Styrene epoxidation catalysed by manganese(III) salen complex supported on activated carbons Ma´rio Cardoso, Ana Rosa Silva, Baltazar de Castro, Cristina Freire * REQUIMTE, Departamento de Quı ´mica, Faculdade de Cieˆncias, Universidade do Porto, 4169-007 Porto, Portugal Received 18 October 2004; received in revised form 9 February 2005; accepted 14 February 2005 Available online 12 March 2005 Abstract The hydroxyl functionalised manganese(III) salen complex, bearing a large p 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. # 2005 Elsevier B.V. All rights reserved. Keywords: Styrene epoxidation; Manganese(III) salen complex; Activated carbons 1. Introduction Currently, the immobilisation of transition metal com- plexes with catalytic activity in homogenous phase on several supports is an area of intense research in order to make expensive homogeneous catalysts recyclable and economical. Increased stability upon immobilisation, under the catalytic conditions, has been observed for some homogeneous catalysts [1–3]. This is the case of manganese(III) salen complexes, which were found in the mid-1980s, by Kochi and coworkers [4], to be very active and selective catalysts in the epoxidation of unfunctionalised alkenes, and in the early 1990s, independently by the Jacobsen [5] and Katuski groups, to be highly enantioselective [6]. Due to their actual practical use in industrial and laboratory scale, this system has been recently heterogenised on organic polymers, zeolites, clays, and inorganic mesoporous materials, using several immobilisation procedures. These new heteroge- neous catalysts show activity in the epoxidation of unfunctionalised alkenes, but generally with lower perfor- mance than the corresponding homogeneous counterparts in solution [1–3]. Because activated carbons have a porous structure and surface chemistry [7] that can be easily tuned by thermal and chemical processes [8] we have been exploiting these properties to the surface anchoring of transition metal Schiff base complexes [9–12]. In previous work we have accomplished the preparation of active, chemoselective, stable and reusable heterogeneous catalysts by immobilisa- tion of functionalised achiral manganese(III) salen com- plexes onto oxidised activated carbons [13,14] and their chiral enantioselective counterparts [15]. www.elsevier.com/locate/apcata Applied Catalysis A: General 285 (2005) 110–118 * Corresponding author. Tel.: +351 226082890; fax: +351 226082959. E-mail address: acfreire@fc.up.pt (C. Freire). 0926-860X/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2005.02.014