The Role of Catalytic Oxo Metal Clusters in Natural and Artificial Photosynthesis

The conversion of solar energy into a useful chemical fuel represents a major scientific goal in the drive towards a society powered by renewable energy. Useful rates of solar fuel production must rely on an efficient oxidation that generates electrons and protons. In nature's photosynthesis, this is accomplished by a tetra-manganese oxo cluster (the oxygen-evolving complex, OEC), which yields 4 protons and 4 electrons by the photo-oxidation of water. This water-splitting half-reaction must be catalyzed for solar fuel applications to make it energetically feasible. Transition-metal oxo cubane clusters related to the OEC represent intriguing model systems and design motifs for new water-splitting catalysts based on abundant metals. Molecularly derived catalysts of this type offer potential advantages, including the synthetic tunability of catalytic and chemical properties. In addition, studying high-valent molecular species can provide key insights into the mechanism of water oxidation and help bridge the gap between solid-state and molecular systems to allow for a more rational design of catalysts. This presentation will describe high-valent metal complexes and clusters and a detailed mechanism for the evolution of oxygen via water oxidation at a tetranuclear cobalt oxo cubane. An important aspect of this catalysis relates to how metals cooperate to mediate multi-electron, multi-proton oxidations. In further pursuit of these concepts, the synthesis and study of related heterometallic oxo clusters have been targeted.

Speaker: T. Don Tilley, UC Berkeley