A breakthrough in the design of chiral ionic liquids: synthesis and application of "inherently chiral" ionic liquids"

In "inherently chiral" materials, the coincidence of the stcrcogenic element responsible for chirality with the molecular portion responsible for their specific properties results in outstanding enantiorecognition properties. We successfully experimented this concept in designing chiral organic semiconductors employed as highly stereoselective electrode surfaces I This strategy is now applied to the preparation of "inherently chiral" ionic liquids (lCILs) and transport electrolytes: atropisomcnc U'-biimidazolium 1. or 3,3' -bipyridinium 2 scaffolds characterize these unconventional organic salts. 'Several members of both the families have been obtained by alkylation of 2.2"-dialkyl-L 1'¬ fU Dibenzimidazoles2 and 3,3·-bicollidme. prepared III tum through syntheses scaled up to several ,..J'- tenths of grams. involving inexpensive reagents. The racemates of neutral bihetcroaryls have been e;r-' resolved into highly configurationally stable enantiomers bv semi-preparative HPLC on CSP in the ',;>,('- former case] and by crystallization of the diastereomeric salts with chiral acids in the lattcr The U li,G-:: long-chained dialkyl salts 2 display melting points below room T and are. therefore. the first l'r '- Li--''C. atroptsornenc ILs )A..--- Both the new inherently chiral ILs and the solid terms carrying short alkyl chains. when employed as low concentration additives in commercial achiral ionic liquids. afford outstanding discrimination of the oxidative potentials of the enanuomers of structurally different chiral probes (DOPA. MeDOPA, N,N-dimethyl-l-ferrocenylethylamine, chiral sexithiophene BT2T. I ) on achiral electrodes. Tlns work wos ,upponed hy Fondaztone Cariplo (reg. No 21111, l1i51) and CNR.