FORMATION AND FATE OF IRON CARBENE COMPLEXES IN REACTIONS BETWEEN A DIAZOALKANE AND IRON PORPHYRINS - RELEVANCE TO THE MECHANISM OF FORMATION OF N-SUBSTITUTED HEMES IN CYTOCHROME-P-450 DEPENDENT OXIDATION OF SYDNONES

Reaction of the diazocompound PhCH2CHN2with Fe(TpClPP = tetra-p-chlorophenylporphyrin)(Cl) at-30 °C and under argon led to a bridged carbene complex FeIII-CH(CH2Ph)-N(TpClPP)(Cl) (1) with a PhCH2CH moiety inserted between the iron and a pyrrole nitrogen atom. The visible and 1H NMR spectra of complex 1 were very similar to those of the previously described Fe(III)-porphyrin complex with a vinylidene moiety (C = CAr2) inserted into an Fe-N porphyrin bond, suggesting that 1 was also an intermediate spin (S = 3/2) Fe(III) complex. Upon electrochemical and chemical (Zn-Hg) reduction of complex 1, a diamagnetic (TpClPP)FeII(CHCH2Ph) carbene complex was obtained and characterized by visible and 1H NMR spectroscopy and mass spectrometry. The electrochemical and chemical oxidation of complex 1 led to the FeII(NCH=CHPhTpClPP)(Cl) complex 3 with an E configuration of the double bond in high yields. Treatment of 1 by HCl under anaerobic conditions also led to this N-vinylporphyrin complex and to the FeII(NCH2CH2PhTpClPP)(Cl) complex. The formation of complex 1 and its transformation into complex 3 provide a first model for the previously described formation of N-CH=CHPh-heme during the cytochrome P-450 dependent oxidative metabolism of a sydnone derivative which involves PhCH2CHN2as a reactive metabolite. Possible mechanisms for the reactions leading from 1 to 3 are discussed and compared to those proposed for the corresponding cytochrome P-450 reactions. © 1990, American Chemical Society. All rights reserved.