Preparation of chromium complexes for ethylene tetramerization catalyst

One of the remaining challenges in the commercialization of a highly efficient ethylene tetramerization catalyst, [ 1 ‐CrCl 2 ][B(C 6 F 5 ) 4 ] ( 1 =iPrN[P(C 6 H 4 Si(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) 3 Al was the most effective choice. Building on the observation that [iPrN(PPh 2 ) 2 ]CrCl 3 (THF) was not completely alkylated by the action of excess Me 3 Al to form ([iPrN(PPh 2 ) 2 ]Cr(μ 2 ‐Cl)(ClMe 2 AlClAlMe 3 )) 2 , we synthesized [ ortho ‐(MeO)C 6 H 4 CH 2 ‐η 1 C:κO] 3 Cr, developing a catalytic system comprising this precursor, PNP ligand 1 , and [MeN(H)(C 18 H 37 ) 2 ][B(C 6 F 5 ) 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 ‐CrCl 2 ][B(C 6 F 5 ) 4 ], we successfully achieved the conversion of [(EtOH) 4 CrCl 2 ][B(C 6 F 5 ) 4 ] to [(CH 3 CN) 4 CrCl 2 ][B(C 6 F 5 ) 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 ‐CrCl 2 ][B(C 6 F 5 ) 4 ].