Interplay of Stereochemistry and Charge Governs Guest Binding in Flexible ZnII4L4 Cages.

Abstract

Here, we report the synthesis of a family of chiral Zn^II₄L₄ 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 Δ₄ and Λ₄ enantiopure cages, in contrast to the racemates that resulted from the incorporation of achiral 4-methoxyaniline. The stereochemistry of these Zn^II₄L₄ 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 Δ₄-Zn^II₄L₄ cage retained their Δ handedness. In contrast, the metal stereocenters of the enantiomeric Λ₄-Zn^II₄L₄ 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.