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

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Silylated Fullerenes 199 EPR studies showed that R3Si: radicals (R ¼ Me, Et, i-Pr and t-Bu), obtained by hydrogen abstraction from the parent silanes by photogenerated t-BuO: radicals, add to C60 to form the corresponding adducts [29]. The spectra of Me3Si- and t-Bu3Si-adducts have hyperfine structure due to 9 and 27 equivalent protons, respectively, at 27 8C suggesting free rotation of Si w C bonds on the EPR time scale. On the other hand, the middle members of the series, Et3Siand i-Pr3Si-adduct radicals, showed a unexpected hyperfine manifold which has been accommodated with free rotation about the Si w C60 and frozen rotation about the Si w R bonds on the EPR time scale. Photolysis of some disilanes having phenyl substituents or mixed phenyl/tertbutyl substituents in the presence of C60 with a low-pressure mercury lamp (254 nm) resulted exclusively in the formation of 1,16-adducts 29 in 54–62 % yield (Reaction 8.14) [30–32]. Evidence that the initial step is the homolytic cleavage of Si w Si bond, followed by silyl radical addition to fullerene has been obtained. Similar 1,16-adducts were obtained by mixing the silyllithium derivative (t-Bu) 2PhSiLi or (Me3Si) 3SiLi with C60 at –78 8C in 69–72 % yield [33]. Although the mechanism of this reaction is unknown, the formation of a 1,16adduct suggested an involvement of radicals or radical ions [34]. The redox properties of 1,16-adduct 29 when R ¼ Ph and R 0 ¼ t-Bu consist of three reversible reductions ( 1.19, 1.59 and 2.18 V) and two irreversible oxidations (þ0.33 and þ1.20 V) in 1,2-dichlorobenzene [32]. It is worth underlining the remarkably low oxidation potential of this adduct ( þ 0:33 V) compared to C60 (þ1:21 V). R R Ph Si Si Ph R' R' + C 60 hν (254 nm) PhRR'Si SiR'RPh (8.14) R = R' = Ph 29 R = Ph, R' = t-Bu R = R' = t-Bu R = R' = SiMe3 For R ¼ R0 ¼ Me3Si, the 1,16-adduct 29 is formed in a 43 % yield (Reaction 8.14) together with the adduct 30 as a by-product in a 24 % yield (Reaction 8.15). This unusual 1,2-adduct is observed in higher yields as the only product by replacing one silyl group by phenyl, or both by isopropyl groups [30,31]. R R Ph Si Si Ph R' R' + R = R' = SiMe 3 R = Ph, R' = SiMe 3 R = R' = i-Pr C 60 hν (254 nm) H SiRR'Ph R R' Si H 30 (8.15)
200 Silyl Radicals in Polymers and Materials Interestingly, 1,2-adducts 33, 34 and 35 have also been obtained in a 69 % yield and a ratio of 1:10:9, when PhSi(SiMe3) 3 is photolysed in the presence of C60, which clearly indicates the intermediacy of silyl-adduct radical 31 followed by an intramolecular addition to the phenyl ring (32) prior to combining with Me3Si: radicals to provide these unusual adducts (Scheme 8.7) [30,31]. Me 3Si Me 3Si Si Me3Si Si Me3Si H 31 32 Me H 3Si Si Me3Si H SiMe3 33 Me 3 Si H Me3Si Si Me3Si H SiMe 3 Me 3Si H Me3Si Si Me3Si H 34 35 Scheme 8.7 Reaction paths for the formation of 1,2-adducts 33, 34 and 35 obtained from the photolysis of PhSi(SiMe3) 3 in the presence of C60 The photoreaction of polysilanes with C60 has also been investigated [35]. Reaction (8.16) shows an example in which the irradiation in benzene with a low-pressure mercury-arc lamp afforded a product that contains 14 wt% of C60 into the polysilane chain. The incorporation of C60 into the polysilane backbone has not been observed upon irradiation with l > 300 nm, when the cleavage of Si w Si bond does not take place. The adduct obtained from Reaction (8.16) has a lower oxidation potential than C60( þ 0:77 vs þ 1:21 V) and a lower reduction potential than polysilane ( 1:24 vs 2 V). Ph Si Me n + C 60 hν (254 nm) C 60 —polysilane (8.16) Laser flash photolysis experiments showed that the C60 triplet state ( 3 C 60 ), obtained by 532 nm excitation, reacts with poly(methylphenylsilane) by an
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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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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 163 and 164: 158 Consecutive Radical Reactions O
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
Page 203: 198 Silyl Radicals in Polymers and
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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