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)(ClO 4 ) 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 H 2 O 2 , when compared to the iron porphyrin Fe〚TDCPN 5 P = meso -tetra-(2,6-dichlorophenyl)-β-pentanitroporphyrin〛Cl. At the opposite, Fe(TPAA)(ClO 4 ) 2 is a much better catalyst for the hydroxylation of arenes by H 2 O 2 ; 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 H 2 O 2 . Interestingly, in Fe(TPAA)-catalysed oxidations of anisole, toluene and ethylbenzene by H 2 O 2 , 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.