Kinetic studies on thiolato-ligand substitution reactions with halide ions of square-planar palladium(II) complex with bis(2-(diphenylphosphino)ethyl)phenylphosphine

The square-planar thiolato palladium(II) complex with a terdentate phosphine bound ligand, [Pd(pt)(p₃)](BF₄) (p₃=bis(2-(diphenylphosphino)ethyl)phenylphosphine, pt=1-propanethiolate) has been synthesized and characterized by ³¹P NMR spectroscopy. The solid state structure of [PdI(p₃)]I was determined by an X-ray crystal structure analysis. The kinetic parameters for the thiolato-ligand substitution reactions with halide ions, [Pd(pt)(p₃)]⁺+X^-→[PdX(p₃)] ⁺+pt^- (X^-=Cl^-, Br^-, I^-), in chloroform were obtained as follows: k²⁹⁸=7.22, 1.68 and 10.1×10^-4 s^-1, ΔH^‡=67±2, 56±2 and 63±3 kJ mol^-1 and ΔS^‡=-80±7, -128±6 and -92±11 J mol^-1 K^-1, respectively. These kinetic results are compared with those for the corresponding reactions of the trigonal-bipyramidal complex with an analogous phosphine bound ligand, [Pd(pt)(pp₃)](BF₄) (pp₃=tris(2-(diphenylphosphino)ethyl)phosphine).