Reversible 1e Research Articles

Proton-Coupled Electron Transfer Reduction of a Quinone by an Oxide-Bound Riboflavin Derivative

The redox properties of a surface-bound phosphate flavin derivative (flavin mononucleotide, FMN) have been investigated on planar-FTO and nanoITO electrodes under acidic conditions in 1:1 CH3CN/H2O (V:V). On FTO, reversible 2e-/2H+ reduction of FTO|-FMN to FTO|-FMNH2 occurs with the pH and scan rate dependence expected for a 2e-/2H+ surface-bound couple. Addition of tetramethylbenzoquinone (Me4Q) results in rapid electrocatalyzed reduction to the hydroquinone by a pathway first order in quinone and first order in acid with kH = (2.6 ± 0.2) × 106 M–1 s–1. Electrocatalytic reduction of the quinone also occurs on derivatized, high surface area nanoITO electrodes with evidence for competitive rate-limiting diffusion of the quinone into the mesoporous nanostructure.

DFT estimates of water environment impact on the reversible 2e− + 2H+ oxidation of aniline tetramer

The PCM (IEFPCM) and CPCM implicit models of water environment have been embodied to the DFT calculations of the reversible 2e−+2H+ process of aniline tetramer. The molecular structure of six reactants as well as reaction energy characteristics of their six reactions have been determined and compared to the vacuum model.The clear difference in reaction energy between two types of processes, electron transfers and proton transfers, is the advantage of the solvent model approach in comparison to the most simple gas phase calculations. The results corresponding to the electron transfer reactions, namely the redox potentials, are much closer to empirical expectations than DFT determinations done for the vacuum environment of the isolated tetramer.

Evolutionary Design of Low Molecular Weight Organic Anolyte Materials for Applications in Nonaqueous Redox Flow Batteries

The integration of renewable energy sources into the electric grid requires low-cost energy storage systems that mediate the variable and intermittent flux of energy associated with most renewables. Nonaqueous redox-flow batteries have emerged as a promising technology for grid-scale energy storage applications. Because the cost of the system scales with mass, the electroactive materials must have a low equivalent weight (ideally 150 g/(mol·e(-)) or less), and must function with low molecular weight supporting electrolytes such as LiBF4. However, soluble anolyte materials that undergo reversible redox processes in the presence of Li-ion supports are rare. We report the evolutionary design of a series of pyridine-based anolyte materials that exhibit up to two reversible redox couples at low potentials in the presence of Li-ion supporting electrolytes. A combination of cyclic voltammetry of anolyte candidates and independent synthesis of their corresponding charged-states was performed to rapidly screen for the most promising candidates. Results of this workflow provided evidence for possible decomposition pathways of first-generation materials and guided synthetic modifications to improve the stability of anolyte materials under the targeted conditions. This iterative process led to the identification of a promising anolyte material, N-methyl 4-acetylpyridinium tetrafluoroborate. This compound is soluble in nonaqueous solvents, is prepared in a single synthetic step, has a low equivalent weight of 111 g/(mol·e(-)), and undergoes two reversible 1e(-) reductions in the presence of LiBF4 to form reduced products that are stable over days in solution.

Electrochemical studies of Ru(II) diimine bioconjugates

The electrochemical behavior of the ruthenium(II) diimine complexes [Ru(CO)(CF3CO2)(dppene)(5-R-phen)][PF6] (dppene=1,2-diphenylphosphinoethene; phen=1,10-phenanthroline; R=H, 1; R=NH2, 2; R=cholestoryl carbamate, 3; R=1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine, 4), [Ru(CO)(H)(4,4′-R-bpy)(R′Ph2P)2][PF6] (bpy=2,2′-bipyridine; R=H, R′=Ph, 5; R=H, R′=1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine, 6; R=1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine, R′=Ph, 7), [Ru(bpy)2(5-R-phen)][PF6]2 (R=NH2, 8; R=cholestoryl carbamate, 9; R=1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine, 10) is reported. Complexes 1–6 give cyclovoltammetric (CV) responses with multiple ill-defined reduction waves and one oxidation wave, all of which were chemically irreversible. Complexes 5 and 7, containing axially coordinating phosphines, showed reversible oxidation and reduction CV responses, while 6 showed redox waves similar to 3. Complexes 8–10 show a metal-centered irreversible oxidation around +1.4V that, in the case of 8 and 9, is heavily modified by adsorption phenomena. In the negative part of the CV, 9 and 10 show a single chemically and electrochemically reversible 1e− reduction both at E°′=−1.29V, about 500mV cathodically shifted with respect to 8. The interactions of complexes 1 and 2 with bovine serum albumin (BSA) and double stranded DNA (ds-DNA) were also studied by electrochemical methods. Both complexes showed strong binding to BSA. Evidence for intercalation of both complexes with DNA is presented, with 1 showing a stronger interaction than 2.

An UV–vis spectroelectrochemical approach for rapid detection of phenazines and exploration of their redox characteristics

Phenazines are widely distributed in the environment and play an important role in various biological processes to facilitate microbial metabolism and electron transfer. In this work, an efficient and reliable spectroelectrochemical method is developed to quantitatively detect 1-hydroxyphenazine (1-OHPZ), a representative phenazine, and explore its redox characteristics. This approach is based on the sensitive absorption change of 1-OHPZ in response to its changes under redox state in rapid electrochemical reduction. The redox reaction of 1-OHPZ in aqueous solution is a proton-coupled electron transfer process, with a reversible one-step 2e−/2H+ transfer reaction. This spectroelectrochemical approach exhibits good linear response covering two magnitudes to 1-OHPZ with a detection limit of 0.48µM, and is successfully applied to detect 1-OHPZ from a mixture of phenazines produced by Pseudomonas aeruginosa cultures. This method might also be applicable in exploring the abundance and redox processes of a wide range of other redox-active molecules in natural and engineered environments.

Through space interaction between ferrocenes mediated by a thioether

A series of conformationally constrained 2,6-bisferrocenylphenyl thioethers were synthesized via Suzuki–Miyaura cross coupling reactions. Structural information was obtained using X-ray crystallography and dynamic 1H NMR spectroscopic studies, showing highly constrained m-terphenyl systems. Interaction of the ferrocene moieties through space mediated by the sulfur were studied by ultra-violet photoelectron spectroscopy (UPS), cyclic voltammetry, differential pulse voltammetry, UV–Vis–NIR spectroscopy and DFT computations. Electrochemical results show two, fully reversible 1e− redox processes for the ferrocenes where the separation of peaks is affected by both solvent and supporting electrolyte, suggesting significant electrostatic interaction which is further confirmed in the gas phase by UPS studies.

Organo Ruthenium–Nickel Dithiolates with Redox-Responsive Nickel Sites

Described is a new family of RuNi dithiolates featuring geometrically flexible Ni centers, which enable both acid–base and redox chemistry, behavior that is characteristic of the hydrogenases. Treatment of Ni(pdt)(dxpe) with (cymene)2Ru2Cl4 affords the salt [(cymene)Ru(Cl)(pdt)Ni(diphos)]Cl (pdt2– = 1,3-propanedithiolate, diphos = dppe = 1,2-bis(diphenylphosphino)ethane ([1Cl]Cl) and diphos = dcpe = 1,2-bis(dicyclohexylphosphino)ethane ([2Cl]Cl)). Cyclic voltammetry revealed that in CH2Cl2 solution [1Cl]Cl reduces irreversibly near −1.6 V vs Fc0/+ followed by the appearance of a reversible 1e– couple assigned to the [1]0/+ couple. Reduction of [1Cl]Cl and [2Cl]Cl with cobaltocene produced the neutral derivatives (cymene)Ru(pdt)Ni(diphos) ([1]0, [2]0). Crystallographic characterization of these compounds revealed short Ru–Ni distance of 2.5539(5) ([1]0) and 2.600(3) Å ([2]0). The 2e– reduction of these chlorides converts the Ni site from square planar to tetrahedral, highlighting the flexibility of the Ni center in these complexes. Variable-temperature NMR studies show that [1]0 and [2]0 are dynamic by virtue of ring flipping in the RuNi(pdt) core. Complexes [1]0 and [2]0 are basic: their conjugate acids, [H1]+ and [H2]+, exhibit pKaPhCN values of 18.94 and 21.65, respectively. Crystallographic characterization of [H1]+ as its aryl borate salt revealed an unsymmetrical Ru–H···Ni interaction and confirmed that the Ni center converted from tetrahedral to square planar, again demonstrating the flexibility of this site.

Synthesis, Electrochemistry, and Electrogenerated Chemiluminescence of Two BODIPY-Appended Bipyridine Homologues

Two new 2,2'-bipyridine (bpy) derivatives containing ancillary BODIPY chromophores attached at the 5- and 5'-positions (BB3) or 6- and 6'-positions (BB4) were prepared and characterized. In this work, the basic photophysics, electrochemistry, and electrogenerated chemiluminescence (ECL) of BB3 and BB4 are compared with those previously reported for a related bpy-BODIPY derivative (BB2) (J. Phys. Chem. C 2011, 115, 17993-18001). Cyclic voltammetry revealed that BB3 and BB4 display reversible 2e(-) oxidation and reduction waves, which consist of two closely spaced (50-70 mV) 1e(-) events. This redox behavior is consistent with the frontier molecular orbitals calculated for BB3 and BB4 and indicates that the 2,2'-bipyridine spacer of each bpy-BODIPY homologue does not facilitate efficient electronic communication between the tethered indacene units. In the presence of a coreactant such as tri-n-propylamine (TPA) or benzoyl peroxide (BPO), BB3 and BB4 exhibit strong ECL and produce spectra that are very similar to their corresponding photoluminescence profiles. The ECL signal obtained under annihilation conditions, however, is significantly different and is characterized by two distinct bands. One of these bands is centered at ∼570 nm and is attributed to emission via an S- or T-route. The second band occurs at longer wavelengths and is centered around ∼740 nm. The shape and concentration dependence of this long-wavelength ECL signal is not indicative of emission from an excimer or aggregate, but rather it suggests that a new emissive species is formed from the bpy-BODIPY luminophores during the annihilation process.

Effect of Acid Blue BRL on morphology and electrochemical properties of polypyrrole nanomaterials

The spherical or plate-shaped polypyrrole (PPy) nanomaterials were prepared via the chemical oxidative polymerization of pyrrole in the presence of Acid Blue BRL (2-anthracenesulfonic acid, 4-[[4-(acetylmethylamino)phenyl]amino]-1-amino-9, 10-dihydro-9, 10-dioxo, monosodium salt) as both dopant and surfactant. Cyclic voltammetry, electrochemical AC impedance spectroscopy, and galvanostatic charge–discharge tests at various current densities were used to characterize the electrochemical characteristics of the PPy/Acid Blue BRL nanomaterials. A reversible 2e−/ 2H+ redox process was observed for all the PPy/Acid Blue BRL samples. The enhancement of UV–vis characteristic absorption of the π–π* transition of polypyrrole and thermostability of the samples was also observed, due to the doping reaction. The flake-shaped PPy/Acid Blue BRL sample exhibited the highest electrical conductivity of 8.33 S cm− 1 and the highest specific capacitance of 514 F g− 1. The electrochemical data indicated that the formation of the plate-shaped structure of the PPy/Acid Blue BRL nanomaterials improved the electrochemical properties of PPy.

Thioacetate-Functionalized Fullerene: Redox Properties and Self-Assembly on the Au(111) Surface

C60 molecules have been functionalized according to the Prato method with the short S-acetyl-protected chains. The redox properties of this fullerene derivative in the solution reveal reversible 1e reduction - oxidation steps similar to those of C60 but shifted to more negative potentials. The in situ deprotected fullerenethioacetate compound forms a stable uniform electroactive monolayer on the (111) surface of gold with the most common diameter of the molecule in range 1.4 ± 0.2 nm. It undergoes both stepwise electroreduction playing the role of an efficient electron acceptor and electrooxidation to radical cation at highly positive potentials. This indicates that fullerenethioacetate formed ordered SAMs while maintaining the unique electronic properties of C60 molecules.

Electrochemistry and Electrogenerated Chemiluminescence of π-Stacked Poly(fluorenemethylene) Oligomers. Multiple, Interacting Electron Transfers

The electrochemistry, spectroscopy, and electrogenerated chemiluminescence (ECL) of a series of π-stacked poly(fluorenemethylene) oligomers (Fn, n = 1-6) were investigated. The pendant cofacially oriented fluorene moieties are essentially in contact with each other by Van der Waals interaction promoting electronic delocalization in these species. All six compounds give successive cyclic voltammetric one-electron (1e) oxidations in 1:1 acetonitrile/benzene (MeCN/Bz), and the multiple 1e transfer properties of all these compounds were confirmed by chronoamperometric experiments with an ultramicroelectrode and digital simulations. The potentials for oxidation of the successive 1e transfers can be explained in terms of electrostatic interactions among the fluorenes. The monomer (F1) shows one irreversible wave, while F2 shows two reversible 1e waves. F3 shows only two reversible 1e oxidation waves, which is consistent with the large energy to remove a third electron because of the greater electrostatic repulsion, so the third wave is shifted toward more positive potentials. Both F4 and F5 show three reversible 1e oxidation waves, while F6 shows four reversible 1e waves. The removal of the first electron from an oligomer becomes easier as n increases. The stability of the radical cations also increases with n. The removal of consecutive electrons from Fn can be correlated with the distance between fluorene moieties. No reduction peaks were observed except for some broad ones at ~-3.2 V vs SCE in THF, which is consitent with the wide highest occupied molecular orbital-lowest unoccupied molecular orbital gap in these compounds (absorbance at about 300 nm). No characteristic annihilation ECL signal was observed for these compounds in 1:1 MeCN/Bz mixed solvent. However, the ECL of F6 in the presence of the coreactant C(2)O(4)(2-) showed a long-wavelength ECL emission that was proposed to be electrolyzed byproduct from the radical cation.

The preparation, spectroscopy, structure and electrochemistry of some [Co(η4-C4Ph4)(η5-C5H4C[tbnd]C–CH[dbnd]Y)], [Fe(η5-C5H5)(η5-C5H4C[tbnd]C–CH[dbnd]Y)], and related complexes

[Co(η4-C4Ph4)(η5-C5H4CC–CHO)], 4a, has been prepared from [Co(η4-C4Ph4)(η5-C5H4CHO)], 1a, by reactions similar to those used previously to convert [Fe(η5-C5H5)(η5-C5H4CHO)], 1b, to [Fe(η5-C5H5)(η5-C5H4CC–CHO)], 4b, i.e. via the dibromoethene [Co(η4-C4Ph4)(η5-C5H4CHCBr2)], 2a, and alkyne [Co(η4-C4Ph4)(η5-C5H4CCH)], 3a. Both 4a and 4b undergo the normal aldehyde reactions with malononitrile and 2,4-dinitrophenylhydrazines to give their respective condensation products [Co(η4-C4Ph4){η5-C5H4CC–CHC(CN)2}], 5a, and [Fe(η5-C5H5){η5-C5H4CC–CHC(CN)2}], 5b; [Co(η4-C4Ph4){η5-C5H4CC–CHN–N(H)C6H3(NO2)2-2,4}], 6a, and [Fe(η5-C5H5){η5-C5H4CC–CHN–N(H)C6H3(NO2)2-2,4}], 6b, as separable mixtures of syn- and anti-isomers; and the anti-isomers of [Co(η4-C4Ph4){η5-C5H4CC–CHN–N(Me)C6H3(NO2)2-2,4}], 7a, and [Fe(η5-C5H5){η5-C5H4CC–CHN–N(Me)C6H3(NO2)2-2,4}], 7b. With [Fe2(η-C5H5)2(CO)2(μ-CO)(μ-CMe)][BF4] 4a and 4b form blue-green [Fe2(η-C5H5)2(CO)2(μ-CO)(μ-C–CHCH-CC–C5H4-η5)Co(η4-C4Ph4)][BF4], [8a][BF4], and black [Fe2(η-C5H5)2(CO)2(μ-CO)(μ-C–CHCH–CC–C5H4-η5)Fe(η5-C5H5)][BF4], [8b][BF4] salts. 4a and 4b also react with the Wittig reagent [Fe(η5-C5H5)(η5-C5H4–CH2PPh3)][I]/nBuLi to give mixtures of Z and E-[Co(η4-C4Ph4)(η5-C5H4–CC–CHCH–C5H4-η5)Fe(η5-C5H5)], 9a, and [Fe(η5-C5H5)(η5-C5H4–CC–CHCH–C5H4-η5)Fe(η5-C5H5)], 9b, which are separable for 9b but not 9a. The Wittig reagent obtained from [Co(η4-C4Ph4)(η5-C5H4–CH2PPh3)][Cl]/nBuLi failed to react with 4a or 4b, but the reaction of 4a with [ClCH2PPh3][Cl]/tBuOK gives very low yields of one expected product, E-[Co(η4-C4Ph4)(η5-C5H4–CC–CHCH–C5H4-η5)Co(η4-C4Ph4)], E-10a, together with a number of other unidentified compounds. The IR, 1H NMR and 13C NMR, and UV/Vis spectra of 4–9 are reported, assigned and discussed. They confirm that 4–9 are Donor–π–Acceptor complexes in which Co(η4-C4Ph4)(η5-C5H4–) is a weaker donor than Fe(η5-C5H5)(η5-C5H4–), the acceptor strength increases for Acceptor CHCHFc < CHN–N(R)C6H3(NO2)2-2,4 < CHO < CHC(CN)2 < (–CHCH–Cμ+)(μ-CO)(CO)2Fe2(η5-C5H5)2, and that an ethyne linker, π = CC, is less effective than an ethene linker, π = CHCH, in promoting electronic communication between the Donor and Acceptor. The molecular structures of 2a, 3a, 4a, 4b, 5b, syn-6a, syn-6b (two crystal forms) and anti-7b have been determined by X-ray diffraction. They have normal molecular dimensions, and the C5H4–CC–CHY moiety does not deviate greatly from planarity with angles between the C5H4 and C–C(H)Y planes of 4.2–19.6°. This contrasts with the structures of Fc–CC–R (R = aryl) complexes where the C5H4 and aryl planes are orthogonal or close to it. The electrochemistry of 3a/3b, 4a/4b, 5a/5b, syn-6a/6b, anti-7a/7b, E/Z-9a, Z-9b, E-9b and [Co(η4-C4Ph4)(η5-C5H4–CC–C6H5)] has been studied. The Co(η4-C4Ph4)(η5-C5H4–) complexes undergo reversible 1e oxidations at higher E° than their Fe(η5-C5H5)(η5-C5H4–) counterparts with E° increasing as the electron-withdrawing ability of the acceptor group increases. Furthermore, like their ferrocenyl counterparts, the alkyne derivatives [Co(η4-C4Ph4)(η5-C5H4–CC–X)] are oxidised at a more positive E° than the alkene complexes [Co(η4-C4Ph4)(η5-C5H4–CHCH–X)]. The UV/Visible spectrum of the oxidized species [Co(η4-C4Ph4)(η5-C5H4–CC–C6H5)]+ shows an absorption band at 960 nm due to a C6H5 → Co(η4-C4Ph4)(η5-C5H4–) charge transfer transition; its equivalent in the spectrum of [Fe(η5-C5H5)(η5-C5H4–CC–C6H5)]+ is found at 797 nm. This implies that {Co(η4-C4Ph4)(η5-C5H4–)}+ is a stronger acceptor than {Fe(η5-C5H5)(η5-C5H4–)}+.

Linear 6,6′-Biazulenyl Framework Featuring Isocyanide Termini: Synthesis, Structure, Redox Behavior, Complexation, and Self-Assembly on Au(111)

The key step in accessing the title species (5), the first nonbenzenoid diisocyanobiaryl, involved an unexpected homocoupling of a 6-bromoazulene derivative. The reversible 2e(-) reduction of 5 was addressed electrochemically and computationally. The shifts in energies of the S(0)→S(1) and S(0)→S(2) transitions for a series of related 6,6'-biazulenyl derivatives correlate with the e(-)-donating/-withdrawing strength of their 2,2'-substituents but follow opposite trends. Species 5 adsorbs end-on (η(1)) to the Au(111) surface via one of its -NC groups to form a 2-nm-thick film. In addition, bimetallic coordination of 5's -NC termini can be readily achieved.

Voltammetry and spectroelectrochemistry of solid indigo dispersed in carbon paste

Cyclic voltammetry, square wave voltammetry and double potential step UV–vis spectroelectrochemistry were used to study the redox processes of indigo microparticles dispersed in a solid carbon paste electrode. The spectroelectrochemical measurements were performed in a home-made long-path-length thin-layer electrolysis cell. Both the indigo/leucoindigo and indigo/dehydroindigo redox couples underwent reversible 2e −/2H + surface-confined reactions. Alkaline electrolytes showed more negative effect on the reduction of indigo to leucoindigo than on its oxidation to dehydroindigo. A new species (probably indolone) was monitored in the re-oxidation of leucoindigo, while isatin was found in the oxidation of indigo at enough positive potential. More detailed electrochemical mechanisms were proposed for the two redox systems, respectively. The present work shows that the microparticle-dispersed carbon paste is an attractive electrode material not only for solid state voltammetry but also for stripping spectroelectrochemistry.

Modified carbon nanoparticle-chitosan film electrodes: Physisorption versus chemisorption

Surface functionalised carbon nanoparticles of ca. 8 nm diameter co-assemble with chitosan into stable thin film electrodes at glassy carbon surfaces. Robust electrodes for application in sensing or electrocatalysis are obtained in a simple solvent evaporation process. The ratio of chitosan binder backbone to carbon nanoparticle conductor determines the properties of the resulting films. Chitosan (a poly- d-glucosamine) has a dual effect (i) as the binder for the mesoporous carbon composite structure and (ii) as binding site for redox active probes. Physisorption due to the positively charged ammonium group (p K A ≈ 6.5) occurs, for example, with anionic indigo carmine (a reversible 2e −–2H + reduction system in aqueous media). Chemisorption at the amine functionalities is demonstrated with 2-bromo-methyl-anthraquinone in acetonitrile (resulting in a reversible 2e −–2H + anthraquinone reduction system in aqueous media). Redox processes within the carbon nanoparticle-chitosan films are studied and at sufficiently high scan rates diffusion of protons (buffer concentration depended) is shown to be rate limiting. The chemisorption process provides a much more stable interfacial redox system with a characteristic and stable pH response over a pH 2–12 range. Chemisorption and physisorption can be employed simultaneously in a complementary binding process.

High spin d5 complexes of tris(6-hydroxymethyl-2-pyridylmethyl)amine (H3L): hepta-coordinated [Mn(H3L)]Cl2and linear trinuclear [Fe3L2](ClO4)3

Reaction of MnCl(2).4H(2)O with H(3)L (H(3)L = tris(6-hydroxymethyl-2-pyridylmethyl)amine) in methanol gives hepta-coordinated [Mn(H(3)L)]Cl(2) involving attachment of Mn(II) to all four nitrogens and three hydroxymethyl arms. Reaction of H(3)L with Fe(ClO(4))(2).6H(2)O in CH(3)CN in the presence of NaO(2)CC(6)H(5) in an attempt to make [Fe(III)OH(H(3)L)(O(2)CC(6)H(5))](ClO(4)), a putative model for soybean lipoxygenase-1, instead gave rise to the linear triiron(III) complex [Fe(3)L(2)](ClO(4))(3) with all three hydroxymethyl arms deprotonated and forming three alkoxide bridges between each Fe(III) centre. The central Fe(III) is hexa-coordinated to only the alkoxide bridges and flanked by two hepta-coordinated iron(III) centres analogous to the Mn(ii) complex. [Fe(3)L(2)](ClO(4))(3) exhibits two reversible 1e(-) reductions to mixed-valence [Fe(3)L(2)](2+) and [Fe(3)L(2)](+) forms. Structure data and magnetochemistry on [Fe(3)L(2)](ClO(4))(3) reveals the tightest Fe-O-Fe angle (87.4 degrees ) and shortest Fe...Fe distance (2.834 A) yet found for any weakly antiferromagnetically-coupled high spin alkoxide-bridged di- or triiron(iii) system and challenges current theories involved in correlating the extent/nature of magnetic interactions in such systems based on Fe-O(bridge) distances and Fe-O-Fe angles. The central hexa-alkoxide coordinated Fe(III) is novel and shows a remarkable resistance towards reduction to Fe(II).

Synthesis, structure, photophysical and electrochemical behavior of 2-amino-anthracene triosmium clusters

The reactions of 2-amino-anthracene with [Os3(CO)10(CH3CN)2] have been studied and the products structurally characterized by spectroscopic, X-ray diffraction, photophysical and electrochemical techniques. At room temperature in CH2Cl2 two major, isomeric products are obtained [Os3(CO)10(μ-η2-(N-C(1))-NH2C14H8)(μ-H)] (1, 14%) and [Os3(CO)10(μ-η2-(N-C(3))-NHC14H9)(μ-H)] (2, 35%) along with a trace amount of the dihydrido complex [Os3(CO)9(μ-η2-(N-C(3))-NHC14H8)(μ-H)2] (3). In refluxing tetrahydrofuran only complexes 2 and 3 are obtained in 24% and 28%, respectively. A separate experiment shows that complex 1 slowly converts to 2 and that the rearrangement is catalyzed by adventitious water and involves proton transfer to the anthracene ring. Complex 1 is stereochemically non-rigid; exhibiting edge to edge hydride migration while 2 is stereochemically rigid. Complex 3 is also stereochemically non-rigid showing a site exchange process of the magnetically nonequivalent hydrides typical for trinuclear dihydrides. Interestingly, 2 decarbonylates cleanly to the electronically unsaturated 46e− cluster [Os3(CO)9(μ3-η2-(N-C(3))-NHC10H9)(μ-H)] (4, 68%) in refluxing cyclohexane, while photolysis of 2 in CH2Cl2 yields only a small amount of 3 along with considerable decomposition. The mechanism of the conversion of 1 to 2 and the dependence of the product distribution on solvent are discussed. All four compounds are luminescent with compounds 1–3 showing emissions that can be assigned to radiative decay associated with the anthracene ligand. Complexes 1–3 all show irreversible 1e− reductions in the range of −1.85–2.14V while 4 shows a nicely reversible 1e− wave at −1.16V and a quasi-reversible second 1e− wave at −1.62V. Irreversible oxidations are observed in the range from +0.35 to +0.49V. The relationship between the cluster ligand configurations and the observed electrochemical and photochemical behavior is discussed and compared with that of the free ligand.

Selenium-catalyzed oxidative halogenation

Abstract Organoselenides catalyze the oxidation of halides by H2O2. Furthermore, these selenides catalyze the transfer of oxidized halogens from N-halosuccinimides to olefins and ketones. Thus, organoselenides catalyze oxidative halogenation reactions including halolactonization, α-halogenation of ketones, and allylic halogenation. The ability of selenium to undergo reversible 2e− oxidation–reduction chemistry facilitates halogenation through selenium-bound halogen intermediates.

A bis-quinone-functionalized Au-electrode subjected to hydrophobic magnetic nanoparticles acts as a three-state “Write-Read-Erase” information storage system

A monolayer consisting of two quinone units Q A and Q B is assembled on a Au electrode and interacted with an aqueous electrolyte/toluene biphase system, where hydrophobic magnetic nanoparticles are dispersed in the toluene phase. The bis-quinone monolayer exposed to the aqueous electrolyte solution reveals two reversible 2e −/2H +-waves at E 1° = −0.36 V and E 2° = −0.16 V (vs. SCE) for the Q A and Q B units in the cyclic voltammogram, respectively. The electrochemical features of the monolayer allow electrochemical encoding of information in the monolayer by applying three different potentials, −0.05 V, −0.3 V or −0.6 V, generating the Q A–Q B, Q A–Q BH 2 or Q AH 2–Q BH 2 states, respectively. The encoded states of the monolayer are read out by the magnetic attraction of the hydrophobic magnetic nanoparticles to the electrode surface, and by analyzing the electrochemical properties of the different monolayer states in the hydrophobic environment provided by the nanoparticles. The oxidized quinone units in the hydrophobic environment reveal a stepwise one-electron reduction process, while the hydroquinone units are electrochemically mute in the same potential range. The encoded information is erased, in the presence of the hydrophobic magnetic nanoparticles, by sweeping the potential to a positive value of 0.4 V that results in the oxidation of the Q AH 2 and Q BH 2 states. The magnetic removal of the hydrophobic nanoparticles from the electrode surface and the exposure of the modified surface to the aqueous electrolyte solution reset the Q A and Q B units for a further cycle of the information storage.

Redox chemistry of the acetato-bridged clusters [M3(µ3-O)n(µ-O2CCH3)6(H2O)3]2+(M = Mo, W, n = 1, 2): reversible redox between mono-µ3-oxo d8MIII2MIVand d9MIII3forms

A cyclic voltammogram of aqueous 0.1 mol dm(-3) triflic acid solutions of the d6 bioxo-capped M-M bonded cluster [Mo3(mu3-O)2(O2CCH3)6(H2O)3]2+ at a glassy carbon electrode at 25 degrees C gives rise to an irreversible 3e- cathodic wave to a d9 Mo(III)3 species at -0.8 V vs. SCE which on the return scan gives rise to two anodic waves at +0.05 V vs. SCE (E(1/2), 1e- reversible to d8 Mo(III)2Mo(IV)) and +0.48 V vs. SCE (2e- irreversible back to d6 Mo(IV)3). The number of electrons passed at each redox wave has been confirmed by redox titration and controlled potential electrolysis which resulted in 90% recovery of [Mo3(mu3-O)2(O2CCH3)6(H2O)3]2+ following electrochemical re-oxidation at +0.8 V. A corresponding CV study of the d8 monoxo-capped W(III)2W(IV) cluster [W3(mu3-O)(O2CCH3)6(H2O)3]2+ gives rise to a reversible 1e- cathodic process at -0.92 V vs. SCE to give the d9 W(III)3 species [W3(mu3-O)(O2CCH3)6(H2O)3]+; the first authentic example of a W(III) complex with coordinated water ligands. However the cluster is too unstable (O2/water sensitive) to allow isolation. Comparisons with the cv study on [Mo3(mu3-O)2(O2CCH3)6(H2O)3]2+ suggest irreversible reduction of this complex to monoxo-capped [Mo(III)3(mu3-O)(O2CCH3)6(H2O)3]+ followed by reversible oxidation to its d8 counterpart [Mo3(mu3-O)(O2CCH3)6(H2O)3]2+ (Mo(III)2Mo(IV)) and finally irreversible oxidation back to the starting bioxo-capped cluster. Exposing the d9 Mo(III)3 cluster to air (O2) however gives a different final product with evidence of break up of the acetate bridged framework. Corresponding redox processes on d6 [W3(mu3-O)2(O2CCH3)6(H2O)3]2+ are too cathodic to allow similar generation of the monoxo-capped W(III)3 and W(III)2W(IV) clusters at the electrode surface.