A Selective Stepwise Heme Oxygenase Model System: An Iron(IV)-Oxo Porphyrin π‑Cation Radical Leads to a Verdoheme-Type Compound via an Isoporphyrin Intermediate

The selective oxidation of the α-position of two heme-Fe^III tetraarylporphryinate complexes occurs when water­(hydroxide) attacks their oxidized Cmpd I-type equivalents, high-valent Fe^IVO π-cation radical species ((P^+•)­Fe^IVO). Stepwise intermediate formation occurs, as detected by UV–vis spectroscopic monitoring or mass spectrometric interrogation, being iron­(III) isoporphyrins, iron­(III) benzoyl-biliverdins, and the final verdoheme-like products. Heme oxygenase (HO) enzymes could proceed through heterolytic cleavage of an iron­(III)-hydroperoxo intermediate to form a transient Cmpd I-type species