Avoiding MAO: Alternative Activation Methods in Selective Ethylene Oligomerization

An ionic chromium(III) species, [CrCl 2 (THF) 4 ][Al(OC 4 F 9 ) 4 ] ( 2 ), has been synthesized and is shown to react with a variety of bidentate diphosphine ligands to yield complexes of the type [CrCl 2 (diphosphine) 2 ][Al(OC 4 F 9 ) 4 ]. When compound 2 is combined with diphosphines Ar 2 PN(Me)PAr 2 (Ar = 2-MeO-C 6 H 4 ) and Ph 2 PN( i -Pr)PPh 2, after activation with small amounts of AlMe 3, active species for the selective oligomerization of ethylene with catalyst productivities of up to 25010 g g Cr –1 h –1 are observed. Selectivity to 1-hexene or 1-octene is a function of ligand structure in an identical fashion to the MAO-activated system. A novel Cr(II) species, [Cr(Ar 2 PN(Me)PAr 2 ) 2 ][Al(OC 4 F 9 ) 4 ] 2 ( 5 ), was isolated from the catalytic mixture. Compound 5 alone does not oligomerize ethylene, but reaction with MAO yields a highly active catalyst for selective ethylene oligomerization.