ISOLATION AND CHARACTERIZATION OF AN IRON BILIVERDIN-TYPE COMPLEX THAT IS FORMED ALONG WITH VERDOHEMOCHROME DURING THE COUPLED OXIDATION OF IRON(II) OCTAETHYLPORPHYRIN

The coupled oxidation process, which is a model for oxidative heme degradation, has been shown to produce not only verdoheme, which was first described in 1930, but also a paramagnetic iron complex. Treatment of (OEP)-Fe(II)(py)2 (OEP is the dianion of octaethylporphyrin) with air and ascorbic acid in pyridine (py) solution yields 50% diamagnetic [(octaethyloxaporphyrin)Fe(II)(py)2]Cl, a verdoheme, and 32% paramagnetic {(OEB)Fe(III)2 (OEB is the octaethylbilindione trianion, a biliverdin analog). Dimeric {(OEB)Fe(III))2 has been identified by a combination of H-1 NMR and X-ray crystallographic studies. In this dimer, each iron is coordinated to four nitrogen atoms from one OEB trianion and an oxygen from another OEB ligand. Treatment of {(OEB)Fe(III))2 with hydrochloric acid gives blue octaethylbilindione in 91% yield. In pyridine-d5 solution, H-1 NMR studies show that {(OEB)Fe(III)}2 undergoes cleavage of the Fe-O bond to form (OEB)Fe(III)(py)2. This process is reversible.