Guest‐Facilitated Heteroleptic Assembly of Helical Anionocages Enables Reversible Chirality Modulation

Abstract

We report a novel strategy for reversible modulation of supramolecular chirality, based on guest‐facilitated heteroleptic assembly of helical anionocages. Two triple‐stranded helical anionocages, including a chiral cage 1 (A2L13) and a crown ether functionalized, achiral cage 2 (A2L23) were synthesized by anion coordination of bis‐monourea‐based ligands and PhPO32‐. Both cages exhibited favorable binding with tetraethylammonium TEA+ and cobaltocenium Cob+ (endo‐guest, bound in the cavity). Additionally, cage 2 could reversibly release and recapture of the guests through binding the exo‐guest potassium ions (K+) in the crown ethers and subsequent removal of the K+ by [2,2,2]‐cryptand. The circular dichroism (CD) spectrum of cage 1 was not significantly affected by guest encapsulation, or mixing with the “empty”cage 2. However, in the presence of both cage 2 and an endo‐guest/exo‐guest, the Cotton effects were reversed at 391 nm and significantly enhanced at 310 nm. This observation was attributed to the guest‐facilitated formation of heteroleptic cages that enabled effective chirality transfer from the chiral to the achiral ligands. The CD changes induced by K+ could be fully reversed by removing it with [2,2,2]‐cryptand. Sequential addition and removal of K+ allowed reversible modulation of the chirality for at least 10 cycles without significant attenuation.