mu-Oxo bridged diiron(III) complexes and hydrogen peroxide: oxygenation and catalase-like activities

The crystal structures of two dinuclear iron(III) compounds with a bent mu-oxo bridge, [Fe2O(CH3CO2)(tpa)(2)][ClO4](3).2H(2)O and [Fe2O(CH3CO2)(mep)(2)][ClO4](3), were determined, where tpa and mep represent tris(2-pyridylmethyl)-amine and N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine, respectively Their structural features which include a (mu-oxo)(mu-acetato)diiron(III) core are very similar. In spite of this, these two complexes exhibit very different reactivity towards hydrogen peroxide in solution; the tpa complex showed high catalase-like activity, whereas that of the mep complex was negligible. In the oxygenation of cyclohexane the mep complex-H2O2 system exhibited high activity giving cyclohexanol and cyclohexanone, but formation of oxygenated products was negligible with the tpa complex-H2O2. The absorption spectrum of the tpa complex shows no change in the presence of H2O2; however a drastic change was observed in the spectrum of the mep complex on addition of H2O2. Based on the structural and spectroscopic data, the structures of the active species for catalase-and oxygenase-like functions and the origin of the differences in reactivity observed for these two compounds are discussed.