Enantioselective hydrogenation of 1-phenyl-propane-1,2-dione on immobilised cinchonidine Pt/SiO₂ catalysts

Chirally modified SiO₂ containing different amounts of cinchonidine was prepared by the chemical modification of cinchonidine (CD) with trimethoxysilane over SiO₂ that had been chemically activated with 1,4-dioxane/HCl. This solid was used to support Pt catalysts containing 1 wt%Pt obtained by the chemical reduction of hexachloroplatinic acid with H₂ at 298 K and 40 bar. The materials were characterised by elemental analyses of C, H, and N, as well as thermal gravimetry (TG), DRIFT, ¹³C NMR, ²⁹Si solid state NMR, N₂ adsorption-desorption at 77 K, X-ray diffraction (XDR), XPS, and HR-TEM. Catalytic activity for the hydrogenation of 1-phenyl-propane-1,2-dione was evaluated in a batch reactor at 298 K and 40 bar, and recycling of the catalysts yielding the largest enantiomeric excess in the products were also studied. All catalysts were found to be active in the reaction, with enantiomeric excesses of the target product (1-R-phenyl-1-hydroxy-2-propanone) ranging from 35 to 50%. The best catalyst studied was SiO₂-supported, with a nominal content of 7.5 mmolCD/L g. The recycling tests showed a loss of activity that was attributed to the surface modification of the catalyst.