ISOLATION AND CHARACTERIZATION OF AN IRON BILIVERDIN-TYPE COMPLEX THAT IS FORMED ALONG WITH VERDOHEMOCHROME DURING THE COUPLED OXIDATION OFIRON(II) OCTAETHYLPORPHYRIN
Al. Balch et al., ISOLATION AND CHARACTERIZATION OF AN IRON BILIVERDIN-TYPE COMPLEX THAT IS FORMED ALONG WITH VERDOHEMOCHROME DURING THE COUPLED OXIDATION OFIRON(II) OCTAETHYLPORPHYRIN, Journal of the American Chemical Society, 115(20), 1993, pp. 9056-9061
The coupled oxidation process, which is a model for oxidative heme deg
radation, has been shown to produce not only verdoheme, which was firs
t described in 1930, but also a paramagnetic iron complex. Treatment o
f (OEP)-Fe(II)(py)2 (OEP is the dianion of octaethylporphyrin) with ai
r and ascorbic acid in pyridine (py) solution yields 50% diamagnetic [
(octaethyloxaporphyrin)Fe(II)(py)2]Cl, a verdoheme, and 32% paramagnet
ic {(OEB)Fe(III)2 (OEB is the octaethylbilindione trianion, a biliverd
in analog). Dimeric {(OEB)Fe(III))2 has been identified by a combinati
on 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 a
n oxygen from another OEB ligand. Treatment of {(OEB)Fe(III))2 with hy
drochloric acid gives blue octaethylbilindione in 91% yield. In pyridi
ne-d5 solution, H-1 NMR studies show that {(OEB)Fe(III)}2 undergoes cl
eavage of the Fe-O bond to form (OEB)Fe(III)(py)2. This process is rev
ersible.