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The complex [Fe(Hdmg) 2 (MeIm) 2 ] 1, referred to as ferroxime(), was found to be the precursor of a selective catalyst for the oxidative dehydrogenation of 3,5-di-tert-butylcatechol (H 2 dbcat) 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 H 2 dbcat via a hydrogen-bonded ternary active intermediate, affording the semiquinone anion radical dbsq Ϫ and [Fe III (Hdmg) 2 (MeIm)(O 2 H)]. Utilising an electron and a proton from H 2 dbcat, the latter undergoes heterolytic cleavage to yield a ferryl species, which rapidly oxidises a second H 2 dbcat. Complexation of dbsq Ϫ with [Fe II (Hdmg) 2 (MeIm)] affords a strongly coloured paramagnetic species [Fe II (Hdmg) 2 (MeIm)(dbsq Ϫ )], which persists throughout the catalytic reaction, acting as buffer for dbsq Ϫ . The proposed mechanism involves steps similar to those of the known cytochrome P450 cycle, with H 2 dbcat acting as both ancillary electron source and substrate.

Styrene is oxidized by 2,3-diclaloro-5,6-dicyano-p-benzoquinone (DDQ), affording hydroquinune mono(2-phenylethyl) ether. Kinetic studies (50~ in CHCI3) show that the reaction is faster under N2 than under air and takes place via intramolecular H-atom transfer within the 1:1 and 1:2 DDQ -styrene chargetransfer complexes. The semiquinone radical intermediate is reoxidized to DDQ by O2 when the latter is present, therefore, the apparent rate of DDQ reduction is lower. Stability constants of the CT-complexes and kinetic parameters for the oxidation are reported.

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