Author: Juanzhu Yan, Haifeng Su, Huayan Yang, Chengyi Hu, Sami Malola, Shuichao Lin, Boon K. Teo*, Hannu Häkkinen, and Nanfeng Zheng*

Abstract:

In this work, a facile ion-pairing strategy for asymmetric synthesis of optically active negatively charged chiral metal nanoparticles using chiral ammonium cations is demonstrated. A new thiolated chiral three-concentric-shell cluster,  [Ag₂₈Cu₁₂(SR)₂₄]^4–, was first synthesized as a racemic mixture and characterized by single-crystal X-ray structure determination. Mass spectrometric measurements revealed relatively strong ion-pairing interactions between the anionic nanocluster and ammonium cations. Inspired by this observation, the as-prepared racemic mixture was separated into enantiomers by employing chiral quaternary ammonium salts as chiral resolution agents. Subsequently, direct asymmetric synthesis of optically active enantiomers of  [Ag₂₈Cu₁₂(SR)₂₄]^4– was achieved by using appropriate chiral ammonium cations (such as N-benzylcinchoninium vs N-benzylcinchonidinium) in the cluster synthesis. These simple strategies, ion-pairing enantioseparation and direct asymmetric synthesis using chiral counterions, may be of general use in preparing chiral metal nanoparticles.

FULLLINK：http://pubs.acs.org/doi/abs/10.1021/jacs.6b08100