Catalytic Systems Based on Chromium(III) Silylated-Diphosphinoamines for Selective Ethylene Tri-/Tetramerization

Abstract

The N-substituents on the backbone of Ph 2 PN(R)Si(CH 3 ) 2 CH 2 PPh 2 -and [Ph 2 PCH 2 Si(CH 3 ) 2 ] 2 N-(R)-type silylated-diphosphinoamine (Si-PNP) systems have been observed to have a significant impact on their catalytic performance in ethylene oligomerization reactions. Cr precatalyst 3, bearing an isopropyl ( i Pr) substituent, affords the most efficient catalytic system and exhibited the highest selectivity (83%) toward 1-octene (1-C 8 ) and showed a catalytic activity of more than 76,700 g(product)•g(Cr) −1 •h −1 under experimental conditions. Single-crystal analysis results revealed the influence of steric constraints around the catalytically active center and established a relationship between the product selectivity and the P−Cr−P bite angle. Furthermore, DFT calculations indicate that the catalytic system based on precatalyst 3 faces a low energy barrier in the formation of 1-C 8 and therefore shows high selectivity toward the 1-C 8 fraction. Modification in the backbone length may alter the binding mode of the ligands from mononuclear-bidentate (k 2 -P, P) to mononuclear-tridentate (k 3 -P, N, P), which consequently switches the ethylene tetramerization systems to ethylene trimerization systems.

Chromium Complexes Supported by Phenyl Ether‐Pyrazolyl [N,O] Ligands as Catalysts for the Oligo‐ and Polymerization of Ethylene

“…The identity of these complexes was established on the basis of combustion elemental analysis, IR spectroscopy and high‐resolution mass spectrometry (HRMS). Upon reaction with CrCl 3 (THF) 3 , either [CrCl 3 (N,O)(THF)] or the dimer [Cr(N,O)Cl 3 ] 2 were expected, both of which would maintain the favored hexacoordination of chromium (III) [ 14,24,27,28,45,46 ] ; however, the elemental analyses of complexes Cr1‐Cr3 confirmed the formation of dimeric species of general formula [CrCl 2 (N,O)(μ‐Cl)] 2 . Furthermore, the ESI‐HRMS results indicated the formation of [M‐Cl] + ions for all chromium complexes (Figures S1‐S3).…”

“…However, we cannot rule out the possibility that the absence of “free” TMA could also decrease the chain‐transfer rate of the growing chain from the catalyst to the aluminum, and thus resulting in a formation of higher quantity of polyethylene. [ 27,108,109 ] The role of Al activators on catalytic performance of chromium catalysts in homogeneous ethylene oligomerization has been recently studied by Tromp, Brückner and co‐workers. [ 110,111 ] With regards to product distribution within the liquid fraction, Cr3 /PMAO‐IP catalytic system leads to a more balanced distribution of oligomers, with a drastic decreases in α‐C 4 (30.20 mol %) and increase in α‐C 8 (16.80 mol %) and α‐C 10 (10.80 mol %) fractions (Figures S9 and S10).…”

“…[ 13–16 ] In this way, significant efforts have been dedicated to the synthesis of new families of ligands based on a wide variety of donor‐group combinations aiming to generate more efficient chromium catalyst systems that are capable of selectively forming α‐olefins with high productivities. [ 17–81 ] In particular, chromium catalysts stabilized by pyrazolyl‐based tridentate ligands have been successfully synthetized and their catalytic application in ethylene oligomerization explored in details. [ 51,81–91 ] Selected examples are presented in Chart 1.…”

Synthesis and application of chromium complexes bearing hyperbranched PNP ligands in the ethylene oligomerization

“…The co-catalyst composition had a considerable impact on the catalyst behavior. [34] Therefore, the influences of co-catalyst composition on ethylene oligomerization with Cr1 as precatalyst were investigated in this work and the results are listed Table 2 (entries 1-4). For the four co-catalysts investigated, the catalytic activity of Cr1 in ethylene oligomerization using MAO as co-catalyst in toluene were highest, and the catalytic activity were lowest using EADC as co-catalyst.…”

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

“…Catalyst development for ethylene oligomerization is an ongoing research topic in both academia and industry. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] 4 ] À (2.0 eq), CrCl 3 (THF) 3 , and PNP ligand that exhibited high activity (up to 4000 kg/g-Cr/h) when combined with common and inexpensive alkylaluminum iBu 3 Al (Scheme 1). [46] We presumed that the chloride-bridged adduct (i. e., [(PNP)Cr(Cl)(THF)(μ 2 -Cl) 2 Al(acac)] 2 + [B(C 6 F 5 ) 4 ] À 2 ) might be formed between the cationic Cr species [(PNP)CrCl 2 ] + [B(C 6 F 5 ) 4 ] À and the cationic Al species [ClAl(acac)] + [B(C 6 F 5 ) 4 ] À .…”