Ligand-free catalysts typically involve metal nanoparticles or metal surfaces where the catalytic activity is derived from the metal itself rather than from complex metal-ligand interactions. The active sites on these metal surfaces can interact directly with the reactant molecules, facilitating various transformations. For instance, palladium nanoparticles are widely used in ligand-free systems for carbon-carbon coupling reactions, such as the Suzuki-Miyaura and Heck reactions.
