Conditions Favoring the Formation of Monomeric Pt III Derivatives in the Electrochemical Oxidation of trans ‐[Pt II {( p ‐BrC 6 F 4 )NCH 2 CH 2 NEt 2 }Cl(py)]

Characterization of the anticancer active compound trans ‐[Pt II {( p ‐BrC 6 F 4 )NCH 2 CH 2 NEt 2 }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 ‐BrC 6 F 4 )NCH 2 CH 2 NEt 2 }Cl(py)] + . Electron paramagnetic resonance spectra obtained from highly non‐coordinating dichloromethane/([Bu 4 N][B(C 6 F 5 ) 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 ‐BrC 6 F 4 )NCH 2 CH 2 NEt 2 }‐ Cl(py)], and the solvent/electrolyte. In the low‐polarity solvent CH 2 Cl 2 containing the very weakly coordinating electrolyte [Bu 4 N][B(C 6 F 5 ) 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 ‐BrC 6 F 4 )NCH 2 CH 2 NEt 2 }Cl(py)] favors the formation of monomeric [Pt III {( p ‐BrC 6 F 4 )NCH 2 CH 2 NEt 2 }Cl(py)] + . Simulations allow the reversible potential of the Pt II /Pt III process and the diffusion coefficient of [Pt III {( p ‐BrC 6 F 4 )‐ NCH 2 CH 2 NEt 2 }Cl(py)] + to be calculated. Reversible electrochemical behavior, giving rise to monomeric platinum(III) derivatives, is rare in the field of platinum chemistry.