Nickel Complexes Based on Salicylaldehyde-imine Ligands: Synthesis, Characterization and Catalytic Oligomerization of Ethylene

Abstract

A series of nickel complexes {NOONR}Ni(A: R=Me; B: R=t-Bu; C: R=OMe) based on salicylalde-hyde-imine ligands was synthesized through Schiff base condensation and metal complexation reaction. Upon activa-tion with methylaluminoxane(MAO), nickel complexes A―C all exhibited good catalytic activity([turnover fre-quency=5.2×105―16.3×105 g/(mol Ni h)] and oligomer selectivity(above 85%, mass fraction) in ethylene oligomerization. In addition, C8―C12 olefins occupied an important proportion in the products of oligomers. Under the conditions of 4.0 MPa, 25 °C and Al/Ni molar ratio of 275, the catalytic selectivity of A/MAO system toward C8―C12 was about 30.1%(mass fraction), and the content of C8―C12 α-olefins was consistently above 70%. Furthermore, besides the ligand environment, the catalytic properties of A―C were substantially affected by experimental parameters, such as the reaction pressure, reaction temperature and Al/Ni ratio.