Hypercoordinated Dicarbanion-Bonded Ag19 Cluster: Synergistic Substrate Activation and Dynamic Surface Reorganization in Catalysis.

Surface ligands are crucial for maintaining the structural stability and integrity of metal nanoclusters, yet high ligand coverage often hinders substrate access to active metal sites. In this work, we demonstrate that an in situ generated aryl dianion ligand Py-Indole with a high coordination mode of μ5-C,C,N-η3,η2,η1 can significantly reduce surface coverage and expose accessible metal sites. As a result, only six Py-Indole ligands are enough to stabilize an ellipsoidal Ag19 nanocluster core. The low ligand coverage on the Ag19 cluster surface exposes two Ag3 caps, which enable the binding and activation of terminal alkynes and lead to the isolation of several acetylide-bonded Ag19 intermediates. Meanwhile, the basic dicarbanion sites of Py-Indole readily deprotonate the hydroxyl group in substrates, which together with the alkyne activation by silver atoms synergistically promote an intramolecular cyclization reaction at room temperature. The newly formed aryl dicarbanions undergo a recurring double proton exchange process with incoming substrate molecules to sustain the catalytically active state and drive the cyclization reaction forward with aturnover number up to 320. The synergistic integration of low-coverage ligand architecture, polymetallic activation, and substrate-ligand-product role-switching mechanism provides a transformative strategy for developing highly active and structurally resilient cluster catalysts in the future.