Application of the "Inherent Chirality" Concept to Ionic Liquids Design: Effective Chiral Electroanalysis on Achiral Electrodes

In "inherently chiral" materials the coincidence of the stereogenic element responsible for chirality with the molecular portion responsible for their specific properties results in outstanding chiroptical and enantiorecognition properties. We successfully experimented this concept in designing chiral organic semiconductors employed as highly stereoselective electrode surfaces.1 This strategy is now applied to the preparation of "inherently chiral" ionic liquids (ICILs) and transport electrolytes: atropisomeric 1,1'-biimidazolium 1 or 3,3'-bipyridinium 2 scaffolds (in particular 1,1'-bibenzimidazolium and 3,3'-bicollidinium) characterize these unconventional organic salts (Scheme 1). Several members of both the families have been obtained by alkylation of 2,2'-dialkyl-1,1'-benzimidazoles and 3,3'-bicollidine, prepared through easy syntheses from inexpensive reagents. The racemates of neutral scaffolds have been resolved by semi-preparative HPLC on CSP in the former case2 and by crystallization of the diastereomeric salts with chiral acids in the latter. The long-chained dialkyl salts 2 display melting points below room T and are, therefore, the first atropisomeric CILs. Scheme 1 The new dionium salts, employed as low concentration additives in commercial achiral ILs, afford outstanding enantiodiscrimination of structurally different chiral probes on achiral electrodes.