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

• Three new nickel complexes were synthesized and characterized structurally.
• Nickel complexes were evaluated as ethylene oligomerization catalysts.
• All the nickel complexes oligomerize ethylene to produce C4C18 fractions at activities of up to 2.63 × 106 g/mol Ni·h.
• Activity and selectivity were solvent, co-catalyst, reaction condition and catalyst structure dependent.

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.

Activation of hyperbranched salicylaldimine nickel complexes with DEAC in toluene solvent resulted in the formation of active catalysts to produce C4–C18 fractions at activities of up to 2.63 × 106 g/mol Ni·h at 35 °C.Figure optionsDownload as PowerPoint slide