The Synthesis and Characterization of Sterically Encumbered Bithiazole Ligands: Novel Scaffolds for Metal-Based Polymerization Catalysts

The copolymerization of ethylene with vinyl co-monomers is an ongoing, and generally, unsolved problem in organometallic chemistry. Prior work has established the importance of the steric bulk (size and shape) of the catalyst in both catalytic performance and resulting polymer microstructure. Bithiazole ligands are neutral, four-electron, N-donor bidentate chelating ligands. Importantly, these bithiazole ligands may be prepared in one step from readily available a-bromoketones and dithiooxamide. Despite the striking resemblance of bithiazole to the widely studied a–diimine system, there are no reports of bithiazole-based catalysts currently in the literature. It is our hypothesis that suitably substituted bithiazole ligands will serve as catalysts in the copolymerization of ethylene and carbon monoxide (CO). We will prepare the bithiazole ligands by treatment of dithiooxamide with the appropriately bulky a-bromoketones. Subsequent reaction with commercially available nickel and palladium sources will afford the corresponding precatalysts which are capable of in-situ activation. We will initially screen their activity in the polymerization of ethylene to verify formation of polyethylene. This presentation will describe our initial efforts to prepare a novel series of bithiazole ligands. Moreover, the conversion of these ligands into metal-complexes will also be addressed.