Strained-ring silicon-centred radicals: silacyclobut-1-yl and related radicals

Abstract

Silacyclobut-1-yl, 1-methylsilacyclobut-1-yl and 3-methylsilacyclobut-1-yl radicals have been prepared by γ-irradiation of the parent silane in adamantane matrices. Electron paramagnetic resonance studies show that the radicals have non-planar rings; the SOMO on silicon is pseudo-equatorial. There is a substantial long range coupling of 16.4 G to the pseudo-equatorial γ-proton in the silacyclobut-1-yl radical and a smaller δ-coupling is shown to the pseudo-equatorial methyl protons in the 3-methylsilacyclobut-1-yl radical. In fluid solution at −40°C t-butoxy radicals react with silacyclobutane by an S H2 reaction at silicon to give 4-t-butoxy-4-silabut-1-yl rdicals, rather than by the expected hydrogen abstraction to give silacyclobut-1-yl radicals.