Stoichiometrically Activated Catalysts for Ethylene Tetramerization using Diphosphinoamine-Ligated Cr Tris(hydrocarbyl) Complexes

A new, stoichiometric activation mode is presented for Cr-PNP (PNP = diphosphinoamine) complexes for ethylene tetramerization catalysis. To access suitable precatalysts, two robust Cr(III) multiaryl compounds were synthesized as THF adducts. These complexes are supported by a facially coordinated bis(aryl) ligand with an additional ether donor. From these precursors, Cr-PNP tris(hydrocarbyl) complexes were synthesized. Using 1 equiv of Brønsted acid as an activator, an active species for the catalytic tetramerization of ethylene was produced, without the need for excess alkylaluminum reagents.