Protonation-Induced Single-Ligand Elimination of Thiolate-Protected Gold Nanoclusters.

Ligand elimination from fully protected gold nanoclusters (AuNCs) to expose the metal core can induce high reactivity in catalytic reactions such as carbon dioxide reduction. However, there have been almost no reports of the preparation of partially ligand-eliminated species with controlled number and positions of removed ligands. Herein, we demonstrate regioselective single-ligand elimination of the thiolate-protected Au25 cluster anion [Au25(SR)18]- (SR = thiolate) to form [Au25(SR)17]0 through the protonation of an SR ligand with a Bro̷nsted acid. The number of eliminated SR ligands was experimentally confirmed through 1H nuclear magnetic resonance spectroscopy and electrospray ionization-mass spectrometry measurements. In contrast to the behavior of anionic [Au25(SR)18]-, the absence of SR elimination from the oxidized cluster ([Au25(SR)18]0) highlights the oxidation state-dependent reactivity of ligand elimination. The oxidation of [Au25(SR)18]- occurs in the Au13 core, so the contrasting reactivities of [Au25(SR)18]- and [Au25(SR)18]0 suggest the regioselective elimination of the Au13 core-bound SR ligand. The effects of the SR ligand on the reactivity of [Au25(SR)18]- reveal the importance of the electronic state of the Au13 core in regulating the SR-elimination reactivity. The similar trends were also confirmed in the reaction of other AuNCs bearing different Au core structures, and these electronic state-controlled reactivities of AuNCs have a resemblance with those of molecular transition metal complexes. The precisely controlled ligand elimination from AuNCs will facilitate the design of finely tuned Au-based catalysts with high reactivity and durability.