| Abstract |
Helical mesoporous materials of the MCM-41 type with different pore sizes were prepared, choosing as templates myristyl (C-14) or cetyl (C-16) trimethyl ammonium salts, and functionalized with Mo(II) active sites based on MoI2(CO)(3) (1) and MoBr(eta(3)-C3H5)(CO)(2) (2) fragments, respectively, using a pyridine-2-carbaldehyde ligand as anchor. The new materials were tested as the catalytic precursors in the epoxidation of cis-cyclooctene, styrene, R-(+)-limonene, trans-hex-2-en-1-ol, cis-3-hex-1-ol, and geraniol using tert-butylhydroperoxide (tbhp) as oxidant. All catalysts were moderately to highly selective toward the epoxide products. The materials with larger pores (C-16 template) displayed a better catalytic activity, leading in general to higher conversions and selectivities, as well as faster kinetics. For instance, geraniol is epoxidized (more than 90\%) with conversions above 90\%. The major achievement of these catalysts, however, is the excellent product selectivity control, which is boosted when the allyl complex 1 is used, reaching 100\% of the 2S, 3R species in the epoxidation of trans-hex-2-en-1-ol. The catalysts were also found to be stable through recycling experiments and truly heterogeneous with little or no leaching. (C) 2015 Elsevier B.V. All rights reserved. |
