Transition Metal-Catalyzed Olefin Polymerization: Mechanistic Studies and Catalyst Design

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One of the most important industrial processes is the conversion of olefins, i.e. hydrocarbon molecules containing double bonds, to polymers. Examples of two such polymers are polyethylene and polypropylene. Although organometallic catalysts have been used in the commercial polymerization of olefins for several decades, remarkably little is understood about the detailed mechanism of the catalytic processes, and catalyst design has been largely empirical. The Principal Investigator has developed chemistry which promises to yield mechanistic details of olefin polymerization and allow more logical design of catalyst systems. Migratory insertion reactions of transition metal alkyl olefin complexes are key transformations in hetero- and homogeneous olefin polymerization reactions and numerous stoichiometric carbon-carbon bond forming reactions. The proposed work focuses on understanding fundamental aspects of this reaction coupled with preparation and study of new olefin polymerization catalysts. The Principal Investigator has obtained results recently which suggest that there is a relationship between the structure and dynamics of ethylene hydride complexes and their alkyl analogs and that ethylene hydride complexes which exist as bridged or agostic structures can serve as ethylene polymerization catalysts. A cobalt complex possessing an agostic ethyl group has been discovered which catalyzes living polymerization of ethylene. Goals of the research are (1) to synthesize and explore the reactivity and catalytic activity of cationic and neutral Co(III) complexes containing an agostic ethyl group, a neutral or anionic two-electron donor group, and either a Cp or a Cp* ligand, (2) to prepare new agostic ethylene hydride complexes and evaluate these species as olefin polymerization catalysts, (3) to develop these new complexes for living polymerization of a diverse group of olefins, with emphasis on correlations of mechanistic features with polymer structure and utilizing living systems for block and copolymerization, and 4) to develop methods to functionalize or cap one or both ends of the polymer chain with functional groups.