Lu Weiqing, Wang Hui, Fan Weigang, Dai Shengyu
Institutes of Physical Science and Information Technology, Key Laboratory of Structure and Functional Regulation of Hybrid Materials of Ministry of Education, Anhui University, Hefei, Anhui 230601, China.
School of Chemical and Environmental Engineering, Anhui Polytechnic University, Wuhu, Anhui 241000, China.
Inorg Chem. 2022 May 9;61(18):6799-6806. doi: 10.1021/acs.inorgchem.1c03969. Epub 2022 Apr 27.
The branching density of polyethylene generated in the α-diimine Pd(II) system is usually very high, largely independent of simple ligand modifications with steric or electronic perturbations, or the polymerization conditions. In this study, we designed and synthesized a class of bulky hybrid α-diimine Pd(II) catalysts combining -diarylmethyl and -phenyl moieties to explore the relationship between the polyethylene microstructure and the spatial structure of catalysts. In ethylene polymerization, the hybrid α-diimine Pd(II) catalysts exhibited high activities (well above 10 g·mol·h) and yielded highly branched (90-110/1000C) polyethylenes with high molecular weights (up to 278.3 kg/mol). Compared with the two corresponding symmetrical -diarylmethyl-based or -phenyl-based Pd(II) catalysts, the hybrid catalysts generated polyethylene of significantly higher branching densities (92 vs 28-34/1000C) in marked higher activities. Similar phenomena are also observed in the copolymerization of ethylene with polar monomers. Moreover, the hybrid Pd(II) catalysts can more efficiently promote the copolymerization of ethylene with various polar monomers in comparison to the corresponding symmetrical catalysts. The more open spatial environment around the metal center by using a hybrid steric strategy was proposed to be responsible for above advantages.
在α-二亚胺钯（II）体系中生成的聚乙烯支化密度通常非常高，很大程度上与通过空间位阻或电子扰动进行的简单配体修饰以及聚合条件无关。在本研究中，我们设计并合成了一类结合了二芳基甲基和苯基部分的大位阻杂化α-二亚胺钯（II）催化剂，以探索聚乙烯微观结构与催化剂空间结构之间的关系。在乙烯聚合反应中，杂化α-二亚胺钯（II）催化剂表现出高活性（远高于10 g·mol⁻¹·h⁻¹），并生成了高分子量（高达278.3 kg/mol）的高度支化（90 - 110/1000C）聚乙烯。与两种相应的对称二芳基甲基基或苯基基钯（II）催化剂相比，杂化催化剂以明显更高的活性生成了支化密度显著更高（92对28 - 34/1000C）的聚乙烯。在乙烯与极性单体的共聚反应中也观察到类似现象。此外，与相应的对称催化剂相比，杂化钯（II）催化剂能够更有效地促进乙烯与各种极性单体的共聚反应。通过采用杂化空间位阻策略在金属中心周围形成的更开放的空间环境被认为是上述优势的原因。
