An Electrochemical Study of Key Catalytically Active Gold Complexes.

Gold catalysis has long been dominated by the ability of gold(I) to activate unsaturated systems as a carbophilic Lewis acid. However, recent advances have highlighted the significance of Au(I)/Au(III) redox transitions, unlocking new catalytic pathways. Among the strategies facilitating these oxidative processes, electrochemical anodic oxidation has emerged as a powerful tool. Despite its potential, the electrochemical properties of key gold complexes remain largely underexplored. In this study, we systematically investigate the oxidative behavior of a series of gold complexes using cyclic voltammetry. A comprehensive electrochemical scale is established, revealing that N-heterocyclic carbene (NHC)-based gold complexes are among the least prone to oxidation, whereas phosphorylated ligands significantly enhance oxidizability. Within triphenylphosphine gold complexes, the nature of the X-type anionic ligand plays a crucial role in determining oxidative behavior, a trend rationalized through density functional theory (DFT) calculations of the highest occupied molecular orbital (HOMO). Additionally, hemilabile P^N ligands dramatically facilitate oxidation, correlating with their ability to promote oxidative addition. These findings provide fundamental insights into the redox properties of gold complexes, offering valuable guidelines for the design of new gold-catalyzed transformations.