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

A series of iron(III)porphyrins containing NO 2-substituents in the meso- ortho-phenyl or COOH-substituents in the meso- para-phenyl rings (FeP) have been used to catalyse hydrocarbon oxidation by iodosylbenzene. The FeP series were efficient and selective catalysts for alkene epoxidation and alkane hydroxylation. The most promising iron porphyrin, 5,10,15-tri(2-nitrophenyl)20-mono-(4-carboxyphenyl)porphyrin iron(III) chloride, Fe(TNMCPP)Cl, was covalently bound to aminopropylated silica (APS) through covalent binding between COOH groups in the FeP (after activation by reaction with SOCl 2) and NH 2 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 through electrostatic binding, resulting the heterogeneous catalyst SiNH 3 +(TNMCPP)FeCl. The iron centres are in different surroundings on the two supports 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 coordination by the free NH 2 groups of the support with the iron centre. Both effects are unfavourable for the interaction between the non-polar substrates and the catalyst.