Homogeneous Models of Ziegler-Natta Catalysts

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With support from the Inorganic, Bioinorganic and Organometallic Chemistry Program, Dr. Gregory S. Girolami will synthesize and study soluble models of the heterogeneous catalysts used widely for the industrial synthesis of such polymers as polyethylene, the so-called Ziegler-Natta catalysts. The results of the project are expected to aid in the identification of the species responsible for the catalytic activity and in the formulation of a detailed mechanism for the catalytic process. Homogeneous models of Ziegler-Natta catalysts will be synthesized and studied, with particular emphasis on the preparation and reactivity of electronically unsaturated alkyl derivatives of the early transition elements. Among the effects to be examined are the unexpected spin-state changes which occur as a result of the extremely strong pi-electron donation by the early transition metals, e.g., those of group 4, to ligand acceptor orbitals. Although octahedral geometries are generally assumed for Ziegler-Natta catalysts, d-zero metal alkyls can adopt non-octahedral geometries, and the role of the latter geometries in the catalytic process will be probed. Studies of new chromium-based polymerization systems and mechanistic studies related to the thermolysis of transition metal alkyls will be pursued also.