(mu-peroxo)bis[pyridine(phthalocyaninato)iron(III)] as a convenient catalyst for the four-electron reduction of dioxygen

A remarkable increase in the selectivity of four-electron reduction of O-2 at an iron phthalocyanine complex adsorbed on a carbon electrode is accompl ished by the use of a peroxo-bridged pyFe(III)Pc-O-2-PcFe(III)py (py = pyri dine, Pc = phthalocyanine dianion). Electroreduction of the dimer adsorbed on an electrode produced two solid state, cofacially fixed iron(II) phthalo cyanine molecules under acidic conditions. Raman studies on the adsorbate r evealed the restricted dynamics of the phthalocyanine rings adsorbed on a s olid support that was responsible for the facile accommodation of an O-2 mo lecule between the adjacent two iron(II) atoms. The contrast with the catal ytic behavior of a mononuclear iron(II) stems from the formation of a mu-pe roxo bond upon the reaction with O-2, which subsequently cleaves under acid ic conditions to produce two molecules of H2O.