The Chemistry of Two-Electron Mixed Valence Excited States

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This award in the Inorganic, Bioinorganic, and Organometallic Chemistry Program supports research on two-electron transfer reactions by Dr. Daniel G. Nocera of the Chemistry Department, Massachusetts Institute of Technology. The goal of the research is to elucidate excited state reaction pathways for oxidation-reduction reactions occurring in two-electron steps at photoactivated metal centers. Each complex studied will contain two metal atoms in different oxidation states, linked by either single or multiple metal-metal bonds. In the case of single metal-metal bonded species, the oxidation states of the metals differ by two. For example, photoelimination of dihydrogen or dihalogen from hydrido halides of dirhodium bridged by difluorophospine ligands is expected to proceed through a Rh2(II,0) mixed valence intermediate that can be characterized. Additional complexes, including ones containing asymmetric ligands to stabilize the two-electron mixed valence centers, will be synthesized and studied. In the case of dimers linked by multiple bonds, two-electron mixed valency will be achieved by photogenerating a core with M-M+ character. Such species can be obtained from complexes with quadruple bonds or with an edge-sharing bioctahedral arrangement. Photoinitiated bond addition and atom transfer reactions for a variety of substrates will be explored.Multielectron reactions are not well understood, but occur in many important processes, including photocatalysis, energy conversion, and information processing. The reactions studied here are unusual in that one photon promotes the movement of two-electrons. Understanding the mechanism of multielectron transfer should open the way to new reactions involving transition metals and small molecule phototransformations. Students involved in the project will experience both synthetic techniques and physical methods.