A series of oxovanadium(V) complexes containing amine pyridine(s) phenolate ligands [ONN] (2a–f) have been synthesized in high yields (68–83%) by reacting VO(OnPr)3 with 1.0 equiv. of the ligands in CH2Cl2. These complexes were characterized by 1H, 13C and 51V NMR spectroscopy and elemental analysis. X-ray structural analysis for 2a, 2c and 2d revealed that these complexes adopt a six-coordinate distorted octahedral geometry around the vanadium center in the solid state. Upon treatment with Et2AlCl and CCl3COOEt, these complexes displayed high catalytic activities for ethylene polymerization even at elevated reaction temperatures, depending on ligand structures. The resulting polymers possessed high molecular weight and unimodal molecular weight distributions, indicative of the formation of a single catalytically active species during the polymerization catalysis. Excitingly, these vanadium(V) complexes could efficiently promote ethylene/norbornene copolymerization. The observed catalytic activity for the copolymerization was higher than that for ethylene homopolymerization. Moreover, the molecular weights of the resulting copolymers increased upon increasing the norbornene feed. These results indicated that introducing a suitable amount of norbornene into the system not only could accelerate the polymerization rate but also could restrain chain transfer reactions to some extent.
通过将 VO(OnPr)3 与 1.0 等量的
配体在
CH2Cl2 中反应,高产率(68-83%)地合成了一系列含有胺
吡啶酚配体 [ONN] 的氧
钒(V)配合物(2a-f)。这些配合物通过 1H、13C 和 51V NMR 光谱和元素分析进行了表征。对 2a、2c 和 2d 进行的 X 射线结构分析表明,这些配合物在固态时围绕
钒中心呈六配位畸变八面体几何形状。用 Et2AlCl 和 CCl3COOEt 处理这些配合物后,根据
配体结构的不同,即使在较高的反应温度下,这些配合物对
乙烯聚合也显示出较高的催化活性。生成的聚合物具有高分子量和单峰分子量分布,表明在聚合催化过程中形成了单一的催化活性物种。令人兴奋的是,这些
钒(V)配合物能够有效地促进
乙烯/
降冰片烯的共聚。观察到的共聚催化活性高于
乙烯均聚催化活性。此外,随着
降冰片烯进料量的增加,所得共聚物的分子量也随之增加。这些结果表明,在体系中引入适量的
降冰片烯不仅能加快聚合速率,还能在一定程度上抑制链转移反应。