Synthesis of Phosphonates, Phosphinates and Tertiary Phosphine Oxides by Pd- or Ni-Catalyzed Microwave-Assisted P-C Coupling Reactions without the Addition of Conventional Ligands

Microwave (MW)-assistance may be a powerful tool in the Hirao P-C coupling reactions of vinyl/aryl halides with dialkyl phosphites in the presence of Pd-catalysts/P-ligands elaborated forty years ago. This review surveys the development of this reaction by showing the expansion of the reagents and catalysts, as well as the information accumulated. The stress was laid on the green aspects, the simplification of the catalyst systems, and the reliable mechanistic details in order to be able to establish the optimum conditions. The best protocol involves the use of some excess of the >P(O)H reagent to ensure the Pd-II -> Pd-0 re-duction and, via its trivalent tautomeric form (>POH), also the P-ligand. The overall rate is the result of two factors, the activity of the catalyst complex formed, and the reactivity of the reactants in the P-C coupling reactions. The nature of the aryl substituents in Ar2P(O)H influences both components. Ni-II salts may also be used as the catalyst precursor, however, despite the Pd-II -> Pd-0 -> Pd-II route, in this case, a Ni-II -> Ni-IV -> Ni-II sequence was proved.

Automated summary

This review discusses the development of Hirao P-C coupling reactions assisted by microwaves, focusing on green chemistry aspects, simplification of mechanisms, and determination of optimal conditions.