Accelerated Catalysis of Atomically Precise Thiolate-Protected Gold Nanoclusters by Supramolecular Ligand Engineering

Abstract

We herein report the reaction acceleration effect of a supramolecular reaction field constructed with dendritic peptide thiolate ligands on the Au₂₅ nanocluster toward the catalytic cyclization of alkynoic acids. A remarkable reaction acceleration was achieved by peptide dendron thiolate ligands, which was 40 times greater than that achieved by simple alkyl thiolate ligands. Association experiments with ¹H NMR spectroscopy revealed that the unprecedented intermolecular hydrogen bonds between peptide dendron ligands and ammonium salts of alkynoic acids play a critical role in the reaction acceleration effect. The high stability of the nanocluster catalyst bearing the supramolecular reaction field was also represented by the turnover number over 820,000 in this catalytic reaction. Mechanistic investigations revealed the involvement of pi-coordinated alkynes and subsequent vinyl–Au intermediates. DFT calculations support the possible reaction pathway, including both the anionic and neutral forms of the nanocluster as the catalyst. Our findings demonstrate the usefulness of the supramolecular ligand approach for metallic nanocluster catalysis, enabling enhanced catalytic efficiency and selectivity toward various organic transformations.