Ge You, Cai Qi, Wang Yuyin, Gao Jiangang, Chi Yue, Dai Shengyu
School of Chemical and Environmental Engineering, Anhui Polytechnic University, Wuhu, China.
Institutes of Physical Science and Information Technology, Key Laboratory of Structure and Functional Regulation of Hybrid Materials of Ministry of Education, Anhui University, Hefei, China.
Front Chem. 2022 May 4;10:886888. doi: 10.3389/fchem.2022.886888. eCollection 2022.
Most pyridine-imine Ni(II) and Pd(II) catalysts tend to yield low-molecular-weight polyethylene and ethylene-based copolymers in olefin insertion polymerization, as the unilateral axial steric structure of such complexes often cannot provide effective shielding of the metal center. In this study, we synthesized a series of hybrid "semi-sandwich" and "sandwich" type pyridine-imine Ni(II) complexes by incorporating diarylmethyl or dibenzosuberyl groups onto 8-aryl-naphthyl motif. The as-prepared Ni(II) complexes afforded highly branched polyethylene with high molecular weights (level of 10 g/mol), and moderate activities (level of 10 g/(molh)) in ethylene polymerization. Most interestingly, compared to "semi-sandwich" Ni(II) complexes bearing (2-diarylmethyl-8-aryl)naphthyl units, the "full-sandwich" counterpart containing (2-dibenzosuberyl-8-aryl)naphthyl motif was able to produce higher-molecular-weight polyethylene with higher branching density. In addition, the effect of remote non-conjugated electronic substituents in diarylmethyl groups of the Ni(II) system was also observed in ethylene polymerization.
在烯烃插入聚合反应中，大多数吡啶 - 亚胺镍（II）和钯（II）催化剂往往会生成低分子量聚乙烯和基于乙烯的共聚物，因为这类配合物的单边轴向空间结构通常无法为金属中心提供有效的屏蔽。在本研究中，我们通过将二芳基甲基或二苯并亚甲硅烷基团引入8 - 芳基萘基结构单元，合成了一系列杂化的“半夹心”和“夹心”型吡啶 - 亚胺镍（II）配合物。所制备的镍（II）配合物在乙烯聚合反应中得到了高分子量（10⁶g/mol水平）且具有中等活性（10³g/（mol·h）水平）的高度支化聚乙烯。最有趣的是，与带有（2 - 二芳基甲基 - 8 - 芳基）萘基单元的“半夹心”镍（II）配合物相比，含有（2 - 二苯并亚甲硅烷基 - 8 - 芳基）萘基结构单元的“全夹心”对应物能够生成具有更高支化密度的更高分子量聚乙烯。此外，在乙烯聚合反应中还观察到了镍（II）体系中二芳基甲基基团中远程非共轭电子取代基的影响。
