N‐Heterocyclic Carbene‐Stabilized Ultrasmall Gold Nanoclusters in a Metal‐Organic Framework for Photocatalytic CO2Reduction

Abstract Ultrafine gold nanoclusters (Au‐NCs) are susceptible to migrate and aggregate, even in the porosity of many crystalline solids. N‐heterocyclic carbenes (NHCs) are a class of structurally diverse ligands for the stabilization of Au‐NCs in homogeneous chemistry, showing catalytic reactivity in CO 2 activation. Herein, for the first time, we demonstrate a heterogeneous nucleation approach to stabilize ultrasmall and highly dispersed gold nanoclusters in an NHC‐functionalized porous matrix. The sizes of gold nanoclusters are tunable from 1.3 nm to 1.8 nm based on the interpenetration of the metal‐organic framework (MOF) topology. Control experiments using amine or imidazolium‐functionalized MOFs afforded the aggregation of Au species. The resultant Au‐NC@MOF composite exhibits a steady and excellent activity in photocatalytic CO 2 reduction, superior to control mixtures without NHC‐ligand stabilization. Mechanistic studies reveal the synergistic catalytic effect of MOFs and Au‐NCs through the MOF‐NHC‐Au covalent‐bonding bridges.