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Oxidation of cyclohexene over Mn(TMPyP) porphyrin-exchanged Al,Si-mesoporous molecular sieves

Abstract:

The mesoporous silicas of the MMS (HMS)-type, containing different amounts of Al, have been prepared using dodecylamine as a structure directing agent. Encapsulation of the +4 charge cationic chloro[meso-tetra(4-N-methylopyridinio)-porphirynato] manganese(III) tetrachloride (Mn(TMPyP)) metalloporphyrin has been carried out by means of cation exchange. In all Al-substituted materials, the porphyrin species are firmly bound to the solid matrix, in contrast to the purely siliceous support. The preparation procedure provides a simple means of controlling the amount of the supported porphyrin. The solids are active in oxidation of cyclohexene with iodosylbenzene yielding only allylic oxidation products and no epoxide. It is argued that the regioselective effect is due to the narrowness of the structural pores, which prohibits the formation of the transient complex required for the formation of the epoxide. In contrast to previous studies in which increased loading of porphyrin has been found to result in a de crease in activity, in the present case an increase in the catalytic activity with increased porphyrin loading is observed. © 2001 Elsevier Science B.V. All rights reserved.