Atropisomeric N,N'-dialkyl-3,3'-bipyridinium salts: "Inherently Chiral" ionic liquids and additives for chiral electroanalysis on achiral electrodes

Abstract. 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. This concept, successfully tested by us in designing chiral organic semiconductors employed as highly stereoselective electrode surfaces,1 is now applied to the preparation of chiral ionic liquids and transport electrolytes. They are characterized by an atropisomeric 1,1'-biimidazolium 1 or 3,3'-bipyridinium 2 scaffolds (Scheme 1). 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.3 Salts 2 with long alkyl chains, obtained by alkylation of 3,3'-bicollidine, are liquid at r.t., therefore, they are the first atropisomeric CILs. Scheme 1 The new dionium salts afford outstanding enantiodiscrimination of structurally different chiral probes on achiral electrodes when they are employed as low concentration additives in commercial achiral ILs.