Flexible Porous Capsules Catalyze Reaction

A few years ago, Ira A. Weinstock of Ben-Gurion University of the Negev, in Israel, and coworkers showed that the flexible pores of molybdenum oxide-based capsules could adjust to accommodate unexpectedly large “guest” molecules (C&EN, April 6, 2009, page 26). They had speculated that the capsules—discovered by Achim Müller of the University of Bielefeld, in Germany—might be useful for promoting reactions. They have now achieved that goal for the reversible catalytic cleavage and reformation of methyl tert-butyl ether in water (J. Am. Chem. Soc., DOI: 10.1021/​ja304513t). They attribute the catalytic activity to the availability in each of the capsules of 60 cationic molybdenum(V) centers, which become acidic and are activated catalytically when acetate ligands bound to the centers are controllably replaced by water ligands. The controllability makes it possible to tune the capsules’ catalytic power. Weinstock notes that the active metal cations could also be used as substrate-binding sites to catalyze regio- and enantioselective C–C bond-forming reactions and that the capsules “present new possibilities for investigating the effects of nanoconfinement on catalysis in water.”