Designing new catalytic nanoreactors for the regioselective epoxidation of geraniol by the post-synthetic immobilization of oxovanadium(IV) complexes on a ZrIV-based metal-organic framework

Two post-synthetic strategies have been used to prepare oxovanadium(IV) complexes covalently anchored to the organic linkers of UiO-66(NH2) (UiO = University of Oslo) metal-organic framework. In the first method, the available amino groups of UiO-66(NH2) were treated with salicylaldehyde to form the modified UiO-66 (UiO-66-SI). The synthesized UiO-66-SI was then treated with [VO(acac)(2)] to produce UiO-66-SI/VO(acac). In the second method, UiO-66(NH2) was directly treated with [VO(acac)(2)] to form UiO-66-N/VO(acac)(2). The synthesized compounds were characterized by FTIR, XRD, N-2 sorption, FE-SEM, TEM, EDX, ICP-AES, TGA and UV-Vis spectroscopy. The catalytic performances of UiO-66-SI/VO(acac) and UiO-66-N/VO(acac)(2) were assessed in the epoxidation of geraniol with tert-butyl hydroperoxide. The results indicated 100% conversion with 100% selectivity towards 2,3-epoxygeraniol after 60 and 120 min of reaction time. These excellent catalytic activities can be attributed to the high dispersion of the catalytic sites on MOF and the proper pore size of UiO-66(NH2). Moreover, the structure of both catalysts remains intact during the catalytic reaction and the catalysts can be successfully recycled three times. High yields and excellent selectivity towards the 2,3-epoxygeraniol product, short reaction time, mild reaction conditions and recyclability of the solid catalysts are some of the advantages of these catalytic systems.