Mechanistic Insights into Chromium-Catalyzed Ethylene Trimerization

Gunasekara, Thilina; Kim, Jungsuk; Preston, Andrew Z.; Steelman, D. Keith; Medvedev, Grigori A.; Delgass, W. Nicholas; Sydora, Orson L.; Caruthers, James M.; Abu-Omar, Mahdi M.

doi:10.1021/acscatal.8b00468

Cited by 26 publications

(30 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These observations lead to two hypotheses: i) either the first ethene coordination event is endergonic in nature and coordination of ethene cannot be observed in the experiment as performed or ii) a minority species is responsible for catalysis and the majority species is incapable of coordinating ethene. The first hypothesis is in line with a recent kinetic study of a {Cr(PN)} ethene tetramerization system, where it is demonstrated that the first and/or the second ethene coordination event is reversible . The second hypothesis has been proposed by Bercaw and coworkers in a {Cr(PNP)} ethene trimerization system …”

Section: Resultssupporting

confidence: 80%

“…The first hypothesis is in line with a recent kinetic study of a {Cr (PN)} ethene tetramerization system, where it is demonstrated that the first and/or the second ethene coordination event is reversible. [31] The second hypothesis has been proposed by Bercaw and coworkers in a {Cr(PNP)} ethene trimerization system. [32] To investigate the first hypothesis, we resorted to different substrates.…”

Section: Spectroscopic Investigation Of the Activation Process In Thementioning

confidence: 98%

See 1 more Smart Citation

Investigating the Active Species in a [(R‐SN(H)S‐R)CrCl₃] Ethene Trimerization System: Mononuclear or Dinuclear?

et al. 2019

View full text Add to dashboard Cite

Cr-catalyzed ethene trimerization is an industrially important process to produce 1-hexene. Despite its industrial relevance, the changing oxidation state and the structural rearrangements of the metal center during the catalytic cycle remain unclear. In this study, we have investigated the active species in a [(R-SN (H)SÀ R)CrCl 3 ] (R = C 10 H 21 ) catalyzed ethene trimerization system using a combination of spectroscopic techniques (XAS, EPR and UV/VIS) and DFT calculations. Reaction of the octahedral Cr III complex with modified methylaluminoxane (MMAO) in absence of ethene gives rise to the formation of a square-planar Cr II complex. In the presence of ethene (1 bar), no coordination was observed, which we attribute to the endergonic nature of the coordination of the first ethene molecule. Employing an alkyne as a model for ethene coordination leads to the formation of a dinuclear cationic Cr III alkyne complex. DFT calculations show that a structurally related dinuclear cationic Cr III ethene complex could form under catalytic conditions. Comparing a mechanism proceeding via mononuclear cationic Cr II /Cr IV intermediates to that proceeding via dinuclear cationic Cr II /Cr III intermediates demonstrates that only the mechanism involving mononuclear cationic Cr II /Cr IV intermediates can correctly explain the observed product selectivity.[a] B.

show abstract

Section: Resultssupporting

confidence: 80%

Section: Spectroscopic Investigation Of the Activation Process In Thementioning

confidence: 98%

Investigating the Active Species in a [(R‐SN(H)S‐R)CrCl₃] Ethene Trimerization System: Mononuclear or Dinuclear?

et al. 2019

View full text Add to dashboard Cite

show abstract

“…The origin of the selectivity towards ethylene trimerization shown with a number of chromium catalysts (see section 3) is considered to take place by metallacyclic-based mechanism, as initially proposed by Manyik [151], later modified by Briggs [152] and by a number of subsequent studies (Scheme 2) [153][154][155]. The first step of the catalytic cycle is to cis-coordinate two ethylene molecules to the metal center, which then undergoes oxidative cyclization to form a chromacyclopentane.…”

Section: Tri-/tetramerization Of Ethylenementioning

confidence: 99%

Recent advances in homogeneous chromium catalyst design for ethylene tri-, tetra-, oligo- and polymerization

Bariashir

Huang

Solan

et al. 2019

Coordination Chemistry Reviews

114

View full text Add to dashboard Cite

This review focuses on recent progress made using well-defined molecular chromium complexes that, upon suitable activation, can catalyze the tri-, tetra, oligo-and/or polymerization of ethylene. In particular, emphasis will be placed on the tuning of the performance characteristics of these homogeneous catalysts through structural modifications made to the multidentate ligand manifold (e.g., donor atoms, charge, backbone and strain) and the effects these changes have on the resulting ethylene derivatives. While the ability of these catalysts to mediate the formation of high molecular weight linear polyethylene continues to see many developments, their capacity to form polyethylene waxes and oligomers has witnessed some major advances. Moreover, the impressive selectivity of some chromium systems to generate commercially important 1-hexene and more recently 1-octene has seen the implementation of this technology at the industrial level. The types of precatalysts to be discussed will be divided broadly on the basis of their ability to generate either polymers/oligomers or short chain αolefins; the effects of co-catalyst and reaction conditions (e.g., temperature, pressure, solvent) on catalytic activity and selectivity, will be also developed. In addition, current proposals as to the mechanistic details displayed by these versatile chromium catalysts will be highlighted.

show abstract

“…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. Catalyst development for ethylene oligomerization is still an active research topic in both academia and industry …”

Section: Introductionmentioning

confidence: 99%

MAO‐free and extremely active catalytic system for ethylene tetramerization

Kim

Lee

Park

et al. 2019

Applied Organom Chemis

View full text Add to dashboard Cite

The original Sasol catalytic system for ethylene tetramerization is composed of a Cr source, a PNP ligand, and MAO (methylaluminoxane). The use of expensive MAO in excess has been a critical concern in commercial operation. Many efforts have been made to replace MAO with non‐coordinating anions (e.g., [B(C6F5)4]−); however, most of such attempts were unsuccessful. Herein, an extremely active catalytic system that avoids the use of MAO is presented. The successive addition of two equivalent [H(OEt2)2]+[B(C6F5)4]− and one equivalent CrCl3(THF)3 to (acac)AlEt2 and subsequent treatment with a PNP ligand [CH3(CH2)16]2C(H)N(PPh2)2 (1) yielded a complex presumably formulated as [1‐CrAl (acac)Cl3(THF)]2+[B(C6F5)4]−2, which exhibited high activity when combined with iBu3Al (1120 kg/g‐Cr/h; ~4 times that of the original Sasol system composed of Cr (acac)3, iPrN(PPh2)2, and MAO). Via the introduction of bulky trialkylsilyl substituents such as –SiMe3, –Si(nBu)3, or –SiMe2(CH2)7CH3 at the para‐position of phenyl groups in 1 (i.e., by using [CH3(CH2)16]2C(H)N[P(C6H4‐p‐SiR3)2]2 instead of 1), the activities were dramatically improved, i.e., tripled (2960–3340 kg/g‐Cr/h; more than 10 times that of the original Sasol system). The generation of significantly less PE (<0.2 wt%) even at a high temperature is another advantage achieved by the introduction of bulky trialkylsilyl substituents. NMR studies and DFT calculations suggest that increase of the steric bulkiness on the alkyl‐N and P‐aryl moieties restrict the free rotation around (alkyl)N–P (aryl) bonds, which may cause the generation of more robust active species in higher proportion, leading to extremely high activity along with the generation of a smaller amount of PE.

show abstract

Mechanistic Insights into Chromium-Catalyzed Ethylene Trimerization

Cited by 26 publications

References 35 publications

Investigating the Active Species in a [(R‐SN(H)S‐R)CrCl₃] Ethene Trimerization System: Mononuclear or Dinuclear?

Investigating the Active Species in a [(R‐SN(H)S‐R)CrCl₃] Ethene Trimerization System: Mononuclear or Dinuclear?

Recent advances in homogeneous chromium catalyst design for ethylene tri-, tetra-, oligo- and polymerization

MAO‐free and extremely active catalytic system for ethylene tetramerization

Contact Info

Product

Resources

About

Mechanistic Insights into Chromium-Catalyzed Ethylene Trimerization

Cited by 26 publications

References 35 publications

Investigating the Active Species in a [(R‐SN(H)S‐R)CrCl3] Ethene Trimerization System: Mononuclear or Dinuclear?

Investigating the Active Species in a [(R‐SN(H)S‐R)CrCl3] Ethene Trimerization System: Mononuclear or Dinuclear?

Recent advances in homogeneous chromium catalyst design for ethylene tri-, tetra-, oligo- and polymerization

MAO‐free and extremely active catalytic system for ethylene tetramerization

Contact Info

Product

Resources

About

Investigating the Active Species in a [(R‐SN(H)S‐R)CrCl₃] Ethene Trimerization System: Mononuclear or Dinuclear?

Investigating the Active Species in a [(R‐SN(H)S‐R)CrCl₃] Ethene Trimerization System: Mononuclear or Dinuclear?