Synthesis and Characterization of Tridentate Nickel Complexes Bearing P^∧N^∧N and P^∧N^∧P Ligands and Their Catalytic Property in Ethylene Oligomerization

A series of nickel(II) complexes ligated by the N-(1-(2-(diarylphosphino)phenyl)methylidene)quinolin-8-amines (P∧N∧N) and 2-(diphenylphosphino)-N-[2-(diarylphosphino)benzylidene]anilines (P∧N∧P) were synthesized and characterized by elemental analysis, spectroscopy, and X-ray crystallography. X-ray crystallographic analyses reveal complexes 16 and 20 as having a five-coordinated distorted trigonal-bipyramidal geometry, while complex 12 displays a distorted square-pyramidal geometry and complex 13 is distorted square planar. Upon activation with MAO and AlEtCl2, these complexes exhibited considerably high activity (up to 1.34 × 106 g·mol-1(Ni)·h-1) of ethylene oligomerization. It was found that ligand environment and reaction conditions significantly affect the activity of the catalysts. In addition, a cobalt analogue with a distorted tetrahedral coordination geometry was investigated, which showed low activity of ethylene oligomerization.