Electron spin resonance studies of aryl-substituted cyclopolysilane anion-radicals

Abstract

Several aryl-substituted cyclopolysilanes have been reduced to anion-radicals and have been studied by ESR spectroscopy. Compounds investigated were Si 5Me 9X (X  phenyl, biphenyl, p-Me 3SiC 6H 4, p-MeC 6H 4) and p-MeC 6H 4) and Si 5Me 9SiMe 2X (X  phenyl, p-Me 3SiC 6H 4 and p-Me 2NC 6H 4). The species have ESR spectra typical of delocalized cyclopentasilane anion-radicals except for biphenylnonamethylcyclopentasilane, which gives an ESR pattern indicating that the unpaired electron is mainly associated with the biphenyl ring system. An analysis of 1H and 13C hyperfine coupling constants for Si 5Me 9X −. suggests that the principal effect of the aryl substituents is inductive. The anion-radicals of Si 5Me 9SiMe 2X decay to Si 5Me 9H −., and the electronic nature of the aryl substituent has no major effect on the stability of the parent radical.