Mechanistic Insights into Multisilver-Mediated Synergistic Activation of Terminal Alkynes

Synergistic effect extensively exists in multimetal-involved catalytic or mediated processes of group 11 metals due to their remarkable metallophilic interactions. Herein, we present a multiple synergism model for alkynyl substrates and conduct theoretical investigations on various multimetallic bonding modes and the corresponding synergistic activations. We computationally screen nine alkynyl multisilver coordination modes and sequence their reactivity shown in an intramolecular nucleophilic addition reaction by the trend of active μ₄-η¹η¹η²η² and μ₃-η¹η¹η² to the relatively inert μ₂-η¹η². The transition-state (TS) stabilization of the high-nuclearity mode mainly comes from the significant negative interaction energies between Ag and the substrate based on the distortion/interaction analysis. Energy decomposition analysis-natural orbitals for chemical valence (EDA-NOCV) analysis further reveals the charge-accepting reservoir effect of the polysilver moiety and the orbital match between the alkynyl group and specific spatial arrangement of silver atoms to account for this efficient activation. In addition, tests on different ligands coordinated to silver atoms show a correlation of the ligand conformation adjustability with the reactivity of the alkynyl unit, and the accommodable η² activation unit embodies a lower deformation energy than the other homonuclear synergistic modes. Privileged multiple synergistic models have been further evidenced based on on-bench experiments by isolating trisilver and tetrasilver alkynyl complexes. This study not only systematically evaluates the multimetallic synergism of different coordination modes in alkyne activation but also provides a guidance for the future design of multimetallic catalysts.