Participation of two distinct hydroxylating intermediates in iron(III) porphyrin complex-catalyzed hydroxylation of alkanes

Abstract

We have obtained evidence that acylperoxo-iron(III) porphyrin complexes 1a are involved as reactive hydroxylating intermediates in the hydroxylation of alkanes by m-chloroperoxybenzoic acid (m-CPBA) catalyzed by electron-deficient iron(III) porphyrin complexes containing chloride as an anionic axial ligand in a solvent mixture of CH2Cl2 and CH3CN at -40 °C. In addition to the intermediacy of 1a, oxoiron(IV) porphyrin cation radical complexes 2 are formed as the reactive hydroxylating intermediates in the alkane hydroxylations by m-CPBA catalyzed by the iron(III) porphyrin complexes containing triflate (CF3SO3 -) as an anionic axial ligand under the same reaction conditions. In line with the recent proposal by Newcomb, Coon, Vaz, and co-workers for cytochrome P-450 reactions, these results suggest that two distinct electrophilic oxidants such as 1a and 2 effect the alkane hydroxylations in iron porphyrin models, depending on the reaction conditions such as the nature of the anionic axial ligands of iron(III) porphyrin complexes.