Coupling, organometallic phosphine ligands

C—C Coupling Reactions. This field of aqueous organometallic catalysis is dominated by the use of palladium complexes with sulfonated phosphine ligands however, iV-heterocyclic carbene complexes have also appeared on the scene (196,197). Most of the synthetic procedures were developed on a laboratory scale, where recycling of the catalyst was not a top priority. Therefore, many of the reactions were carried out in homogeneous solutions, either in water or in... 

The mechanism involves oxidative addition of the halide or triflate to the initial palladiumfO phosphine complex to form a palladium(II) species. The key slow step is a transmetallation, so calk because the nucleophile (R1) is transferred from the metal in the organometallic reagent to the palla dium and the counterion (X = halide or triflate) moves in the opposite direction. The new palladi um(II) complex with two organic ligands undergoes reductive elimination to give the couple product and the palladium(O) catalyst ready for another cycle. 

---