Preparation of chromium complexes for ethylene tetramerization catalyst

One of the remaining challenges in the commercialization of a highly efficient ethylene tetramerization catalyst, [1-CrCl₂][B(C₆F₅)₄] (1=iPrN[P(C₆H₄Si(Octyl)₃)₂]₂), is the generation of small amounts of polyethylene (PE). To address this issue, we explored different activator options and found that (Octyl)₃Al was the most effective choice. Building on the observation that [iPrN(PPh₂)₂]CrCl₃(THF) was not completely alkylated by the action of excess Me₃Al to form ([iPrN(PPh₂)₂]Cr(μ₂-Cl)(ClMe₂AlClAlMe₃))₂, we synthesized [ortho-(MeO)C₆H₄CH₂-η¹C:κO]₃Cr, developing a catalytic system comprising this precursor, PNP ligand 1, and [MeN(H)(C₁₈H₃₇)₂][B(C₆F₅)₄]. However, this catalytic system exhibited a long induction time (~30 min) and generated a significant amount of PE. Returning to the catalytic system of [1-CrCl₂][B(C₆F₅)₄], we successfully achieved the conversion of [(EtOH)₄CrCl₂][B(C₆F₅)₄] to [(CH₃CN)₄CrCl₂][B(C₆F₅)₄] at a large scale by designing a specialized glass apparatus. Finally, we discovered that the generation of PE could be reduced by adjusting the reaction conditions during the synthesis of [1-CrCl₂][B(C₆F₅)₄].