Catalytic behavior tuning via structural modifications of silylated-diphosphine Ni(II) complexes for ethylene selective dimerization

The methylene spacers and an uncoordinated diphenylphosphine moiety in the scaffold of the CH 3 Si(CH 2 ) n (PPh 2 ) 3 and Si(CH 2 PPh 2 ) 4 -type silylated diphosphine Ni(II) complex systems have a marked impact on their catalytic performance in selective ethylene dimerization. Ni(II)-based precatalyst 1 , bearing two methylene spacers in its framework, exhibited the highest catalytic activity of 1.29 × 10 8 g (mol Ni ) -1 h -1 , while precatalyst 3 , with three methylene spacers, affords the highest product selectivity (88%) toward the C 4 fraction. Crystallographic investigations revealed that the precatalyst 3 adopts the mononuclear bidentate binding mode and the steric constraints of its uncoordinated diphenylphosphine moiety may successfully tailor the catalytic environment of the catalyst. The precatalyst 4 may form a dinuclear complex and exhibits high catalytic activity by changing the ligand/Ni molar ratio. The high C 4 selectivity of precatalyst 3 has been rationalized by density functional theory (DFT) calculations and found to be consistent with the experimental results. The study also revealed that designing new systems of Ni(II)-based complexes and their systematic modifications may further provide potential and industrially viable catalyst systems for selective ethylene oligomerization.