Dynamic nuclear magnetic resonance study of the effects of cis-chelate ligands on 1,2-metallotropic shifts in trimethylplatinum(IV) complexes of pyridazine

The complexes fac-[PtMe3(L–L)(pydz)][BF4](L–L = neutral bidentate chelate ligand; pydz = pyridazine) were readily prepared from fac-[PtlMe3(L–L)] by the action of silver(I) salts in the presence of an excess of pyridazine. Pyridazine is acting as a monodentate ligand, which undergoes a facile 1,2-metallotropic shift between the two equivalent, contiguous nitrogen donor atoms. The solutionstate stereodynamics of these complexes have been elucidated by two-dimensional exchange spectroscopy and accurate activation parameters deduced. Energy barriers [ΔG‡(298 K)] are in the range 58–78 kJ mol–1. The effects of the chelate ligand on the energetics of the fluxional shift are discussed and rationalised. The crystal structure of fac-[PtMe3(bipy)(pydz)][BF4](bipy = 2,2′-bipyridyl) was determined to confirm the fac-octahedral co-ordination geometry of the complexes.