Nickel complexes incorporating pyrazole-based ligands for ethylene dimerization to 1-butylene

• Bidentate nickel complexes were evaluated as ethylene dimerization catalysts.
• Pre-catalysts activated with MAO, Et2AlCl and EtAlCl2 co-catalysts.
• Activity and selectivity were temperature, Al/Ni ratio and co-catalysts dependent.
• Ligand substituents and bridging atoms had a great influence on the activity.

In this study we synthesized and characterized bis(3,5-dimethylpyrazolyl)dimethylsilane (L1) and bis(3,5-dimethylpyrazolyl)phenylphosphine (L2) and then prepared bidentate (NˆN) nickel complexes by reacting L1 or L2 with NiBr2(DME). In combination with methylaluminoxane, diethylchloroaluminum or ethyldichloroaluminum (EADC) as co-catalyst, L1/Ni and L2/Ni complexes exhibited moderate catalytic activities (240–1310 kg/molNi h) and high selectivities (up to 93.2%) for ethylene dimerization toward 1-butylene. The catalytic performance was substantially affected by the co-catalyst type and ligand environment, especially the bridge atom.

The nickel complexes with MAO, EADC or DEAC showed moderate activity for ethylene dimerization toward 1-C4. The catalysts showed higher catalytic activity with DEAC than other cocatalysts. The catalysts give the highest selectivity when MAO use as cocatlys.Figure optionsDownload as PowerPoint slide