Examining Ionic Liquid Effects on Mononuclear Rearrangement of Heterocycles Using QM/MM Simulations

Caley Allen, Robel Ghebreab, Brian Doherty, Bin Li, Orlando Acevedo

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

The mononuclear rearrangement of heterocycles (MRH) reaction of the Z-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into 4-benzoylamino-2,5-diphenyl-1,2,3-triazole derives a sizable rate enhancement in the 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] ionic liquid as compared to the hexafluorophosphate-based [BMIM][PF6] and conventional organic solvents. However, the origin of the rate difference between [BMIM][BF4] and [BMIM][PF6] has proven difficult to rationalize as no experimental trend relates the physical properties of the solvents, e.g., polarity and viscosity, to the rates of reaction. QM/MM calculations in combination with free-energy perturbation theory and Monte Carlo sampling have been carried out for the MRH reaction to elucidate the disparities in rates when using ionic liquids, methanol, and acetonitrile. Activation barriers and solute-solvent interactions have been computed for both an uncatalyzed and a specific base-catalyzed mechanism. Energetic and structural analyses determined that favorable π+-π interactions between the BMIM cation, the substrate phenyl rings, and the bicyclic quasi-aromatic 10π oxadiazole/triazole transition state region imposed a preordered geometric arrangement that enhanced the rate of reaction. An ionic liquid clathrate formation enforced a coplanar orientation of the phenyl rings that maximized the electronic effects exerted on the reaction route. In addition, site-specific electrostatic stabilization between the ions and the MRH substrate was more prevalent in [BMIM][BF4] as compared to [BMIM][PF6].

Original languageEnglish (US)
Pages (from-to)10786-10796
Number of pages11
JournalJournal of Physical Chemistry B
Volume120
Issue number41
DOIs
StatePublished - Oct 20 2016

Fingerprint

Ionic Liquids
Ionic liquids
liquids
Oxadiazoles
Triazoles
simulation
Substrates
Acetonitrile
Organic solvents
Free energy
Methanol
Cations
Electrostatics
Stabilization
Physical properties
Positive ions
Chemical activation
Viscosity
Ions
Sampling

ASJC Scopus subject areas

  • Surfaces, Coatings and Films
  • Physical and Theoretical Chemistry
  • Materials Chemistry

Cite this

Examining Ionic Liquid Effects on Mononuclear Rearrangement of Heterocycles Using QM/MM Simulations. / Allen, Caley; Ghebreab, Robel; Doherty, Brian; Li, Bin; Acevedo, Orlando.

In: Journal of Physical Chemistry B, Vol. 120, No. 41, 20.10.2016, p. 10786-10796.

Research output: Contribution to journalArticle

Allen, Caley ; Ghebreab, Robel ; Doherty, Brian ; Li, Bin ; Acevedo, Orlando. / Examining Ionic Liquid Effects on Mononuclear Rearrangement of Heterocycles Using QM/MM Simulations. In: Journal of Physical Chemistry B. 2016 ; Vol. 120, No. 41. pp. 10786-10796.
@article{a7b92c7445ae41e38398cd7d7042533d,
title = "Examining Ionic Liquid Effects on Mononuclear Rearrangement of Heterocycles Using QM/MM Simulations",
abstract = "The mononuclear rearrangement of heterocycles (MRH) reaction of the Z-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into 4-benzoylamino-2,5-diphenyl-1,2,3-triazole derives a sizable rate enhancement in the 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] ionic liquid as compared to the hexafluorophosphate-based [BMIM][PF6] and conventional organic solvents. However, the origin of the rate difference between [BMIM][BF4] and [BMIM][PF6] has proven difficult to rationalize as no experimental trend relates the physical properties of the solvents, e.g., polarity and viscosity, to the rates of reaction. QM/MM calculations in combination with free-energy perturbation theory and Monte Carlo sampling have been carried out for the MRH reaction to elucidate the disparities in rates when using ionic liquids, methanol, and acetonitrile. Activation barriers and solute-solvent interactions have been computed for both an uncatalyzed and a specific base-catalyzed mechanism. Energetic and structural analyses determined that favorable π+-π interactions between the BMIM cation, the substrate phenyl rings, and the bicyclic quasi-aromatic 10π oxadiazole/triazole transition state region imposed a preordered geometric arrangement that enhanced the rate of reaction. An ionic liquid clathrate formation enforced a coplanar orientation of the phenyl rings that maximized the electronic effects exerted on the reaction route. In addition, site-specific electrostatic stabilization between the ions and the MRH substrate was more prevalent in [BMIM][BF4] as compared to [BMIM][PF6].",
author = "Caley Allen and Robel Ghebreab and Brian Doherty and Bin Li and Orlando Acevedo",
year = "2016",
month = "10",
day = "20",
doi = "10.1021/acs.jpcb.6b07205",
language = "English (US)",
volume = "120",
pages = "10786--10796",
journal = "Journal of Physical Chemistry B Materials",
issn = "1520-6106",
publisher = "American Chemical Society",
number = "41",

}

TY - JOUR

T1 - Examining Ionic Liquid Effects on Mononuclear Rearrangement of Heterocycles Using QM/MM Simulations

AU - Allen, Caley

AU - Ghebreab, Robel

AU - Doherty, Brian

AU - Li, Bin

AU - Acevedo, Orlando

PY - 2016/10/20

Y1 - 2016/10/20

N2 - The mononuclear rearrangement of heterocycles (MRH) reaction of the Z-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into 4-benzoylamino-2,5-diphenyl-1,2,3-triazole derives a sizable rate enhancement in the 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] ionic liquid as compared to the hexafluorophosphate-based [BMIM][PF6] and conventional organic solvents. However, the origin of the rate difference between [BMIM][BF4] and [BMIM][PF6] has proven difficult to rationalize as no experimental trend relates the physical properties of the solvents, e.g., polarity and viscosity, to the rates of reaction. QM/MM calculations in combination with free-energy perturbation theory and Monte Carlo sampling have been carried out for the MRH reaction to elucidate the disparities in rates when using ionic liquids, methanol, and acetonitrile. Activation barriers and solute-solvent interactions have been computed for both an uncatalyzed and a specific base-catalyzed mechanism. Energetic and structural analyses determined that favorable π+-π interactions between the BMIM cation, the substrate phenyl rings, and the bicyclic quasi-aromatic 10π oxadiazole/triazole transition state region imposed a preordered geometric arrangement that enhanced the rate of reaction. An ionic liquid clathrate formation enforced a coplanar orientation of the phenyl rings that maximized the electronic effects exerted on the reaction route. In addition, site-specific electrostatic stabilization between the ions and the MRH substrate was more prevalent in [BMIM][BF4] as compared to [BMIM][PF6].

AB - The mononuclear rearrangement of heterocycles (MRH) reaction of the Z-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into 4-benzoylamino-2,5-diphenyl-1,2,3-triazole derives a sizable rate enhancement in the 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] ionic liquid as compared to the hexafluorophosphate-based [BMIM][PF6] and conventional organic solvents. However, the origin of the rate difference between [BMIM][BF4] and [BMIM][PF6] has proven difficult to rationalize as no experimental trend relates the physical properties of the solvents, e.g., polarity and viscosity, to the rates of reaction. QM/MM calculations in combination with free-energy perturbation theory and Monte Carlo sampling have been carried out for the MRH reaction to elucidate the disparities in rates when using ionic liquids, methanol, and acetonitrile. Activation barriers and solute-solvent interactions have been computed for both an uncatalyzed and a specific base-catalyzed mechanism. Energetic and structural analyses determined that favorable π+-π interactions between the BMIM cation, the substrate phenyl rings, and the bicyclic quasi-aromatic 10π oxadiazole/triazole transition state region imposed a preordered geometric arrangement that enhanced the rate of reaction. An ionic liquid clathrate formation enforced a coplanar orientation of the phenyl rings that maximized the electronic effects exerted on the reaction route. In addition, site-specific electrostatic stabilization between the ions and the MRH substrate was more prevalent in [BMIM][BF4] as compared to [BMIM][PF6].

UR - http://www.scopus.com/inward/record.url?scp=84992183777&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84992183777&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcb.6b07205

DO - 10.1021/acs.jpcb.6b07205

M3 - Article

VL - 120

SP - 10786

EP - 10796

JO - Journal of Physical Chemistry B Materials

JF - Journal of Physical Chemistry B Materials

SN - 1520-6106

IS - 41

ER -