Controlled-potential Bulk Electrolysis Research Articles

Cobalamin-Mediated Electrocatalytic Reduction of Ethyl Chloroacetate in Dimethylformamide

The catalytic reduction of ethyl chloroacetate (ECA) by hydroxocobalamin (HOCbl) in dimethylformamide was studied electrochemically and spectroelectrochemically to identify initial steps in the reaction between the electrogenerated Co(I) center of cobalamin (cob(I)alamin) and ECA. Cyclic voltammograms of HOCbl in the presence of ECA show a small increase in current related to reduction of Co(II) to Co(I), and a new peak at more negative potentials related to reduction of an ethyl carboxymethyl-Cbl intermediate. The oxidation state of HOCbl during catalysis was monitored by means of spectroelectrochemical controlled-potential bulk electrolysis. Addition of ECA to electrogenerated cob(I)alamin initially generates the Co(II) form (cob(II)alamin) followed by a gradual formation of an ethyl carboxymethyl-Cbl intermediate. Controlled-potential bulk electrolysis was performed to identify products formed from catalytic reduction of ECA by electrogenerated cob(I)alamin and quantify the number of electrons transferred per molecule of ECA. Product distributions and coulometric results, together with the results of voltammograms and spectroelectrochemical controlled–potential bulk electrolysis, were interpreted to propose a reaction mechanism.

Electrochemical Investigation of some Flavonoids in Aprotic Media

AbstractCyclic voltammerty data for the oxidation of 15 flavonoids in acetonitrile have been presented. Up to three peaks in different potential regions appear in the CV curves, depending on the structure of a flavonoid. The peak in the first potential region (+0.79÷+1.03 V vs SCE) occurs when a flavonoid molecule has an o‐dihydroxy moiety in the ring A or B. From the data in the literature, the formation of o‐quinone is responsible for the occurrence of the peak. When the o‐dihydroxy moiety is in ring B and the hydroxyl group is at position 3, the second peak in the potential region+1.08÷+1.32 V, is present. It is an agreement that the peak is due to oxidation of benzofuranone derivative formed in reaction of o‐quinone with water. Molecules with an o‐quinone moiety located in ring A seem to be less reactive, and the peak in the second potential region does not occur. However, the existence of an o‐quinone in the ring B is not necessary for the peak in the second potential region to be present. The oxidation of kaempferol and morin, which have hydroxyl groups at positions 3 and 4’, takes place at 0.98 V and 0.97 V, respectively, and leads to the formation of p‐quinone methide. We have shown that the peak in the second potential region also appears when the hydroxyl group in the flavonoid molecule is only at position 3 or at position 4’. For 3‐hydroxyflavone and apigenin, which are oxidized at +1.10 V and 1.49 V respectively, p‐quinone methide was detected after controlled potential bulk electrolysis. A mechanism which includes the reaction of the carbon radical with a trace of water has been proposed. For flavonoids that have an o‐dihydroxy moiety in ring B and the hydroxyl group at position 3, two oxidation peaks are observed in the CV curves in the second potential region for low scan rates (below 0.1 V s−1). An explanation of this behavior has been proposed.

Iron complex of a quadruply fused porphyrin: Synthesis, structure and redox properties

An iron(II) complex of a quadruply ring-fused porphyrin (QFP), Fe-1, in which four mesityl groups were introduced at the periphery to improve the solubility in organic solvents, has been newly synthesized and characterized. In the pyridine solution, two pyridine molecules bind to the low-spin Fe[Formula: see text] center of Fe-1 as axial ligands to make the complex stable even under air. Characterization of Fe-1 was performed using 1H NMR spectroscopy, MALDI-TOF-MS spectrometry and single-crystal X-ray diffraction analysis. The 1H NMR signals of Fe-1 were observed in the diamagnetic region, reflecting the low-spin state of the FeII center. In the differential pulse voltammogram of Fe-1, three oxidation waves and four reduction waves were observed in pyridine; the first oxidation wave at -0.08 V vs. Fc/Fc[Formula: see text] can be ascribed to the oxidation process of the FeII center, FeII/FeIII, and other six waves can be assigned to the redox processes of the QFP ligand. Furthermore, the ESR measurement of 1e[Formula: see text]-reduced Fe-1 upon controlled-potential bulk electrolysis in pyridine exhibited a signal at [Formula: see text] = 2.003 with a well-resolved 45-line hyperfine splitting at room temperature, due to the coupling with four nitrogen nuclei and twelve hydrogen ones of the QFP ligand. This indicates that the ligand radical anion of Fe-1 is stabilized by delocalization of the spin density owing to the peripheral ring fusion and resultant expansion of the [Formula: see text]-conjugation.

Electroreductive dechlorination of γ-Hexachlorocyclohexane catalyzed by Rh2(dpf)4 in nonaqueous media, where dpf = N,N′-Diphenylformamidinate (1-) ion

The electroreductive dechlorination of γ-hexachlorocyclohexane (lindane) was investigated in non-aqueous media using as a catalyst the dirhodium complex Rh2(dpf)4, where dpf=the anion of N, N′-diphenylformamidinate. Rh2(dpf)4 undergoes two reversible one-electron redox processes in pyridine and/or N,N′-dimethylformamide (DMF), corresponding respectively to Rh24+/Rh25+ and Rh24+/Rh23+. Electrochemical and spectroelectrochemical measurements indicate that lindane reacts with the Rh23+ center in singly reduced [Rh2(dpf)4]−, giving a transient carbon-bonded dirhodium complex along with Cl−. Further catalytic dechlorination of lindane subsequently occurs with the activity of Rh2(dpf)4 as a catalyst depending upon the solvent conditions. Rh2(dpf)4 shows a higher catalytic reduction current in pyridine than in DMF for the degradation of lindane. This catalytic current can be further enhanced if 6% water (v/v) is added to the pyridine solution. Bulk controlled-potential electrolysis combined with GC–MS verified that although the addition of water to the neat pyridine increased the catalytic activity of Rh2(dpf)4, neat pyridine is still a better solvent for the formation of more extensively dechlorinated products of lindane. In neat pyridine, lindane can be converted stepwise to tetrachlorocyclohexene, dichlorobenzene isomers, chlorobenzene and the fully dechlorinated product benzene, the last of which becomes predominant at the end of the electrolysis. In pyridine having 6% added water, other than those dechlorinated products seen above, trichlorobenzene isomers are formed upon lindane degradation. Meanwhile, the relative concentrations of dichlorobenzene isomers and chlorobenzene become higher, while the yield of benzene becomes lower than the corresponding results obtained in neat pyridine. Based on the measured distribution of the products under the different solvent conditions, an overall pathway for the degradation of lindane is proposed.

Vis-Near-IR Spectroscopic and Time-Dependent DFT Study of Reduced Singly Bonded C60 Species.

Reduced fullerenes and fullerene derivatives exhibit intense absorptions in the vis-near-IR (vis-NIR) region. The absorptions are sensitive toward the addition pattern, number of addends, and oxidation state of the fullerene species and are used as an important benchmark for identifying anionic fullerene species. Similar absorptions are also shown for the reduced singly bonded C60 species, which are electronically different from reduced fullerene derivatives. However, much less work has been carried out on the vis-NIR spectroscopic study of the anionic singly bonded C60 species, likely due to the difficulty in controlled production of these species. Herein, we report the vis-NIR spectroscopic study of the mono- and dianions of the singly bonded C60 species (RC60(-), R(-)C60(-), and RC60(2-•)), which are selectively generated by controlled-potential bulk electrolysis (CPE) of the singly bonded C60 dimer and C60 oxazolino heterocycles. Time-dependent density functional theory (TD-DFT) calculations were performed to rationalize the experimental results.

Using the Alkynyl-Substituted Rhenium(I) Complex (4,4′-Bisphenyl-Ethynyl-2,2′-Bipyridyl)Re(CO)3Cl as Catalyst for CO2 Reduction—Synthesis, Characterization, and Application

The synthesis, structure, photophysics, and spectroscopic characterization of an organometallic rhenium multichromophore compound carrying a central 2,2′-bipyridyl acceptor moiety with additional phenylethynyl substituents conjugated at the 4,4′-positions of the acceptor ligands and its effect on the electron density of the central rhenium atom as metal center for CO2 reduction is reported. The results were compared to fac-(2,2′-bipyridyl)Re(CO)3Cl and fac-(5,5′-bisphenylethynyl-2,2′-bipyridyl)Re(CO)3Cl. Cyclovoltammetric studies and rotating disk electrochemistry were performed for electrochemical characterization. Ultraviolet and visible (UV-vis) absorption, Fourier transform infrared (FTIR), and luminescence measurements were carried out for a spectroscopic characterization and compared to theoretical calculations at the density functional theory (DFT) level. In addition, the rhenium complex fac-(4,4′-bisphenyl-ethynyl-2,2′-bipyridyl)-Re(CO)3Cl was used as a novel catalyst for the electrochemical reduction of CO2 in homogeneous solution. Results showed an 11-fold increase in the current density under CO2 saturation and a catalytic second-order rate constant for CO formation of about 560 M−1 s−1 on a Pt working electrode. For further characterization of the CO2 reduction capabilities, bulk controlled potential electrolysis experiments were performed using a CO2-saturated acetonitrile electrolyte solution. The headspace product gas analysis yields CO as main reduction product with faradaic efficiencies of about 12 % over 5-h electrolysis time.

Propagation of U(V)-reduction in the presence of U(IV) aggregate in a weakly acidic solution

Reduction processes of UO22+ in weakly acidic solutions were investigated based on electrochemical and spectrophotometric measurements. A reversible one-electron reduction of UO22+ to UO2+ and a further irreversible reduction of UO2+ were observed voltammetrically at a gold microdisk electrode in weakly acidic perchlorate solutions of pH from 2.0 to 3.5. Aggregates of U(IV) were formed as a deposit on the electrode and a colloid in the bulk solution, when the controlled-potential bulk electrolysis was carried out at a gold gauze electrode, even though the potential applied was that available for the first one-electron reduction wave of UO22+ observed at a gold microdisk electrode. It was elucidated that the aggregate was produced by the combination of the one-electron reduction to UO2+ and the disproportionation of UO2+ producing U(IV) and UO22+. The aggregate enhanced the rate of the disproportionation of UO2+, and hence the reduction current of UO22+ increased abruptly when a definite amount of aggregate was formed on the electrode, in the solution, or both. The aggregate of a two-electron reduction product of UO22+ was determined to be poorly crystallized UO2 of fluorite-type structure, and the characteristics of the aggregate were different from the crystalline UO2

Voltammetric Studies on Vitamins D2 and D3 in Organic Solvents

The electrochemical behavior of vitamins D2 and D3 were examined by performing cyclic voltammetry (CV), rotating disk electrode voltammetry, controlled potential electrolysis and chemical oxidation in aprotic organic solvents. Both vitamins were electrochemically oxidized in dichloromethane and acetonitrile (Epox ∼ +0.8 vs. (Fc/Fc+)/V, where Epox is the anodic peak potential and Fc=ferrocene) via a one-electron chemically irreversible process on the short voltammetric time scale (≤seconds). Varying the scan rate (0.1Vs−1 to 20Vs−1) and temperature (233K to 293K) did not strongly affect the voltammetric response recorded on platinum and glassy carbon electrode surfaces with the oxidation process remaining chemically irreversible over the range of scan rates and temperatures tested, indicating that the initially formed cation radical was not long-lived. Repetitive CV experiments indicated that the oxidized product partially adsorbed onto the electrode surface, resulting in diminishing peak currents with multiple scans. Bulk controlled potential electrolysis of the vitamin D compounds performed by alternating several cycles of oxidative electrolysis and reductive pulsed stripping proved to be effective in stripping the adsorbed species off the electrode surfaces. Longer time scale bulk electrolysis experiments led to the detection of a new oxidation peak appearing at less positive potentials as the electrolysis progressed, suggesting that the compounds underwent oxidation on long time scales (minutes to hours) via a two electron process. The vitamins were most likely initially oxidized via one-electron (E-step) to form a cation radical, which reacts homogeneously in two chemical steps (C-steps) where one chemical step is fast (< 1 s) and one is relatively slow (> 1 s). On the electrolysis timescale, the oxidized product then undergoes a second electron transfer (E) at less positive potentials, so the overall mechanism is an ECCE process. Chemical oxidation of vitamin D3 with 2mol equiv of the one-electron oxidant, NO+SbF6− in acetonitrile/dichloromethane 1:4 ratio (v/v) resulted in the complete oxidation of the starting material in an overall two-electron process, with NMR analysis of the reaction mixture indicating that the triene moiety is absent from the products.

Synthesis and characterization of novel Wells-Dawson-type mono vanadium(V)-substituted tungsto-polyoxometalate isomers: 1- and 4-[S2VW17O62](5-).

Two vanadium(V)-substituted tungsto-polyoxometalate isomers, 1- and 4-[S2VW17O62](5-), were prepared as their tetra-alkyl ammonium salts from a W(VI)-H2SO4-V(V) reaction mixture in aqueous CH3CN solution. X-ray crystallographic structural analysis revealed that both isomers have a Wells-Dawson-type structure with a higher occupancy of vanadium at polar sites and belt sites for 1- and 4-[S2VW17O62](5-), respectively. The isomers were also characterized by elemental analysis, infrared, Raman, UV-vis, and (51)V NMR spectroscopies as well as voltammetry, and the data obtained were compared with that derived from [S2W18O62](4-). Significantly, the reversible potentials for the vanadium(V/IV) couple for both 1- and 4-[S2VW17O62](5-) in CH3CN (0.1 M n-Bu4NPF6) are considerably more positive than the tungstate reduction process exhibited by the [S2W18O62](4-) framework, implying that the presence of vanadium should be useful in catalytic reactions. The one-electron-reduced [S2V(IV)W17O62](6-) forms of both isomers were prepared in solution by controlled potential bulk electrolysis and characterized by voltammetry and EPR spectroscopy.

Differences in Proton-Coupled Electron-Transfer Reactions of Flavin Mononucleotide (FMN) and Flavin Adenine Dinucleotide (FAD) between Buffered and Unbuffered Aqueous Solutions

The electrochemical reduction mechanisms of flavin mononucleotide (FMN) in buffered aqueous solutions at pH 3-11 and unbuffered aqueous solutions at pH 2-11 were examined in detail using variable-scan-rate cyclic voltammetry (ν = 0.1-20 V s(-1)), controlled-potential bulk electrolysis, UV-vis spectroscopy, and rotating-disk-electrode voltammetry. In buffered solutions at pH 3-5, FMN undergoes a two-electron/two-proton (2e(-)/2H(+)) reduction to form FMNH2 at all scan rates. When the buffered pH is increased to 7-9, FMN undergoes a 2e(-) reduction to form FMN(2-), which initially undergoes hydrogen bonding with water molecules, followed by protonation to form FMNH(-). At a low voltammetric scan rate of 0.1 V s(-1), the protonation reaction has sufficient time to take place. However, at a higher scan rate of 20 V s(-1), the proton-transfer reaction is outrun, and upon reversal of the scan direction, less of the FMNH(-) is available for oxidation, causing its oxidation peak to decrease in magnitude. In unbuffered aqueous solutions, three major voltammetric waves were observed in different pH ranges. At low pH in unbuffered solutions, where [H(+)] ≥ [FMN], (FMN)H(-) undergoes a 2e(-)/2H(+) reduction to form (FMNH2)H(-) (wave 1), similar to the mechanism in buffered aqueous solutions at low pH. At midrange pH values (unbuffered), where pH ≤ pKa of the phosphate group and [FMN] ≥ [H(+)], (FMN)H(-) undergoes a 2e(-) reduction to form (FMN(2-))H(-) (wave 2), similar to the mechanism in buffered aqueous solutions at high pH. At high pH (unbuffered), where pH ≥ pKa = 6.2 of the phosphate group, the phosphate group loses its second proton to be fully deprotonated, forming (FMN)(2-), and this species undergoes a 2e(-) reduction to form (FMN(2-))(2-) (wave 3).

Competing Hydrogen-Bonding, Decomposition, and Reversible Dimerization Mechanisms during the One- and Two-Electron Electrochemical Reduction of Retinal (Vitamin A)

Retinal (R) can be sequentially voltammetrically reduced in CH3CN in two one-electron processes to form first the anion radical (R(•-)) at -1.75 (±0.04) V vs Fc/Fc(+) (Fc = ferrocene) then the dianion (R(2-)) at -2.15 (±0.04) V vs Fc/Fc(+). The anion radical undergoes a reversible dimerization reaction to form the dianion (R2(2-)) with a forward dimerization rate constant k(dim) = 8 × 10(2) L mol(-1) s(-1) and a reverse monomerization rate constant k(mon) = 2 × 10(-2) s(-1) at 295 K. All three anion species (anion radical, dianion, and dimer dianion) undergo hydrogen-bonding interactions with water that is present at millimolar levels in the solvent. As the water content of the solvent increases, the fate of the reduced compounds is determined by chemically irreversible hydrolysis reactions with H2O and decomposition reactions of the highly charged R(2-). Bulk-controlled potential electrolysis experiments combined with NMR analysis of the reaction solutions indicate that the reduction occurs at the aldehyde group of retinal. The electrochemical data obtained under a range of experimental conditions (varying voltammetric scan rates, temperatures, H2O content of solutions, and retinal concentrations) were modeled by digital simulation techniques to determine the kinetic and thermodynamic parameters associated with all of the homogeneous reactions.

Homogeneous Electron-Transfer Reaction between Electrochemically Generated Ferrocenium Ions and Amine-Containing Compounds

The homogeneous catalytic oxidation of propylamine (PrA), diethylamine (DEA), pyrrolidine (Pyr), and triethylamine (TEA) has been investigated for the first time in the presence of electrochemically generated ferrocenium ions as the catalyst. Mechanistic details for this electrocatalytic process have been investigated by cyclic voltammetry and other electrochemical techniques. A one-electron oxidative process was observed for all amines. Deviation from this mechanism was only observed during controlled-potential bulk electrolysis of ferrocene in the presence of high concentrations of propylamine, where problems with electrode fouling and catalyst deactivation processes were encountered. The catalytic efficiency and the catalytic oxidation rate constants were estimated and found to follow the order TEA > Pyr > DEA > PrA. Interestingly, the catalytic reaction was not observed when ferrocene was replaced by decamethylferrocene. This observation was analyzed in terms of thermodynamic and structural effects, a...

Electrocatalytic Reduction of Carbon Dioxide to Carbon Monoxide by a Polymerized Film of an Alkynyl‐Substituted Rhenium(I) Complex

The alkynyl-substituted ReI complex [Re(5,5′-bisphenylethynyl-2,2′-bipyridyl)(CO)3Cl] was immobilized by electropolymerization onto a Pt-plate electrode. The polymerized film exhibited electrocatalytic activity for the reduction of CO2 to CO. Cyclic voltammetry studies and bulk controlled-potential electrolysis experiments were performed by using a CO2-saturated acetonitrile solution. The CO2 reduction, determined by cyclic voltammetry, occurs at approximately −1150 mV versus the normal hydrogen electrode (NHE). Quantitative analysis by GC and IR spectroscopy was used to determine a Faradaic efficiency of approximately 33 % for the formation of CO. Both values of the modified electrode were compared to the performance of the homogenous monomer [Re(5,5′-bisphenylethynyl-2,2′-bipyridyl)(CO)3Cl] in acetonitrile. The polymer formation and its properties were studied by using SEM, AFM, and attenuated total reflectance (ATR) FTIR and UV/Vis spectroscopy.

Eletrochemical reduction of patulin and 5-hydroxymethylfurfural in both neutral and acid non-aqueous media. Their electroanalytical determination in apple juices

The electro-reduction of patulin mycotoxin and 5-hydroxymethylfurfural at glassy carbon electrodes in acetonitrile +0.1molL−1 tetrabutylammonium perchlorate, in both the absence and the presence of different aliquots of trifluoroacetic acid is reported. 5-hydroxymethylfurfural is the most common interference in the determination of patulin in products derived from apples. The electrochemical techniques were cyclic and square wave voltammetries, and controlled potential bulk electrolysis. The number of electrons exchanged in the patulin electro-reduction of n=1 could be inferred from controlled potential bulk electrolysis measurements. Ultraviolet-visible and infrared spectroscopies were used to identify patulin electro-reduction product/s. A value of (2.1±0.1)×10−5cm2s−1 for the patulin diffusion coefficient was calculated from convoluted cyclic voltammograms. A method based on square wave voltammetry was developed for the quantitative determination of patulin in both fresh, and commercial apple juices in the presence of 5-hydroxymethylfurfural. Calibration curves obtained from solutions of the commercial reagent, and commercial apple juices were linear in the range from 3.0×10−7 to 2.2×10−5molL−1. The lowest concentration measured experimentally for a signal to noise ratio of 3:1 was 3×10−7molL−1 (45ppb) and a recovery percent of 84% was determined for commercial apple juices. This electroanalytical methodology appears as a good screening method for the determination of patulin in apple juices.

Electrochemical degradation of trichloroacetic acid in aqueous media: influence of the electrode material

The electrochemical degradation of trichloroacetic acid (TCAA) in water has been analysed through voltammetric studies with a rotating disc electrode and controlled-potential bulk electrolyses. The influence of the mass-transport conditions and initial concentration of TCAA for titanium, stainless steel and carbon electrodes has been studied. It is shown that the electrochemical reduction of TCAA takes place prior to the massive hydrogen evolution in the potential window for all electrode materials studied. The current efficiency is high (>18%) compared with those normally reported in the literature, and the fractional conversion is above 50% for all the electrodes studied. Only dichloroacetic acid (DCAA) and chloride anions were routinely detected as reduction products for any of the electrodes, and reasonable values of mass balance error were obtained. Of the three materials studied, the titanium cathode gave the best results.

Electrocatalytic and photocatalytic reduction of carbon dioxide to carbon monoxide using the alkynyl-substituted rhenium(I) complex (5,5′-bisphenylethynyl-2,2′-bipyridyl)Re(CO)3Cl

The rhenium complex fac-(5,5′-bisphenylethynyl-2,2′-bipyridyl)Re(CO)3Cl was used as a novel catalyst for the electro- and photochemical reduction of CO2 to CO in homogeneous solution. The results were compared to (2,2′-bipyridyl)Re(CO)3Cl as a benchmark compound. Cyclic voltammetric studies as well as bulk controlled potential electrolysis experiments were performed using a CO2 saturated solution in acetonitrile. (5,5′-bisphenylethynyl-2,2′-bipyridyl)Re(CO)3Cl showed a 6.5-fold increase in current density under CO2 at −1750 mV versus normal hydrogen electrode (NHE) as compared to the operation without CO2. Quantitative analysis by gas chromatography (GC) and infrared spectroscopy showed a Faradaic efficiency of around 45% for the formation of CO.

ChemInform Abstract: Synthesis of Metallic Nanoparticles Using Electrogenerated Reduced Forms of [α‐SiW12O40]4‐ as Both Reductants and Stabilizing Agents.

AbstractReduced forms of [α‐SiW12O40]4‐ are produced by controlled potential bulk electrolysis with little or no supporting electrolyte.

Spectroelectrochemical study of trichloroacetic acid reduction at copper electrodes in an aqueous sodium sulfate medium

The electrochemical reduction of trichloroacetic acid (TCAA) in water has been analyzed through voltammetric studies with a copper rotating disc electrode supported by controlled-potential bulk electrolysis and electrochemical surface-enhanced Raman spectroscopy (SERS) experiments. The influences of the mass-transport conditions and concentration were studied. It has been pointed out that the electrochemical reduction of trichloroacetic acid takes place prior to the massive hydrogen evolution. Strong adsorption was observed on the electrode surface, and dichloroacetic acid (DCAA), monochloroacetic acid (MCAA), and chloride anions were detected as reduction products. The SERS experiments point to a secondary mechanism in which dissociative adsorption of the trichloroacetic acid gives rise to the adsorption of CO, and therefore, to the production of 1C molecules as by-products of the electrochemical reduction.

Electrochemical study of tris(4-bromophenyl)amine and 2,2,6,6-tetramethylpiperidine-1-oxyl in room-temperature ionic liquids

The electrochemical behavior of tris(4-bromophenyl)amine (TBPA) and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was comparatively studied in room temperature ionic liquids (RTILs) containing 1-butyl-3-methylimidazolium cation [BMIm] + and the anions BF 4 −, PF 6 −and CF 3SO 3 −. TEMPO showed a well-defined electrochemical reversibility with anodic to cathodic peak current ratio ( I a/ I c) equals to unity in all RTILs, at a glassy carbon electrode. In contrast, I a/ I c ratio greater than unity was observed at all scan rates employed (10–1000 mV s −1) in cyclic voltammograms (CV) of TBPA in RTILs. Controlled-potential bulk electrolysis of TBPA in RTILs yielded a dark blue colored solution of monocation TBPA +, which is stable under nitrogen. Diffusion coefficient of TBPA + cation was determined in all three ILs by chronoamperometry and found to be at least one order of magnitude less than the calculated value of TBPA. This effect, in conjunction with the deviation of the I a/ I c ratio from unity could be ascribed to ion-pairing interaction between the TBPA + cation and the anion of the RTILs.

First electrogeneration of a platinum(iv) porphyrin: elucidation of the PtII/IV and PtIV/II oxidation-reduction processes in nonaqueous media

The first example for electrogeneration of a Pt(IV) porphyrin from its Pt(II) form is presented and the Pt(II/IV) and reverse Pt(IV/II) oxidation-reduction processes are elucidated by electrochemistry and thin-layer UV-visible spectroelectrochemistry. Three products, [(TPP˙(+))Pt(II)](+), [(TPP)Pt(IV)](2+) and [(TPP˙(+))Pt(IV)](3+), produced by electrooxidation of the Pt(II) porphyrin have been characterized by in situ spectroelectrochemistry and ESR measurements after controlled potential bulk electrolysis. The first definitive evidence for the electrochemical conversion of a Pt(iv) porphyrin to its Pt(II) form is also presented. The potential for this electroreduction is highly dependent upon the nature of the anion, ClO(4)(-) or Cl(-). A mechanism for the reversible conversion between Pt(II) and Pt(IV) tetraphenylporphyrins is proposed.