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.

协同效应（synergistic effect）广泛存在于第11族金属（group 11 metals）参与的多金属催化或介导过程中，这源于该族金属显著的亲金属相互作用（metallophilic interactions）。据此，我们提出了适用于炔基底物（alkynyl substrates）的多重协同模型，并针对多种多金属成键模式（multimetallic bonding modes）及其对应的协同活化过程开展了理论研究。我们通过计算筛选出9种炔基多银配位模式，并对其在分子内亲核加成反应中的反应活性进行排序，活性顺序从高活性的μ4-η1η1η2η2和μ3-η1η1η2模式，到相对惰性的μ2-η1η2模式。基于畸变-相互作用分析（distortion/interaction analysis），高核度模式的过渡态（transition-state, TS）稳定化主要源于银原子簇（Agn）与底物之间显著的负相互作用能。能量分解分析-化学价自然轨道（EDA–NOCV）分析进一步揭示了多银片段（polysilver moiety）的电荷接受储库效应（charge-accepting reservoir effect），以及炔基与银原子特定空间排布之间的轨道匹配性，以此解释了该高效活化过程。此外，针对与银原子配位的不同配体（ligands）的测试表明，配体构象可调性（conformation adjustability）与炔基单元（alkynyl unit）的反应活性存在相关性；相较于其他同核协同模式（homonuclear synergistic modes），可适配的η2活化单元展现出更低的形变能（deformation energy）。通过分离得到三银（trisilver）和四银（tetrasilver）炔基配合物（alkynyl complexes）的实验室湿实验（on-bench experiments），进一步验证了具备优势的多重协同模型。本研究不仅系统评估了炔烃活化过程中不同配位模式的多金属协同效应，还为未来多金属催化剂（multimetallic catalysts）的设计提供了指导方向。