Preparation of nickel catalysts bearing Schiff base macrocycles and their performance in ethylene oligomerization

Abstract

Two Schiff base macrocyclic ligands (L1 and L2) were synthesized using ethylenediamine and terephthalaldehyde (or isophthalaldehyde) as raw materials in acetonitrile solvent. Surprisingly, series of Schiff base macrocyclic ligands with different combination modes (L2-1, L2-2 and L2-3) with isophthalaldehyde as raw material were synthesized. Two Schiff base macrocyclic nickel complexes (Ni-1 and Ni-2) based on L1 and L2 for ethylene oligomerization were obtained with (DME)NiCl₂. The synthesized ligands and their corresponding complexes were characterized by various analysis techniques to confirm their chemical structure and thermal stability. And the catalytic properties of the two nickel complexes were also investigated for ethylene oligomerization. When the ethylene pressure was 0.5 MPa, the Al/Ni ratio was 500:1, and the reaction time was 30 min in the presence of MAO, the catalytic activities of Ni-1 and Ni-2 were 4.53 × 10⁴ g/(mol Ni·h) and 4.73 × 10⁴ g/(mol Ni·h), respectively. Compared with PS-Ni complex based on 2,3-butanedione and p-phenylenediamine and three other nickel complexes with simpler ligand structures, Ni-1 and Ni-2 had lower catalytic activities and higher selectivity for C₄ olefin because of the higher spatial resistance of the macrocycles.