Conditions Favoring the Formation of Monomeric PtIII Derivatives in the Electrochemical Oxidation of trans-[PtII{(p-BrC6F4)NCH2CH2NEt2}Cl(py)]

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

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Abstract

Characterization of the anticancer active compound trans-[PtII{(p-BrC6F4)NCH2CH2NEt2}Cl(py)] is described along with identification of electrochemical conditions that favor formation of a monomeric one-electron-oxidized PtIII 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 PtIII 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 PtIII complex, which is proposed to be monomeric [PtIII{(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 PtIII assignment rather than formation of a PtII cation radical. However, the voltammetric behavior is highly dependent on the timescale of the experiments, temperature, concentration of trans-[PtII{(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 [PtIII{(p-BrC6F4)NCH2CH2NEt2}Cl(py)]+. Simulations allow the reversible potential of the PtII/PtIII process and the diffusion coefficient of [PtIII{(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.

Original languageEnglish
Pages (from-to)1048-1061
Number of pages14
JournalChemElectroChem
Volume2
Issue number7
DOIs
Publication statusPublished - 15 Jul 2015

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