Photo-Induced Electron-Transfer Reactions of Cyclic Organosilanes and Related Compounds

Under photo-induced ET conditions in the presence of CCl4 and BF4-, a Si-Si σ-bond readily undergoes chlorinative and fluorinative cleavage, and gives the corresponding chloro- and fluoro-silanes in good yields. In contrast co-photolysis of an aromatic nitrile with a disilane and a tetraalkyl group 14 metal effects selective silylation and alkylation of the nucleus at the position where spin density is high on its radical anion. Chlorination with CCl4 and the intra-molecular trap with the hydroxy group have clarified the radical cationic nature of the intermediate in the photo-induced electron transfer reactions of organooligosilanes. On the other hand, on photo-induced electron transfer, 7-silabicyclo[2.2.1]heptadiene derivatives undergo skeletal rearrangement to give 2-silabicyclo[3.2.0]heptadiene and 1-silabicyclo[2.2.1]heptadiene derivatives which are also the products from the direct photolysis. 7,8-Disilabicyclo[2.2.2]octadiene derivatives afford 1,2-dimethoxydisilane and 1,2-difluorodisilane, respectively on photo-induced electron transfer in the presence of methanol and BF4-. 1,2-Disilacyclohexadiene derivatives undergo ring contraction to give the corresponding silacyclopentadienes under photo-induced electron transfer conditions. Structural and electronic characteristics of the radical cation derived from these cyclic unsaturated organosilanes by MO calculations have been discussed.