Artificial Chiral Metallo-pockets Including a Single Metal Serving as Structural Probe and Catalytic Center

A series of capped metallo-cyclodextrins were synthesized, affording a variety of artificial chiral metallo-pockets through modulation of the space around the metal. Carbene ligands were used as caps for placing a silver, gold, or copper center at a well-defined location inside the cyclodextrin cavity. Multiple weak interactions involving the d10 metal center and intra-cavity hydrogen atoms, including anagostic interactions, were observed in solution. Thus, the metal was used as a probe for assessing intra-cavity metal–H distances for building 3D models, revealing the very different shapes of capped α-, β-, and γ-cyclodextrins and the helical shape of the chiral pocket of some modified cyclodextrins. This series of N-heterocyclic-carbene-based cyclodextrins were compared in gold-catalyzed cycloisomerization reactions, for which the 3D models were used to rationalize the observed regio- and stereoselectivities.