Treten in der N‐heterozyklischen Carben‐Organokatalyse wirklich Carbene auf?

Gehrke, Sascha; Hollóczki, Oldamur

doi:10.1002/ange.201708305

Cited by 25 publications

(3 citation statements)

References 34 publications

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“…As for many ILs, the investigation of the hydrogen bond dynamics is hindered by the interference due to the ionicity , of the system ranging from charge transfer or polarization to the formation of neutral species. In the case of the imidazolium cation, this means that carbene formation, with additional hydrogen bonds as acceptors, or even carbene catalysis can play a role. − On top of this, the HBs in imidazolium-based ILs are donated by a carbon ring atom and are therefore of a relatively weak type. , …”

Section: Introductionmentioning

confidence: 99%

Robustness of the Hydrogen Bond and Ion Pair Dynamics in Ionic Liquids to Different Parameters from the Reactive Flux Method

Gehrke

Kirchner

2019

J. Chem. Eng. Data

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Both hydrogen bonding and ionic interactions have an extreme influence on the properties of all kinds of materials. Ionic liquids mostly possess both of them. In the present work, we calculate with the aid of the reactive flux theory the dynamics of hydrogen bonds as well as of the ionic network for different 1-butyl-3-methylimidazolium-based ionic liquids. To apply this method, we carry out molecular dynamics simulations over broad temperature and simulation parameter ranges. Hydrogen bond lifetimes vary with temperature in the range of 10 ps (400 K)−60 ps (300 K) for the more fluid systems to 60 ps (400 K)−2000 ps (300 K) for the more viscous systems. The ion pair dynamics behave differently. While the more fluid systems show ion pairs which possess a factor of 4 longer lifetimes than the hydrogen bonds, the ion pair lifetimes of the more viscous systems actually are a factor of 0.6 smaller and thus faster than the hydrogen bond lifetimes. Although the choice of the hydrogen bond angle is less sensitive, a deviation in the distance criterion of up to 5% from the radial pair distribution functions' minimum leads to a change of less than 10% in the calculated lifetime. The ion pair dynamics are less sensitive with respect to the variation of the geometrical parameter. Interestingly, for both kinds of dynamics the impact on the activation energy is even less prone to the different cutoff values than the lifetime. In fact, the cutoff for the distance criteria causes the activation energies to remain almost unchanged. We find that the stability of the method is sufficient if the simulation time is at least a factor of 10 longer than the corresponding lifetime.

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Section: Introductionmentioning

confidence: 99%

Robustness of the Hydrogen Bond and Ion Pair Dynamics in Ionic Liquids to Different Parameters from the Reactive Flux Method

Gehrke

Kirchner

2019

J. Chem. Eng. Data

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“…In this regard, it was observed that compared with the structuring and dynamics within the pure IL, the addition of water to [C 2 C 1 Im][OAc] modifies and widely disturbs the dipole moment of the ions and the hydrogen bond network of the IL. Furthermore, it hinders a possible carbene formation, besides the fact that a free carbene is not likely. ,, Feng and Voth investigated the effect of the side chain length of the cation and the effect of the anion, for the IL–water mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([C 4 C 1 Im][BF 4 ]), 1-octyl-3-methylimidazolium tetrafluoroborate ([C 8 C 1 Im][BF 4 ]), and 1-octyl-3-methylimidazolium chloride ([C 8 C 1 Im][Cl]) with water mole fractions ranging from 0.2 to 0.9615, on the mixture dynamics and structures . While replacing [C 4 C 1 Im] + by [C 8 C 1 Im] + only leads to an increasing microheterogeneity due to a stronger agglomeration of the cations, exchanging [BF 4 ] − for [Cl] − results in a decrease in the diffusion due to stronger electrostatic interactions between [Cl] − and water as compared with the relatively weakly coordinating anion [BF 4 ] − .…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, it hinders a possible carbene formation, besides the fact that a free carbene is not likely. 33,58,59 Feng and Voth investigated the effect of the side chain length of the cation and the effect of the anion, for the IL−water mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate…”

Section: ■ Introductionmentioning

confidence: 99%

Hydrophilic Ionic Liquid Mixtures of Weakly and Strongly Coordinating Anions with and without Water

et al. 2018

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With the aid of ab initio molecular dynamics simulations, we investigate an ionic liquid (IL) mixture composed of three components 1-butyl-3-methylimidazolium [C 4 C 1 Im] + , tetrafluoroborate [BF 4 ] − , and chloride [Cl] − without and with water. In the pure IL mixture, we observe an already complex network of interactions between cations and anions, and addition of water to the system even extends the complexity. Observed number integrals show that the coordination number between cations and anions is reduced in the system with water compared to that in the pure system. Further studies show that the Coulombic network of the strongly coordinating anion [Cl] − is disturbed by water, while that of the weakly coordinating anion [BF 4 ] − is not. These observations can also be confirmed by the Voronoi polyhedra analysis, which shows that the polar network of microheterogeneous IL collapses by the introduction of water. Hydrogen-acceptor interactions revealed that the [Cl] − anions are transferred from being situated in the IL to the water continuum, while [BF 4 ] − is almost unperturbed; these effects mainly influence the interplay of the ionic liquid network.

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ADUC‐Preise: U.‐P. Apfel, P. Heretsch, O. Hollóczki / Carl‐Duisberg‐Gedächtnispreis: B. Morandi / Neu in der Académie des Sciences: E. Charpentier, J. Cossy, I. Marek / Max‐Delbrück‐Nachwuchspreis: S. Disch / Novartis Early Career Award: B. Morandi und R. R. Knowles

2018

Angewandte Chemie

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Treten in der N‐heterozyklischen Carben‐Organokatalyse wirklich Carbene auf?

Cited by 25 publications

References 34 publications

Robustness of the Hydrogen Bond and Ion Pair Dynamics in Ionic Liquids to Different Parameters from the Reactive Flux Method

Robustness of the Hydrogen Bond and Ion Pair Dynamics in Ionic Liquids to Different Parameters from the Reactive Flux Method

Hydrophilic Ionic Liquid Mixtures of Weakly and Strongly Coordinating Anions with and without Water

ADUC‐Preise: U.‐P. Apfel, P. Heretsch, O. Hollóczki / Carl‐Duisberg‐Gedächtnispreis: B. Morandi / Neu in der Académie des Sciences: E. Charpentier, J. Cossy, I. Marek / Max‐Delbrück‐Nachwuchspreis: S. Disch / Novartis Early Career Award: B. Morandi und R. R. Knowles

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