Electrochemical and chemical oxidation of the antitumour agent [Pt{((p-HC6F4)NCH2)2}(py)2] – detection of platinum(III) intermediates

The electrochemical (platinum and glassy carbon electrodes, cyclic and rotating disk electrode voltammetry, bulk electrolysis, voltammetric simulation) and chemical oxidation (NO+) of the organoamidoplatinum(II) complex, [Pt{((p-HC6F4)NCH2)2}(py)2], has been studied in acetonitrile and acetone. The initial process is a complicated function of concentration, temperature, and method of oxidation. The products formed have been probed by in situ spectroelectrochemical techniques (UV/Visible and EPR spectroscopy), and ex situ by 1H, 19F and 195Pt NMR spectroscopy and electrospray mass spectrometry. Under conditions of cyclic voltammetry, the initial oxidation process (at high concentration) is an overall irreversible one-electron process, complicated by crossover of current on the reverse scan. This and many (but not all) features are simulated by a sequence of electron transfer steps and coupled chemical reactions which requires the formation of two structurally different dinuclear intermediates. Regeneration of [Pt{((p-HC6F4)NCH2)2}(py)2] by reduction is possible under short timescale conditions, but not long timescale conditions, implying that the finally observed product from long timescale experiments may be oligomeric. The observation of moderately stable diamagnetic diplatinum(III) compounds is attributed to the formation of bridged complexes containing Pt-Pt bonds. Oxidation of all platinum(III) intermediates gives rise to the same or very closely related platinum(IV) complexes. Features of the organoamide ligand that enable the formation of moderately stable platinum(III) complexes are considered.