Pd(Acac)2–Chiral Stabilizer–H2 Colloidal System in the Enantioselective Hydrogenation of N-Acetyl-α-Amidocinnamic Acid

Abstract

It has been shown that the Pd(Acac)₂–mod–H₂ colloidal system, where mod denotes chiral stabilizers of molecular (8S,9R)-cinhonidine, (–)-Сin, and ionic (–)-Cin*HCl and (–)-Cin*2HCl types, exhibits catalytic activity in the asymmetric hydrogenation of N-acetyl-α-amidocinnamic acid (AACA) at room temperature and an H₂ pressure of 5 atm. The esterification reaction of the product, N-acetylphenylalanine (N-APhA), occurs in the presence of protonated forms of cinchonidine. The excess of the R-(–)-enantiomer of N-acetylphenylalanine is as large as 78% for the Pd(Acac)₂–(–)-Сin–H₂ system at (–)-Сin/Pd = 1.5, while the protonated forms of the quinine alkaloid show lower efficiency as modifiers of the catalytic system with respect to chiral induction. The X-ray diffraction analysis and high-resolution transmission electron microscopy have been employed to show the formation of palladium nanoparticles with average sizes of 5.3 ± 0.8 and 4.2 ± 0.5 nm for the Pd(Acac)₂–(–)-Cin–H₂ and Pd(Acac)₂–(–)-Сin *HCl–H₂ systems, respectively.