Approach to inherently chiral Ionic Liquids

Chiral Ionic Liquids (CILs) constitute a class of solvents which got an increasing importance in the last ten years on account of some peculiar properties (low vapor pressure, chemical and thermal stability, solvating ability, non-flammability). CILs are used as solvents in asymmetric synthesis and in stereoselective polymerization, as chiral phases for gas chromatography, as chiral shift reagents in NMR spectroscopy and, in some cases, to generate cholesteric liquid crystals. Most of known CILs, are onium salts characterized by chiral substituents having one or several stereocenters. The aim of the research is to design, synthesize, characterize and test in electrochemical oxo-reduction processes a new family of CILs in which the stereogenic element (a stereogenic axis) coincides with the function responsible for the IL properties. Using the successful strategy recently employed for designing "inherently chiral" oligotiophenes,1 some "inherently chiral" CILs have been prepared based on bis-imidazolium atropisomeric scaffolds. In the series of the 1,1'-bisbenzimidazoles precursors of CILs carrying progressively longer R' groups (Fig. 1) a surprising inversion in the elution times of the enantiomers on the amylose tris(3,5-dimethylphenyl carbamate) chiral stationary phase (Chiralpak AD-3) under normal phase mode was investigated.