Pd(0) nanoparticles (NPs) as catalysts in cross-coupling reactions and the homogeneous vs. heterogeneous debate

The use of transition metal catalysts for the formation of new C-C bonds is one of the most important reactions in organic synthesis. Palladium has undoubtedly been the metal of choice for most of these transformations. The bulk of research has involved homogeneous catalysis. More recently heterogeneous catalysis for C-C bond formation has been identified as an alternative methodology, offering many advantages. In this respect, the use of nanoparticles will become increasingly common as they display excellent surface area to volume ratios. The ability of nanoparticles to catalyse coupling reactions also poses some interesting mechanistic questions. Ultimately however, easy catalyst recovery and reuse will be crucial to the success of the evolving field. This chapter reviews the preparation of Pd-nanoparticles, their use in C-C coupling reactions (paying particular attention to Suzuki-Miyaua coupling) and the difficulties in identifying truly hetereogeneous catalysis.