NHC-coated gold clusters obtained from organometallic Au(I) complexes

Abstract

Gold nanoclusters (AuNCs) are nanoscopic species consisting of a core of a few to several hundred goldatoms, typically under 2 nm in size, placing them between small molecules and larger nanoparticles.[1] Due to their small size, AuNCs exhibit quantum confinement effects, discrete energy levels and a variety of uniqueproperties, including excellent catalytic activity, NIR absorption or photoluminescence.N-heterocyclic carbenes (NHCs) have emerged as one of the most significant organic ligands incoordination chemistry and have recently increased attention in nanoscience for their ability to stabilize metal nanoclusters and nanoparticles. NHCs are characterized by their robust bonding ability, which combines both σ-donating and π-accepting interactions. Their electronic and steric properties are highly sensitive to structural modifications, providing great flexibility for design. Additionally, tunable properties can be obtained by the easy incorporation of functional groups at the position of nitrogen substituents or backbone.[2],[3] In this work, organometallic precursors NHC-Au-X (X = Cl or C6F5) were synthetized by reacting [Au(C6F5)(tht)] or [Au(Cl)(tht)] (tht = tetrahydrothiophene) with the corresponding imidazolium salts in the presenceof Tl(acac). Subsequent thermolysis or reduction of these organometallic precursors NHC-Au-X led to theformation of ultrasmall gold nanoparticles (see figure). UV-Vis-NIR absorption spectroscopy, electron microscopy (HAADF-STEM) and Nuclear magnetic resonance (NMR) have been used to characterize the final AuNCs.