Pyrazolylimine complexes Ni(II) – Precatalysts for the synthesis branched polyethylene

Seven new and one previously described pyrazolylimine complex NiBr2 with aryl substituents exhibiting different electronic effects on the imine carbon atom were synthesized and characterized. It was shown that the obtained compounds are effective catalysts for ethylene polymerization in the presence of diethylaluminum chloride (DEAC). The influence of the electronic properties of the R substituents on the catalytic performance of the complexes was systematically investigated. A clear correlation between ligand electron-donating or -withdrawing character and both polymer molecular weight and catalytic activity was observed, providing insight into the electronic factors governing the efficiency of these nickel-based systems. © 2025 Elsevier B.V.