Journal of Molecular Catalysis A-Chemical, Vol.287, No.1-2, 115-120, 2008
Non-heme iron polyazadentate complexes as catalysts for aromatic hydroxylation by H2O2: Particular efficiency of tetrakis(2-pyridylmethyl)ethylenediamine-iron(II) complexes
Two iron(II) complexes with ligands related to TPEN, N,N,N',N'-tetrakis-(2-pyridylmethyl)ethane-1,2diamine, were prepared, characterized and compared as catalysts for the hydroxylation of aromatic compounds by H2O2. The (TPEN)Fell complex gave the best yields ever reported for such iron polyazadentate catalysts with yields up to 86, 59,59 and 38% for the hydroxylation of anisole, benzene, chlorobenzene and ethylbenzene, respectively. Experiments using (H2O2)-O-18 and (H2O)-O-18 clearly showed that the oxygen atom incorporated in the aromatic substrates almost exclusively comes from H2O2. Preliminary experiments on the effects of O-2 and spintraps on the reactions suggested a minor contribution of uncontrolled radicals such as center dot OH. From the presently available data, a tentative mechanism based on the hydroxylation of substrates by a (FeOOH)-O-III intermediate or, more probably, by a species resulting from the O-O bond cleavage of this intermediate, such as [(FeO)-O-IV + center dot OH], is proposed. (c) 2008 Elsevier B.V. All rights reserved.