Comparison of heterogeneous B(OiPr)3-MCM-41 and homogeneous B(OiPr)3, B(OEt)3 catalysts for chemoselective MPV reductions of unsaturated aldehydes and ketones
Boron tri-isopropoxide, B(OiPr)3, was immobilized on mesoporous material, MCM-41, and denoted as “B(OiPr)3-MCM-41”. The prepared new heterogeneous catalyst, B(OiPr)3-MCM-41, was characterized in details by using PXRD, FT-IR-, 11B NMR-, 29Si NMR-, 13C NMR-, TEM, EDX, N2 adsorption and ICP-OES. The results demonstrated the successful homogenous distribution of the B(OiPr)3 on the MCM-41 support. Heterogeneous B(OiPr)3-MCM-41 catalyst in comparison with the homogeneous B(OiPr)3 and B(OEt)3 catalysts, display similiar catalytic activity in the Meerwein–Ponndorf–Verley (MPV) reduction of unsaturated aldehydes and ketones with alcohols as reductants. Reduced reaction times, higher rate constants and very high selectivities for the unsaturated alcohols were obtained with the heterogenous catalyst than the homogeneous catalysts. In most cases, there were no side products other than the desired alcohol. The B(OiPr)3-MCM-41 catalyst was found to be encouraging as the catalyst is recyclable up to six cycles without any significant loss in its catalytic activity. This work enriches the family of heterogeneous MPV catalysts for chemoselective reductions of unsaturated aldehydes and ketones.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (156 K)Download as PowerPoint slideHighlights► Boron alkoxide-containing ordered mesoporous silica material (B(OiPr)3-MCM-41) was prepared. ► B(OiPr)3-MCM-41was successfully applied in the MPV reduction of unsaturated carbonyl compounds. ► High selectivity for the unsaturated alcohols was obtained with “B(OiPr)3-MCM-41” catalyst. ► B(OiPr)3-MCM-41 was compared with the homogeneous B(OiPr)3 and B(OEt)3 catalysts. ► In comparison with homogeneous catalysts, B(OiPr)-MCM-41 showed higher activity and better selectivity.
Journal: Applied Catalysis A: General - Volumes 435–436, 5 September 2012, Pages 204–216