Aminophosphine-Based Chromium Catalysts for Selective Ethylene Tetramerization

Abstract

Chromium complexes of three new ligands, Ph2PN(Me)(CH2)2-X [X = NMe2 (PNN); PPh2 (PNP); Py (PNPy)], have been examined vis-à-vis their ability to promote ethylene tetramerization, (PNN)CrCl3(L) [L = THF (1); CH3CN (2)], (PNPy)CrCl3(L) [L = THF (3); CH3CN (4)], and (PNP)CrCl3(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 Et3Al afforded the dinuclear [(HN(Me)(CH2)2Py)CrCl2Et]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.

Selective Ethylene Oligomerization with Chromium Complexes Bearing Pyridine–Phosphine Ligands: Influence of Ligand Structure on Catalytic Behavior

“…In a related Craminophosphine system, a similar reduction of the PE formation has been reported, albeit that in this case the selectivity switched from C 8 toward C 6 while the overall C 6 and C 8 selectivity remained unchanged. 18 Similar to 1a, a higher ethylene pressure increased the catalytic activity of 4a, with only a slight influence on the product distribution (Table 2, entry 9). Although 4a produces a large amount of PE, over 50% of 1-octene selectivity for the liquid fraction indicates the existence of an active species for selective ethylene tetramerization, which is intriguing.…”

“…In an analogous octahedral complex [Py(CH 2 ) 2 N(Me)PPh 2 ]-CrCl 3 THF, the THF also resides trans to the phosphine functionality. 18 The ortho-methyl substitutions in the two otolyl groups are oriented opposite to each other. This might be attributed to steric factors as was revealed by DFT calculations (B3LYP/TZVP level) showing a 2.4 kcal/mol difference in energy between the most and least stable conformations.…”

“…All non-hydrogen atoms of the target compound were refined anisotropically. Final Flack parameter value due to chiral space group was refined to −0.015 (18).…”

Ethylene Trimerisation with Cr-PNP Catalysts: A Theoretical Benchmarking Study and Assessment of Catalyst Oxidation State

“…[9] It is also the case that the majority of catalysts selectively produce 1-hexene (trimerisation), whereas far fewer systems are capable of also selectively producing 1-octene (tetramerisation). [14][15][16][17][18] The best-known system for combined trimerisation and tetramerisation was reported by researchers from the company Sasol for the first recently been commercialised by Sasol on a 100 kt pa À1 scale (Chart 1).…”

A survey of pendant donor-functionalised (N,O) phosphine ligands for Cr-catalysed ethylene tri- and tetramerisation

“…1,4,5 At the same time, new ligand structures which support tetramerisation catalysis continue to be developed. [15][16][17][18] A particularly interesting ligand, bearing marked similarity to Sasol's PNP system, was described in the patent literature in 2009. 19,20 The ligand (II) contains the PNP backbone and, when unactivated, binds to chromium in a similar fashion with coordination to the metal centre through both phosphorous atoms as a bidentate ligand.…”