Experimental Evidence for Large Ring Metallacycle Intermediates in Polyethylene Chain Growth Using Homogeneous Chromium Catalysts

Tomov, Atanas K.; Chirinos, Juan; Jones, David J.; Long, Richard J.; Gibson, Vernon C.

doi:10.1021/ja051523f

Cited by 156 publications

(133 citation statements)

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“…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.…”

Section: Introductionmentioning

confidence: 86%

“…18,30,31,33 The catalysts 1, 3 and 4 result in a Schultz-Flory distribution of linear α-olefins (LAO), while catalyst 2 gives a slightly different product distribution due to an additional, but minor, chain transfer to aluminum process. Chain transfer to aluminum is a common termination mechanism for catalyst 2 in the presence of MAO co-catalyst.…”

Section: H 4 Oligomerizationmentioning

confidence: 99%

“…17 With certain chromium catalysts higher molecular weight oligomers can be obtained via this mechanism. 18,19,20 Scheme 1. Ethylene oligomerization/polymerization mechanisms.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2009

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A series of co-oligomerization and co-polymerization reactions of C 2 H 4 /C 2 D 4 (1:1) mixtures have been carried out using various transition metal catalysts based on Cr, Co and Fe in combination with MAO. The oligomeric α-olefin products have been analysed by GC and GC/MS and the experimental results have been compared with the theoretical mass spectra derived from mathematical models. Solid polymer samples have been analysed by 13 C{ 1 H} and 13 C DEPT-135 NMR spectroscopy. C 2 H 4 /C 2 D 4 co-oligomerization can be used as a method to differentiate between a metallacyclic or a Cossee-type chain growth mechanism in oligomerization systems. In the case of a metallacyclic mechanism, no H/D scrambling is observed whereas for a Cossee-type mechanism, similar rates of chain propagation and chain termination (β-H elimination) result in rapid H/D scrambling of the C 2 H 4 /C 2 D 4 feed. This method is therefore limited to oligomerization systems and cannot be applied in polymerization systems where the rate of chain propagation is much faster than the rate of chain termination.

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Section: Introductionmentioning

confidence: 86%

Section: H 4 Oligomerizationmentioning

confidence: 99%

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

et al. 2009

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“…39 The total oligomer yield obtained at different gauge pressures from 1-4 bar follows a first order dependence on ethylene concentration (see Figure S2). The order in ethylene concentration for individual LAOs is conveniently determined from the slope in a ln(rate) versus ln[ethylene] plot, 44 whereby ethylene pressure is a reliable proxy for concentration in solution.…”

Section: Effect Of Pressurementioning

confidence: 98%

Alternating α-Olefin Distributions via Single and Double Insertions in Chromium-Catalyzed Ethylene Oligomerization

et al. 2016

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The catalytic oligomerization of ethylene with chromium-based complexes containing bis(benzimidazolemethyl)amine (BIMA) ligands results in alternating distributions of linear α-olefins (LAOs). Extremely high activities are obtained (>100 000 g mmol–1 h–1 bar–1) with N-alkyl-substituted BIMA ligands, whereas bulky groups on the central nitrogen or alternative central donors result in much lower activities. Variations in the ligand backbone, as well as methylation of the benzimidazole units, lead to reduction in activity. The alternating LAO distributions have been mathematically analyzed using second-order recurrence relations. The shape of the distributions is affected by ethylene pressure (1–4 bar) and by the cocatalyst to some degree. On the basis of the results and analysis presented herein, we propose that the alternating behavior originates from the ability of these chromium BIMA catalysts to undergo single as well as double ethylene insertion reactions. A minor second distribution (<5 wt %) of 2-ethyl-1-alkenes is obtained under certain conditions, resulting from incorporation of 1-butene. DFT studies (M06L) and experimental observations regarding the reaction between AlMe3 and the N-methyl BIMA ligand 2 have shown that deprotonation of the benzimidazole N–H units can occur, which suggests a change in coordination of the BIMA ligand under oligomerization conditions.

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“…It is reported that chromium complexes ligated by NNN species such as bis(imino)pyridine, (2-pyridylmethyl)amines, β-diketimate and pyrrolide-imine ligands can polymerize or oligomerize ethylene with great activity [21,[23][24][25].…”

Section: Nnn Ligandsmentioning

confidence: 99%

Recent Research Progress in Preparation of Ethylene Oligomers with Chromium-Based Catalytic Systems

Zhu

Wang

2011

Designed Monomers and Polymers

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Ethylene oligomers, notably 1-hexene and 1-octene, are usually used as co-monomers in the production of linear low-density polyethylene (LLDPE). Because of the great value of 1-hexene and 1-octene, there have been many reports on the selective oligomerization of ethylene to 1-hexene and 1-octene recently. Research of ethylene oligomerization focuses mainly on the synthesis of catalysts and the mechanism of oligomerization. Much of this research concerns investigation into a catalytic system that can oligomerize ethylene to 1-hexene or 1-octene with high selectivity and activity. Different kinds of catalysts have been synthesized to catalyze the reactions, and the chromium-based homogeneous catalysts are found to be the most suitable ones. This article reviews the recent research progress in synthesis of chromium catalyst systems and study on the mechanism of ethylene oligomerization catalyzed by these catalysts.

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Experimental Evidence for Large Ring Metallacycle Intermediates in Polyethylene Chain Growth Using Homogeneous Chromium Catalysts

Cited by 156 publications

References 20 publications

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

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

Alternating α-Olefin Distributions via Single and Double Insertions in Chromium-Catalyzed Ethylene Oligomerization

Recent Research Progress in Preparation of Ethylene Oligomers with Chromium-Based Catalytic Systems

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Experimental Evidence for Large Ring Metallacycle Intermediates in Polyethylene Chain Growth Using Homogeneous Chromium Catalysts

Cited by 156 publications

References 20 publications

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

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

Alternating α-Olefin Distributions via Single and Double Insertions in Chromium-Catalyzed Ethylene Oligomerization

Recent Research Progress in Preparation of Ethylene Oligomers with Chromium-Based Catalytic Systems

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

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