MECHANISM OF THE FORMATION OF PALLADIUM COMPLEXES SERVING AS CATALYSTS IN HYDROGENATION REACTIONS. II. REACTIVITY OF PALLADIUM PHOSPHINE HALIDES TOWARDS MOLECULAR HYDROGEN

Article abstract of DOI:10.1016/S0022-328X(00)85858-1

<(PPh3)3(PPh2)2Pd3Cl>Cl, benzene and aniline hydrochloride were isolated as products of the reactions of (PPh3)2PdCl2 or <(PPh3)PdCl2>2 with H2 in organic amines (Am).Similar products were obtained when (Ph3P)2Pd(Ph)Br was treated with H2 both in amines and aromatic solvents.The reaction between H2 and <(PBu3)PdCl2>2 resulted in the formation of <(PBu3)(PBu2)PdCl>2*2Am.The kinetic data for H2 absorption by solutions of palladium(II) complexes are consistent with the heterolytic mechanism of cleavage of the H-H bond in the coordination sphere of palladium(II); the function of the H⁺ acceptor being performed by the bases (e.g.Am or Ph).The reaction between the palladium complexes and H2 is autocatalytic.Reduction of the initial Pd^II complexes leads to lower oxidation state palladium complexes, which catalyse the reduction of Pd^II complexes.In the coordination sphere of the lower oxidation state palladium complexes, the oxidative addition of PR3 to Pd takes place with formation of compounds containing a Pd-R bond.It is the reaction between these complexes and H2 that yields palladium compounds with PR2 ligands.