New trends in the functionalization of metallic gold: from organosulfur ligands to N-heterocyclic carbenes

Abstract

In this Tutorial Review, we describe the development of new ligands for functionalizing and stabilizing metallic gold in the form of planar gold surfaces and gold nanoparticles (NPs). Starting from the state-of-the-art of organosulfur ligands, we describe the gold-sulfur bond formation and the nature of the resulting interface. In addition, we explain methods to prepare ordered monolayers on planar surfaces and stable ligand shells around NPs, illustrating important pioneering studies and examples of current research. Moreover, we highlight recent advancement in functionalizing gold by N-heterocyclic carbenes (NHCs), a promising alternative ligand class regarding stability and variable design strategies. We discuss the chemistry of the carbene-gold bond and report on advantages of this new ligand. Additionally, selected examples of current research illustrate the formation of ultra-stable self-assembled monolayers of NHCs on gold surfaces as well as the preparation of NHC-stabilized gold NPs.

Direct Synthesis of N‐Heterocyclic Carbene‐Stabilized Copper Nanoparticles from an N‐Heterocyclic Carbene–Borane

“…The taming of these compounds has unlocked a wide range of new applications from academia to industry, in organometallic chemistry, organocatalysis, surface chemistry, and nanoparticles synthesis . Although metallic nanoparticles (NPs) have a promising range of applications, depending on the physical and chemical properties of the metal, examples of NHC‐stabilized nanoparticles are still limited to few metals (Scheme , left) . Common strategies for their preparation rely on the reduction of an organometallic precursor (isolated or generated in situ) or ligand exchange .…”

Multidentate Anchors for Surface Functionalization

“…Recent works by Crudden and co‐workers demonstrate that NHCs are excellent ligands for the functionalization of metal electrodes and the resulting gold/NHCs surfaces exhibit much higher stability with respect to the conventional gold/thiolate surface . Stimulated by these results, a flexible tripodal NHC ligand 7 was recently reported by Wen and Chang, which was used to modify palladium electrode (Figure ) .…”

Ultra‐small sugar‐substituted N‐heterocyclic carbene‐protected palladium nanoparticles and catalytic activity

“…Metal nanoparticles (NPs) have been studied extensively due to their numerous applications in green chemistry, catalysis, biology and medicine . Such metal NPs are usually stabilized with ligands including phosphines, amines, thiols and thioethers .…”

“…Such metal NPs are usually stabilized with ligands including phosphines, amines, thiols and thioethers . The neutral, electron‐rich N‐heterocyclic carbenes (NHCs) are an emerging class of protected anchor for metal NPs due to their strong σ‐donation, since Arduengo et al . reported the isolation of free NHCs in 1991 .…”

“…Most recently, NHCs were used as alternative anchors for metal (including Au, Pd, Pt, Ru, Ag, etc.) surface modifications and so provided many notable properties, which might make them surpass thiol‐based systems . Just a few examples of NHC‐protected Pd NPs are reported in the literature, and the exchange strategy is an outstanding method because it employs preformed Pd NPs with known shapes and sizes .…”