High Enantioselection Performances of Inherently Chiral Ionic Liquids with Axial, Helical and Central Stereogenicity

We define as "inherently chiral" functional materials the compounds in which the stereogenic scaffold responsible for chirality and the molecular group responsible for their specific properties coincide. This structural combination results in outstanding enantioselection properties, much higher than those exhibited by compounds in which stereogenic unit and functional group are independent moieties. The validity of this concept was proved in the design of high symmetry (Dn) macrocyclic oligo-thiophenes in which chirality results from a tailored torsion of regio-regular thiophene sequences. They were employed as highly stereoselective electrode surfaces. Here we report the results of the application of the inherent chirality concept to Chiral Ionic Liquids (CILs). We checked first the effects produced by a stereogenic axis and then extended the research to Inherently Chiral Ionic Liquids (ICILs) based on helices and stereocenters. In our project the ICILs based on a stereogenic axis are characterized by suitably substituted 3,3’- bipyridinium or 1,1’-bibenzimidazolium atropisomeric scaffolds. Considering that pyridinium and imidazolium groups are classical IL functionalities, and that a pair of them are involved in the hindered rotation around the interanular bond, responsible for chirality, it is evident that the attribute of ICILs to these compounds is correct. Aza- and di-aza-hexahelicenium cations also fulfill the requirements to be defined as ICILs, since the pyridinium unit is essential part of the helical scaffold. As for ICILs based on stereogenic centers, we have planned the alkylation of configurationally stable phosphanes like DIPAMP. Synthesis and characterization of all new ICILs and electrochemical enantiodifferentiation performances of the antipodes of several chiral probes are discussed in comparison with the behavior of CILs designed according to classical strategies.