ZnCl2 Capture Promotes Ethylene Polymerization by a Salicylaldiminato Ni Complex Bearing a Pendent 2,2′-Bipyridine Group

The effect of ZnCl2 additives on a series of (salicylaldiminato)­Ni ethylene polymerization catalysts is reported. While ZnCl2 acts solely as a pyridine scavenger for simple imine catalyst frameworks such as the biphenylimine 4, in the case of complexes containing a 2,2′-bipyridine pendent group such as 5, ZnCl2 can coordinate to generate a bimetallic Ni/Zn active species that produces a polymer with significantly higher Mn value. 5 is not catalytically active in the absence of ZnCl2, and control experiments indicate that Zn coordination of the bpy pocket to generate a heterobimetallic Ni/Zn complex is critical for productive catalysis to occur. A heterobimetallic Ni/ZnCl2 precatalyst 7 has also been synthesized and structurally characterized and shows activity similar to that of the in situ bimetallic generated from 5 + ZnCl2.

本文报道了氯化锌（ZnCl₂）添加剂对一系列水杨醛亚胺基（salicylaldiminato）镍（Ni）乙烯聚合催化剂的影响。尽管氯化锌仅作为吡啶清除剂作用于联苯亚胺4这类简单亚胺催化剂骨架；但对于带有2,2'-联吡啶（2,2′-bipyridine）侧基的金属配合物（如5）而言，氯化锌可通过配位作用生成双金属镍/锌活性物种，该物种可制备出数均分子量（Mn）显著更高的聚合物。配合物5在无氯化锌的条件下不具备催化活性，对照实验表明，氯化锌与联吡啶（bpy）配位空腔配位生成异双金属镍/锌配合物，是实现有效催化的关键。本研究还合成了异双金属Ni/ZnCl₂预催化剂7并对其进行了结构表征，其催化活性与由5与氯化锌原位生成的双金属活性物种相当。