Alkene epoxidation by manganese(III) complexes immobilized onto nanostructured carbon CMK-3

New heterogeneous catalysts were prepared through immobilization of Mn(III) complexes onto CMK-3 with different surface treatments. The [Mn(TF5PP)Cl] and [Mn(5-HOsalhd)Cl] complexes were anchored by a microwave-assisted protocol (CAT I and CAT III, respectively) and the Jacobsen catalyst was immobilized using conventional synthesis conditions (CAT II). XPS and FTIR revealed that the CMK-3 target functionalities for immobilization were the surface oxygen groups. XRD showed that the support treatments led to a decrease of its 2D-hexagonal order, but the complex grafting did not induce changes on the microstructure. CAT I was active in the epoxidation of cis-cyclooctene by H2O2, with substrate conversions and epoxide selectivities in the ranges of 38-30% and 100-97%, respectively, in three cycles with almost no complex leaching. CAT II was active in the epoxidation of 6-cyano-2,2-dimethylchromene using m-CPBA/NMO system with a substrate conversion similar to that of the free complex and higher ee %, but with some Mn leaching in the catalytic runs. CAT III was active in the epoxidation of indene, by H2O2, in ethanol with substrate conversions, epoxide selectivities and ee % values in the ranges of 45-37%, 83-86% and 10-12%, respectively. A correlation between the structural properties of the supports and the reaction times could be proposed. These results highlight the potentiality of CMK-3 to act as support for metal complexes with catalytic properties in oxidation reactions. (C) 2012 Elsevier B. V. All rights reserved.