Formation and Role of Palladium Chalcogenide and Other Species in Suzuki-Miyaura and Heck C-C Coupling Reactions Catalyzed with Palladium(II) Complexes of Organochalcogen Ligands: Realities and Speculations

Palladium(II) complexes of organochalcogen ligands have emerged as viable alternatives to complexes of phosphine/carbene ligands for Suzuki-Miyaura and Heck C-C cross coupling reactions, as thermal stability and air and moisture sensitivity are not impediments with many of them. Sometimes they outperform their phosphorus analogues. The ease in handling and synthesis of palladium(II) complexes of organochalcogen ligands has made them attractive. For such complexes in situ generation of palladium containing nanoparticles (NPs) or palladium(0) species and their role in catalysis have been reported. However, in a large number of reports such species are ill defined or speculated, particularly due to limited experimental investigations. Recently in some cases in situ generated palladium species have been studied in detail to establish their identities, which appear to be palladium chalcogenides phases or Pd(0) protected with organochalcogen fragments. In this review the current status regarding in situ generated such species is summarized and critically analyzed to demarcate realities from speculative propositions.