Styrene epoxidation catalysed by manganese(III) salen complex supported on activated carbons

Abstract

The hydroxyl functionalised manganese(III) salen complex, bearing a large π delocalisation, [Mn(4-HOsaldPh)Cl], was immobilised onto a commercial activated carbon and its air and acid oxidised forms using three different metal loadings. For all the materials the manganese contents were determined by ICP-AES and they were screened as heterogeneous catalysts in the epoxidation of styrene, using iodosylbenzene as oxygen source and acetonitrile as reaction media. All the heterogeneous catalysts were as chemoselective towards the styrene epoxide as the homogeneous counterpart, with the exception of the complex supported onto the acid oxidised activated carbon, which exhibited the lowest styrene epoxide selectivities, a consequence of its acidic oxygen surface groups; the highest styrene conversions and styrene epoxide yields were obtained for that complex immobilised onto the air oxidised activated carbon. Generally, an increase in styrene conversion and styrene epoxide selectivity with the manganese(III) complex loading onto all supports was observed. Upon reuse all the heterogeneous catalysts do not lose their styrene epoxide selectivity, but generally a slight decrease in the styrene epoxide yield is observed; catalyst aging studies done for one of the material prepared, [Mn(4-OHsaldPh)Cl]@C2_1%, revealed high stability and the same catalytic efficiency for almost 2 months.