Several novel mono( ?-enaminoketonato) vanadium complexes bearing constrained cyclic skeleton, including[(C6H5)C6H3C(O) = C(CH2)nCH = N ― Ar]VCl2(THF)2(V3a: n = 1, Ar = C6H5; V4a: n = 2, Ar = C6H5; V4b: n = 2, Ar =C6F5; V4c: n = 2, Ar =(C3H7)2C6H3; V5a: n = 3, Ar = C6H5), were synthesized and their structure and properties were characterized. The structures of V4 c and V5 a in solid-state were further confirmed by X-ray crystallographic analysis.Density functional theory(DFT) results indicated that these complexes showed enhanced steric hindrance around the metal center as compared with the acyclic analogues. Upon activation with Et2 Al Cl and in the presence of ethyl trichloroacetate as a reactivator, all of the complexes exhibited high catalytic activities(107 g PE/(mol V·h)) toward ethylene polymerization, and the obtained polymers exhibited unimodal distributions(Mw/Mn = 2.0-2.3) even produced at elevated temperatures(70-100 °C) and prolonged reaction time. When MAO was employed as a cocatalyst, they only showed moderate catalytic activities(105 g PE/(mol V·h)), but the resulting polymers had higher molecular weights(168-241 kg/mol). These vanadium complexes with cyclic skeleton also showed high catalytic activities toward ethylene/norbornene copolymerization. The produced copolymers displayed approximate alternating structure at high in-feed concentration of norbornene. The catalytic capabilities of these complexes could be tuned conveniently by varying ligand structure. Furthermore, the cyclic voltammetry results also proved that these complexes exhibited better redox stabilities than the complexes bearing linear skeleton.
设计合成了一系列以吡啶二亚胺、吡啶胺-亚胺和吡啶二胺为螯合配体的三价钒配合物2a^2e,并通过红外和元素分析等技术手段对其进行了结构表征。在助催化剂和再生活化剂的存在下,这些催化剂展示出了高活性和良好的高温稳定性。得到高相对分子质量、单峰分布聚乙烯表明聚合体系为单活性中心。以吡啶二胺为螯合配体的配合物2e(2,6-bis[2,6-(iPr)2PhN C(Me)]2(C5H3N)VCl)在50℃下显示出的活性高达6.96 kg PE/mmolV·h,且在70℃时仍保持高的催化活性,这表明双阴离子吡啶二胺能更好的保护催化活性中心。此外,这类三价钒催化剂能高活性催化乙烯-降冰片烯及乙烯-己烯共聚,在温和条件下即可得到较高单体插入率(降冰片烯37.3%,己烯4.8%)的共聚物。
Vanadium(Ⅲ) complexes bearing thiophenol-phosphine ligands (2a-2b) (2-R-6-PPh2-C6H2S) VCl2(THF)2 (2a: R=H; 2b: R=Me3Si) were prepared from VCl3(THF)3 by treating with 1.0 equiv of the ligand in tetrahydrofuran in the presence of excess triethylamine. The two complexes were characterized by FTIR and mass spectra as well as elemental analyses. On activation with Et2AlCl, these complexes exhibited high catalytic activities (up to 22.1 kg PE/(mmolV·h·bar)) even at high temperature (70℃), and produced high molecular weight polymers with unimodal molecular weight distributions, indicating the polymerization took place in a single-site nature. This result may be attributed to benefits of introduction of second-row donor atoms for adjusting charge density of the vanadium centers. In addition, these complexes also exhibited high catalytic activities for ethylene/1-hexene copolymerization. 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.
