Polynuclear (alpha-diimine) nickel(II) complex as catalyst for ethylene oligomerization

Late transition metal catalysts with single or multiple active centers have great attention in the ethylene oligomerization application owing to their unique properties. A new polynuclear (alpha-diimine) nickel(II) complex (PS-Ni complex) bearing the conjugated poly(Schiff-base) ligand (PS-ligand) was synthesized. The structures and the composition of the PS-ligand and the PS-Ni complex were characterized by Fourier transform infrared (rTTIR) analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric (TG) analysis, nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The PS-Ni complex was used as precatalyst in ethylene oligomerization combined with methylaluminoxane (MAO) and has good catalytic activity for ethylene oligomerization under mild conditions. Compared with the corresponding mononuclear (alpha-diimine) nickel(10 complex, the PS-Ni complex showed higher activity of 17.62 x 10(5) g/(mol Ni.h), and the main products were C-4 and C-6 olefins in cyclohexane when the dosage of precatalyst was 2 mu mol, the Al/Ni molar ratio was 500, the ethylene pressure was 0.5 MPa, the reaction time was 60 min, and the reaction temperature was 25 degrees C. The main oligomers were alpha-olefins, and the selectivity was up to 98.68%, due to the more electron-deficient catalytic centers of the conjugated structure of poly(Schiff-base) ligand.