A Free N‐Heterocyclic Carbene and Its Metal Complex

Abstract

ABSTRACT Classical carbenes are highly reactive species that have traditionally been regarded as transient intermediates, making direct structural characterization a challenge. Among them, N‐heterocyclic carbenes (NHCs) stand out for their stability and broad applicability, yet atomic‐scale insights into their structure and electronic properties remain limited. Here, we report the on‐surface single‐molecule characterization of a free NHC deposited on ultrathin insulating NaCl layers on Au(111), enabling direct investigation of a reactive carbene in its free form. Using a combination of scanning tunneling microscopy (STM), atomic force microscopy (AFM), and density functional theory (DFT), we resolve its molecular structure and frontier orbital with sub‐molecular resolution. We further demonstrate the reactivity of the free NHC through its on‐surface complexation with a gold atom. These results demonstrate that real‐space techniques enable direct insights into the structure and reactivity of free NHCs, helping to connect molecular properties with their broader functional applications.