Mesoporous silica beads containing active and stable tin species for the Baeyer-Villiger oxidations of cyclic ketones

Abstract

Porous anion-exchange resin was introduced as hard template to hydrothermally synthesize tin-containing mesoporous silica beads (Sn-MesoSB) with the diameter in the range of 0.3–0.9 mm. The characterization results showed the existence of continuous large-mesopore channels and tetrahedral tin species in the bead samples. Sn-MesoSB proved to exhibit high catalytic performances in the Baeyer-Villiger oxidation of adamantanone by using H2O2 as green oxidant, mainly attributed to the enhancement of the access to the catalytic tin sites through the continuous large-mesopore channels. Under the optimized experimental conditions, the conversion of adamantanone approached ca.100% in dioxane for 3 h at 90 °C. Notably, the bead format of such material could be remained during the catalysis procedure, which favors to the straightforward separation from the reaction system without any means of filtration or centrifugation. Working as a liquid-phase heterogeneous catalyst, this is pretty appealing to potential industrial applications. The catalyst was robust and can be reused up to 5 times without significant loss of activity and selectivity, pointing out that the tin species incorporated in the framework possessed high stability. Moreover, the bead material exhibits activity and selectivity in the Baeyer-Villiger oxidations with a broad range of substrates.