Highly selective nickel catalysts for ethylene oligomerization based on tridentate pyrazolyl ligands

Abstract A series of new nickel complexes NiCl 2 (L) based on tridentate NZN ligands ( 1 , L = bis[2-(3,5-dimethyl-pyrazolyl)methyl]benzylamine; 2 , L = bis[2-(3,5-dimethyl-l-pyrazolyl)methyl]butylamine; 3 , L = bis[2-(3,5-dimethyl-l-pyrazolyl)methyl]sulfide; 4 , L = bis[2-(3-phenyl-l-pyrazolyl)methyl]sulfide)) has been prepared and characterized by elemental analysis. Upon activation with methylaluminoxane (MAO) or diethylaluminum chloride (DEAC), these new pre-catalysts show high activity in ethylene oligomerization (TOF = 1.7–104.5 × 10 3  mol(ethylene) (mol(Ni)) −1  h −1 ), giving predominantly 1-butene (70–94% yield). The catalytic performance is substantially affected by the co-catalyst type and ligand environment, especially the bridge donor atom. Under optimized conditions ([Ni] = 10 μmol, 30 °C, 20 bar ethylene, MAO-to-Ni = 250), pre-catalyst 3 leads to TOF = 104.5 × 10 3  h −1 and 70% selectivity for 1-butene.