Voltammetric and Spectroscopic Studies Related to Platinum(II) and Platinum(IV) Dithiocarbamate Redox Chemistry: Electrochemical, ESR, and Electrospray Mass Spectrometric Identification of a Moderately Stable Platinum(III) Cation: [Pt(S2CNEt2)(η3-P2P′)]2+ (P2P′ = Ph2P(CH2)2P(Ph)(CH2)2PPh2)

Alan M. Bond, Ray Colton, Dirk A. Fiedler, Janette E. Kevekordes, Vanda Tedesco, Terence F. Mann

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Cyclic voltammetric oxidation of Pt(R2dtc)2 (R2dtc = S2CNR2 = dithiocarbamate) and reduction of [Pt(R2dtc)3]+ both failed to show evidence of a Pt(III) intermediate, even at ‒70 °C and using scan rates up to 10 000 V s-1. Under similar conditions, cyclic voltammetric reduction of a range of cis- or trans-Pt(R2dtc)2X2 complexes (X = Cl, Br, I) showed loss of halide but no evidence for Pt(III) intermediates. In contrast, cyclic voltammetric oxidation of the Pt(II) compound [Pt(η1 -S2CNEt2)(η3-P2P′)]PF6 (P2P′ = Ph2P(CH2)2P(Ph)(CH2)2PPh2) occurs at room temperature via two well-resolved one-electron-transfer processes in dichloromethane and acetone at platinum, glassy carbon, and gold electrodes. The first oxidation process is chemically and electrochemically reversible under conditions of cyclic voltammetry (scan rate = 20‒1000 mV s-1). This result suggests that the combination of a bulky tridentate phosphine ligand and a monodentate dithiocarbamate ligand enables a relatively stable monomeric Pt(III) complex [Pt(S2CNEt2)(η3-P2P′)]2+ to be formed on the voltammetric time scale. Bulk electrolysis experiments demonstrate that the dication is moderately stable on the longer synthetic time scale. An ESR spectrum obtained in frozen dichloromethane after bulk oxidative electrolysis confirms the presence of paramagnetic Pt- (III). Additionally, chemical oxidation of [Pt(η1-S2CNEt2)(η3-P2P′)]+ with [N(C6H4Br)3]SbCl6 allowed direct observation of [Pt(S2CNEt2)(η3-P2P′)]2+ in solution by electrospray mass spectrometry (ESMS). However, data obtained by ESMS and 31P NMR spectroscopy demonstrated that diamagnetic Pt(II) and Pt(IV) are the major products of the oxidation, indicating that disproportionation of [Pt(S2CNEt2)(η3-P2P′)]2+ occurs on the synthetic, but not voltammetric, time scale. The new data, combined with that from other studies, suggest that bulky ligands are required to enhance the lifetime of monomeric Pt(III) species, which are presumably present only as shortlived intermediates in the commonly observed overall two-electron Pt(IV)/Pt(II) redox reactions.

Original languageEnglish
Pages (from-to)5761-5766
Number of pages6
JournalInorganic Chemistry
Issue number25
Publication statusPublished - 1 Dec 1994

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