Novel NHC-Based Au(I) Complexes as Precursors of Highly Pure Au(0) Nuggets under Oxidative Conditions

• Published in: Molecules (Basel, Switzerland) Vol. 28; no. 5; p. 2302
• Main Authors: Font, Pau, Tzouras, Nikolaos V, Papastavrou, Argyro T, Vougioukalakis, Georgios C, Ribas, Xavi
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 01.03.2023; MDPI
• Subjects: Acidic oxides; Au nuggets; Catalysis; Catalysts; Chemical reactions; Decomposition; Gold; iodosylbenzene-type oxidants; Ligands; NHC-Au(I) complexes; Oxidants; Oxidation; oxidized NHC=O compounds; Oxidizing agents; pendant ligands; Substrates; NHC-Au(I) complexes; Au nuggets; oxidized NHC=O compounds; iodosylbenzene-type oxidants; pendant ligands
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules28052302

The Lewis-acidic character and robustness of NHC-Au(I) complexes enable them to catalyze a large number of reactions, and they are enthroned as the catalysts of choice for many transformations among polyunsaturated substrates. More recently, Au(I)/Au(III) catalysis has been explored either by utilizing external oxidants or by seeking oxidative addition processes with catalysts featuring pendant coordinating groups. Herein, we describe the synthesis and characterization of N-heterocyclic carbene (NHC)-based Au(I) complexes, with and without pendant coordinating groups, and their reactivity in the presence of different oxidants. We demonstrate that when using iodosylbenzene-type oxidants, the NHC ligand undergoes oxidation to afford the corresponding NHC=O azolone products concomitantly with quantitative gold recovery in the form of Au(0) nuggets ~0.5 mm in size. The latter were characterized by SEM and EDX-SEM showing purities above 90%. This study shows that NHC-Au complexes can follow decomposition pathways under certain experimental conditions, thus challenging the believed robustness of the NHC-Au bond and providing a novel methodology to produce Au(0) nuggets.