The Formation of Imidazolium Salt Intimate (Contact) Ion Pairs in Solution

Zanatta, Marcileia; Girard, Anne‐Lise; Simon, Nathália Marcolin; Ebeling, Günter; Stassen, Hubert; Livotto, Paolo Roberto; Santos, Francisco P. dos; Dupont, Jaı̈rton

doi:10.1002/anie.201408151

Cited by 44 publications

(46 citation statements)

References 43 publications

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“…Using ion pairs of ILs containing the BMMI cation and anions such as chloride, prolinate, formiate, and bicarbonate, stable contact ion pairs have been maintained in chloroform, transient ion pairs in DMSO, and instantaneous ion pair dissociation has been observed in water. [74] These findings are in agreement with the experimentally detected tendency of lower association constants for ion pair formation in more polar solvents.…”

Section: Molecular Dynamics Simulationssupporting

confidence: 88%

“…[71,72] This behaviour remains if small amounts of water are added which then compete with the CO 2 for the favourite interaction sites. [73] 1 H, 13 C-HOESY experiments also revealed that contact ion pairs are maintained for BMI·HCO 3 [74] Moreover, these species display reactivity as contact ion pairs and not as solvent-separated ions when diluted in CDCl 3 , CD 3 CN and even in DMSO, but not in D 2 O (see below).…”

Section: Long-lived Contact Ion Pairs Detected By Nmr Spectroscopymentioning

confidence: 97%

“…These two salts undergo H/D reactions preferentially at the "least" acidic C(2)ÀMe group rather than at C(4)/C(5) of the imidazolium ring in CDCl 3 in which the contact ion pairs are maintained, but not in D 2 O where solvent separated ions are present (Scheme 3). [74] Note that these H/D reactions do not occur with other imdiazolium salts associated with classical and even more basic anions such as halides, acetate, formiate, azide, PF 6 , BF 4 or NTf 2 . It was proposed that the ILs act as D-transfer catalysts between CDCl 3 and the IL pair due to the presence of a labile proton in its anion structure.…”

Section: Mmol Mol à1mentioning

confidence: 99%

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Imidazolium Salt Ion Pairs in Solution

Stassen

Ludwig

Wulf

et al. 2015

Chemistry A European J

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169

151

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The formation, stabilisation and reactivity of contact ion pairs of non-protic imidazolium ionic liquids (ILs) in solution are conceptualized in light of selected experimental evidence as well theoretical calculations reported mainly in the last ten years. Electric conductivity, NMR, ESI-MS and IR data as well as theoretical calculations support not only the formation of contact ion pairs in solution, but also the presence of larger ionic and neutral aggregates even when dissolved in solvents with relatively high dielectric constants, such as acetonitrile and DMSO. The presence of larger imidazolium supramolecular aggregates is favoured at higher salt concentrations in solvents of low dielectric constant for ILs that contain shorter N-alkyl side chains associated with anions of low coordination ability. The stability and reactivity of neutral contact species are also dependent on the nature of the anion, imidazolium substituents, and are more abundant in ILs containing strong coordinating anions, in particular those that can form charge transfer complexes with the imidazolium cation. Finally, some ILs display reactivities as contact ion pairs rather than solvent-separated ions.

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Section: Molecular Dynamics Simulationssupporting

confidence: 88%

Section: Long-lived Contact Ion Pairs Detected By Nmr Spectroscopymentioning

confidence: 97%

Section: Mmol Mol à1mentioning

confidence: 99%

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Imidazolium Salt Ion Pairs in Solution

Stassen

Ludwig

Wulf

et al. 2015

Chemistry A European J

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169

151

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“…Therefore, the oxidized palladium component increases with the decrease of the ionic bond strength between the imidazolium cation and anions, i.e., the stronger the ionic interaction between the cation and anion, the less "ionic" is the contact ion pair. Hence, the interaction of the IL with the metal surface is via IL contact pairs (or aggregates) 54,55 rather than by charged species, corroborating the proposed supramolecular model for formation and stabilization of M-NPs in ILs. [56][57][58] …”

Section: Chemical State and Local Atomic Order Of The Pd Atomssupporting

confidence: 74%

Catalytically Active Membranelike Devices: Ionic Liquid Hybrid Organosilicas Decorated with Palladium Nanoparticles

et al. 2016

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Ionic liquid (IL)-hybrid organosilicas based on 1-n-butyl-3-(3-trimethoxysilylpropyl)-imidazolium cations associated with hydrophilic and hydrophobic anions decorated with well dispersed and similar sized (1.8-2.1 nm) Pd nanoparticles (PdNPs) are amongst the most active and selective catalysts for the partial hydrogenation of conjugated dienes to monoenes. The location of the sputter-imprinted Pd-NPs on different supports, as determined by RBS and HS-LEIS analysis, is modulated by the strength of the contact ion pair formed between the imidazolium cation and the anion, rather than the IL-hybrid organosilica pore size and surface area. In contrast, the pore diameter and surface area of the hybrid supports display a direct correlation with the anion hydrophobicity. XPS analysis showed that the Pd(0) surface component decreases with increasing ionic bond strength between the imidazolium cation and the anions (contact ion pair). The finding is corroborated by changes in the coordination number associated with the Pd-Pd scattering in EXAFS measurements. Hence, the interaction of the IL with the metal surface is found to occur via IL contact pairs (or aggregates). The observed selectivities of ≥99% to monoenes at full diene conversion indicate that the selectivity is intrinsic to the electron deficient Pd-metallic surfaces in this "restricted" ionic environment. This suggests that ILhybrid organosilica/Pd-NPs under multiphase conditions ("dynamic asymmetric mixture") operate akin to catalytically active membranes, i.e. far from the thermodynamic equilibrium. Detailed kinetic investigations show that the reaction rate is zero-order with respect to hydrogen and dependent on the fraction of catalyst surfaces covered by either the substrate and/or the product. The reaction proceeds via rapid inclusion and sorption of the diene to the IL/Pd metal surface saturated with H species. This is followed by reversible hydride migration to generate a π-allyl intermediate. The reductive elimination of this intermediate, the formal ratedetermining step (RDS), generates the alkene that is rapidly expelled from the IL phase to the organic phase.

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“…[3][4][5] One of the most singularp roperties of ionicl iquids( ILs)resultingf rom their supramolecular structuralo rganization-is the presence of nonhomogeneousn anodomains that can easily accommodate both polar and nonpolar compounds. Consequently,c ooperative networks (based on dispersive forces andh ydrogen bonds)o fc lassical imidazolium ILs such as BMIm·BF 4 and BMIm·PF 6 are only marginally disrupted and the cation-anionc ontact ion pair [13,14] is unaffected by the inclusion of CO 2 . [4,7,8] This is mainly owed to the high CO 2 solubility in ILs as well as the possibility to fine-tune the sorption properties of the ionic material.…”

Section: Introductionmentioning

confidence: 99%

Carbon Dioxide Capture by Aqueous Ionic Liquid Solutions

et al. 2017

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Confined water in aqueous solutions of imidazolium-based ionic liquids (ILs) associated with acetate and imidazolate anions react reversibly with CO to yield bicarbonate. Three types of CO sorption in these "IL aqueous solutions" were observed: physical, CO -imidazolium adduct generation, and bicarbonate formation (up to 1.9 mol mol of IL), resulting in a 10:1 (molar ratio) total absorption of CO relative to imidazolate anions in the presence of water 1:1000 (IL/water). These sorption values are higher than the classical alkanol amines or even alkaline aqueous solutions under similar experimental conditions.

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The Formation of Imidazolium Salt Intimate (Contact) Ion Pairs in Solution

Cited by 44 publications

References 43 publications

Imidazolium Salt Ion Pairs in Solution

Imidazolium Salt Ion Pairs in Solution

Catalytically Active Membranelike Devices: Ionic Liquid Hybrid Organosilicas Decorated with Palladium Nanoparticles

Carbon Dioxide Capture by Aqueous Ionic Liquid Solutions

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