µ-Oxo-bridged diiron(III) complexes and H2O2: monooxygenase- and catalase-like activities

Abstract

The µ-oxo-bridged diiron(III) complex [Fe₂O(bipy)₄(OH₂)₂][ClO₄]₄1(bipy = 2,2′-bipyridine) was found to exhibit monooxygenase-like activity, using H₂O₂ as the oxidant. The system oxidizes alkanes to alcohols and ketones quite efficiently (46 mmol of cyclohexanol + cyclohexanone per rnmol complex in 10 min). In the case of adamantane, selectivity for the tertiary hydrogen was indicated by a high normalized C₃:C₂ ratio of 9:1. The same reaction yields and rates were obtained whether argon or dioxygen was bubbled through the solution. Dimethyl sulfide was transformed into dimethyl sulfoxide and dimethylsulfone and benzene into phenol. These results exclude O₂ as a key reactant in this system and suggest that high-valent oxoiron intermediates and hydroxyl radicals are the active species. The potential of this system is strongly limited by the instability of the catalyst and by its strong catalase-like activity. Complex 1 is actually a very efficient catalyst for hydrogen peroxide dismutation, thus transforming 50% of the excess of H₂O₂ into O₂ in 10 min.