Synthesis and catalytic properties of manganese(II) and oxovanadium(IV) complexes anchored to mesoporous MCM-41
authors Fernandes, TA; Nunes, CD; Vaz, PD; Calhorda, MJ; Brandao, P; Rocha, J; Goncalves, IS; Valente, AA; Ferreira, LP; Godinho, M; Ferreira, P
nationality International
journal MICROPOROUS AND MESOPOROUS MATERIALS
author keywords mesoporous materials; MCM-41; manganese; oxovanadium; nitrogen ligands; epoxidation
keywords EFFECTIVE CORE POTENTIALS; TRANSITION-METAL ATOMS; MOLECULAR CALCULATIONS; ACTIVE-SITES; BASIS SET; EPOXIDATION; SILICA; SIEVES; CYCLOOCTENE; METALLOPROTEINS
abstract Reaction of [Mn(III)(acaC)(3)] and [V(IV)O(acac)(2)] with the 1,4-diazabutadiene (DAB) ligands Ph-DAB-(CH(2))(3)R [R = Si(OEt)(3)(1a); H (1b)] (L) leads to complexes of the type [Mn(II)(acaC)(2)L] and [V(IV)O(acac)L]Cl in good yields. These complexes were characterised by spectroscopic techniques, and magnetic measurements showed that in the case of the manganese the metal was reduced during the reaction with the nitrogen ligand. The oxovanadium and manganese complexes bearing the ligand with triethoxysilyl groups Ph-DAB-(CH(2))(3)Si(OEt)(3)(1a) were immobilised in ordered MCM-41 by carrying out a grafting reaction. Tethered complexes of the same type were prepared by treating MCM-41 first with a toluene solution of la under reflux; manganese(III) and oxovanadium(IV) precursors were then introduced into the MCM-41-ligand by pore volume impregnation of complex solutions. The modified materials were characterised by powder X-ray diffraction, solid-state NMR ((13)C, (29)Si), FTIR, thermogravimetric studies and low temperature nitrogen adsorption isotherms. The grafted materials contained 0.7 wt% Mn and 0.8 wt% V, while higher metal loadings were achieved when the materials were prepared by tethering (2.9 wt% Mn and 2.4 wt% V). The modified materials are active catalysts for the oxidation of cis-cyclooctene using tert-butylhydroperoxide as oxygen donor, at 328 K, yielding 1,2-epoxycyclooctane as the main reaction product and 1,2-cyclooctanediol as a by-product. The vanadium-containing materials are more efficient epoxidation catalysts than the manganese ones. The catalytic behaviour of the heterogenised catalysts was also compared with that observed in homogeneous phase for the complexes [Mn(acaC)(2)L] and [VO(acac)L]Cl. The vanadium catalysts exhibited the highest catalytic activity, whereas the manganese catalysts were the least active and selective to epoxide formation. (C) 2007 Elsevier Inc. All rights reserved.
publisher ELSEVIER SCIENCE BV
issn 1387-1811
year published 2008
volume 112
issue 1-3
beginning page 14
ending page 25
digital object identifier (doi) 10.1016/j.micromeso.2007.09.009
web of science category Chemistry, Applied; Chemistry, Physical; Nanoscience & Nanotechnology; Materials Science, Multidisciplinary
subject category Chemistry; Science & Technology - Other Topics; Materials Science
unique article identifier WOS:000256713300002
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journal impact factor 4.551
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