Star iminopyridyl iron, cobalt and nickel complexes: synthesis, molecular structures, and evaluation as ethylene oligomerization catalysts

Abstract

A novel star iminopyridyl ligand was synthesized in modest yield with 1.0 G star macromolecule and pyridine-2-carboxaldehyde as the raw materials. Reactions of the star iminopyridyl ligand with Fe(II), Co(II) and Ni(II) salts afforded metal complexes (Cat-Fe, Cat-Co and Cat-Ni) in good yields. The compounds were characterized by FT-IR, 1H NMR, 13C NMR, UV–Vis, ESI–MS and ICP-MS. In the presence of methylalumoxane (MAO), the iron, cobalt and nickel complexes have demonstrated higher ethylene oligomerization activity (up to 4.28 × 105 g/(mol Co h)), affording C4 as the major product as well as C6, C8 and C10-18 oligomers. The catalytic activity was quite sensitive to the kind of species. The nature of solvent and co-catalyst significantly affected both the catalytic activity and product distribution. Moreover, the effect of oligomerization parameters (reaction temperature, [Al]/[Co] molar ratio, ethylene pressure) on the catalytic activity and the product distribution was investigated.