First direct evidence of N-heterocyclic carbene in BMIm acetate ionic liquids. An electrochemical and chemical study on the role of temperature

Chiarotto, Isabella; Feroci, Marta; Inesi, Achille

doi:10.1039/c7nj00779e

Cited by 31 publications

(34 citation statements)

References 27 publications

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“…Nevertheless, the exogenous proton exchange equilibrium (1) is the only equilibrium of proton exchange operative involving Ac − at T < 60 °C (Scheme , eq. 1) …”

Section: Resultsmentioning

confidence: 99%

“…1). [5] In fact, the effectiveness of an equilibrium of the endogenous proton exchange between BMIm + and Ac À , in pure BMImAc or in organic solvent at T < 60 8C, was definitively ruled out by us via electrochemical analysis that revealed that this equilibrium is operative at T > 60 8C. [13] As a consequence, in the Knovenagel mixture selected by us, the cation BMIm + behaves as a better counter ion of reactive anions Ac À and HCO 3 À as it shows a lower ion pairing ability than Na + and possibly enhances the reaction rate due to its hydrogen bond donor ability.…”

Section: Resultsmentioning

confidence: 99%

“…The acidity of the imidazolium cation BMIm + (pKa=22 in DMSO) and the possible basicity of its counter ion (Ac − , pKa=4.76 in H 2 O, 12.6 in DMSO; HCO 3 − , pKa=6.36 in H 2 O, 10.25 in DMSO) are reported by many authors. The mutual interactions between BMIM + and X − were recently analysed . The formation of a new C−C bond could be a serious hindrance (and an intriguing challenge) in a procedure of organic synthesis.…”

Section: Introductionmentioning

confidence: 99%

“…The mutual interactions between BMIM + and X À were recently analysed. [5] The formation of a new CÀC bond could be a serious hindrance (and an intriguing challenge) in a procedure of organic synthesis. The Knovenagel condensation between activated methylene compounds and aldehydes is a versatile reaction for the formation of CÀC bond through losing a molecule of water.…”

Section: Introductionmentioning

confidence: 99%

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Role of Anion and Cation in the 1‐Methyl‐3‐butyl Imidazolium Ionic Liquids BMImX: The Knoevenagel Condensation

2018

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1‐Methyl‐3‐butylimidazolium ionic liquids BMImX (X anions: Ac−, HCO3−, Cl−, BF4−, PF6−, I−, CF3CO2−, (CF3SO2)2N−, CF3SO3−) were used as catalysts in the Knoevenagel condensation reaction. The catalytic activity was compared with that of the inorganic salts NaAc, NaHCO3, NaCl. Whereas it is quite important to select suitable cation and anion depending on the purpose, the basicity of the anion X− and the ability of the counter‐ion BMIm+ to avoid the ion pairing with anion X− was investigated. 1‐Methyl‐3‐butyl imidazolium acetate [BMImAc] and 1‐methyl‐3‐butyl imidazolium hydrogen carbonate [BMImHCO3] show the most significant catalytic power and their catalytic effect was studied on a wide range of aromatic, heteroaromatic or aliphatic aldehydes or ketones with active methylene compounds. The corresponding substituted alkenes were obtained in excellent yields (up to 98%) in the absence of any solvent at room temperature within short times. The interesting feature of this study includes explanation on role of the cation BMIm+ as proton donor (versus anions Ac− or HCO3−), in ion pair formation (with anion X−) and activator of the aldehyde structure.

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“…Nevertheless, the exogenous proton exchange equilibrium (1) is the only equilibrium of proton exchange operative involving Ac − at T < 60 °C (Scheme , eq. 1) …”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Role of Anion and Cation in the 1‐Methyl‐3‐butyl Imidazolium Ionic Liquids BMImX: The Knoevenagel Condensation

2018

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“…15,16 The existence of NHC derived from {[Bmim]AcO} was later determined at 120ºC by cyclic voltammetry (Scheme 1). 17 Thiazolium and imidazolium cations from ionic liquids as pre-catalysts in benzoin condensation-a mini review…”

Section: Formation Of N-heterocyclic Carbenes From Ionic Liquids Usedmentioning

confidence: 99%

Thiazolium and imidazolium cations from ionic liquids as pre-catalysts in benzoin condensation–a mini review

Villamizar-Mogotocoro

Urbina-González

2018

JAPLR

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Synthesis of benzoins and their substituted derivatives is well known for more than a century since the original work of Liebig and Wöhler. This important strategy to create new CC bonds now uses N-heterocyclic carbenes (NHC) as catalysts, mainly derived from azolium cations obtained from different ionic liquids. Although numerous reports have been published to date, this article covers just the main aspects in the NHC formation from azolium pre-catalysts.

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On the Carbene‐Like Reactions of Imidazolium Acetate Ionic Liquids: Can Theory and Experiments Agree?

et al. 2018

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The N‐heterocyclic carbene organocatalytic reactivity of the 1‐ethyl‐3‐methylimidazolium acetate ionic liquid was investigated on the model reaction between this solvent and anisaldehyde. The formation of carbenes by a proton transfer from the cation to the anion was compared to a direct reaction mechanism, in which the proton transfer and the C–C bond formation between catalyst and substrate occurs in a single elementary step. Interestingly, the two reaction mechanisms show a much smaller difference in activation energies than those observed for analogous catalytic systems with neutral bases, showing that the mechanism might switch from one to the other at different temperatures or with different substrates. In this particular case, however, the direct reaction mechanism, avoiding free carbenes in the solution, is apparently more feasible. Based on the detailed analysis of this reaction path, the earlier contradictions between theory and experiments can be resolved, resulting in a consistent mechanistic picture for the related processes. Additionally, we show on the example of a platinum surface that introducing metal probes into the liquid may induce carbene‐like reactions, as the formation of a strong coordinative bond between the carbene and a platinum atom at the surface is highly exothermic, shifting the acid‐base equilibrium considerably.

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First direct evidence of N-heterocyclic carbene in BMIm acetate ionic liquids. An electrochemical and chemical study on the role of temperature

Abstract: Cyclic voltammetry measurements provide the first direct evidence of N-heterocyclic carbene in neat 1-butyl-3-methylimidazolium acetate ionic liquid at temperatures over 120 °C.

Cited by 31 publications

References 27 publications

Role of Anion and Cation in the 1‐Methyl‐3‐butyl Imidazolium Ionic Liquids BMImX: The Knoevenagel Condensation

Role of Anion and Cation in the 1‐Methyl‐3‐butyl Imidazolium Ionic Liquids BMImX: The Knoevenagel Condensation

Thiazolium and imidazolium cations from ionic liquids as pre-catalysts in benzoin condensation–a mini review

On the Carbene‐Like Reactions of Imidazolium Acetate Ionic Liquids: Can Theory and Experiments Agree?

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