Novel nickel complexes with hyperbranched structure: Synthesis, characterization and performance in ethylene oligomerization

Abstract

Two novel nickel complexes with hyperbranched structure were synthesized with 1.0 generation hyperbranched polyamine molecules (1.0G), salicylaldehyde and anhydrous nickel chloride as materials via the Schiff’s base and the complexation reactions. The structures of the novel hyperbranched ligands and their nickel complexes were characterized by FT-IR, 1H NMR, UV, ESI-MS and elemental analysis. The hyperbranched nickel complexes were evaluated as catalyst precursors for ethylene oligomerization after being activated with methylaluminoxane (MAO), diethylaluminum chloride (Et2AlCl) and ethylaluminum sesquichloride (EASC). The influence of Al/Ni ratio, temperature and ethylene pressure on ethylene oligomerization was also investigated using the novel hyperbranched nickel complexes as pre-catalysts and MAO as co-catalyst. The catalytic activities of the two hyperbranched nickel complexes with dodecyl and octadecyl as cores (R12-complex and R18-complex) were 2.33×105g/(mol Ni·h) and 1.23×105g/(mol Ni·h), respectively, and the selectivities for C8+ oligomers of R12-complex and R18-complex were 56.16% and 88.64% respectively, when the Al/Ni molar ratio was 500:1, the temperature was 25°C, the pressure of ethylene was 0.5MPa and the co-catalyst was MAO. The catalytic activities and product distribution were largely dependent on the nature of the co-catalysts and the structures of nickel complexes. The catalytic activities decreased with increasing of the length of alkyl chain of the hyperbranched nickel complexes.