Experimental Evidence for a Dual Site Mechanism in Sn-Beta and Sn-MCM-41 Catalysts for the Baeyer-Villiger Oxidation

It is postulated that the catalytic active centre in Sn-Beta and Sn-MCM-41 zeolites for Baeyer-Villiger oxidations involves not only the framework Sn sites but also an associated "basic" oxygen that stabilises the reaction transition state through hydrogen bonding. The presence of these "basic" sites has been studied by cross-polarization MAS NMR H → Sn, and by carrying out the condensation of ketones with malononitrile. The reaction proceeds highly selectively and the reactivity of the substrates corresponds to that of the ketones in the Baeyer-Villiger oxidation with hydrogen peroxide, catalysed with tin-containing molecular sieves.