Cyclohexene oxidation by Fe-, Co-, and Mn-metalloporphyrins supported on aluminated mesoporous silica

Water soluble cationic metalloporphyrins with different metal centres (Mn, Fe, Co) and/or different porphyrin ligands(TMPyP, TTAPP) have been supported on aluminated mesoporous silica of the MMS (HMS) type by means of cation exchange. The porphyrin species are firmly bound to the solid matrix. Their catalytic properties in the oxidation of cyclohexene with iodosobenzene depend primarily on the nature of the metal centre. Mn and Fe porphyrins are active in converting cyclohexene to allylic oxidation products, while Co porphyrin is inactive. Preferential formation of allylic compounds (100% selectivity for Mn porphyrins and 80% for Fe porphyrin) is associated with the location of porphyrin centres at the inner pore walls where steric hindrances prohibit formation of epoxide. Appearance of a small amount of epox-de in the case of supported Fe(TMPyP) is attributed to the presence of a certain amount of porphyrin attached to the external surface, possibly by means of Fe ligation to surface oxygens. The change of the porphyrin ligand when passing from Mn(TMPyP) to Mn(TTAPP) hAs no significant effect on the catalytic performance of supported catalysts. The use of support is beneficial for the stability of metalloporphyrins. (C) 2004 Elsevier B.V. All rights reserved.