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DOI: 10.1039/A907373F (Paper) Reference Section for: J. Chem. Soc., Dalton Trans., 1999, 4529-4533

Ferroxime(II)-catalysed oxidation of 3,5-di-tert-butylcatechol by O2. Kinetics and mechanism[hair space]†

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Tatiana L. Simándi and László I. Simándi

Abstract

The complex [Fe(Hdmg)2(MeIm)2] 1, referred to as ferroxime(II), was found to be the precursor of a selective catalyst for the oxidative dehydrogenation of 3,5-di-tert-butylcatechol (H2dbcat) to the corresponding 1,2-benzoquinone (dtbq) at room temperature and atmospheric dioxygen pressure. The observed kinetic behaviour in MeOH is consistent with solvolysis of one MeIm ligand and binding of dioxygen to the five-co-ordinate intermediate to form a superoxo complex. The latter abstracts an H atom from H2dbcat via a hydrogen-bonded ternary active intermediate, affording the semiquinone anion radical dbsq˙– and [FeIII(Hdmg)2(MeIm)(O2H)]. Utilising an electron and a proton from H2dbcat, the latter undergoes heterolytic cleavage to yield a ferryl species, which rapidly oxidises a second H2dbcat. Complexation of dbsq˙– with [FeII(Hdmg)2(MeIm)] affords a strongly coloured paramagnetic species [FeII(Hdmg)2(MeIm)(dbsq˙–)], which persists throughout the catalytic reaction, acting as buffer for dbsq˙–. The proposed mechanism involves steps similar to those of the known cytochrome P450 cycle, with H2dbcat acting as both ancillary electron source and substrate.

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