Kinetics and Mechanisms of Organometallic Reactions

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This award in the Inorganic, Bioinorganic, and Organometallic Program will provide continued support to Dr. Theodore L. Brown of the Chemistry Department, University of Illinois at Urbana-Champaign, for the study of reaction mechanisms of transition metal organometallic compounds in solution. Three main lines of investigation will be pursued. First, the loss of carbonyl ligands from selected compounds will be promoted photochemically, and the reaction intermediates studied using low temperature infrared spectroscopy. Dinuclear metal carbonyls, chromium carbene complexes, hydrostannation and hydrosilation will be studied using this method. Secondly, linear free energy reationships for organometallic reactions will be developed, based on the assumptions of Marcus theory. The purpose of this portion of the reseach is to enhance the ability to predict changes in reaction rates that result from modification of reaction conditions. In particular, the consequences of changes in electronic or steric factors as ligands are varied will be investigated, especially in atom transfer and associative substitution reactions. Thirdly, molecular mechanics will be used to evaluate ligand steric effects. Early results indicate that the influence of ligand cone angles can be successfully interpreted using this approach. %%% Investigation of reaction mechanisms of organometallic compounds is reaching a stage in which the results can begin to be systematized and generalized. This work will provide guidelines for predicting reactivity in some reactions involving loss of a carbonyl ligand, atom transfer, and ligand exchange. Particular attention will be paid to assessing the effect of ligands on reactivity. These studies are important for the fundamental understanding of organometallic chemistry and catalytic processes involving organometallic compounds, and could be helpful for catalyst design.