| Abstract
| - We have synthesized a series of structurally novel chiral ionic liquids which have a either chiral cation,chiral anion, or both. Cations are an imidazolium group, while anions are based on a borate ion withspiral structure and chiral substituents. Both (or all) stereoisomeric forms of each compound in the seriescan be readily synthesized in optically pure form by a simple one-step process from commercially availablereagents. In addition to the ease of preparation, most of the chiral ILs in this series are liquid at roomtemperature with a solid to liquid transformation temperature as low as −70 °C and have relatively highthermal stability (up to at least 300 °C). Circular dichroism and X-ray crystallographic results confirmthat the reaction to form the chiral spiral borate anion is stereospecific, namely, only one of two possiblespiral stereoisomers was formed. Results of NMR studies including 1H{15N} heteronuclear single quantumcoherence (HSQC) show that these chiral ILs exhibit intramolecular as well as intermolecular enantiomericrecognition. Intramolecularly, the chiral anion of an IL was found to exhibit chiral recognition towardthe cation. Specifically, for a chiral IL composing with a chiral anion and a racemic cation, enantiomericrecognition of the chiral anion toward both enantiomers of the cation lead to pronounced differences inthe NMR bands of the cation enantiomers. The chiral recognition was found to be dependent on solventdielectric constant, concentration, and structure of the ILs. Stronger enantiomeric recognition was foundin solvent with relatively lower dielectric constants (CDCl3 compared to CD3CN) and at higherconcentration of ILs. Also, stronger chiral recognition was found for anions with a relatively largersubstituent group (e.g., chiral anion with a phenylmethyl group exhibits stronger chiral recognitioncompared to that with a phenyl group, and an anion with an isobutyl group has the weakest chiralrecognition). Chiral anions were also found to exhibit intermolecular chiral recognition. Enantiomericdiscrimination was found for a chiral IL composed of a chiral anion and achiral cation toward anotherchiral molecule such as a quinine derivative.
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