• Shiddiky, Muhammad J. A.
• Junk, Peter C.
• Ojha, Ruchika
• Nafady, Ayman
• Mason, Dayna
• Torriero, Angel A. J.
• Deacon, Glen B.
• Bond, Alan M.
• Boas, John F.

Abstract

<p>Characterization of the anticancer active compound trans-[Pt^II{(p-BrC₆F₄)NCH₂CH₂NEt₂}Cl(py)] is described along with identification of electrochemical conditions that favor formation of a monomeric one-electron-oxidized Pt^III derivative. The square-planar organoamidoplatinum(II) compound was synthesized through a carbon dioxide elimination reaction. Structural characterization by using single-crystal X-Ray diffraction reveals a trans configuration with respect to donor atoms of like charges. As Pt^III intermediates have been implicated in the reactions of platinum anticancer agents, electrochemical conditions favoring the formation of one-electron-oxidized species were sought. Transient cyclic voltammetry at fast scan rates or steady-state rotating disc and microelectrode techniques in a range of molecular solvents and an ionic liquid confirm the existence of a well-defined, chemically and electrochemically reversible one-electron oxidation process that, under suitable conditions, generates a Pt^III complex, which is proposed to be monomeric [Pt^III{(p-BrC₆F₄)NCH₂CH₂NEt₂}Cl(py)]⁺. Electron paramagnetic resonance spectra obtained from highly non-coordinating dichloromethane/([Bu₄N][B(C₆F₅)₄]) solutions, frozen to liquid nitrogen temperature immediately after bulk electrolysis in a glove box, support the Pt^III assignment rather than formation of a Pt^II cation radical. However, the voltammetric behavior is highly dependent on the timescale of the experiments, temperature, concentration of trans-[Pt^II{(p-BrC₆F₄)NCH₂CH₂NEt₂}- Cl(py)], and the solvent/electrolyte. In the low-polarity solvent CH₂Cl₂ containing the very weakly coordinating electrolyte [Bu₄N][B(C₆F₅)₄], a well-defined reversible one-electron oxidation process is observed on relatively long timescales, which is consistent with the stabilization of the cationic platinum(III) complex in non-coordinating media. Bulk electrolysis of low concentrations of [Pt{(p-BrC₆F₄)NCH₂CH₂NEt₂}Cl(py)] favors the formation of monomeric [Pt^III{(p-BrC₆F₄)NCH₂CH₂NEt₂}Cl(py)]⁺. Simulations allow the reversible potential of the Pt^II/Pt^III process and the diffusion coefficient of [Pt^III{(p-BrC₆F₄)- NCH₂CH₂NEt₂}Cl(py)]⁺ to be calculated. Reversible electrochemical behavior, giving rise to monomeric platinum(III) derivatives, is rare in the field of platinum chemistry.</p>

Topics

• impedance spectroscopy
• compound
• Carbon
• x-ray diffraction
• experiment
• simulation
• Platinum
• Nitrogen
• cyclic voltammetry