| Popis: |
Two iron(II) complexes with ligands related to TPEN, N , N , N ′, N ′-tetrakis-(2-pyridylmethyl)ethane-1,2-diamine, were prepared, characterized and compared as catalysts for the hydroxylation of aromatic compounds by H 2 O 2 . The (TPEN)Fe II 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 H 2 18 O 2 and H 2 18 O clearly showed that the oxygen atom incorporated in the aromatic substrates almost exclusively comes from H 2 O 2 . Preliminary experiments on the effects of O 2 and spin-traps on the reactions suggested a minor contribution of uncontrolled radicals such as OH. From the presently available data, a tentative mechanism based on the hydroxylation of substrates by a Fe III OOH intermediate or, more probably, by a species resulting from the O–O bond cleavage of this intermediate, such as [Fe IV O + OH], is proposed. |
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