Vanda Tedesco

The electrochemical oxidation of cobalt tris(dithiocarbamates) and tris(diselenocarbamates) in acetonitrile; a combined spectroscopic and voltammetric study

Abstract The electrochemical oxidation of cobalt(III) dithiocarbamates and diselenocarbamates (CoL 3 ) in acetonitrile+0.1 M Bu 4 NPF 6 is shown to occur via the mechanism: (E) CoL 3 ↔[CoL 3 ] + +e − ; (C 2 ) 2[CoL 3 ] + →[Co 2 L 5 ] + +oxidized ligand; (C) [Co 2 L 5 ] + +2CH 3 CN→CoL 3 +[CoL 2 (CH 3 CN) 2 ] + . A combination of electrochemical, electrospray mass spectrometry, and 59 Co/ 77 Se NMR experiments confirms that the binuclear species, [Co 2 L 5 ] + , reacts with acetonitrile forming CoL 3 and [CoL 2 (CH 3 CN) 2 ] + . At the electrode surface, CoL 3 species generated by this reaction may then be reoxidised resulting in an enhanced peak or limiting current. Consequently, the oxidation of CoL 3 in acetonitrile represents an overall EC 2 C mechanism. The data obtained from cyclic voltammetry at Pt disc electrodes and steady-state hydrodynamic voltammetry at platinum channel electrodes for oxidation of CoL 3 were modelled according to this EC 2 C scheme using the commercial DigiSim electrochemical simulation package and the backwards implicit finite difference technique, respectively. Good fits between experiment and simulation were obtained using the same kinetic parameters for both methods. The calculated dimerisation rate constant (C 2 step) is similar to the value obtained in dichloromethane, which is uncomplicated by reaction of [Co 2 L 5 ] + with the solvent. It was observed that if either voltammetric technique was used in isolation, a wider range of combinations of kinetic parameters could be utilised in order to obtain satisfactory fits between experiment and theory.

Electrochemistry of dimeric organopalladium(II) complexes containing bridging [pyridin-2-yl(phenyl)methyl-C,N]− and [bis(pyridin-2-yl)phenylmethyl-C,N,N′]− groups

The electrochemistry of the palladium(II) dimers [Pd(CHPhpy)(L)Cl]2 (L = 4-methylpyridine (4-Mepy) (1a), 3,4-dimethylpyridine (3,4-Me2py) (1b), 3,5-dimethylpyridine (3,5-Me2py) (1c), 2-benzylpyridine (2-Bzpy) (1d) and [Pd(CPhpy2)Cl]2 (2) has been investigated in dichloromethane and acetonitrile. Under cyclic voltammetric conditions, complexes 1 were found to undergo a chemically reversible one electron oxidation at moderate scan rates in dichloromethane and fast scan rates in acetonitrile. The reversible potential of this process is essentially solvent independent. A second, solvent dependent, irreversible one electron oxidation is observed at more positive potentials. The following equation summarises the short time domain data: [Pd(II)Pd(II)][Pd(III)Pd(II)]+[Pd(III)Pd(III)]2+[L-Pd(III)Pd(III)-L]n+→Products In the presence of a coordinating ligand, the first oxidation becomes a two electron process on the synthetic timescale presumably leading to a [Pd(III)Pd(III)] dimer with a metal-metal interaction while the coordinating ligand occupies the vacant axial site on each palladium atom. Thus, long time domain electrochemical experiments occur via a different mechanism. For the formation of both one electron and two electron oxidation products, it is possible that oxidation of the ligand rather than metal centres has occurred. If Pd(III) centres are formed then metal-metal bond formation may occur to give bond orders of 0.5 for [Pd(III)Pd(II)]+ and 1.0 for [Pd(III)Pd(III)]2+. Complex 2 exhibits essentially the same electrochemical behaviour as complexes 1 except that the one electron oxidative product [Pd(III)Pd(II)]+ is more stable. Thus, evidence for oxidation state +III for organopalladium complexes has been obtained, but no further oxidation to Pd(IV) was observed.

Novel features associated with the electrochemically driven bis(η5-pentaphenylcyclopentadienyl)iron(II)–iron(III) redox transformation at an electrode–microcrystal–solvent (electrolyte) interface

Abstract Electrochemical oxidation of microcrystals of the iron(II) compound, Fe(η 5 -C 5 Ph 5 ) 2 and reduction of the corresponding iron(III) [Fe(η 5 -C 5 Ph 5 ) 2 ]BF 4 salt, mechanically attached to graphite and gold electrodes placed in aqueous media and in a (70:30) water:acetonitrile solvent mixture containing electrolyte has been investigated by voltammetric, electrochemical quartz crystal microbalance, and micro-analytical techniques. When interconversion of Fe(η 5 -C 5 Ph 5 ) 2 to [Fe(η 5 -C 5 Ph 5 ) 2 ]X (X − =ClO 4  − , BF 4  − , Cl − , F − ) and vice versa occurs at the microcrystal–electrode–aqueous electrolyte interface via redox cycling of the electrode potential, then the reaction can be summarised by the process [ Fe ( η 5 - C 5 Ph 5 ) 2 ] + [ X − ] ( solid ) + e − ⇌Fe ( η 5 - C 5 Ph 5 ) 2( solid ) + X − ( solution ) However, when CH 3 CN (in aqueous 0.1 M NaClO 4 ) is present at the interface, data obtained are consistent with co-insertion of the organic solvent into the structure to give formally the [Fe(η 5 -C 5 Ph 5 ) 2 ] 1+/0.5+/0  (solid) redox system containing interacting iron atoms in the solid structure. The formation of the new phase is voltammetrically associated with the conversion from the single chemically reversible one electron [Fe(η 5 -C 5 Ph 5 ) 2 ] +/0 process with a large separation in reduction and oxidation peak potentials ( E p  red =385 mV, E p  ox =980 mV) to two formally 0.5 electron processes with more closely spaced peak potentials (first 0.5 electron reduction: E p  red =665 mV, E p  ox =715 mV; second 0.5 electron reduction: E p  red =545 mV, E p  ox =610 mV). Mechanistic aspects of the substantial changes that are introduced by the incorporation of acetonitrile into the solid state structure are discussed.

ELECTRON-, ANION-, AND PROTON-TRANSFER PROCESSES ASSOCIATED WITH THE REDOXCHEMISTRY OF FE(ETA 5-C5PH5)((ETA 6-C6H5)C5PH4 AND ITS PROTONATED FORM FE(E TA 5-C5PH5)((ETA 6-C6H5)C5PH4H)BF4 AT MICROCRYSTAL-ELECTRODE-SOLVENT (ELECT ROLYTE) INTERFACES

Voltammograms of microcrystals of Fe(η5-C5Ph5)((η6-C6H5)C5Ph4) and [Fe(η5-C5Ph5)((η6-C6H5)C5Ph4H)]BF4 mechanically attached to graphite or gold electrodes are well-defined when the electrode is placed in (70:30) water/acetonitrile (0.1 M electrolyte) media. The simplest processes at the electrode−solvent (electrolyte) interface are the chemically reversible oxidation of Fe(η5-C5Ph5)((η6-C6H5)C5Ph4), Fe(η5-C5Ph5)((η6-C6H5)C5Ph4)(solid) + X-(solution) ⇌ [Fe(η5-C5Ph5)((η6-C6H5)C5Ph4)][X](solid) + e- when X- is the electrolyte anion (ClO4-, BF4-, Cl-, or F-), and the chemically reversible reduction of [Fe(η5-C5Ph5)((η6-C6H5)C5Ph4H)]BF4, [Fe(η5-C5Ph5)((η6-C6H5)C5Ph4H)][BF4](solid) + e- ⇌ Fe(η5-C5Ph5)((η6-C6H5)C5Ph4H)(solid) + BF4-(solution), when BF4- is the electrolyte anion. Anion exchange between BF4-(solid) in [Fe(η5-C5Ph5)((η6-C6H5)C5Ph4H)]BF4 and the electrolyte anion, X-(solution), is rapid so that the potentials of both processes are dependent on the electrolyte anion. Cyclic voltammograms scanned over...