Hydrogen-bond and metal-ligand coordination bond hybrid supramolecular capsules: identification of hemicapsular intermediate and dual control of guest exchange dynamics.

Hybrid supramolecular capsules self-assemble by simultaneously forming hydrogen and metal-ligand coordination bonds on mixing a C2-symmetrical cavitand (calix[4]resorcinarene-based cavitands with ureide and terminal 4-pyridyl units) with platinum or palladium complexes ([Pt(OTf)2] or [Pd(OTf)2] with chelating bisphosphines) in 1:1 ratio. Hemicapsular assemblies formed in the presence of excess amounts of cavitand relative to the platinum or palladium complexes are identified as intermediates in the above self-assembly process by 2D-NOESY spectroscopy. External-anion-assisted encapsulation of a neutral guest, 4,4'-diiodobiphenyl, inside the hybrid supramolecular capsules accompanied conformational changes in the hydrogen-bonding moieties. The in/out exchange ratio of the encapsulated guest depends on the bite angle of the bisphosphine ligand. Addition of DMSO accelerates guest exchange by weakening the hydrogen bonds in the encapsulation complex. Therefore, variations in the structure of the metal complex and amount of polar solvent exert dual control on the dynamics of the guest exchange.