Mono salicylaldiminato vanadium(Ⅲ) complexes(1a-1f)[RN = CH(ArO)]VCl_2(THF)_2(Ar = C_6H_4(1a-1e),R = Ph,1a;R = p-CF_3Ph,1b;R = 2,6-Me_2Ph,1c;R = 2,6-iPr_2Ph,1d;R = cyclohexyl,1e;Ar = C_6H_2tBu_2(2,4),R = 2,6-iPr_2Ph, 1f) and bis(salicylaldiminato) vanadium(Ⅲ) complexes(2a-2f)[RN = CH(ArO)]_2VCl(THF)_x(Ar = C_6H_4(2a-2e),x = 1 (2a-2e),R = Ph,2a;R =p-CF_3Ph,2b;R = 2,6-Me_2Ph,2c;R = 2,6-iPr_2Ph,2d;R = cyclohexyl,2e;Ar = C_6H_2tBu_2(2,4),R = 2,6-iPr_2Ph,x = 0,2f) have been evaluated as the active catalysts for ethylene/1-hexene copolymerization in the presence of Et_2AlCl.The ligand substitution pattern and the catalyst structure model significantly influenced the polymerization behaviors such as the catalytic activity,the molecular weight and molecular weight distribution of the copolymers etc.The highest catalytic activity of 8.82 kg PE/(mmol_V·h) was observed for vanadium catalyst 2d with two 2,6-diisopropylphenyl substituted salicylaldiminato ligands.The copolymer with the highest molecular weight was obtained by using mono salicylaldiminato vanadium catalyst 1f having ligands with tert-butyl at the ortho and para of the aryloxy moiety.
The net charges on central metals of a serial non-metallocene early transition metal catalysts (FI catalyst) with similar steric hindrance were caculated with MM-QEq (molecular mechmism-charge equilibration) method and associated with ethylene polymerization activities of these FI catalyts. It was found that the activity increased with the net charge on metal if ignoring the influence of the steric hindrance. In other words, introduction of strong and/or more electron-withdrawing groups onto the ligand of FI catalyst would enhance the activity of the catalyst. This conculsion gave a direction to designing new FI catalyst with higher activity.
