Design and self-assembly of hexahedral coordination cages for cascade reactions

The search for supramolecular reactors that contain no catalytically active sites but can promote chemical transformations has received significant attention, but it remains a synthetic challenge. Here we demonstrate a strategy of incorporating bulky and electro-rich aromatic linkers into metallocages to induce cascade reactions. Two hexahedral cages with a framework formula [(Zn₈L₆)(OTf)₁₆] are assembled from six tetrakis-bidentate ligands derived from tetraphenylethylene and eight zinc(II)tris(pyridylimine) centers. The cage cavities can accommodate different molecules such as anthranilamide and aromatic aldehyde through supramolecular interactions, allowing for a cascade condensation and cyclization to produce nonplanar 2,3-dihyroquinazolinones. The reaction is highly efficient with high rate enhancements (up to k_cat/k_uncat = 38,000) and multiple turnovers compared to the bulk reaction mixture. Control experiments and molecular simulations suggest that the acceleration is attributed to inherent strength of binding affinity for reactants and the release of products to establish catalytic turnover is due to the host-guest geometry discrepancy.