Synthesis and nuclear magnetic resonance investigation of 1-phenylpropane-1,2-dione 2-oxime complexes of trimethylplatinum(IV)

Abstract

The ionised monoxime 1-phenylpropane-1,2-dione 2-oximate (ppdm) reacted smoothly with trimethylplatinum(IV) sulfate in aqueous acetone to form the complex fac-[PtMe₃(ppdm)(H₂O)]1 in high yield. Complex 1 reacted with 3,5-dimethylpyridine (dmpy) and 2,2′-bipyridine (bipy) to form stable 1 : 1 adducts, viz. fac-[PtMe₃(ppdm)(dmpy)]2 and fac-[PtMe₃(ppdm)(bipy)]3. In complexes 1 and 2 the ionised monoxime behaves as a N,O bidentate chelate, whereas in 3 ppdm is co-ordinated to the metal in a monodentate fashion, via the N-donor atom. The parent complex 1 dissolves in polar solvents to form species of general formulae fac-[PtMe₃(ppdm)(solv)](solv = Me₂SO, methanol or acetone), which undergo an intramolecular ‘windscreenwiper’ fluxional rearragement. The stereodynamics of the fluxional process have been measured in CD₃OD and (CD₃)₂SO solution by two-dimensional exchange spectroscopy; ΔG^‡(298 K) is 73.6 kJ mol^–1 and 88.5 kJ mol^–1, respectively. The effects of the solvent on the energetics and a possible mechanism for the fluxional process are discussed.