Grafted non-ordered niobium-silica materials: Versatile catalysts for the selective epoxidation of various unsaturated fine chemicals

•Mesoporous Nb(V)-silica catalysts prepared via dry impregnation or grafting technique.•Used as catalysts with aqueous H2O2 for the epoxidation of unsaturated terpenes.•Robust in the presence of water and versatile with various alkene substrates.•High yields (up to 73%) and excellent selectivities to epoxides (up to 98%).

Two kinds of niobium(V)-silica catalysts for the selective epoxidation were synthesised by post-synthesis modification of non-ordered mesoporous silica supports, starting from niobocene dichloride via solvent-less organometallic precursor dry impregnation or conventional liquid-phase grafting technique. Grafted Nb/SiO2 solids were used as catalysts, in the presence of aqueous H2O2, for the epoxidation of unsaturated cyclic and terpenic compounds of interest for fine and specialty chemistry, in particular: cyclohexene, 1-methylcyclohexene, limonene, carveol, α-terpineol, isopulegol, carvotanacetol, carvone, as well as squalene and isopulegyl acetate. These catalysts showed high yields (up to 73%) and excellent chemoselectivities to the desired epoxides (up to 98%), also in short reaction times (down to 1 h).

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