Effect of variation in ligand ring size upon the inversion barrier at sulphur in complexes of palladium(II) and platinum(II). A dynamic hydrogen-1 nuclear magnetic resonance study

Abstract

The series of complexes trans-[MX₂{[graphic omitted]R₂)_n}₂](M = Pd^II or Pt^II; X = Cl, Br, or I; R = H and/or Me; n= 2–5) have been synthesised, and accurate analysis of their variable-temperature n.m.r. spectra by band-shape fitting methods has been used to determine the barrier to pyramidal inversion at the sulphur atom. Barrier energies in chloro-complexes are 2–3 kJ mol^–1 higher than in the corresponding bromides, which are in turn 4–5 kJ mol^–1 higher than in the iodo-complexes. The pyramidal inversion energies are very dependent upon ligand ring size; those for five- and six-membered rings are comparable with complexes of linear sulphides, but the complexes of four-membered rings show a considerable heightening of the pyramidal sulphur inversion barrier. For the complexes of the three-membered ring sulphides no inversion was detectable up to the temperature where decomposition commenced, this being the first reported example of such rigidity in dialkyl sulphide metal complexes.