Photoinduced ionic and free-radical reactions of some organosilicon iodides

Abstract

U.v. irradiation (medium-pressure Hg lamp) induces reaction of TsiSiPh2l (1a)[Tsi =(Me3Si)3C] with methanol to give both the unrearranged and rearranged methoxides TsiSiPh2OMe and (Me3Si)2C(SiPh2Me)(SiMe2OMe); in the presence of LiNO3some (Me3Si)2C(SiPh2Me)(SiMe2ONO2) is also formed. The analogous solvolysis in PhNH2gives the rearranged anilide (Me3Si)2C(SiPh2Me)(SiMe2NHPh). These reactions are thought to involve the intermediate formation of a silico-cation. On the other hand the exclusive formation of the unrearranged chloride TsiSiPh2Cl upon irradiation in CCl4appears to involve a free-radical process. The photoinduced rearrangement of (1a) to (Me3Si)2C(SiPh2Me)(SiMe2l) in n-C5H12, n-C6H14, Et2O, and PhOMe may involve a cationic intermediate, but a free radical rearrangement cannot be ruled out; the subsequent formation of a disilaindane derivative (6) in PhOMe probably involves cyclization of a free radical. The iodide TsiSiPhMel also undergoes rearrangement to (Me3Si)2C(SiPhMe2)(SiMe2l) upon irradiation in n-C5H12. The methanolysis of TsiSiMe2l is also photo-catalysed, though less effectively than that of (1a).