Nickel(II) Complexes Chelated by 2-Arylimino-6-benzoxazolylpyridine: Syntheses, Characterization, and Ethylene Oligomerization

2-(2-Benzoxazolyl)-6-(1-(arylimino)-ethyl)pyridines (L) were designed as ligands, and their nickel complexes LNiX2 (X = Cl, 1a−7a; X = Br, 1b−7b) were formed. All ligands were fully characterized by NMR, FT-IR spectra, and elemental analyses, while the nickel complexes were examined by FT-IR spectra and elemental analyses. The molecular structures of nickel complexes were established by single-crystal X-ray diffraction. Complex 6a possesses coordination number 6 by coordination of one ligand, two moles of methanol, and one chloride anion, whereas complexes 1b and 5b possess coordination number 5 with distinct distortions, for 1b toward trigonal-bipyramidal geometry and for 5b toward square-pyramidal geometry. The nickel complex 1a was evaluated in the catalytic oligomerization of ethylene with different alkylaluminums as cocatalysts, and diethylaluminum chloride (Et2AlCl) proved to be the most effective. Upon activation with Et2AlCl, all nickel complexes showed outstanding thermal stability and good catalytic activity toward ethylene dimerization with high selectivity for α-C4.

本研究设计合成了2-(2-苯并恶唑基)-6-(1-(芳亚氨基)乙基)吡啶类配体(L)，并制备了其镍配合物LNiX₂（其中X为Cl时记为1a~7a，X为Br时记为1b~7b）。所有配体均通过核磁共振(NMR)、傅里叶变换红外光谱(FT-IR)以及元素分析进行了全面表征，而镍配合物则通过傅里叶变换红外光谱与元素分析完成表征。镍配合物的分子结构通过单晶X射线衍射法得以确定：配合物6a的配位数为6，由1个配体、2摩尔甲醇分子与1个氯离子配位构成；配合物1b与5b的配位数为5且存在显著结构畸变，其中1b趋近于三角双锥构型，5b则趋近于四方锥构型。以不同烷基铝为助催化剂，对镍配合物1a开展了乙烯催化齐聚反应评价，结果显示氯化二乙基铝(Et₂AlCl)的催化效果最优。经Et₂AlCl活化后，所有镍配合物均表现出优异的热稳定性，以及对乙烯二聚反应良好的催化活性与极高的α-C₄选择性。