Fine-Tuning of Chiral Microenvironments within Triple-Stranded Helicates for Enhanced Enantioselectivity

Here we report the formation of an unexpected and unique family of chiral helicates. Crystal structures show that these triple-stranded Zn^II₂ L₃ complexes are held together by subcomponent assembly of axially chiral diamine-functionalized 1,1'-biphenol ditopic with 2-formylpyridine and Zn^II . Specifically, the molecular helicity of the complexes can be controlled by the absolute configurations of the bimetallic vertices, which has been shown to be homoconfiguration (ΔΔ) or mesomeric configuration (ΔΛ), depending critically on the bulky groups and length of the spacers. Fascinatingly, in this system we can engineer the space-restricted chiral microenvironments with varied polar and apolar moieties, which profoundly influence the binding affinities and chiral discrimination properties of the helicates, leading to highly enantio- and helix-sense-selective recognition for chiral amino alcohols (up to 9.35). This work reveals the transformation of single-molecule chirality to global supramolecular chirality within well-defined helicates and demonstrates that their chiral discrimination are highly dependent on the superior microenvironments.