NMR investigation of Pd(II)-Pd(0) reduction in the presence of mono- and ditertiary phosphines

The reduction of Pd(II) to Pd(0) was investigated in the presence of both monodentate (PPh3) and bidentate (dppp = 1,3-bis(diphenylphosphino)propane) phosphines. It was shown by P-31 NMR measurements that triphenylphosphine can reduce Pd(OAc)(2) to zerovalent palladium in toluene and dppp is mainly responsible for the reduction in dmf resulting in dppp hemioxide and dppp dioxide. Both mono- and bidentate coordinations of dppp in intermediate species are proposed on the basis of in situ NMR studies. In the presence of two equivalents of silver triflate, the formation of the [Pd(dppp)(PPh3)(2)](2+) square-planar complex cation has been observed without any reduction of Pd(II) to Pd(0) species. (C) 1999 Elsevier Science S.A. All rights reserved.