Unusual efficiency of a non-heme iron complex as catalyst for the hydroxylation of aromatic compounds by hydrogen peroxide: comparison with iron porphyrins

The non-heme iron complex, Fe(TPAA = tris-[N-(2-pyridylmethyl)-2-aminoethyl]amine)(ClO4)(2), is a bad catalyst for the epoxidation of alkenes such as cyclooctene, cyclohexene and cis-stilbene and for the hydroxylation of alkanes such as adamantane by H2O2, when compared to the iron porphyrin Fe[TDCPN5P = meso-tetra-(2,6-dichlorophenyl)-beta-pentanitroporphyrin]Cl. At the opposite, Fe(TPAA)(ClO4)2 is a much better catalyst for the hydroxylation of arenes by H2O2; in its presence, anisole, toluene, ethylbenzene, benzene and chlorobenzene are transformed into the corresponding phenols, with respective yields of 53, 17, 24, 22 and 13% based on H2O2. Interestingly, in Fe(TPAA)-catalysed oxidations of anisole, toluene and ethylbenzene by H2O2, hydroxylation of the aromatic ring is by far the major reaction, even when compared to usually favoured reactions such as benzylic oxidation and oxidative demethylation. (C) 2002 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.