Coupled oxidation of heme without pyridine. Formation of cyano complexes of iron oxophlorin and 5-oxaporphyrin (verdoheme) from octaethylheme

Oxidative degradation of iron porphyrins under coupled oxidation conditions, which generally has involved pyridine as solvent and source of axial Ligands, results in the production of verdoheme, the iron complex of 5-oxaporphyrin in which an oxygen atom replaces a methine,group. Under pyridine-free conditions, ClFeIII(OEP) (OEP is the dianion of octaethylporphyrin) and {Fe-III(OEPO)}(2) (OEPO is the trianion of octaethyloxophlorin) have been converted into the 5-oxaporphyrin complex (verdoheme) {(NC)(2)Fe-III(OEOP)} (OEOP is the anion of octaethyl-5-oxaporphyrin). Additionally, through control of;the cyanide ion concentration, the:oxidation of ClFeIII(OEP) can be stopped to produce {Fe-III(OEPO)}2 or allowed to proceed to give {(NC)(2)Fe-III(OEOP)}. A convenient method for the preparation of {Fe-III(OEPO)}(2), and from it the free base H2OEPOH, is reported. Anionic complexes, [(NC)(py)Fe(OEPO)](-) and [(NC)(2)Fe(OEPO)](2-), related to these oxidative degradation processes have been obtained through the addition of bis(triphenylphosphine)iminium cyanide to (py)(2)Fe(OEPO) in pyridine solution or through cleavage of {Fe-III(OEPO)}(2) with potassium cyanide in methanol or with tetra(n-butyl)ammonium cyanide in chloroform solution. The products have been characterized principally through their characteristic H-1 NMR spectra, which show sizable hyperfine shifts with meso resonances upfield and methylene resonances with both up-and downfield shifts. in the presence of air, [(NC)(2)Fe(OEPO)](2-) undergoes oxidation to form the 5-oxaporphyrin complex (verdoheme) {(NC)(2)Fe-III(OEOP)}. Treatment of BrFeIII(OEPO .) with CN- produces [(NC)(2)Fe(OEPO)](-), which can also be obtained through oxidation of [(NC)(2)Fe(OEPO)](2-) with diiodine.