Free radical chemistry associated with H(RSiH) nH

Abstract

Polysilanes of the type H(RSiH) n H, where R= n-hexyl or phenyl, have been used as radical-based reducing agents for organic halides. They rival the effectiveness of the other group 14 hydrides in reduction processes. The repetitive hydrogen transfer from the same molecule of H(RSiH) n H allows these compounds to be used in small quantities. Lower (5 × 10 4 M −1 s −1) and higher (6 × 10 5 M −1 s −1) limit values for the rate constant of the reaction of primary alkyl radicals with each SiH moiety of H(PhSiH) n H have been obtained by using unimolecular radical reactions as timing devices. The photochemical behavior of these polysilanes in the pi esence or absence of di- tert-butyl peroxide have been studied by EPR spectroscopy, and the −SiHR−SiR−SiHR radical (R= n-hexyl) has been identified as a transient species. Silyl radicals, obtained from H(RSiH) n H and thermally generated tert-butoxyl radicals, add to a variety of substrates containing double bonds to give the corresponding adducts for which EPR spectra have been recorded.