One-step synthesis and XPS investigations of chiral NHC-Au(0)/Au(i) nanoparticles

Although N-heterocyclic carbenes (NHCs) have been demonstrated as suitable ligands for the stabilisation of gold nanoparticles (AuNPs) through a variety of methods, the manner in which such AuNPs form is yet to be fully elucidated. We report a simple and fast one-step synthesis of uniform chiral (l/d)-histidin-2-ylidene stabilised gold nanoparticles using the organometallic Au(i) complex as a well defined starting material. The resulting nanoparticles have an average size of 2.35 +/- 0.43 nm for the L analog whereas an average size of 2.25 +/- 0.39 nm was found for the D analog. X-ray photoelectron spectroscopy analyses reveal the presence of Au(i) and Au(0) in all NHC stabilised AuNPs. In contrast, measured X-ray photoelectron spectra of dodecanethiol protected gold nanoparticles showed only the presence of a Au(0) species. This observation leads us to postulate that AuNPs synthesised from organometallic NHC-Au(i) complexes exhibit a monolayer of Au(i) surrounding a Au(0) core. This work highlights the importance of synthetic method choice for NHC-stabilized AuNPs, as this could determine Au oxidation states and resulting AuNP properties such as catalytic activities and stabilities.