Synthesis and Ethylene Oligomerization of Hyperbranched Salicylaldimine Nickel Complexes

Abstract A series of new hyperbranched salicylaldimine nickel complexes were synthesized by the Schiff's base and the complexation reactions with 1.0 generation hyperbranched macromolecules, salicyladehyde and nickel chloride hexahydrate as materials by employing two‐step synthesis and one‐pot synthesis, respectively. The hyperbranched salicylaldimine ligands and the complexes were characterized by FT ‐ IR , 1 H NMR , UV , and ESI ‐ MS . All nickel complexes, activated with Methylaluminoxane, exhibited high activities for ethylene oligomerization ( TOF = 1.92–4.93 g/mol Ni h) and showed good selectivities for the longer chain oligomers produced (36.35–60.33%). When activated with ethylaluminum dichloride, it was found that a tandem process occurred in which ethylene oligomerization was followed by Friedel–Crafts alkylation of the reaction solvent, toluene. On increasing the pressure of ethylene and Al/Ni ratio, the catalytic activities of precatalyst increased and the processes became more selective for the shorter oligomers. Not only the polymerized parameters but also the length of alkyl chain of the ligands influenced the catalytic activities and selectivities for the longer chain oligomers. The catalytic activities and selectivities for the longer chain oligomers declined with the increase in length of alkyl chain of ligand.