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 sigma -bond readily undergoes chlorinative and fluorinative cleavage, and gives the corresponding chloro- and fluoro-silanes in good yields. In contr ast co-photolysis of an aromatic nitrile with a disilane and a tetraalkyl g roup 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 clarifi ed the radical cationic nature of the intermediate in the photo-induced ele ctron transfer reactions of organooligosilanes. On the other hand, on photo -induced electron transfer, 7-silabicyclo[2.2.1]heptadiene derivatives unde rgo skeletal rearrangement to give 2-silabicyclo[3.2.0]heptadiene and 1-sil abicyclo[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-Disilacyclohex adiene derivatives undergo ring contraction to give the corresponding silac yclopentadienes under photoinduced electron transfer conditions. Structural and electronic characteristics of the radical cation derived from these cy clic unsaturated organosilanes by MO calculations have been discussed.