Synthesis of nickel complexes [N, N]NiBr2 and their catalysis for ethylene oligomerization

Ni-based complexes [N,N] NiBr2, in which [N,N] is a bidentate nitrogen ligand N-(2-pyridylmethylene) phenylamine with different substituents, were synthesized. [N,N] NiBr2, exhibits high activity for ethylene oligomerization in the presence of activator containing aluminum, as long as [N,N] is chosen suitably. The main factor governing the activity and the polymer structure is the steric bulk of [N,N]. For [N,N] NiBr2, larger ortho-substituents on aryl ring of the ligand [N,N] tend to form the higher active site. MAO-activated catalysts showed higher activity than Et2AlCl-activated ones, and the reaction in toluene resulted in much higher activity than that in hexane. The oligomers obtained by this system is characteristic of highly branched structure with low alpha-olefin content. However, it is possible to promote the alpha-olefin content by adjusting the catalytic reaction conditions.