Ultra stable self-assembled monolayers of N-heterocyclic carbenes on gold

Since the first report of thiol-based self-assembled monolayers (SAMs) 30 years ago, these structures have been examined in a huge variety of applications. The oxidative and thermal instabilities of these systems are widely known, however, and are an impediment to their widespread commercial use. Here, we describe the generation of N-heterocyclic carbene (NHC)-based SAMs on gold that demonstrate considerably greater resistance to heat and chemical reagents than the thiol-based counterparts. This increased stability is related to the increased strength of the gold–carbon bond relative to that of a gold–sulfur bond, and to a different mode of bonding in the case of the carbene ligand. Once bound to gold, NHCs are not displaced by thiols or thioethers, and are stable to high temperatures, boiling water, organic solvents, pH extremes, electrochemical cycling above 0 V and 1% hydrogen peroxide. In particular, benzimidazole-derived carbenes provide films with the highest stabilities and evidence of short-range molecular ordering. Chemical derivatization can be employed to adjust the surface properties of NHC-based SAMs. Thiol-based self-assembled monolayers have a huge variety of potential applications but are hampered by oxidative and thermal instability. Now, N-heterocyclic carbenes are shown to form densely packed layers on Au(111) that are considerably more stable than thiol films, resisting hot organic solvents, acid, base, oxidant and oxidative electrohemical etching.