Stoichiometrically Activated Catalysts for Ethylene Tetramerization using Diphosphinoamine-Ligated Cr Tris(hydrocarbyl) Complexes

Abstract

A new, stoichiometric activation mode is presented for Cr-PNP (PNP = diphosphinoamine) complexes for ethylene tetramerization catalysis. To access suitable precatalysts, two robust Cr(III) multiaryl compounds were synthesized as THF adducts. These complexes are supported by a facially coordinated bis(aryl) ligand with an additional ether donor. From these precursors, Cr-PNP tris(hydrocarbyl) complexes were synthesized. Using 1 equiv of Brønsted acid as an activator, an active species for the catalytic tetramerization of ethylene was produced, without the need for excess alkylaluminum reagents.

MAO‐free and extremely active catalytic system for ethylene tetramerization

“…The preparation of a Cr‐complex bearing common [B(C 6 F 5 ) 4 ] − was attempted ( II in Scheme ), but the attained activity, when combined with Et 3 Al or iBu 3 Al, was unsatisfactorily low compared with the MAO‐based original Sasol system (80 vs. 260 kg/g‐Cr/h) . A completely alkylaluminum‐free system has also been attempted but the achieved activity was also unsatisfactory (~5 kg/g‐Cr/h) . Sasol disclosed in a patent that a highly active MAO‐free system was eventually developed, overcoming the failure, through the introduction of lipophilic groups in a Cr‐source (e.g., Cr(2,2,6,6‐tetramethyl‐3,5‐heptanedionato) 3 ), a PNP ligand (e.g., CH 3 (CH 2 ) 5 C(H)(Me)N(PPh 2 ) 2 ), and/or ammonium borate (e.g., [(C 18 H 37 ) 2 N(Me)H] + [B(C 6 F 5 ) 4 ] − ) .…”

“…[21] A completely alkylaluminum-free system has also been attempted but the achieved activity was also unsatisfactory (~5 kg/g-Cr/h). [22] Sasol disclosed in a patent that a highly active MAO-free system was eventually developed, overcoming the failure, through the introduction of lipophilic groups in a Cr-source (e.g., Cr(2,2,6,6tetramethyl-3,5-heptanedionato) 3 ), a PNP ligand (e.g., CH 3 (CH 2 ) 5 C(H)(Me)N(PPh 2 ) 2 ), and/or ammonium borate (e.g., [(C 18 H 37 ) 2 N(Me)H] + [B(C 6 F 5 ) 4 ] − ). [23] Herein, we report another type of MAO-free and extremely active catalytic system, whose activity is more than 10 times that of the original MAO-based Sasol system.…”

Extremely Active Ethylene Tetramerization Catalyst Avoiding the Use of Methylaluminoxane: [iPrN{P(C6H4‐p‐SiR3)2}2CrCl2]+[B(C6F5)4]−

“…Even though the reported activity of the typical Sasol system calculated based on Cr was extremely high (1200 kg/g‐Cr), the productivity calculated based on the feed amount of MMAO was unsatisfactory (∼2.0 kg/g‐MMAO) . Consequently, attempts have been made to replace expensive MMAO with inexpensive iBu 3 Al or Et 3 Al in combination with a stoichiometric amount of discrete non‐coordinating anions (e. g., [Ph 3 C] + [B(C 6 F 5 ) 4 ] − or [PhN(H)Me 2 ] + [B(C 6 F 5 ) 4 ] − ) . However, most of these attempts, especially with commonly used [Ph 3 C] + [B(C 6 F 5 ) 4 ] − and [PhN(H)Me 2 ] + [B(C 6 F 5 ) 4 ] − , have been unsuccessful .…”

“…[16,17] Consequently, attempts have been made to replace expensive MMAO with inexpensive iBu 3 Al or Et 3 Al in combination with a stoichiometric amount of discrete non-coordinating anions (e. g., [Ph 3 C] + [B(C 6 F 5 ) 4 ] À or [PhN(H)Me 2 ] + [B(C 6 F 5 ) 4 ] À ). [15,[18][19][20][21][22][23] However, most of these attempts, especially with commonly used [Ph 3 C] + [B(C 6 F 5 ) 4 ] À and [PhN(H)Me 2 ] + [B(C 6 F 5 ) 4 ] À , have been unsuccessful. [24,25] The low working temperature (~60°C) is also an issue.…”

Alloyed Tetranuclear Metal Chains of Pd4−nPtn (n=0–3) Scaffolded by a New Linear Tetraphosphine Containing a PNP Bridge

“…We have then intended to design Ph 2 PCH 2 P(Ph)N(R)P(Ph)CH 2 PPh 2 type linear tetraphosphines because the centralN Rg roup is easily varied by commercially availableprimary amines,and enablesb oth steric and electronic tuning of the central part of linear tetraphosphines.W hereas many phosphazane compounds formulated R 2 PN(R')PR 2 have been used to synthesize mono-, di-, andt rinuclearc omplexes with some functionalities concerning to the NR' substituents, [8][9][10][11][12][13][14][15][16][17][18] multidentate linear phosphine ligands with PNP bridgesa re no longer synthesized so far,e xcept some phosphazane macrocyclic ligands. [19] In the present study,anew linear tetraphosphine containing aP N(Ph)P phosphazane bridge, rac-bis[(diphenylphosphinomethyl)phenylphosphino]phenylamine (rac-dpmppan),w as synthesized and effectively utilized to stabilize as eries of Pd/Pt mixed metal tetranuclear chains, [Pd 4Àn Pt n (m-racdpmppan) 2 (XylNC) 2 ](PF 6 ) 2 (XylNC = xylyl isocyanide; n = 0: Pd 4 (1), 1: PtPd 3 (2), 2: PtPd 2 Pt (3), 2: Pt 2 Pd 2 (4), 3: Pt 2 PdPt (5)), in which the number and positionso fa dditional Pt atoms were remarkably controlled, and their electronic structures are finely tuned as alloyed metal chains by atomically precise Pt incorporation.…”