Nickel and cobalt complexes with ferrocenyl Schiff bases: preparation, characterization, and application in ethylene oligomerization

Abstract

Two aliphatic diamine-bridged ferrocene ligands (C2-Fe-Ligand and C6-Fe-Ligand) were synthesized with aliphatic diamine and formylferrocene, and the corresponding bimetallic active site complexes (Ni-C2-Fe, Co-C2-Fe, and Ni-C6-Fe) were prepared to catalyze ethylene oligomerization. The ligands and the corresponding complexes were characterized by FTIR, 1H NMR, TG, ESI-MS, XRD, and SEM. The SEM results of the ligands confirmed that the length of the bridged group had an influence on the morphology, and an increase in the carbon length led to irregular short rods to the irregular flakes with a large size. The bimetallic complexes catalyzed efficiently ethylene oligomerization with MAO as co-catalyst, and these complexes produced C4 and C6 olefins. Ni-C2-Fe showed higher activity of 6.31 × 104 g·(mol Ni·h)−1 in cyclohexane at Al/Ni molar ratio of 700, temperature of 25 °C, and pressure of 0.5 MPa. Compared with single active site catalysts, the bimetallic active site catalysts had a higher selectivity for C4 olefin because of the competitive insertion of ethylene between different active centers. The modification of the metal center tuned the catalytic performance of the complexes in ethylene oligomerization.