Acylperoxo-iron porphyrin complexes

However, several questions remain to be answered (1) Is the postulated formation of an acylperoxo-iron(III) complex correct (2) If the answer is yes, how can it be proved (3) Does the peroxo-iron(III) porphyrin complex afford an oxoferryl porphyrin cation radical Recently such an acylperoxo-iron(III) porphyrin complex (16) in solution at low temperature has been directly observed and characterized (78). It was found that 16 did indeed react to yield the oxoferryl porphyrin cation radical 14. 

P-450 have also been discussed, especially homolysis and heterolysis of the acylperoxo-iron(lll) complex. In both cases, we consider the active species to be oxoferryl porphyrin cation radicals however, many different reactivities exist between peroxidases and P-450. Ortiz de Montellano et al. have proposed that the position of substrates in the active site might depend on the spatial characteristics of the individual enzymes and influence the detailed course of the reaction (139). These propositions should be carefully examined. Scheme XXV illustrates all of the intermediates that have been observed and/or proposed in the oxygen activation mechanism by P-450 and that have been prepared by the model systems. 

G. Preparation, Characterization, and Reaction OF Acylperoxo-Iron(III) Porphyrin Complexes... 

The oxidation of Fe(III)TMP(wi-chlorobenzoate) with 2 equivalents of mCPBA in toluene has been reported by Groves and Watanabe to give iron(III) porphyrin W-oxide (23, (89) Fig. 9). The reaction proceeded quantitatively only at low concentrations of the heme. The presence of an acid such as benzoic acid drastically depressed the formation of 23. The EPR spectrum, H NMR chemical shifts, and solution magnetic moment (5.4 /Zg) indicated that 23 was a high-spin ferric complex. Inspection of the reaction mechanism indicated that the reaction proceeded via the formation of the acylperoxo-iron(III) precursor 16, similar to the reaction carried out in dichloromethane. 

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