Expanding the cavity size: preparation of 2:1 inclusion complexes based on dinuclear square metallocycles

Abstract

The self-assembly of two new ligands based on the trans-1,2-bis(4-pyridyl)ethylene motif with palladium or platinum complexes led to quadrangular metallocycles. 1,1'-Methylenebis(4-((E)-2-(pyridin-4-yl)vinyl)pyridinium gave the square metallocycles, while the second ligand, which is less symmetrical, gave a mixture of the regioisomeric metallocyles. The metallocycles display the ideal disposition of the pi-acceptor units to maximize the pi-stacking interactions with aromatic guests. Thus, molecular recognition of pi-donor aromatic guests by square metallocycles produced the corresponding 2:1 inclusion complexes. On the other hand, starting from the mixture of regioisomers, the incorrect regioisomer rearranged to the correct metallocycle upon the addition of aromatic guests. On the basis of this behavior, a [3]catenane was obtained regioselectively from the mixture of the regioisomeric metallocycles and the appropriate cyclophane. The formation of this catenane was confirmed by NMR and X-ray crystallographic studies.