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Synthesis, Structural Characterization, and Ethylene Polymerization Behavior of the Vanadium(III) Complexes Bearing Salicylaldiminato Ligands

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posted on 11.08.2008, 00:00 by Ji-Qian Wu, Li Pan, Ning-Hai Hu, Yue-Sheng Li
Vanadium(III) complexes bearing salicylaldiminato ligands (2ak) [RNCH(ArO)]VCl2(THF)2 (Ar = C6H4, R = Ph, 2a; p-CF3Ph, 2b; p-CH3Ph, 2c; 2,6-Me2Ph, 2d; 2,6-iPr2Ph, 2e; cyclohexyl, 2f; Ar = C6H3tBu(2), R = Ph, 2g; 2,6-iPr2Ph, 2h; Ar = C6H2tBu2(2,4), R = Ph, 2i; 2,6-iPr2Ph, 2j; Ar = C6H2Br2, R = Ph, 2k) were prepared from VCl3(THF)3 by treating with 1.0 equiv of (RNCH)ArOH in tetrahydrofuran (THF) in the presence of excess triethylamine (TEA). The reaction of VCl3(THF)3 with 2.0 equiv of (RNCH)ArOH in THF in the presence of excess TEA afforded vanadium(III) complexes bearing two salicylaldiminato ligands (3ak), [RNCH(ArO)]2VCl(THF)x (Ar = C6H4, x = 1, R = Ph, 3a; p-CF3Ph, 3b; p-CH3Ph, 3c; 2,6-Me2Ph, 3d; 2,6-iPr2Ph, 3e; cyclohexyl, 3f; Ar = C6H3tBu(2), x = 1, R = Ph, 3g; x = 0, 2,6-iPr2Ph, 3h; Ar = C6H2tBu2(2,4), x = 1, R = Ph, 3i; 2,6-iPr2Ph, x = 0, 3j; Ar = C6H2Br2, x = 1, R = Ph, 3k). These complexes were characterized by FTIR and mass spectra as well as elemental analysis. Structures of complexes 2a, 2b, 2g, 2i, 2k, 3b, 3c, 3e, 3j, and 3k were further confirmed by X-ray crystallographic analysis. The complexes were investigated as catalysts for ethylene polymerization in the presence of Et2AlCl. Complexes 2ak exhibited high catalytic activities (up to 22.3 kg PE/mmolV·h·bar) and afforded high molecular weight polymers (Mw > 100 kg/mol) with unimodal molecular weight distributions at room temperature, while displaying relatively low catalytic activities, and produced polymers with low molecular weight (Mw < 30 kg/mol) and broad molecular weight distributions at 70 °C. Complexes 3ak were also effective catalyst precursors for ethylene polymerization. Even at 70 °C these complexes produced polyethylenes with unimodal distributions. These results indicated that the structural model of the salicylaldiminato vanadium(III) complexes greatly affected the ethylene polymerization behaviors.