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.
Bibliographical noteFunding Information:
Financial support was provided by the University of Minnesota (startup funds) and the ACS Petroleum Research Fund (ACSPRF 54225-DNI3). The Bruker-AXS D8 Venture diffractometer was purchased through a grant from the NSF/MRI (1224900) and the University of Minnesota. Equipment purchases for the NMR facility were supported through a grant from the NIH (S10OD011952) with matching funds from the University of Minnesota.
© 2016 American Chemical Society.