Facile aerobic oxidation of dpms-platinum(II) ethylene complexes (dpms = di(2-pyridyl)methanesulfonate)

Di(2-pyridyl)methanesulfonato hydroxo platinum(II) ethylene complex 4b, LPtII(C2H4)OH, reacts readily with oxygen in aqueous solution to cleanly produce unsymmetrical 2-hydroxyethyl platinum(IV) complex unsym-6b, LPtIV(C2H4OH)(OH)(2). The latter eliminates ethylene oxide and ethylene glycol in virtually quantitative yield in neutral aqueous solution at 80 degrees C and produces the dinuclear mu-hydroxo platinum(II) complex 7 as another reaction product. The oxidation reaction was shown to proceed via an anionic 2-hydroxyethyl hydroxo platinum(II) intermediate, 5b. The chloro analogues 4a and 5a are inert toward dioxygen but can be converted to 6b under air in the presence of 1 equiv of NaOH. As established by DFT calculations, both the formal charge on the platinum(II) center and the nature of ligands coordinated to it have a crucial effect on the energy of the HOMO of the complexes, which may be related to their ability to undergo an aerobic oxidation.