A Polyaromatic Metallotube With a Dual Multi-Functionalization Ability

Post-functionalization is an advanced, key synthetic method in supramolecular systems, whereas the previous method relies heavily on the substitution on the organic frameworks. Here we report a polyaromatic metallotube capable of dually multi-functionalizing the metal sites in an efficient post-assembly fashion. The Pt(II)-linked tube with tetrachloro groups is prepared from two PtCl₂ hinges and two bent bispyridine ligands in high yield. The new metallotube efficiently converts to tetra-substituted tubes by the first multiple functionalization, through the replacement of the chloro groups with various alkynyl groups. The tubular structures before/after the functionalization are unequivocally confirmed by X-ray crystallographic analysis. A resultant tetraammonium-attached Pt(II)-tube exhibits high water solubility and uptake abilities toward spherical and rod-like compounds. The metallotube strongly binds one molecule of fullerene C₆₀ in the polyaromatic cavity yet releases it through the second multi-functionalization by tetrabromination of the metal hinges in a quantitative and reversible manner. Even after Bingel reaction within the tube, sterically demanding bis-substituted fullerenes (>∼80% selectivity) are readily released by the second functionalization. The present method, i.e., the use of simple PtCl₂ hinges, will be applicable to wide-ranging metallo-supramolecules to enhance their structural and functional versatilities via post-multi-functionalizations.