Synthesis, Structural Characterization, and Ethylene Polymerization Behavior of (Arylimido)Vanadium(V) Complexes Bearing Tridentate Schiff Base Ligands

摘要

A series of novel (arylimido)vanadium(V) complexes bearing tridentate salicylaldiminato chelating ligands, V(N-2,6- Me_2C_6H_3)Cl_2[(O-2-~tBu-4-R-C_6H_3)CH@ND] (R 5 H, D 5 2- CH_3OAC_6H_4 (2a); 2-CH_3SAC_6H_4 (2b); 2-Ph_2PAC_6H_4 (2c); 8-C_9H_6N (quinoline) (2d); CH_2C_5H_4N (2e); R 5 ~tBu, D 5 2-Ph_2PAC_6H_4 (2f)), were prepared from V(NAr)Cl_3 by reacting with 1.0 equiv of the ligands in the presence of triethylamine in tetrahydrofuran. These complexes were characterized by ~1H, ~(13)C, ~(31)P, and 51V NMR spectra and elemental analysis. The structures of 2c and 2f were further confirmed by X-ray crystallographic analysis. These (arylimido)vanadium(V) complexes are effective catalyst precursors for ethylene polymerization in the presence of Et_2AlCl as a cocatalyst and ethyl trichloroacetate as a reactivating agent. Complex 2c with a APPh_2 group in the sidearm was found to exhibit an exceptional activity up to 133800 kg polyethylene/ molV h for ethylene polymerization at 75°C, which is one of the highest activities displayed by homogeneous vanadium(V) catalysts at high temperature. Moreover, high molecular weight polymers with unimodal molecular weight distribution can be obtained, indicating the single site behavior of these catalysts.