New Iron-Porphyrin Complexes with Metal-Carbon Bond - Biological Implications

Abstract

A study of the reactions of ferroporphyrins, in the presence of an excess of a reducing agent, with various polyhalogenated compounds, has led to a general method of preparation of iron-carbene complexes, Fe(porphyrin)(CRR'). It has thus been possible to obtain iron complexes of the dihalogenocarbenes CCl2, CBr2 CF2 CFBr and CFCl, which are thermally stable (up to 100°C) and not dissociated in solution, but which react irreversibly with dioxygen and nucleophiles such as pyridine or primary amines. The corresponding Fe(porphyrin)(CI2) complex has not been isolated since it reacts rapidly with another Fe11(porphyrin) to give a heme dimer bridged by a carbon atom, Fe=C=Fe. Fungicides of the RSCCl3 type are reduced by ferroporphyrins with formation of Fe-CC1SR carbene complexes which are transformed into very stable thiocarbonyl-iron porphyrin complexes upon treatment by a Lewis acid. The insecticide DDT, (pClC6H4)2CHCCl3, forms, upon reaction with ferroporphyrins, very stable vinylidene carbene complexes Fe [porphyrin] C=C (pClC6H4)2. These results strongly support the formation of cytochrome P 450-Fell-carbene complexes during reductive metabolism of various polyhalogenated compounds, as proposed previously. Cytochromes P 450-carbene complexes are also formed by in situ oxidation of the methylene group of 1,3-benzodioxole derivatives. This is strongly indicated by the spectral properties of the model complex Fe(tetraphenylporphyrin) (1,3-benzodioxol-2-carbene)(nBuS') prepared by the general method here described, from 2,2-dichloro-1,3-benzodioxole. The possible biological implications of the formation of these cytochrome P 450-iron-carbon bonds, are discussed. © IUPAC