Self-assembly of Palladium(II)-templated covalent macrocycles, cages and larger structures

Most supramolecular assemblies involving palladium(II) revolve around the use of two to four pyridyl-based ligands coordinated to the palladium center. As one of the rare exceptions, we recently described the self-assembly of anilines, 2,6-diformylpyridine and Pd(II) to form covalent macrocycles, (pseudo)rotaxanes and catenanes. The diiminopyridyl tridentate motif present in these assemblies binds Pd(II) while leaving one free coordination site which can accommodate a mono-dentate ligand. We have now reached a higher level of complexity with this tridentate motif and Pd(II) by assembling larger macrocycles, bridged macrocycles and tridimensional cages with a completely covalent backbone. Furthermore, we developed soft reduction conditions to reduce the imines and obtain, after demetallation, stable organic macrocycles and cages.0