Palladium(II)-Induced Activation of Carbon-Nitrogen Single Bond of Coordinated N4S Ligand. Characterization of Product with Modified Ligand Structure: Kinetics versus Thermodynamic Considerations

The pentadentate N4S ligands, methyl ((2-(â-bis((3,5-dimethylpyrazol-1-yl)methyl)amino)ethyl)amino)cyclopent-1-ene1-dithiocarboxylate (Hmmecd) and its propyl homologue (Hmmpcd)1 with pendent pyrazolyl groups, offer interesting variations in their coordination behavior with the available metal ion types. With copper(II), zinc(II), and cobalt(II) ions, the ligands use all five potential donor sites to form pentacoordination complexes of distorted geometries. Transformation from a tetragonal to trigonal structure becomes apparent when the copper(II) complex is doped (5%) into its zinc(II) counterpart as revealed from EPR and electronic spectral studies.2 In the case of nickel(II), however, the ligand molecules undergo alcoholysis reaction through the activation of C-N single-bond linkage.3 The products obtained are square planar complexes with modified ligand structures, involving N3S donor set and a pendent arm that holds the alkoxy group provided by the solvent. When the complexation reaction with Ni(II) is carried out in solvents other than alcohol, the product obtained is intractable solid of unknown composition. To gain further insight into the mechanistic aspect of this unprecedented alcoholysis reaction as observed earlier with nickel(II),3 comparable studies have been extended to palladium(II) system. It was anticipated that palladium(II) being kinetically more inert, there would be opportunities for the isolation and characterization of the compound(s) formed during the alcoholysis process. Herein, we report the syntheses, crystal structure and spectroscopic characterization of square planar palladium(II) complexes obtained during this solvolysis process. Mechanistic implications of the formation of these products are also described.