Aminophosphine-based chromium catalysts for selective ethylene tetramerization

Abstract

Chromium complexes of three new ligands, Ph 2PN(Me)(CH 2) 2-X [X = NMe 2(PNN); PPh 2 (PNP); Py (PNPy)], have been examined vis-à-vis their ability to promote ethylene tetramerization, (PNN)CrCl 3(L) [L = THF (1); CH 3CN (2)], (PNPy)CrCl 3(L) [L = THF (3); CH 3CN (4)], and (PNP)CrCl 3(THF) (5). In the case of 2 and 4, it was possible to grow crystals suitable for X-ray diffraction. The reaction of 3 with Et 3Al afforded the dinuclear [(HN(Me)(CH 2) 2Py)CrCl 2Et] 2 (6) containing a trivalent chromium connected to an Et group. During the alkylation though, the ligand has been fragmented with removal of the side arm and protonation of the N atom of the remaining NP residue. All the complexes have been tested for ethylene oligomerization activity. Complex 1 displayed the highest selectivity for 1-octene, upon activation with DMAO in MeCy. Contrary to expectations, complex 6 is not a self-activating catalyst. © 2012 American Chemical Society.