Pt nanoparticles entrapped in mesoporous metal–organic frameworks MIL-101 as an efficient and recyclable catalyst for the asymmetric hydrogenation of α-ketoesters

Abstract

Pt/MIL-101 catalyst was prepared via a facile impregnation method and was tested for the chiral hydrogenation of α-ketoesters after chirally modified with cinchona alkaloid. The powder XRD, N2 adsorption–desorption, TEM, and CO chemisorption were employed to characterize the Pt/MIL-101 catalyst. The Pt/MIL-101 catalyst was proved effective for the asymmetric hydrogenation of ethyl pyruvate and ethyl 2-oxo-4-phenylbutyrate after chirally modified with cinchonidine. Up to 4469h−1 TOF with 76.5% ee of (R)-(+)-ethyl lactate was obtained with the cinchonidine-modified Pt/MIL-101 catalyst in acetic acid. The fastest chiral hydrogenation of ethyl pyruvate with the cinchonidine-modified Pt/MIl-101 catalyst took place in neat water with medium enantioselectivity. While for the chiral hydrogenation of ethyl 2-oxo-4-phenylbutyrate with the cinchonidine-modified Pt/MIL-101 catalyst, over 2000h−1 TOF with 76.8% ee value was achieved in a mixed solvent containing acetic acid and ethanol with an equal volume. Of particular note is that the Pt/MIl-101 catalyst could be reused at least four times without distinct loss in activity or enantioselectivity with addition of fresh chiral modifier each time in the chiral hydrogenation of ethyl pyruvate. The catalytic performance of Pt/MIL-101 catalyst was also compared for the chiral hydrogenation of ethyl pyruvate with the commercial Pt/C and Pt/Al2O3 catalysts after modification with cinchona alkaloid.