O2 activation and external substrate oxidation capability of a Co(II)–semiquinonato complex

The synthesis, characterization and catalytic oxidizing activity of a cobalt(II)–semiquinonato complex with hydrotris(3,5-dimethyl-1-pyrazolyl)borate (=TpMe2) 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.