Well-Defined Silica-Supported Nickel-Alkyl Complexes for Ethylene Oligomerization: Crucial Role of Halogenated Lewis Acid

Easily accessible single-site surface nickel-alkyl complexes have been synthesized on silica partially dehydroxylated at 700 °C following a simple and robust method consisting of the reaction of (PMe3)2Ni(CH2SiMe3)2, (py)2Ni(CH2SiMe3)2, or (bpy)Ni(CH2SiMe3)2 with the remaining OH groups of the partially dehydroxylated silica support. In addition to mass balance analysis, infrared and solid-state NMR spectroscopic studies allowed us to define precisely the three surface species and, in particular, the alkyl active site, which is expected to initiate the oligomerization reaction of ethylene. Precatalysts were combined with a simple Lewis acid (AlCl3) to induce catalytic activity. This combination constitutes an efficient oligomerization catalyst reaching activities as high as 29, 900 mol of ethylene converted per mol of Ni per hour. The crucial role of AlCl3 beyond simple Lewis base abstraction in the activation of the catalyst precursor has been evidenced.