Crystal structures and coordination-site exchange reactions of palladium(II) and platinum(II) complexes containing tris[2-(tert-butylthio)ethyl]amine

Palladium(II) and platinum(II) complexes, [PdX(NS3 1Bu)]BPh4 (X=Cl, Br, I; NS3 1Bu=tris[2-(tert-butylthio)ethyl]amine) and [PtCl(NS3 1Bu)]BPh4, were prepared, and their structures were determined by X-ray analyses. The geometry around the palladium and platinum atoms is square planar. The NS3 1Bu ligand functions as a tridentate ligand and one sulfur atom is not coordinated to the metal. The 1H NMR spectrum of [PdCl(NS3 1Bu)]BPh4 in acetone-d6 exhibited a dynamic behavior. At 20°C the spectrum showed a singlet signal at 1.60 ppm that can be assigned to tert-butyl protons, whereas at −70°C three singlet signals were observed at 1.36, 1.61, and 1.70 ppm with an intensity ratio of 1: 0.25: 2. The signals at 1.36 and 1.70 ppm are assigned to the tert-butyl protons in the square-planar structure, and these signals are consistent with the X-ray structure. The signal at 1.61 ppm can be assigned to the tert-butyl protons in a trigonal-bipyramidal structure where the three tert-butyl groups are magnetically equivalent. Thus, we concluded that the coordination-site exchange occurred via a trigonal-bipyramidal intermediate. The square-planar and trigonal-bipyramidal species of [PdCl(NS3 1Bu)]BPh4 are in equilibrium in acetone-d6. The equilibrium was shifted toward the square-planar species on decreasing the temperature. The 1H NMR spectra for [PdX(NS3 1Bu)]BPh4 (X=Cl, Br, and I) were similar to one another at the same temperature, suggesting that the site-exchange process is insensitive to the kind of coexisting halogen ligand. The site exchange reaction of [PtCl(NS3 1Bu)]BPh4 seems to occur more slowly than that of the palladium(II) analogue.