Oxidation of the Platinum(II) Anticancer Agent [Pt{(p-BrC₆F₄)NCH₂CH₂NEt₂}Cl(py)] to Platinum(IV) Complexes by Hydrogen Peroxide

Pt^IV coordination complexes are of interest as prodrugs of Pt^II anticancer agents, as they can avoid deactivation pathways owing to their inert nature. Here, we report the oxidation of the antitumor agent [Pt^II(p-BrC₆F₄)NCH₂CH₂NEt₂}Cl(py)], 1 (py = pyridine) to dihydroxidoplatinum(IV) solvate complexes [Pt^IV{(p-BrC₆F₄)NCH₂CH₂NEt₂}Cl(OH)₂(py)].H₂O, 2·H₂O with hydrogen peroxide (H₂O₂) at room temperature. To optimize the yield, 1 was oxidized in the presence of added lithium chloride with H₂O₂ in a 1:2 ratio of Pt: H₂O_2, in CH₂Cl₂ producing complex 2·H₂O in higher yields in both gold and red forms. Despite the color difference, red and yellow 2·H₂O have the same structure as determined by single-crystal and X-ray powder diffraction, namely, an octahedral ligand array with a chelating organoamide, pyridine and chloride ligands in the equatorial plane, and axial hydroxido ligands. When tetrabutylammonium chloride was used as a chloride source, in CH₂Cl₂, another solvate, [Pt^IV{(p-BrC₆F₄)NCH₂CH₂NEt₂}Cl(OH)₂(py)].0.5CH₂Cl_2, 3·0.5CH₂Cl₂, was obtained. These Pt^IV compounds show reductive dehydration into Pt^II [Pt{(p-BrC₆F₄)NCH=CHNEt₂}Cl(py)], 1H over time in the solid state, as determined by X-ray powder diffraction, and in solution, as determined by ¹H and ¹⁹F NMR spectroscopy and mass spectrometry. 1H contains an oxidized coordinating ligand and was previously obtained by oxidation of 1 under more vigorous conditions. Experimental data suggest that oxidation of the ligand is favored in the presence of excess H₂O₂ and elevated temperatures. In contrast, a smaller amount (1Pt:2H₂O₂) of H₂O₂ at room temperature favors the oxidation of the metal and yields platinum(IV) complexes.