768368-04-3Relevant academic research and scientific papers
Mechanistic studies on monodentate-ligand substitution of five-coordinate trigonal-bipyramidal platinum (II) complexes with tris[2-(diphenylphosphino) ethyl]phosphine
Aizawa, Sen-Ichi,Kobayashi, Tadashi,Kawamoto, Tatsuya
, p. 2319 - 2326 (2005)
Reaction of the five-coordinate trigonal-bipyramidal platinum(II) complex, [Pt(pt)(pp3)](BF4) (pt = 1-propanethiolate, pp3 = tris[2-(diphenylphosphino)ethyl]phosphine), with I- in chloroform gave the five-coordinate square-pyramidal complex with a dissociated terminal phosphino group and an apically coordinated iodide ion in equilibrium. The thermodynamic parameters for the equilibrium between the trigonal-bipyramidal and square-pyramidal geometries, [Pt(pt)(pp3)]+ + I - ? [PtI(pt) (pp3)], and the kinetic parameters for the chemical exchange were obtained as follows: Kex298=7.5×10-1mol-1kg, ΔH0 = - 10 ± 2.4 kJ mol-1, ΔS 0 = - 36 ± 10 J K-1 mol-1, kex298=1.3×104s-1, ΔH? = 34 ± 4.7 kJ mol-1, ΔS? = - 50 ± 21 J K -1 mol-1. The square-planar trinuclear platinum(II) complex was formed by bridging reaction of one of the terminal phosphino groups of trigonal-bipyramidal [PtCl(pp3)]Cl with trans-[PtCl 2(NCC6H5)2] in chloroform. From these facts, ligand substitution reactions of [PtX(pp3)]+ (X = monodentate anion) are expected to proceed via an intermediate with a dissociated phosphino group. The rate constants for the chloro-ligand substitution reactions of [PtCl(pp3)]+ with Br- and I- in chloroform approached the respective limiting values as concentrations of the entering halide ions are increased. These kinetic results confirmed the preassociation mechanism in which the square pyramidal intermediate with a dissociated phosphino group and an apically coordinated halide ion is present in the rapid pre-equilibrium.
