Direct evidence for a coordination–insertion mechanism of ethylene oligomerization catalysed by neutral 2,6-bisiminopyridine iron monoalkyl complexes

Cartes, Marcela; Rodríguez‐Delgado, Antonio; Palma, Pilar; Sánchez, Luis; Cámpora, Juan

doi:10.1039/c4cy00612g

Cited by 12 publications

(3 citation statements)

References 18 publications

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“…Odd-electron, neutral pyridine(diimine) iron alkyl complexes have also demonstrated C–C bond-forming activity. , For example, Talsi and co-workers obtained evidence for the formation of iron alkyl complexes as intermediates in the polymerization of ethylene. , Cámpora and co-workers reported the oligomerization of ethylene from the neutral pyridine(diimine) iron methyl complex ( iPr PDI)FeCH 3 and conducted 1 H NMR spectroscopic studies to observe intermediates consistent with an associative coordination–insertion mechanism . In both cationic and neutral pyridine(diimine) iron complexes, electronic and chemical participation of the ligand was either directly observed or implicated. − …”

Section: Introductionmentioning

confidence: 99%

“…2,12 Caḿpora and co-workers reported the oligomerization of ethylene from the neutral pyridine(diimine) iron methyl complex ( iPr PDI)FeCH 3 and conducted 1 H NMR spectroscopic studies to observe intermediates consistent with an associative coordination− insertion mechanism. 21 In both cationic and neutral pyridine- (diimine) iron complexes, electronic and chemical participation of the ligand was either directly observed or implicated. 22−24 In addition to iron alkyl complexes, five-coordinate pyridine(diimine) formally iron(0) complexes have been synthesized and are active for a range of intra- 25 and intermolecular 26−33 cycloaddition reactions of unactivated alkene−alkene, alkene−diene, and diene−diene partners (Scheme 1B).…”

Section: ■ Introductionmentioning

confidence: 99%

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Bimolecular Reductive Elimination of Ethane from Pyridine(diimine) Iron Methyl Complexes: Mechanism, Electronic Structure, and Entry into [2+2] Cycloaddition Catalysis

et al. 2023

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The application of bimolecular reductive elimination to the activation of iron catalysts for alkene–diene cycloaddition is described. Key to this approach was the synthesis, characterization, electronic structure determination, and ultimately solution stability of a family of pyridine(diimine) iron methyl complexes with diverse steric properties and electronic ground states. Both the aryl-substituted, (MePDI)FeCH3 and (EtPDI)FeCH3 (RPDI = 2,6-(2,6-R2-C6H3NCMe)2C5H3N), and the alkyl-substituted examples, (CyAPDI)FeCH3 (CyAPDI = 2,6-(C6H11NCMe)2C5H3N), have molecular structures significantly distorted from planarity and S = 3/2 ground states. The related N-arylated derivative bearing 2,6-di-isopropyl aryl substituents, (iPrPDI)FeCH3, has an idealized planar geometry and exhibits spin crossover behavior from S = 1/2 to S = 3/2 states. At 23 °C under an N2 atmosphere, both (MePDI)FeCH3 and (EtPDI)FeCH3 underwent reductive elimination of ethane to form the iron dinitrogen precatalysts, [(MePDI)Fe(N2)]2(μ-N2) and [(EtPDI)Fe(N2)]2(μ-N2), respectively, while (iPrPDI)FeCH3 proved inert to C–C bond formation. By contrast, addition of butadiene to all three iron methyl complexes induced ethane formation and generated the corresponding iron butadiene complexes, (RPDI)Fe(η4-C4H6) (R = Me, Et, iPr), known precatalysts for the [2+2] cycloaddition of olefins and dienes. Kinetic, crossover experiments, and structural studies were combined with magnetic measurements and Mössbauer spectroscopy to elucidate the electronic and steric features of the iron complexes that enable this unusual reductive elimination and precatalyst activation pathway. Transmetalation of methyl groups between iron centers was fast at ambient temperature and independent of steric environment or spin state, while the intermediate dimer underwent the sterically controlled rate-determining reaction with either N2 or butadiene to access a catalytically active iron compound.

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Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Bimolecular Reductive Elimination of Ethane from Pyridine(diimine) Iron Methyl Complexes: Mechanism, Electronic Structure, and Entry into [2+2] Cycloaddition Catalysis

et al. 2023

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“…In recent years, research on iron-based catalysts for ethylene oligomerization has mainly focused on ligands [94][95][96], which could be classified into NNN, NN, NNOO, NNO, and NNNNOO by the element attached to Fe in the ligand. The ligands of iron catalysts are highly modifiable [97][98][99], and some researchers are devoted to obtaining better catalytic effects by changing the spatial resistances [97,100], substituent groups [101][102][103], and functional groups [104,105] of the ligands.…”

Section: Iron-based Homogeneous Catalystsmentioning

confidence: 99%

Ethylene Oligomerization Catalyzed by Different Homogeneous or Heterogeneous Catalysts

Peng,

Huang,

2024

Catalysts

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Linear α-olefins (LAOs) are linear alkenes with double bonds at the ends of the molecular chains. LAOs with different chain lengths can be widely applied in various fields. Ethylene oligomerization has become the main process for producing LAOs. In this review, different homogeneous or heterogeneous catalysts recently reported in ethylene oligomerization with Ni, Fe, Co, Cr, etc., as active centers will be discussed. In the homogeneous catalytic system, we mainly discuss the effects of the molecular structure and the electronic and coordination states of complexes on their catalytic activity and selectivity. The Ni, Fe, and Co homogeneous catalysts are discussed separately based on different ligand types, while the Cr-based homogeneous catalysts are discussed separately for ethylene trimerization, tetramerization, and non-selective oligomerization. In heterogeneous catalytic systems, we mainly concentrate on the influence of various supports (metal–organic frameworks, covalent organic frameworks, molecular sieves, etc.) and different ways to introduce active centers to affect the performance in ethylene oligomerization. Finally, a summary and outlook on ethylene oligomerization catalysts are provided based on the current research. The development of highly selective α-olefin formation processes remains a major challenge for academia and industry.

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Oligomerization and Polymerization

2017

Hydrocarbon Chemistry, Two Volume Set

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Direct evidence for a coordination–insertion mechanism of ethylene oligomerization catalysed by neutral 2,6-bisiminopyridine iron monoalkyl complexes

Abstract: 1H NMR studies on ethylene oligomerization catalyzed by compound 3 allowed direct observation of alkyl iron intermediate species as well as reversible ethylene coordination to the metal center.

Cited by 12 publications

References 18 publications

Bimolecular Reductive Elimination of Ethane from Pyridine(diimine) Iron Methyl Complexes: Mechanism, Electronic Structure, and Entry into [2+2] Cycloaddition Catalysis

Bimolecular Reductive Elimination of Ethane from Pyridine(diimine) Iron Methyl Complexes: Mechanism, Electronic Structure, and Entry into [2+2] Cycloaddition Catalysis

Ethylene Oligomerization Catalyzed by Different Homogeneous or Heterogeneous Catalysts

Oligomerization and Polymerization

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