Tripodal 4-pyridyl-derived host ligands and their metallo-supramolecular chemistry: stella octangula and bowl-shaped assemblies

The synthesis of five new cyclotriveratrylene derivatives with 4-pyridyl side arms is reported, along with the crystal structures of three of these. Three ligands with extended 4-pyridylphenyl side arms and a ligand derived from cyclotriphenolene have been shown to form [Pd6L8]12+ stella octangula assemblies using diffusion-ordered spectroscopy NMR and electrospray MS techniques. This confirms the generality of the stella octagula assembly, providing that the ligand arms show a degree of rigidity. The more flexible ether-linked ligand tris(4-pyridylmethyl)cyclotriguaiacylene forms a smaller [Pd3L4]6+ bowl-shaped assembly in the solid state and in solution. The previously reported ligand tris(4-pyridylmethylamino)cyclotriguaiacylene forms a similar assembly in solution.