Helicate-based supramolecular switches in catalysis

层状组装的锂桥螺旋和锂依赖的可膨胀/可压缩螺旋作为立体选择性反应的平台。在层状形成的螺旋中，观察到二聚螺旋和单体络合物之间的溶剂依赖的平衡。在对映体纯配体的情况下，络合物的立体化学信息是固定的，而在单体的情况下，发现了高动力学和高空间化学不稳定性。不同形式的可膨胀/可压缩螺旋可以通过阳离子交换来相互转化。对于等量纯的配体，可以根据所存在的阳离子得到具有相反扭曲的螺旋体，外围的化学反应取决于螺旋体的开关状态的反应性和选择性。它被用来控制Diels-Alder反应以及SEC。通过两种不同的方法得到合适的对映体和反应性螺旋：(1)引入带有反应单元的手性配体或(2)与手性、非反应性和非手性反应性配体形成统计异构性络合物。不会发生新的催化反应，但将在螺旋体上进行众所周知的反应，作为选择性控制的新平台。

Hierarchically assembled lithium-bridged helicates and lithium-dependent expandable/compressable helicates are introduced as platform for stereoselective reactions.In case of the hierarchically formed helicates a solvent dependent equilibrium between the dimeric helicate and the monomeric complex is observed. In case of enantiomerically pure ligands the sterochemical information at the complex is fixed, while in case of the monomer high dynamics and high sterochemical lability is found.The different forms of the expandable/compressable helicates can be interconverted by exchange of the cations. In case of enqantiomerically pure ligands, the helicates with opposite twist can be specifically obtained based on the cations which are present.Chemical reactions in the periphery are depending in reactivity and selectivity on the switching state of the helicate. This is used to control Diels-Alder reactions as well as sec. amine based organocatalysis, biphenol-based catalysis or catalysis with phosphane/phosphaamidite systems at the helicates and to influence or invert the stereoselectivity of the respective reaction.Appropriate enantiomerically pure and reactive helicates are obtained in two different approaches: (1) chiral ligands which bear the reactive units are introduced or (2) statistical heteroleptic complexes are formed with chiral, unreactive and achiral, reactive ligands.No new catalytic reactions will be developed but well known reactions will be performed at the helicates as novel platform for selectivity control.