Fluxional characteristics of palladium(II) halide complexes of cyclic selenoethers. A dynamic nuclear magnetic resonance study

Abstract

The series of complexes [PdX₂{[graphic omitted]H₂)_n}₂s](n= 4–6; X = Cl, Br, or I) and [PdX₂{S[graphic omitted]H₂}₂](X = Cl, Br, or I) have been synthesised and their stereodynamics investigated by variable- temperature ¹H n.m.r. spectroscopy. Whereas conformational changes of the various sized ligand rings were always fast on the n.m.r. chemical shift time- scale, the rates of inversion of the co- ordinated selenium atoms were much slower and directly measurable by bandshape fitting methods. ΔG^‡ values for selenium inversion were in the range 66–78 kJ mol^–1. Values were observed to increase consistently with decreasing ligand ring size and are explained in terms of the extents of angle strain required to achieve the transition- state structure of the inversion process. The inversion energies of all four series of complexes reflect a cis halogen influence of 5.1–7.3 kJ mol^–1.