Development of Group 4 Metal Complexes Bearing Fused-Ring Amido-Trihydroquinoline Ligands with Improved High-Temperature Catalytic Performance toward Olefin (Co)polymerization

Abstract

The development of homogeneous metal catalysts with high activity and high thermal stability is vital for the synthesis of polyolefin elastomers (POEs) in solution-phase olefin polymerization processes. In this contribution, the stoichiometric reactions of 8-(2,6-(R1)2-4-R2-anilide)-5,6,7-trihydroquinoline (1–3; 1, R1 = iPr, R2 = H; 2, R1 = Me, R2 = H; 3, R1 = Me, R2 = Me) with MMe4 (M = Hf, Zr) afforded metal complexes 1-HfMe3, 2-HfMe3, 3-HfMe3, and 1-ZrMe3 in high yields. Treatment of ligand 1 with Ti(NMe2)4 resulted in the formation of 1-Ti(NMe2)3, which reacted with SiMe2Cl2 to form 1-TiCl3. 1-TiMe3 was obtained by alkylation of 1-TiCl3 with MeMgBr. All metal complexes were characterized by 1H and 13C NMR spectroscopy, and the molecular structures of complexes 1-HfMe3, 2-HfMe3, 1-ZrMe3, and 1-TiMe3 were determined by single-crystal X-ray diffraction, revealing an approximate trigonal-bipyramidal geometry around the metal center in all of the structures. The complexes showed extremely high activity toward ethylene polymerization (up to 13860 kg of PE (mol of M)−1 h–1) and ethylene/1-octene copolymerization (up to 49000 kg of PE (mol of M)−1 h–1) at elevated temperatures (up to 140 °C). The catalytic properties were highly dependent on the appropriate matching of the metal and cocatalyst. In the presence of [Ph3C][B(C6F5)4], the activity of metal complexes with the same ligand was in the order Hf > Zr > Ti; with B(C6F5)3 as the cocatalyst, this order followed Zr > Ti > Hf; using MAO as the cocatalyst, the Ti complex was highly active, while the Hf and Zr complexes were inactive. The Hf and Zr complexes showed both high-molecular-weight capability and high 1-octene incorporation ability. Therefore, high-molecular-weight polyethylene homopolymers and ethylene/1-octene elastomers were successfully prepared, and the 1-octene incorporations of copolymers could be readily tuned from 1.3 to 43.5 mol % depending on different catalysts and polymerization conditions.