Chirality transfer in ionic liquids via ion pairing effects

尽管有许多关于手性离子液体合成的出版物，但迄今为止将其应用于手性诱导有机合成的成功例子尚不多见。作为手性离子液体领域的先驱研究小组之一，我们从过去的实验结果中得出结论，离子液体的手性离子不容易将其手性信息转移到反应的过渡态，因为它通常与自身的反离子相互作用更强。为了验证这一假设，我们打算在本项目中系统地研究前手性离子在其手性和对映体纯反离子存在下的反应，作为离子液体中离子配对亲密性的探针。事实上，我们对该项目的制备研究表明，使用非手性异相Ru催化剂，可以将[N-（丁基-3′- 1）-N-甲基咪唑][(S)-樟脑磺酸盐]加氢为相应的手性[N-（3′-羟基丁基）-N-甲基咪唑][(S)-樟脑磺酸盐]，阳离子中有明显的对映体过量。我们希望在项目中详细研究和了解的重要参数涉及不同离子结构、催化剂（手性和非手性、均相和非均相）、反应参数（例如氢压力）以及附加溶剂的作用的影响。在这里，我们期望使用极性溶剂的离子对分离效应和使用非极性溶剂的离子对压缩效应。该研究还将提供一些新的、功能化的和手性离子液体。

Despite of a number of publications on the synthesis of chiral ionic liquids, successful examples to apply those for chiral induction in organic synthesis are rare so far. As one of the pioneering research groups in the field of chiral ionic liquids we have concluded from our experimental results in the past that a chiral ion of an ionic liquid does not easily transfer its chiral information to the transition state of a reaction due to the usually much stronger interaction with its own counter-ion. To verify this hypothesis we intend in this project to investigate systematically reactions of prochiral ions in the presence of their chiral and enantiomeric-pure counter-ions as a probe for the intimacy of ion pairing in ionic liquids. Indeed, our preparative studies for this project have shown that it is e.g. possible to hydrogenate [N-(butyl-3´-one)-N-methylimidazolium] [(S)-camphorsulphonate] to the corresponding chiral [N-(3´-hydroxybutyl)-N-methylimidazolium] [(S)-camphorsulphonate] with significant enantiomeric excess in the cation, using an achiral, heterogeneous Ru catalyst. Important parameters that we like to investigate and understand in detail in the project concern the influence of different ion structures, catalysts (chiral and achiral, homogeneous and heterogeneous), reaction parameters (e.g. hydrogen pressure) as well as the role of additional solvents. Here we expect ¿ion-pair separation effects¿ using polar solvents and ¿compression effects¿ using unpolar solvents. The study will also give access to a number of new, functionalized and chiral ionic liquids.