The reaction of mu-oxo-bis(phthalocyaninato)iron(III) with hydrogen sulphide in the presence of pyridine. Evidence for axial coordination of dichloromethane

The oxo-bridged complex (py)FePc-O-FePc(py) (py = pyridine, Pc = phthalocyaninato dianion) reacts in dichloromethane with hydrogen sulphide giving elementary sulphur and the reduced (py)(2)(FePc) complex in the stoichiometric ratio 1:1. Under excess py and H,S, the reaction is first-order and the rate constant at a given py concentration is an increasing function of the reducing agent concentration, with asymptotic tendency to a limiting value. This latter depends on the pyridine concentration being higher the lower is the base concentration. When the reaction is carried out in pure pyridine, the rate constant is, instead, a strictly linear function of [H2S], with zero intercept. A reaction mechanism is proposed where the dichloromethane is directly involved in the axial coordination about the iron centers and H2S competes efficiently with both pyridine and solvent. Copyright (c) 2005 Society of Porphyrins & Phthalocyanines.