Abstract: A new chiral heterogeneous catalyst, Pd-chitosan(CS) complex supported on mesoporous molecular sieve MCM-48 was prepared and characterized by X-ray photoelectron spectroscopy, X-ray diffraction, and N2 adsorption-desorption measurements. The specific surface area, average pore diameter, and pore volume of the Pd-CS/MCM-48 catalyst were 527 m2/g, 2.1 nm, and 0.63 cm3/g, respectively. The asymmetric transfer hydrogenation of two prochiral ketones, acetophenone and 4-methyl-2-pentanone, was catalyzed by Pd-CS/MCM-48 using 2-propanol as the H-donor. The enantiomeric excess (ee) of (R)-1-phenylethanol reached 99.0% with a conversion of 61.9% after reaction for 4 h at 50 ℃, and the ee of (R)-4-methyl-2-pentanol was 82.4% with a conversion of 48.7% after reaction for 8 h at 50 ℃. The results indicated that the Pd-CS/MCM-48 catalyst possessed a high catalytic activity and enantioselectivity for the asymmetric transfer hydrogenation of these two prochiral ketones. Moreover, the effects of Pd content, reaction temperature, reaction time, and KOH concentration on the conversion and enantioselectivity for the asymmetric transfer hydrogenation of the prochiral ketones were investigated.

Key words: palladium, chitosan, complex, chiral catalyst, MCM-48 molecular sieve, acetophenone, 4-methyl-2-pentanone, transfer hydrogenation