Control of Interlocking Mode in Pd4L8 Cage Catenanes

Abstract

Precise control over the catenation process in interlocked supramolecular systems remains a significant challenge. Here, we report a system in which a lantern-shaped Pd2L4 cage can dimerize to form two distinct Pd4L8 catenanes with different interlocking degree: a previously described quadruply interlocked double cage motif of D4 symmetry and an unprecedented triply interlocked structure of C2h symmetry. While the former structure features a linear arrangement of four Pd(II) centers, separated by three mechanically linked pockets, the new motif has a staggered shape. Both assemblies are topological isomers, coexisting in equilibrium in solution. The triply interlocked species is thermodynamically more stable due to extended noncovalent interactions between the ligands, as supported by X-ray structure analysis and electronic structure calculations. Notably, the degree of interlocking in the double cage system can be controlled by a change of temperature and through anion exchange. Cage-to-cage transformations were followed by NMR, MS and TIMS methods.