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Regional Electrophilic and Nucleophilic Fukui Functions Efficiently Highlight the Lewis Acidic/Basic Regions in Ionic Liquids
journal contribution
posted on 2014-04-03, 00:00 authored by Andrea Cerda-Monje, Rodrigo Ormazábal-Toledo, Carlos Cárdenas, Patricio Fuentealba, Renato ContrerasThe origin of catalysis and selectivity
induced by room temperature
ionic liquids in several organic reactions has putatively been associated
with the concept of cation effect (hydrogen bond
donor ability of the ionic liquids) or anion effect (hydrogen bond accepting ability of the ionic liquids). We show
that there may be cases where this a priori classification may not
be correctly assigned. Cations may concentrate both Lewis acidity
and basicity functions in one fragment of the ionic liquid: an effect
we tentatively call bifunctional distribution of the molecular Lewis
acidity/basicity. Bifunctionality on the cation is however anion dependent
through electronic polarization effects. The molecular distribution
of the Lewis acidity/basicity may simply be assessed by evaluating
the regional Fukui function within a reference ion pair structure.
The model is tested for a set of nine ionic liquids based on the 1-butyl-3-methylimidazolium
cation commonly used as solvent to run organic reactions.