Switchable Ethylene Tri-/Tetramerization with High Activity: Subtle Effect Presented by Backbone-Substituent of Carbon-Bridged Diphosphine Ligands

The effect of backbone-substituent of carbon-bridged diphosphine ligands of the types {Ph2PCH­(R)­CH2PPh2} and {Ph2PC­(R)CHPPh2} on the catalyst performance in ethylene oligomerization has been explored. Cr complex bearing a methyl-substituted diphosphine ligand with saturated linker exhibited the highest selectivity of 64.7% toward 1-octene. Cr complex bearing a tert-butyl-substituted diphosphine ligand with unsaturated linker showed a high activity of 4238 kg/(g Cr/h) at 40 bar and 40 °C and achieved a high total selectivity of 79.1% toward valuable 1-hexene and 1-octene. The 1-hexene selectivity could be improved up to 55.2% (19.4% 1-octene) at 20 bar and 80 °C. Some of the new complexes are even more active than the well-known most efficient ethylene tri/tetramerization catalyst systems.