abstract
Arenetricarbonyl complexes, or the general formula -C(6)H(4)Mo(CO)(3)-, were incorporated into crystal-like mesoporous phenylene-silica by liquid-phase deposition of molybdenum hexacarbonyl [Mo(CO)(6)]. By adjusting the reaction conditions, different molybdenum loadings of 1.5 and 5.9 wt% were obtained, which correspond to 3% and 14% of the phenylene contents. The texture properties of the materials as well as the nature of the surface-fixed complexes were characterized by powder X-ray diffraction, transmission electron microscopy (TEM), N(2) adsorption, FT-IR. UV-vis and MAS ((13)C, (29)Si) NMR spectroscopy. The derivatized organosilicas were examined as catalyst precursors for the liquid-phase epoxidation of cis-cyclooctene, 1-octene, trans-2-octene and (R)-(+)-limonene at 55 degrees C, using tert-butyl hydroperoxide as the oxidant. For each olefin the corresponding epoxide was the only product detected. In the case of cyclooctene, the intrinsic reaction rates per surface molybdenum atom were similar for both Mo loadings (TOF similar to 1150 mol mol(Mo)(1) h(-1)), suggesting that the resultant materials act as single site epoxidation catalysts. Leaching tests and metal analyses of reaction solutions showed that the catalytic activity stemmed from the immobilized species and not from the leaching of active species into solution. The oxidation of limonene gave limonene oxide as the only product in 95% yield at 3 h. which reveals an outstanding regioselectivity to the epoxidation of the endocyclic double bond.
keywords
LIMONENE EPOXIDATION; SCALE PERIODICITY; BENZENE-SILICA; PORE-SIZE; SELECTIVE OXIDATION; ORGANOSILICAS PMOS; HYDROGEN-PEROXIDE; HYBRID MATERIALS; ORGANIC GROUPS; MCM-41
subject category
Chemistry
authors
Coelho, AC; Balula, SS; Bruno, SM; Alonso, JC; Bion, N; Ferreira, P; Pillinger, M; Valente, AA; Rocha, J; Goncalves, IS
our authors
Anabela Tavares Aguiar Valente
Principal Researcher
Isabel Maria de Sousa Gonçalves
Associate Professor
João Rocha
Full Professor
Martyn Pillinger
Principal Researcher
Paula Celeste da Silva Ferreira
Research Coordinator
Sofia M. Bruno
Assistant ResearcherGroups
G1 - Porous Materials and Nanosystems
G2 - Photonic, Electronic and Magnetic Materials
G4 - Renewable Materials and Circular Economy
Projects
Periodic mesoporous organic-inorganic hybrids (POCI/CTM/55648/2004)
RMNE-UA-National Network of Electron Microscopy (REDE/1509/RME/2005 )
acknowledgements
The authors are grateful to the Fundacao para a Ciencia e a Tecnologia (FCT), POCI 2010, OE and FEDER (Projects POCI/CTM/55648/2004, PPCDT/CTM/55648/2004 and PTDC/QUI/71198/2006), and to RNME (Project FCT: REDE/1509/RME/2005) for financial support. The FCT is acknowledged for a doctoral grant to A.C.C. and a post-doctoral grant to S.M.B.