Chirally Modified Platinum Nanoparticles Stabilized by Dendritic Core‐Multishell Architectures for the Asymmetric Hydrogenation of Ethyl Pyruvate

In this paper we present the asymmetric hydrogenation of α‐keto esters with platinum nanoparticles homogeneously stabilized in dendritic core‐multishell architectures. The main focus lies on recycling and metal leaching, because little is reported so far about these aspects. It is shown that the stabilizing polymer allows for the efficient modification of the Pt surface with the chiral alkaloid cinchonidine, thereby inducing enantioselectivity and enhancing the reaction rate in the asymmetric hydrogenation of ethyl pyruvate. After optimization of the reaction conditions 63% ee for (R)‐ethyl lactate was obtained. During recycling it was found that this value could even be increased upon ultrafiltration of the catalyst prior to use. Recycling was accomplished for 10 cycles with stable activity and enantioselectivity (∼73% ee) in the first eight runs. Aggregation of the initially well dispersed nanoparticles was observed by transmission electron microscope (TEM) analysis, leading to reduced conversion after the 8^th cycle, but metal leaching into the product has been observed only in the very first run.