Development of Late Transition Metal Insertion Polymerization Catalysts
Polyolefins are the number one commercially produced polymeric material by volume, and find ubiquitous uses as plastics, elastomers, and fibers. They are produced from gaseous olefins such as ethylene and propylene by the action of a transition metal catalyst. Despite tremendous academic and industrial efforts and successes in catalyst development over the past decades, the copolymerization of polar functionalized olefins with sufficiently high activities still remains a largely unsolved issue. Late transition metal catalysts were shown to be more suitable for this kind of polymerization reaction due to their generally lower oxophilic character. The main goal of this thesis was the development of novel late transition olefin polymerization catalysts based on ruthenium and palladium. Prior to this work, only few active olefin polymerization Ru-catalysts
Several series of complexes based on ruthenium were synthesized, characterized and
investigated for olefin polymerization. Ru(II)-complexes of the type RuCl2(N,N,N)L with facially coordinating nitrogen donor ligands (N,N,N = trispyridyl-, trispyrazoyl-, trisimidazoyl-methane derivatives) were found to be inactive towards ethylene polymerization. Employing bisanionic disulfonate phosphines as ligands gave Ru-complexes that produced linear, high-molecular weight polyethylene in the presence of an aluminum-alkyl based cocatalyst. Increasing the electrophilicity of the complex, by decreasing the donor strength of the ligand and using higher oxidation state Ru(IV)-complexes, the polymerization activity could be increased, and one of the highest activities for any Ru-based catalyst was observed. Polar additives such as acetone fully inhibited even the most electron-rich catalysts and copolymerization reactions yielded no polymer.
In a different approach to solve the same problem, Pd-diimine complexes were modified
with pendant olefin and boronate groups. Pd-diimine complexes can facilitate the copolymerization of ethylene with acrylates, and interactions of the pendant Lewis acid group with the functional, Lewis basic comonomer was anticipated to increase catalyst activity. However, no effect of a pendant pinacol boronate was observed on the incorporation ratio of methyl acrylate in room temperature copolymerizations. The ability of the pendant olefin to coordinate to cationic Pd-species resulted in hemilabile effects. Increased catalyst stability at the cost of decreased activities was found in comparison with unfunctionalized ligands.