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.

1,2,3-Triazolylidene-based mesoionic carbene boranes have been synthesized in a convenient one-pot protocol from the corresponding 1,2,3-triazolium salts, base, and borane. Borenium ions are obtained by hydride abstraction and serve as catalysts in mild hydrogenation reactions of imines and unsaturated N-heterocycles at ambient pressure and temperature.

New mono- and bidentate 1,2,3-triazol-5-ylidene mesoionic carbene (MIC) ligands have been synthesized and reacted with silver oxide, forming cationic 1:2 and 2:2 Ag:MIC ([AgL2]Br and [Ag2L2]­[Ag2Br4]) complexes, respectively. These complexes have been isolated and characterized. They were further found to be potent transmetalation agents toward rhodium, resulting in the preparation of mono- and bimetallic rhodium complexes. The reaction of the 2:2 Ag:L complex with [Rh­(COD)2]­BF4 results in the first reported example of a cationic bimetallic rhodium MIC complex. This complex was fully characterized, and its X-ray structure is reported. Interestingly, this complex exhibits various secondary noncovalent interactions in the solid state of the general type C–H···X, where X = F, Cl.

New mono-and bimetallic 1,2,3-triazol-5-ylidene mesoionic carbene (MIC) complexes of Pd have been synthesized, isolated, and characterized. We have described the synthesis of a bis(MIC) complex via transmetalation from a Ag-MIC complex and two PEPPSI-type complexes which are directly available from their respective triazolium salts by treatment with PdCl 2 in pyridine. The X-ray structures are reported for all complexes described herein. Interestingly, each complex described exhibits various secondary noncovalent interactions in the solid state of the general type C−H•••Cl, which appear to be important for the stabilization of the solid-state structure of the complexes. We further demonstrated the utility of the new PEPPSI complexes in the Mizoroki−Heck reaction. In the case of aryl iodides and electron-deficient bromides, high conversion is observed with methyl acrylate. Hg poisoning tests suggest that, even with an easily dissociated ligand, the reaction likely proceeds via Pd nanoparticles.