Grafting of Molecularly Ordered Mesoporous Phenylene‐Silica with Molybdenum Carbonyl Complexes: Efficient Heterogeneous Catalysts for the Epoxidation of Olefins

Abstract

Arenetricarbonyl complexes, or the general formula À C 6 H 4 Mo(CO) 3 À , were incorporated into crystal-like mesoporous phenylene-silica by liquidphase 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 liquidphase epoxidation of cis-cyclooctene, 1-octene, trans-2-octene and (R)-(+)-limonene at 55 8C, using tertbutyl 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~1150 mol mol Mo À1 h À1), 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.

Investigation of a molybdenum-containing silica catalyst synthesized by the sol–gel process in heterogeneous catalytic esterification reactions using methanol and ethanol

“…A large variety of molybdenum complexes and molybdenum carbonyl compounds have also been immobilized on different inorganic and organic solids such as mesoporous MCM-41and in Mg/Al hydrotalcite (HTC) [21][22][23]; hybrid matrix synthesized by the sol-gel process, classed as ureasil, which combines a reticulated siliceous backbone linked by short polyether-based segments [24]; crystal-like mesoporous phenylene-silica [25]; polymers (e.g., polybenzimidazole, polystyrene 2-(aminomethyl)pyridine, and poly(4-vinylpyridine) [26,27]); and hydrotalcite clay materials [28]. The resulting solids have been used as catalysts for the oxidation of different substrates, like cis-cyclooctene, cyclohexene, styrene, 1-octene, trans-2-octene, (R)-(+)-limonene, and R-pinene.…”

The Versatility of Immobilized Mo Complexes in Organic Transformations - Epoxidation and Metathesis Reactions

“…More recently another report dealt with the immobilization of Mo(CO) 3 cores on the bridging phenylene moieties of a periodic mesoporous material [107]. This material was prepared by the hydrolysis and polymerization of silica-bridging phenylene moieties according to Scheme 15, which was subsequently treated with the Mo precursor to afford the organometallic pre-catalytic material.…”

“…Immobilized Mo II precatalyst in a periodic hybrid mesoporous material[107]. In fact the catalysts based on the hybrid material were better in the case of Scheme 15.…”

MoO 2 (acac) 2 anchored on organic copolymer-inorganic hybrid zirconium phosphonate-phosphate functionalized by pyridines as highly efficient, reusable catalysts for alkene epoxidation

“…Molybdenum-based catalysts have been widely used in this reaction [13][14][15][16][17][18][19][20][21][22][23][24]. Molybdenum-based catalysts used in homogeneous phase had shown remarkable catalytic activity and efficient use of oxidant in olefin epoxidation processes but display industrial problems associated with corrosion and deposition of the catalyst as well as difficulty in catalyst recovery [25][26][27][28][29][30].…”