Interplay of Stereochemistry and Charge Governs Guest Binding in Flexible Zn<sup>II</sup><sub>4</sub>L<sub>4</sub> Cages
Weichao Xue, Élie Benchimol, Alexandre Walther, Nianfeng Ouyang, Julian J. Holstein, Tanya K. Ronson, Joseph Openy, Yujuan Zhou, Kai Wu, Rituparno Chowdhury, Guido H. Clever, Jonathan R. Nitschke
Abstract
High Resolution Image Download MS PowerPoint Slide Here, we report the synthesis of a family of chiral Zn II 4 L 4 tetrahedral cages by subcomponent self-assembly. These cages contain a flexible trialdehyde subcomponent that allows them to adopt stereochemically distinct configurations. The incorporation of enantiopure 1-phenylethylamine produced Δ 4 and Λ 4 enantiopure cages, in contrast to the racemates that resulted from the incorporation of achiral 4-methoxyaniline. The stereochemistry of these Zn II 4 L 4 tetrahedra was characterized by X-ray crystallography and chiroptical spectroscopy. Upon binding the enantiopure natural product podocarpic acid, the Zn II stereocenters of the enantiopure Δ 4 -Zn II 4 L 4 cage retained their Δ handedness. In contrast, the metal stereocenters of the enantiomeric Λ 4 -Zn II 4 L 4 cage underwent inversion to a Δ configuration upon encapsulation of the same guest. Insights gained about the stereochemical communication between host and guest enabled the design of a process for acid/base-responsive guest uptake and release, which could be followed by chiroptical spectroscopy.