New iron-porphyrin complexes with metal-carbon bond - biological implications

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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 Fe-carbene complexes, Fe (porphyrin) (CRR''). Fe complexes of the dihalogenocarbenes CCl2, CBr2, CF2, CFBr and CFCl, were obtained which are thermally stable (up to 100.degree. 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 was not isolated since it reacts rapidly with another FeII (porphyrin) to give a heme dimer bridged by a C atom, Fe = C = Fe. Fungicides of the RSCCl3 type are reduced by ferroporphyrins with formation of Fe-CClSR carbene complexes which are transformed into very stable thiocarbonyl-Fe 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 P450-FeII-carbene complexes during reductive metabolism of various polyhalogenated compounds, as proposed previously. Cytochrome P450-carbene complexes are 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 P450-Fe bonds are discussed.