ToF-SIMS Analysis of NHC-Modified Naturally Oxidized Cu and Au Surfaces Providing Evidence for Covalent Bonding

N -heterocyclic carbenes (NHCs) are surface functionalization agents that have been shown to bind to the surface of various metals via a strong covalent bond. Among various NHC subtypes, 1,3-diisopropyl-1 H -benzoimidazolylidene (iPrNHC) has been extensively studied. Herein, we describe the use of time-of-flight secondary ion mass spectrometry (ToF-SIMS) to probe the interactions between iPrNHC and Cu and Au surfaces. This study provides unambiguous ToF-SIMS evidence of covalent bonding between the iPrNHC, deposited in solution, and the naturally oxidized copper surface by the detection of iPrNHC-Cu (C 13 H 18 N 2 Cu + ), including the corresponding isotope pattern. Depending on the treatment after deposition, covalently bound mono- or biscarbene-Cu complexes were observed. The biscarbene-Cu complexes were readily removed by solvent rinsing, whereas the monocarbene–Cu complex was uniformly distributed in a surface-bound layer. A carbene layer that was vapor-deposited on Au was also examined by ToF-SIMS, which confirmed the presence of biscarbene-Au complexes (C 26 H 36 N 4 Au + ) and much weaker monocarbene-Au complexes (C 13 H 18 N 2 Au + ), corroborating results obtained by other analytical techniques. This study provides a robust methodological approach for analyzing interfacial bonds, NHC-metal complexes, and their distribution on metal surfaces using ToF-SIMS.