Pt/B-SiO2 as a Facile and Efficient Heterogeneous Catalyst for Enantioselective Hydrogenation: Effect of Support Modification with Boron

The development of chiral catalysts is key to the production of enantiopure compounds, which are of great interest to the pharmaceutical and fine chemical industries. The features of heterogeneous catalysts, such as their high stability, easy separation, and facile reusability, are particularly beneficial for practical applications. Supported and chirally modified Pt catalysts have shown high potential in enantioselective hydrogenation of α-keto esters. In this study, we report a highly efficient and versatile Pt/B-SiO2 catalyst. Specially, commercially available SiO2 support was modified with varying amounts of boron via a facile impregnation method. For the enantioselective hydrogenation of methyl pyruvate, 1 wt % Pt/B-SiO2 with a molar ratio of B/Pt = 60 achieved 96% enantiomeric excess (ee) even at H2 pressure of 0.1 MPa and maintained high enantioselectivity during 10 consecutive cycles. For various α-keto esters, the Pt/B-SiO2 catalyst also showed significantly higher activity and enantioselectivity than unmodified Pt/SiO2. Moreover, 0.5 wt % Pt/B-SiO2 outperformed 5 wt % Pt/γ-Al2O3, one of the most efficient catalysts reported for this reaction, despite its 10-times lower Pt loading. The enhanced adsorption capability of B-SiO2 for a chiral modifier and the resulting chiral modification of the Pt surface were found to be responsible for the superior performance of Pt/B-SiO2. This strategy based on the facile surface modification of a commercially available support material provides an opportunity to develop practical and efficient heterogeneous enantioselective catalysts.