Evolution of Multicomponent [Pd2ABCD] Cages

Abstract

Synthetic supramolecules, inspired by biological hosts, catalysts and machines, promise to find application in sustainable synthesis, separation, energy conversion and medicine. However, the implementation of multiple functionalities within distinct self- assembled structures still poses considerable challenges. In particular metal-mediated assemblies are difficult to form from multiple chemically different building blocks without falling into narcissistic self-sorting or a statistical mess. Here we report a systematic series of integratively self-assembled heteroleptic cages in which two square-planar PdII cations are bridged by four chemically different bis-pyridyl ligands A, B, C and D via a collection of synergistic effects to form a single isomer of lantern-shaped cage [Pd2ABCD] as exclusive product. This ultimate self-sorting goal, forming just one out of 55 possible structures, is reached under full thermodynamic control and can be realized progressively (by combining heteroleptic progenitors such as [Pd2A2C2] with [Pd2B2D2]), directly from ligands and PdII cations, or most impressively by mixing all four corresponding homoleptic cages. Structural and mechanistic details were comprehensively examined by NMR and mass spectrometry and nine single crystal X-ray structures. The rational design of complex multicomponent assemblies, formed in high yield under thermodynamic control, allows to incorporate different chemical moieties in a modular approach and advance the application level of functional nanosystems.