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

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-methylopyri dinio)-porphirynato] manganese(III) tetrachloride (Mn(TMPyP)) metalloporphy rin 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 provide s 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 regio selective effect is due to the narrowness of the structural pores, which pr ohibits the formation of the transient complex required for the formation o f the epoxide. In contrast to previous studies in which increased loading o f porphyrin has been found to result in a decrease in activity, in the pres ent case an increase in the catalytic activity with increased porphyrin loa ding is observed. (C) 2001 Elsevier Science B.V. All rights reserved.