Palladium(II) complexes containing a P, N chelating ligand Part III. Influence of the basicity of tridentate hydrazonic ligands on the hydrogenating activity of unsaturated C-C bonds

摘要

Several potentially tridentate hydrazonic ligands containing a PNO donor atom set were synthesised and used to prepare the corresponding acetato palladium(II) complexes. These were used as catalysts in the homogeneous hydrogenation of styrene and other unsaturated C-C bonds under mild conditions. Depending on the basicity of the hydrazonic nitrogen of the ligand, a different catalytic activity of the complexes was observed. This substantiates a heterolytic activation of the molecular hydrogen, which leads to the protonation of the ligand and formation of a palladium(II) hydride complex. Kinetic studies of the hydrogenation of styrene in methanol were performed, using complex 1a as catalyst. A dependence, approximately of first order in hydrogen and catalyst concentrations and zero order in styrene concentration, was found. Two kinetic equations derived from a statistic processing are compared. The X-ray crystal structure of complex 1a is also reported.