Nitrogen-Linked Diphosphine Ligands with Ethers Attached to Nitrogen for Chromium-Catalyzed Ethylene Tri- and Tetramerizations

A series of bis(diphenylphosphino)amine ligands with a donor group attached to the nitrogen linker have been prepared. Metalation of these ligands with chromium trichloride provides precursors to highly active, relatively stable, and selective catalysts for trimerization and tetramerization of ethylene. It has been demonstrated in oligomerization reactions performed at 1 and 4 atm of ethylene that these new systems increase total productivity by enhancing catalyst stability, as compared with those lacking a donor group on the diphosphine ligand. Furthermore, the use of chlorobenzene solvent (rather than toluene) significantly improves productivity, stability, and selectitvity. The product distributions and minor byproducts provide information relevant to mechanistic issues surrounding these types of reactions.