Epoxide C–O bond activation intrigued by waisted flexibility of the Au₁₃Ag₁₂ clusters

The atomic precision of the coin metal nanoclusters lays the foundation for the elucidation of the structure-property correlations at the atomic/molecular level. Herein, the bi-icosahedral [Au₁₃Ag₁₂(PPh₃)₁₀Cl₈]PF₆ and [Au₁₃Ag₁₂(PPh₂Py)₁₀Cl₈]PF₆ (loaded on activated carbon) have been developed as the catalyst for the epoxide cycloaddition with CO₂. The [Au₁₃Ag₁₂(PPh₂Py)₁₀Cl₈]/AC catalytic system shows better performance than its PPh₃-analogue, with turnover number (TON) reaching 3.03 × 10⁴. Specifically, the catalyst shows high substrate tolerance, and is widely applicable to different epoxide substrates bearing aryl, alkyl, halogen, alkenyl and ether groups (yield: 72%–96%). The mechanistic investigation with ultraviolet–visible absorption spectroscopy (UV–Vis), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance spectroscopy (NMR), cyclic voltammetry (CV) and density functional theory (DFT) calculations indicate that both the waisted coordination flexibility and pyridine N atom are important: the electron transfer from epoxide to the electrophilic, waisted Ag center drives the entire reaction, and the pyridyl N-atoms facilitates the CO₂-migration and the subsequent cycloaddition processes. This study proposes the possibility for utilizing structural flexibility of metal nanoclusters as an efficient strategy to activate the substrates, which could hopefully benefit the development of more catalytic systems.