"Mercaptan-Tail" Porphyrins: Synthetic Analogues for the Active Site of Cytochrome P-450

Article abstract of DOI:10.1021/ja00369a041

The synthesis and characterization of a series of tetraarylporphyrins which bear covalently attached alkyl and aryl mercaptans designed to serve as axial ligands are described.The coordination chemistry of the iron(II) complexes of these "mercaptan-tail" porphyrins has been investigated by 1H NMR, IR, and electronic absorption spectroscopy, magnetic circular dichroism, and magnetic susceptibility measurements.Ferrous complexes of the alkyl mercaptan-tail porphyrins appear to remain four-coordinate, intermediate spin (S = 1) in solution.The situation is less clear in the case of appended aryl mercaptans and a "tail-on/tail-off" equilibrium is implicated.In the presence of carbon monoxide, however, binding of thiol trans to CO is observed in both the alkyl and aryl cases.By the addition of an appropriate base, six-coordinate mercaptide-Fe(II)-CO complexes can be generated; these reproduce quite well the characteristic absorption and MCD spectra of cytochrome P-450, suggesting that such compounds are indeed viable models for the active site of cytochrome P-450.