Reactivity of peroxoiron(III) porphyrin complexes: Models for deformylation reactions catalyzed by cytochrome P-450

Abstract

Oxoiron (IV) porphyrin π-cation radical is considered as a common reactive intermediate in cytochrome P-450 catalyzed monooxygenation. However, a ferric peroxo complex has been also proposed as a reactive intermediate in deformylation reactions catalyzed by cytochrome P-450s. In spite of the importance of the peroxo complex in biological functions, reactivities of the peroxo complex have not been well elucidated. Thus, we employed several peroxo–Fe III TPP derivatives to examine the reactions with alkyl aldehydes. A reaction of [TPPFe IIIO 2] −K + (TPP=tetrakis-5,10,15,20-phenylporphyrin dianion) with cyclohexanecarboxyaldehyde in acetonitrile under He atmosphere gave cyclohexanone as a deformylated compound, along with 3-cyclohexylacrylonitrile, which was formed by the condensation of the aldehyde with acetonitrile. Similar reactions were also observed when other aldehydes were employed as the substrate. We propose that the ferric peroxo porphyrin complex attacks the aldehyde carbon as a nucleophile in these reactions. Those aldehydes were simply oxidized to the corresponding carbonic acids when OFe IVTMP (TMP, tetrakis 5,10,15,20-mesitylporphyrin dianion) π-cation radical was used as the oxidant. The results by these model studies indicate possible involvement of the peroxo complex in deformylation reactions observed in P-450 systems.