Helicate-based supramolecular switches in catalysis

分层组装的锂桥式螺旋和锂依赖的可扩展/可压缩螺旋被引入作为立体选择反应的平台。在分层形成螺旋的情况下，观察到二聚体螺旋和单体配合物之间的溶剂依赖平衡。对于对映体纯配体，配合物的体化学信息是固定的，而对于单体，则具有高动力学和高体化学不稳定性。不同形式的可伸缩/可压缩螺旋可以通过交换阳离子相互转换。在定量纯配体的情况下，可以根据所存在的阳离子特异性地获得具有相反扭转的螺旋。外围的化学反应的反应活性和选择性取决于螺旋构型的开关状态。它用于控制Diels-Alder反应，以及以第二胺为基础的有机催化，以双酚为基础的催化或在螺旋上与磷烷/磷酰胺体系催化，并影响或逆转各自反应的立体选择性。有两种不同的方法可以获得适当的对映体纯螺旋和反应性螺旋：(1)引入带有反应单元的手性配体或(2)手性、非反应性和非手性、反应性配体形成统计异位络合物。没有新的催化反应将被开发，但已知的反应将在螺旋上进行，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.