Nickel complexes based on hyperbranched salicylaldimine ligands: Synthesis, characterization, and catalytic properties for ethylene oligomerization

Abstract

A series of new nickel complexes based on hyperbranched salicylaldimine ligands have been prepared in good yields and characterized by FT-IR, 1H NMR, UV, ESI-MS and TGA. Upon activation with methylaluminoxane (MAO) or diethylaluminum chloride (DEAC), these new precatalysts showed high activity in ethylene oligomerization, and notably remarkably high selectivity of high carbon olefins in the presence of DEAC. The catalytic performance was substantially affected by the solvent type, reaction conditions and the structure of catalyst. Under optimized conditions, precatalyst C1 led to TOF = 13.65 × 105 g/mol Ni·h and 21.53% selectivity for high carbon olefins. The result of thermal analysis revealed that the complex C1 was stable up to 298.4 °C. The research result of the kinetics of ethylene oligomerization found that the pressure drop of ethylene consumption sharply increased in the initial stage, however with the prolonged reaction time, the pressure drop of ethylene consumption varied a little.