Guest-Facilitated Heteroleptic Assembly of Helical Anionocages Enables Reversible Chirality Modulation.

We report a novel strategy for reversible modulation of the supramolecular chirality based on guest-facilitated heteroleptic assembly of helical anionocages. Two triple-stranded helical anionocages including a chiral cage 1 (A 2 L 1 3 ) and a crown ether functionalized achiral cage 2 (A 2 L 2 3 ) were synthesized by anion coordination of bis-monourea-based ligands and PhPO 3 2- . 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 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.