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

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. Gold is a key metal in nanotechnology but ligands are required for surface stabilization and functionalization. This tutorial review highlights the recent progress from organosulfur to N-heterocyclic carbene surface ligands for gold.