Silver- and gold-catalyzed azide−alkyne cycloaddition by functionalized NHC-based polynuclear catalysts: Computational investigation and mechanistic insights

Abstract

This study evaluated the catalytic efficiency of Au(I), Ag(I), and Cu(I) complexes in the azide‒alkyne cycloaddition (AAC) reaction through density functional theory (DFT) calculations. Cu(I) complexes exhibit superior catalytic performance, with lower energy barriers (8.8 kcal/mol) and a favorable Gibbs free energy of -0.9 kcal/mol in the key cycloaddition step, significantly outperforming Ag and Au complexes. Structural analysis revealed that shorter M−C bond lengths in the Cu complex contributed to increased stability. Additionally, the copper complex has a more negative Gibbs free energy for the formed metallacycle, indicating a thermodynamically favorable reaction pathway. Noncovalent interaction (NCI) and reduced density gradient (RDG) analyses of the Cu, Ag, and Au systems highlighted distinct interaction patterns influencing the reactivity. Furthermore, electron localization function (ELF) and localized orbital locator (LOL) analyses revealed bonding characteristics in those complexes. This study offers valuable insights into the mechanistic differences among Au(I), Ag(I), and Cu(I) complexes, paving the way for future research on enhancing the catalytic activity of copper, silver and gold complexes through ligand modification.