Nickel complexes based on hyperbranched bispyridylamine ligands as catalyst precursors for ethylene oligomerization

Abstract

A series of nickel complexes containing bispyridylamine ligands is synthesized and characterized by UV-Vis, FTIR, 1H NMR, ESI-MS, and elemental analysis. All nickel complexes activated with methylaluminoxane exhibited moderate activity for ethylene oligomerization (5.30 × 104 to 2.54 × 105 g/(mol·Ni·h)), producing oligomers in the range C4–C18. The effects of reaction temperature, reaction pressure, Al/Ni molar ratio, and solvent type on the catalytic activity and product selectivity are also investigated. The resulting products are mainly low-carbon olefins (C4 and C6). Under the optimized conditions, the complex with R1 = C4H9 formed by the reaction of the corresponding ligand R1 = C4H9 with NiCl2·6H2O showed a higher catalytic activity of 2.54 × 105 g/(mol·Ni·h) compared to the complex with R2 = C6H13 and R3 = C6H11 using toluene as the solvent. Moreover, the selectivity for the C4 and C6 oligomers can reach up to 82%.