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.