Assembly of six types of heteroleptic Pd2L4 cages under kinetic control

Difficulty in multi-component self-assembly under thermodynamic control arises from increasing the number of possible isomers with similar thermodynamic stabilities. Past efforts on multi-component self-assembly of metal-organic cages have mainly focused on finding a suitable combination of building blocks to lead to a single multi-component self-assembly as the thermodynamically most stable product. Here, we present another approach to selectively produce multi-component Pd(II)-based self-assemblies under kinetic control based on the selective ligand exchanges of weak Pd–L coordination bonds retaining the original orientation of the metal centers in a kinetically stabilized cyclic structure and on local reversibility given in a certain area of the energy landscape in the presence of the assist molecule that facilitates error correction of coordination bonds. The kinetic approach enabled us to build all six types of Pd2L4 cages and heteroleptic tetranuclear cages composed of three kinds of ditopic ligands. Though the cage complexes thus obtained are metastable, they are stable for 1 month or more at room temperature.