A Self-Folding Metallocavitand

The synthesis and characterization of novel metallocavitand 6 are described. This is a covalent hybrid of a deepened, self-folding cavity and a Zn−phenanthroline fragment. Host 6 features a large molecular cavity of ∼8 × 10 Å dimensions, and the metal binding site is directed in toward the cavity. Binding abilities of the metallocavitand in solution was demonstrated for quinuclidine 11 and Dabco 12 using UV−vis and 1H NMR spectroscopy. Intramolecular hydrogen bonds at the upper rims of cavitand 6 resist the unfolding of the inner cavities and thereby increase the energetic barrier to guest exchange. The exchange is slow on the NMR time scale (at ambient temperatures, CD2Cl2), and kinetically stable complexes result. Both the polyaromatic cavity and metallosite participate simultaneously in the binding event. Zinc-containing deep cavities may be attractive as catalytic chambers for hydrolysis and esterification.