Asymmetric hydrogenation of α-ketoesters on chirally modified Pt catalysts supported on MPC-61 ordered mesoporous carbon

The Pt catalysts with mass fractions of 4% and 10% were supported on MPC-61, a kind of ordered mesoporous carbon, by an impregnation method using two different Pt precursors, ethanolic solution and aqueous solution of H₂PtCl₆. These Pt/MPC-61 catalysts were characterized by XRD, N₂-sorption, TEM and CO chemisorption. The Pt/MPC-61 catalysts were applied in the asymmetric hydrogenation of ethyl pyruvate after chirally modified with cinchonidine. The Cat-4Pt-E catalyst derived from the ethanolic solution of H₂PtCl₆ afforded higher conversions of ethyl pyruvate due to smaller Pt particle size with higher Pt dispersion. While the Cat-4Pt-W catalysts derived from the aqueous solution of H₂PtCl₆ showed higher chiral induction ability. The catalyst Cat-4Pt-W-150, which was calcined at 150°C under vacuum, gave higher conversion and enantioselectivity than Cat-4Pt-W did, the highest TOF reaching 8820 h^-1 in water. A 66%e.e. value was furnished by Cat-10Pt-E catalyst in acetic acid. In particular, the Cat-4Pt-W catalyst showed superior catalytic activity to the commercial 5%(mass fraction) Pt/C catalyst, mainly due to the ordered mesoporous structure feature of MPC-61 support. Cat-4Pt-W can also be reused for more than 10 times without distinct loss of activity or enantioselectivity. The 4%Pt/MPC-61 catalysts can also be effectively applied in the asymmetric hydrogenation of ethyl 2-oxo-4-phenylbutyrate, of which the hydrogenation product can be used to produce A.C.E inhibitors. Under the optimal conditions, the catalyst Cat-4Pt-W-150 gave a 61%e.e. value of (R)-(+)-ethyl 2-hydroxyl-4-phenylbutyrate in acetic acid.