Performance evaluation of mesoporous host materials in olefin epoxidation using Mo(II) and Mo(VI) active species-Inorganic vs. hybrid matrix

The [(MoCl2)-Cl-VI(thf)(2)] and [Mo(II)l(2)(CO)(3)(MeCN)(2)] precursor complexes, were immobilized in a hybrid periodic mesoporous organosilicas (PMO)-type material. These new hybrid matrix materials were prepared in one pot synthesis, containing the bidentate N,N'-ligand (glypy) in the material. In a second approach, the ordered mesoporous silica MCM-glypy was prepared using a tethered approach by a step-wise procedure. The metal complexes were grafted in both types of materials to obtain heterogeneous pre-catalysts. The modified materials have been characterized by powder X-ray diffraction, N-2 adsorption, and solid-state CP MAS NMR (C-13,Si-29). All metal containing materials were tested as catalysts in epoxidation of 1-octene, cyclooctene and styrene with tert-butylhydroperoxide (TBHP) at 328 K. Selectivity to octene and cyclooctene epoxides was complete. The new PM0 materials described in this work are outstanding catalysts for any of the transformations described. In fact, cyclooctene selectivity based on TBHP consumption is found to be almost independent of the mol ratio attesting the efficiency of the catalysts. They are also effective under stoichiometric olefin/oxidant ratio. In addition, a mechanism for acid catalyzed benzaldehyde formation is proposed as well as the conversion of Mo(II) to Mo(VI) under catalysis. (C) 2011 Elsevier B.V. All rights reserved.