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 pre-ordered 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].
This research output has an Altmetric Attention Score of 1. This is our high-level measure of the quality and quantity of online attention that it has received. This Attention Score, as well as the ranking and number of research outputs shown below, was calculated when the research output was last mentioned on 10 October 2016.
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