Synthesis, Characterization and Ethylene Oligomerization Studies of Chromium Complexes Bearing Imino-Furfural Ligands

A series of chromium(III) complexes bearing imino-furfural ligands (Cr1-Cr4) were synthesized and characterized by high-resolution mass spectrometry (HRMS). All chromium precatalysts, activated with methylaluminoxane (MAO), exhibited moderate to high activities for ethylene oligomerization [turnover frequency (TOF) = 11,008-23,200 mol(ethylene) mol(Cr)^-1 h^-1)] producing oligomers in the range C₄-C₁₂₊ with good selectivity for α-olefins. The in situ chromium precatalysts formed by mixing imino-furfural ligand L¹ with [CrCl₃(THF)₃] or [Cr(acac)₃] showed low activities, producing oligomers together with varying amounts of polyethylene. The use of different chromium sources and cocatalysts influences the activity as well as the selectivities toward α-olefin production, which suggests that different active species are formed.

imino-fufural ligands; chromium complexes; ethylene oligomerization