Ji-Qian Wu

Vanadium(III) complexes bearing tridentate salicylaldiminato ligands (2a−f) [OC6H4CH═NL]VCl2(THF) (L = CH2CH2OMe, 2a; CH2CH2NMe2, 2b; CH2C5H4N, 2c; 8-C9H6N (quinoline), 2d; 2-MeSC6H4, 2e; 2-Ph2PC6H4, 2f) and tridentate β-enaminoketonato ligands [OC6H8CH═N-2-Ph2PC6H4]VCl2(THF) (2g) and [O(Ph)C═CHCH═N-2-Ph2PC6H4]VCl2(THF) (2h) were prepared from VCl3(THF)3 by treating with 1.0 equiv of the deprotonated ligands in tetrahydrofuran (THF). These complexes were characterized by FTIR and mass spectrometry as well as elemental analysis. Structures of complexes 2e, 2f, and 2h were further confirmed by X-ray crystallographic analysis. These complexes were investigated as catalysts for olefin polymerization in the presence of organoaluminum compounds. On activation with Et2AlCl, complexes 2a−h exhibited high catalytic activities toward ethylene polymerization (up to 20.64 kg PE/mmolV·h·bar) even at high temperature, suggesting these catalysts possess high thermal stability. Moreover, high molecular weight polymers with unimodal molecular weight distribution can be obtained, indicating the single site behavior of these catalysts. The copolymerizations of ethylene and norbornene or 1-hexene with catalysts 2a−h were also explored in the presence of Et2AlCl, which led to high molecular weight poly(ethylene-co-1-hexene)s (Mw up to 138 000) and poly(ethylene-co-norbornene)s (Mw up to 164 000). Catalytic activity, comonomer incorporation, and polymer molecular weight can be controlled in a wide range by the variation of catalyst structure and the reaction parameters such as Al/V molar ratio, comonomer feed concentration, and polymerization reaction temperature.

Vanadium(III) complexes bearing salicylaldiminato ligands (2a−k) [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 (3a−k), [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 2a−k 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 3a−k 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.

A series of novel vanadium(III) complexes bearing iminopyrrolide chelating ligands [2-(RN=CH)C4H3N]V(THF)2Cl2 (2a: R = cyclohexyl; 2b: R = Ph; 2c: R = 2,6-iPr2C6H3; 2d: R = p-CF3C6H4; 2e: R = C6F5) have been synthesized and characterized. Single-crystal X-ray diffraction revealed that complexes 2a, 2c and 2e adopt an octahedral geometry around the vanadium center. In the presence of Et2AlCl as a co-catalyst, these complexes displayed high catalytic activities up to 48.6 kg PE mmol(V)(-1) h(-1) bar(-1) for ethylene polymerization, and produced high molecular weight polymers. 2a-e/Et2AlCl catalytic systems were tolerant to elevated temperature (70 degrees C) and yielded unimodal polyethylenes, indicating the single site behaviour of these catalysts. By pre-treating with equimolar amounts of alkylaluminums, functional alpha-olefin 10-undecen-1-ol can be efficiently incorporated into polyethylene chains. 10-Undecen-1-ol incorporation can easily reach 15.8 mol% under the mild conditions. When compared with VCl3(THF)3 or rac-Et[Ind]2ZrCl2, these vanadium(III) complexes exhibited higher activities towards the copolymerization, and can incorporate more 10-undecen-1-ol into polymer chains under the similar conditions.

A series of novel neutral nickel complexes based on cyclic β-ketiminato ligands, [(2,6-iPr2C6H3)N═CHC6H8O]Ni(Ph)(PPh3) (3b), [(2,6-iPr2C6H3)N═CHCn+3H2n+2O(C6H4)]Ni(Ph)(PPh3) (6a−c), and [(2,6-iPr2C6H3)N═CHCn+3H2n+2O(C6H4)]Ni(CH3)(Py) (7a−c: a, n = 0; b, n = 1; c, n = 2) have been synthesized and characterized. These conveniently accessible complexes proved to be highly active catalysts for ethylene polymerization without an activator. Under the optimized conditions, an activity of 71.4 kg of PE/((mol of Ni) h atm) was observed using 6c as a catalyst. Particularly, it is of great interest that a bulky substituent proximate to the oxygen atom of the β-ketiminato complex is no longer a prerequisite to attain high catalytic efficiency, which is much different from the case for salicylaldiminato neutral nickel catalysts. This is effectively supported by the lower activation enthalpy changes of complexes 3b and 6a−c relative to values for the classic salicylaldiminato complexes. Moreover, for complexes 6a−c and 7a−c, the degree of conjugation between the phenylene ring and the corresponding nickel chelate of the complex can be tuned via changes in the ligand structure, which remarkably influence the molecular weights and the microstructures of the resulting polyethylenes. In comparison with the highly conjugated complexes 6a and 7a, complexes 6b,c and 7b,c, with a low degree of conjugation, produced polyethylenes with much higher molecular weights and lower branch contents. X-ray crystallographic analysis of 3b and 6a−c provides detailed information about the differences among these structures, and various typical angles and bond distances produce evidence of the conjugation modulation effect.