Formation of palladium(0) complexes from Pd(OAc)2 and a bidentate phosphine ligand (dppp) and their reactivity in oxidative addition

A Pd-0 complex is spontaneously generated from Pd(OAc)(2) and a bidentate phosphine such as dppp (1,3-bis(diphenylphosphino)propane). dppp is the reducing agent and is oxidized to the hemioxide dppp(O). The intramolecular reduction step is reversible. A stable Pd-0 complex is quantitatively formed in the presence of 2 equiv of dppp, water, and a base (NEt3). The oxidative addition of PhI gives a cationic complex, PhPd(dppp)(dppp(O))(+), in which dppp(O) behaves as a monodentate ligand. PhPd(OAc)(dppp) is formed in the presence of added AcO-. The oxidative addition of PhI is an intricate reaction whose kinetics has been investigated only in the presence of added AcO-. It involves reactive dimeric or/and monomeric Pd-0 complexes ligated by AcO- whose relative reactivity is a function of the PhI concentration.