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Homolytic Organosilicon Group Transfer 137 Si Si Me Si Me 85 – 86 Me3Si Me Si SiMe3 SiMe3 Me3Si Si SiMe3 83 84 Me Me Si Me Me Si Me Si Me Me Si Me Si Si Me Me Me Me hν 85 Si Si Si Me Me Si Si Si Ph Me Me Ph Me Me S H i 86 Si Si + Si Me Scheme 6.18 Reaction mechanism for the photolysis of cyclic compounds 85 and 86 6.5 HOMOLYTIC ORGANOSILICON GROUP TRANSFER As we showed previously in this chapter, silicon easily expands its valence shell to become a penta-coordinated species. Therefore, it is expected that an intramolecular transfer of organosilicon group from X to Y may occur via a radical mechanism, provided that the R substituents on the silicon atom are not good leaving groups (Reaction 6.20). R Si X Y R R R Si Y R R R R R Si X X Y Me (6.20) Radical rearrangements that involve a homolytic 1,2 transfer of organosilicon group between similar or different atoms are well documented. Scheme 6.19 shows the classes of reaction that involve 1,2 silyl group migration between atoms of the second row of the periodic table. Examples of 1,2 organosilicon group migration from carbon to carbon can be found in the expansion of five- to six-membered rings, previously discussed in this chapter (see Section 6.1.1). An example of 1,2 organosilicon group transfer from carbon to oxygen is given by the radical Brook rearrangement discussed in Section 5.3.3. Examples of migration from carbon to nitrogen are also discussed in Chapter 5 in connection with
138 Unimolecular Reactions R3Si C C R3Si C N R3Si C O R 3 Si O N SiR 3 Scheme 6.19 Radical 1,2 silyl migrations SiR3 C C SiR3 C N SiR3 C O SiR3 O N SiR3 the addition of silyl radicals to C N bonds (see Section 5.4). Similar 1,2 silyl shifts from oxygen to nitrogen were w observed in solution (Scheme 6.19) [34]. In the majority of cases, only a penta-coordinated transition state, derived from the frontside attack as in Reaction (6.20), is possible. Examples of 1,2 migration of silyl group from silicon to other atoms are also well documented. Reaction (6.21) that involves a transfer from silicon to carbon has been observed in the gas phase at elevated temperatures [35]. From the measured Arrhenius parameters, i.e. log A=s 1 ¼ 12:3 and Ea ¼ 90 kJ=mol, it is clear that the reaction is unimportant around room temperature. However, this type of reaction is probably the essential step in the formation of silicon–carbon fibres by pyrolysis of methylpolysilanes. Me3Si Me Si Me CH2 SiMe3 Me Si CH2 Me (6.21) Silanethiols 87 readily undergo a radical-induced skeletal rearrangement to give 88 (Reaction 6.22) [36,37]. The key step for these reactions is the 1,2 migration of silyl group from silicon to sulfur (Reaction 6.23). Based on this reactivity, silanethiols 87 have been used as reducing agents for a fast hydrogen donation (see Section 4.6). Me3Si Me3Si Si SH AIBN, 80 �C Me3Si H Si X X 87 X = Me or SiMe3 88 Me3Si Si S SiMe3 Si S SSiMe 3 (6.22) (6.23)
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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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Page 93 and 94: 88 Addition to Unsaturated Bonds te
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Page 97 and 98: 92 Addition to Unsaturated Bonds 5.
Page 99 and 100: 94 Addition to Unsaturated Bonds R
Page 101 and 102: 96 Addition to Unsaturated Bonds Ph
Page 103 and 104: 98 Addition to Unsaturated Bonds EP
Page 105 and 106: 100 Addition to Unsaturated Bonds 5
Page 107 and 108: 102 Addition to Unsaturated Bonds T
Page 109 and 110: 104 Addition to Unsaturated Bonds R
Page 111 and 112: 106 Addition to Unsaturated Bonds a
Page 115 and 116: 110 Addition to Unsaturated Bonds S
Page 117 and 118: 112 Addition to Unsaturated Bonds T
Page 119 and 120: 114 Addition to Unsaturated Bonds I
Page 125 and 126: 120 Unimolecular Reactions 1 Si(H)M
Page 127 and 128: 122 Unimolecular Reactions t-Bu t-B
Page 129 and 130: 124 Unimolecular Reactions MeO Si O
Page 131 and 132: 126 Unimolecular Reactions t-Bu t-B
Page 133 and 134: 128 Unimolecular Reactions R 1 R 2
Page 135 and 136: 130 Unimolecular Reactions From the
Page 137 and 138: 132 Unimolecular Reactions rearrang
Page 139 and 140: 134 Unimolecular Reactions H 3 C +
Page 141: 136 Unimolecular Reactions Br O Si(
Page 145 and 146: 140 Unimolecular Reactions Me3Si O
Page 147 and 148: 142 Unimolecular Reactions 43. Albe
Page 149 and 150: 144 Consecutive Radical Reactions c
Page 151 and 152: 146 Consecutive Radical Reactions O
Page 153 and 154: 148 Consecutive Radical Reactions a
Page 155 and 156: 150 Consecutive Radical Reactions d
Page 157 and 158: 152 Consecutive Radical Reactions T
Page 159 and 160: 154 Consecutive Radical Reactions M
Page 161 and 162: 156 Consecutive Radical Reactions F
Page 167 and 168: 162 Consecutive Radical Reactions i
Page 169 and 170: 164 Consecutive Radical Reactions A
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
Page 189 and 190: 184 Consecutive Radical Reactions 8
Page 191 and 192: 186 Silyl Radicals in Polymers and
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188 Silyl Radicals in Polymers and
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220 List of Abbreviations PED photo
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222 Index Carbonyl sulfide 111 Carb
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224 Index Organosilicon boranes 2,
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226 Index Triethylsilane as mediato
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"Front Matter". In: Organosilanes in Radical Chemistry - Index of

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