Development of metal complexes for water oxidation

Abstract: In the course of developing a water oxidation catalyst, five metal complexes have been synthesised, characterised and studied for catalytic activity. Three of them are dinuclear complexes (Ru, Co and Cu) of 2,6-bis[(2-hydroxybenzyl)-(2-pyridylmethyl)aminomethyl]-4-methylphenol (H3bbpmp). The fourth is a dimeric ruthenium complex with a ligandcontaining imidazoles and phenols. The fifth is a dinuclear manganese complex with benzimidazoles and carboxylates coordinating to the metal atoms.All complexes were characterised by cyclic voltammetry, UV/Vis spectroscopy, ESIMS and their catalytic activities were investigated. Furthermore, all dinuclear complexes were characterised by single crystal X-ray diffraction and EPR studies were performed on the dimeric ruthenium complex and the dinuclear manganese complex.The potential of the three complexes of H3bbpmp as catalysts for oxidation of organic compounds was investigated and it was found that the ruthenium complex catalyses the oxidation of alcohols to the corresponding ketone or aldehyde using (diacetoxyiodo)benzene as oxidant. The cobalt complex functions as an electron transfer mediator in a coupled catalytic system for allylic oxidation using oxygen gas. The oxidation of 3,5-di-tert-butylcatechol to the corresponding ortho-quinone with oxygen gas using the copper complex proved that it can be considered as a model of catecholase.The dimeric ruthenium complex and the manganese complex proved to catalyse water oxidation when using stoichiometric amounts of the oxidant Ru(bpy)3(PF6)3. Furthermore, both catalyse the oxidition of water photochemically using Ru(bpy)2(deeb)(PF6)3 as photosensitiser and Na2S2O8 as electron acceptor.