Helicate-based supramolecular switches in catalysis

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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.