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

Abstract

In this paper we present the asymmetric hydrogenation of a-keto esters with platinum nanoparticles homogeneously stabilized in dendritic coremultishell 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.

Dendrimer/inorganic nanomaterial composites: Tailoring preparation, properties, functions, and applications of inorganic nanomaterials with dendritic architectures

“…As the authors pointed out, this approach opens a new avenue to endow the chirality to metal nanoparticles, which might have a promising application as chiral catalysts for asymmetric synthesis. In relation to this work, Haag and coworkers have reported that Pt DSNs allows the modification of Pt NP surface with a small chiral agent, and then can be used to catalyze hydrogenation with a relative high enantiometric excess (ee) value [37].…”

Core–shell nanoparticles: synthesis and applications in catalysis and electrocatalysis

“…Then, using a controlled etching technique (by treating the sample with strong base at elevated temperature), allowed formation of a thin shell surrounding the Au-NP core. 250 Mainly comprising ''organic'' materials, special types of coremultishell NPs have been introduced recently involving supramolecular dendritic assemblies, which have potential applications in drug/dye/metal ions delivery 251-257 as well as catalysis [258][259][260] etc. 12).…”

“…12). [258][259][260] 3.1.1.3.3. 244 The particle-size (and also shell thickness) was shown to be easily controllable and in good agreement with calculated values.…”

Bimetallic Dendrimer-encapsulated Nanoparticle Catalysts

“…The evaluation of the catalytic activity of DENs catalysts are generally from the selectivity, activity (such as the turnover frequency, TOF the number of revolutions of the catalytic cycle per unit time, typically sec, min, or hrs), and stability. DENs catalysts have been shown to be able to considerably enhance the stability 82,83 and selectivity 84 of the metal catalyst. In addition, Bronstein and Shifrina reported that catalytically active metal nanoparticles are formed in a void in its host dendrimer and their surface could not be completely covered by the ligands, which thus provides a unique access for the reactant molecules to be adsorbed on the surface thereby facilitating the catalytic reaction.2…”