Designing heterogeneous oxovanadium and copper acetylacetonate catalysts: Effect of covalent immobilisation in epoxidation and aziridination reactions

Abstract

Oxovanadium(IV) and copper(II) acetylacetonate complexes were immobilised onto a porous clay heterostructure (PCH) and SBA-15 previously functionalised with 3-aminopropyltriethoxysilane (APTES). The materials were characterised by chemical analysis, nitrogen adsorption–desorption isotherms at −196 °C, powder X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The results indicated that APTES was grafted onto PCH and SBA-15 with 75% and 67% of efficiencies, respectively. Both complexes were successfully anchored onto the APTES-functionalised supports, although with different immobilisation efficiencies: [VO(acac) 2] was anchored with 57% and 91% of efficiencies onto PCH and SBA-15, respectively, whereas [Cu(acac) 2] was immobilised onto PCH and SBA-15 with 31% and 95% of efficiencies, respectively. The [VO(acac) 2] heterogeneous materials acted as active catalysts in the epoxidation of geraniol using tert-butyl hydroperoxide as oxidant, presenting moderate substrate conversions, high selectivities towards 2,3-epoxygeraniol and very high stabilities upon reuse for two cycles. The [Cu(acac) 2] based materials were tested in the aziridination of styrene using [ N-( p-tolylsulfonyl)imino]phenyliodinane as nitrogen source, showing moderate substrate conversions, but with considerable complex leaching after three cycles, indicating that the complex grafting methodology was not stable under aziridination catalytic conditions. Generically, the PCH based catalysts, although presenting lower metal contents, acted as more active and robust catalysts in the reactions tested.