Novel unsymmetric alpha-diimine nickel(II) complexes: suitable catalysts for copolymerization reactions.

We established a strategy to synthesize novel unsymmetric 2,3-diaza-1,4-dithiane ligands. Reaction of [Ni(acac)2] and trityl tetrakis(pentafluorophenyl)borate in the presence of these ligands afforded the corresponding salt-type complexes. All new compounds were characterized by means of elemental analysis and NMR spectroscopy, and the complexes additionally by mass spectroscopy. NMR spectroscopic experiments on polymers generated by the symmetric ligand/trimethylaluminum catalyst system showed that all products were nearly linear, independent of the polymerization conditions. By contrast, polymers produced by the unsymmetric ligand/trimethylaluminum catalyst system under homopolymerization conditions were branched (15-24 per thousand). Additionally, copolymerization experiments with propylene and 1-hexene afforded copolymers with a branching level of up to 50 per thousand.