Design and Assembly of a Chiral Metallosalen-Based Octahedral Coordination Cage for Supramolecular Asymmetric Catalysis.

ABSTRACT

Supramolecular containers featuring both high catalytic activity and high enantioselectivity represent a design challenge of practical importance. Herein, it is demonstrated that a chiral octahedral coordination cage can be constructed by using twelve enantiopure Mn(salen)-derived dicarboxylic acids as linear linkers and six Zn4 -p-tert-butylsulfonylcalix[4]arene clusters as tetravalent four-connected vertices. The porous cage features a large hydrophobic cavity (≈3944 Å3 ) decorated with catalytically active metallosalen species and is shown to be an efficient and recyclable asymmetric catalyst for the oxidative kinetic resolution of racemic secondary alcohols and the epoxidation of olefins with up to >99 % enantiomeric excess. The cage architecture not only prevents intermolecular deactivation and stabilizes the Mn(salen) catalysts but also encapsulates substrates and concentrates reactants in the cavity, resulting in enhanced reactivity and enantioselectivity relative to the free metallosalen catalyst.