"Front Matter". In: Organosilanes in Radical Chemistry - Index of

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Radical Chemistry on Silicon Surfaces 213 8.5.4 ADDITION OF ALKENES ON Si(100) SURFACES The method of heating at 200 8C without radical initiator has been extended to the monolayer formation on a Si(100) surface (see Figure 8.3) [66]. The reaction works also well with v-functionalized alkenes and allows further manipulation of the monolayers, such as the removal of protecting groups of acids or alcohols. A major limitation of the above mentioned hydrosilylation procedures, is the large excess of alkene required since the freshly prepared fluoride ion-etched silicon hydride surface was placed in pure liquid alkene. It was reported that it is possible to work in solution with dilute alkene but the choice of solvent has an influence on the molecular ordering of the alkyl monolayers [67]. Mesitylene was the only solvent in the study that provided well ordered monolayers and it was suggested that it is too large to fit in pinholes of the forming film and thus, it cannot interfere with the monolayer formation process. It is worth underlining two fundamental aspects of organosilicon hydrides in solution that may be also important to surface radical chain reactions: (i) The dissociation enthalpy of H w Si bond in the surface should be strongly dependent on the nature of the surface. Based on the available thermochemical data of organosilicon hydrides reported in Chapter 2, the H w Si(111) is expected to be about 10 kJ/mol weaker than the Si w H bond in dihydride-terminated Si(100) surfaces. Consequently, the rate constant for hydrogen abstraction should vary substantially depending on the nature of the silicon surface (cf. Chapter 3). (ii) The hydrogen donor abilities of solvent could also play an important role like that observed in reduction reactions (cf. Chapter 4). For example, it would be not very surprising to discover that mesitylene is also a mediator in the hydrosilylation of dihydride-terminated Si(100) surface with 1-alkenes. Therefore, attention should be paid to extrapolating a mechanistic scheme from one to another silicon surface or in comparing two similar reaction products derived from different silicon material. Under ultrahigh vacuum conditions and exposure to hydrogen atoms it is possible to produce the so-called Si(100) 2 1 dimer surface, in which the Si w H surface bonds decrease from two per silicon to only one (Scheme 8.12) [46,48]. It was shown that the addition of styrene to H w Si(100) surface could be initiated from isolated surfaces silyl radicals created using the tip of the scanning tunnelling microscope [68]. Sequence of STM images showed that by increasing the exposure to styrene, growth lines up to 13 nm long (corresponding to 34 adsorption sites) were observed. However, growth of the lines was observed to stop at pre-existing defects of the surface. It was proposed that the reaction proceeds through a surface radical chain reaction as shown in Scheme 8.12. The mechanism consists of the addition of surface silyl radical to styrene followed by a 1,5 hydrogen shift to generate another surface silyl radical that continues the chain. The interesting consequence of the anisotropic nature of the H w Si(100) surface is the preferential growth along one edge of the silicon dimer row, whereas in the analogous H w Si(111) surface experiment compact
214 Silyl Radicals in Polymers and Materials Si Si Si Si Si Si Si Si Si Si Si Si H H––Si(100) Ph H H H Si H Si H Si Si Si Si Si Si Si Si H H H Si H Si H Si Si Si Si Si Si Si Si Ph Ph H Si H Si H Si Si Si Si Si Si Si Si Ph 1,5-H shift H Ph 1,5-H shift STM tip Si Si Si Si Si Si Si Si Si Si Si Si H H H Si H Si H Si Si Si Si Si Si Si Si Ph H H Si H Si H Si Si Si Si Si Si Si Si Ph Ph H Si H Si H Si Si Si Si Si Si Si Si Scheme 8.12 Proposed mechanism of the growth of styrene line along the edge of a dimer of aH w Si(100) surface
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Organosilanes in Radical Chemistry
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DEDICATION To my parents XrZstoB an
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viii Contents 3.6 Hydrogen Atom: An
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PREFACE A large number of papers de
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ACKNOWLEDGEMENTS I thank Keith U. I
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2 Formation and Structures of Silyl
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10 Formation and Structures of Sily
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2 Thermochemistry 2.1 GENERAL CONSI
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Bond Dissociation Enthalpies 21 Tab
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Bond Dissociation Enthalpies 23 2.2
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Ion Thermochemistry 25 Table 2.4 Re
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Ion Thermochemistry 27 Table 2.5 El
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References 29 3. Goumri, A., Yuan,
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32 Hydrogen Donor Abilities of Sili
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4 Reducing Agents 4.1 GENERAL ASPEC
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General Aspects of Radical Chain Re
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Tris(trimethylsilyl)silane 53 Therm
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Tris(trimethylsilyl)silane 55 4.3.1
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Tris(trimethylsilyl)silane 57 A goo
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Tris(trimethylsilyl)silane 59 C(O)C
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Tris(trimethylsilyl)silane 61 radic
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Tris(trimethylsilyl)silane 63 86% y
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Tris(trimethylsilyl)silane 65 RO RO
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Tris(trimethylsilyl)silane 67 O AcO
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Tris(trimethylsilyl)silane 69 Tris(
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Other Silicon Hydrides 71 The reduc
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Other Silicon Hydrides 73 The decre
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Other Silicon Hydrides 75 Ph MeS O
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Other Silicon Hydrides 77 Table 4.6
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Silicon Hydride / Thiol Mixture 79
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Silylated Cyclohexadienes 81 and (4
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References 83 34. Kawashima, E., Uc
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References 85 104. Gimisis, T., Bal
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88 Addition to Unsaturated Bonds te
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90 Addition to Unsaturated Bonds ap
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92 Addition to Unsaturated Bonds 5.
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94 Addition to Unsaturated Bonds R
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96 Addition to Unsaturated Bonds Ph
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98 Addition to Unsaturated Bonds EP
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100 Addition to Unsaturated Bonds 5
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102 Addition to Unsaturated Bonds T
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104 Addition to Unsaturated Bonds R
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106 Addition to Unsaturated Bonds a
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110 Addition to Unsaturated Bonds S
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112 Addition to Unsaturated Bonds T
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114 Addition to Unsaturated Bonds I
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120 Unimolecular Reactions 1 Si(H)M
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122 Unimolecular Reactions t-Bu t-B
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124 Unimolecular Reactions MeO Si O
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126 Unimolecular Reactions t-Bu t-B
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128 Unimolecular Reactions R 1 R 2
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130 Unimolecular Reactions From the
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132 Unimolecular Reactions rearrang
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134 Unimolecular Reactions H 3 C +
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136 Unimolecular Reactions Br O Si(
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138 Unimolecular Reactions R3Si C C
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140 Unimolecular Reactions Me3Si O
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142 Unimolecular Reactions 43. Albe
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144 Consecutive Radical Reactions c
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146 Consecutive Radical Reactions O
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148 Consecutive Radical Reactions a
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150 Consecutive Radical Reactions d
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152 Consecutive Radical Reactions T
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154 Consecutive Radical Reactions M
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156 Consecutive Radical Reactions F
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Page 167 and 168: 162 Consecutive Radical Reactions i
Page 169 and 170: 164 Consecutive Radical Reactions A
Page 171 and 172: 166 Consecutive Radical Reactions O
Page 173 and 174: 168 Consecutive Radical Reactions r
Page 175 and 176: 170 Consecutive Radical Reactions E
Page 179 and 180: 174 Consecutive Radical Reactions A
Page 181 and 182: 176 Consecutive Radical Reactions P
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Page 187 and 188: 182 Consecutive Radical Reactions 1
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Page 191 and 192: 186 Silyl Radicals in Polymers and
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Page 225 and 226: 220 List of Abbreviations PED photo
Page 227 and 228: 222 Index Carbonyl sulfide 111 Carb
Page 229 and 230: 224 Index Organosilicon boranes 2,
Page 231 and 232: 226 Index Triethylsilane as mediato
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