A Chromium Ethylidene Complex as a Potent Catalyst for Selective Ethylene Trimerization

Licciulli, Sebastiano; Albahily, Khalid; Fomitcheva, Valeria; Korobkov, Ilia; Gambarotta, Sandro; Duchateau, Robbert

doi:10.1002/anie.201006953

Cited by 49 publications

(27 citation statements)

References 44 publications

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“…The authors also isolated the catalytically inactive dinuclear Cr(II) complex [{(κN-2,5-(Me 3 C) 2 C 4 H 2 N)Cr(thf )} 2 (μ-Cl) 2 ] from the reaction of [{(η 5 -2,5-(Me 3 C) 2 C 4 H 2 N)CrEt} 2 (μ-Cl) 2 ] with AlEt 3 . 18 Both observations further strengthen the hypothesis of a Cr(I)/Cr(III) catalytic cycle.…”

Section: Introductionsupporting

confidence: 58%

Coordination chemistry of sterically encumbered pyrrolyl ligands to chromium(ii): mono(pyrrolyl)chromium and diazachromocene formation

et al. 2014

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A series of diazachromocenes with sterically demanding pyrrolyl ligands, 2,5-(Me3C)2C4H2N (1), 2,5-(Me3C)2-3,4-Me2C4N (2) and 2,3,5-(Me3C)3C4HN (3), was prepared and investigated by various spectroscopic techniques, and in some cases by X-ray diffraction and magnetic susceptibility studies. The diazachromocenes exhibit an S = 1 ground state; no indication of a spin-equilibrium was obtained. With the same ligands mono(pyrrolyl)chromium(II) complexes are accessible, [{(κN-2,5-(Me3C)2C4H2N)Cr(thf)}2(μ-Cl)2] (1-CrCl(thf)), [(κN-2,5-(Me3C)2-3,4-Me2-C4H2N)Cr(Cl)(tmeda)] (2-CrCl(tmeda) and [(η(5)-2,3,5-(Me3C)3C4HN)Cr(μ-Cl)2] (3-CrCl), which show either η(5)- or η(1)-(κN) coordination depending on the substitution pattern. (1)H NMR spectroscopy serves as a valuable tool to distinguish between these coordination modes. The Cr(II) atoms in the mono(pyrrolyl) complexes adopt a high spin configuration (S = 2) and in dimeric species antiferromagnetic coupling between the spin carriers was observed. However, none of these mono(pyrrolyl)chromium complexes is an effective or selective ethylene oligomerization catalyst on activation with MAO or AlMe3, supporting the importance of a Cr(I)/Cr(III)-based catalytic cycle.

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Section: Introductionsupporting

confidence: 58%

Coordination chemistry of sterically encumbered pyrrolyl ligands to chromium(ii): mono(pyrrolyl)chromium and diazachromocene formation

et al. 2014

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“…Interesting is the close resemblance between our proposed structure and self-activating catalysts isolated by Duchateau and Korobkov and co-workers, as depicted in Scheme 3. 7,8,18 Structural resemblence between our proposed structure and these self-activating catalysts include a π-bound ligand and formation of a dative bond with aluminum. Two of these self-activating catalysts are also dinuclear in nature.…”

Section: Resultsmentioning

confidence: 91%

Spectroscopic Investigation of the Activation of a Chromium-Pyrrolyl Ethene Trimerization Catalyst

et al. 2018

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1-Hexene is an important α-olefin for polyethylene production and is produced from ethene. Recent developments in the α-olefin industry have led to the successful commercialization of ethene trimerization catalysts. An important industrially applied ethene trimerization system uses a mixture of chromium 2-ethylhexanoate, AlEt3, AlEt2Cl, and 2,5-dimethylpyrrole (DMP). Here, we have studied the activation of this system using catalytic and spectroscopic experiments (XAS, EPR, and UV–vis) under conditions employed in industry. First, chromium 2-ethylhexanoate was prepared and characterized to be [Cr3O(RCO2)6(H2O)3]Cl. Next, the activation of chromium 2-ethylhexanoate with AlEt3, AlEt2Cl, and DMP was studied, showing immediate reduction (<5 ms) of the trinuclear Cr(III) carboxylate and formation of a neutral polynuclear Cr(II) carboxylate complex. Over time, this Cr(II) carboxylate complex is partially converted into a chloro-bridged dinuclear Cr(II) pyrrolyl complex. In cyclohexane, small quantities of an unknown Cr(I) complex (∼1% after 1 h) are observed, while in toluene, the quantity of Cr(I) is much higher (∼23% after 1 h). This is due to the formation of cationic bis(tolyl)Cr(I) complexes, which likely leads to the observed inferior performance using toluene as the reaction solvent. Catalytic studies allow us to exclude some of the observed Cr(I) and Cr(II) complexes as the active species in this catalytic system. Using this combination of techniques, we have been able to structurally characterize complexes of this selective Cr-catalyzed trimerization system under conditions which are employed in industry.

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“…[29][30][31][32] Gambarotta and Duchateau reported discrete η 5 -pyrrole chromium complexes (1 and 2) as an active species in the Phillips ethylene trimerization system (Chart 1). [33][34][35] Herein, we suggest a new chromium precursor for the Phillips catalyst system that shows improved and consistent catalytic performance. unsaturated hydrocarbon.…”

Section: Introductionmentioning

confidence: 99%

A chromium precursor for the Phillips ethylene trimerization catalyst: (2-ethylhexanoate)₂CrOH

et al. 2015

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The conventional Phillips ethylene trimerization catalyst prepared by reacting Cr(EH)3 (EH = 2-ethylhexanoate), 2,5-dimethylpyrrole (Me2C4H2NH), Et3Al, and Et2AlCl in an aromatic hydrocarbon solvent was improved to obtain a congener composed of a new chromium precursor (EH)2CrOH, (Me2C4H2N)AlEt2, and Et3Al·ClAlEt2. Reaction of CrCl3 with 3 equiv. Na(EH) in water did not generate Cr(EH)3, but unexpectedly produced (EH)2CrOH. In comparison with the erratic catalytic performance of the original Phillips system, due to the ill-defined nature of the Cr(EH)3 source (16 or 6.8 × 10(6) g per mol-Cr h depending on the source), the improved system exhibited consistently high activity (54 × 10(6) g per mol-Cr h). Reaction of (EH)2CrOH with (Me2C4H2N)AlMe2·OEt2 afforded the dimeric Cr(II)-complex (6) coordinated by (η(5)-Me2C4H2N)AlMe2(NC4H2Me2) and μ2-κ(1):η(2)-Me2C4H2N ligands. 6 provided highly active species when activated with Et3Al·ClAlEt2.

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A Chromium Ethylidene Complex as a Potent Catalyst for Selective Ethylene Trimerization

Cited by 49 publications

References 44 publications

Coordination chemistry of sterically encumbered pyrrolyl ligands to chromium(ii): mono(pyrrolyl)chromium and diazachromocene formation

Coordination chemistry of sterically encumbered pyrrolyl ligands to chromium(ii): mono(pyrrolyl)chromium and diazachromocene formation

Spectroscopic Investigation of the Activation of a Chromium-Pyrrolyl Ethene Trimerization Catalyst

A chromium precursor for the Phillips ethylene trimerization catalyst: (2-ethylhexanoate)₂CrOH

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A Chromium Ethylidene Complex as a Potent Catalyst for Selective Ethylene Trimerization

Cited by 49 publications

References 44 publications

Coordination chemistry of sterically encumbered pyrrolyl ligands to chromium(ii): mono(pyrrolyl)chromium and diazachromocene formation

Coordination chemistry of sterically encumbered pyrrolyl ligands to chromium(ii): mono(pyrrolyl)chromium and diazachromocene formation

Spectroscopic Investigation of the Activation of a Chromium-Pyrrolyl Ethene Trimerization Catalyst

A chromium precursor for the Phillips ethylene trimerization catalyst: (2-ethylhexanoate)2CrOH

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A chromium precursor for the Phillips ethylene trimerization catalyst: (2-ethylhexanoate)₂CrOH