Organometallic Charge Transfer and the Reduction of Carbon Dioxide

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Dr. Clifford P. Kubiak, Department of Chemistry, Purdue University, is supported by the Inorganic, Bioinorganic, and Organometallic Program of the Chemistry Division for an investigation of charge transfer in organometallic systems that occur on the vibrational time scale and that can be interpreted within the framework of the Marcus-Hush theories of electron transfer. Intervalence charge transfer occurs near the vibrational time scale in some triruthenium clusters, as evidenced by coalescence of carbonyl infrared stretching bands, and differences in the electron exchange rates in these complexes reflect differences in the electronic coupling within the complexes. In this project the factors that control this coupling will be delineated. A self consistent physical description of the phenomenon will be developed through detailed spectroscopic studies of the dynamical IR averaging in the triruthenium complexes. The picture then will be generalized by investigations of three additional, strongly coupled organometallic charge transfer complexes: (i) laterally interconnected dimers of trinuclear clear nickel clusters; (ii) oligomeric metal clusters with strong metal-metal interactions; and (iii) new tetra(diphenylphosphino) quinodimethane bridged dinuclear metal complexes. Many of these complexes have appropriate redox potentials and catalytic properties for the electrochemical reduction of carbon dioxide, and this aspect of their chemistry will be developed. The transfer of electrons between reactants and products is a critical step in many chemical reactions. In these processes the maximum rate of electron transfer is defined by the rate of vibrations within and solvent motions about the reactant and product molecules. This study addresses electron transfer processes that take place at the same speed as molecular vibrations and will determine the factors that control the electron transfer rate. The results will permit both a better basic understanding of electron transfer and provide a basis to design systems with tuned electron transfer properties. The application of the basic knowledge gained in the project will be demonstrated by devising systems that are capable of chemically activating carbon dioxide.