Radical reactions in the co-ordination field of transition metals. VIII—σ-phenoxy and σ-cyclohexadienoneoxy radicals co-ordinated to cobalt (III) and their generation by tert-butylperoxy radicals or by molecular oxygen complexed to cobalt
The formation of a ternary complex between phenols, Co (II)-acetylacetonate and molecular oxygen has been established at ambient temperature and in non-polar solvents. After intramolecular electron transfer the transient radical enhances the homolytic scission of the ? O? H bond of the complexed phenol. The low g value of the observed ESR spectra, the net spin delocalization to the cobalt nucleus and the interaction of the unpaired electron with only a limited number of benzene ring protons, indicate the presence of co-ordinated s?-phenoxy radicals generated from unhindered phenols (g = 2.0006 ～ 1.9997) and of co-ordinated s?-cyclohexadienoneoxy radicals generated from hindered phenols (g=1.9990 ～ 1.9980). Without the cobalt-chelating acetylacetonate ligands neither the co-ordinated s?-phenoxy nor the co-ordinated s?-cyclohexadienoneoxy radicals can be prepared, whereas co-ordinated π-tert-butylperoxy radicals Co(III)BuO2·] are generated in a high concentration during the reaction of tert-butyl hydroperoxide with CoCl2 in acetone.
