Ionic Liquids in Palladium-Catalyzed Cross-Coupling Reactions

This chapter surveys the most significant developments in the field of palladium-catalyzed cross-coupling reactions in ionic liquids. The beneficial effect of the ionic liquids in terms of activity, selectivity, and recyclability is commented for all types of reactions discussed, namely the Heck, Suzuki–Miyaura, Stille, Sonogashira, Ullmann, and Negishi cross-couplings. Insights into the reaction mechanisms reveal that the effect of the ionic liquid on C–C bond forming reactions manifests itself not only in the energy lowering of polar transition states (or intermediates) involved in the catalytic cycles but also, depending on the cases, in the stabilization of palladium nanoparticles, the synthesis of molecular Pd complexes with the IL anions, the enhancement of the chemical reactivity of reactants, and others. The synergistic effect found by using appropriate mixtures of ionic liquids is also discussed.