Ethylene/1-hexene copolymerization by salicylaldiminato vanadium(III) complexes activated with diethylaluminum chloride

Mono salicylaldiminato vanadium(III) complexes (1a-1f) [RN = CH(ArO)]VCl₂(THF)₂ (Ar = C₆H₄ (1a–1e), R = Ph, 1a; R = p-CF₃Ph, 1b; R = 2,6-Me₂Ph, 1c; R = 2,6-iPr₂Ph, 1d; R = cyclohexyl, 1e; Ar = C₆H₂ tBu2(2,4), R = 2,6-iPr₂Ph, 1f) and bis(salicylaldiminato) vanadium(III) complexes (2a–2f) [RN = CH(ArO)]₂VCl(THF) _x (Ar = C₆H₄ (2a–2e), x = 1 (2a–2e), R = Ph, 2a; R = p-CF₃Ph, 2b; R = 2,6-Me₂Ph, 2c; R = 2,6-iPr₂Ph, 2d; R = cyclohexyl, 2e; Ar = C₆H₂ tBu₂(2,4), R = 2,6-iPr₂Ph, x = 0, 2f) have been evaluated as the active catalysts for ethylene/1-hexene copolymerization in the presence of Et₂AlCl. 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.