Imidazolium Ionic Liquids: C2 Substitution and Acidity

Room temperature ionic liquids (RTILs) are continuing to attract a great deal of attention, particularly as solvent alternatives for a wide range of organic reactions. In examining the RTILs employed in virtually all of these efforts, the core structure is most frequently a dialkylimidazolium cation. Although rather robust to a wide range of chemical conditions, this species is readily able to undergo deprotonation at the 2 position, resulting in the formation of a carbene. This carbene can be very useful, serving as a ligand for many transition metal complexes and even as a nucleophilic catalyst itself. At the same time, the reactivity of this carbene can be detrimental in other situations as has been observed by Aggarwal and ourselves. To that end, we have begun a study both of the acidity of the 2 position as well as convenient methods for substituting this position to avoid base-induced complications.