[VO(acac)2] hybrid catalyst: from complex immobilization onto silicananoparticles to catalytic application in the epoxidation of geraniol

Abstract

This work reports the preparation of a novel hybrid nanocatalyst through the immobilization of oxidovanadium^IV acetylacetonate ([VO(acac)₂]) onto silica nanoparticles functionalized with 3-aminopropyltriethoxysilane (APTES) and its catalytic application in the allylic epoxidation of geraniol. All the nanomaterials were characterized by chemical analysis, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The parent and amine-functionalized silica nanoparticles were also analyzed by ²⁹Si and ¹³C solid-state nuclear magnetic resonance and the supported [VO(acac)₂] nanomaterial was characterized by magnetic susceptibility measurement. The APTES organosilane was grafted onto the silica nanoparticles with an efficiency of 90%, through mono- and bidentate covalent grafting. The [VO(acac)₂] complex was covalently anchored on the surface of the APTES-functionalized silica nanoparticles with 25% of efficiency. Magnetic susceptibility measurements in combination with XPS indicated that the oxidation state of the metal center (VO²⁺) was preserved upon the immobilization reaction. The catalytic performance of the novel hybrid [VO(acac)₂] nanocatalyst was evaluated in the epoxidation of geraniol, at room temperature, using tert-butyl hydroperoxide as an oxygen source. The nanocatalyst presented 100% of substrate conversion, 99% of selectivity towards the 2,3-epoxygeraniol product and was stable upon reuse in further four cycles.