High-Throughput Discovery and Optimization of Hafnium Heteroaryl-amido Catalysts for the Isospecific Polymerization of Propylene

New nonmetallocene catalysts for the isospecific polymerization of propylene were discovered using high-throughput screening. These hafnium heteroaryl-amido catalysts are structural analogues of the highly successful hafnium pyridyl-amido catalysts. Initial primary and secondary screening of a library of five thiazole-amine ligands with Zr and Hf with propylene resulted in the discovery of highly active catalysts with high activity, high molecular weight capability, and stereoinduction that ranged from low to high, depending on the ligand and activation conditions. Subsequent screening revealed that bulky aryl substituents at the N-aryl (R1), thiazole ortho position (R2) and the bridge position (R3) were preferred for high activity, although stereoinduction was lower than that observed for the pyridyl-amidos. The thiazole-amine catalysts containing a 2-methoxyphenyl substituent at R2 and activation conditions that included B(C6F5)3 formed highly isotactic polypropylene with low catalyst activity. Subseque...