PHOTOCHEMICAL CARBON SILICON BOND-FORMING REACTION ON ELECTRON-DEFICIENT ALKENES BY DISILANES AND POLYSILANES VIA PHOTOINDUCED ELECTRON-TRANSFER

The phenanthrene-sensitized photoreaction of electron-deficient alkenes with disilanes in acetonitrile gave silylated alkanes in high yields. The photosilylation occurred in a highly regioselective manner at the position beta to the electron-withdrawing groups of the alkenes. With asymmetrically substituted disilanes and polysilanes, silyl groups bearing more bulky substituents were preferentially introduced to the alkenes. The photoreactions were sensitized by aromatic hydrocarbons such as phenanthrene and triphenylene, but not by pyrene or anthracene. In the absence of aromatic hydrocarbons, the photoreactions were not appreciable. The key step of the photoreactions was the reaction with the radical anions of electron-deficient alkenes of silyl radicals, which were generated by a nucleophile-assisted cleavage of the radical cations of disilanes and polysilanes. The mechanistic features of the photoreaction are discussed.