Khalid Areej, Mahmood Qaiser, Razzaq Ayesha, Ma Yanping, Ren Geng, Wang Yizhou, Liang Tongling, Sun Wen-Hua
Key Laboratory of Engineering Plastics, Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences Beijing 100190 China
Chemistry and Chemical Engineering Guangdong Laboratory Shantou 515031 China
RSC Adv. 2025 Sep 3;15(38):31597-31608. doi: 10.1039/d5ra05407a. eCollection 2025 Aug 29.
Iminopyridine nickel catalysts are typically prone to facile chain transfer reactions, resulting in low molecular weight polyethylenes. In this study, a spatial proximity strategy was employed in 5-dibenzosuberyl-modified iminopyridine nickel catalysts to enhance ethylene polymerization. Using a template reaction between acetylpyridine and 5-dibenzosuberyl-functionalized aniline, a series of 2-(1-(2,6-bis(5-dibenzosuberyl)-4-(alkyl)phenylimino)ethyl)pyridine ligands were synthesized and subsequently reacted with (1,2-dimethoxyethane)NiBr to afford the corresponding nickel complexes. Single-crystal X-ray diffraction revealed a sandwich-like arrangement in the resulting nickel complexes, with short centroid-to-plane distances (average: 3.194 Å for Ni1 and 3.268 Å for Ni2 ), suggesting close spatial proximity between the benzosuberyl phenyl caps and the chelate plane. Compared to DEAC, activation with MAO resulted in a higher activity (up to 2.2 × 10 g mol h), significantly increased molecular weights (56-182 kg mol), and a narrower dispersity (PDI = 1.5-1.8). Notably, the polymer molecular weights were 10 to 100 times greater than those of most previously reported iminopyridine nickel catalysts lacking benzosuberyl steric substituents, indicating the strong and advantageous impact of the spatial proximity of benzosuberyl toward the chelate plane on polymerization. Moreover, in the case of substituent variations in the catalyst, dibenzosuberyl substituents at all the - and -positions of aniline demonstrated a positive effect on both the monomer insertion rate and chain propagation, leading to high catalytic activity and polymer molecular weights. The resulting polyethylene predominantly contained methyl branches, with an overall branching density of 53 to 99/1000C, as confirmed by high-temperature NMR measurements.
亚氨基吡啶镍催化剂通常易于发生链转移反应，导致聚乙烯分子量较低。在本研究中，在5-二苯并亚甲基修饰的亚氨基吡啶镍催化剂中采用空间邻近策略来增强乙烯聚合反应。通过乙酰吡啶与5-二苯并亚甲基官能化苯胺之间的模板反应，合成了一系列2-(1-(2,6-双(5-二苯并亚甲基)-4-(烷基)苯基亚氨基)乙基)吡啶配体，随后与(1,2-二甲氧基乙烷)溴化镍反应得到相应的镍配合物。单晶X射线衍射表明，所得镍配合物呈现夹心状排列，质心到平面的距离较短（镍1平均为3.194 Å，镍2平均为3.268 Å），表明苯并亚甲基苯基帽与螯合平面之间空间邻近。与二乙基铝氯相比，用甲基铝氧烷活化导致更高的活性（高达2.2×10⁶ g mol⁻¹ h⁻¹）、显著增加的分子量（56 - 182 kg mol⁻¹）和更窄的分散度（PDI = 1.5 - 1.8）。值得注意的是，聚合物分子量比大多数先前报道的缺乏苯并亚甲基空间取代基的亚氨基吡啶镍催化剂的分子量高10至100倍，表明苯并亚甲基与螯合平面的空间邻近对聚合反应具有强烈且有利的影响。此外，在催化剂存在取代基变化的情况下，苯胺的所有邻位和对位的二苯并亚甲基取代基对单体插入率和链增长均表现出积极影响，从而导致高催化活性和聚合物分子量。通过高温核磁共振测量证实，所得聚乙烯主要含有甲基支链，总支化密度为53至99/1000C。
