Aminophosphine-Based Chromium
Catalysts for Selective Ethylene Tetramerization
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Abstract
Chromium complexes of three new ligands, Ph<sub>2</sub>PN(Me)(CH<sub>2</sub>)<sub>2</sub>-X [X = NMe<sub>2</sub> <b>(PNN</b>); PPh<sub>2</sub> (<b>PNP</b>); Py <b>(PNPy</b>)], have
been examined vis-à-vis their ability to promote ethylene tetramerization,
(PNN)CrCl<sub>3</sub>(L) [L = THF (<b>1</b>); CH<sub>3</sub>CN (<b>2</b>)], (PNPy)CrCl<sub>3</sub>(L) [L = THF (<b>3</b>); CH<sub>3</sub>CN (<b>4</b>)], and (PNP)CrCl<sub>3</sub>(THF)
(<b>5</b>). In the case of <b>2</b> and <b>4</b>, it was possible to grow crystals suitable for X-ray diffraction.
The reaction of <b>3</b> with Et<sub>3</sub>Al afforded the
dinuclear [(HN(Me)(CH<sub>2</sub>)<sub>2</sub>Py)CrCl<sub>2</sub>Et]<sub>2</sub> (<b>6</b>) 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 <b>1</b> displayed
the highest selectivity for 1-octene, upon activation with DMAO in
MeCy. Contrary to expectations, complex <b>6</b> is not a self-activating
catalyst
