Ethylene polymerization with imine and phosphine nickel complexes containing isothiocyanate

Three isothiocyanate complexes of nickel(II) containing diimine [ArN=C(Me)-C(Me)=NAr]Ni-(NCS)(2) (1), iminophosphine [Ph2PC6H4CH=NAr]Ni(NCS)(2) (2), or diphosphine (dppe)Ni(NCS)(2) (3), [Ar = 2,6-Pr-i-C6H3; dppe = 1,2-bis(diphenylphosphine)ethane] were synthesized and examined for ethylene polymerization activated by methylaluminoxane (MAO). Their behavior was compared with those of the corresponding halide analogues [ArN=C(Me)-C(Me)=NAr]NiBr2 (4), [Ph2PC6H4CH=NAr]NiBr2 (5), and (dppe)NiCl2 (6). The diimines showed the highest polymerization activity. Replacement of the halide for the NCS pseudo halide affected the activity and decreased the molecular weight of the polymer formed. The highest molecular weights were obtained with the diimine complexes. Highly branched polyethylenes were obtained with the bulkier complexes 1 and 4. Replacement of the halide for NCS in the diimine complexes also caused an increase in the branching content, whereas the opposite occurs for the iminophosphine complexes. The different activities and behavior of the catalyst systems with halide versus NCS in the polymerization of ethylene and the characteristics of the final products suggest a modification in the active species caused by the non-chelating ligand. Polymer molecular weight and branching content is dependent on the MAO/Ni molar ratio and on the working temperature. Copyright (C) 2004 John Wiley Sons, Ltd.