A two-dimensional nuclear magnetic resonance exchange study of the fluxionality of [PtIMe3(MeSCH2CH2SEt)]
Abstract
Two-dimensional n.m.r. exchange spectroscopy has been used to measure the kinetics of four-site exchange associated with pyramidal sulphur inversion in the complex [PtIMe3(MeSCH2CH2SEt)]. Ethyl sulphur inversion occurs more readily than methyl sulphur inversion with ΔG‡ values for the processes differing by 3.3–7.2 kJ mol–1 depending on which pathways are considered. Application of the same n.m.r. method to the three-site exchange of the Pt-methyl groups has led to ΔG‡ values of 90.9 ± 0.5, 92.6 ± 0.4, and 97.7 ± 1.9 kJ mol–1. The first two values are attributed to ligand (180°)/PtMe3(120°) correlated rotations, the different values depending on which equatorial Pt-methyl group is interchanged. The third ΔG‡ value, arising from direct exchange of the two equatorial Pt-methyl environments, refers to independent ligand rotation and/or Pt-methyl scrambling.