Hafnium and Zirconium Complexes Bearing SNN-Ligands Enhancing Catalytic Performances toward Ethylene/1-Octene Copolymerization

Abstract

The development of efficient catalysts is an ongoing pursuit in the field of olefin polymerization in order to synthesize desired polyolefins and to advance the present polymerization processes. In this contribution, the synthesis and characterization of a class of Hf and Zr complexes bearing SNN-tridentate ligands were described. The Hf (Hf1 and Hf2) and Zr (Zr1 and Zr2) trimethyl complexes were synthesized by one-pot reactions of thio-imino-quinoline ligands with in situ formed MMe4 (M = Hf, Zr). Both NMR analysis and X-ray diffraction study suggest the formation of thio-amido-quinoline metal complexes via methyl migration from Hf (or Zr) to the carbon of imine. These Hf and Zr complexes exhibited high activity and excellent thermal stability toward ethylene/1-octene copolymerization and an activity as high as 2.57 × 106 g(PE)·mol–1(cat)·h–1 was obtained by Hf1 even at 150 °C. The resultant polymers had moderate to high molecular weights (6.1–41.3 × 104 g·mol–1) with very broad distributions (D̵ = 6.8–34.7). NMR study revealed that multiple active species were formed when Hf1 was activated by 1 equiv. of [Ph3C][B(C6F5)4]