A Double-Cavity-Containing Porphyrin Host as a Highly Stable Epoxidation Catalyst

We describe a manganese porphyrin catalyst containing two adjacent cavities, which can be used for the epoxidation of alkenes by sodium hypochlorite. A pyridine ligand bound in one of the cavities regulates the rate and selectivity of the epoxidation reaction that takes place in the adjoining cavity. Pyridine binding studies suggest that site-to-site communication exists between the two cavities. The alkene substrates are completely converted into epoxides by the manganese double-cavity catalyst, but the observed epoxidation rates are low. These low rates are proposed to be a result of the energetically less favourable binding of the substrate into the cavity containing the active site due to an allosteric pinching effect. In the manganese double-cavity arrangement the catalytically active manganese complex is efficiently protected against decomposition, leading to a catalytic system with enhanced stability. The presented work may open a new route to the construction of highly stable catalysts of which the activity and selectivity may eventually be controlled by allosteric interactions.