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

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.