Electrochemical and Catalytic Studies of a Manganese(III)Complex with a Tetradentate Schiff-Base Ligand Encapsulated in NaY Zeolite

The manganese(III) complex with a Schiff-base salen-type ligand (1,5-bis{[(1E)-(2-hydroxyphenyl)methylene]amino}-1H-imidazole-4-carbonitrile) has been encapsulated in the nanopores of a Y zeolite by using two different methodologies, the flexible ligand and in situ complex preparation methods. Cyclic voltammetry studies revealed that the neat complex undergoes reversible oxidation in dmf, which has been attributed to the MnII/III redox couple, whereas the two heterogeneous catalysts show different electrochemical behaviour in aqueous medium. The encapsulated and non-encapsulated homogeneous MnIIIsalen complexes were screened as catalysts for olefin oxidation by using tBuOOH as the oxygen source in different solvents. Under the optimized conditions, the catalysts exhibited moderate activity. Both heterogeneous catalysts catalysed the oxidation of cyclohexene with tBuOOH, primarily to give the allylic oxidation products. These catalysts were found to be reusable after the catalytic cycle, but with some loss of activity. A DFT study confirmed the distortion of the complex in the zeolite cage, the main difference being observed for the bonded chloride. I. K.- B. thanks the Fundacao do Ministério de Ciência e Tecnologia (FCT) for a contract under the program Ciência 2007. The authors thank the FCT and the Fundo Europeu de Desenvolvimento Regional (FEDER)) [COMPETE-QREN-EU, grant number PEst-C/QUI/UI0686/2011 (FCOMP-01-0124-FEDER-022716)] for financial support to the Research Centre at the Centro de Quimica, Universidade do Minho.