Models for Verdoheme Hydrolysis. Paramagnetic Products from the Ring Opening of Verdohemes, 5-Oxaporphyrin Complexes of Iron(II), with Methoxide Ion

Abstract

Studies of the reaction of 5-oxaporphyrin iron complexes (verdohemes) with methoxide ion have been undertaken to provide models for the initial step in hydrolysis of verdohemes. Treatment of both low-spin [(py)2FeII(OEOP)]Cl and high-spin {ClFeII(OEOP)} (OEOP is the monoanion of octaethyl-5-oxaporphyrin) with methoxide ion in either pyridine or methanol solution is shown to cause ring opening and addition of methoxide to one end of the tetrapyrrole. Black {FeII(OEBOMe)}2 has been isolated in crystalline form from the reaction of {ClFeII(OEOP)} with methoxide in methanol and studied by single-crystal X-ray diffraction. The molecule has a centrosymmetric dimeric structure composed of two helical Fe(OEBOMe) units with FeN4 coordination which are connected by a pair of Fe−O bonds. Each iron ion has approximately trigonal bipyramidal geometry. Evidence is presented which suggests that {FeII(OEBOMe)}2 dissolves in dichloromethane in the presence of methanol or pyridine to form high-spin {(MeOH)nFeII(OEBOMe)} or...