VOLTAMMETRIC AND SPECTROSCOPIC STUDIES RELATED TO PLATINUM(II) AND PLATINUM(IV) DITHIOCARBAMATE REDOX CHEMISTRY - ELECTROCHEMICAL, ESR, ANDELECTROSPRAY MASS-SPECTROMETRIC IDENTIFICATION OF A MODERATELY STABLEPLATINUM(III) CATION - [PT(S(2)CNET(2))(ETA(3)-P2P')](2+) (P2P'=PH(2)P(CH2)(2)P(PH)(CH2)(2)PPH(2))

Cyclic voltammetric oxidation of Pt(R(2)dtc)(2) (R(2)dtc = S(2)CNR(2) = dithiocarbamate) and reduction of [Pt(R(2)dtc)(3)](+) both failed to show evidence of a Pt(III) intermediate, even at -70 degrees C and us ing scan rates up to 10 000 V s(-1). Under similar conditions, cyclic voltammetric reduction of a range of cis- or trans-Pt(R(2)dtc)(2)X(2) 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(eta(1)-S(2)CNEt(2))(eta(3)-P2P')]PF6 (P2P' = Ph(2 )P(CH2)(2)P(Ph)(CH2)(2)PPh(2)) occurs at room temperature via two well -resolved one-electron-transfer processes in dichloromethane and aceto ne at platinum, glassy carbon, and gold electrodes. The first oxidatio n process is chemically and electrochemically reversible under conditi ons of cyclic voltammetry (scan rate = 20-1000 mV s(-1)). This result suggests that the combination of a bulky tridentate phosphine Ligand a nd a monodentate dithiocarbamate ligand enables a relatively stable mo nomeric Pt(III) complex [Pt(S(2)CNEt(2))(eta(3)-P2P')](2+) to be forme d on the voltammetric time scale. Bulk electrolysis experiments demons trate that the dication is moderately stable on the longer synthetic t ime scale. An ESR spectrum obtained in frozen dichloromethane after bu lk oxidative electrolysis confirms the presence of paramagnetic Pt(III ). Additionally, chemical oxidation of [Pt(eta(1)-S(2)CNEt(2))(eta(3)- P2P')](+) with [N(C6H4Br)(3)]SbCl6 allowed direct observation of [Pt(S (2)CNEt(2))(eta(3)-P2P')](2+) in solution by electrospray mass spectro metry (ESMS). However, data obtained by ESMS and P-31 NMR spectroscopy demonstrated that diamagnetic Pt(II) and Pt(IV) are the major product s of the oxidation, indicating that disproportionation of [Pt(S(2)CNEt (2))(eta(3)-P2P')](2+) occurs on the synthetic, but not voltammetric, time scale. The new data, combined with that from other studies, sugge st that bulky ligands are required to enhance the lifetime of monomeri c Pt(II) species, which are presumably present only as short-lived int ermediates in the commonly observed overall two-electron Pt(IV)/Pt(II) redox reactions.