Syntheses and Ethylene Polymerization Behavior of Supported Salicylaldimine-Based Neutral Nickel(II) Catalysts

Two novel salicylaldimine-based neutral nickel(II) complexes, [(2,6-iPr2C6H3)NCH(2-ArC6H3O)]Ni(PPh3)Ph (6, Ar = 2-(OH)C6H4; 8, Ar = 2-OH-3-(2,6-iPr2C6H3NCH)C6H3), have been synthesized,
and their structures have also been confirmed by X-ray crystallography, elemental analysis, and 1H and
13C NMR spectra. An important structural feature of the two complexes is the free hydroxyl group,
which allows them to react with silica pretreated with trimethylaluminum under immobilization by the
formation of a covalent bond between the neutral nickel(II) complex and the pretreated silica. As active
single-component catalysts, the two complexes exhibited high catalytic activities up to 1.14 and 1.47 ×
106 g PE/molNi·h for ethylene polymerization, respectively, and yielded branched polymers. Requiring
no cocatalyst, the two supported catalysts also showed relatively high activities up to 4.0 × 105 g PE/molNi·h and produced polyethylenes with high weight-average molecular weights of up to 120 kg/mol
and a moderate degree of branching (ca. 13−26 branches per 1000 carbon atoms).

本文合成了两种基于水杨醛亚胺(salicylaldimine)的中性镍(II)配合物，其结构式为[(2,6-二异丙基苯基)N=CH(2-芳基苯酚)]Ni(PPh3)Ph（其中配合物6的Ar为2-羟基苯基，配合物8的Ar为2-羟基-3-(2,6-二异丙基苯基亚胺甲基)苯基）；并通过X射线单晶衍射(X-ray crystallography)、元素分析(elemental analysis)以及氢谱(1H NMR)与碳谱(13C NMR)对其结构进行了确证。两种配合物的重要结构特征之一是带有游离羟基，使其可与经三甲基铝(trimethylaluminum)预处理的二氧化硅发生反应，通过在中性镍(II)配合物与预处理二氧化硅之间形成共价键实现固载。作为活性单组分催化剂，两种配合物分别对乙烯聚合展现出高达1.14×10^6和1.47×10^6 g 聚乙烯(PE)/(mol Ni·h)的高催化活性，所得产物为支化聚乙烯。无需额外添加助催化剂时，两种固载型催化剂同样表现出较高的催化活性，最高可达4.0×10^5 g 聚乙烯(PE)/(mol Ni·h)，所制备的聚乙烯重均分子量高达120 kg/mol，且支化度适中（约每1000个碳原子带有13~26条支链）。