Aromatic hydroxylation using an oxo-bridged diiron(iii) complex: a bio-inspired functional model of toluene monooxygenases

Abstract

In biology, aromatic hydroxylation is carried out using a family of heme and nonheme oxygenases, such as cytochrome P450, toluene monooxygenases (TMOs), and methane monooxygenase (MMO). In contrast, a vast majority of synthetic iron based catalysts employed so far in aromatic hydroxylation are monomeric in nature. Herein, we have employed a diferric complex of an aminopyridine ligand ([(bpmen)₂Fe₂O(μ-O)(μ-OH)](ClO₄)₃ (2), bpmen = N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)-1,2-diaminoethane) towards aromatic hydroxylation with H₂O₂ and acetic acid. The diiron(III) complex shows promising reactivity in the hydroxylation of benzene and alkylbenzenes with a higher selectivity towards aromatic ring hydroxylation over alkyl chain oxidation. The μ-oxo diiron(III) core has been shown to be regenerated at the end of catalytic turnover. However, mechanistic studies indicate that the diiron(III) complex undergoes dissociation into its monomeric congener and the resulting iron(III) complex mitigates aromatic hydroxylation.