Main content area

Asymmetric Synthesis of Chiral Bimetallic [Ag28Cu12(SR)24]4– Nanoclusters via Ion Pairing

Yan, Juanzhu, Su, Haifeng, Yang, Huayan, Hu, Chengyi, Malola, Sami, Lin, Shuichao, Teo, Boon K., Häkkinen, Hannu, Zheng, Nanfeng
Journal of the American Chemical Society 2016 v.138 no.39 pp. 12751-12754
X-radiation, ammonium salts, cations, enantiomers, mass spectrometry, nanoparticles
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.