Palladium Nanoparticles in Polyols: Synthesis, Catalytic Couplings, and Hydrogenations

Alcohols, in particular polyols, are well-known for the synthesis of metal nanoparticles, often acting as reducing agents, solvents, and stabilizers. Given not only their structural flexibility depending on the number of OH functions and their inherent H bonding interactions, but also the wide range of polyol molecular weights readily available, different physicochemical properties (boiling point, polarity, viscosity) could be exploited toward the synthesis of well-defined nanomaterials. In particular, the relevance of the supramolecular structure of polyols has a fundamental impact on the formation of metal nanoparticles, thereby favoring the dispersion of the nanoclusters. In the field of the metal-based nanocatalysis, palladium occupies a privileged position mainly due to its remarkable versatility in terms of reactivity representing a foremost tool in synthesis. In this review, we describe the controlled synthesis of Pd-based nanoparticles in polyol medium, focusing on the progress in terms of tailoring size, morphology, structure, and surface state. Moreover, we discuss the use of palladium nanoparticles, in a polyol solvent, applied in two of the most relevant Pd-catalyzed processes, i.e., couplings and hydrogenation reactions, including multistep processes.