Abstract
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.