N-Heterocyclic carbene-functionalized magic number gold nanoclusters

Magic number metal nanoclusters are atomically precise nanomaterials that have enabled unprecedented insight into structure-property relationships in nanoscience. Thiolates are the most common ligand, binding to the cluster via a staple motif in which only central gold atoms are in the metallic state. The lack of other strongly-bound ligands for nanoclusters with different bonding modes has been a significant limitation in the field. Herein, we report a previously unknown ligand for gold (0) nanoclusters: N-heterocyclic carbenes (NHCs), which feature a robust metal-carbon single bond, and impart high stability to the corresponding gold cluster. The addition of a single NHC to gold nanoclusters results in significantly improved stability and catalytic properties in the electrocatalytic reduction of CO<sub>2</sub>. By varying the conditions, nature and number of equivalents of the NHC, predominantly or exclusively monosubstituted NHC-functionalized clusters result. Clusters can also be obtained with up to five NHCs, as a mixture of species.