Catalytic activity of nitro- and carboxy-substituted iron porphyrins in hydrocarbon oxidation - Homogeneous solution and supported systems

A series of iron(III)porphyrins containing NO2-substituents in the meso-ort ho-phenyl or COOH-substituents in the meso-para-phenyl rings (FeP) have bee n used to catalyse hydrocarbon oxidation by iodosylbenzene. The FeP series were efficient and selective catalysts for alkene epoxidation and alkane hy droxylation. The most promising iron porphyrin, 5,10,15-tri(2-nitrophenyl)2 0-mono-(4-carboxyphenyl)porphyrin iron(IE) chloride, Fe(TNMCPP)Cl, was cova lently bound to aminopropylated silica (APS) through covalent binding betwe en -COOH groups in the FeP (after activation by reaction with SOCl2) and -N H2 groups on the funcionalised silica resulting in the anchored catalyst Si -NH-(TNMCPP)FeCl. This system proved to be a highly efficient catalyst for alkene epoxidation. The same iron porphyrin was also supported on APS throu gh electrostatic binding, resulting the heterogeneous catalyst Si-NH3+-(TNM CPP)FeCl. The iron centres are in different surroundings on the two support s as demonstrated by EPR, UV/VIS and oxidation reactions results. The Si-NH 3+-(TNMCPP)FeCl is not a good catalyst for hydrocarbon oxidation, which can be attributed to the higher polarity of this support and the bis-axial coo rdination by the free -NH2) groups of the support with the iron centre. Bot h effects are unfavourable for the interaction between the non-polar substr ates and the catalyst. (C) 2001 Elsevier Science B.V. All rights reserved.