Nuclear magnetic resonance study of inversion at sulphur and selenium atoms in complexes of palladium(II) and platinum(II). Part 2. Complexes of methyl and phenyl trimethylsilylmethyl sulphide and selenide

Abstract

Inversion barriers at sulphur and selenium atoms in organic sulphide and selenide complexes of Pd^II and Pt^II. [MY₂{XR(CH₂SiMe₃)}₂](M = Pd^II or Pt^II, Y = Cl or Br, X = S or Se, R = Me or Ph), have been measured by accurate n.m.r. band-shape methods. The energies vary within the range 51–84 kJ mol^–1 and depend to various extents on the nature of the pyramidal atom, the attached transition metal, and the organic ligand. Selenium barrier energies are 15–20 kJ mol^–1 higher than corresponding sulphur barrier energies. Detailed line-shape studies indicate that the inversion mechanism is intramolecular and occurs predominantly at single S or Se atoms. Any synchronous double inversion is of low probability and does not contribute significantly to the observed changes in n.m.r. line shape.