Cobalt(III) Alkylperoxy Complexes. Synthesis, X-ray Structure, and Role in the Catalytic Decomposition of Alkyl Hydroperoxides and in the Hydroxylation of Hydrocarbons.

Article abstract of DOI:10.1021/ja00298a022

Novel cobalt(III) alkylperoxy complexes with the general formula Co(R''BPI)(OCOR')(OOR) and Co(BPB)(OOt-Bu)(4-Mepy) were synthesized from the reaction of alkyl hydroperoxides with their Co(II) precusor, and characterized by physicochemical methods.The X-ray structure of Ib (R'' = H, R' = Ph, R = t-Bu) revealed a distorted octahedral environment with a chelating carboxylate moiety and an apically bonded tert-butylperoxy group.The reactivity of cobalt(III) alkylperoxy complexes toward hydrocarbons was found to be dependent on their thermal decomposition rate, with type I complexes being the most reactive ones.Saturated hydrocarbons are oxidized by Co(III) tert-butylperoxy complexes into alcohols, ketones, and tert-butylperoxy products.The hydroxylation reaction preferentally occurs at the more nucleophilic C-H bonds with extensive epimerization at the hydroxylated carbon atom.Hydrocarbons having labile allylic or benzylic C-H bonds react beginning at room temperature to give a large amount of allylic or benzylic tert-butyl peroxide.Olefins having no allylic hydrogen atom are preferentially transformed into epoxides.The catalytic hydroxylation of alkanes by t-BuOOH in the presence of complexes I-III has the same characteristics as the stoichiometric reaction.The homolytic decomposition and reactivity of cobalt(III) alkylperoxy complexes is discussed in the context of the Haber-Weiss mechanism of alkyl hydroperoxide decomposition and of hydrocarbon hydroxylation by first-row transition-metal peroxides.