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The use of [5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrinato] manganese(III) chloride [TDCPP(Mn)Cl] embedded in polydimethylsiloxane (PDMS) is reported for the oxidation of cyclic alcohols to ketones with t -butylhydroperoxide from an aqueous solution. Two important observations are made which both can be ascribed to the sorption exercised by the polymer. Firstly, compared to a homogeneous set-up much higher activities are reached with the PDMS-system. Secondly, the increase in activity is more pronounced as the ring size of the alcohol increases. The increase in TON going from a five ring to a seven ring is related to the sorption of the respective alcohols in the membrane. Thus, PDMS can be considered as a support with a threefold function. Besides immobilizing and dispersing the complexes, the carrier takes part in the reaction process by selectively sorbing the reagents. Furthermore, the catalyst retained its activity in a second run, proving the stability of this heterogeneous system. The encapsulation of metallo-porphyrins in PDMS creates a heterogeneous selective oxidation catalyst that discriminates among molecules on the basis of their mutual affinity. |
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