Organometallic Radical Chemistry; Cage Effects and Reactivity in Aqueous Solution

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In this project, which is supported by the Inorganic, Bioinorganic, and Organometallic Chemistry Program, Dr. David R. Tyler of the Department of Chemistry, University of Oregon, will continue his studies on organometallic radical reactivity. The first part of the project involves using time-resolved pump/probe spectroscopy and `slow` kinetic methods to measure the cage effect for a series of photochemically and thermally generated organometallic radicals, including substituted cyclopentadienyl compounds of Mo, titanocenes, and cobaloximes. The cage effect refers to the phenomenon that the probability of combination of a radical pair is greater in solution than in the gas phase. Cage effects are necessary to explain kinetic observations and fundamental reaction phenomena for chemical reactivity in solution in all areas of chemistry and biochemistry. Experiments will probe the effect of radical size, shape, and mass on the cage effect. The concepts of `microscopic inertia` and solvent `microviscosity` will be probed as they relate to the cage effect. Radicals with long chains will also be examined as these are directly relevant to polymer and bio-chemistry. The goal of this research is to acquire a predictive understanding of the cage effect. The second part of this project will focus on studies of the reactivity of water soluble organometallic radical species in aqueous solution. Substitution reactions of photochemically and electrochemically generated 17-electron species will be studied, as will oxidatively-induced migratory insertion reactions. The kinetics and activation parameters of these reactions will be determined by infrared spectroscopy and chronocoulometry experiments, with the goal of determining reaction mechanisms. Electron-transfer-chain reactions catalyzed by organometallic radicals will also be studied with an emphasis on determining the differences in radical reactivity between aqueous and nonaqueous solutions. Several new water soluble phosphine ligands will also be synthesized and tested in biphasic hydroformylation and hydrogenation catalysis experiments using Rh complexes. This project will provide useful and fundamentally important information on the nature of reactions in solution that involve radicals, reactive chemical compounds with an odd number of electrons. Radical reactions are ubiquitous in chemistry and biochemistry and include polymerization reactions (plastics and fibers) and life sustaining enzyme reactions. Results of the work with water soluble organometallic catalysts will be fundamental and practical. Most chemicals produced in industry involve catalysis and many processes use volatile and toxic organic solvents. There are compelling environmental reasons to develop catalysts that can use water as a solvent.