Selective synthesis of heteroleptic Pd₂A₃B-cages: modulating size-preference of supramolecular hosts via endo-functionalization

The size complementarity between a host and a guest is a critical prerequisite for selective molecular recognition. Numerous artificial host systems have been designed to achieve size-selective recognition and chemical transformations. However, the inherent challenge lies in the fixed selectivity governed by a size-exclusion mechanism dictated by the host’s structure. Modulating the selectivity necessitates structural modifications of hosts. Examples of host systems with modifiable size-selectivity are rare. In this study, we present an approach to modulating guest-selectivity via endo-functionalization of supra-molecular cavities. Heteroleptic Pd₂A₃B-cages are constructed with a Pd₂A₃ precursor or directly from palladium ions and relevant ligands. Furthermore, the simultaneous and selective formation of multiple hetero-cages was achieved by simply mixing Pd^II and the free ligands in a one-pot reaction. The fidelity of the assembly process relies on cooperative steric control at the periphery and within the cavity of the hetero-cages, respectively. The central steric group also functions as the endohedral moiety. Variations of the endohedral groups facilitate facile and modular derivatization of the microenvironment within the cages, enabling the fine-tuning of guest binding affinities as evidenced by titration experiments. This strategy offers a new solution for the development of customized host structures.