Homolytic organometallic reactions. Part III. An electron spin resonance study of homolytic t-butoxydealkylation of organometallic compounds. Rate constants for the reaction at boron

Abstract

When di-t-butyl peroxide is photolysed in the presence of a variety of organometallic compounds (RM) in an e.s.r. cavity, the alkoxyl radicals which are formed induce an S_H2 reaction at the metal centre, and the e.s.r. spectrum of the displaced alkyl radical R· can be observed [equation (i)]. The rates of these S_H2 reactions for a variety of trialkyl- [graphic omitted] boranes and trialkylboroxines have been studied by causing the organoboranes to compete with cyclopentane for reaction with the t-butoxyl radicals [equation (ii)], and monitoring the relative concentrations of the alkyl and cyclopentyl radicals by e.s.r. The reactions are very fast (k_i= 10⁵–10⁷ M^–1 s^–1) and are characterised by low activation energies (0–5 kcal mol^–1), and A factors generally in the range 10⁷–10⁸.