Efficient base- and ligand-free palladium catalysed O-arylation of phenols in choline chloride:triethanolamine as a...

In this paper, we present a novel and sustainable approach using choline chloride:triethanolamine as a green, efficient and reusable deep eutectic solvent (DES) for Pd-catalysed O-arylation reactions with Pd/BaSO₄ (10%). By using the unique properties of DESs, we successfully achieved C-O bond formation without the need for additional solvents, bases and ligands. This solvent/catalyst system ([ChCl][TEA]₂) functioned as a dual catalyst and solvent system, enabling fast and environmentally friendly C-O bond formation from phenol derivatives and electron-deficient aryl halides, leading to remarkable yields under mild reaction conditions. To identify and characterize this DES, we employed differential scanning calorimetry, thermogravimetric analysis, Fourier-transform infrared spectroscopy, refractive index, viscosity, the potential of hydrogen (pH) and conductivity measurements. One of the remarkable advantages of this DES system is its exceptional stability. This solvent/catalyst system exhibited high stability throughout the reaction cycles, showing no significant loss of activity. As a result, this DES and catalyst (Pd/BaSO₄ (10%)) can be easily recycled and re-used for up to three consecutive cycles, making it an economically and environmentally attractive option for organic reactions. Our approach offers several key benefits, including simple catalyst preparation, quick reaction times and excellent production efficiency.