Ethylene tetramerization catalyst systems discovered by Sasol consist of Cr(III) source (Cr(acac)3 or CrCl3), PNP ligand (RN(PPh2)2), and MAO are useful for the production of 1-octene through selective ethylene oligomerization. When it comes to the large scale use of the Sasol system, The use of MAO in excess has economic burden because of expensive price of MAO. In this work, we developed a catalytic system using inexpensive alkylaluminum in place of MAO. We prepared catalyst precursors with Cr, PNP ligand([CH3(CH2)16]2CHN(PPh2)2) (1), and [B(C6F5)4]- anion in 1 : 1 : 2 mole ratios. [1-CrAlCl4]2+[B(C6F5)4]-2 exhibited high activity with satisfactory selectivity when activated with common trialkylaluminum species (Et3Al, iBu3Al, and trioctylaluminum) in methylcyclohexane (activated with iBu3Al, 1110 Kg/g-Cr/h; 1-hexene 22%, 1-octene 63%, PE 1.7%). Compared to original Sasol system ((iPrN(PPh2)2)Cr(acac)3/MAO (280 Kg/g-Cr/h; 1-hexene 13%, 1-octene 71%, PE 0.4%)), These selectivity and activity are comparable.
Moreover, [1-CrAlCl3(acac)]2+[B(C6F5)4]-2 catalyst system shows higher activity with reasonable selectivity (1400 Kg/g-Cr/h; 1-hexene 17%, 1-octene 68%, PE 0.9%) than [1-CrAlCl4(THF)3]2+[B(C6F5)4]-2 catalyst system.
