Enantioselective hydrogenation of ethyl pyruvate catalyzed by PVP-stabilized rhodium nanoclusters

The enantioselective hydrogenation of ethyl pyruvate catalyzed by polyvinylpyrrolidone-stabilized rhodium nanocluster (Rh/PVP) modified by cinchonidine and quinine was studied. The results show that cinchonidine and quinine not only can induce the enantioselectivity in the hydrogenation of ethyl pyruvate, but also can greatly accelerate the reaction. Under the optimum conditions, 298 K, 5 MPa of hydrogen pressure and 4.3×10⁻³ mol/l of cinchonidine in tetrahydrofuran, the enantiomeric excess of R-(+)-ethyl lactate and turnover frequency (TOF) of ethyl pyruvate reach up to 42.2% e.e. and 941 h⁻¹, respectively. The rate of hydrogenation is faster by a factor of about 50 in the presence of cinchonidine than that without it. Quinine exhibits the similar effect.