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 AlEtCl 2, these complexes exhibited considerably high activity (up to 1.34 × 10 6 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.