Aminophosphine-Based Chromium Catalysts for Selective Ethylene Tetramerization

Chromium complexes of three new ligands, Ph 2 PN(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 3 CN ( 2 )], (PNPy)CrCl 3 (L) [L = THF ( 3 ); CH 3 CN ( 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 3 Al afforded the dinuclear [(HN(Me)(CH 2 ) 2 Py)CrCl 2 Et] 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.