Determination of the separate barrier energies for six-membered ligand ring reversal and pyramidal sulphur inversion in complexes of palladium(II) and platinum(II). A dynamic hydrogen-1 and carbon-13 nuclear magnetic resonance study

Abstract

The series of complexes trans-[MX₂{[graphic omitted]H₂)₅}₂](M = Pd; X = Cl, Br, or I; M = Pt; X = Cl) have been synthesised and, by accurate analysis of their variable-temperature ¹H and ¹³C n.m.r. spectra using total band-shape fitting methods, energy barriers for ligand ring reversal and for sulphur inversion have been separated and calculated for the first time. The barriers to ring reversal in the complexes are similar to those already known for the unco-ordinated ligand, whereas those for sulphur inversion are also similar to values known for analogous non-cyclic ligand complexes. The power of ¹³C dynamic n.m.r. spectral analysis was demonstrated by the fact that no simplifications in the conformational analyses were needed in order to account for the ¹³C spectral line changes. This was in marked contrast to the ¹H spectra, which, in order for their analyses to be possible, had to be attributed to the conformations of either six-membered heterocyclic ring rather than to total conformational structures of the complexes.