Carpenter's method for the hydrolysis of dichlorosilanes.304 A yellow oil was produced in both cases and the infrared spectra (neat, NaC1 plates) show a broad OH band at — 3400 cm-1. The 1H NMR spectra, however, are similar to those of the corresponding trichlorosilanes, although broader in the CH2 region (no accurate integration possible) and no OH peaks are readily observable. It is possible, that the OH peaks, if present, may be obscured by the complicated spectra of the CH2 groups between 3 and 4 ppm. The experiments were repeated and similar results obtained. The formation of the white solid Et3N.HC1 during the hydrolysis reaction, however, and the infrared spectra indicate that hydrolysis of the chlorosilane groups has occurred to some extent. The formation of siloxane condensation products is not easy to determine by infrared spectroscopy as the ether group also shows a strong absorption in the 1000 - 1100 cm-1 region. Interpretation of these spectra, therefore, is difficult and the results are inconclusive.

Since the yellow colouration of the oil produced in both hydrolyses was due to the yellow colour of the original chlorosilane, attempts were made at decolourising the chlorosilane. Although boiling the chlorosilane over decolourising charcoal removed the colour slightly, vacuum transfer of the chlorosilane produced an almost colourless liquid. The chlorosilane, however, rapidly went from yellow to brown upon storage even under nitrogen and in the dark. Therefore, the colourless trimethoxysilanes were proposed as better intermediates in the preparation of the silanetriols. The presence of three methoxy groups attached to silicon would also be readily observable by 1H NMR spectroscopy, thus enabling their hydrolysis to be monitored.

191 Chapter 4 Synthesis and structures of miscellaneous silanols

The trimethoxysilanes, CH30(CH2CH20)n(CH2)3Si(OMe)3 (n = 2, 3) were successfully prepared using HSi(OMe)3 in the hydrosilylation reaction. The hydrolyses were then attempted from an ether solution containing a small amount of 0.01 M acetic acid over a period of four hours, by a method similar to that used in the preparation of PhSi(OH)3.311 In both cases, colourless oils were produced upon removal of the solvent and their infrared spectra (neat, NaCI plates) display a broad OH band in the 3400 cm-1 region. Again, interpretation and quantitative analysis of the 1H NMR spectra is difficult due to the complexity of the CH2 region, although the Si(OMe)3 peak is clearly still present in both spectra, but decreased in size by approximately one third. In the case of n = 3 the peak due to the CH3OC group is also split into two. New peaks at 3.46 and 2.21 ppm are also present for the n = 2 and n = 3 derivatives respectively. For the n = 3 derivative the peak is broad which is consistent with the presence of OH groups.

Time did not permit further experimental work on the preparation of these silanetriols to be carried out. Optimisation of the hydrolysis reactions is required, with emphasis on the pH of the hydrolysis solutions and analysis of the hydrolysis products.

Theoretical studies on the silanetriols, CH30(CH2CH20)n(CH2)3Si(OH)3 where n = 2 and 3 were carried out, therefore, and the most stable conformations of the silanetriols obtained by 3-21G(*) Ab Initio calculations (Mac Spartan Plus software, Wavefunction Inc. California). The results are shown in Figures 4.6 and 4.7. For CH3O(CH2CH2O)2(CH2)3Si(OH)3 (Figure 4.6) it can be seen clearly that stabilisation of the silanetriol by intramolecular hydrogen bonding is not found in the structure calculated at this level of theory, and intermolecular silanol - silanol or silanol - ether interactions are more likely. The calculations also suggest that the most stable configuration for CH3O(CH2CH2O)3(CH2)3Si(OH)3 does not involve intramolecular hydrogen bonding to the ether groups (Figure 4.7). In both cases the calculated Si-O bond lengths are between 1.62 and 1.63 A, typical of silanols. The C-O-C angles are between 114.57 and 116.63 A and the C-C-O angles between 105.30 and 109.11 A which are within the range expected for chain ethers. The large size of these molecules has precluded the calculation of the structures at the higher 6-31G(*) level but it seems unlikely that a dramatic change in

192 Chapter 4 Synthesis and structures of miscellaneous silanols

Figure 4.6. Ab Initio, 3-21G(*), structure calculated for CH3O(CH2CH2O)2(CH2)3Si(OH)3.

Figure 4.7. Ab Initio, 3-21G(*), structure calculated for CH3O(CH2CH2O)3(CH2)3Si(OH)3.

193 Chapter 4 Synthesis and structures of miscellaneous silanols structure will occur to form intramolecular interactions similar to those shown in Figure

4.5. It thus seems that although Figure 4.5 looks attractive, it probably has little contribution to the real structure and the lack of such intramolecular stabilisation prevents the facile isolation of the triols. From Table 2.1 (Section 2.2), it can be seen that the MOH values for the hydrogen bonding interactions of silanols with ethers in CC14 solution can be larger than the AuOH values for self-association, e.g. for Ph3SiOH Avoll self-association is 233 cm-1 whereas with diethyl ether ZWoH is 319 cm-1. For (HOMe2Si)20, however, the AV0H value of

389 cm-1 for self-association is larger than that of 273 cm-1 for hydrogen bonding to diethyl ether. It is therefore difficult to predict the hydrogen bonding arrangement which may exist in the liquid silanetriols since intermolecular SiOH • • • OHSi and SiOH • - • ether interactions are both equally possible, steric factors presumably being the determining factor. No IR solution studies of the hydrogen bonding interactions of silanols with water have been carried out, presumably due to the immiscibility of water with the 'inert' solvents used for such studies and the general insolubility of silanols in water alone. A number of silanols, however, have been shown to form hydrogen bonded adducts with water in the solid state (Section 1.4.5). Another possibility for the outstanding stability of these silanetriols in aqueous solution, therefore, may be due to hydrogen bonding interactions between the silanol group and water molecules.

4.5 Compounds containing four Si-OH groups

The ring compound, cis-cis-cis-2,4,6,8-tetraphenylcyclotetrasiloxanetetrol, cis,cis,cis-[(HO)PhSiO]4, was prepared as a potentially suitable hydrogen bond donor for crown ethers, as discussed in Section 3.6.7. The preparation was carried out by the method of Brown which involved the hydrolytic condensation of trichlorophenylsilane and was recrystallised from ether/hexane to give a white powdery solid.291 The structure of the tetrasilanol, with an all cis- arrangement of OH groups, was originally assigned by Brown from the infrared spectrum and by derivatisation studies.291 The X-ray structure

194 Chapter 4 Synthesis and structures of miscellaneous silanols of this compound was, therefore, sought for confirmation. Despite numerous attempts at recrystallisation from both ether/hexane and by slowly adding a dilute solution in acetone to ten volumes of a 4:1 water/acetone mixture at 0 °C,291 a crystalline form was unable to be obtained for X-ray crystallography. Slow evaporation of solutions of the tetrol were not attempted since condensation reactions of sensitive silanols are often encouraged by prolonged periods of time in solution. During the course of these studies, however, Feher et al.256 crystallised the ether solvate of cis, cis,cis-[(HO)PhSiO]4 by slow evaporation from an Et20/C6H6 solution. This was shown by X-ray structural analysis to comprise a strongly hydrogen bonded dimer of tetrol molecules, with one ether of crystallisation per tetrol (Figure 4.8). The ether is only weakly hydrogen bonded and the colourless solvated crystal were found to reduce rapidly to a fine white powder when dried in vacuo (25 °C, 1 Torr). The cis, cis, cis- conformation of the tetrol is as expected.

09a C41a • C21 08a Si4a

06 S•2 05a C1la 02 g 03o Sila C31 -• S13 01 • Si3a 07 Ola S 1 03 °7° 02a Si2o C11 411V 05 • 04 4." 08 06a Si4 • Cl C21a. C41 C2 09

Figure 4.8. Hydrogen bonded structure of the ether solvate of cis,cis,cis-[(HO)PhSiO]4.256 Only the ipso carbons of the phenyl rings are shown.

195 CHAPTER 5 Nuclear magnetic resonance studies of silanols and their adducts Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

CHAPTER 5 Nuclear magnetic resonance studies of silanols and their adducts

5.1 Introduction

Silicon 29 NMR spectroscopy has become a routine analytical tool in the study of organosilicon compounds since the advent of pulsed and decoupled techniques performed by Fourier Transform spectrometers. The factors determining acquisition of 29Si NMR spectra are dominated by the nuclear Overhauser effect (NOE) and long spin relaxation times which are described in more detail in a number of excellent books and reviews.316-319

Due to hydrogen bonding interactions the 29Si NMR chemical shifts of silanols are strongly concentration and solvent dependent, as is the case in 1H NMR spectroscopy. For example, the 29Si chemical shift of Ph3SiOH is -12.6 ppm in CHC13 and is shifted upfield to -16.2 ppm in acetone and -17.9 ppm in DMS0.32° Silicon may also pentacoordinate with strong donor solvents.

The solid state hydrogen bonded adducts prepared in Chapter 3 give rise to only one resonance in their solution 29Si NMR spectra, even when a number of inequivalent silicon atoms are present, as identified by X-ray crystallographic studies. This may be attributed to rapid exchange processes or the dissociation of the adducts in solution. Solid state 29Si NMR spectra, therefore, were recorded on some of the adducts of silanols whose structures have been determined, in an attempt to correlate NMR spectroscopic data with structure. Combined with infrared spectroscopic studies, such correlations may be useful in the prediction of structures of adducts which are obtained as microcrystalline or amorphous powders.

Since 1H, 13C and 29Si NMR data for silanols in solution are widely available, the use of solution 170 NMR spectroscopy in the study of silanols was also investigated.

197 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

5.2 Solid state 29Si NMR studies

In order to observe the crystallographically inequivalent silicon atoms in (HOPh2Si)20 and Ph3SiOH and their hydrogen bonded adducts, the technique of 29Si CPMAS NMR spectroscopy321,322 was used. In solids, both the dipolar coupling and chemical shift anisotropy, which are averaged to zero by isotropic motion in solution, cause line broadening. Linewidths are narrowed by the technique of MAS (magic angle spinning) by which rapid spinning of the sample at 54.7 ° to the applied magnetic field reduces the angular dependent chemical anisotropy to zero. Successful line narrowing can only be obtained by using a rotation frequency at least of the order of the chemical shift anisotropy linewidth. The rotation frequency used in the following experiments was ca. 3500 Hz. The intensity of the signal is enhanced by exploitation of the strong dipolar coupling between rare spins and abundant nuclei (e.g. protons) in solids. This process is known as cross-polarization, CP. For such studies, a sample mass of approximately 500 mg is usually required.

The 29Si CPMAS NMR chemical shift values for Ph3SiOH and (HOPh2Si)20, and a selection of their adducts are displayed in Table 5.1. For comparison the 29Si chemical shifts of the adducts in CDC13 solutions are also given. It may be seen that the values for the 29Si chemical shifts in solution are slightly downfield from the average values in the solid state which may be indicative of the stronger hydrogen bond interactions formed in the solid state. The crystal structure of Ph3SiOH comprises two sets of crystallographically inequivalent hydrogen bonded tetramers (Figure 1.7, Section 1.4.4.1) giving rise to eight inequivalent silicon atoms.87,88 In the 29Si CPMAS NMR spectrum there are six peaks ranging from -11.07 to -16.31 ppm [Figure 5.1(a), Table 5.1]. The peaks at -11.07 and -12.85 ppm, however, are larger and slightly broader than the other peaks and may be due to two overlapping peaks, which would then give a total of eight silicon atoms.

198 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

Table 5.1. 29Si CPMAS NMR chemical shift values, ppm, for (HOPh2S 020 and Ph3SiOH and their adducts. Solution 29Si NMR chemical shift values are included for comparison.

Compound 8 29Si , ppm 8 29Si, ppm

Solid state, Solution, (CDC13)b

CPMAS a

Ph3SiOH -11.07 -11.98 -12.85 -12.6 -14.18 -15.83 -16.31

(Ph3SiOH)2.12-crown-4 -13.26 -13.21

(Ph3SiOH)2.18-crown-6.(H20)2 -16.31 -12.28 -14.69 (Ph3SiOH)2.TMEDA -12.82 -18.62 (HOPh2Si)20 -33.46 -35.32 -36.11 -35.9 -37.60

(HOPh2S020.TMEDA -43.94 -39.18

(HOPh2Si)20.dioxane -42.61 -35.64 -38.20 [(110Ph2S020]4•(Et2NH)2 -38.88 -36.49 -39.63 -40.76

(HOPh2Si)20. { [HOPh2SiOSiPh20][Et3N11]1 -35.71 -37.96 -37.11 -40.20 a Spectra recorded at 53.6 MHz. b Spectra recorded at 59.6 MHz.

199

Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

ww(loitii \w";44 I I I I -5 -10 -15 -20 -25 -5 -10 -15 -20 -is PPM PPM

(a) (b) Figure 5.1. 29Si CPMAS NMR spectra of (a) Ph3SiOH and (b) (Ph3SiOH)2.12-crown-4.

I I -5 -10 -15 -20 -25 -10 -15 -20 -25 PPM PPM

(a) (b) Figure 5.2. 29Si CPMAS NMR spectra of (Ph3SiOH)2.TMEDA (a) after 434 scans, 36 minutes and (b) after 2000 scans, 167 minutes.

200 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

Care must be taken in the quantitative interpretation of CPMAS NMR spectra, however, since the intensities of lines depend on cross-polarisation rates, which differ from silicon to silicon, although in this case as the silicon atoms are in very similar environments this is not likely to be significant.

Since the area of solid state NMR spectroscopy is still relatively young, the relationship between chemical shift and crystallographic position has not yet been established and an assignment of the NMR peaks to silicon sites in the unit cell determined by X-ray crystallography is not possible.

Upon formation of the centrosymmetric adducts (Ph3SiOH)2.12-crown-45 and (Ph3SiOH)2.18-crown-6.(H20)2 (Figure 3.24, Section 3.5.3.1), the crystallographically equivalent Ph3SiOH molecules give rise to one signal in the 29Si CPMAS NMR spectra at -13.26 and -16.31 ppm respectively, as may be expected (Table 5.1). For example, the single peak in the spectrum of (Ph3SiOH)2.12-crown-4 in Figure 5.1(b) clearly contrasts with the multiple peaks in the spectrum of Ph3SiOH itself [Figure 5.1(a)]. The 29Si CPMAS NMR spectrum of the centrosymmetric adduct (Ph3SiOH)2.TMEDA (Figure 3.20, Section 3.5.1.3.1), however, displays two peaks which change in intensity with time [Table 5.1, Figures 5.2(a) and (b)]. This type of behaviour may be caused by a phase change occurring at ambient temperature or by decomposition. Neither of these explanations, however, appear satisfactory for (Ph3SiOH)2.TMEDA since in DSC studies (Section 3.9) no other endotherms except for that due to the release of the amine at 81 °C are present. It is also unlikely that after standing in a sample vial for a number of weeks the sample would 'decompose' during the time scale of the NMR experiment. In addition, the possible 'decomposition' reactions which could occur are loss of the amine to leave Ph3SiOH or condensation to the disiloxane, both of which are inconsistent with the spectrum observed. Further work, including perhaps 13C and 15N CPMAS NMR spectroscopy needs to be carried out to determine the cause of this surprising result.

Tetraphenyldisiloxanediol forms a hydrogen bonded chain in which there are three inequivalent disiloxanediol molecules, and therefore six inequivalent silicon atoms

201 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

[Figure 1.6(g), Section 1.4.4.2].104,105 The 29Si CPMAS NMR spectrum of

(HOPh2Si)20 [Figure 5.3(a)] is not as clearly resolved as that of Ph3SiOH [Figure 5.1(a)]. Four peaks ranging between -33.46 and -37.60 ppm may be observed (Table 5.1), although these are broad and of varying intensity, suggesting the presence of a number of overlapping peaks. The infinite hydrogen bonded chains formed by (HOPh2Si)20.TMEDA (Figure 1.15, Section 1.4.5) and (HOPh2Si)20.dioxane (Figure 3.16, Section 3.4.3.1) give rise to only one signal in the 29Si CPMAS NMR spectra at -43.94 and -42.61 ppm respectively, e.g. the spectrum of (HOPh2Si)20.TMEDA is shown in Figure 5.3(b). In

(HOPh2Si)20.dioxane, however, each disiloxanediol in the chain actually contains two crystallographically inequivalent silicon atoms, but the differences between them are presumably so small that they are not resolved in the NMR spectrum. The 29Si CPMAS NMR spectrum of [(HOPh2Si)20]4.(Et2NH)2 [Figure 5.3(c)] is more complicated, as may be expected from the crystal structure (Figure 3.6, Section 3.4.1.2.1). Only four signals are resolved ranging between -38.20 and -40.76 ppm (Table 5.1), although there are eight inequivalent silicon atoms. The small crystallographic differences in the disiloxanediol molecules probably explains the narrow range of signals observed and overlapping of the peaks presumably occurs. In the adduct (HOPh2S i)20.1[HOPh2SiOSiPh20][Et3NH] there are four crystallographically inequivalent atoms (Figure 3.11, Section 3.4.1.3.1). These give rise to three distinct signals in the 29Si CPMAS NMR spectrum [Figure 5.3(d)] at -35.71, -37.96 and -40.20 ppm (Table 5.1). The intensity of the peak at -40.20 ppm is almost twice that of the other two peaks suggesting that it may correspond to two almost equivalent silicon atoms. Since proton transfer occurs from only one of the four silanol groups it may be proposed that the signal at -35.71 corresponds to this silicon atom which would be consistent both with the increased shielding of a siloxy anion and the greater chemical inequivalence from the two silanol silicon atoms at -40.20 ppm. Although it is not yet possible to assign peaks directly in the 29Si CPMAS NMR spectra to specific structural arrangements of silicon atoms, useful information may be

202

Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

-30 -35 -40 -45 -50 -30 -35 -40 -45 -50 PPM PPM

(a) (b)

itimud."1.0601

-30 -35 -40 -45 -50 -38 -35 -40 -45 -30 PPM PPM

Figure 5.3. 29Si CPMAS NMR spectra of (a) (HOPh2Si)20, (b) (HOPh2Si)20.TMEDA, (c) RHOPh2S02014.(Et2NH)2 and (d) (HOPh2Si)20. { [HOPh2SiOSiPh20][Et3NH]1.

203 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts gained from these spectra. For example, a single peak in the 29Si CPMAS NMR spectrum of an adduct formed by Ph3SiOH with a molecule with two or more hydrogen bond acceptor sites, and a stoichiometry of 2:1, may be indicative of a centrosymmetric adduct. This information cannot readily be gained from infrared spectroscopy or solution NMR studies. Although Raman spectroscopy may also be used to detect the presence of symmetry in a complex, unequivocal analysis of the spectra is not always possible. The presence of a single peak in the 29Si CPMAS NMR spectrum of a 1:1 adduct with (HOPh2Si)20 suggests the presence of a chain structure of alternating disiloxanediol and hydrogen bond acceptor molecules. 29Si CPMAS NMR spectra of adducts containing more than one (HOPh2Si)20 molecule with many peaks in the -35 to -41 ppm range may be indicative of structures containing both silanol to donor/acceptor molecule hydrogen bonds and silanol to silanol hydrogen bonds. Unfortunately, the adducts of Ph3SiOH with azacrowns and azacrown ethers (Sections 3.5.2 and 3.5.4) were not synthesised in sufficient quantity, due to the relative expense of the crowns, for 29Si CPMAS NMR spectra to be recorded. This technique, however, may have proved invaluable in the assignment of structures for these adducts, since crystals suitable for X-ray crystallography could not be obtained.

5.3 170 NMR

Although oxygen has three naturally occuring stable isotopes, 160, 170 and 180, only 170 is magnetically active, with a spin quantum number, I, of 5/2. As can be seen from Table 5.2 it has a moderate electric quadrupole moment (eQ = -2.63x10-26 cm2) and a low natural abundance (0.037 %) which renders it difficult to observe by NMR spectroscopy.323 Due to the chemical importance of the element oxygen along with the recent advances in NMR instrumentation and increased availability of 170 enriched materials, the technique has become more widespread.323-326 The successful acquisition of spectra using natural abundance 170 requires a large number of scans (103- 106) which is facilitated by the use of a short pulse delay (-0.1 s) and fast acquisition time (-10 ms).

Chemical shifts are referenced relative to H2O (0 ppm).

204 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

Table 5.2. Properties of the 170 isotope.323

Property Spin number 5/2 Nuclear magnetic moment -1.893997 Nuclear magneton Magnetogyric ratio -3.628 Radians sec-1 Tessla-1 Resonance frequency (at 2.114 Tessla) 12.2 MHz (1H 90 MHz) Chemical shift range 1500 ppm Quadrupole moment -0.0263 x 10-24 Electron cm2 Nuclear Quadrupole Coupling Constant Range -10 to +14 MHz Relaxation times __0.2 sec Natural abundance 0.037 % Relative sensitivity per nucleus (H = 1) 2.9 x 10-2 Relative sensitivity at natural abundance (H = 1) 1.1 x 10-5 (Receptivity)

There have been several reviews on the application of 170 NMR to a range of organic and inorganic compounds323-326 but there is only a relatively small amount of literature available for organosilicon compounds. Systematic studies of these compounds began predominantly in the 1980's and will be reviewed over the following pages.

5.3.1 Experimental considerations323-326 Since 170 is a quadrupolar nucleus, the linewidth, Av1/2, is related to the transverse relaxation time, T2 (Equation 5.1):

AD1/2 = 7ET 1 (5.1) 2

In extreme narrowing conditions, generally held to obtain for non-polymeric materials the relaxation time is defined by (Equation 5.2):

205 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

211+ ,T 1 _ 1 ... .47c (5.2) T1 — T2 125 ( 3 )'' c

where T1 - longitudinal relaxation time ri - electrical field gradient asymmetry parameter x - nuclear quadrupole coupling constant

tic - molecular correlation time

Combination of Equations 5.1 and 5.2 gives Equation 5.3:

Au = 12 ic[1+B2_.Jr, (5.3) 1/2 125 3 -

For isotropic motion the rotational correlation time, 're, is related to viscosity, ri, by the

Stokes-Einstein-Debye equation, Equation 5.4:

47cria3 "C c = 3kT (5.4)

where k - Boltzmann constant (1.38 x 10-23 JK-1) T - temperature in Kelvin

Thus, from Equations 5.3 and 5.4, the broad linewidths inherent to 170 NMR spectroscopy may be narrowed by: i) raising the solution temperature, T. ii) lowering the solution viscosity, ii, by using a solvent of low viscosity, using a

low concentration of sample in solvent or by raising solution temperature. iii) using molecules with a small molecular radius, a.

A further important factor for quadrupole nuclei is the electric field gradient at the nucleus which is related to the local symmetry of the molecule. Thus, sites of tetrahedral or octahedral symmetry have zero field gradient and show sharper lines than those sites of low symmetry which possess a significant field gradient which leads to greater linewidths.

206 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

5.3.2 170 NMR studies on organosilicon compounds Alkoxysilanes

Harris and Kimber carried out the first 170 NMR studies on the methyl(ethoxy)silanes MenSi(OEt)4_n (n = 0 to 3) relative to (EtO)4Si.327 They found that 6170 shows a maximum for n = 2 and proposed that this was due to the decreasing effectiveness of n-bonding in reducing electron density at oxygen as the number of alkoxy groups increases. Thus, the effect of substitution on 8170 is largest on going from one to two alkoxy groups and after this the inductive effect presumably dominates, increasing the charge on oxygen by more than can be lost by 7c-bonding.

Lukevics et (2/.328 obtained 170 NMR spectra for over one hundred mono-, di-, tri- and tetra-alkoxysilanes, R4_nSi(OR')n where R = CnH2n+1, Ph, CH2C1, CH2Br; W =

CnH2n+1, CH2Ph, CH2CH2C1, CH2CH=CH2, CH2CCH, CH2CF3, (CH2)3C1, (CH2)3CN. The chemical shifts vary over a range of 85 ppm (-30.8 ppm for Et3SiOMe and 54.0 ppm for C13Si0Et) and the peak half-widths range from 110 Hz (Me3SiOCH2CF3) to 680 Hz [Si(005H11)41.

A linear correlation was observed between 170 chemical shifts in alkoxysilanes and those in the corresponding alcohols.329 Another linear correlation was found between the 170 chemical shifts in the alkoxysilanes Et3SiOR (Equation 5.5) and MePh2SiOR (Equation 5.6) and the OH stretching frequencies of the corresponding alcohols ROH.33°

8(170) = 3718(±21) - 3.2(±0.6)1)(OH) (5.5)

(r= 0.97; n= 6) R = Me, Et, Pr, iPr, Bu, sBu

8(170) = 3722(±21) - 3.2(±0.6)1)(OH) (5.6)

(r= 0.97;n= 6) R = Me, Et, Pr, iPr, Bu, sBu

207 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

A linear relationship between the 170 NMR chemical shifts for methyl ethers, MeOR and the OH stretching frequencies v0H of the corresponding saturated alcohols ROH has previously been found (Equation 5.7).331

8(170) = 6413.7 - 1.17705u(OH) (5.7)

(r= 0.987;n= 11)

R = Et, Pr, 1Pr, Bu, 1Bu, SBu, tBu, Me3CCH2, Me2CHCH2CHCH3, Me3CCH2CH2

Equations 5.5 - 5.7 above suggest that 170 chemical shifts in alkoxysilanes are more sensitive to the effects of substituents at the oxygen atom than in ethers, which Lukevics proposed may be due to partial 7c-bonding in the Si-O fragment of alkoxysilanes.328 Also similar coefficients in Equations 5.5 and 5.6 suggest that the phenyl group at the Si atom has an insignificant effect on the properties of oxygen nuclei. Lukevics328 studied the dependence of 6170 on the number of alkoxy substituents within a series of different alkoxysilanes and observed the same trend as Harris and Kimber.327 Upon going from n = 1 to n = 2 6170 moves downfield appreciably, whereas upon subsequent substitution a gradual upfield shift is observed. For the series R4_nSi(OR')n, the 6170 should increase smoothly with increasing n if inductive effects alone are taken into account since CNDO/2 calculations show an increase in the negative charge at the oxygen atom as the number of alkoxy groups increases. Lukevics explained the experimental curves in terms of the degree of participation of each oxygen lone pair in (p-d)n interactions and it-charge.328

Aryloxysilanes

Lukevics et a/.332 studied the 170 NMR spectra of the trialkyl(aryloxy)silanes p-R3SiOC6H4X where R = Me; X = OMe, Me, iPr, H, F, Cl, Br, F, NO2 and R = Et; X = OMe, iPr, sBu, H, Cl. The chemical shifts for the siloxy oxygen range from 62.2 ppm

(Et3SiOiPr) to 94.9 ppm (p-Me3SiOC6H4NO2) and the half widths range from 340 Hz

(p-Me3SiOC6H4F) to 820 Hz (p-Et3Si0C6H41Pr). The 170 chemical shifts of the triethyl

208 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts derivatives are shifted upfield by 9 - 11 ppm in comparison to the trimethyl derivative, probably due to an increase in the inductive effect of the R3Si substituent and also to the shielding effect. They found that in trimethyl(aryloxy)silanes the 170 chemical shifts are more sensitive to the resonance effect than to the induction effect of the substituent in the phenyl ring. They proposed that in these molecules the oxygen atom enters into both (p-707c conjugation with the benzene ring and (p-d)7E conjugation with the silicon atom.

The 170 chemical shifts of the methylphenoxysilanes Me4_nSi(OC6H5)n were also studied and showed a similar trend as for the alkoxysilanes on going from n = 1 to n = 4.332

Cyclic siloxanes

Bassindale and Panne11333 found that the 170 chemical shifts of the series (Me2SiO)n where n = 3 - 9 and 12, measured as neat liquids, were identical within experimental error, at 73 ppm, suggesting that the magnetic environments of the oxygen nuclei are similar for each compound. The linewidths, however, did show the expected increase from 50 to 450 Hz as the viscosity of the siloxane, q, increased and this was found to be a direct relationship. This suggested that viscosity is a reliable indicator of expected 170 linewidths for small silicones and vice versa. It was also proposed that any conformational changes in these silicones, therefore, have little effect on the 170 linewidths.

Linear siloxanes

Riihlmann et a/.334 were interested in the basicities of siloxane oxygen atoms as part of their studies on the acid-catalysed hydrolysis of chlorosiloxanes. They employed

170 NMR spectroscopy to a variety of siloxanes in an attempt to obtain information about the nature of the bonding between silicon and oxygen as well as about the basicity of the siloxy oxygens. Initially they obtained 170 NMR data for 10 compounds but extended this to 35 compounds in a further paper to gain more detailed information about the influence of substituent effects on the 170 chemical shifts in such compounds.335 They found that for symetrically substituted disiloxanes with methyl, phenyl, chlorine and

209 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts trimethylsiloxy groups the resonance is shifted towards higher field if methyl groups are replaced by phenyl groups, there is a strong deshielding if methyl groups are replaced by chlorine and the introduction of one Me3SiO group on each silicon atom shifts the resonance to lower field, the second Me3SiO group causes a considerably smaller low field shift and the third Me3SiO group causes a strong shift back to higher field. This shows that the 170 chemical shift of a siloxane oxygen is not solely dependent on the inductive effects of the group attached to the silicon atoms. They also found that the chemical shift of a siloxane oxygen atom, to a first approximation, depends only on the substituents directly attached to the two siloxane silicon atoms. Substituent effects are not transmitted along the chain, since these effects are small and lie within experimental error.

From these results, Riihlmann et a/.335 were able to set up a simple incremental system for calculation of the 170 chemical shift of siloxanes R1 - 0 - R2:

5(170) = IR1 + IR2

The increments, IRn, were calculated as either one half of the shift value for symmetrically substituted siloxanes or, for trimethylsiloxy-substituted compounds, as the difference between the shift observed and the increment of the trimethylsilylgroup. The increment for H as a substituent is zero. They found good agreement between the measured and calculated values and went on to apply the system to ethoxy- and phenoxysilanes. Although this system did not work for [(Et0)3Si]20, it can predict the 170 NMR shift values for a large number of varied siloxanes and may provide a new tool for the simple structure analysis of such compounds.

Lukevics et a/.336 have also applied 170 NMR spectroscopy to a series of hetarylaminoalkylsiloxanes and their hydrochlorides and methiodides,

Me3_n(Me3SiO)nSi(CH2)mNR2. The 170 chemical shifts of the compounds investigated were virtually independent of the number of siloxy groups, the type of amino substituent,

210 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts or the number of CH2 groups that seperate the silicon and nitrogen i.e. the location of the

170 resonance signal is determined primarily by the directly bonded Me3Si substituents and the presence of more remote substituents is sensed to a lesser extent. The linewidth of the salts was greater than that of the corresponding siloxanes which was accounted for by the increase in volume associated with the salt.

Acyloxysilanes Lycka et al .337 carried out 170 NMR studies on two series of compounds: i) Me3Si0C(0)R where R = H, CH3, C2H5, (CH3)2CH, CH3COCH2CH2, C6H5CH2,

C6H5, etc. ii) Me(XCH2)Si[OC(0)Me]2 where X = H, Cl, CH3C(0)0 For the first series of acyloxysilanes two well resolved 170 NMR signals were observed at 350 K for the compounds as neat liquids. A number of trends were also observed: the signals shifted to higher field were ascribed to oxygen atoms of C-0- Si(CH3)3 moiety and, compared to analogous organic esters, shifted downfield by 24 - 29 ppm. For the second series of diacetoxysilanes, coalescence of the 170 NMR signals was observed.

Lukevics et al.338 studied the compounds R1R2R3Si0C(0)R where RiR2R3 Me3, Eta, MePh2 and R = Me, Ph, tBu, Pr, CHnC13_n (n = 0 - 2), CF3. They also displayed two well resolved 170 resonance signals, the ether oxygen lying within the range 150 - 176 ppm and the carbonyl oxygen within the 330 - 376 ppm range. The effect of the substituent R on the chemical shift of both oxygens differed to that in the isostructural methyl acetates ( although the conditions were also different) and no satisfactory correlations between 170 chemical shift and substituent R constants were found.

Schraml et al.339 obtained 170 NMR data for (EtO)n(Me)3_nSiCH20C(0)Me compounds and found a similar trend in chemical shift to that found in methylethoxysilanes.

211 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

Other organosilicon compounds

170 NMR spectroscopy has been used in the characterisation of tris- triphenylsiloxy compounds of aluminium.340 The 170 NMR chemical shifts of the terminal siloxides are close to that of the free silanol. The reaction intermediates at each stage in the prehydrolysis method of aluminosilicate sol-gel synthesis have also been examined by 170 NMR spectroscopy using water enriched in 170.341 Babonneau used

170 NMR spectroscopy to characterise the formation of hybrid siloxane-oxide systems and also published the first direct observation by 170 liquid NMR of co-condensation reactions between methyl-substituted silicon alkoxides. 342-345 170 NMR studies have also been used in the identification and characterisation of the hydrolytic stability of heterometallic Si-O-Ti bonds.346

170 NMR spectroscopy, combined with mathematical modelling has been used to investigate the reactivity of the siloxane bond in relation to the base in the disiloxanes formed in the potassium trimethylsilanoate-tetramethyldivinyldisiloxane system.347

5.3.3 170 NMR studies of silanols

5.3.3.1 170 NMR chemical shifts of silanols No systematic studies on the 170 NMR chemical shifts of silanols have been reported in the literature. The 170 NMR chemical shifts of the analogous alcohols, however, have been widely studied. Linear correlations between the 170 chemical shift of alcohols and their OH stretching frequencies within a series of similar compounds,331 and the 13C chemical shifts for the methyl groups of the analogous hydrocarbons329 have been observed. Since many alcohols are liquids, 170 NMR spectra have been recorded for neat samples with the 170 in natural abundance (0.037 %) and at temperatures ranging from 35 °C to 80 °C. The majority of silanols, however, are solids and obtaining 170 NMR spectra of silanols with the 170 in natural abundance poses many problems. The concentrations of the solutions must be suitably high to obtain spectra at natural abundance but the solvent must be chosen so that hydrogen bonding interactions between the silanol and solvent are

212 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts at a minimum. Therefore, solvents such as ether or acetone, in which silanols are generally very soluble may not be used. The viscosity and, therefore, the linewidth are also decreased by raising the solution temperature. Such conditions preclude recording of natural abundance spectra of silanols which readily undergo condensation reactions. Silanols which are relatively stable towards condensation reactions under these conditions are those with bulky substituents at silicon, e.g. tBu or Ph, which in turn have larger masses, and this in itself leads to line broadening (Equation 5.4). The 170 chemical shifts for Ph3SiOH (8 8.9 ppm) and (Me3SiO)2SiMe(OH) (8

38.0 ppm OH, 8 57.6 ppm Si-O-Si), however, have been reported by Riihlmann et a/.335 during their work on siloxanes. These spectra were recorded as approximately 2.5 M solutions in anhydrous toluene at a temperature of 60 °C. An identical chemical shift value for Ph3SiOH was obtained for a 22.3 % 170 enriched sample in CH2C12:CDC13 (1:1) at ambient temperature.340 The linewidth is reported as 414 Hz.340 The 170 chemical shift of 10 % 170 enriched Ph2Si(OH)2 in dioxane has also been reported as 25.5 ppm (linewidth 240 Hz).346

The increment system proposed by Riihlmann et al.335 for predicting the chemical shift of linear siloxanes was successful in predicting the shifts of alkoxysilanes and it was also used to calculate the value for the silanol oxygen in (Me3SiO)2SiMe(OH), giving a calculated value of 37.2 ppm which is in good agreement with the experimental value of 38.0 ppm. From the values given in the increment system it was possible to calculate values for the chemical shifts of the silanols given in Table 5.3 for this work. Since Rtihlmann et al.335 found that substituent effects were not transmitted along a siloxane chain and to a first approximation the chemical shift depends only on the substituents directly bonded to the adjacent silicon atoms it may be inferred that for any series HO(R2SiO)nH the chemical shift of the silanol oxygens will be the same for all values of n.

213 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

Table 5.3. 170 Chemical shift values, ppm, for some silanols calculated from Riihlmann's increment system (this work).

Silanol 8170 of SiOH, ppm, calculated

Ph2MeS i0H 14.9

PhMe2S i0H 16.6

Me3SiOH 21.4

(HOPh2Si)20 29.1 (58.2 Si-O-Si)

(HOMePhSi)20 32.7 (65.4 Si-O-Si)

(HOMe2Si)20 35.5 (71.0 Si-O-Si)

(HOMeHSi)20 33.8 (67.6 Si-O-Si) 29.1 HO(Ph2SiO)nH where n = 3, 4, 5 (58.2 Si-O-Si) 35.5 HO(Me2SiO)nH where n = 3, 4, 5 (71.0 Si-O-Si)

Increment values were calculated by Riihlmann et al.335 from the 170 NMR spectra of neat siloxanes.

Attempts were, therefore, made to obtain experimental data to compare with the calculated values. Initial attempts were made at obtaining spectra of some of the silanols at natural abundance. Silanols which were considered relatively stable to condensation reactions were chosen so that high temperatures could be employed. Anhydrous toluene was chosen as the solvent since it is a weak hydrogen bond donor, the silanols are reasonably soluble in it at elevated temperatures and it has a high boiling point (b.p. 110 °C). Although CC14 and cyclohexane are 'inert' solvents towards hydrogen bonding interactions, the silanols are not sufficiently soluble in them and they have lower

214 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts boiling points, 76-77 and 80 °C respectively. The 170 chemical shifts obtained for a variety of silanols are summarised in Table 5.4. The half linewidths of the peaks are in the region of 310 to 370 Hz, although precise values for each silanol cannot be measured as the noisy baseline precludes an accurate peak height to be determined. The 170 NMR spectrum of the liquid silanol tBuMe2SiOH at 65 °C is shown in Figure 5.4, for example.

Table 5.4. 170 Chemical shift values, ppm, for some silanols at natural abundance.

Silanol 8170 of SiOH, Solvent Temperature,

ppm (Concentration, M) °C

Ph3SiOH 9.0 Toluene (2.5) 80

tBuMe2SiOH 11.1 Neat 65

(o-tolyl)3SiOH 13.6 Toluene (1.0) 80

tBu2Si(OH)2 10.7 Toluene (0.15) 80

TsiSi(OH)3 43.2 Toluene (0.2) 80

(HOMePhSi)20 31.4 Toluene (0.5) 80 62.3 Si-O-Si)

(HOPh2Si)20 29.3 Toluene (0.75) 80

HO(Me2Si0)3H -45 CC14, 1:1 v/v 23 (72.5 Si-O-Si)

HO(Me2Si0)4H -45 CC14, 1:1 v/v 23 (72.5 Si-O-Si)

8170 are in ppm, ± 0.5 ppm. H2O was used as the external reference at 0.0 ppm. The spectra were recorded on saturated solutions of the silanols, approximate concentrations of which are shown in the table for the given temperature. At these concentrations the silanols will be self-associated. The number of scans obtained was 105.

215 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

100.0 0 -162 X : part. per Million : 170

Figure 5.4. 170 NMR spectrum of tBuMe2SiOH, neat, at 65 °C.

The 170 NMR spectrum of a solution of approximately 2.5 M Ph3SiOH in toluene at 80 °C was obtained after 105 scans. The chemical shift is at 9.0 ppm which is in good agreement with the literature values of 8.9 ppm in both anhydrous toluene

(2.5 M, 60 °C)335 and as a 22.3 % enriched sample in CH2C12:CDC13 (1:1, R.T.).34° The low solubility of Ph2Si(OH)2 in toluene or any other 'inert' solvent did not allow a spectrum to be obtained for the self-associated silanol. A solution of approximately

0.75 M (HOPh2S020 in toluene gave an 170 chemical shift of around 29.3 ppm at 80 °C. Unfortunately the baseline was rather noisy and it was difficult to distinguish a peak due to the siloxane oxygen. The 170 chemical shift of the silanol group, however, is in very good agreement with the value of 29.1 ppm predicted from Riihlmann's increment system (Table 5.3). An attempt at obtaining a spectrum of the next member of the series, HO(Ph2Si0)3H as a 0.8 M solution in anhydrous toluene at 80 °C failed. No peaks due to the silanol or even the siloxane could be observed above the noise, even after 105 scans.

216 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

This may be due to the large molecular mass of the compound combined with the low concentration.

The 170 chemical shift values obtained for a 0.5 M solution of (HOMePhSi)20 in anhydrous toluene at 80 °C are in reasonably good agreement with those predicted from Riihlmann's increment system, 31.4 ppm (32.7 ppm calculated) for the Si-OH group and 62.3 ppm (65.4 ppm calculated) for the Si-O-Si group. The disiloxanediol (HOMe2Si)20 is too sensitive towards condensation reactions to attempt to obtain a 170 NMR spectra at elevated temperatures. The siloxanediols HO(Me2SiO)nH where n = 3, 4, however, are liquids and so natural abundance spectra were attempted. Due to the viscosity of these compounds spectra of the neat samples were unable to be obtained so they were diluted 1:1 with anhydrous CC14. They were not subjected to high temperatures because of their high propensity to condense under such conditions. The spectra obtained after 105 scans were very noisy. For both siloxanediols a peak centred around 73 ppm was observed due to the siloxane oxygens and a much smaller peak centred around 45 ppm was observed due to the silanol oxygens. The siloxane peaks are in good agreement with the value calculated from Riihlmann's increment system (71.0 ppm) but for the silanol peaks (35.5 ppm calculated) there is a large difference. A neat sample of the liquid silanol tBuMe2SiOH was analysed by 170 NMR at room temperature. After 105 scans no spectrum was obtained, presumably due to the viscosity of the sample. Decreasing the viscosity of the silanol by diluting with CC14 1:1 also failed to give a spectrum at room temperature. On increasing the temperature, however, of a neat sample to 65 °C, a 170 NMR spectrum was obtained after 105 scans, although the baseline was still quite noisy. The chemical shift of the silanol is at 11.1 ppm. The relatively stable silanediol, tBu2Si(OH)2, gave an 170 chemical shift of 10.7 ppm as a 0.15 M solution in anhydrous toluene at 80 °C. The related stable silanetriol, tBuSi(OH)3, however was insufficiently soluble in hot toluene to obtain a 170 NMR spectrum.

217 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

The sensitivity of the 170 chemical shift towards substitution on the phenyl rings of Ph3SiOH was investigated by recording a spectrum of 1.0 M (o-tolyl)3SiOH in toluene at 80 °C. The signal was shifted downfield from 9.0 ppm to 13.6 ppm. Increasing the bulk of the substituents at silicon to (1-naphthy1)3SiOH also failed to give a spectrum (0.15M in toluene, 80 °C, 105 scans) due to the higher molecular weight and lower solubility.

Despite the bulk of the (Me3Si)3C (Tsi) group it was attempted to obtain a spectrum of TsiSi(OH)3 since this molecule has three OH groups, is very stable towards condensation, and is fairly spherical. An 170 NMR spectrum was obtained as a 0.2 M solution in toluene at 80 °C. The chemical shift is at 43.2ppm. This is the first 170 NMR chemical shift of a silanetriol to be reported.

Since 170 NMR data for a related series of silanols could not be obtained, correlations with other spectroscopic data such as IR or 295i NMR cannot be made. This may be possible if a series of, for example, monosilanols were studied in a hydrogen bond donor solvent such as ether. The effect of donor solvents on the chemical shift of Ph3SiOH has been studied in the following section.

170 NMR data for the direct carbon analogues of the silanols studied are not available for comparison.

5.3.3.2 Effect of hydrogen bonding on the 170 NMR chemical shift A previous 29Si NMR study of six silanols in solvents of varying basicity found that a linear correlation existed between the silanol 29Si chemical shift and solvent donor ability due to hydrogen bonding interactions between the silanol and solvent.320 An upfield shift of the 29Si resonance was obtained with increasing solvent basicity e.g. from Ph3SiOH in CDC13 8 -12.6 ppm to Ph3SiOH in 25% NaOEt/EtOH 8 -25.4 ppm

(predominantly Ph3Si0-). The solutions were 10 - 30 % by weight Ph3SiOH with a small amount of Cr(acac)3 added to shorten the 29Si spin lattice relaxation time. No shifts were observed upon further dilution or in the absence of Cr(acac)3. Since the chemical shift range for 170 is much larger than for 29Si it may be predicted that the solvent effects will be greater for 170 than 29Si. 170 NMR studies of Ph3SiOH were, thus carried out in a

218 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts range of solvents of varying basicity using 10 % 170 enriched Ph3SiOH prepared by a modified method of Apblett et a/.34° The solutions were approximately 20 % by weight Ph3SiOH, within the concentration range reported for the 29Si NMR studies.320 Isotropic enrichment of the silanol enabled good quality spectra to be obtained after 103 - 104 scans (approx. 2 hours). The studies were carried out both at Imperial College and at Dow Corning, Barry. The results can be seen in Table 5.5. The Gutmann donor number, where available, is also included in the table in order that comparisons may be made between 170 chemical shift and solvent donor ability.348 The Gutmann donor number is obtained by measuring the heat of reaction of the solvent with the strong Lewis acid SbC15 in 1,2-dichloroethane.348 From Table 5.5 it can be seen that the 170 chemical shifts range from 4.5 ppm in

MIBK to 21.6 ppm in Et3N. It is not clear why some of the values recorded at Dow Corning differ from those obtained at Imperial College, although time did not permit repeat values to be obtained at Dow Coming to check for reproducibility. As discussed previously the chemical shift of Ph3SiOH in anhydrous toluene at 60 °C or as a 170 enriched sample in CH2C12:CDC13 (1:1) is 8.9 ppm. From Table 5.5 it can also be seen that Ph3SiOH in CDC13 alone gives a chemical shift of 8.2 ppm. These values are downfield from those observed for Ph3SiOH in the ketones and ethers which reflects the high level of self-association of Ph3SiOH in poor hydrogen bond accepting solvents. Upon hydrogen bonding to more basic solvents, however, a downfield shift is observed with increasing solvent basicity, as expected. A plot of 170 chemical shift for Ph3SiOH in the various solvents versus Gutmann's donor number is given in Figure 5.5. Data for solvents with a donor number of less than 15 have not been included since the similarity in their chemical shift values to that of Ph3SiOH in anhydrous toluene suggests that self- association interactions of the silanol predominate. From the plot in Figure 5.5, however, it can be seen that the 170 chemical shifts of Ph3SiOH give a linear correlation with solvent donor ability for solvents with donor number > 15. Unfortunately, it is not clear how a knowledge of this correlation will help in characterising solution interactions of silanols better than solution IR studies.

219 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

Table 5.5. Influence of solvent on 170 chemical shift of Ph3SiOH compared with Gutmann's donor number.

Solvent 6170, ppm 6170, ppm Gutmann

(Dow Corning) (Imperial College) donor number

CDC13 8.2 <10

Benzonitrile 8.0 11.9

MIRK 4.5

Acetone 4.6 6.1 17.0

Acetophenone 8.2 5.4

Methanol 7.0 19.0

Et20 7.1 7.9 19.2

THE 5.5 20.0

DMF 9.8 26.6

TMEDA 14.5

Pyridine 15.2 33.1

Piperidine 18.8 51

Et2NH 20.2 21.2 >50

Et3N 21.6 61.0

6170 (Imperial College) are ± 0.5 ppm (from repeat spectra). The error in 8170 (Dow

Corning) is not known because repeat spectra were not carried out, although the error should not be significantly greater than for IC.

220 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

25 1 I I 1111 1 1111 1 111 0 Imperial College 0 Dow Corning

m 20 pp

hift, 15 0 l s ica 10

•

017 Chem II

111 1111 0 10 20 30 40 50 60 70 Gutmann Donor Number

Figure 5.5. 170 Chemical shifts of Ph3SiOH, ppm, in a range of solvents versus Gutmann's donor number.

5.3.4 170 exchange reactions

The hydrolytic polycondensation reactions of alkoxysilanes are of great importance in sol-gel chemistry. The reactions involve the formation of alkoxysilanols as intermediates (Equation 5.8) which then undergo water- and alcohol-forming polycondensation (Section 1.1.2, Scheme 1.1). Numerous mechanistic studies of the process have been made, including detailed kinetic investigations of the hydrolysis and alcoholysis reactions occurring in the first stage,349-352 shown in Equation 5.8.

hydrolysis (R0)4Si + H2O (R0)3SiOH + ROH etc. alcoholysis (5.8)

No work, however, appears to have been carried out to investigate the importance of exchange reactions between the OH groups in the silanol species and water. This cannot be carried out by conventional methods but it is possible if isotopically labelled

221 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts water is used as an OH source. In particular 170 labelled water would allow the reaction to be monitored by 170 NMR spectroscopy . In order to investigate the extent to which OH exchange actually occurs between silanols and water, initial work was carried out on Ph3SiOH as it is stable to condensation reactions and has no alkoxy groups, thus ensuring that OH exchange was the only possible reaction being monitored. A solution of Ph3SiOH in anhydrous dioxane and a fourteen fold molar excess of 10 % 170 enriched H2O was prepared in a Youngs NMR tube to prevent moisture entering or leaving the tube and the temperature of the tube maintained at 80 °C. Dioxane is the most commonly used solvent in polycondensation reactions. The 170 NMR spectrum of the reaction solution was recorded at 80 °C, 105 scans, at the beginning of the experiment and at weekly intervals. Unfortunately, it was not possible to ascertain whether OH exchange was occurring as the large excess of 170 labelled H2O prevented changes in intensity of the comparitatively small peak due to Ph3SiOH to be observed (Figure 5.6).

30.0 40.0 30.0 20.0 10.0 0 -10.0 -20.0 -30.0 -40.0 X : parts per Million : 170

Figure 5.6. 170 NMR spectrum of 0.44 M Ph3SiOH and 6.17 M 10 % 170 enriched H2O in dioxane.

222 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

The chemical shift difference between H2O (-12.2 ppm) and Ph3SiOH (0.2 ppm) in dioxane (relative to external pure water at 0 ppm) is also -450 Hz (170 operating frequency of 36.67 MHz on a 270 MHz instrument) which is the same order of magnitude as the linewidths, adding to the difficulties encountered in observation. After 5 weeks at 80 °C and weekly monitoring by 170 NMR spectroscopy had been inconclusive, the solvent was removed under vacuum and the resulting white solid vacuum dried overnight. A 170 NMR spectrum of an approximately 20 % by weight solution of the white solid in CDC13 was obtained after 24,000 scans (-1.5 hours) at room temperature. The chemical shift was 7.8 ppm which is in reasonable agreement with that of 8.2 ppm obtained previously for 10 % 170 enriched Ph3SiOH in CDC13. The rapid acquisition time indicated that substantial 170H exchange had occurred as a natural abundance spectrum would have required around 105 scans at elevated temperature. The

11-1 NMR spectrum revealed that a small amount of dioxane was still present in an 8:1 silanol:dioxane molar ratio (not in the 4:1 ratio previously reported in the hydrogen bonded adduct147), but no water remained. The infrared spectrum (KBr disc) displayed a broad asymmetric OH peak shifted towards lower wavenumbers at 3220 cm-1 compared with 3250 cm-1 in the natural abundance silanol and Si-O stretches at 846 and 817 cm-1, compared with 855 and 835 cm-1. Due to the presence of hydrogen bonded dioxane, however, it is not possible to draw any conclusions from the infrared spectrum. An El mass spectrum of the white solid, therefore, was recorded in order to quantify the extent of 170H exchange. Commercially available 170 enriched water is prepared by thermal diffusion which involves simultaneous isotopic enrichment with 180 (- 5 times as abundant as 170). The isotope ratio 160: 170: 180 in the 10 % enriched H2O employed in these studies was 32.2: 10.5: 57.3. The natural isotopic abundance of oxygen is 160: 170: 180 99.76: 0.04: 0.20. From these values it is possible to calculate the isotope pattern expected for the molecular ion of Ph3SiOH with natural abundance oxygen and if complete 170H exchange has taken place. The relative intensities of the isotope peaks were calculated using Isotope v.5.2 software for Macintosh and the

223 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts calculated isotope patterns for the molecular ions of both Ph3SiOH with natural abundance oxygen and 10 % 170 enriched Ph3SiOH are shown in Figures 5.7(a) and (b) respectively. Comparison of the EI mass spectrum of the white solid with the calculated mass spectra indicated that complete 170H exchange had occurred, the isotope pattern for the molecular ion of the white solid being almost identical to that shown in Figure 5.7(b). The experiment was then repeated over a shorter time period of 2 weeks to determine the rate of reaction. A 20 % by weight solution of the white solid produced gave a 170 NMR spectrum in CDC13 after 42,148 scans (— 1.75 hours) and the chemical shift was 7.0 ppm, lower than that obtained previously. The 1H NMR spectrum again revealed the presence of residual dioxane but in a 6:1 silanol:dioxane ratio. The infrared spectrum (KBr disc) was similar to that obtained after 5 weeks in the OH stretching region, with a broad asymmetric OH peak shifted towards lower wavenumbers at 3218 cm-1 but the Si-O stretches were at 854 and 823 cm-1. The molecular ion isotope pattern in the EI mass spectrum [Figure 5.7(c)], however, was markedly different from that for

Ph3SiOH with natural abundance oxygen [Figure 5.7(a)] and with 10 % 170 enrichment [Figure 5.7(b)]. By comparison of the spectrum with calculated relative peak intesities for the molecular ion of Ph3SiOH with various degrees of 170 enrichment, the 170H exchange reaction was found to have gone to approximately 50 % completion. Therefore, OH exhange of the silanol group is measurable, although slow and this appears to be the first demonstration of such an exchange reaction. Further work on alkoxysilanols themselves is required to determine the extent to which OH exchange may play a role in their reactions and whether such exchanges need to be considered when modelling industrially important sol-gel processes. It would also be of interest to investigate the effects of acid and base catalysts on OH exchange reactions.

224 Chapter 5 Nuclear magnetic resonance studies of silanols and their adducts

(a) (b)

I 276 277 278 279 mass units 276 277 278 279 280 281 Calculated isotope pattern for the Calculated isotope pattern for the molecular ion of Ph3SiOH with molecular ion of Ph3SiOH with natural abundance oxygen ratio, ie. oxygen isotope ratio 160: 170: 180 160: 170: 180 of 99.76 : 0.04: 0.20 of 32.2: 10.5 : 57.3

(c) Figure 5.7. Calculated and experimental isotope patterns for the molecular ion of Ph3SiOH. Masses of < 1% are not shown.

276 277 278 279 280 Experimental isotope pattern for the molecular ion of Ph3SiOH after 2 weeks exchange reaction.

225 CHAPTER 6 Experimental Chapter 6 Experimental

CHAPTER 6 Experimental

6.1 Preparation of silanols and their adducts in the solid state

6.1.1 General techniques

Reactions involving moisture-sensitive chlorosilanes or alkoxysilanes or other air or moisture sensitive reagents were carried out under an inert atmosphere of oxygen free dry nitrogen using standard Schlenk line techniques.

6.1.2 Instrumentation

All NMR spectra were recorded using a JEOL EX-270 FT-NMR spectrometer and the chemical shifts are in ppm relative to TMS. The 1H NMR spectra were recorded at 270.1 MHz as solutions in CDC13, unless otherwise stated, using the protio impurities of the deuterated solvent as the internal reference. 13C NMR spectra were recorded at 67.9 MHz as solutions in CDC13, the 13C resonance of the solvent being used as the internal reference. 29Si NMR spectra were recorded at 53.6 MHz, using a pulse delay of 10 seconds, as solutions in CDC13. TMS was used as the external reference. Solid State 29Si CPMAS NMR spectra were recorded on a Bruker MSL300 MHz NMR spectrometer by the University of London Solid State NMR Service. IR spectra were recorded on either a Perkin-Elmer 1720 FT-IR spectrometer or Mattson Research Series spectrometer as KBr discs or as neat liquids between NaC1 plates.

Raman spectra were recorded as powders on a Perkin-Elmer 1760 X FT-IR instrument fitted with a 1700 X NIR FT-Raman accessory (Spectron Nd:YAG laser, 1064 nm excitation).

Melting points were determined using a Stuart Scientific SMP1 melting point apparatus in open capillary tubes and are corrected.

227 Chapter 6 Experimental

Elemental analyses were carried out by the Imperial College Microanalytical Laboratory.

Mass spectra were obtained by either chemical ionisation (CI, NH3), electron ionisation (EI) or fast atom bombardment (CI, positive ion) on a VG Autospec-Q by the Imperial College Mass Spectrometry Service.

Controlled thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) measurements of the complexes were carried out using a Polymer Laboratories 1500H simultaneous thermal analyser, controlled by a Omni Pro 486DX-33 PC. The mass of the samples investigated was between 4 - 22 mg. The measurements were carried out in alumina crucibles under an atmosphere of flowing (25 cm3 min-1) nitrogen gas, using heating rates of 5 °C min-I. The reaction involving a sonic bath was carried out in a rectangular Pulsatron 125H ultrasonic cleaner from Kerry Ultrasonics using a frequency of 38kHz±10%, with the round-bottomed flask placed in the position of maximum intensity in the centre of the cleaning tank.

6.1.3 Solvents Diethyl ether and tetrahydrofuran from Aldrich were stored over 4A molecular sieves and then freshly distilled from sodium wire and benzophenone prior to use. Toluene and pentane obtained from Aldrich were stored over 4A molecular sieves and further dried by distillation from sodium wire prior to use. Ethanol, obtained form Aldrich was stored over 4A molecular sieves and freshly distilled from magnesium turnings and iodine prior to use. Anhydrous p-dioxane, water content < 0.005 %, was obtained from Aldrich packaged under nitrogen in a Sure/Sea1TM bottle. NMR solvents were dried over 4A molecular sieves.

228 Chapter 6 Experimental

6.1.4 Starting materials Ph3SiOH and Ph2Si(OH)2 were obtained from Aldrich Chemicals Co. and used without further purification. (-)MePhNaphthSiH, TsiSiPh2OH and TsiSi(OH)3 were supplied by Dr. P. D. Lickiss. tBu2SiH(OH) was donated by Dr. R. G. Taylor. Chlorosilanes were obtained from either Aldrich Chemicals Co. or Lancaster Synthesis Ltd.

6.1.5 Preparation of compounds containing one Si-OH group, silanols

6.1.5.1 Preparation of (-)methylphenylnaphthylsilanol Attempted oxidation of (-)methylphenylnaphthylsilane and other bulky silanes using OXONE®

The silane (0.16 mmol) was dissolved in acetone (1 cm3) and a solution of potassium hydrogencarbonate (0.14 g, 1.37 mmol) in water (1 cm3) was added with stirring followed by a solution of OXONE® (potassium peroxymonosulfate) (0.12 g, 0.20 mmol) in water (1 cm3). The flask was covered in foil and the solution left to stir. The reaction was monitored by infrared spectroscopy. The reaction mixture was then extracted with dichloromethane (3 x 3 cm3), dried over magnesium sulfate and the solvent removed under vacuum. Ph3SiH was oxidised to Ph3SiOH within half an hour, as determined by infrared spectroscopy, whereas the more bulky silanes, (-)MePhNaphthSiH, TsiSiPh2H, TsiSiMe2H and TsiSiH3 , were not oxidised even after stirring for two days.

Oxidation of (-)methylphenylnaphthylsilane to (-)methylphenylnaphthylsilanol using potassium permanganate in the sonic bath (method of Lickiss and Lucas290) (-)Methylphenylnaphthylsilane (2.48 g, 10.0 mmol, 1 equiv.), and potassium permanganate (1.66 g, 10.5 mmol, 1.05 equiv.) were placed in a flask under a stream of nitrogen followed by dry THF (190 cm3). The flask was placed in the centre of the sonic bath and the reaction mixture sonicated overnight. The flask was removed from the bath, the reaction mixture filtered through Celite and washed with THF. The solvent was

229 Chapter 6 Experimental removed under vacuum line to give (-)methylphenylnaphthylsilanol as a viscous oil (2.42 g, 92 %), [a]D -13.8° (c 0.15 M in ether) [lit.353 [a]D -20.5° (c 6.66 M in ether)].

1H NMR: 8 7.32-8.13 (m, 12H, C10H7 + C6H5), 2.43 (s, 1H, OH), 0.81 (s, 3H, CH3) ppm. IR (NaC1 plates, cm-1): 3335 (s, br, v0H), 3067 (s), 3057 (s), 2961 (s), 1955 (w),

1756 (w), 1586 (m), 1504 (m), 1427 (s), 1320 (m), 1258 (s), 1114 (s), 1053 (m), 1024 (m), 985 (s), 852 (s), 824 (s), 797 (s), 736 (s), 699 (s).

6.1.5.2 Preparation of tert-butyldimethylsilanol

[ButMe2SiOH]2.H20 was prepared by the method of Sommer and Tyler152 and then dehydrated by placing in a flame-dried flask containing anhydrous carbon tetrachloride and magnesium sulfate. After the solution had been dried it was removed from the magnesium sulfate into another flame-dried flask by cannulation and the solvent removed by vacuum to leave tBuMe2SiOH as a viscous colourless liquid.

1H NMR: 8 3.2 (s, br, 1H, OH), 0.85 (s, 9H, tBu), 0.03 (s, 6H, CH3) ppm.

6.1.6 Preparation of compounds containing an Si(OH)2 group, silanediols, or two Si-OH groups, a,w-siloxanediols

6.1.6.1 Preparation of dimethylsilanediol, tetramethyldisiloxane-1,3-diol, hexamethyltrisiloxane-1,5-diol and octamethyltetrasiloxane-1,7-diol

Tetramethyldisiloxane-1,3-diol, hexamethyltrisiloxane-1,5-diol and octamethyltetrasiloxane-1,7-diol were synthesised from the corresponding chlorosilanes by the method of Cella and Carpenter.304 Residual Et3N from the preparation of the liquid siloxanediols HO(SiMe20)nH (n = 3 and 4) was removed by dissolving the siloxanediols in CH2C12 and rapidly removing the solvent under vacuum three times. Dimethylsilanediol was also prepared as colourless plates by the method of Cella and Carpenter.304 The melting point, however, was 75 °C (lit. 282,300,301,304,305 m.p.s range from 96-101 °C). 1H NMR (DMSO-d6): 8 5.80 (s, 2H, OH), -0.05 (s, 6H, CH3) ppm. 13C NMR (DMSO-d6): 8 4.69 ppm. 29Si NMR (DMSO-d6): 8 -19.1 ppm.

230 Chapter 6 Experimental

IR (KBr disc, cm-1): 3196 (m, br, DOH), 2962 (m), 1256 (m), 1181 (w), 1064 (w),

910 (s), 874 (s), 786 (m), 695 (w), 386 (w), 346 (m). Anal. Calcd for C2H8O2Si: C, 26.08; H, 8.76. Found: C, 26.10; H, 7.96. rn/z (CI): 168 (22 %, RHOMe2Si)20+2Hi+),

151 (16 %, RHOMe2Si)20-Mer), 110 (91 %, [M+NH4]+), 93 (100 %, [M+11]±), 77 (46 %, [M-Me]+ ), 52 (21 % ). Dimethylsilanediol was recrystallised from ether/pentane, acetone/pentane and by slow evaporation from a benzene solution with no improvement in the melting point and without producing crystals suitable for X-ray structural analysis.

6.1.6.2 Preparation of methylphenylsilanediol

Methylphenylsilanediol (3.4 g, 37%), m.p. 75-76 °C (Lit.306'307 74-75 °C, 73-75 °C), was isolated instead of meso-1,3-dimethyl-1,3-diphenylsiloxanediol, on one occasion, from the hydrolysis of methylphenyldichlorosilane (11.7 g, 10 cm3, 0.06 mol) in neutral medium (Section 6.1.6.5).306 1H NMR: 8 7.62 - 7.66 (m, 2H, ortho C6H5),

7.37 - 7.40 (m, 3H, meta + para C6H5), 2.74 (s, 2H, OH), 0.41 (s, 3H, CH3) ppm. 13C NMR (DMSO-d6): 8 140.00 (ipso C6H5), 134.04 (ortho C6H5), 129.78 (para C6H5), 128.09 (meta C6H5), 0.09 (CH3) ppm. 29Si NMR (DMSO-d6): 8 —21.0 ppm. IR (KBr disc, cm-1): 3174 (s, br, DOH), 2158 (w, br), 1590 (w), 1428 (m), 1264 (m),

1124 (s), 887 (s), 776 (m), 741 (m), 719 (m), 697 (s), 479 (m), 421 (m). Anal. Calcd for C7H10O2Si: C, 54.51; H, 6.53. Found: C, 54.03; H, 6.12. m/z (CI): 308 (15 %, [(HOMePhSi)20+NH4]+), 172 (100 %, [M+NH4]+), 156 (30 %, [M-MeH]+), 94 (26 %, [M-PhH+NH4]+)

Methylphenylsilanediol was recrystallised by the vapour diffusion method from ether-petroleum ether 40/60 and ether-pentane. The vapour diffusion method did not work with acetone-petroleum ether 40/60 or acetone-pentane. Slow evaporation of an acetone solution of methylphenylsilanediol failed to produce any crystals and slow evaporation from an ether solution resulted in a powdery solid. The sample was stored in a glass sample vial in the refrigerator but after a month some condensation had started to occur: 29Si NMR (DMSO-d6): 8 -20.9 [MePhSi(OH)2],

231 Chapter 6 Experimental

-26.9, -27.3, -33.6 ppm. Relative intensities of peaks 14 : 4 : 4 : 3. m/z (CI): 562 (69 %, [(MePhSi0)4+NH4]±), 444 (41 %, [HO(MePhS i0)3H + N H4]+) , 426 (100 %, [(MePhSi0)3+NH4]÷), 308 (90 %, [(HOMePhSi)20+NH4]+), 172 (16 %, [M+NH4]+), 94 (12 %, [M-PhH+NH4]+).

6.1.6.3 Preparation of 1,3-dimethyl-1,3-diphenyldisiloxanediol

Attempted preparations of (HOMePhSi)20 by the hydrolysis of MePhSiC12 with ammonium carbonate31° and by the hydrolysis of MePhSiC12 in an alkaline medium3°6 resulted in the formation of a white viscous oil which was shown to be a mixture of polymerisation products by 1H NMR spectroscopy.

Preparation of 1,3-dimethy1-1,3-diphenyldisiloxanediol from phenylmethyldiethoxysilane

i) Preparation of phenylmethyldiethoxysilane

Excess dry ethanol (47.1 g, 60 cm3, 1.02 mol) was added dropwise to methylphenyldichlorosilane (53.9 g, 46 cm3, 0.28 mol) with stirring over a period of one hour. The solution was then refluxed for three hours and the unreacted ethanol removed under vacuum to give methylphenyldiethoxysilane (50.0 g, 52.0 cm3, 86 %). 1H NMR: 5 7.52 — 7.59 (m, 2H, ortho C6H5), 7.25-7.31 (m, 3H, meta + para C6H5), 3.86 (q, 4H, CH2, J = 6.93 Hz), 1.27 (t, 6H, CH3, J = 6.92 Hz), 0.39 (s, 3H, CH3) ppm. ii) Preparation of 1,3-dimethyl-1,3-diphenyldisiloxanediol from phenylmethyldiethoxysilane3o2 The reaction was carried out in a thermostatically controlled cold bath (containing isopropanol) set at 0°C. An overhead stirrer connected to a timer switch was used.

Phenylmethyldiethoxysilane (49 g, 51 cm3, 0.23 mol) and 1x10-4 N sulfuric acid

(40 cm3) were stirred for 30 min and then ether (120 cm3) and benzene (40 cm3) were added. The mixture was stirred for 15 min every 45 min over a period of 72 h and benzene (40cm3) was added at the end of 24 h and 48 h. The two layers formed were separated, the organic layer was dried over magnesium sulfate and then the solvent removed under vacuum to leave a white viscous oil. Hexane was added to the oil and

232 Chapter 6 Experimental crystals started to precipitate. The solution was left overnight and the crystals collected by vacuum filtration. (2.3 g, 6.9%), m.p. 110-111°C (Lit.310 110 °C). 1H NMR: 8 7.59 -

7.63 (m, 4H, ortho C6H5), 7.34 - 7.39 (m, 6H, meta + para C6H5), 2.63 (s, 2H, OH), 0.40 (s, 6H, CH3) ppm. 13C NMR: 5 136.39 (ortho C6H5), 133.33 (ipso C6H5), 130.10 (para C6H5), 127.89 (meta C6H5), —1.06 (CH3) ppm. 29Si NMR: 5 -22.4 ppm. IR (KBr disc, cm-1): 3216 (s, br, uOH), 3070 (m), 1592 (w), 1430 (m), 1260 (m),

1127 (s), 1066 (s), 895 (s), 851 (s), 786 (m), 732 (m), 721 (s), 697 (m), 479 (m). Anal. Calcd for CigH1803Si2: C, 57.89; H, 6.25. Found: C, 56.68; H, 6.29.

Modified hydrolysis of methylphenyldichlorosilane in neutral medium by Shostakovsky et a1.306

Dry ether (200 cm3) and several drops of bromothymol blue were placed in a three necked flask cooled in a mixture of ice and salt and fitted with stirrer, thermometer and two pressure equalizing dropping funnels. 1M aqueous sodium hydroxide solution was placed in one of the dropping funnels and a solution of methylphenyldichlorosilane

(10 cm3, 11.7 g, 0.06 mol) in dry ether (200cm3) was placed in the other. The contents of both dropping funnels were then added simultaneously with constant stirring to the flask over a period of fifteen to twenty minutes keeping the medium neutral. The temperature of the reaction medium did not exceed +1°C. The water and ether layers were then separated and the ether layer concentrated to around half its volume under vacuum. At this point an excess of pentane was added and a white solid formed. The solution was further concentrated until no more white solid formed. This solid was collected by vacuum filtration and washed with cold pentane to give the meso form of 1,3-dimethyl-

1,3-diphenyldisiloxanediol (2.1 g, 24%) as white needles, mp 109-111°C (Lit.310 110 °C). The NMR and IR spectroscopic data were identical to those obtained for meso- (HOMePhSi)20 above. Anal. Calcd for C18H18O3Si2: C, 57.89; H, 6.25. Found: C, 56.07; H, 5.80.

233 Chapter 6 Experimental

Meso-1,3-Dimethyl-1,3-diphenyldisiloxanediol was recrystallised by the vapour diffusion method from ether-petroleum ether 40/60 and ether-pentane, and by slow evaporation from an ether solution.

6.1.6.4 Preparation of tetraphenyldisiloxane-1,3-diol Modified method of Prescott and Se1in142 A solution of dichlorodiphenylsilane (41.5 cm3, 50 g, 0.2 mol) in acetone (about 40 cm3 ) was added dropwise with stirring to a mixture of acetone (80 cm3 ) and water (80 cm3 ) over a twenty minute period. The solution became cloudy and warm. The mixture was stirred for a further 15 minutes, treated with water (100 cm3 ) and left to stand overnight. The two phases obtained were seperated and the lower layer was diluted with an equal volume of benzene, washed twice with water (2 x 50 cm3 ) and dried over magnesium sulfate. The magnesium sulfate was removed by filtration and the solvents removed under vacuum. The white residue was redissolved in benzene (100 cm3 ) and left standing overnight to allow diphenylsilanediol to crystallize out. This was filtered off and hexane (250 cm3 ) was added to the filtrate. White crystals immediately began to form. The solution was allowed to stand overnight and the white crystals were filtered off to give 1,1,3,3-tetraphenyldisiloxanediol (23.3 g, 56%) as white crystals, m.p. 110-112 °C (lit.354 113-114 °C). 1H NMR: 8 7.61 - 7.65 (m, 8H, ortho C6H5), 7.28 -7.40 (m, 12H, meta + para C6H5), 2.86 (s, 2H, OH) ppm. 13C NMR: 5 134.49 (ipso C6H5), 134.30 (ortho C6H5), 130.23 (para C6H5), 127.78 (meta C6H5) ppm. 29Si NMR: 8 -35.9 ppm. IR (KBr disc, cm-1): 3197 (s, br, DOH), 3071 (s), 3049 (s), 1961 (w), 1892 (w), 1824 (w),

1774 (w), 1592 (m), 1488 (w), 1429 (s), 1127 (s), 1084 (s), 887 (s), 848 (s), 740 (m), 718 (s), 697 (s), 511 (s), 482 (m).

234 Chapter 6 Experimental

6.1.6.5 Preparation of hexaphenyltrisiloxane-1,5-diol

Modified method of Selin284

i) Preparation of disodium hexaphenyltrisiloxane-1,5-diolate.p-dioxane complex

Diphenylsilanediol (5.4 g, 25.0 mmol) was dissolved in dry dioxane with stirring. A reflux condenser was attached to the flask. Freshly cut sodium (1.5 g, 65.2 mmol) in the form of approximately 0.2 g chunks was added to the solution and the solution stirred under nitrogen for 7 hours. The temperature ranged from 10 - 30 °C and a white solid precipitated. The reaction mixture was then left to stand overnight at room temperature. The reaction mixture was filtered through a Buchner funnel (without filter paper) to allow the white solid to go through the funnel but the unreacted sodium to remain. The white solid was then collected in a sintered glass funnel by vacuum filtration, washed with dioxane and dried under a stream of nitrogen to give disodium hexaphenyltrisiloxane-1,5- diolate.p-dioxane (4.35 g, 70%) as a white powder, mp 210-235 °C dec. (lit.284 mp 206- 228 dec.).

ii) Preparation of hexaphenyltrisiloxane-1,5-diol

To a mixture of diethyl ether (10 cm3) and 5% aqueous acetic acid (20 cm3) in a separating funnel was added disodium hexaphenyltrisiloxane-1,5-diolate.p-dioxane (2.0 g, 2.68 mmol). The mixture was shaken well and the ether layer isolated, washed twice with water and dried briefly over sodium sulfate. The solvent was removed on the rotary evaporator to leave a white viscous oil which did not crystallise upon standing. The viscous oil was dissolved in the minimum amount of benzene and hexane added. Crystals began to form. The solution was allowed to stand overnight and the crystals were filtered off to give hexaphenyltrisiloxane-1,5-diol (1.1 g, 67%) as fine white crystals, m.p. 108- 110 °C (lit.284 112-113 °C). 1H NMR: 8 7.14-7.59 (m, 30H, C6H5), 3.53 (s,br, 2H, OH) ppm. 13C NMR: 8 135.04 (ortho C6H5), 130.94 (para C6H5), 130.87 (ipso C6H5), 128.49 (meta C6H5) ppm. 29Si NMR: 8 -36.0 (HOPh2Si-), -44.1 (OSiO) ppm.

IR (KBr disc, cm-1): 3232 (s, br, OH), 3070 (s), 3048 (s), 1961 (w), 1893 (w), 1826 (w),

235 Chapter 6 Experimental

1590 (m), 1429 (s), 1126 (s), 1078 (s), 997 (m), 867 (s), 719 (s), 698 (s). Anal. Calcd for C36H32O4Si3: C, 70.54; H, 5.26. Found: C, 69.92; H, 5.21.

6.1.7 Compounds containing an Si(OH)3 group, silanetriols

6.1.7.1 Preparation of phenylsilanetriol

Phenylsilanetriol was prepared as a white powder, m.p. 127-130 °C (lit.303'311 128-130 °C), by the method of Tyler.311 111 NMR (DMSO-d6): 7.62 - 7.71 (m, 2H, ortho C6H5), 7.41-7.47 (m, 3H, meta + para C6H5), 6.95 (s, 311, OH) ppm.

13C NMR (DMSO-d6): 8 141.25 (ipso C6H5), 138.52 (ortho C6H5), 133.76 (para C6H5), 131.89 (meta C6H5) ppm. 29Si NMR (DMSO-d6): 8 —54.2 ppm. IR (KBr disc, cm-1): 3210 (s, br, v0H), 1592 (m), 1430 (s), 1135 (s), 1039 (m), 906 (s), 885 (s), 844 (s),

738 (s), 697 (s), 475 (s). Anal. Calcd for C6H8O3Si: C, 46.13; H, 5.16. Found: C, 45.10; H, 4.77. m/z (CI): 174 (90 %, [M+NH4]+), 156 (100 %, [(M-H20)+NH4]±), 96 (24 %,

[(Ph+H)+NH4]+), 78 (32 %, [Ph+H]+). Rapid recrystallation of phenylsilanetriol was attempted from ether/hexane, methyl acetate/petroleum ether 40/60, acetone/petroleum ether 40/60 and by concentration of a solution of phenylsilanetriol in methyl acetate and 2-butanone under vacuum,303 but no crystalline material suitable for X-ray structural analysis was obtained.

6.1.7.2 Attempted preparation of CH30(CH2CH20)2(012)3Si(OH)3 i) Preparation of CH3O(CH2C H20)2CH2CHCH2 (modified method of Pittman et ct1.315 )

Into a pre-dried flask equipped with stirrer, dropping funnel and condenser was placed dry p-dioxane (50 cm3) and sodium hydride dispersed in mineral oil (10.0 g of 60% active dispersion, 0.25 mol). Diethyleneglycolmonomethylether (29.7 g, 0.25 mol) was then added dropwise with rapid stirring. The mixture turned from grey to brown and heat was given off. This was followed by the dropwise addition of allyl bromide (90.3 g, 64.8 cm3, 0.75 mol) in dry p-dioxane (25 cm3) whilst cooling the reaction solution with an ice/water bath. Sodium bromide was seen to precipitate from the mixture during the

236 Chapter 6 Experimental addition. The reaction mixture was then allowed to stir overnight at room temperature, the sodium bromide removed by vacuum filtration and the excess allyl bromide removed under vacuum. The p-dioxane was then distilled off at 102 °C at atmospheric pressure. Fractional distillation of the residue gave CH3O(CH2CH2O)2CH2CHCH2 as a colourless liquid (26.4 g, 66%) with b.p. 73 °C at 5 mm Hg pressure (lit.314'315 b.p. 86 °C/15 mm Hg, -73 °C/5 mm Hg). 1H NMR: 8 5.82 - 5.97 (m, 1H, CH), 5.12 - 5.29 (m, 2H,

CH=CH2), 3.95 - 4.04 (m, 2H, OCH2CH), 3.48 - 3.63 [m, 8H, (CH2CH2O)2], 3.32 (s, 3H, CH3O) ppm. 13C NMR: 8 135.40 (CH), 117.80 (CH=CH2), 72.91 (OCH2CH), 72.59

(CH3OCH2), 71.31 + 71.22 (CH2OCH2CH2OCH2), 70.07 (CH3OCH2CH2), 59.70 (CH3O) ppm.

ii) Hydrosilylation of CH3O(CH2CH2O)2CH2CHCH2 to give CH3O(CH2CH2O)2(CH2)3SiC13 To a mixture of CH30(CH2CH20)2CH2CHC H2 (8.0 g, 0.05 mol) and trichlorosilane (10.8 g, 8.0 cm3, 0.08 mol) in dry THF (20 cm3) was added, with rapid stirring, a solution of H2PtC16.xH2O (10.2 mg, 0.0025 mmol) in THF (20 cm3). The temperature of the solution rose to 43 °C and the colour changed from colourless to black. The solution was then refluxed at 60 °C overnight to give a yellow solution. The THF and excess trichlorosilane were removed under vacuum and the residue subjected to fractional distillation to give CH30(CH2CH20)2(CH2)3SiC13 as a slightly yellow liquid (8.7 g, 59 %), b.p. 115 - 116 °C at 1 mm Hg (lit.315 - 115 - 116 °C/1 mm Hg).

1H NMR: 5 3.45 - 3.62 [m, 10H, (CH2CH2O)2CH2], 3.33 (s, 3H, CH3O), 1.75 - 1.86 (m,

2H, CH2CH2Si), 1.41 - 1.47 (m, 2H, CH2Si) ppm. 13C NMR: 5 72.11 (CH3OCH2),

71.54 (CH2CH2CH2), 70.63 + 70.55 (CH2OCH2CH2O), 70.01 (CH3OCH2CH2), 59.04 (CH3O), 22.86 (CH2CH2Si), 21.16 (CH2Si) ppm.

237 Chapter 6 Experimental

iii) Hydrosilylation of CH30(CH2CH20)2CH2CHCH2 to give CH3O(CH2CH2O)2(CH2)3Si(OMe)3 The reaction was carried out by the same method as for CH3O(CH2CH2O)2(CH2)3SiC13 [Section 6.1.7.2(ii)], using trimethoxysilane (8.5 g, 8.9 cm3, 0.07 mol) in place of trichlorosilane. The solution remained black even after refluxing for 2 days, although 1H NMR spectroscopy indicated that the reaction had gone to completion. Fractional distillation of the solution gave

CH3O(CH2CH2O)2(CH2)3Si(OMe)3 as a colourless liquid (10.3 g, 73 %) with b.p. 118- 120 °C at -2 mm Hg pressure. 1H NMR: 5 3.47 - 3.61 [m, 19H, (CH2CH2O)2CH2 +

Si(OCH3)3], 3.33 (s, 3H, CH3OCH2), 1.58 - 1.70 (m, 2H, CH2CH2Si), 0.58 - 0.64 (m, 2H, CH2Si) ppm. 13C NMR: 5 74.08 (CH3OCH2), 72.60 (CH2CH2CH2), 71.30 + 71.19

(CH2OCH2CH2O), 70.65 (CH3OCH2CH2), 59.66 (CH3O), 51.16 [(OCH3)3], 23.34 (CH2CH2Si), 5.85 (CH2Si) ppm.

iv) Attempted hydrolysis of CH3O(CH2CH2O)2(CH2)3SiC13 to give CH3O(CH2CH2O)2(CH2)3Si(OH)3

CH3O(CH2CH2O)2(CH2)3SiC13 (2.94 g, 11.0 mmol) in dry ether (13 cm3) was added dropwise to a solution of dry ether (30 cm3), triethylamine (3.54 g, 4.9 cm3, 35.0 mmol, 3.15 equiv.), acetone (3 cm3) and water (0.65 g, 0.65 cm3) with vigorous stirring at -5 °C. Addition of the chlorosilane was complete within 30 minutes and the mixture was then stirred for a further hour at -5 °C. The triethylamine hydrochloride was removed by vacuum filtration and the ether removed under vacuum to give a yellow viscous oil. The 1H NMR spectrum showed a single peak at 3.31 ppm due to the methoxy group and many peaks in the CH2O region between 3.4 and 3.6 ppm. The peaks around 1.6 ppm and 0.5 ppm due to the CH2 groups had become broad but no OH peaks were readily observable. The 13C NMR spectrum showed a broad noisy peak around 10 ppm and many CH2 peaks. The 29Si NMR showed many peaks between -50 and -70 ppm.

The IR spectrum showed a strong broad OH peak around 3434 cm-1 and also a broad band between 1130 - 1000 cm-1. Interpretation of this region of the spectrum is difficult since both ether and siloxane groups show strong absorptions in this region.

238 Chapter 6 Experimental v) Attempted hydrolysis of CH30(CH2C H20)2(CH2)3Si(OMe)3 to give CH3O(CH2CH2O)2(CH2)3Si(OH)3

0.01 M acetic acid (0.2 cm3 ) was added to a solution of

CH3O(CH2CH2O)2(CH2)3Si(OMe)3 (0.42 g, 1.50 mmol) in ether (10 cm3). The mixture was cooled to 10 °C and stirred vigorously for 4 hours. The solution was then dried over magnesium sulfate and the ether removed under vacuum to give a colourless viscous oil. The 1H NMR spectrum was complicated in the CH2O region between 3.4 and 3.8 ppm, although the peak due to Si(OMe)3 was clearly still present but decreased in intensity by about one third. A new peak at 3.46 ppm was also present. The 13C NMR spectrum showed many CH2 peaks. The IR spectrum showed a broad OH band around 3465 cm-1 and a broad band between 1100 - 1000 cm-1

6.1.7.3 Attempted preparation of CH3O(CH2CH2O)3(CH2)3Si(OH)3 i) Preparation of CH3O(CH2CH2O)3CH2CHCH2 The same procedure as for CH3O(CH2CH2O)2CH2CHCH2 [Section 6.1.7.2(i)] was followed using CH3O(CH2CH2O)3H (41.0 g, 0.25 mol), except that the reaction mixture was heated at 80 °C overnight. Fractional distillation of the residue gave the allyl ether of triethyleneglycol, CH3O(CH2CH2O)3CH2CHCH2, as a colourless liquid (56.3 g, 55 %) with b.p. 88 °C at 2 mm Hg pressure. 1H NMR: 8 5.64 - 5.78 (m, 1H, CH), 4.95 -

5.12 (m, 2H, CH=CH2), 3.81 - 3.83 (m, 2H, OCH2CH), 3.33 - 3.49 [m, 12H, (CH2CH2O)3], 3.18 (s, 3H, CH3O) ppm. 13C NMR: 8 135.37 (CH), 117.72 (CH=CH2),

72.85 (OCH2CH), 72.54 (CH3OCH2), 71.23 + 71.13 [CH20 (CH2CH20)2], 70.01

(CH3OCH2CH2), 59.64 (CH3O) ppm. ii) Hydrosilylation of CH3O(CH2CH2O)3CH2CHCH2 to give CH3O(CH2CH2O)3(CH2)3SiC13 The same method as for the preparation of CH3O(CH2CH2O)2(CH2)3SiC13 [Section 6.1.7.2(ii)] was followed using CH3O(CH2CH2O)3CH2CHCH2 (10.0 g, 0.05 mol). The solution was refluxed at 60 °C for 24 hours before the colour changed from black to yellow. Fractional distillation of the dark yellow solution gave

239 Chapter 6 Experimental

CH3O(CH2CH2O)3(CH2)3SiC13 as a yellow liquid (11.7 g, 69 %), b.p. 118 - 119 °C at 6 mm Hg pressure. 1H NMR: 6 3.48 - 3.62 [m, 14H, (CH2CH2O)3CH2] 3.34 (s, 3H,

CH3O), 1.80 - 1.86 (m, 2H, CH2CH2Si), 1.44 - 1.49 (m, 211, CH2Si) ppm.

13C NMR: 5 72.04 (CH3O CH2), 71.50 (CH2CH2CH2), 70.71 + 70.65 + 70.27

[CH2O(CH2CH2O)2], 69.97 (CH3OCH2CH2), 58.99 (CH3O), 22.81 (CH2CH2Si), 21.12 (CH2Si) ppm.

iii) Hydrosilylation of CH3O(CH2CH2O)3CH2CHCH2 to give CH3O(CH2CH2O)3(CH2)3Si(OMe)3 The reaction was carried out by the same method as for

CH3O(CH2CH2O)3(CH2)3 S i C 1 3 [Section 6.1.7.3(ii)], using CH3O(CH2CH2O)3CH2CHCH2 (10.0 g, 0.05 mol) and trimethoxysilane (8.5 g, 8.9 cm3, 0.07 mol) in place of trichlorosilane. The solution was refluxed at 60 °C for 36 hours but remained pale yellow throughout. A small sample of the solution was taken, the THF removed under vacuum and analysed by 1H NMR spectroscopy. Peaks attributable to the allyl ether remained but were very small so the reaction solution was removed from the heat and the THF and excess trimethoxysilane removed under vacuum to give a yellow solution. Fractional distillation gave CH3O(CH2CH2O)3(CH2)3Si(OMe)3 as a colourless liquid (10.3 g, 63 %), b.p. 146 °C at - 2mm Hg pressure. 1H NMR: 8 3.48 - 3.61 [m,

2311, (CH2CH2O)3CH2 Si(OCH3)3], 3.33 (s, 311, CH3O), 1.60 - 1.71 (m, 2H, CH2CH2Si), 0.58 - 0.64 (m, 211, CH2Si) ppm. 13C NMR: 6 74.05 (CH3OCH2), 72.59

(CH2CH2CH2), 71.27 + 71.17 [CH20 (CH2CH20)2], 70.65 (CH3OCH2CH2), 59.65 (CH3O), 51.13 [(OCH3)3], 23.36 (CH2CH2Si), 5.87 (CH2Si) ppm.

iv) Attempted Hydrolysis of CH3O(CH2CH2O)3(CH2)3SiC13 to give CH3O(CH2CH2O)3(CH2)3Si(OH)3 This was attempted by the same method as for CH30(CH2CH20)2(CH2)3SiC13 [Section 6.1.7.2(iv)], using CH3O(CH2CH2O)3(CH2)3SiC13 (3.72 g, 11.0 mmol). A viscous yellow oil was produced which gave NMR and IR spectra very similar to those described in Section 6.1.7.2(iv).

240 Chapter 6 Experimental

v) Attempted Hydrolysis of CH3O(CH2CH2O)3(CH2)3Si(OMe)3 to give CH3O(CH2CH2O)3(CH2)3Si(OH)3

This was attempted by the same method as for

CH3O(CH2CH2O)2(CH2)3Si(OMe)3 [Section 6.1.7.2(v)], using CH3O(CH2CH2O)3(CH2)3Si(OMe)3 (0.49 g, 1.50 mmol). A colourless oil was produced which gave NMR and IR spectra very similar to those described in Section

6.1.7.2(v). In the 1H NMR spectrum, however, the peak due to the CH3O group was split into two and a new broad peak at 2.21 ppm was present which suggested the presence of OH groups.

6.1.8 Preparation of compounds containing four Si-OH groups

6.1.8.1 Preparation of cis-cis- cis-2,4,6,8-tetraphenylcyclotetrasiloxanetetrol Modified method of Brown291

To an ice/water slurry (1000 g) in a 31 flange flask equipped with dropping funnel and mechanical stirrer phenyltrichlorosilane (27.5 g, 20.8 cm3, 0.13 mol), dissolved in cold dry acetone (47 cm3), was added in a thin stream with vigorous stirring. The solution was stirred for a further ten minutes and then left to stand in an ice/water bath in the fridge at 0°C overnight. The mixture of crystalline and resinous solids which had precipitated were filtered off to give 15.3 g of air dried solid. This was stirred with carbon disulfide (32 cm3), cooled to 0°C, filtered and washed with carbon disulfide to leave the crude tetrol (8.48 g, 47%) as a white solid. The solid was recrystallised by dissolving in ether, drying over silica gel, filtering and adding an excess of hexane to give cis-cis-cis-2,4,6,8-tetraphenylcyclotetrasiloxanetetrol as a white powder, mp 156-161 °C (lit.291 166-174 °C). 1H NMR (acetone-d6): 5 7.32-7.91 (m, 2011, C6H5), 6.44 (s, br, 4H, OH) ppm. 13C NMR (acetone-d6): 5 133.70 (ortho C6H5), 133.15 (ipso C6H5), 129.52

(para C6H5), 127.07 (meta C6H5) ppm. 29Si NMR (acetone-d6): 8 -69.7 PP111- 11Z (KBr disc, cm-1): 3218 (s, br, DOH), 3073 (s), 1594 (w), 1430 (m), 1133 (s), 1108 (s),

906 (m), 738 (m), 696 (m), 588 (w), 485 (s). Anal. Calcd for C24H24O8Si4: C, 52.15%; H, 4.38%. Found: C, 49.65%, H, 4.38%.

241 Chapter 6 Experimental

The cyclic tetrol was also recrystallised by slowly adding a dilute solution in acetone to ten volumes of a 4:1 water-acetone mixture at 0 °C291 but only a powder precipitated. Repeated crystallisations from ether/hexane also failed to produce crystals suitable for X-ray crystallography.

6.1.9 Preparation of hydrogen bonded adducts of silanols

The attempted preparation of adducts with silanols was generally carried out by one of the following two methods. Only experimental data for successful adduct preparations are included in this section. Unless the experimental method differed substantially from Methods 1 or 2, the details of unsuccessful adduct preparations may be found in Chapter 3 and will not be discussed any further.

Method 1

The silanol (0.5 mmol) was dissolved in toluene (0.5 cm3) by stirring and warming to around 50 - 60 °C, the hydrogen bond acceptor molecule (0.5 mmol) added and the solution stirred for between 2-5 minutes. The solution was then removed from the heat and left to cool to room temperature. If no crystals formed upon cooling, hexane

(2 - 10 cm3) was added until the solution went cloudy or crystals started to form. The reaction vessel was sealed and left to stand at room temperature. If crystals had not formed after a few days the reaction vessel was left open for the solvent to evaporate slowly. Any solid product was then collected by vacuum filtration and air dried. When the hydrogen bond acceptor molecule was a solid the volume of toluene was increased to 2 cm3•

Method 2

The hydrogen bond acceptor molecule (0.77 mmol) was added to a solution of the silanol (0.77 mmol) in ether and the solution stirred for between 1-5 hours. The solvent was then removed under reduced pressure to dryness if the hydrogen bond acceptor molecule was a low boiling point liquid or until crystals started to form if the hydrogen bond acceptor was a solid or high boiling point liquid.

242 Chapter 6 Experimental

6.1.9.1 Adducts of (HOPh2Si)20

The preparation of hydrogen bonded adducts of (HOPh2Si)20 with a range of amines, alcohols, ethers, crown ethers, amino acids and phosphines was attempted. The reactions were generally carried out by Method 1 using (HOPh2Si)20 (0.207 g, 0.5 mmol). Reference spectroscopic and analytical data for hexaphenylcyclotrisiloxane, (Ph2SiO)3, are included below since this was commonly formed as a condensation product in the attempted preparation of adducts with amines.

(Ph2SiO)3

Colourless crystals, m.p. 190 °C. 1H NMR: 7.61 - 7.75 (m, 12H, ortho C6H5), 7.24 - 7.50 (m, 18H, meta + para C6H5) ppm. IR (KBr disc, cm-1)355: 1579 (w), 1575 (vw), 1492 (vw), 1433 (s), 1312 (vw), 1270 (vw), 1132 (vs), 1122 (vs), 1043 (vs), 1020 (vs), 998 (vs), 772 (w), 730 (vs), 698 (vs), 677 (s), 528 (vs), 488 (vs), 415 (s).

RHOPh2Si)2014.(Et2NH)2

The preparation was carried out by Method 1 using Et2NH (0.037 g, 0.05 cm3, 0.5 mmol, 1 equiv.). Colourless needle-like crystals began to form immediately hexane (5 cm3) was added. The crystals were filtered off under vacuum and air dried to give [(HOPh2Si)20]4.(Et2NH)2 (0.137 g, 61 %), m.p. 102-104 °C dec. 1H NMR: 57.61 - 7.65

(m, 16H, ortho C6H5), 7.24 - 7.40 (m, 24H, meta + para C6H5), 2.94 (s, br, 4H, OH),

2.42 - 2.47 (q, 4H, CH2), 0.92 - 0.97 (t, 6H, CH3) ppm. 13C NMR: 8 135.95 (ipso C6H5), 135.06 (ortho C6H5), 130.66 (para C6H5), 128.38 (meta C6H5), 43.30 (CH2), 14.69 (CH3) ppm. 29Si NMR: 8 -36.49 ppm. IR (KBr disc, cm-1): 3230 (m, vI\TH), 3066 (m),

3018 (m), 1590 (w), 1429 (m), 1118 (s), 1045 (s), 1024 (s), 997 (m), 908 (s), 746 (m), 713 (s), 701 (s). (OH band obscured by CH and NH peaks). Anal. Calcd for C1o4H110012N2Sig: C, 69.22; H, 6.14; N, 1.55. Found: C, 69.47; H, 5.93; N, 1.52. Crystals suitable for X-ray crystallography were obtained from toluene/hexane.

243 Chapter 6 Experimental

(HOPh2Si)20.piperazine

The preparation was carried out by Method 1 using piperazine (0.043 g, 0.5 mmol, 1 equiv.) and toluene (2 cm3). A white powdery solid precipitated rapidly from solution without the addition of hexane. The solid was filtered off under vacuum and air dried to give (HOPh2Si)20.piperazine (0.232 g, 93 %), m.p. 124-126 °C dec. 1H NMR: 8 7.60 -

7.64 (m, 8H, ortho C6H5), 7.25 - 7.40 (m, 12H, meta + para C6H5), 3.28 (s, br, 4H, NH + OH), 2.62 (s, 8H, CH2) ppm. 13C NMR: 8 136.55 (ipso C6H5), 135.04 (ortho C6H5), 130.54 (para C6H5), 128.34 (meta C6H5), 46.72 (CH2) ppm. 29Si NMR: 8 -38.54 ppm.

IR (KBr disc, cm-1): 3293 (m, NH), 3270 (m, NH), 3062 (m), 3050 (m), 3018 (m), 3002 (m), 2948 (m), 2856 (m), 2738 (m, br, OH), 1589 (w), 1429 (s), 1367 (m), 1122 (s), 1037 (s), 1024 (s), 995 (s), 944 (s), 912 (s), 836 (s), 748 (m), 711 (s), 701 (s). Anal. Calcd for C28H32O3N2Si2: C, 67.17; H, 6.45; N, 5.60. Found: C, 66.89; H, 6.20; N, 5.33. The adduct was sparingly soluble in toluene or ether. Recrystallisation of the adduct by slow evaporation of an acetone solution or from acetone/hexane failed to produce crystals suitable for X-ray crystallography.

(HOPh2Si)20.{[HOPh2SiOSiPh2Si0][Et3M-I]l The preparation was carried out by Method 1 using Et3N (0.051 g, 0.07 cm3, 0.5 mmol, 1 equiv.). Upon addition of hexane (5 cm3) clumps of colourless needle-like crystals formed after two hours. The crystals were filtered off and air dried to give (HOPh2Si)20. [HOPh2SiOSiPh2SiO] [Et3NHll (0.156 g, 67 %), m.p. 85-88 °C dec.

1H NMR: 8 7.61 - 7.65 (m, 16H, ortho C6H5), 7.27 - 7.42 (m, 2411, meta + para C6H5), 2.97 (s, 4H, br, OH), 2.43 - 2.49 (q, 6H, CH2), 0.93 - 0.98 (t; 9H, CH3) ppm. 13C NMR:

8 136.23 (ipso C6H5), 135.09 (ortho C6H5), 130.52 (para C6H5), 128.29 (meta C6H5), 45.46 (CH2), 10.40 (CH3) ppm. 29Si NMR: 8 -37.11 ppm. IR (KBr disc, cm-1): 3280 (m, br, OH), 3066 (m), 3045 (w), 3021 (m), 3002 (w), 1590 (w), 1475 (w), 1456 (w), 1429 (s), 1263 (w), 1118 (s), 1049 (s), 1006 (s), 995 (m), 912 (s), 744 (m), 711 (s), 700 (s). Anal. Calcd for C54H5906NSi4: C, 69.71; H, 6.39; N, 1.51. Found: C, 69.40; H, 5.76; N, 1.40.

Crystals suitable for X-ray crystallography were obtained from toluene/hexane.

244 Chapter 6 Experimental

(HOPh2Si)20.DABCO

The preparation was carried out by Method 1 using DABCO (0.056 g, 0.5 mmol,

1 equiv.) and toluene (2 cm3). A white powder rapidly precipitated from the colourless solution initially formed, without the addition of hexane. The powder was filtered off and air dried to give (HOPh2Si)20.DABCO (0.255g, 97 %), m.p. 144-146 °C dec. 1H NMR: 5 7.62 - 7.65 (m, 8H, ortho C6H5), 7.26 - 7.41 (m, 12H, meta + para C6H5), 2.61 (s, 12H,

CH2) ppm. 13C NMR: 8136.61 (ipso C6H5), 135.11 (ortho C6H5), 130.51 (para C6H5), 128.31 (meta C6H5), 46.53 (CH2) ppm. 29Si NMR: 8 -38.67 ppm. IR (1(13r disc, cm-1):

3068 (m), 3050 (w), 3023 (m), 3002 (w), 2946 (m), 2879 (m), 2730 (m, br, OH), 1590 (w), 1463 (m), 1429 (s), 1357 (m), 1321 (m), 1122 (s), 1060 (s), 1047 (s), 997 (m),

944 (s), 914 (m), 856 (vw), 835 (w), 802 (w), 777 (s), 746 (m), 713 (s), 701 (s). Anal. Calcd for C30H34O3N2Si2: C, 68.40; H, 6.51; N, 5.32. Found: C, 67.60; H, 5.99; N, 5.20. Recrystallisation of the adduct from toluene/hexane and by slow evaporation of an ether solution failed to give crystals suitable for X-ray crystallography.

[(HOPh2Si)20]2.DABCO

The preparation was carried out by Method 1 using DABCO (0.028 g, 0.25 mmol, 0.5 equiv.) and toluene (2 cm3). A white powder rapidly precipitated from the colourless solution initially formed, without the addition of hexane. The powder was filtered off and air dried to give [(HOPh2Si)20]2.DABCO (0.214 g, 91 %), m.p. 160-165 dec. 1H NMR: 8 7.62 - 7.65 (m, 16H, ortho C6H5), 7.26 - 7.41 (m, 24H, meta + para C6H5), 2.63 (s, 12H, CH2) ppm. 13C NMR: 8 136.11 (ipso C6H5), 135.08 (ortho C6H5), 130.93 (para C6H5), 128.52 (meta C6H5), 47.29 (CH2) ppm. 29Si NMR: 8 -37.23 ppm. IR (KBr disc, cm-1): 3293 (m, br, OH), 3068 (m), 3048 (w), 3023 (w), 3000 (w), 2948 (w), 2881 (w), 1590 (w), 1459 (w), 1429 (s), 1324 (w), 1116 (s), 1091 (s), 997 (w), 914 (m), 829 (w), 779 (s), 742 (m), 713 (s), 700 (s).

Recrystallisation of the adduct from toluene/hexane and by slow evaporation of an ether solution failed to give crystals suitable for X-ray crystallography.

245 Chapter 6 Experimental

(HOPh2Si)20.TMEDA (for 29Si CPMAS experiments) The preparation was carried out by Method 1 using TMEDA (0.058 g, 0.08 cm3, 0.5 mmol, 1 equiv.). Upon addition of hexane (5 cm3) colourless crystals started to form. The crystals were filtered and air dried to give (HOPh2Si)20.TMEDA (0.259 g, 98 %), mp 107-109 °C dec. 1H NMR (CDC13): 8 7.61 - 7.66 (m, 8H, ortho C6H5), 7.25 - 7.42

(m, 12H, meta + para C6H5), 2.29 (s, 4H, CH2), 1.99 (s, 12H, CH3) ppm. 13C NMR: 8 136.94 (ipso C6H5), 135.14 (ortho C6H5), 130.40 (para C6H5), 128.31 (meta C6H5), 57.02 (CH2), 45.63 (CH3) ppm. 29Si NMR: 8 -39.18 ppm. IR (KBr disc, cm-1): 3066 (s), 2983 (s), 2839 (s), 2790 (s), 1590 (s), 1465 (m), 1445 (s), 1429 (w),

1116 (s), 1022 (s), 916 (s), 826 (s), 746 (m), 740 (m), 714 (s), 710 (s), 683 (m) cm-1 (OH band obscured by CH peaks). Anal. Calcd for C30H38O3N2Si2: C, 67.88; H, 7.22; N, 5.28. Found: C, 67.58; 11, 6.95; N, 5.11.

(HOPh2Si)20.imidazole

The preparation was carried out by Method 1 using imidazole (0.034 g, 0.5 mmol,

1 equiv.) Fine white crystals formed about 2 hours after the addition of hexane (5 cm3). The crystals were filtered and air dried to give (HOPh2Si)20.imidazole (0.198 g, 82 %), m.p. 67 °C dec. 1H NMR (DMSO): 8 7.25 - 7.62 (m, 21H, C6H5 and N=CH), 7.04 (s,

2H, CH) ppm. IR (KBr disc, cm-1): 3159 (m, NH), 3069 (m), 3049 (m), 3022 (w), 2957 (w), 2870 (w), 1590 (w), 1482 (w), 1429 (m), 1333 (w), 1125 (s), 1103 (s), 1067 (s), 878 (s), 828 (m), 743 (m), 716 (s), 699 (s), 657 (m) (OH band obscured by CH peaks). Recrystallisation of the adduct from toluene/hexane or slow evaporation of an ether solution did not produce crystals suitable for X-ray crystallography.

[(HOPh2Si)20]2.(2-methylimidazole)3

The preparation was carried out by Method 1 using 2-methylimidazole (0.041 g, 0.5 mmol, 1 equiv.) A white powder formed about 2 hours after the addition of hexane (5 cm3 ). The powder was filtered off and air dried to give [010Ph2S020]2.(2-methylimidazole)3 (0.127 g, 71 %), m.p. 102 °C dec.

246 Chapter 6 Experimental

1H NMR (DMSO): 8 7.25 - 7.62 (m, 40H, C6H5), 6.95 (s, 6H, CH), 2.26 (s, 9H, CH3) ppm. IR (KBr disc, cm-1): 3197 (m, NH), 3104 (m), 3070 (m), 3051 (m), 3024 (w), 2959 (w), 2923 (w), 1591 (m), 1568 (m), 1429 (s), 1125 (s), 1088 (m), 902 (s), 741 (m), 717 (s), 699 (s) (OH band obscured by CH peaks).

Recrystallisation of the adduct from toluene/hexane or slow evaporation of an ether solution did not produce material suitable for X-ray crystallography.

(HOPh2Si)20.1,2-dimethylimidazole The preparation was carried out by Method 1 using 1,2-dimethylimidazole (0.048 g, 0.5 mmol, 1 equiv.) Colourless fine needle-like crystals formed about 2 hours after the addition of hexane (5 cm3). The crystals were filtered and air dried to give (HOPh2Si)20.1,2-dimethylimidazole (0.239 g, 94 %), m.p. 83 °C dec.

1H NMR (CDC13): 8 7.26 - 7.65 (m, 20H, C6H5), 6.72 - 6.75 (d, 2H, CH), 3.49 (s, 3H,

CH3), 2.23 (s, 3H, CH3) ppm. IR (KBr disc, cm-1): 3260 (m, br, OH), 3137 (w), 3067 (m), 3020 (m), 3005 (w), 1615 (w), 1590 (m), 1430 (s), 1277 (m), 1120 (s), 1050 (s), 1026 (m), 997 (m), 910 (s), 748 (m), 714 (s), 702 (s).

Recrystallisation of the adduct from toluene/hexane or slow evaporation of an ether solution did not produce crystals suitable for X-ray crystallography.

(HOPh2Si)20.1,4-dioxane

The preparation was carried out by Method 1 using 1,4-dioxane (0.044 g,

0.04 cm3, 0.5 mmol, 1 equiv.). Upon addition of hexane (2 cm3) clumps of colourless needle-like crystals formed. The crystals were filtered off under vacuum and air dried to give (HOPh2Si)20.1,4-dioxane (0.210 g, 84 %), m.p. 76-78 °C dec. 1H NMR: 5 7.60 -

7.64 (m, 8H, ortho C6H5) , 7.26 - 7.41 (m, 12H, meta + para C6H5), 3.62 (s, 8H, CH2) 3.47 (s, br, 2H, OH) ppm. 13C NMR: 8 135.19 (ipso C6H5), 135.01 (ortho C6H5), 131.01 (para C6H5), 128.56 (meta C6H5), 67.73 (CH2) ppm. 29Si NMR: 8 -35.64 ppm.

IR (KBr disc, cm-1): 3357 (m, br, OH), 3068 (m), 3050 (m), 2971 (m), 2919 (m), 2861 (m), 1963 (w), 1891 (w), 1826 (w), 1589 (m), 1429 (s), 1369 (w), 1255 (m),

247 Chapter 6 Experimental

1120 (s), 1101 (s), 997 (m), 889 (s), 862 (s), 742 (m), 713 (s), 698 (s). Anal. Calcd for C28H30O5Si2: C, 66.90; H, 6.02. Found: C, 66.66; H, 5.93. Crystals suitable for X-ray crystallography were obtained from toluene/hexane.

6.1.9.2 Adducts of Ph3SiOH The attempted preparation of adducts of Ph3SiOH with a range of amines, crown ethers, acids and phosphines was generally carried out by Method 1. With pentaerythritol, a modification of Method 2 was used in which methanol (50 cm3) was used as the solvent instead of ether.

With amine hydrochlorides, Method 2 was used but the heterogeneous reaction mixtures were filtered prior to removal of the ether solvent under reduced pressure. The preparation of adducts of Ph3SiOH with azacrowns and azacrown ethers involved a different experimental approach and these preparations have been described in more detail below.

Ph3SiOH.tris(2-aminoethyl)amine

The preparation was carried out by Method 1 using tris(2-aminoethyl)amine (0.073 g, 0.07 cm3, 0.5 mmol, 1 equiv.). Upon addition of hexane (10 cm3) two layers were formed. The solution was agitated until colourless needle-like crystals started to form and the solution was left overnight to allow complete crystallisation of the complex. The crystals were filtered under vacuum and air dried to give Ph3SiOH.tris(2- aminoethyl)amine (0.136 g, 64 %), 45-50 °C dec. 1H NMR: 5 7.59 - 7.62 (6H, m, ortho

C6H5), 7.31 - 7.43 (m, 9H, meta + para C6H5), 2.63 - 2.67 (t, 6H, NCH2), 2.39 - 2.43 (t, 6H, CH2NH2) ppm; 13C NMR: S 136.68 (ipso C6H5), 135.65 (ortho C6H5), 130.51 (para C6H5), 128.48 (meta C6H5), 57.97 (NCH2), 40.37 (CH2NH2) ppm; 29Si NMR: 8 -14.54 ppm. IR (KBr disc, cm-1): 3363 (w, NH), 3343 (w, NH), 3299 (s, br, OH), 3064 (m), 3045 (w), 3019 (m), 2948 (w), 2813 (m), 1589 (w), 1483 (w), 1463 (w), 1427 (s), 1305 (w), 1114 (s), 898 (s), 744 (m), 707 (s).

248 Chapter 6 Experimental

The stoichiometry of the adduct remained the same when two or three equivalents of tris(2-aminoethyl)amine were employed in the preparation. Crystals suitable for X-ray crystallography were obtained from the preparation without recrystallisation.

(Ph3SiOH)2.piperazine The preparation was carried out by Method 1, using piperazine (0.043 g,

0.5 mmol, 1 equiv.) and toluene (2 cm3). Colourless needle-like crystals started to form immediately upon addition of hexane (2 cm3). The crystals were filtered off under vacuum and air dried to give (Ph3SiOH)2.piperazine (0.143 g, 90 %), m.p. 130-132 °C dec. 1H NMR: 5 7.59 - 7.64 (m, 12H, ortho C6H5), 7.31 - 7.44 (m, 18H, meta + para C6H5), 3.20 (s, 4H, br, NH + OH), 2.65 (s, 8H, CH2) ppm. 13C NMR: 5 135.29 (ipso

C6H5), 134.47 (ortho C6H5), 129.39 (para C6H5), 127.32 (meta C6H5), 45.91 (CH2) ppm. 29Si NMR: 8 -14.42 ppm. IR (KBr disc, cm-1): 3306 (m, NH), 3064 (m), 3048 (m),

2948 (m), 2872 (w), 2839 (w), 2730 (m, br, OH), 1585 (w), 1483 (m), 1458 (m), 1426 (s), 1378 (m), 1325 (m), 1260 (m), 1114 (s), 1079 (m), 997 (w), 964 (w), 912 (s), 871 (w), 840 (m), 745 (m), 704 (s). Anal. Calcd for C40H4202N2Si2: C, 75.20; H, 6.63; N, 4.39. Found: C, 75.42; H, 6.42; N, 4.38.

Crystals suitable for X-ray crystallography were obtained from toluene/hexane.

(Ph3SiOH)2.TMEDA

The preparation was carried out by Method 2 using TMEDA (0.089 g, 0.12 cm3, 0.77 mmol, 1 equiv.). The solution was stirred for 2 hours and then evaporation of the solvent under reduced pressure gave (Ph3SiOH)2.TMEDA as a white solid (0.167 g, 65 %), m.p. 72-74 °C dec. 1H NMR: 8 7.60 - 7.64 (m, 12H, ortho C6H5), 7.32 - 7.41 (m, 1811, meta + para C6H5), 2.33 (s, 4H, CH2), 2.16 (s, 12H, CH3) ppm. 13C NMR: 8

136.05 (ipso C6H5), 135.67 (ortho C6H5), 130.73 (para C6H5), 128.57 (meta C6H5), 58.00 (CH2), 46.39 (CH3) ppm. 29Si NMR: 5 -12.82 ppm. IR (KBr disk, cm-1): 3247 (m,

br, OH), 3068 (m), 3021 (m), 3010 (w), 2998 (w), 2962 (w), 2871 (vw), 2836 (w),

249 Chapter 6 Experimental

2790 (w), 1959 (w), 1887 (w), 1824 (w), 1587 (w), 1484 (w), 1463 (w), 1427 (s), 1334 (w), 1303 (w), 1261 (m), 1118 (s), 1016 (m), 997 (m), 890 (m), 854 (m), 833 (s), 738 (m), 712 (s), 698 (s). Anal. Calcd for C42H48O2N2Si2: C, 75.40; H, 7.23; N, 4.19. Found: C, 75.70; H, 7.14; N, 4.03.

Colourless rectangular crystals suitable for X-ray diffraction were obtained by slow evaporation of the diethyl ether solution.

(Ph3SiOH)4.(DABCO)3

The reaction was carried out by Method 1, using DABCO (0.056 g, 0.5 mmol, 1 equiv.) and toluene (2 cm3). Upon addition of hexane (2 cm3) colourless hexagonal crystals started to form. The crystals were filtered off under vacuum and air dried to give (Ph3SiOH)4.(DABCO)3 (0.154 g, 86 %), m.p. 124 - 126 °C dec. 1H NMR: 8 7.59 - 7.63

(m, 2411, ortho C6H5), 7.36 - 7.42 (m, 36H, meta + para C6H5), 2.72 (s, 36H, CH2) ppm. 13C NMR: 8 137.10 (ipso C6H5), 135.66 (ortho C6H5), 130.33 (para C6H5), 128.37

(meta C6H5), 46.97 (CH2) ppm. 29Si NMR: 8 -16.09 ppm. IR (KBr disc, cm-1): 3066 (m), 3048 (w), 3021 (w), 2962 (m), 2935 (m), 2871 (m), 2732 (m, br, OH), 1587 (w), 1459 (m), 1427 (s), 1321 (s), 1114 (s), 1058 (m), 997 (m), 894 (s), 862 (w),

829 (m), 777 (s), 746 (m), 705 (s). Anal. Calcd for C901-110004N6Si4: C, 74.96; H, 7.00; N, 5.83. Found: C, 74.71; H, 6.95; N, 5.73.

Crystals of (Ph3SiOH)4.(DABCO)3 suitable for X-ray crystallography could not be obtained by slow evaporation of benzene, acetone, ether or chloroform solutions of the adduct or from ether/hexane.

(Ph3SiOH)4.DABCO The reaction was carried out by Method 1, using DABCO (0.028 g, 0.25 mmol,

0.5 equiv.) and toluene (2cm3). Upon addition of hexane (2cm3) colourless needle-like crystals started to form. The crystals were filtered off under vacuum and air dried to give

(Ph3SiOH)4.DABCO (0.124 g, 82 %), m.p. 127 ° softened, 150-157 °C dec.

11-1 NMR: 5 7.59 - 7.63 (m, 24H, ortho C6H5), 7.33 - 7.43 (m, 36H, meta + para C6H5),

250 Chapter 6 Experimental

2.95 (s, br, 4H, OH), 2.70 (s, 12H, CH2) ppm. 13C NMR: 5 136.11 (ipso C6H5), 135.68

(ortho C6H5), 130.72 (para C6H5), 128.57 (meta C6H5), 47.48 (CH2) ppm. 29Si NMR: 8 -15.01 ppm. IR (KBr disc, cm-1): 3301 (m, br, OH), 3066 (m), 3023 (w), 3008 (w), 2998 (w), 2973 (w), 2950 (w), 2883 (w), 1587 (w), 1484 (w), 1461 (w), 1427 (s), 1116 (s), 1060 (w), 998 (w), 900 (m), 854 (m), 779 (m), 740 (m), 709 (s), 700 (s). Anal. Calcd for C78H76O4N2Si4: C, 76.94; H, 6.30; N, 2.30. Found: C, 76.94; H, 6.41; N, 2.33. Crystals suitable for X-ray crystallography were obtained from tolune/hexane.

(Ph3SiOH)4.1,4,7-triazacyclononane

Triphenylsilanol (0.080 g, 0.289 mmol, 3 equiv.) was added to a solution of 1,4,7- triazacyclononane (0.012 g, 0.096 mmol, 1 equiv.) in anhydrous toluene (50 cm3). The solution was stirred for 3 hours at 50 °C and then allowed to cool to room temperature. The solution was reduced under vacuum to about one third of its original volume and the flask placed in the refrigerator. After 1 week no crystals had formed. The volume of the solvent was reduced further to about 2 cm3 and the flask returned to the refrigerator for 2 days. Still no crystals had formed so anhydrous pentane (3 cm3) was added. Small colourless crystals began to form immediately. The flask was returned to the refrigerator for a further 2 days to allow complete crystallisation. The small rectangular crystals were then filtered off under vacuum and air dried to give (Ph3SiOH)4.1,4,7-triazacyclononane (0.063 g, 71 %), m.p. 73-80 °C. 1H NMR: 5 7.59 - 7.64 (m, 2411, ortho C6H5), 7.32 -

7.46 (m, 36H, meta + para C6H5), 2.84 (s, br, 7H, OH + NH), 2.57 (s, 12H, CH2) ppm. 13C NMR: 5 136.35 (ipso C6H5), 135.68 (ortho C6H5), 130.62 (para C6H5), 128.53 (meta C6H5), 47.06 (CH2) ppm. 29Si NMR: 5 -13.75 ppm. IR (KBr disc, cm-1): 3370

(m, NH), 3256 (m, br, OH), 3067 (m), 3048 (w), 3021 (w), 2998 (w), 2941 (w), 2928 (w), 2915 (w), 2858 (w), 1960 (w), 1889 (w), 1826 (w), 1773 (w), 1612 (w), 1589 (m), 1535 (m), 1479 (m), 1427 (s), 1405 (m), 1349 (m), 1304 (m), 1279 (m), 1117 (s), 1066 (w), 1027 (w), 997 (m), 894 (m), 882 (m), 859 (m), 835 (m), 739 (m), 710 (s), 699 (s). Anal. Calcd for C78H79O4N3Si4: C, 75.87; H, 6.45; N, 3.40. Found: C, 74.03; H, 6.21; N, 3.74.

251 Chapter 6 Experimental

Recrystallisation of the adduct from toluene/pentane, toluene/hexane, or slow evaporation of an ether or acetone solution of the adduct failed to produce crystals suitable for X-ray crystallography.

Ph3SiOH.1,5,9-triazacyclododecane Triphenylsilanol (0.241 g, 0.875 mmol, 3 equiv.) was added to a solution of 1,5,9- triazacyclononane (0.050 g, 0.291 mmol, 1 equiv.) in anhydrous toluene (50 cm3). The solution was stirred for 3 hours at 50 °C and then allowed to cool to room temperature. The solution was reduced under vacuum to around one third of its original volume and placed in the refrigerator. After 3 days crystals of unreacted Ph3SiOH had formed. The remaining solution was transferred via a filter stick into another flask and anhydrous pentane (30 cm3) was added. The flask was placed in the freezer and after 2 days thick needle like crystals had formed which were filtered off and air-dried to give Ph3SiOH.1,5,9-triazacyclododecane (0.088 g, 68 %), m.p. 100 °C (softens) -150 °C (melts with dec.). 1H NMR: 5 7.60 - 7.64 (m, 6H, ortho C6H5), 7.32 - 7.41 (m, 911, meta + para

C6H5), 2.69 - 2.73 (m, 12H, HNCH2), 2.0 (s, br, 411, OH + NH), 1.56 - 1.64 (m, 6H, CH2CH2CH2) ppm. 13C NMR: 5 136.19 (ipso C6H5), 135.70 (ortho C6H5), 130.60 (para

C6115), 128.51 (meta C6H5), 49.41 (NHCH 2), 27.76 (CH2CH2CH2) PP111- 29Si NMR: 8 -18.57 ppm. IR (KBr disc, cm-1): 3413, (m, br, OH), 3291 (m, NH),

3180 (m, NH), 3066 (m), 3048 (m), 2921 (m), 2885 (m), 2796 (m), 1488 (m), 1427 (s), 1305 (w), 1263 (w), 1114 (s), 927 (m), 881 (w), 825 (w), 744 (w), 701(s). Anal. Calcd for C27H37ON3Si: C, 72.44; H, 8.33; N, 9.39. Found: C, 71.09; H, 7.65; N, 8.97.

Recrystallisation of the adduct from toluene/pentane, toluene/hexane, or slow evaporation of an ether or acetone solution of the adduct failed to produce crystals suitable for X-ray crystallography.

252 Chapter 6 Experimental

(Ph3SiOH)4.1,4,7,10-tetraazacyclododecane To a solution of 1,4,7,10-tetraazacyclododecane (0.025 g, 0.145 mmol, 1 equiv.) in anhydrous toluene (50 cm3) was added Ph3SiOH (0.160 g, 0.584 mmol, 4 equiv.). The solution was stirred for 3 hours at 50 °C and then allowed to cool to room temperature.

The solution was concentrated to around one third of its original volume under vacuum and placed in the refrigerator. After 5 days no crystals had formed. The volume of the solvent was reduced further to around 2 cm3 and returned to the refrigerator. After another 2 days no crystals had formed so anhydrous pentane (3 cm3) was added and the flask returned to the refrigerator. After 1 week colourless rectangular crystals had formed which were filtered off under vacuum and air dried to give (Ph3SiOH)4.1,4,7,10- tetraazacyclododecane (0.171 g, 92 %), m.p. 84 °C (softens), 136-140 °C (melts with dec.). 1H NMR (CDC13): 7.60 - 7.63 (m, 24H, ortho C6H5), 7.34 - 7.42 (m, 36H, meta + para C6H5), 2.59 (s, 16H, CH2) ppm. 13C NMR: 8 136.40 (ipso C6H5), 135.42 (ortho C6H5), 130.13 (para C6H5), 128.33 (meta C6H5), 48.21 (CH2) ppm. 29Si NMR: 8 -15.02 ppm. IR (KBr disc, cm-1): 3384 (vw, NH), 3311 (m), 3268 (w), 3241 (m), 3066 (m), 3046 (w), 3019 (w), 2996 (w), 2954 (w), 2933 (m), 2856 (w), 1727 (m), 1587 (w), 1483 (w), 1427 (s), 1265 (m), 1116 (s), 997 (w), 917 (m), 854 (m), 836 (m), 806 (m), 740

(m), 709 (s), 700 (s). Anal. Calcd for C801-18404N4Si4: C, 75.19; H, 6.63; N, 4.38. Found: C, 75.37; H, 6.33; N, 4.10. Recrystallisation of the adduct from toluene/pentane, toluene/hexane, or slow evaporation of an ether solution of the adduct failed to produce crystals suitable for X-ray crystallography.

(Ph3SiOH)2.1,4,8,11-tetraazacyclotetradecane Triphenylsilanol (1.376 g, 4.96 mmol, 4 equiv.) was added to a solution of 1,4,8,11-tetraazacyclotetradecane (0.250 g, 1.24 mmol, 1 equiv.) in anhydrous toluene

(50 cm3). The solution was stirred for 4 hours at 50 °C, allowed to cool to room temperature and left overnight at room temperature. Crystals of unreacted silanol had formed. The remaining solution was transferred via a filter stick into another flask and

253 Chapter 6 Experimental anhydrous pentane (100 cm3) was added. The flask was placed in the refrigerator and after 3 days, long thick 'needle' like crystals had formed which were filtered off and air- dried to give (Ph3SiOH)2.1,4,8,11-tetraazacyclododecane (0.759 g, 81 %), m.p. 142- 147 °C dec. 1H NMR: 6 7.60 - 7.64 (m, 12H, ortho C6H5), 7.31 - 7.43 (m, 18H, meta + para C6H5), 3.1 (s, br, 6H, OH + NH), 2.59 - 2.63 (m, 8H, HNCH2CH2CH2NH), 2.52 (s, 8H, HNCH2CH2NH), 1.58 - 1.66 (m, 4H, HNCH2CH2CH2NH) ppm.

13C NMR: 6 137.38 (ipso C6H5), 135.73 (ortho C6H5), 130.27 (para C6H5), 128.37

(meta C6H 5 ), 51.31 (HNCH2CH2NH), 49.34 (HNCH2CH2CH2NH), 29.26 (HNCH2CH2CH2NH) ppm. 29Si NMR: 6 -17.05 ppm. IR (KBr disc, cm-1): 3288 (m,

NH), 3249 (m, NH), 3066 (m), 3046 (m), 3019 (w), 2996 (w), 2929 (m), 2813 (m), -2700 (m, br, OH), 1454 (m), 1427 (s), 1375 (w), 1332 (m), 1213 (m), 1106 (s), 925 (s), 881 (m), 821 (m), 769 (m), 742 (m), 701 (s). Anal. Calcd for C46H56O2N4Si2: C, 73.37; H, 7.50; N, 7.44. Found: C, 72.60; H, 7.02; N, 7.40.

Recrystallisation of the adduct from toluene/pentane, toluene/hexane, or slow evaporation of an ether solution of the adduct failed to produce crystals suitable for X-ray crystallography.

(Ph3SiOH)2.18-crown-6.(H20)2

The preparation was carried out by Method 1 using 18-crown-6 (0.066 g, 0.25 mmol, 0.5 equiv.). Upon addition of hexane (5 cm3) colourless rectangular crystals began to form immediately and the solution was left overnight to allow complete crystallisation. The crystals were isolated by filtration under vacuum and air dried to give (Ph3SiOH)2.18-crown-6.(H20)2 (0.202 g, 95 %), m.p. 66-69 °C. 1H NMR: 8 7.60 - 7.63

(m, 12H, ortho C6H5), 7.34 - 7.42 (m, 1811, meta + para C6H5), 3.66 (s, 24H, CH2) ppm.

13C NMR: S 135.86 (ipso C6H5), 135.66 (ortho C6H5), 130.77 (para C6H5), 128.59 (meta C6H5), 71.38 (CH2) ppm. 29Si NMR: 8 -12.28 ppm. IR (KBr disc, cm-1): 3550 [m,

OH (1120)], 3500 [m, OH (H20)], 3232 [m, br, OH (Ph3SiOH)], 3064 (m), 3043 (m), 2900 (m), 2884 (m), 1972 (w), 1901 (w), 1629 (m), 1587 (m), 1483 (m), 1471 (m),

1453 (m), 1426 (s), 1350 (s), 1300 (w), 1285 (m), 1249 (m), 1110 (s), 997 (m), 962 (s),

254 Chapter 6 Experimental

900 (s), 840 (m), 742 (s), 709 (s). Anal. Calcd for C48H60O10Si2: C, 67.57; H, 7.09. Found: C, 67.54; H, 7.23. The stoichiometry of the adduct remained the same when one equivalent of 18- crown-6 was employed in the preparation. Crystals suitable for X-ray crystallography were obtained from toluene/hexane.

(Ph3SiOH)3.1-aza-12-crown-4

Triphenylsilanol (0.630 g, 2.28 mmol, 4 equiv.) was added to a solution of 1-aza- 12-crown-4 (0.010 g, 0.57 mmol, 1 equiv.) in anhydrous toluene (40 cm3). The solution was stirred for 4 hours at 50 °C, allowed to cool to room temperature and then the volume of toluene reduced under vacuum to about 15 cm3. The flask was placed in the refrigerator and after 2 days large colourless crystals of Ph3SiOH formed. The remaining solution was transferred via a filter stick into another flask and anhydrous pentane (15 cm3) was added. Small colourless crystals of Ph3SiOH immediately began to form on the sides of the flask. The remaining solution was again transferred via a filter stick into another flask and the flask placed in the refrigerator. After 2 weeks small needle-like crystals had formed which were filtered off under vacuum and air dried to give (Ph3SiOH)3.1-aza-12-crown-4 (0.263 g, 55 %), m.p. 41-45 °C dec. 1H NMR: 5 7.57

- 7.63 (m, 18H, ortho C6H5), 7.33 - 7.45 (m, 27H, meta + para C6H5), 3.52 - 3.64 (m, 12H, CH2O), 2.64 - 2.67 (m, 4H, CH2NH). 13C NMR: 8 136.03 (ipso C6H5), 135.67

(ortho C6H5), 130.71 (para C6H5), 128.57 (meta C6H5), 71.64 (HNCH2CH2O), 70.03 (CH2OCH2), 69.81 (HNCH2CH2OCH2), 48.52 (CH2NH). 29Si NMR: 8 -13.05.

IR (KBr disc, cm-1): 3343 (m, br, OH), 3266 (m, NH), 3066 (m), 3048 (m), 3019 (w), 2915 (m), 2865 (m), 1587 (w), 1427 (s), 1116 (s), 1087 (m), 1027 (w), 997 (w), 885 (m), 838 (m), 740 (m), 711 (s), 700 (s). Anal. Calcd for C62H65O6NSi3: C, 74.15; H, 6.53; N, 1.40. Found: C, 73.62; H, 6.31; N, 1.27. Attempts at recrystallising the adduct from toluene/pentane, toluene/hexane and slow evaporation of an acetone solution failed to produce crystals suitable for X-ray crystallography. X-ray structural analysis was attempted on crystals grown by slow

255 Chapter 6 Experimental evaporation of an ether solution of the adduct but the crystals proved too small and the data set too large.

(Ph3SiOH)2.1-aza-15-crown-5 To a solution of 1-aza-15-crown-5 (0.250 g, 1.14 mmol, 1 equiv.) in anhydrous toluene (50 cm3) was added Ph3SiOH (1.573 g, 5.69 mmol, 5 equiv.). The solution was stirred for 4 hours at 50 °C, allowed to cool to room temperature and then the volume of toluene reduced under vacuum to about 20 cm3. The flask was then placed in the refrigerator. After 2 days small colourless crystals of Ph3SiOH crystallised out. The remaining solution was transferred via a filter stick into another flask and anhydrous pentane (20 cm3) was added. The flask was placed in the refrigerator overnight and more small colourless crystals of Ph3SiOH crystallised out. Thick needle-like crystals identified by 1H NMR spectroscopy as (Ph3SiOH)2.1-aza-15-crown-5 had also formed near the top of the flask. The remaining solution was again transferred via a filter stick into another flask and the flask placed in the freezer overnight. Large opaque needle-like crystals formed which were filtered off under vacuum and air dried to give (Ph3SiOH)2.1- aza-15-crown-5 (0.571 g, 65 %), m.p. 57-59 °C dec. 1H NMR: 6 7.60 - 7.63 (m, 12H, ortho C6H5), 7.33 - 7.46 (m, 18H, meta + para C6H5), 3.65 + 3.62 (d, 16H, OCH2), 2.75 - 2.79 (m, 4H, CH2NH) ppm. 13C NMR: 6 136.30 (ipso C6H5), 135.67 (ortho C6H5),

130.61 (para C6H5), 128.51 (meta C6H5), 71.01 (HNCH2CH2O), 70.64 + 70.58 (CH2OCH2CH2OCH 2), 69.99 (HNCH2C H20C H 2), 49.42 (CH2NH) ppm.

29Si NMR: 8 -14.52 ppm. IR (103r disc, cm-1): 3361 (m, br, OH), 3278 (m), 3062 (m),

3018 (m), 2927 (m), 2886 (m), 1587 (w), 1429 (m), 1357 (w), 1118 (s), 1095 (m), 997 (w), 892 (m), 875 (m), 842 (w), 742 (m), 709 (s). Anal. Calcd for C46H53O6NSi2: C, 71.56; H, 6.92; N, 1.81. Found: C, 70.87; H, 6.24; N, 1.73.

Attempts at recrystallising the adduct from toluene/hexane and from slow evaporation of an ether solution failed to produce crystals suitable for X-ray crystallography. In all cases a white powder was formed.

256

Chapter 6 Experimental

6.1.9.3 Attempted preparation of adducts of Ph2Si(OH)2 The attempted preparation of adducts of Ph2Si(OH)2 with amines was carried out by Method 2 (Section 3.6.1). The attempted preparation of adducts with crown ethers was carried out by Method 1 except that the silanol was added to a toluene solution of the crown ether (Section 3.6.1).

6.1.9.4 Attempted preparation of adducts of HO(SiPh2O)3H The attempted preparation of adducts of HO(SiPh2O)3H with amines was carried out by Method 1 (Section 3.6.2).

6.1.9.5 Attempted preparation of adducts of meso-(HOMePhSi)20 and (HOMe2Si)20

The attempted preparation of adducts of meso-(HOMePhSi)20 and (HOMe2Si)20 with amines was carried out by Method 1, except pentane was used instead of hexane (Section 3.6.3).

6.1.9.6 Preparation of adducts of the bulky silanols TsiSi(OH)3 and TsiSiPh2OH

The attempted preparation of adducts of TsiSi(OH)3 and TsiSiPh2OH with amines was carried out by Method 2 (Section 3.6.4).

[TsiSi(OH)3]4.(TMEDA)3 The preparation was carried out by Method 2 using TsiSi(OH)3 (0.239 g,

0.77 mmol, 1 equiv.) and TMEDA (0.089 g, 0.12 cm3, 0.77 mmol, 1 equiv.). Upon removal of the ether solvent on the rotary evaporator colourless crystals began to form. The crystals were filtered off and air dried to give [(TsiSi(OH)3]4.(TMEDA)3 (0.287 g, 94 %), m.p. 62 °C dec. 1H NMR (CDC13): 5 2.38 (s, 3H, CH2), 2.21 (s, 9H, Me), 0.23 (s, 27 H, (Me3Si)3C) ppm. 29Si NMR: 5 -1.34 [(Me3Si)3C], -40.17 (SiOH) ppm. IR (KBr

disc): —3206 (m, v br, OH), 2980 (m), 2957 (m), 2899 (m), 2869 (w), 2832 (m), 2788 (w),

257 Chapter 6 Experimental

1466 (m), 1251 (s), 1164 (w), 1099 (w), 1037 (m), 1023 (m), 878 (s), 864 (s), 837 (s),

675 (m) cm-1. Anal. Calcd for C581-1168012N6Si16: C, 43.80; H, 10.66; N, 5.29. Found: C, 42.40; H, 10.16; N, 4.88. Recrystallisation of the adduct from toluene/hexane and toluene/cyclohexane and by slow evaporation of solvent from both ether and acetone solutions of the adduct failed to produce crystals suitable for X-ray crystallography.

(TsiSiPh2OH)2.TMEDA The preparation was carried out by Method 2 using TsiSiPh2OH (0.331 g, 0.77 mmol, 1 equiv.) and TMEDA (0.089 g, 0.12 cm3, 0.77 mmol, 1 equiv.). Upon removal of the ether solvent on the rotary evaporator colourless crystals began to form. The crystals were filtered off and air dried to give (TsiSiPh2OH)2.TMEDA (0.326 g, 87 %), m.p. 114 °C dec. 1H NMR: 8 7.27 - 7.84 (m, 10H, C6H5), 2.36 (s, 2H, CH2), 2.21 (s, 6H, Me), 0.22 [s, 27H, (Me3Si)3C] ppm. 13C NMR: 8 140.36 (ipso C6H5), 136.36 (ortho

C6H5), 129.70 (para C6H5), 127.83 (meta C6H5), 57.96 (CH2), 46.37 (CH3), 6.94 [RCH3)3SibC) ppm (the central quaternary carbon was not observed). IR (KBr disc, cm-1): 3074 (m), 3033 (m), 2982 (s), 2957 (s), 2899 (m), 2834 (m), 2787 (m), 1467 (m), 1426 (m), 1252 (s), 1100 (m), 894 (m), 853 (s), 834 (s), 799 (m), 741 (m), 704 (s), 677 (m) (OH band obscured by CH peaks). Anal. Calcd for C50H92O2N2Si8: C, 61.44; H, 9.49; N, 2.87. Found: C, 61.26; H, 9.32; N, 2.85. The adduct was recrystallised from toluene/hexane and toluene/cyclohexane and by slow evaporation of solvent from both ether and acetone solutions of the adduct. Crystals suitable for X-ray crystallography were obtained by slow evaporation of solvent from an ether solution of the adduct.

6.1.9.7 Attempted preparations of adducts of (-)MePhNaphthSiOH The attempted preparation of adducts of (-)MePhNaphthSiOH with amines was carried out by Method 2 (Section 3.6.5). Slow evaporation of the solvent from a chloroform solution of the silanol and excess dioxane also failed to produce an adduct.

258 Chapter 6 Experimental

6.1.9.8 Attempted preparation of adducts of tBuMe2SiOH An excess of amine, TMEDA, pyridine or aniline, was added to tBuMe2SiOH and the solutions obtained stirred under nitrogen for a couple of days. The excess amine was then removed under vacuum to leave just tBuMe2SiOH and no adducts. The solid, either amino acid N-glycylglycine or pentaerythritol, was added to an excess of tBuMe2SiOH and the reaction mixture stirred for a few days. The reaction mixture remained heterogeneous throughout. The tBuMe2SiOH was removed from the solid by cannulation. The solid was analysed by FTIR spectroscopy and shown to be either N-glycylglycine or pentaerythritol respectively and the liquid analysed by 1H NMR spectroscopy which showed that it consisted of the silanol only.

6.1.9.9 Attempted preparation of adducts of cis-cis-cist(HO)PhSiOl4 i) With crown ethers The crown ethers employed were 12-crown-4 and 15-crown-5.

cis-cis-cis-[(HO)PhSiO] 4 (0.212g, 3.84x10-4 mol, 1 equiv.) was dissolved in ether (2 cm3) to give a colourless solution. The crown ether (3.84x10-4 mol, 1 equiv.) was then added with stirring. In the case of 12-crown-4 the solution immediately went turbid. After stirring for a couple of minutes hexane was added and, in all cases, a white precipitate formed which was filtered off. The white precipitate was analysed by 1H NMR and FTIR spectroscopy. Although peaks due to the crown ethers Were present in all spectra, integration of the 1H NMR spectra varied each time the experiment was repeated and a consistent stoichiometry could not be reached. ii) with barium salts A suspension of BaC12.2H20 (0.24 g, 1.0 mmol) in methanol (2 cm3) was added to a solution of cis-cis-cis-[(HO)PhSiO]4 (0.55 g, 1.0 mmol) in methanol (2 cm3) with vigorous stirring. The mixture was left to stir for 3 hours, during which time the mixture remained heterogeneous. The solution was then filtered under vacuum to give a white solid and the filtrate concentrated on the rotary evaporator until white crystals began to

259 Chapter 6 Experimental appear. The crystals were collected by vacuum filtration. Analysis of both the solids collected, by FTIR spectroscopy, was inconclusive as to whether they just contained a mixture of the two starting materials or whether any complexation had occurred. Similar results were obtained when Ba(OH)2.8H20 was employed.

6.1.10 Attempts at co-crystallising mixtures of silanols This was carried out by both Method 1 and Method 2. Molar ratios of 1:1 for (HOPh2Si)20 and (HOMe2S020, both 2:1 and 1:1 for (HOPh2Si)20 and Ph3SiOH and

2:1 for (HOMe2Si)20 and Ph3SiOH were employed. Analysis by melting point and by

1H NMR and FTIR spectroscopy showed that in all cases just mixtures of the two silanols and not new stoichiometric adducts were present.

6.2 Infrared spectroscopic studies 6.2.1 Materials

The silanols were either prepared by the methods described previously in Section 6.1, obtained from Aldrich or donated (Section 6.1.4) and used without further purification. For the variable temperature infrared studies, to obtain thermodynamic data, Ph3SiOH was recrystallised from anhydrous toluene/pentane and dried under vacuum for 24 hours prior to storage over anhydrous silica gel in a vacuum dessicator. Anhydrous CC14, DMSO, pyridine, di-n-butylether and dioxane, water content <0.005 % were obtained from Aldrich packaged under nitrogen in Sure /SealTM bottles. Diethyl ether and THE were distilled from sodium wire and benzophenone prior to use. Mesitylene was stored over 4A molecular sieves.

The cyclic siloxanes, e.g. D3 were donated by the Dow Corning Corporation. Silyl ethers and alkenes were purchased from Aldrich Chemical Co. or Lancaster Synthesis.

260 Chapter 6 Experimental

6.2.2 Qualitative studies of the hydrogen bonding interactions of silanols with suitable bases and themselves

The infrared spectra were recorded on a Mattson Research Series spectrometer in the OH stretching region (3800 - 3000 cm-1) using a Graseby/Specac 1500 Variable Pathlength cell, variable from 0 - 6 mm, with NaC1 windows. The instrument controls were set at a resolution of 4.

The pathlength was set at 1 mm for silanol concentrations of 0.01 - 0.03 M in CC14 and at 6 mm for silanol concentrations of 0.005 M in CC14. Frequencies of the bands due to the self-association of silanols were recorded at a concentration of 0.03 M. The hydrogen bonding interactions of silanols with bases were examined at concentrations at which the degree of self-association of the silanol was negligible, between 0.005 and 0.01 M (Table 2.1). The bases were used at a concentration of

0.05 M, silyl ethers at 0.5 M, and siloxanes and alkenes at 1 M. Background spectra were recorded of the appropriate concentration of base in CC14.

The solutions of tBuMe2SiOH with bases were prepared under nitrogen in flame dried flasks and the solution cell filled under nitrogen to prevent moisture reacting with tBuMe2SiOH.

For the studies of the hydrogen-bonding interactions between mixtures of silanols, the concentrations at which the degree of intermolecular hydrogen-bonding was negligible were 0.01 M for Ph3SiOH and 0.005 M for (HOPh2Si)20 and (HOMe2Si)20. The silanols in excess were at concentrations of 0.05 M. The experiments were repeated at least three time to ensure consistency.

6.2.3 Determination of thermodynamic data for hydrogen bonded adducts of Ph3SiOH

A Graseby/Specac Variable Temperature infrared apparatus controlled by a Temperature Controller (± 0.1 °C) was used for these studies.

Infrared spectra were recorded in the OH stretching region (3800 - 3000 cm-1) of CC14 solutions containing a fixed concentration of Ph3SiOH and a series of increasing

261 Chapter 6 Experimental concentrations of ether. At each ether concentration the temperature was varied from 25 to 60 °C in increments of 5 °C. The instrument controls were set at a resolution of 4 and 32 scans were recorded at each temperature.

Ph3SiOH was used at a concentration of 0.01 M at which the degree of self- association was negligible. The ethers were used in the concentration range of 0.1 to 0.6 M. The solutions were prepared in volumetric flasks fitted with a Young's adaptor which were oven dried overnight and cooled under a stream of dry nitrogen prior to use. The solution cell (NaCl windows, 1 mm pathlength) was flushed with nitrogen and then filled with solution under nitrogen. The sides of the solution cell were lightly coated with silicone grease to improve thermal contact with the variable temperature apparatus and the apparatus evacuated. Background spectra of the appropriate concentration of ether in CC14 were recorded.

6.3 170 NMR studies 6.3.1 Instrumentation

At Imperial College 170 NMR spectra were recorded on a JEOL EX-270 FT- NMR spectrometer operating at 36.585 MHz. The chemical shifts are in ppm relative to H2O as the external standard. The number of collected data points was 4096, which with a field sweep width of 1250 ppm gave rise to an acquisition time of 37 ms and 26.8 Hz resolution per point ( the relative broadness of the lines being measured allows the collection of data with relatively low digital resolution ). A 101.ts (90°) pulse width and a pulse delay of 0.1s were used. Digital resolution was restored at the processing stage by twice zero-filling the data ( equivalent to having collected 16384 data points ). The very broad rolling baseline and peaks caused by the glass tube and insert were removed by collecting the data using a Carr-Purcel-Meiboom-Gill pulse sequence ( CPMG ). A spin echo of the peaks to be observed is seen, but the very broad unwanted signals relax before the data is acquired.

At Dow Corning, Barry, 170 NMR spectra were recorded on a JEOL 400 NMR spectrometer operating at 54.2 MHz. A pulse width of lOgs (90°) and a pulse delay of

262 Chapter 6 Experimental

0.1s were used. 32768 data points were employed with an acquisition time of 1310 ms and resolution of 0.76 Hz. A broadening factor of 10 was employed at the processing stage.

Spectra of natural abundance 170 silanols were recorded of saturated solutions of the silanol in anhydrous toluene at 80 °C, 105 scans. Spectra of 10 % 170 enriched Ph3SiOH were recorded as 20 % by weight solutions of the silanol in the required solvent at room temperature, 103 - 104 scans.

6.3.2 Solvents

Diethyl ether, THF, toluene and methanol were dried by methods described previously (Section 6.1.3). Anhydrous CC14, Et2NH, pyridine and 1,4-dioxane, water content <0.005 %, were obtained from Aldrich packaged under nitrogen in Sure /Sea1TM bottles. Benzonitrile, DMF, piperidine, acetophenone, MIBK and CDC13 were dried over 4A molecular sieves.

10% 170 enriched H2O (160: 170: 180, 32.2: 10.5: 57.3) was obtained from Goss Scientific.

6.3.3 Silanols

Natural abundance 170 silanols were either prepared by the methods described previously in Section 6.1, obtained from Aldrich or donated (Section 6.1.4).

Preparation of 170 labelled triphenylsilanol

Modified method of Apblett et A 340 Water (0.13 cm3, 0.13 g, 7.8 mmol) enriched in 170 (10%) was added dropwise with stirring to a solution of triphenylsilylchloride (2.16 g, 7.3 mmol) in thy THF (4.0 cm3). The solution was left to stir for a further 8 hours and then the solvent was removed under vacuum to leave an off white solid. The solid was recrystallised from 50/50 diethyl ether/pentane (9.2 cm3) at -25 °C to give colourless crystals of triphenylsilanol (1.42 g, 71 %), m.p. 155 °C. 1H NMR (CDC13): 5 7.60 - 7.67 (m, 6H, ortho C6H5), 7.34 - 7.46

263 Chapter 6 Experimental

(m, 9H, meta + para C6H5), -2.35 (s, br, OH) ppm. 170 NMR (CDC13): 8 8.2 ppm.

IR (KBr disc): 3255 (m, br, OH), 3068 (m), 3050 (w), 2988 (w), 1959 (w), 1887 (w), 1822 (w), 1772 (vw), 1589 (m), 1484 (m), 1427 (s), 1261 (w), 1187 (w), 1118 (s), 1068 (w), 1027 (w), 997 (m), 852 (s), 835 (s), 738 (m), 711 (s), 698 (s).

6.3.4 Exchange reactions between Ph3SiOH and 10 % 170 enriched 1120. Into a Young's NMR tube was placed Ph3SiOH (0.11 g, 0.40 mmol, 1 equiv.), anhydrous 1,4-dioxane (0.8 cm3) and 10 % 170 enriched H2O (0.10 g, 0.1 cm3, 5.56 mmol, 14 equiv.). The NMR tube was placed in a silicone oil bath and maintained at 80

°C. Attempts were made to monitor the reaction by 170 NMR spectroscopy but any changes in the weak peak due to Ph3SiOH were difficult to observe in comparison to the very large peak due to the excess of 170 enriched H2O. After 5 weeks the solvents were removed under vacuum, the white solid obtained further dried under vacuum overnight and a 170 NMR recorded of a 20 % by weight solution in CDC13. A 170 NMR spectrum was obtained after 24,000 scans ( -1.5 hours) at room temperature which indicated the presence of significant 170H exchange. 1H NMR spectroscopy revealed that a 8:1 Ph3SiOH:dioxane adduct had been formed. 170 NMR (CDC13): 8 7.8 ppm. 1H NMR (CDC13): 6 7.60 - 7.65 (m, 48H, ortho C6H5), 7.34 - 7.47 (m, 72H, meta + para C6H5),

3.64 (s, 8H, CH2), 2.76 (s, br, 8H, OH) ppm. IR (KBr disc, cm-1): 3220 (m, br, asymm., OH), 3066 (m), 3050 (w), 3023 (w), 1961 (w), 1889 (w), 1824 (w), 1774 (w), 1589 (w), 1484 (w), 1427 (s), 1118 (s), 997 (w), 846 (m), 817 (m), 740 (m), 711 (s), 698 (s). The same experimental procedure was repeated for 2 weeks. Again, a 20 % by weight solution in CDC13 produced a 170 NMR spectrum after 42,148 scans (-1.75 hours) at room temperature. In this case, however, 1H NMR spectroscopy revealed that a 6:1 Ph3SiOH:dioxane adduct had been formed. 170 NMR (CDC13): 8 7.8 ppm. 1H NMR (CDC13): 8 7.59 - 7.64 (m, 36H, ortho C6H5), 7.33 - 7.46 (m, 54H, meta + para C6H5),

3.67 (s, 8H, CH2), 2.15 (s, br, 6H, OH) ppm. IR (KBr disc, cm-1): 3218 (m, br, asymm., OH), 3066 (m), 3050 (w), 3023 (w), 1961 (w), 1891 (w), 1822 (w), 1776 (w), 1589 (w),

1484 (w), 1427 (s), 1118 (s), 997 (w), 854 (m), 823 (m), 740 (m), 711 (s), 698 (s).

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285 APPENDIX Appendix

Crystallographic data for (Me2SiO)5, D5

A capillary containing a sample of D5 was mounted on the goniometer head of a Stoe Stadi-4 diffractometer equipped with an Oxford Cryosystems low-temperature device. After establishing a solid-liquid equilibrium within the sample at 219 K it was held at this temperature for 30 min, and then at 218 K and 217 K for the same period. The sample was then cooled to 110 K and data collection performed in the usual way.

Table 1. Crystal data and structure refinement for D5 at 110(2) K.

Empirical formula C10113005Si5 Formula weight 370.79 Wavelength 0.71073 A Crystal system Triclinic Space group Pr Unit cell dimensions a = 8.255(4) A alpha = 87.63(4)0 b = 9.747(s) A beta = 75.08(3)° c = 13.800(7) A gamma = 77.59(3)° Volume 1047.7(9) A3 Number of reflections for cell 28 (12 < theta < 13 °) Z 2 Density (calculated) 1.175 Mg/m3 Absorption coefficient 0.352 mm-1 F(000) 400 Crystal description Colourless cylinder Crystal size 0.46 x 0.46 x 0.21 Theta range for data collection 2.61 to 25.01 ° Index ranges -9 .11.9,-11 11, 0 1 16 Reflections collected 4141 Independent reflections 3692 [R(int) = 0.0260] Scan type omega-theta Data / restraints / parameters 3669/0/192 (Full-matrix least-squares on F2) Goodness-of-fit on F2 1.067 Conventional R [F>4a(F)] R1 = 0.0406 [2912 data] R indices (all data) R1 = 0.0612, wR2 = 0.1078 Extinction coefficient 0.0028(14) Final maximum delta/sigma -0.001 Largest cliff. peak and hole 0.384 and -0.268 eA-3

287 Appendix

Table 2. Bond lengths (A), angles and torsions (*) for D5.

Si(1)-0(1) 1.619(2) Si(3)-C(32) 1.842(3) Si(1)-0(5) 1.628(2) Si(3)-C(31) 1.849(3) Si(1)-C(11) 1.834(3) 0(3)-Si(4) 1.624(2) Si(1)-C(12) 1.847(3) Si(4)-0(4) 1.637(2) 0(1)-Si(2) 1.627(2) Si(4)-C(42) 1.850(3) Si(2)-0(2) 1.630(2) Si(4)-C(41) 1.852(4) Si(2)-C(21) 1.840-3) 0(4)-Si(5) 1.632(2) Si(2)-C(22) 1.845(4) Si(5)-0(5) 1.631(2) 0(2)-Si(3) 1.628(2) Si(5)-C(52) 1.846(3) Si(3)-0(3) 1.621(2) Si(5)-C(51) 1.846(3)

0(1)-Si(1)-0(S) 109.17(12) 0(2)-Si(3)-C(31) 108.03(14) 0(1)-Si(1)-C(11) 109.80(15) C(32)-Si(3)-C(31) 112.40(15) 0(5)-Si(1)-C(11) 107.62(14) Si(3)-0(3)-Si(4) 155.5(2) 0(1)-Si(1)-C(12) 108.21(15) 0(3)-Si(4)-0(4) 109.32(12) 0(5)-Si(1)-C(12) 110.22(15) 0(3)-Si(4)-C(42) 106.68(14) C(11)-Si(1)-C(12) 111.8(2) 0(4)-Si(4)-C(42) 108.93(15) Si(1)-0(1)-Si(2) 156.8(2) 0(3)-si(4)-C(41) 111.2(2) 0(1)-Si(2)-0(2) 109.28(13) 0(4)-Si(4)-C(41) 107.45(14) 0(1)-Si(2)-C(21) 108.05(15) C(42)-Si(4)-C(41) 113.2(2) 0(2)-Si(2)-C(21) 108.10(15) Si(5)-0(4)-Si(4) 138.64(14) 0(1)-Si(2)-C(22) 110.3(2) 0(5)-Si(5)-0(4) 109.11(12) 0(2)-Si(2)-C(22) 108.88(15) 0(5)-Si(5)-C(52) 109.83(14) C(21)-Si(2)-C(22) 112.2(2) 0(4)-Si(5)-C(52) 107.56(14) Si(3)-0(2)-Si(2) 144.2(2) 0(5)-Si(5)-C(51) 108.20(14) 0(3)-Si(3)-0(2) 109.36(13) 0(4)-Si(5)-C(51) 109.61(14) 0(3)-Si(3)-C(32) 108.51(14) C(52)-Si(5)-C(51) 112.5(2) 0(2)-Si(3)-C(32) 110.28(14) Si(1)-0(5)-Si(5) 144.91(15) 0(3) Si(3)-C(31) 108.19(14)

0(5)-Si(1)-0(1)-Si(2) 86.2(4) C(11)-Si(1)-0(1)-Si(2) -31.6(4) C(12)-Si(1)-0(1)-Si(2) -153.8(4) Si(1)-0(1)-Si(2)-0(2) -84.7(4) Si(1)-0(1)-Si(2)-C(21) 157.9(4) Si(1)-0(1)-Si(2)-C(22) 35.0(4) 0(1)-Si(2)-0(2)-Si(3) 35.6(3) C(21)-Si(2)-0(2)-Si(3) 152.9(3) C(22)-Si(2)-0(2)-Si(3) -84.9(3) Si(2)-0(2)-Si(3)-0(3) -82.0(3) Si(2)-0(2)-Si(3)-C(32) 37.3(3) Si(2)-0(2)-Si(3)-C(31) 160.5(3) 0(2)-Si(3)-0(3)-Si(4) -5.5(4) C(32)-Si(3)-0(3)-Si(4) -125.8(4) C(31)-Si(3)-0(3)-Si(4) 112.0(4) Si(3)-0(3)-Si(4)-0(4) 89.2(4) Si(3)-0(3)-Si(4)-C(42) -153.2(4) Si(3)-0(3)-Si(4)-C(41) -29.3(4) 0(3)-Si(4)-0(4)-Si(5) 23.5(3) C(42)-Si(4)-0(4)-Si(5) -92.8(2) C(41)-Si(4)-0(4)-Si(5) 144.3(2) Si(4)-0(4)-Si(5)-0(5) -74.5(2) Si(4)-0(4)-Si(5)-C(52) 166.4(2) Si(4)-0(4)-Si(S)-C(S1) 43.8(3) 0(1)-Si(1)-0(S)-Si(S) 82.7(3)

288 Appendix

C(11)-Si(1)-0(5)-Si(5) -158.2(2) C(12)-Si(1)-O(5)-Si(5) -36.0(3) 0(4)-Si(5)-0(5)-Si(1) -54.9(3) C(52)-Si(5)-O(5)-Si(1) 62.7(3) C(51)-Si(5)-O(5)-Si(1) -174.1(2)

289 Appendix

Crystallographic data for [(HOPh2Si)20]4.(Et2NH)2

Table 1. Crystal data and structure refinement for [(HOPh2Si)20]4.(Et2NH)2.

Empirical formula C104H110N2O12Sig Formula weight 1804.66 Temperature 293(2) K Diffractometer used Siemens P4/PC Wavelength 1.54178 A Crystal system Triclinic Space group PT Unit cell dimensions a = 14.8607(12) A alpha = 73.270(11)° b = 17.893(2) A beta = 72.581(8)° c = 21.722(3) A gamma = 65.574(9)° Volume, Z 4927.6(10) A3, 2 Density (calculated) 1.216 Mg/m3 Absorption coefficient 1.509 mm-1 F(000) 1912 Crystal morphology/size Colourless block,0.50 x 0.27 x 0.17 mm 0 range for data Collection 2.17 to 60.00° Limiting indices -16 5._ h 5_ 16, -19 13, -23 5_ 1 24 Reflections Collected 15205 Independent reflections 14554 (Rint = 0.0667) Observed reflections 7581 [F>4a(F)] Absorption correction None Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 14552 / 4 / 1083 Goodness-of-fit on F2 1.028 Final R indices [1>2a(I)] R1 = 0.0984, wR2 = 0.2376 R indices (all data) R1 = 0.1766, wR2 = 0.2978 Largest diff. peak and hole 0.452 and -0.617 eA-3

290 Appendix

Table 2. Bond lengths (A) and angles (°) for [(HOPh2Si)20]4-(Et2NH)2-

Si(1)-0(1) 1.587(6) Si(1)-0(2) 1.632(6) Si(1)-C(10') 1.86(2) Si(1)-C(10) 1.883(9) Si(1)-C(4) 1.890(4) 0(2)-Si(3) 1.625(6) Si(3)-0(3) 1.626(6) Si(3)-C(16) 1.867(6) Si(3)-C(22) 1.873(5) C(4)-C(S) 1.39 C(4)-C(9) 1.39 C(5)-C(6) 1.39 C(6)-C(7) 1.39 C(7)-C(8) 1.39 C(8)-C(9) 1.39 C(10)-C(11) 1.39 C(10)-C(15) 1.39 C(11)-C(12) 1.39 C(12)-C(13) 1.39 C(13)-C(14) 1.39 C(14)-C(15) 1.39 C(10')-C(11') 1.39 C(10')-C(15') 1.39 C(11')-C(12') 1.39 C(12')-C(13') 1.39 C(13')-C(14') 1.39 C(14')-C(15') 1.39 C(16)-C(17) 1.39 C(16)-C(21) 1.39 C(17)-C(18) 1.39 C(18)-C(19) 1.39 C(19)-C(20) 1.39 C(20)-C(21) 1.39 C(22)-C(23) 1.39 C(22)-C(27) 1.39 C(23)-C(24) 1.39 C(24)-C(25) 1.39 C(25)-C(26) 1.39 C(26)-C(27) 1.39 Si(30)-0(30) 1.610(6) Si(30)-0(31) 1.632(6) Si(30)-C(33) 1.880(4) Si(30)-C(39) 1.891(5) 0(31)-Si(32) 1.615(6) Si(32)-0(32) 1.612(5) Si(32)-C(51) 1.876(5) Si(32)-C(45) 1.878(5) C(33)-C(34) 1.39 C(33)-C(38) 1.39 C(34)-C(35) 1.39 C(35)-C(36) 1.39 C(36)-C(37) 1.39 C(37)-C(38) 1.39 C(39)-C(40) 1.39 C(39)-C(44) 1.39 C(40)-C(41) 1.39 C(41)-C(42) 1.39 C(42)-C(43) 1.39 C(43)-C(44) 1.39 C(45)-C(46) 1.39 C(45)-C(50) 1.39 C(46)-C(47) 1.39 C(47)-C(48) 1.39 C(48)-C(49) 1.39 C(49)-C(50) 1.39 C(51)-C(52) 1.39 C(51)-C(56) 1.39 C(52)-C(53) 1.39 C(53)-C(54) 1.39 C(54)-C(55) 1.39 C(55)-C(56) 1.39 C(200)-C(201) 1.43(2) C(201)-N(202) 1.44(2) N(202)-C(203) 1.45(2) C(203)-C(204) 1.48(2) Si(60)-0(60) 1.608(6) Si(60)-0(61) 1.615(6) Si(60)-C(69) 1.877(5) Si(60)-C(63) 1.888(5) 0(61)-Si(62) 1.646(6) Si(62)-0(62) 1.618(6) Si(62)-C(75) 1.873(5) Si(62)-C(81) 1.878(5) C(63)-C(64) 1.39 C(63)-C(68) 1.39 C(64)-C(65) 1.39 C(65)-C(66) 1.39 C(66)-C(67) 1.39 C(67)-C(68) 1.39 C(69)-C(70) 1.39 C(69)-C(74) 1.39 C(70)-C(71) 1.39 C(71)-C(72) 1.39 C(72)-C(73) 1.39 C(73)-C(74) 1.39 C(75)-C(76) 1.39 C(75)-C(80) 1.39 C(76)-C(77) 1.39 C(77)-C(78) 1.39 C(78)-C(79) 1.39 C(79)-C(80) 1.39 C(81)-C(82) 1.39 C(81)-C(86) 1.39 C(82)-C(83) 1.39 C(83)-C(84) 1.39 C(84)-C(85) 1.39 C(85)-C(86) 1.39 Si(90)-0(91) 1.608(6) Si(90)-0(90) 1.636(6) Si(90)-C(93) 1.85(2)

291 Appendix

Si(90)-C(99) 1.867(5) Si(90)-C(93') 1.91(2) 0(91)-Si(92) 1.649(5) 0(92)-Si(92) 1.597(6) Si(92)-C(11') 1.87(2) Si(92)-C(105) 1.888(5) Si(92)-C(111) 1.906(12) C(93)-C(94) 1.39 C(93)-C(98) 1.39 C(94)-C(95) 1.39 C(95)-C(96) 1.39 C(96)-C(97) 1.39 C(97)-C(98) 1.39 C(93')-C(94') 1.39 C(93')-C(98') 1.39 C(94')-C(95') 1.39 C(95')-C(96') 1.39 C(96')-C(97') 1.39 C(97')-C(98') 1.39 C(99)-C(100) 1.39 C(99)-C(104) 1.39 C(100)-C(101) 1.39 C(101)-C(102) 1.39 C(102)-C(103) 1.39 C(103)-C(104) 1.39 C(105)-C(106) 1.39 C(105)-C(110) 1.39 C(106)-C(107) 1.39 C(107)-C(108) 1.39 C(108)-C(109) 1.39 C(109)-C(110) 1.39 C(111)-C(112) 1.39 C(111)-C(116) 1.39 C(112)-C(113) 1.39 C(113)-C(114) 1.39 C(114)-C(115) 1.39 C(115)-C(116) 1.39 C(11')-C(12') 1.39 C(11')-C(16') 1.39 C(12')-C(13') 1.39 C(13')-C(14') 1.39 C(14')-C(15') 1.39 C(15')-C(16') 1.39 C(300)-C(301) 1.33(2) C(301)-N(302) 1.50(2) N(302)-C(303) 1.53(2) C(303)-C(304) 1.40(2)

0(1)-Si(1)-0(2) 112.6(3) 0(1)-Si(1)-C(10') 110.9(8) 0(2)-Si(1)-C(10') 106.3(8) 0(1)-Si(1)-C(10) 111.6(5) 0(2)-Si(1)-C(10) 109.0(5) 0(1)-Si(1)-C(4) 110.8(3) 0(2)-Si(1)-C(4) 106.3(3) C(10')-Si(1)-C(4) 109.8(8) C(10)-Si(1)-C(4) 106.2(5) Si(3)-0(2)-Si(1) 142.3(4) 0(2)-Si(3)-0(3) 112.9(3) 0(2)-Si(3)-C(16) 108.2(3) 0(3)-Si(3)-C(16) 110.4(3) 0(2)-Si(3)-C(22) 108.9(3) 0(3)-Si(3)-C(22) 106.5(3) C(16)-Si(3)-C(22) 110.0(3) C(5)-C(4)-C(9) 120.0 C(5)-C(4)-Si(1) 121.0(3) C(9)-C(4)-Si(1) 118.8(3) C(6)-C(5)-C(4) 120.0 C(7)-C(6)-C(5) 120.0 C(8)-C(7)-C(6) 120.0 C(7)-C(8)-C(9) 120.0 C(8)-C(9)-C(4) 120.0 C(11)-C(10)-C(15) 120.0 C(11)-C(10)-Si(1) 120.8(8) C(15)-C(10)-Si(1) 119.1(8) C(12)-C(11)-C(10) 120.0 C(11)-C(12)-C(13) 120.0 C(14)-C(13)-C(12) 120.0 C(13)-C(14)-C(15) 120.0 C(14)-C(15)-C(10) 120.0 C(11')-C(10')-C(15') 120.0 C(11')-C(101)-Si(1) 116.2(13) C(15')-C(10')-Si(1) 123.3(13) C(12')-C(11')-C(10') 120.0 C(11')-C(12')-C(13') 120.0 C(14')-C(13')-C(12') 120.0 C(13')-C(14')-C(15') 120.0 C(14')-C(15')-C(10') 120.0 C(17)-C(16)-C(21) 120.0 C(17)-C(16)-Si(3) 120.7(4) C(21)-C(16)-Si(3) 119.3(4) C(18)-C(17)-C(16) 120.0 C(17)-C(18)-C(19) 120.0 C(20)-C(19)-C(18) 120.0 C(21)-C(20)-C(19) 120.0 C(20)-C(21)-C(16) 120.0 C(23)-C(22)-C(27) 120.0 C(23)-C(22)-Si(3) 121.2(4) C(27)-C(22)-Si(3) 118.7(4) C(24)-C(23)-C(22) 120.0 C(23)-C(24)-C(25) 120.0 C(26)-C(25)-C(24) 120.0 C(27)-C(26)-C(25) 120.0 C(26)-C(27)-C(22) 120.0 0(30)-Si(30)-0(31) 113.5(3) 0(30)-Si(30)-C(33) 107.8(3) 0(31)-Si(30)-C(33) 106.5(3) 0(30)-Si(30)-C(39) 110.1(3) 0(31)-Si(30)-C(39) 108.0(3) C(33)-Si(30)-C(39) 110.8(3) Si(32)-0(31)-Si(30) 145.5(4) 0(32)-Si(32)-0(31) 112.4(3) 0(32)-Si(32)-C(51) 109.0(3) 0(31)-Si(32)-C(51) 108.5(3)

292 Appendix

0(32)-Si(32)-C(45) 109.4(3) 0(31)-Si(32)-C(45) 108.3(3) C(51)-Si(32)-C(45) 109.3(3) C(34)-C(33)-C(38) 120.0 C(34)-C(33)-Si(30) 119.7(3) C(38)-C(33)-Si(30) 120.3(3) C(35)-C(34)-C(33) 120.0 C(34)-C(35)-C(36) 120.0 C(35)-C(36)-C(37) 120.0 C(38)-C(37)-C(36) 120.0 C(37)-C(38)-C(33) 120.0 C(40)-C(39)-C(44) 120.0 C(40)-C(39)-Si(30) 118.7(3) C(44)-C(39)-Si(30) 121.3(3) C(41)-C(40)-C(39) 120.0 C(40)-C(41)-C(42) 120.0 C(43)-C(42)-C(41) 120.0 C(42)-C(43)-C(44) 120.0 C(43)-C(44)-C(39) 120.0 C(46)-C(45)-C(50) 120.0 C(46)-C(45)-Si(32) 117.7(3) C(50)-C(45)-Si(32) 122.3(3) C(45)-C(46)-C(47) 120.0 C(48)-C(47)-C(46) 120.0 C(47)-C(48)-C(49) 120.0 C(48)-C(49)-C(50) 120.0 C(49)-C(50)-C(45) 120.0 C(52)-C(51)-C(56) 120.0 C(52)-C(51)-Si(32) 119.1(4) C(56)-C(51)-Si(32) 120.9(4) C(51)-C(52)-C(53) 120.0 C(52)-C(53)-C(54) 120.0 C(55)-C(54)-C(53) 120.0 C(56)-C(55)-C(54) 120.0 C(55)-C(56)-C(51) 120.0 C(200)-C(201)-N(202) 116.9(14) C(201)-N(202)-C(203) 115.5(12) N(202)-C(203)-C(204) 115.8(12) 0(60)-Si(60)-0(61) 113.5(3) 0(60)-Si(60)-C(69) 108.6(3) 0(61)-Si(60)-C(69) 107.9(3) 0(60)-Si(60)-C(63) 109.2(3) 0(61)-Si(60)-C(63) 107.7(3) C(69)-Si(60)-C(63) 109.9(3) Si(60)-0(61)-Si(62) 140.5(4) 0(62)-Si(62)-0(61) 113.9(3) 0(62)-Si(62)-C(75) 106.1(3) 0(61)-Si(62)-C(75) 108.0(3) 0(62)-Si(62)-C(81) 111.7(4) 0(61)-Si(62)-C(81) 107.2(3) C(75)-Si(62)-C(81) 109.9(3) C(64)-C(63)-C(68) 120.0 C(64)-C(63)-Si(60) 122.4(4) C(68)-C(63)-Si(60) 117.6(4) C(65)-C(64)-C(63) 120.0 C(66)-C(65)-C(64) 120.0 C(67)-C(66)-C(65) 120.0 C(66)-C(67)-C(68) 120.0 C(67)-C(68)-C(63) 120.0 C(70)-C(69)-C(74) 120.0 C(70)-C(69)-Si(60) 120.2(3) C(74)-C(69)-Si(60) 119.7(3) C(71)-C(70)-C(69) 120.0 C(72)-C(71)-C(70) 120.0 C(71)-C(72)-C(73) 120.0 C(74)-C(73)-C(72) 120.0 C(73)-C(74)-C(69) 120.0 C(76)-C(75)-C(80) 120.0 C(76)-C(75)-Si(62) 120.6(4) C(80)-C(75)-Si(62) 119.3(4) C(75)-C(76)-C(77) 120.0 C(78)-C(77)-C(76) 120.0 C(77)-C(78)-C(79) 120.0 C(78)-C(79)-C(80) 120.0 C(79)-C(80)-C(75) 120.0 C(82)-C(81)-C(86) 120.0 C(82)-C(81)-Si(62) 121.0(4) C(86)-C(81)-Si(62) 119.0(4) C(83)-C(82)-C(81) 120.0 C(82)-C(83)-C(84) 120.0 C(85)-C(84)-C(83) 120.0 C(84)-C(85)-C(86) 120.0 C(85)-C(86)-C(81) 120.0 0(91)-Si(90)-0(90) 112.4(3) 0(91)-Si(90)-C(93) 113.3(8) 0(90)-Si(90)-C(93) 106.5(9) 0(91)-Si(90)-C(99) 108.2(3) 0(90)-Si(90)-C(99) 106.2(3) C(93)-Si(90)-C(99) 110.0(8) 0(91)-Si(90)-C(93') 102.0(8) 0(90)-Si(90)-C(93') 115.4(9) C(99)-Si(90)-C(93') 112.6(8) Si(90)-0(91)-Si(92) 143.9(4) 0(92)-Si(92)-0(91) 112.4(3) 0(92)-Si(92)-C(11') 110.3(9) 0(91)-Si(92)-C(11') 104.3(11) 0(92)-Si(92)-C(105) 112.6(3) 0(91)-Si(92)-C(105) 104.9(3) C(11)-Si(92)-C(105) 111.9(10) 0(92)-Si(92)-C(111) 110.8(6) 0(91)-Si(92)-C(111) 108.3(7) C(105)-Si(92)-C(111) 107.5(5) C(94)-C(93)-C(98) 120.0 C(94)-C(93)-Si(90) 117.7(14) C(98)-C(93)-Si(90) 122.0(14) C(95)-C(94)-C(93) 120.0 C(94)-C(95)-C(96) 120.0 C(97)-C(96)-C(95) 120.0 C(96)-C(97)-C(98) 120.0 C(97)-C(98)-C(93) 120.0 C(94')-C(93')-C(98') 120.0 C(94')-C(93')-Si(90) 120(2) C(98')-C(93')-Si(90) 120(2) C(95')-C(94')-C(93') 120.0 C(94')-C(95')-C(96') 120.0 C(95')-C(96')-C(97') 120.0

293 Appendix

C(98')-C(97')-C(96') 120.0 C(97')-C(98')-C(93') 120.0 C(100)-C(99)-C(104) 120.0 C(100)-C(99)-Si(90) 120.0(4) C(104)-C(99)-Si(90) 119.9(4) C(99)-C(100)-C(101) 120.0 C(102)-C(101)-C(100) 120.0 C(101)-C(102)-C(103) 120.0 C(102)-C(103)-C(104) 120.0 C(103)-C(104)-C(99) 120M C(106)-C(105)-C(110) 120.0 C(106)-C(105)-Si(92) 119.2(3) C(110)-C(105)-Si(92) 120.7(3) C(107)-C(106)-C(105) 120.0 C(106)-C(107)-C(108) 120.0 C(109)-C(108)-C(107) 120.0 C(108)-C(109)-C(110) 120.0 C(109)-C(110)-C(105) 120.0 C(112)-C(111)-C(116) 120.0 C(112)-C(111)-Si(92) 116.7(9) C(116)-C(111)-Si(92) 123.3(9) C(111)-C(112)-C(113) 120.0 C(114)-C(113)-C(112) 120.0 C(113)-C(114)-C(115) 120.0 C(116)-C(115)-C(114) 120.0 C(115)-C(116)-C(111) 120.0 C(12')-C(11')-C(16') 120.0 C(12')-C(11')-Si(92) 129(2) C(16')-C(11')-Si(92) 110(2) C(13')-C(12')-C(11') 120.0 C(14')-C(13')-C(12') 120.0 C(13')-C(14')-C(15') 120.0 C(16')-C(15')-C(14`) 120.0 C(15')-C(16')-C(11') 120.0 C(300)-C(301)-N(302) 118.7(14) C(301)-N(302)-C(303) 115.6(13) C(304)-C(303)-N(302) 120(2)

294 Appendix

Crystallographic data for (HOPh2Si)20.{ [HOPh2SiOSiPh20] [Et3M-1]

Table 1. Crystal data and structure refinement for (HOPh2Si20).{[HOPh2SiOSiPh20][Et3Mi]l•

Empirical formula C54H59N6O6Si4 Crystal size 0.50 x 0.28 x 0.20 Formula weight 930.38 Temperature / K 223(2) Wavelength / A 0.71073 Crystal system Monoclinic Space group la Unit cell dimensions a / A 19.120(2) b / A 11.1690(13) c / A 24.645(3) P 103.215(8) U/ A-3, Z 5123.6(10), 4 Dc / g cm-3 1.206 tt(Mo-Ka) / mm-1 0.165 F(000) 1 976 0-range / ° 1.70 to 25.00 hkl-ranges -20 to 22, -1 to 13, -20 to 29 Reflections collected 5372 Independent reflections 4828 [R(int) = 0.0521 ] Data / restraints / parameters 4828/2/599 Goodness-of-fit on F2 1.037 Final R indices [1>2a(I)] R1= 0.0729, wR2 = 0.1056 R indices (all data) R1= 0.1612, wR2 = 0.1350 Largest diff. peak and hole /eA-3 0.267 and -0.246

295 Appendix

Table 2. Bond lengths (A) and angles (0 ) for (HOPh2Si20).{[HOPh2SiOSiPh20][Et3Mi]l•

Si (1A)-O(IA) 1.603 (6) Si(1A)-O(3A) 1.645 (7) Si(1A)-C(1 1A) 1.859(11) Si(1A)-C(21A) 1.883(10) Si(1B)-0(1B) 1.606(8) Si(1B)-0(3B) 1.639(7) Si( 1B)-C(11B) 1.861(10) Si( 1B)-C(21B) 1.873(9) Si(1B)-0(1B) 1.99(8) Si(2A)-O(2A) 1.606(7) Si(2A)-O(3A) 1.635(7) Si(2A)-C(41A) 1.838(10) Si(2A)-C(31A) 1.867(11) Si(2B)-O(2B) 1.615(7) Si(2B)-O(3B) 1.617(7) Si(2B)-C(31B) 1.859(10) Si(2B)-C(41B) 1.873(10) 0(2A)-H(2A) 0.89(8) 0(1B)-H(1B) 0.74(7) 0(2B)-H(2B) 0.99(10) C(11A)-C(12A) 1.385(13) C(11A)-C(16A) 1.411(13) C(12A)-C(13A) 1.40(2) C(12A)-H(12A) 0.94 C(13A)-C(14A) 1.38(2) C(13A)-H(13A) 0.94 C(14A)-C(15A) 1.39(2) C(14A)-H(14A) 0.94 C(15A)-C(16A) 1.382(13) C(15A)-H(15A) 0.94 C(16A)-H(16A) 0.94 C(21A)-C(26A) 1.382(12) C(21A)-C(22A) 1.404(14) C(22A)-C(23A) 1.371(14) C(22A)-H(22A) 0.94 C(23A)-C(24A) 1.373(14) C(23A)-H(23A) 0.94 C(24A)-C(25A) 1.38(2) C(24A)-H(24A) 0.94 C(25A)-C(26A) 1.373(14) C(25A)-H(25A) 0.94 C(26A)-H(26A) 0.94 C(31A)-C(36A) 1.361(14) C(31A)-C(32A) 1.408(13) C(32A)-C(33A) 1.39(2) C(32A)-H(32A) 0.94 C(33A)-C(34A) 1.33(2) C(33A)-H(33A) 0.94 C(34A)-C(35A) 1.35(2) C(34A)-H(34A) 0.94 C(35A)-C(36A) 1.41(2) C(35A)-H(35A) 0.94 C(36A)-H(36A) 0.94 C(41A)-C(42A) 1.383(13) C(41A)-C(46A) 1.385(13) C(42A)-C(43A) 1.374(14) C(42A)-H(42A) 0.94 C(43A)-C(44A) 1.40(2) C(43A)-H(43A) 0.94 C(44A)-C(45A) 1.35(2) C(44A)-H(44A) 0.94 C(45A)-C(46A) 1.381(14) C(45A)-H(45A) 0.94 C(46A)-H(46A) 0.94 C(11B)-C(16B) 1.379(13) C(11B)-C(12B) 1.391(14) C(12B)-C(13B) 1.40(2) C(12B)-H(12B) 0.94 C(13B)-C(14B) 1.35(2) C(13B)-H(13B) 0.94 C(14B)-C(15B) 1.37(2) C(14B)-H(14B) 0.94 C(15B)-C(16B) 1.403(13) C(15B)-H(15B) 0.94 C(16B)-H(16B) 0.94 C(21B)-C(22B) 1.343(13) C(21B)-C(26B) 1.370(13) C(22B)-C(23B) 1.40(2) C(22B)-H(22B) 0.94 C(23B)-C(24B) 1.32(2) C(23B)-H(23B) 0.94 C(24B)-C(25B) 1.36(2) C(24B)-H(24B) 0.94 C(25B)-C(26B) 1.384(13) C(25B)-H(25B) 0.94 C(26B)-H(26B) 0.94 C(31B)-C(36B) 1.369(14) C(31B)-C(32B) 1.392(13) C(32B)-C(33B) 1.41(2) C(32B)-H(32B) 0.94 C(33B)-C(34B) 1.35(2) C(33B)-H(33B) 0.94 C(34B)-C(35B) 1.41(2) C(34B)-H(34B) 0.94 C(35B)-C(36B) 1.40(2) C(35B)-H(35B) 0.94 C(36B)-H(36B) 0.94 C(41B)-C(46B) 1.358(14) C(41B)-C(42B) 1.396(13) C(42B)-C(43B) 1.37(2) C(42B)-H(42B) 0.94 C(43B)-C(44B) 1.39(2) C(43B)-H(43B) 0.94 C(44B)-C(45B) 1.34(2) C(44B)-H(44B) 0.94 C(45B)-C(46B) 1.40(2) C(45B)-H(45B) 0.94 C(46B)-H(46B) 0.94

296 Appendix

N(1)-C(1C) 1.465(12) N(1)-C(1B) 1.519(13) N(1)-C(1A) 1.51(2) N(1)-H(1N) 1.189(9) C(1A)-C(2A) 1.43(2) C(1A)-H(1A1) 0.98 C(1A)-H(1A2) 0.98 C(2A)-H(2A1 ) 0.97 C(2A)-H(2A2) 0.97 C(2A)-H(2A3) 0.97 C(1B)-C(2B) 1.504(14) C(1B)-H(1B1) 0.98 C(1B)-H(1B2) 0.98 C(2B)-H(2B 1) 0.97 C(2B)-H(2B2) 0.97 C(2B)-H(2B 3) 0.97 C(1C)-C(2C) 1.516(13) C(1C)-H(1C1) 0.98 C(1C)-H(1C2) 0.98 C(2C)-H(2C1) 0.97 C(2C)-H(2C2) 0.97 C(2C)-H(2C3) 0.97

0(1A)-Si(1A)-0(3A) 111.7(3) 0(1A)-Si(1A)-C(11A) 109.3(4) 0(3A)-Si(1A)-C(11A) 106.5(4) 0(1A)-Si(1A)-C(21A) 113.4(4) 0(3A)-Si(1A)-C(21A) 108.0(4) C(11A)-Si(1A)-C(21A) 107.6(4) 0(1B)-Si(1B)-0(3B) 111.2(4) 0(1B)-Si( 1 B)-C(11B ) 111.6(4) 0(3B)-Si( 1 B)-C(11B) 107.5(4) 0(1B)-Si(1B)-C(21B) 106.7(4) 0(3B)-Si( 1 B)-C(21B) 110.6(4) C(11B)-Si( 1B)-C(21B) 109.2(5) 0(2A)-Si(2A)-0(3A) 111.6(4) 0(2A)-Si(2A)-C(41A) 108.5(4) 0(3A)-Si(2A)-C(41A) 109.0(4) 0(2A)-Si(2A)-C(31A) 110.1(5) 0(3A)-Si(2A)-C(31A) 109.7(4) C(41A)-Si(2A)-C(31A) 107.9(5) 0(2B)-Si(2B)-0(3B) 113.6(4) 0(2B)-Si(2B)-C(31B) 110.4(4) 0(3B)-Si(2B)-C(31B) 107.9(4) 0(2B)-Si(2B)-C(41B) 107.2(4) 0(3B)-Si(2B)-C(41B) 107.9(4) C(31B)-Si(2B)-C(41B) 109.8(4) Si(2A)-0(2A)-H(2A) 115(5) Si(2A)-0(3A)-Si(1A) 139.1(4) Si( 1 B)-0(1B)-H(1B) 111(7) Si(2B)-0(2B)-H(2B) 122(5) Si(2B)-0(3B)-Si(1B) 144.6(4) C(12A)-C(11A)-C(16A) 117.2(10) C(12A)-C(11A)-Si(1A) 123.9(9) C(16A)-C(11A)-Si(1A) 118.8(8) C(11A)-C(12A)-C(13A) 120.8(12) C(11A)-C(12A)-H(12A) 119.6(7) C(13A)-C(12A)-H(12A) 119.6(8) C(14A)-C(13A)-C(12A) 120.8(13) C(14A)-C(13A)-H(13A) 119.6(9) C(12A)-C(13A)-H(13A) 119.6(8) C(13A)-C(14A)-C(15A) 119.4(12) C(13A)-C(14A)-H(14A) 120.3(9) C(15A)-C(14A)-H(14A) 120.3(9) C(16A)-C(15A)-C(14A) 119.6(13) C(16A)-C(15A)-H(15A) 120.2(8) C(14A)-C(15A)-H(15A) 120.2(9) C(15A)-C(16A)-C(11A) 122.2(12) C(15A)-C(16A)-H(16A) 118.9(8) C(11A)-C(16A)-H(16A) 118.9(6) C(26A)-C(21A)-C(22A) 115.9(10) C(26A)-C(21A)-Si(1A) 123.5(8) C(22A)-C(21A)-Si(1A) 120.6(8) C(23A)-C(22A)-C(21A) 122.7(11) C(23A)-C(22A)-H(22A) 118.6(7) C(21A)-C(22A)-H(22A) 118.6(6) C(22A)-C(23A)-C(24A) 118.6(12) C(22A)-C(23A)-H(23A) 120.7(8) C(24A)-C(23A)-H(23A) 120.7(8) C(25A)-C(24A)-C(23A) 121.0(11) C(25A)-C(24A)-H(24A) 119.5(7) C(23A)-C(24A)-H(24A) 119.5(8) C(24A)-C(25A)-C(26A) 118.9(12) C(24A)-C(25A)-H(25A) 120.6(7) C(26A)-C(25A)-H(25A) 120.6(8) C(25A)-C(26A)-C(21A) 122.8(12) C(25A)-C(26A)-H(26A) 118.6(8) C(21A)-C(26A)-H(26A) 118.6(7) C(36A)-C(31A)-C(32A) 115.3(11) C(36A)-C(31A)-Si(2A) 125.1(10) C(32A)-C(31A)-Si(2A) 119.5(9) C(33A)-C(32A)-C(31A) 122.1(13) C(33A)-C(32A)-H(32A) 118.9(9) C(31A)-C(32A)-H(32A) 118.9(7) C(34A)-C(33A)-C(32A) 119.0(14) C(34A)-C(33A)-H(33A) 120.5(10) C(32A)-C(33A)-H(33A) 120.5(9) C(33A)-C(34A)-C(35A) 122(2) C(33A)-C(34A)-H(34A) 118.8(10) C(35A)-C(34A)-H(34A) 118.9(10) C(34A)-C(35A)-C(36A) 118.4(14) C(34A)-C(35A)-H(35A) 120.8(10) C(36A)-C(35A)-H(35A) 120.8(9) C(31A)-C(36A)-C(35A) 122.7(13) C(31A)-C(36A)-H(36A) 118.6(8) C(35A)-C(36A)-H(36A) 118.6(9) C(42A)-C(41A)-C(46A) 115.1(10) C(42A)-C(41A)-Si(2A) 126.2(8) C(46A)-C(41A)-Si(2A) 118.7(8) C(43A)-C(42A)-C(41A) 122.5(12) C(43A)-C(42A)-H(42A) 118.8(8) C(41A)-C(42A)-H(42A) 118.8(7) C(42A)-C(43A)-C(44A) 120.4(12) C(42A)-C(43A)-H(43A) 119.8(8) C(44A)-C(43A)-H(43A) 119.8(7)

297 Appendix

C(45A)-C(44A)-C(43A) 118.2(11) C(45A)-C(44A)-H(44A) 120.9(8) C(43A)-C(44A)-H(44A) 120.9(7) C(44A)-C(45A)-C(46A) 120.7(12) C(44A)-C(45A)-H(45A) 119.7(8) C(46A)-C(45A)-H(45A) 119.7(8) C(45A)-C(46A)-C(41A) 123.1(11) C(45A)-C(46A)-H(46A) 118.4(8) C(41A)-C(46A)-H(46A) 118.4(6) C(16B)-C(11B)-C(12B) 118.8(10) C(16B)-C(11B)-Si(1B) 122.9(9) C(12B)-C(11B)-Si(1B) 118.1(8) C(11B)-C(12B)-C(13B) 120.6(11) C(11B)-C(12B)-H(12B) 119.7(6) C(13B)-C(12B)-H(12B) 119.7(8) C(14B)-C(13B)-C(12B) 119.1(13) C(14B)-C(13B)-H(13B) 120.5(8) C(12B)-C(13B)-H(13B) 120.5(8) C(13B)-C(14B)-C(15B) 122.2(13) C(13B)-C(14B)-H(14B) 118.9(8) C(15B)-C(14B)-H(14B) 118.9(8) C(14B)-C(15B)-C(16B) 118.7(11) C(14B)-C(15B)-H(15B) 120.6(8) C(16B)-C(15B)-H(15B) 120.6(7) C(11B)-C(16B)-C(15B) 120.5(11) C(1 1B)-C(16B)-H(16B) 119.8(7) C(15B)-C(16B)-H(16B) 119.8(7) C(22B)-C(21B)-C(26B) 116.7(10) C(22B)-C(21B)-Si(1B) 122.2(9) C(26B)-C(21B)-Si(1B) 120.9(8) C(21B)-C(22B)-C(23B) 120.8(11) C(21B)-C(22B)-H(22B) 119.6(7) C(23B)-C(22B)-H(22B) 119.6(8) C(24B)-C(23B)-C(22B) 121.7(12) C(24B)-C(23B)-H(23B) 119.2(8) C(22B)-C(23B)-H(23B) 119.2(8) C(23B)-C(24B)-C(25B) 118.9(12) C(23B)-C(24B)-H(24B) 120.6(8) C(25B)-C(24B)-H(24B) 120.6(8) C(24B)-C(25B)-C(26B) 119.3(12) C(24B)-C(25B)-H(25B) 120.3(8) C(26B)-C(25B)-H(25B) 120.3(8) C(21B)-C(26B)-C(25B) 122.5(11) C(21B)-C(26B)-H(26B) 118.8(6) C(25B)-C(26B)-H(26B) 118.8(8) C(36B)-C(31B)-C(32B) 116.6(11) C(36B)-C(31B)-Si(2B) 120.9(9) C(32B)-C(31B)-Si(2B) 122.4(9) C(33B)-C(32B)-C(31B) 121.0(13) C(33B)-C(32B)-H(32B) 119.5(9) C(31B)-C(32B)-H(32B) 119.5(7) C(34B)-C(33B)-C(32B) 121(2) C(34B)-C(33B)-H(33B) 119.7(10) C(32B)-C(33B)-H(33B) 119.7(9) C(33B)-C(34B)-C(35B) 121(2) C(33B)-C(34B)-H(34B) 119.7(10) C(35B)-C(34B)-H(34B) 119.7(9) C(36B)-C(35B)-C(34B) 117.1(14) C(36B)-C(35B)-H(35B) 121.4(9) C(34B)-C(35B)-H(35B) 121.4(9) C(31B)-C(36B)-C(35B) 124.2(13) C(31B)-C(36B)-H(36B) 117.9(7) C(35B)-C(36B)-H(36B) 117.9(9) C(46B)-C(41B)-C(42B) 116.7(11) C(46B)-C(41B)-Si(2B) 122.7(9) C(42B)-C(41B)-Si(2B) 120.6(9) C(43B)-C(42B)-C(41B) 121.0(13) C(43B)-C(42B)-H(42B) 119.5(9) C(41B)-C(42B)-H(42B) 119.5(7) C(42B)-C(43B)-C(44B) 120.3(14) C(42B)-C(43B)-H(43B) 119.9(9) C(44B)-C(43B)-H(43B) 119.9(9) C(45B)-C(44B)-C(43B) 119.8(13) C(45B)-C(44B)-H(44B) 120.1(9) C(43B)-C(44B)-H(44B) 120.1(8) C(44B)-C(45B)-C(46B) 119.3(14) C(44B)-C(45B)-H(45B) 120.3(9) C(46B)-C(45B)-H(45B) 120.4(9) C(41B)-C(46B)-C(45B) 122.9(13) C(41B)-C(46B)-H(46B) 118.5(7) C(45B)-C(46B)-H(46B) 118.5(9) C(1C)-N(1)-C(1B) 113.3(9) C(1C)-N(1)-C(1A) 116.4(10) C(1B)-N(1)-C(1A) 105.3(9) C(1C)-N(1)-H(1N) 108.4(7) C(1B)-N(1)-H(1N) 108.2(9) C(1A)-N(1)-H(1N) 104.7(8) C(2A)-C(1A)-N(1) 116.0(11) C(2A)-C(1A)-H(1A1) 108.3(8) N(1)-C(1A)-H(1A1) 108.3(7) C(2A)-C(1A)-H(1A2) 108.3(9) N(1)-C(1A)-H(1A2) 108.3(7) H(1A1 )-C(IA)-H(1A2) 107.4 C(1A)-C(2A)-H(2A1) 109.5(7) C(1A)-C(2A)-H(2A2) 109.5(9) H(2A1)-C(2A)-H(2A2) 109.5 C(1A)-C(2A)-H(2A3) 109.5(8) H(2A1)-C(2A)-H(2A3) 109.5 H(2A2)-C(2A)-H(2A3) 109.5 C(2B)-C(1B)-N(1) 113.4(9) C(2B)-C(1B)-H(1B1) 108.9(7) N(1)-C(1B)-H(1B1) 108.9(6) C(2B)-C(1B)-H(1B2) 108.9(6) N(1)-C(1B)-H(1B2) 108.9(6) H(1B1)-C(1B)-H(1B2) 107.7 C(1B)-C(2B)-H(2B1) 109.5(6) C(1B)-C(2B)-H(2B2) 109.5(6) H(2B1)-C(2B)-H(2B2) 109.5 C(1B)-C(2B)-H(2B3) 109.5(7) H(2B1)-C(2B)-H(2B3) 109.5 H(2B2)-C(2B)-H(2B3) 109.5 N(1)-C(1C)-C(2C) 116.2(9) N(1)-C(1C)-H(1C1) 108.2(6) C(2C)-C(1C)-H(1C1) 108.2(7) N(1)-C(1C)-H(1C2) 108.2(6) C(2C)-C(1C)-H(1C2) 108.2(7)

298 Appendix

H(1C1)-C(1C)-H(1C2) 107.4 C(1C)-C(2C)-H(2C1) 109.5(7) C(1C)-C(2C)-H(2C2) 109.5(7) H(2C1)-C(2C)-H(2C2) 109.5 C(1C)-C(2C)-H(2C3) 109.5(7) H(2C1)-C(2C)-H(2C3) 109.5 H(2C2)-C(2C)-H(2C3) 1 09.5

299 Appendix

Crystallographic data for (HOPh2Si)20.1,4-dioxane

Table 1. Crystal data and structure refinement for (HOPh2Si)20.1,4- dioxane.

Empirical formula C28H30O5Si2 Crystal size 0.20 x 0.42 x 0.48 Formula weight 502.70 Temperature / K 198(2) Wavelength / A 0.71073 Crystal system Triclinic Space group P1 Unit cell dimensions a/A 9.101(2) b hk 9.373(2) c hk 16. 165(3) a /0 88.183(13) 13 /° 73.955(12) 7 /° 84.40(2) U/A-3,Z 1318.9(4), 2 Dc/ g cm-3 1.266 1.t(Mo-Ka)/mm-1 0.170 F(000) 532 0-range /0 1.31 to 25.00 hk/-ranges -1 to 10,-11 to 11,-18 to 19 Reflections collected 5603 Independent reflections 4647 [R(int) = 0.0298] Data / restraints / parameters 4646/0/436 Goodness-of-fit on F2 1.023 Final R indices [I>20(I)] R1= 0.0561, wR2 = 0.1217 (all data) R1= 0.1068, wR2 = 0.1475 Largest duff. peak and hole /eA-3 0.567 and -0.248

300 Appendix

Table 2. Bond lengths (A) and angles (°) for (HOPh2S020.1,4-dioxane.

Si(1)-0(1) 1 .6 1 5(3) Si(1)-0(3) 1 .620(2) Si(1)-C(11) 1.854(3) Si(1)-C(21) 1.862(3) Si(2)-0(3) 1.615(2) Si(2)-0(2) 1.626(3) Si(2)-C(31) 1.858(3) Si(2)-C(41) 1.864(3) 0(4)-C(1) 1.404(6) 0(4)-C(2) 1.444(5) 0(5)-C(3) 1.390(5) 0(5)-C(4) 1.448(6)

C(1)-C(2)#1 1.473(7) C(2)-C(1)#1 1.473(7) C(3)-C(4)#2 1.465(7) C(4)-C(3)#2 1.465(7) C(11)-C(16) 1.396(5) C(11)-C(12) 1.398(5) C(12)-C(13) 1.371(5) C(13)-C(14) 1.370(6) C(14)-C(15) 1.377(6) C(15)-C(16) 1.384(5) C(21)-C(26) 1.398(5) C(21)-C(22) 1.402(5) C(22)-C(23) 1.381(5) C(23)-C(24) 1.372(6) C(24)-C(25) 1.384(5) C(25)-C(26) 1.378(5) C(31)-C(32) 1.389(5) C(31)-C(36) 1.392(5) C(32)-C(33) 1.373(5) C(33)-C(34) 1.388(5) C(34)-C(35) 1.365(6) C(35)-C(36) 1.383(5) C(41)-C(46) 1.390(5) C(41)-C(42) 1.398(5) C(42)-C(43) 1.376(5) C(43)-C(44) 1.379(6) C(44)-C(45) 1.367(6) C(45)-C(46) 1.390(5)

0(1)-11(10) 0.80(4) 0(2)-H(20) 0.92(4) C(1)-H(1A) 1.00(6) C(1)-H(1B) 1.14(6) C(2)-H(2A) 0.95(5) C(2)-H(2B) 1.02(5) C(3)-H(3A) 1.01(5) C(3)-H(3B) 0.92(5) C(4)-H(4A) 1.01(4) C(4)-H(4B) 0.91(6) C(12)-H(12) 1.00(3) C(13)-H(13) 0.94(4) C(14)-H(14) 0.91(4) C(15)-H(15) 0.93(3) C(16)-H(16) 0.90(3) C(22)-H(22) 0.88(4) C(23)-H(23) 0.93(3) C(24)-H(24) 0.92(4) C(25)-H(25) 1.00(4) C(26)-H(26) 0.89(3) C(33)-H(33) 0.91(4) C(32)-H(32) 0.94(3) C(34)-H(34) 0.97(3) C(35)-H(35) 0.93(4) C(36)-11(36) 0.92(4) C(42)-H(42) 0.96(3) C(43)-H(43) 0.91(4) C(44)-H(44) 0.89(4) C(45)-H(45) 0.86(4) C(46)-H(46) 0.92(3)

0(1)-Si(1)-0(3) 112.70(14) 0(1)-Si(1)-C(11) 113.3(2) 0(3)-Si(1)-C(11) 106.82(14) 0(1)-Si(1)-C(21) 104.8(2) 0(3)-Si(1)-C(21) 108.82(14) C(11)-Si(1)-C(21) 110.39(14) 0(3)-Si(2)-0(2) 111.14(14) 0(3)-Si(2)-C(31) 108.60(14) 0(2)-Si(2)-C(31) 106.0(2) 0(3)-Si(2)-C(41) 108.17(14) 0(2)-Si(2)-C(41) 111.5(2) C(31)-Si(2)-C(41) 111.47(14) Si(1)-0(1)-H(10) 124(3) Si(2)-0(2)-H(20) 114(3) Si(2)-0(3)-Si(1) 166.0(2) C(1)-0(4)-C(2) 109.4(3) C(3)-0(5)-C(4) 109.9(4) 0(4)-C(1)-C(2)#1 111.2(4) 0(4)-C(1)-H(1A) 95(4) C(2)#1-C(1)-H(1A) 100(4) 0(4)-C(1)-H(1B) 101(3) C(2)#1-C(1)-H(1B) 116(3) H(1A)-C(1)-H(1B) 132(5) 0(4)-C(2)-C(1)#1 110.2(4) 0(4)-C(2)-H(2A) 108(3) C(1)#1-C(2)-H(2A) 112(3) 0(4)-C(2)-H(2B) 106(3) C(1)#1-C(2)-H(2B) 114(3) H(2A)-C(2)-H(2B) 108(4) 0(5)-C(3)-C(4)#2 112.4(4) 0(5)-C(3)-H(3A) 104(3) C(4)#2-C(3)-H(3A) 110(3) 0(5)-C(3)-H(3B) 105(3) C(4)#2-C(3)-H(3B) 113(3)

301 Appendix

H(3A)-C(3)-H(3B) 112(4) O(5)-C(4)-C(3)#2 110.9(4) O(5)-C(4)-H(4A) 94(3) C(3)#2-C(4)-H(4A) 110(3) O(5)-C(4)-H(4B) 107(4) C(3)#2-C(4)-H(4B) 116(4) H(4A)-C(4)-H(4B) 117(5) C(16)-C(11)-C(12) 116.8(3) C(16)-C(11)-Si(1) 122.7(3) C(12)-C(11)-Si(1) 120.3(3) C(13)-C(12)-C(1 1) 121.3(4) C(13)-C(12)-H(12) 119(2) C(11)-C(12)-H(12) 120(2) C(14)-C(13)-C(12) 120.8(4) C(14)-C(13)-H(13) 119(3) C(12)-C(13)-H(13) 120(3) C(13)-C(14)-C(15) 119.7(4) C(13)-C(14)-H(14) 118(2) C(1S)-C(14)-H(14) 121(3) C(14)-C(15)-C(16) 119.7(4) C(14)-C(15)-H(15) 123(2) C(16)-C(15)-H(15) 117(2) C(15)-C(16)-C(11) 121.6(4) C(15)-C(16)-H(16) 121(2) C(11)-C(16)-H(16) 117(2) C(26)-C(21)-C(22) 117.0(3) C(26)-C(21)-Si(1) 119.8(3) C(22)-C(21)-Si(1) 123.3(3) C(23)-C(22)-C(21) 121.3(4) C(23)-C(22)-H(22) 122(2) C(21)-C(22)-H(22) 117(2) C(24)-C(23)-C(22) 120.2(4) C(24)-C(23)-H(23) 122(2) C(22)-C(23)-H(23) 118(2) C(23)-C(24)-C(25) 120.1(4) C(23)-C(24)-H(24) 120(2) C(25)-C(24)-H(24) 119(2) C(26)-C(25)-C(24) 119.6(4) C(26)-C(25)-H(25) 122(2) C(24)-C(25)-H(25) 118(2) C(25)-C(26)-C(21) 121.9(4) C(25)-C(26)-H(26) 117(2) C(21)-C(26)-H(26) 121(2) C(32)-C(31)-C(36) 116.0(3) C(32)-C(31)-Si(2) 120.1(3) C(36)-C(31)-Si(2) 123.9(3) C(33)-C(32)-C(31) 122.9(4) C(33)-C(32)-H(32) 118(2) C(31)-C(32)-H(32) 119(2) C(32)-C(33)-C(34) 119.4(4) C(32)-C(33)-H(33) 121(3) C(34)-C(33)-H(33) 120(3) C(35)-C(34)-C(33) 119.3(4) C(35)-C(34)-H(34) 122(2) C(33)-C(34)-H(34) 119(2) C(34)-C(35)-C(36) 120.5(4) C(34)-C(35)-H(35) 119(3) C(36)-C(35)-H(35) 121(3) C(35)-C(36)-C(31) 121.8(4) C(35)-C(36)-H(36) 121(2) C(31)-C(36)-H(36) 118(2) C(46)-C(41)-C(42) 117.2(3) C(46)-C(41)-Si(2) 120.3(3) C(42)-C(41)-Si(2) 122.5(3) C(43)-C(42)-C(41) 121.7(4) C(43)-C(42)-H(42) 122(2) C(41)-C(42)-H(42) 116(2) C(42)-C(43)-C(44) 119.6(4) C(42)-C(43)-H(43) 121(3) C(44)-C(43)-H(43) 120(3) C(45)-C(44)-C(43) 120.4(4) C(45)-C(44)-H(44) 121(2) C(43)-C(44)-H(44) 118(2) C(44)-C(45)-C(46) 119.9(4) C(44)-C(45)-H(45) 124(3) C(46)-C(45)-H(45) 116(3) C(45)-C(46)-C(41) 121.2(4) C(45)-C(46)-H(46) 120(2) C(41)-C(46)-H(46) 119(2)

Symmetry transformations used to generate equivalent atoms: #1 -x,-y+2,-z+1 #2 -x+2,-y+1 ,-z

302 Appendix

Crystallographic data for Ph3SiOH.tris(2-aminoethyl)amine

Table 1 . Crystal data and structure refinement for Ph3SiOH.tris(2- aminoethyl)amine.

Empirical formula C24H34N40Si Crystal size 0.25 x 0.38 x 0.42 Formula weight 422.64 Temperature / K 198(2) Wavelength / A 0.71073 Crystal system Triclinic Space group PT Unit cell dimensions a/ A 1 0.806(2) b/ A 11. 1122(14) c/ A 12.166(2) a/ ° 99.490(12) 13/ ° 103.135(14) 11° 118.102(13) U/A-3, Z 1190.4(3), 2 D, I gcm-3 1.179 µ(Mo-Koc)/mm-1 0.121 F(000) 456 8-range r 1.81 to 25.00 hkl-ranges -1 to 12, -12 to 11, -14 to 14 Reflections collected 4869 Independent reflections 4139 [R(int) = 0.0393] Data / restraints / parameters 4139/0/407 Goodness-of-fit on F2 1.028 Final R indices [I>26(I)] R1 = 0.0506, wR2 = 0.0937 (all data) RI = 0.0929, wR2 = 0.1103 Largest cliff. peak and hole /eA-3 0.238 and -0.218

303 Appendix

Table 2. Bond lengths (A) and angles (°) for Ph3SiOH.tris(2- aminoethyl)amine.

Si(1)-O(1) 1.616(2) Si(1)-C(31) 1.869(3) Si(1)-C(11) 1.875(3) Si(1)-C(21) 1.877(3) N(1)-C(1B) 1.464(4) N(1)-C(1A) 1.466(3) N(1)-C(1C) 1.474(3) C(1A)-C(2A) 1.520(4) C(1B)-C(2B) 1.524(5) C(1C)-C(2C) 1.507(4) C(2A)-N(3A) 1.470(4) C(2B)-N(3B) 1.455(5) C(2C)-N(3C) 1.457(4) C(13)-C(14) 1.380(4) C(11)-C(16) 1.398(4) C(11)-C(12) 1.403(3) C(12)-C(13) 1.394(4) C(14)-C(15) 1.385(4) C(15)-C(16) 1.384(4) C(21)-C(22) 1.398(4) C(21)-C(26) 1.399(3) C(22)-C(23) 1.384(4) C(23)-C(24) 1.379(4) C(24)-C(25) 1.385(4) C(25)-C(26) 1.382(4) C(3 1)-C(36) 1.403(4) C(31)-C(32) 1.408(4) C(32)-C(33) 1.385(4) C(33)-C(34) 1.382(4) C(34)-C(35) 1.373(4) C(35)-C(36) 1.390(4)

O(1)-H(10) 0.83(3) C(1A)-H(1A1) 1.05(3) C(1A)-H(2A1) 1.02(3) C(1B)-H(1B1) 1.02(3) C(1B)-H(1B2) 1.03 (3) C(1C)-H(1C2) 1.01(3) C(1C)-H(1C1) 1.05(3) C(2A)-H(2A2) 1.02(3) C(2A)-H(2A1) 0.97(3) C(2B)-H(2B2) 1.02(4) C(2B)-H(2B1) 0.97(4) C(2C)-H(2C1) 0.95(3) C(2C)-H(2C2) 1.04(3) N(3A)-H(3A2) 0.88(3) N(3A)-H(3A1) 0.88(3) N(3C)-H(3C2) 0.86(3) N(3C)-H(3C1) 0.85(4) N(3B)-H(3B2) 0.96(4) N(3B)-H(3B1) 0.97(4) C(12)-H(12) 0.96(2) C(13)-H(13) 1.01(2) C(14)-H(14) 0.91(3) C(15)-H(15) 0.96(3) C(16)-H(12) 1.01(2) C(22)-H(22) 0.94(3) C(23)-H(23) 0.98(3) C(24)-H(24) 0.96(3) C(25)-H(25) 0.99(3) C(26)-H(26) 0.98(2) C(32)-H(32) 1.00(3) C(33)-H(31) 0.95(3) C(34)-H(34) 0.95(3) C(35)-H(35) 0.94(3) C(36)-H(36) 0.93(2)

0(1)-Si(1)-C(31) 112.38(11) O(1)-Si(1)-C(1 1) 105.44(1) C(31)-Si(1)-C(11) 108.98(11) O(1)-Si(1)-C(21) 111.25(1) C(31)-Si(1)-C(21) 107.99(11) C(11)-Si(1)-C(21) 110.79(1) Si(1)-O(1)-H(10) 126(2) C(1B)-N(1)-C(1A) 112.4(2) C(1B)-N(1)-C(1C) 111.3(2) C(1A)-N(1)-C(1C) 110.9(2) N(1)-C(1A)-C(2A) 112.0(2) N(1)-C(1A)-H(1A1) 109(2) C(2A)-C(1A)-H(1A1) 107(2) N(1)-C(1A)-H(2A1) 110.8(14) C(2A)-C(1A)-H(2A1) 109.5(14) H(1A1)-C(1A)-H(2A1) 109(2) N(1)-C(1B)-C(2B) 111.0(3) N(1)-C(1B)-H(1B1) 109(2) C(2B)-C(1B)-H(1B1) 107(2) N(1)-C(1B)-H(1B2) 112(2) C(2B)-C(1B)-H(1B2) 113(2) H(1B1)-C(1B)-H(1B2) 105(2) N(1)-C(1C)-C(2C) 112.0(2) N(1)-C(1C)-H(1C2) 112.0(14) C(2C)-C(1C)-H(1C2) 108(2) N(1)-C(1C)-H(1C1) 108(2) C(2C)-C(1C)-H(1C1) 111(2) H(1C2)-C(1C)-H(1C1) 106(2) N(3A)-C(2A)-C(1A) 113.8(3) N(3A)-C(2A)-H(2A2) 109(2) C(1A)-C(2A)-H(2A2) 110(2) N(3A)-C(2A)-H(2A1) 108(2) C(1A)-C(2A)-H(2A1) 107(2) H(2A2)-C(2A)-H(2A1) 110(2) N(3B)-C(2B)-C(1B) 115.1(3) N(3B)-C(2B)-H(2B2) 105(2) C(1B)-C(2B)-H(2B2) 113(2) N(3B)-C(2B)-H(2B1) 106(2)

304 Appendix

C(1B)-C(2B )-H(2B 1) 107(2) H(2B 2)-C(2B)-H(2B 1) 110(3) N(3C)-C(2C)-C(1C) 115.0(3) N(3C)-C(2C)-H(2C1) 109(2) C(1C)-C(2C)-H(2C1) 109(2) N(3C)-C(2C)-H(2C2) 111(2) C(1C)-C(2C)-H(2C2) 109(2) H(2C1)-C(2C)-H(2C2) 104(3) C(2A)-N(3A)-H(3A2) 110(2) C(2A)-N(3A)-H(3A1) 110(2) H(3A2)-N(3A)-H(3A1) 104(3) C(2C)-N(3C)-H(3C2) 112(2) C(2C)-N(3C)-H(3C1) 109(3) H(3C2)-N(3C)-H(3C1) 100(3) C(2B)-N(3B)-H(3B2) 106(2) C(2B)-N(3B)-H(3B 1) 106(3) H(3B 2)-N(3B)-H(3B 1) 100(3) C(16)-C(11)-C(12) 116.7(2) C(16)-C(11)-Si(1) 123.0(2) C(12)-C(11)-Si(1) 120.3(2) C(13)-C(12)-C(11) 121.8(3) C(13)-C(12)-H(12) 120(2) C(11)-C(12)-H(12) 119(2) C(14)-C(13)-C(12) 119.5(3) C(14)-C(13)-H(13) 124.6(14) C(12)-C(13)-H(13) 115.9(14) C(13)-C(14)-C(15) 120.2(3) C(13)-C(14)-H(14) 123(2) C(15)-C(14)-H(14) 117(2) C(16)-C(15)-C(14) 119.8(3) C(1 6)-C(1 5)-H(15) 120(2) C(14)-C(1 5)-H(15) 121(2) C(15)-C(16)-C(11) 122.0(3) C(15)-C(16)-H(12) 119.2(14) C(11)-C(16)-H(12) 118.8(14) C(22)-C(21)-C(26) 116.4(2) C(22)-C(21)-Si(1) 118.4(2) C(26)-C(21)-Si(1) 125.2(2) C(23)-C(22)-C(21) 122.2(3) C(23)-C(22)-H(22) 121(2) C(21)-C(22)-H(22) 117(2) C(24)-C(23)-C(22) 119.5(3) C(24)-C(23)-H(23) 120(2) C(22)-C(23)-H(23) 121(2) C(23)-C(24)-C(25) 120.1(3) C(23)-C(24)-H(24) 119(2) C(25)-C(24)-H(24) 121(2) C(26)-C(25)-C(24) 119.7(3) C(26)-C(25)-H(25) 120(2) C(24)-C(25)-H(25) 120(2) C(25)-C(26)-C(21) 122.0(3) C(25)-C(26)-H(26) 117.4(14) C(21)-C(26)-H(26) 120.6(14) C(36)-C(31)-C(32) 116.3(3) C(36)-C(31)-Si(1) 121.6(2) C(32)-C(31)-Si(1) 122.0(2) C(33)-C(32)-C(31) 122.2(3) C(33)-C(32)-H(32) 120(2) C(31)-C(32)-H(32) 118(2) C(32)-C(33)-C(34) 119.4(3) C(32)-C(33)-H(31) 118(2) C(34)-C(33)-H(31) 122(2) C(35)-C(34)-C(33) 120.3(3) C(35)-C(34)-H(34) 123(2) C(33)-C(34)-H(34) 117(2) C(34)-C(35)-C(36) 120.2(3) C(34)-C(35)-H(35) 120(2) C(36)-C(35)-H(35) 120(2) C(35)-C(36)-C(31) 121.6(3) C(35)-C(36)-H(36) 121(2) C(31)-C(36)-H(36) 118(2)

305 Appendix

Crystallographic data for (Ph3SiOH)2.piperazine

Table 1. Crystal data and structure refinement for (Ph3SiOH)2.piperazine.

Empirical formula C40H42N2O2Si2 Formula weight 638.94 Temperature 293(2) K Diffractometer Used Siemens P4/PC Wavelength 1.54178 A Crystal system Triclinic Space group P1 Unit cell dimensions a = 7.3759(5) A. alpha = 89.211(8)* b = 9.9099(13) A beta = 80.305(6)° c = 12.6174(8) A gamma = 80.465(7)° Volume, Z 896.44(14) A3, 1 Density (calculated) 1.184 Mg/m3 Absorption coefficient 1.173 mm-1 F(000) 340 Crystal colour/morphology Clear prisms Crystal size 0.67 x 0.50 x 0.27 mm e range for data collection 3.55 to 63.00 Limiting indices 0 5h5 8,-115k5 11, -14 5 1 5 14 Scan type 0)-scans Reflections collected 3095 Independent reflections 2849 (Rini = 0.0943) Observed reflections [F>4a(F)] 2308 Absorption correction Semi-empirical Max. and min. transmission 0.7609 and 0.5105 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 2849 / 2 / 181 Goodness-of-fit on F2 1.031 Final R indices [F>445(F)] R1= 0.0600, wR2 = 0.1617 R indices (all data) RI = 0.0730, wR2 = 0.1754 Extinction coefficient 0.134(8) Largest cliff. peak and hole 0.388 and -0.332 eA-3 Mean and maximum shift/error 0.000 and 0.001

306 Appendix

Table 2. Bond lengths (A) and angles 0 for (Ph3SiOH)2.piperazine.

N-C(1) 1.462(4) N-C(2) 1.467(4) C(1)-C(2)#1 1.502(4) 0-Si 1.615(2) Si-C(20) 1.889(2) Si-C(8) 1.898(2) Si-C(14) 1.901(2) C(1)-N-C(2) 110.2(2) N-C(1)-C(2)#1 109.1(3) N-C(2)-C(1)#1 110.3(3) 0-Si-C(20) 105.45(11) 0-Si-C(8) 112.63(12) C-(20)-Si-C(8) 109.15(9) 0-Si-C(14) 110.74(11) C(20)-Si-C(14) 111.27(9) C(8)-Si-C(14) 107.63(9) C(7)-C(8)-Si 118.59(12) C(3)-C(8)-Si 121.40(12) C(13)-C(14)-Si 119.27(11) C(9)-C(14)-Si 120.73(11) C(19)-C(20)-Si 118.56(11) C(15)-C(20)-Si 121.44(11)

Symmetry transformations used to generate equivalent atoms: #1 -x+1,-y+1,-z+2

307 Appendix

Crystallographic data for (Ph3SiOH)2.TMEDA

Table 1. Crystal data and structure refinement for (Ph3SiOH)2.TMEDA.

Empirical formula C42H48N2O2Si2 Crystal size 0.15 x 0.20 x 0.38 Formula weight 334.50 Temperature / K 213(2) Wavelength / A 0.71073 Crystal system Triclinic Space group P1 Unit cell dimensions a /A 8.6331(7) b /A 10.3477(8) c /A 11.5401(14) cde 99.774(8) Pr 91.109(9) le 1 08.791(9) U/A-3, Z 958.8(2), 2 Dc I gcm-3 1.159 µ(Mo-Koc)/mm-1 0. 129 F(000) 358 0-range /0 1.80 to 25.00 hkl-ranges -1 to 9, -12 to 11, -13 to 13 Reflections collected 4072 Independent reflections 3339 [R(int) = 0.0191] Data / restraints / parameters 3 3 39/0/ 313 Goodness-of-fit on F2 1.016 Final R indices [I>2a(I)] R1 = 0.0409, wR2 = 0.1001 (all data) R1 = 0.0575, wR2 = 0.1106 Largest cliff. peak and hole /eA-3 0.250 and -0.230

308 Appendix

Table 2. Bond lengths (A) and angles (0) for (Ph3SiOH)2.TMEDA.

Si(1)-O(1) 1.628(2) Si(1)-C(11) 1.868(2) Si(1)-C(21) 1.869(2) Si(1)-C(31) 1.872(2) N(1)-C(3) 1.468(3) N(1)-C(1) 1.467(4) N(1)-C(2) 1.470(4) C(3)-C(3)#1 1.495(4) C(11)-C(12) 1.389(3) C(11)-C(16) 1.396(3) C(12)-C(13) 1.394(4) C(13)-C(14) 1.367(4) C(14)-C(15) 1.364(4) C(15)-C(16) 1.382(3) C(31)-C(36) 1.395(3) C(31)-C(32) 1.397(3) C(32)-C(33) 1.382(3) C(33)-C(34) 1.383(3) C(34)-C(35) 1.366(3) C(35)-C(36) 1.385(3) C(21)-C(26) 1.394(3) C(21)-C(22) 1.398(3) C(22)-C(23) 1.378(3) C(23)-C(24) 1.372(4) C(24)-C(25) 1.375(4) C(25)-C(26) 1.394(3)

O(1)-H(10) 0.81(3) C(1)-H(1A) 1.03(5) C(1)-H(1B) 0.87(4) C(1)-H(1C) 0.99(3) C(2)-H(2A) 0.88(4) C(2)-H(2B) 1.00(3) C(2)-H(2C) 0.93(4) C(3)-H(3A) 0.99(2) C(3)-H(3B) 1.03(2) C(12)-H(12) 0.96(2) C(13)-H(13) 0.93(3) C(14)-H(14) 0.96(3) C(15)-H(15) 0.99(3) C(16)-H(16) 0.97(2) C(32)-H(32) 0.95(2) C(33)-H(33) 0.98(3) C(34)-H(34) 0.94(2) C(35)-H(35) 0.94(2) C(36)-H(36) 0.99(2) C(22)-H(22) 1.00(2) C(23)-H(23) 1.02(3) C(24)-H(24) 0.91(3) C(25)-11(25) 0.89(2) C(26)-H(26) 0.93(2)

0(1)-Si(1)-C(11) 107.00(9) O(1)-Si(1)-C(21) 110.07(8) C(11)-Si(1)-C(21) 109.89(9) O(1)-Si(1)-C(31) 110.13(8) C(11)-Si(1)-C(31) 108.94(8) C(21)-Si(1)-C(31) 110.74(9) Si(1)-O(1)-H(10) 118(2) C(3)-N(1)-C(1) 111.2(2) C(3)-N(1)-C(2) 108.2(3) C(1)-N(1)-C(2) 110.4(4) N(1)-C(1)-H(1A) 111(3) N(1)-C(1)-H(1B) 106(2) H(1A)-C(1)-H(1B) 113(4) N(1)-C(1)-H(1C) 108(2) H(1A)-C(1)-H(1C) 113(4) H(1B)-C(1)-H(1C) 105(3) N(1)-C(2)-H(2A) 107(3) N(1)-C(2)-H(2B) 112(2) H(2A)-C(2)-H(2B) 111(4) N(1)-C(2)-H(2C) 103(3) H(2A)-C(2)-H(2C) 109(4) H(2B)-C(2)-H(2C) 114(3) N(1)-C(3)-C(3)#1 112.7(2) N(1)-C(3)-H(3A) 109.8(13) C(3)#1-C(3)-H(3A) 108.7(13) N(1)-C(3)-H(3B) 106.7(13) C(3)#1-C(3)-H(3B) 109.7(14) H(3A)-C(3)-H(3B) 109(2) C(12)-C(11)-C(16) 117.1(2) C(12)-C(11)-Si(1) 121.9(2) C(16)-C(11)-Si(1) 121.0(2) C(11)-C(12)-C(13) 120.5(3) C(11)-C(12)-H(12) 118.6(14) C(13)-C(12)-H(12) 120.9(14) C(14)-C(13)-C(12) 120.9(3) C(14)-C(13)-H(13) 122(2) C(12)-C(13)-H(13) 117(2) C(13)-C(14)-C(15) 119.6(2) C(13)-C(14)-H(14) 121(2) C(15)-C(14)-H(14) 119(2) C(14)-C(15)-C(16) 120.2(3) C(14)-C(15)-H(15) 120(2) C(16)-C(15)-H(15) 120(2) C(15)-C(16)-C(11) 121.7(2) C(15)-C(16)-H(16) 118.3(13) C(1 1)-C(16)-H(16) 120.0(13) C(36)-C(31)-C(32) 116.4(2) C(36)-C(31)-Si(1) 122.7(2) C(32)-C(31)-Si(1) 120.7(2) C(33)-C(32)-C(31) 122.1(2) C(33)-C(32)-H(32) 119.6(14) C(31)-C(32)-H(32) 118.2(14) C(32)-C(33)-C(34) 119.6(2) C(32)-C(33)-H(33) 119(2) C(34)-C(33)-H(33) 121(2) C(35)-C(34)-C(33) 119.9(2)

309 Appendix

C(35)-C(34)-H(34) 118(2) C(33)-C(34)-H(34) 122(2) C(34)-C(35)-C(36) 120.2(2) C(34)-C(35)-H(35) 121(2) C(36)-C(35)-H(35) 119(2) C(35)-C(36)-C(31) 121.8(2) C(35)-C(36)-H(36) 119.3(13) C(31)-C(36)-H(36) 118.9(13) C(26)-C(21)-C(22) 1 17.5(2) C(26)-C(21)-Si(1) 123.8(2) C(22)-C(21)-Si(1) 1 18.7(2) C(23)-C(22)-C(21) 121.6(2) C(23)-C(22)-H(22) 119.6(14) C(21)-C(22)-H(22) 118.7(14) C(24)-C(23)-C(22) 119.8(3) C(24)-C(23)-H(23) 122(2) C(22)-C(23)-H(23) 118(2) C(23)-C(24)-C(25) 120.3(2) C(23)-C(24)-H(24) 120(2) C(25)-C(24)-H(24) 120(2) C(24)-C(25)-C(26) 120.1(3) C(24)-C(25)-H(25) 124(2) C(26)-C(25)-H(25) 116(2) C(25)-C(26)-C(21) 120.7(2) C(25)-C(26)-H(26) 119.9(13) C(21)-C(26)-H(26) 119.4(13)

Symmetry transformations used to generate equivalent atoms: # 1 -x,-y,-z

310 Appendix

Crystallographic data for (Ph3SiOH)2.18-crown-6.(H20)2

Table 1. Crystal data and structure refinement for (Ph3SiOH)2.18-crown-6.(H20)2.

Empirical formula C24H30O10Si2 Crystal size 0.10 x 0.38 x 0.40 Formula weight 853.16 Temperature / K 223(2) Wavelength /A 0.71073 A Crystal system Triclinic Space group PI Unit cell dimensions a /A 9.204(2) b /A 10.9116(12) C /A 12.638(2) a r 97.42(2) f 1° 107.57(2) 7/° 96.09(2) U/ A-3, Z 1185.7(3), 2 Dc / g cm-3 1.195 p,(Mo-Ka.) /mm-1 0.129 F(000) 456 0-range /0 1.72 to 25.00 hk/-ranges -10 to 10, -12 to 12, -15 to 14 Reflections collected 4990 Independent reflections 4143 [R(int) = 0.0441] Data / restraints / parameters 4143/0/391 Goodness-of-fit on F2 1.033 Final R indices [I>2a(I)] R1 .-- 0.0644, wR2 = 0.0996 (all data) R1 = 0.1442, wR2 = 0.1271 Largest cliff. peak and hole / eA-3 0.221 and -0.255

311 Appendix

Table 2. Bond lengths (A) and angles (°) for (Ph3SiOH)2.18-crown-64H20)2.

Si(1)-O(1) 1.629(3) Si(1)-C(31) 1.866(4) Si(1)-C(1 1) 1.868(4) Si(1)-C(21) 1.876(4) 0(2)-C(2) 1.408(5) 0(2)-C(1) 1.427(5) 0(3)-C(4) 1.406(5) 0(3)-C(3) 1.432(5) 0(4)-C(5) 1.420(5) 0(4)-C(6) 1.427(5) C(1)-C(6)#1 1.485(7) C(2)-C(3) 1.490(7) C(4)-C(5) 1.506(7) C(6)-C(1)#1 1.485(7) C(11)-C(12) 1.390(5) C(11)-C(16) 1.393(5) C(12)-C(13) 1.403(6) C(13)-C(14) 1.367(7) C(14)-C(15) 1.377(7) C(15)-C(16) 1.393(6) C(21)-C(26) 1.387(5) C(21)-C(22) 1.405(5) C(22)-C(23) 1.384(5) C(23)-C(24) 1.368(6) C(24)-C(25) 1.384(6) C(25)-C(26) 1.388(5) C(31)-C(36) 1.399(5) C(31)-C(32) 1.399(5) C(32)-C(33) 1.389(6) C(33)-C(34) 1.378(6) C(34)-C(35) 1.378(6) C(35)-C(36) 1.381(6)

C(1)-H(1A) 1.01(5) C(1)-H(1B) 1.03(4) C(2)-H(2A) 1.02(5) C(2)-H(2B) 1.07(4) C(3)-H(3A) 1.03(4) C(3)-H(3B) 0.97(4) C(4)-H(4A) 0.99(4) C(4)-H(4B) 1.07(4) C(5)-H(5A) 0.96(4) C(5)-H(5B) 1.01(4) C(6)-H(6A) 1.05(4) C(6)-H(6B) 1.05(5) C(12)-H(12) 0.96(4) C(13)-H(13) 0.97(4) C(14)-H(14) 0.95(5) C(15)-H(15) 0.98(4) C(16)-H(16) 0.99(3) C(22)-H(22) 0.92(4) C(23)-H(23) 0.97(3) C(24)-H(24) 0.96(3) C(25)-H(25) 0.95(4) C(26)-H(26) 1.00(3) C(32)-H(32) 1.01(4) C(33)-H(33) 0.92(4) C(34)-H(34) 0.97(4) C(35)-H(35) 0.95(3) C(36)-H(36) 0.97(3) 0(1W)-H(1WA) 0.91(5) 0(1W)-H(1 WB) 0.72(4) 0(1)-H(10) 0.78(3)

0(1)-Si(1)-C(31) 106.9(2) 0(1)-Si(1)-C(11) 110.5(2) C(31)-Si(1)-C(1 1) 108.3(2) 0(1)-S i(1)-C(21) 1 12.2(2) C(31)-Si(1)-C(21) 109.8(2) C(11)-Si(1)-C(21) 109.0(2) Si(1)-O(1)-H(10) 112(3) C(2)-O(2)-C(1) 112.1(4) C(4)-0(3)-C(3) 112.2(4) C(5)-0(4)-C(6) 112.2(4) 0(2)-C(1)-C(6)#1 108.8(4) 0(2)-C(1)-H(1A) 110(3) C(6)#1-C(1)-H(1A) 107(3) 0(2)-C(1)-H(1B) 105(2) C(6)#1-C(1)-H(1B) 113(2) H(1A)-C(1)-H(1B) 112(3) 0(2)-C(2)-C(3) 108.4(4) 0(2)-C(2)-H(2A) 109(3) C(3)-C(2)-H(2A) 112(3) 0(2)-C(2)-H(2B) 111(2) C(3)-C(2)-H(2B) 110(2) H(2A)-C(2)-H(2B) 106(3) 0(3)-C(3)-C(2) 109.5(4) 0(3)-C(3)-H(3A) 108(2) C(2)-C(3)-H(3A) 111(2) 0(3)-C(3)-H(3B) 108(3) C(2)-C(3)-H(3B) 112(3) H(3A)-C(3)-H(3B) 109(3) 0(3)-C(4)-C(5) 109.3(4) 0(3)-C(4)-H(4A) 110(2) C(5)-C(4)-H(4A) 109(2) 0(3)-C(4)-H(4B) 111(2) C(5)-C(4)-H(4B) 109(2) 11(4A)-C(4)-H(4B) 109(3) 0(4)-C(5)-C(4) 108.8(4) 0(4)-C(5)-H(5A) 112(2) C(4)-C(5)-H(5A) 109(2) 0(4)-C(5)-H(5B) 108(2) C(4)-C(5)-H(5B) 110(2) H(5A)-C(5)-H(5B) 110(4) 0(4)-C(6)-C(1)#1 109.0(5) 0(4)-C(6)-H(6A) 107(2)

312 Appendix

C(1)#1-C(6)-H(6A) 114(2) O(4)-C(6)-H(6B) 106(2) C(1)#1-C(6)-H(6B) 116(2) H(6A)-C(6)-H(6B) 105(3) C(12)-C(11)-C(16) 117.7(4) C(12)-C(11)-Si(1) 122.7(3) C(16)-C(11)-Si(1) 119.6(3) C(11)-C(12)-C(13) 120.9(5) C(11)-C(12)-H(12) 121(2) C(13)-C(12)-H(12) 118(2) C(14)-C(13)-C(12) 120.1(5) C(14)-C(13)-H(13) 125(3) C(12)-C(13)-H(13) 115(3) C(13)-C(14)-C(15) 120.1(5) C(13)-C(14)-H(14) 119(3) C(15)-C(14)-H(14) 121(3) C(14)-C(15)-C(16) 119.9(5) C(14)-C(15)-H(15) 122(2) C(16)-C(15)-H(15) 118(2) C(1 1)-C(1 6)-C(1 5) 121.3(5) C(11)-C(16)-H(16) 123(2) C(15)-C(16)-H(16) 116(2) C(26)-C(21)-C(22) 117.0(4) C(26)-C(21)-Si(1) 123.0(3) C(22)-C(21)-Si(1) 119.9(3) C(23)-C(22)-C(21) 121.0(4) C(23)-C(22)-H(22) 124(3) C(21)-C(22)-H(22) 115(2) C(24)-C(23)-C(22) 120.3(4) C(24)-C(23)-H(23) 121(2) C(22)-C(23)-H(23) 118(2) C(23)-C(24)-C(25) 120.5(4) C(23)-C(24)-H(24) 119(2) C(25)-C(24)-H(24) 121(2) C(24)-C(25)-C(26) 118.9(4) C(24)-C(25)-H(25) 120(2) C(26)-C(25)-H(25) 121(2) C(21)-C(26)-C(25) 122.3(4) C(21)-C(26)-H(26) 121(2) C(25)-C(26)-H(26) 116(2) C(36)-C(31)-C(32) 116.7(4) C(36)-C(31)-Si(1) 119.8(3) C(32)-C(31)-Si(1) 123.5(3) C(33)-C(32)-C(31) 121.5(4) C(33)-C(32)-H(32) 119(2) C(31)-C(32)-H(32) 120(2) C(34)-C(33)-C(32) 120.0(4) C(34)-C(33)-H(33) 120(3) C(32)-C(33)-H(33) 120(3) C(33)-C(34)-C(35) 119.9(4) C(33)-C(34)-H(34) 119(2) C(35)-C(34)-H(34) 121(2) C(34)-C(35)-C(36) 120.0(4) C(34)-C(35)-H(35) 122(2) C(36)-C(35)-H(35) 118(2) C(35)-C(36)-C(31) 121.9(4) C(35)-C(36)-H(36) 121(2) C(31)-C(36)-H(36) 117(2)

Symmetry transformations used to generate equivalent atoms: #1 -x,-y+1 ,-z

313 Appendix

Crystallographic data for (TsiSiPh2OH)2.TMEDA

Table 1. Crystal data and structure refinement for (TsiSiPh2OH)2.TMEDA.

Empirical formula 2[C22H380Si4].C61116N2 Formula weight 977.98 Temperature 203(2) K Diffractometer Used Siemens P4/RA Wavelength 1.54178 A Crystal system Monoclinic Space group P21/c Unit cell dimensions a = 9.7820(13) A alpha = 90° b = 12.1850(10) A beta = 93.055(12)* c = 24.988(2) A gamma = 90° Volume, Z 2974.2(5) A3, 2 Density (calculated) 1.092 Mg/3 Absorption coefficient 1.968 mm-1 F(000) 1068 Crystal morphology/size Clear prisms, 0.93 x 0.67 x 0.33 mm 0 range for data collection 4.04 to 63.98° Limiting indices -11 5. h 5_ 7, -10 5. k .5_ 14, -29 29 Reflections collected 5180 Independent reflections 4880 (Rint= 0.0727) Observed reflections 4145 [F > 46(F)] Absorption correction Semi-empirical Max. and min. transmission 0.3029 and 0.1652 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 4880 / 1 / 324 Goodness-of-fit on F2 1.028 Final R indices [I>2G(I)] RI = 0.0572, wR2 = 0.1470 R indices (all data) R1 = 0.0680, wR2 = 0.1567 Extinction coefficient 0.0057(11) Largest cliff. peak and hole 0.571 and -0.427 eA-3

314 Appendix

Table 2. Bond lengths (A) and angles (°) for (TsiSiPh2OH)2.TMEDA. N-C(2) 1.460(5) N-C(1) 1.467(4) N-C(3) 1.478(5) C(1)-C(1)#1 1.458(8) 0-Si(1) 1.628(2) Si(1)-C 1.906(3) Si(1)-C(15) 1.9208(14) Si(1)-C(9) 1.9365(14) C-Si(4') 1.852(7) c-si(2') 1.867(6) C-Si(3) 1.909(3) C-Si(2) 1.912(3) C-Si(4) 1.944(3) c-Si(3') 1.975(6) Si(2)-C(22) 1.862(5) Si(2)-C(23) 1.875(7) Si(2)-C(21) 1.885(5) Si(3)-C(31) 1.860(5) Si(3)-C(32) 1.875(5) Si(3)-C(33) 1.89(2) Si(4)-c(42) 1.846(6) Si(4)-C(43) 1.863(5) Si(4)-C(41) 1.883(7) Si(2')-C(23') 1.89(3) Si(2')-C(22') 1.95(2) Si(2')-C(21') 1.99(3) Si(3')-C(31') 1.77(5) Si(3')-C(33') 1.91(3) Si(3')-C(32') 1.93(3) Si(4')-C(41') 1.89(3) Si(4')-C(43') 1.90(5) Si(4')-C(42') 2.15(3)

C(2)-N-C(1) 114.3(4) C(2)-N-C(3) 109.2(3) C(1)-N-C(3) 107.7(3) C(1)#1-C(1)-N 114.0(4) 0-Si(1)-C 105.36(11) 0-Si(1)-C(15) 106.45(9) C-Si(1)-C(15) 116.04(10) 0-Si(1)-C(9) 106.34(9) C-Si(1)-C(9) 118.10(10) C(15)-Si(1)-C(9) 103.69(8) C(8)-C(9)-Si(1) 121.41(9) C(4)-C(9)-Si(1) 118.23(9) C(14)-C(15)-Si(1) 124.05(10) C(10)-C(15)-Si(1) 115.90(10) Si(4')-c-Si(2') 115.3(4) Si(4')-C-Si(1) 108.6(2) Si(2')-C-Si(1) 106.2(2) Si(1)-C-Si(3) 113.11(13) Si(1)-C-Si(2) 110.32(13) Si(3)-C-Si(2) 110.59(14) Si(1)-C-Si(4) 107.82(13) Si(3)-C-Si(4) 108.30(13) Si(2)-C-Si(4) 106.42(13) Si(4')-C-Si(3') 108.6(3) Si(2')-C-Si(3') 107.9(3) Si(1)-C-Si(3') 110.3(2) C(22)-Si(2)-C(23) 102.4(3) C(22)-Si(2)-C(21) 108.1(3) C(23)-Si(2)-C(21) 105.3(3) C(22)-Si(2)-C 114.3(2) C(23)-Si(2)-C 114.3(2) C(21)-Si(2)-C 111.7(2) C(31)-Si(3)-C(32) 105.5(2) C(31)-Si(3)-C(33) 105.6(4) C(32)-Si(3)-C(33) 105.1(5) C(31)-Si(3)-C 113.4(2) C(32)-Si(3)-C 114.1(2) C(33)-Si(3)-C 112.4(4) C(42)-Si(4)-C(43) 106.4(3) C(42)-Si(4)-C(41) 101.6(3) C(43)-Si(4)-C(41) 106.2(3) C(42)-Si(4)-C 114.5(2) C(43)-Si(4)-C 114.6(2) C(41)-Si(4)-C 112.4(3) C-Si(2')-C(23') 118.4(9) C-Si(2')-C(22') 115.8(8) C(23')-Si(2')-C(22') 104.7(12) C-Si(2')-C(21') 108.7(10) C(23')-Si(21)-C(21') 100.1(12) C(22')-Si(2')-C(21') 107.6(11) C(31')-Si(3')-C(33') 109(2) C(31')-Si(3')-C(32') 98(2) C(33')-Si(3')-C(32') 99.6(11) C(31')-Si(3')-C 118.2(14) C(33')-Si(3')-C 113.6(8) C(32')-Si(3')-C 115.6(9) C-Si(4')-C(41') 114.6(9) C-Si(41)-C(431) 111(2) C(41')-Si(4')-C(43') 110(2) C-Si(4')-C(42') 109.8(8) C(41')-Si(4')-C(42') 108.2(11) C(43')-Si(4')-C(42') 102(2)

Symmetry transformations used to generate equivalent atoms: #1 -x+1,-y+1,-z

315 Appendix

Crystallographic data for tBu2SiH(OH)

Table 1. Crystal data and structure refinement for tBu2SiH(OH).

Empirical formula C8I-1200Si Formula weight 160.33 Temperature 293(2) K Diffractometer Used Siemens RA/PC Wavelength 1.54178 A Crystal system Tetragonal Space group 14 Unit cell dimensions a = 15.6297(5) A alpha = 90° b = 15.6297(5) A beta = 90° c = 9.0643(8) A gamma = 90° Volume, Z 2214.3(2) A3, 8 Density (calculated) 0.962 Mg/m3 Absorption coefficient 1.447 mm-1 F(000) 720 Crystal morphology/size Clear prisms, 0.47 x 0.40 x 0.20 mm Orange for data collection 4.00 to 63.97° Limiting indices -18 5.12 2,-18 5_1‘.5. 18, -10 5__l 5_ 1 Reflections collected 2121 Independent reflections 1058 (Rint = 0.0259) Observed reflections 1031 [F > 40(F)] Absorption correction Semi-empirical Max. and min. transmission 0.7872 and 0.6366 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 1058 / 1 / 99 Goodness-of-fit on F2 1.076 Final R indices [1>2a(I)] R1 = 0.0553, wR2 = 0.1463 R indices (all data) R1 = 0.0570, wR2 = 0.1482 Absolute structure parameter -0.01(9) Largest cliff. peak and hole 0.735 and -0.258 eA-3

316 Appendix

Table 2. Bond lengths (A) and angles (°) for tBu2SiH(OH).

Si-O 1.655(3) Si-C(2) 1.876(5) Si-C(1) 1.882(6) C(1)-C(11) 1.513(8) C(1)-C(12) 1.535(8) C(1)-C(13) 1.541(9) C(2)-C(22) 1.508(6) C(2)-C(21) 1.541(9) C(2)-C(23) 1.543(7)

O-Si-C(2) 110.0(2) O-Si-C(1) 108.9(2) C(2)-Si-C(1) 117.6(2) C(11)-C(1)-C(12) 109.3(6) C(11)-C(1)-C(13) 108.1(6) C(12)-C(1)-C(13) 109.0(6) C(11)-C(1)-Si 112.8(4) C(12)-C(1)-Si 110.8(4) C(13)-C(1)-Si 106.6(5) C(22)-C(2)-C(21) 108.0(5) C(22)-C(2)-C(23) 108.1(4) C(21)-C(2)-C(23) 106.5(6) C(22)-C(2)-Si 112.6(4) C(21)-C(2)-Si 108.5(4) C(23)-C(2)-Si 112.9(4)

317