Hafnium and Zirconium Complexes Bearing ONN-Tridentate Ligands and Their Catalytic Properties toward Olefin Polymerization

The development of high-performance catalysts is a goal that is constantly being pursued in the field of polyolefins. In this study, a class of Hf (Hf1 and Hf2) and Zr (Zr1 and Zr2) dimethyl complexes were prepared by one-pot reactions of phenoxyimino-quinoline compounds with MMe4 (M = Hf and Zr). Both NMR spectroscopy and X-ray studies suggested the formation of phenoxyamido-quinoline metal complexes because of methyl migration from the metal center to the carbon atom of imine. These Hf and Zr complexes exhibited moderate to high activity (up to 9060 kg (PE)mol(-1)(M)h(-1)) toward ethylene homopolymerization and copolymerization with 1-octene in the presence of 1 equiv of [Ph3C][B(C6F5)(4)] as a cocatalyst. It was significant that Zr complexes were far more active than Hf complexes bearing the same ligand under otherwise identical conditions, revealing a tremendous metal center effect on catalysis. On the other hand, the nature of the ligand also strongly influenced the catalytic properties, including the activity and properties, of resultant polymers. Thus, Zr complex Zr1 with a sterically demanding and electron-donating Me group on the 2-position of quinoline showed the highest activity and good thermal stability.