Supramolecular self-assembly of macrocycles, catenanes, and cages through coordination of pyridine-based ligands to transition metals

Recent developments in the study of the transition-metal mediated supramolecular self-assembly are reviewed. Focus is on the self-assembly of macrocycles, catenanes, and cages from (en)Pd(NO3)(2) (1) and pyridine-based bridging ligands. Coordination of linear 4,4'-bipyridine on the cis coordination site of palladium complex gives a macrocyclic square supramolecule, whereas macrocyclic dinuclear Pd(II) complexes self-assemble from 1 and flexible bridging ligands. Unprecedented formation of catenanes through rapid slippage of two preformed molecular rings can be achieved by exploiting the labile character of a Pd(II)-linked macrocycle: i.e., a macrocycle assembling from 1 and PyCH(2)C(6)H(4)CH(2)Py exists in rapid equilibrium with its catenated dimer acid the equilibrium is strongly pushed toward the catenane (>99:1) in a polar media. The combination of 1 with tridentate ligands gives three-dimensional cagelike hosts. A spherical M(3)L(2) complex organizes from 1 and a flexible tridentate ligand only in the presence of specific guests providing a model for induced fit. On the other hand, a nanometer-sized hollow supramolecule self-assembles from four rigid tridentate ligands held together by six protected Pd complex 1.