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 M_n 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.