Avoiding MAO: Alternative Activation Methods in Selective Ethylene Oligomerization

An ionic chromium(III) species, [CrCl2(THF)4][Al(OC4F9)4] (2), has been synthesized and is shown to react with a variety of bidentate diphosphine ligands to yield complexes of the type [CrCl2(diphosphine)2][Al(OC4F9)4]. When compound 2 is combined with diphosphines Ar2PN(Me)PAr2 (Ar = 2-MeO-C6H4) and Ph2PN(i-Pr)PPh2, after activation with small amounts of AlMe3, active species for the selective oligomerization of ethylene with catalyst productivities of up to 25010 g gCr–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(Ar2PN(Me)PAr2)2][Al(OC4F9)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.

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