Kinetic data on the synergetic role of amines and water in the reduction of phosphine-ligated palladium(II) to palladium(0)

Tertiary amines such as EtN(iPr)₂ do not reduce [PdCl ₂(PPh₃)₂] into a Pd⁰ complex. The latter is formed only after the addition of water (generation of HO ^-), as was reported by Grushin and Alper for NEt₃. The mechanism of the Pd^II/Pd⁰ reduction performed in the presence of an excess amount of PPh₃ is established quantitatively by means of electrochemical techniques that provide kinetic data (determination of the equilibrium and rate constants) for the disappearance of [PdCl ₂(PPh₃)₂] and the formation of [Pd ⁰(PPh₃)₃]. [PdCl(OH)(PPh₃) ₂] is formed, which allows reductive elimination between OH and the ligated PPh₃ (zero-order reaction for PPh₃), and this leads to a Pd⁰ complex. The reducing agent is ligated PPh ₃, which ultimately yields (O)PPh₃. The rate of the overall reduction process is controlled by the amount of water that imposes the concentration of HO^-.