Mechanisms of the Oxidation of Water by Metal Oxo Complexes

In this project, the researchers propose to investigate the mechanisms of the oxidation of water to O2 by a number of well defined metal-oxo complexes. The oxidation of water to oxygen is one of the most important and fundamental chemical processes. It is a complicated reaction since it requires the loss of four electrons and four protons with the concomitant formation of an O-O bond. This reaction occurs at an enormous scale on our planet in green plants and other photosynthetic organisms, and is responsible for the present oxygen level of around 21% in our atmosphere. In these organisms oxidation of water occurs in a multi-polypeptide complex called photosystem II (PSII). The oxygen-evolving complex (OEC) of PSII is a CaMn4 cluster linked together byμ-oxo bridges. A terminal manganese oxo (Mn=O) species has been proposed as the active intermediate that oxidizes H2O to O2. Direct mechanistic study of PSII has been problematic because of the complexity of the system. A number of synthetic metal complexes are also known to catalyze water oxidation, and metal-oxo species have also been proposed as the active intermediates in these systems. Although kinetics and mechanistic studies have been carried out on these systems, the exact mechanisms have not been established. In this project, the researchers propose to study the mechanisms of the stoichiometric oxidation of water by a number of well defined ruthenium oxo complexes. The photochemical oxidation of water by these complexes will also be investigated. Attempts will be made to develop catalytic systems for water oxidation based on these complexes. In addition they will also make use of Lewis acids to activate a number of metal-oxo species to produce O2, including MnO4-, RuO4-, OsNO3- and Cr2O72-.This research should contribute to the understanding of the mechanism of O2 production in PSII. It should also inspire the development of artificial catalysts for photo-water splitting into molecular oxygen and hydrogen, which would provide a renewable and carbon-free energy source.