Trimethylsilyloxy-radicals from peroxides: electron spin resonance study of homolytic substitution on silicon

Abstract

The photolysis of trimethylsilyl t-butyl peroxide results in homolytic fission of the O–O bond. In the presence of alkenes the e.s.r. spectra of adducts of trimethylsilyloxy-radicals are observed, together with those of allylic radicals derived from hydrogen abstraction. In the absence of reactive substrates, trimethylsilyloxy-radicals are involved in an induced decomposition of the silyl peroxide by an S_H2 reaction at silicon, and the e.s.r. spectrum of the displaced t-butylperoxy-radical can be observed. The latter can also be trapped by 1,3-butadiene and the resultant allylic radical is involved in a further S_H2 reaction with the silyl peroxide. The e.s.r. spectrum observed in this case is due to cis-α-trimethylsilylallyl radical produced by the secondary photolysis of the butadiene adduct with loss of formaldehyde. The possibility of homolytic rearrangement of an allylic intermediate is ruled out.