(μ-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 O₂ at an iron phthalocyanine complex adsorbed on a carbon electrode is accomplished by the use of a peroxo-bridged pyFe^IIIPc-O₂-PcFe^IIIpy (py = pyridine, Pc = phthalocyanine dianion). Electroreduction of the dimer adsorbed on an electrode produced two solid state, cofacially fixed iron(II) phthalocyanine molecules under acidic conditions. Raman studies on the adsorbate revealed the restricted dynamics of the phthalocyanine rings adsorbed on a solid support that was responsible for the facile accommodation of an O₂ molecule between the adjacent two iron(II) atoms. The contrast with the catalytic behavior of a mononuclear iron(II) stems from the formation of a μ-peroxo bond upon the reaction with O₂, which subsequently cleaves under acidic conditions to produce two molecules of H₂O.