N-heterocyclic carbene-functionalized magic-number gold nanoclusters

Magic-number gold 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. Here, 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 CO2. 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. Magic-number Au11 clusters containing N-heterocyclic carbene (NHC) ligands are prepared by ligand exchange on known phosphine clusters and the introduction of even a single NHC results in improved cluster stability. The use of NHC-containing clusters in the electrocatalytic reduction of CO2 to CO is described and correlates with cluster stability.