An Unprecedented α-Olefin Distribution Arising from a Homogeneous Ethylene Oligomerization Catalyst

Abstract

Treatment of the bis(benzimidazolyl)amine chromium complex 2 with ethylene in the presence of MAO affords an exceptionally active oligomerization catalyst and an unprecedented distribution of 1-olefin products in which the C4n series is much more abundant than the C4n+2 series. Deuterium labeling studies are consistent with a metallacyclic chain growth mechanism in which the unusual product distribution arises from the interplay of two sites.

Distinguishing Chain Growth Mechanisms in Metal-catalyzed Olefin Oligomerization and Polymerization Systems: C2H4/C2D4 Co-oligomerization/Polymerization Experiments Using Chromium, Iron, and Cobalt Catalysts

“…25 We were interested to find out whether this technique can also be applied to higher oligomers and polymers and we have therefore carried out Chromium catalysts 1 and 2 shown in Scheme 2 and related systems have been shown previously to be highly active for the oligomerization of ethylene. 18,[26][27][28] Preliminary cooligomerization experiments employing C 2 H 4 /C 2 D 4 (1:1) with these catalysts have shown that the oligomer fraction consists of even-numbered isotopologues only, which is consistent with a metallacyclic chain growth mechanism. 18 In addition, ethylene/1-nonene cooligomerization experiments with catalyst 1 have shown no incorporation of the higher 1-alkene.…”

Substituted tridentate pyrazolyl ligands for chromium and nickel-catalyzed ethylene oligomerization reactions: effect of auxiliary ligand on activity and selectivity

“…Upon activation with methylaluminoxane (MAO), these pre-catalysts showed high turnover frequencies for ethylene oligomerization under optimized conditions 3 mol C 2 H 4 (mol Cr In parallel, the use of nickel complexes such as NiCl 2 {bis [2-(3,5-dimethyl-1-pyrazolyl)methyl] benzylamine} (3) and NiCl 2 {bis [2-(3,5-dimethyl-1-pyrazolyl)ethyl)]ether} (5) in oligomerization reactions carried out in the presence of triphenylphosphine (PPh 3 ) afforded highly active catalytic systems with turnover frequencies (TOFs) varying from 36. 4 …”

“…Et 2 O, thf and toluene were distilled from sodium-benzophenone ketyl under argon and degassed by freeze-thaw-vacuum cycles prior to use. and [CrCl 3 (thf) 3 ] 10 were prepared by literature procedures. …”

“…17 We were curious whether such effects would apply to our nickel catalyst systems. For verifying that, we have chosen the 5-and 6-membered ring nickel complexes NiCl 2 {bis[2-(3,5-dimethyl-1-pyrazolyl)methyl] benzylamine} (3) 8 and NiCl 2 {bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl)]ether} (5) 7 ( Figure 3). Table 3.…”

“…Representative results are summarized in Table 4. Under optimized conditions (toluene as solvent at 30 ºC under 20 bar of ethylene, Al:Ni ratios of 250) the nickel catalysts 3 and 5 are active for dimerization of ethylene in the absence of PPh 3 (3,TOF = 11,300 mol(ethylene) …”