Radical Cage Effects in Organometallic Chemistry

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This award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports Professor David Tyler at the University of Oregon to investigate the fundamental, underlying principles of the cage effect in radical reaction chemistry. The still-confusing role of the solvent will be explored using a new model based on the "microviscosity" of the solvent. Another part of the research will focus on what effect the wavelength of light has on the cage effect in photogenerated radical cage pairs. Preliminary results show a trend opposite to that predicted by theory. Other experiments will probe spin effects on the recombination of two metal radicals, which has not been systematically addressed until now. Another set of experiments will examine the effects of radical mass, size, and shape on the cage effect. In particular, it is proposed that the ratio of the rate constants for cage escape to cage recombination is proportional to the square root of the mass divided by the surface area of the radical. This hypothesis will be tested with radicals of various masses and sizes. If this relationship is general, it will give researchers a powerful tool for predicting cage recombination efficiencies. Femtosecond timescale laser pump-probe experiments will be used to directly observe the shortlived radical cage pair. In these experiments, the cage effect for two randomly colliding radicals will be studied relative to the cage effect for a radical cage pair formed by bond homolysis. As former radicals initially have a random orientation when they meet in a cage, whereas the latter radicals are initially aligned, this difference may show up as a difference in the cage effect and in the reactivity of the cage pair. Graduate students will participate in successful internship programs, which prepare Ph.D. students for successful careers in industry or teaching by placing them in regional companies or in colleges for a one-term internship experience. The research described herein has also fostered closer ties to regional companies and colleges in the form of collaborative research projects. This has led to professors at regional colleges taking sabbatical leaves in the Professor Tyler's laboratory and to students at such colleges and companies using the instrumentation in the University of Oregon Department of Chemistry.