O2activation and external substrate oxidation capability of a Co(ii)–semiquinonato complex

Abstract

The synthesis, characterization and catalytic oxidizing activity of a cobalt(II)–semiquinonato complex with hydrotris(3,5-dimethyl-1-pyrazolyl)borate (=Tp^Me2) have been investigated. The cobalt(II)–semiquinonato complex can be synthesized by two alternative routes; (i) dehydrative condensation of a cobalt(II)–hydroxo complex with 3,5-di-tert-butylcatechol and following O₂ oxidation, or (ii) one-electron oxidation of catechol by a dinuclear cobalt(III)-bis(μ-oxo) complex. The synthesized cobalt(II)–semiquinonato complex can bind O₂ at low temperatures and catalyzes the oxidation of ortho- and para-hydroquinones to the corresponding benzoquinones concomitant with the generation of hydrogen peroxide. The resulting H₂O₂ is utilized as an oxidant for the epoxidation of allyl alcohol catalyzed by peroxotungstate. Aerobic oxidation of benzyl alcohol to the corresponding aldehyde is also promoted by the cobalt(II)–semiquinonato complex.