Effect of Solvent, Leaving and Entering Ligand on Substitution Rates of Square Planar Complexes of Palladium(II)

Nucleophilic substitution in different non-aqueous solvents at square planar complexes of palladium(II) with l-(2-hydroxyphenyl)-3,5-diphenylformazan ( H 2 F 0 ) according to FoPdX + Y -» FoPdY + X , with X = ammonia and pyridine and Y = triphenylphosphine, thiourea and the thiocyanate ion, obeys the rate law: rate = ki[FoPdX] + k2[FoPdX][Y]. Values of ki and k2 were obtained at 25.0 °C. From measured solubilities and literature values of transfer functions the transfer chemical potentials for initial and transition state were calculated. A comparison of these quantities in different solvents leads to the conclusion that non-specific solvation effects are dominant in these compounds. The mutual dependence of the effects of leaving and entering ligands and solvent on the substitution rate indicates a level of synchronicity of bond-breaking and bond-making that is unusually high for palladium(II) complexes.