The [RPPh3]2[Pd2X6] as a Catalyst Precursor for the Heck Cross-Coupling Reaction by in situ Formation of Stabilized Pd(0) Nanoparticles

Pd(II) anionic, square planar complexes of the type [RPPh3](2)[Pd2X2Cl4], where X = Cl, Br, have been applied for the first time as a catalyst precursor for the Heck reaction carried out in DMF at 140 degrees C. The highest yield was obtained for the most reducible ones, [MePPh3](2)[Pd2Br2Cl4], in DMF in the presence of NaHCO3 as a base. It was found that during the reaction, phosphonium halide stabilized Pd(0) nanoparticles of about 10 nm, which have been formed in situ from the palladium(II) precursor and Pd(0) colloidal nanoparticles acts as the reservoir for Pd(II) species via activation of the metal surface through the oxidative addition of aryl halides.