The meso-reactivity of porphyrins and related compounds. Part V. The meso-oxidation of metalloporphyrins

Abstract

The action of hydrogen peroxide in pyridine on a variety of metal complexes (Mn, Fe, Co, Ni, Cu, and Zn) of octa-ethylporphyrin under specified conditions has been shown to give metal octaethyloxophlorin derivatives in those cases where the complexed metal ion has a readily available higher oxidation level. Manganese(III) octaethyloxophlorin and dipyridinecobalt(III) octaethyloxophlorin prepared in this way have been characterised; they are identical with the products'of appropriate metallation of octaethyloxophlorin prepared by ring synthesis. Although iron(III) octaethyloxophlorin has not been isolated from the reaction, direct demetallation gives octaethyloxophlorin, and benzoylation followed by demetallation gives 5-benzoyloxyoctaethylporphyrin, again in each case identical with an authentic sample prepared by ring synthesis. Iron(III) octaethyloxophlorin readily undergoes autoxidation in pyridine to give, after hydrolysis, octaethylbilatriene-abc. The implications of these observations for the chemistry of haem catabolism are discussed.