Ligand exchange is an important strategy to functionalize metal nanoclusters (NCs) for enhanced properties. Thiolates and alkynyls have been widely used for NC protection, however, the possibility for alkynyl-for-thiolate exchange as well as the kinetics for the ligand exchange process have remained largely unexplored. Herein, we reported the first kinetic investigation into the alkynyl-for-thiolate exchange through the reaction of thiolated Au25(SR)18 with the incoming alkynyl ligands. Interestingly, our simulations revealed the electronic and steric effect of alkynyl ligands, and the precursor cluster’s charge state collectively govern the exchange efficiency and regioselectivity. Notably, the alkynyl-for-thiolate exchange is highly facile when reacting with the nucleophilic lithium or gold(I)−alkynyl complex (Au(C≡CR) or Li(C≡CR)), but fails when using HC≡CR as the exchange ligand. The Au(C≡CPh) complex exhibits charge-state-dependent exchange at the S1 or S2 position, whereas the sterically bulky Au(C≡CtBu) complex decelerates the exchange kinetics and universally targets the S1 position as the exchange product. By contrast, the lithium-alkynyl complex (Li(C≡CPh) or Li(C≡CtBu)) preferentially leads to the S1′ exchange isomer, driven by the ionic Li−C bonding that enhances the C≡C π*-electron density and alkynyl nucleophilicity. Our predictions are further validated by the ligand exchange experiments between phenyl ethanethiol (PET) protected [Au25(PET)18]− and Au(C≡CtBu). The electrospray ionization mass spectra (ESI-MS) unambiguously confirms the successful substitution of about 4, 5 and 6 PET ligands by the −C≡CtBu ligand, and the absorption spectrum is drastically changed upon the alkynyl exchange. This work establishes important atomic-level understanding of the alkynyl-for-thiolate exchange mechanism, offering a convenient strategy of realizing alkynyl and thiolate co-protected gold clusters under mild conditions.
