Organometallic peroxy radicals. Part 5. Trialkylsilylperoxy and trialkylstannylperoxy radicals

Abstract

A variety of organosilylperoxy and organostannylperoxy radicals, R3MO2•(R = Me, Et, n-Bu, t-Bu, and Ph and M = Si and Sn) have been prepared and studied by electron spin resonance spectroscopy. Trialkylsilylperoxy radicals exist in equilibrium with a tetroxide at temperatures below 233 K with ΔH0 = −11 ± 2 kcal mol−1 and ΔS0 < −30 cal deg−1 mol−1. Above 233 K these radicals decay either with first-order, one half-order, or zero-order kinetics depending on the radical and its concentration. Trialkylstannylperoxy radicals do not exist in reversible equilibrium with a dimer below ambient temperature and they undergo self-reaction with second-order kinetics. Tri-n-butylstannylperoxy radicals react with 2,6-di-tert-butyl-4-methylphenol and cobalt(II) acetylacetonate and Arrhenius parameters for these two reactions are reported. The structure of R3SiO2•resembles the structure of alkylperoxy radicals whereas the two oxygen nuclei of R3SnO2. are magnetically equivalent and the peroxy group becomes a bidentate ligand. This structural difference has a significant effect on radical reactivity.