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 Agn 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.