Synthesis, characterization, and ethylene oligomerization with star iminopyridine nickel(II) complexes

Abstract

A series of star iminopyridine ligands, containing different groups (H, CH3, Br) in the pyridine ring, have been synthesized and characterized by FT-IR, 1H NMR, and UV-vis. The corresponding nickel(II) complexes have been prepared in good yields. The nature of the Ni complexes has been established by FT-IR, UV-vis, ESI-MS, and ICP. Upon activation with methylaluminoxane (MAO), the nickel complexes were able to oligomerize ethylene to produce C4–C18 fractions at activity of up to 105 g (mol Ni h)−1. The influence of substituent, catalyst structure, solvent, co-catalyst, and reaction conditions on the catalytic activity and product selectivity was investigated. The results showed that substitution on the pyridine ring had large influence on the catalytic activity and product selectivity. The catalytic activity increased at first and then decreased with the increase of reaction temperature and Al/Ni molar ratio. However, the catalytic activity continuously increased with increasing reaction pressure. When toluene was used as solvent and MAO was used as co-catalyst, catalytic activity of 4.39 × 105 g (mol Ni h)−1 and 31.93% selectivity of higher carbon olefins (C8–C18) were obtained at 10 °C, Al/Ni molar ratio 500, and the reaction pressure 1.0 MPa.