One-electron Oxidation Processes Research Articles

Synthesis, Characterization, and Properties of a Titanium(IV)-Tetrathiafulvalene-Based Complex.

To deeply investigate the interaction between a tetrathiafulvalene (TTF) unit and a Ti(IV) center, a monomeric heteroleptic octahedral Ti(IV) complex containing a diimine ligand composed of a 1,10-phenanthroline core fused with a TTF fragment (ligand 2a) was prepared. The stable complex formulated as Ti(1)2(2a), where 1 is a 2,2'-biphenolato derivative, was efficiently synthesized by following a one-step approach. This complex and its model species [Ti(1)2(2b)] were fully characterized in solution, and their solid-state structures were established by single-crystal X-ray diffraction analysis. Density functional theory calculations allowed the assignment of the frontier orbitals involved in the electronic transitions characterized by ultraviolet-visible absorption spectroscopy. Electrochemical and spectroelectrochemical studies revealed that the TTF unit within Ti(1)2(2a) can undergo two reversible one-electron oxidation processes; a reversible one-electron reduction of the Ti(IV) atom was highlighted. The photophysical measurements performed for this donor-acceptor molecular system indicated that an electron transfer process upon light excitation occurred within Ti(1)2(2a).

Synthesis of new [6]helicene derivatives for OLED applications. Experimental photophysical and chiroptical properties and theoretical investigation

Six-membered helicenes with specific functionalities were synthesized in good overall yields (40 %-73 %) through a concise photochemical method, allowing for their comprehensive characterization. The racemic mixtures were effectively resolved into their P- and M-enantiomers with high optical purity (97.56 %-100 % ee) by using chiral HPLC. This separation showcased remarkable optical activity, revealing substantial optical rotations (e.g., +2500–3000 for the (P)-enantiomer at λ = 589 nm) and notable electronic circular dichroism (ECD) signals. The organic helical species showed a strong absorption in the UV region and exhibited a red shifted emission, resulting in a quantum yield of 0.12–0.21. Moreover, they demonstrated irreversible one-electron oxidation and reduction processes, and their HOMO and LUMO energy levels were estimated via electrochemical methods. Utilizing DFT and TD–DFT computational approaches, we accurately predicted the electronic absorption and ECD spectra, as well as the frontier molecular orbitals (FMOs), aligning closely with experimental observations. Furthermore, in-depth analyses of absorption and ECD spectra, molecular electrostatic potential (MEP), and reduced density gradient (RDG) through quantum chemical calculations offered insights into the fundamental characteristics of these materials. The collective properties strongly indicate the potential application of these helicenes in electroluminescent and OLED devices, underscoring their promise as candidates in optoelectronic applications.

Electronic and Magnetic Interactions in 6-Oxoverdazyl Diradicals: Connection through N(1) vs C(3) Revisited.

Four isomeric di-6-oxoverdazyl diradicals connected at their N(1) or C(3) positions with either 1,3- or 1,4-phenylene linkers were obtained and characterized by spectroscopic, electrochemical, magnetic, and structural methods. These results were compared to those for the corresponding 6-oxoverdazyl monoradicals. UV-vis spectroscopy demonstrated that only the N(1)-connected para-through-benzene diradical has a distinct spectrum with significant bathochromic and hypsochromic shifts relative to the remaining species. Electrochemical analysis revealed two one-electron reduction processes in all diradiacals, while only the N(1)-connected para-through-benzene diradical exhibits two one-electron oxidation processes separated by 0.10 V. Variable temperature EPR measurements in polystyrene solid solutions gave negative mean exchange interaction energies J for all diradicals, suggesting the dominance of conformers with significant intramolecular antiferromagnetic interactions for the meta-through-benzene isomers. DFT calculations predict a small preference for the triplet state with the ΔES-T of about 0.25 kcal mol-1 for both meta-through-benzene connected diradicals.

Metal‐Catalyzed Oxidative C−H Bond Functionalization of 1,4‐Benzoxazinones

AbstractThe present review shows metal‐catalyzed oxidative C(sp3)‐H/C(sp2)‐H bond functionalization of 1,4‐benzoxazinones by utilizing various substrates such as indoles, phosphites or phosphine oxides, malonate esters, and resorcinol, which lead to the formation of new C−C or C−P bonds. The metal catalysts used for these couplings include Fe, Cu, Ag, and Ru. This follows a strategy involving either the one‐electron oxidation process (OEO), ball milling technique, or photocatalytic process. The synthesized products in this method show usefulness in natural products, materials, agriculture, and medicinal chemistry.

Visible-Light-Induced Oxidative Generation of o-Quinone Methides for Inverse-Electron-Demand [4+2] Cycloaddition Reactions

AbstractOrganophotoredox-catalyzed oxidative generation of o-quinone methides (o-QMs) for inverse-electron-demand [4+2] cycloaddition reactions has been developed. One-electron oxidation of 2-(sulfanylmethyl)phenols by thioxanthylium photoredox catalyst generated o-QMs, which reacted with various styrenes to produce chromanes with high regioselectivity. This reaction offers a valuable approach for in situ generating o-QMs via one-electron oxidation process under irradiation with mild green light.

Redox Chemistry of Pt(II) Complex with Non-Innocent NHC Bis(Phenolate) Pincer Ligand: Electrochemical, Spectroscopic, and Computational Aspects

A Pt(II) complex bearing chelating tridentate bis-aryloxide tetrahydropyrimidinium-based N-heterocyclic carbene (NHC) was synthesized and characterized by using different techniques. Both cyclic voltammetry and differential pulse voltammetry were used to study the electrochemical properties of the complex, revealing two reversible one-electron oxidation processes. The chemical generation and isolation of one-electron-oxidized species were performed oxidizing the initial complex by means of AgBF4. A combination of spectroscopic (UV-Vis/NIR- and EPR-) and theoretical (density functional theory (DFT)) studies suggests the formation of a Pt(II)-phenoxyl radical complex. The latter open-shell derivative was structurally characterized by means of X-ray diffraction analysis. Finally, the neutral platinum complex was tested as a mediator in the process of electrocatalytic oxidation of 2-(methylamino)ethanol (MEA).

Green Synthesis and Electrochemical Study of Undoped and Doped Al<sub>2</sub>O<sub>3</sub> Nanoparticles Using <i>Hibiscus rosa-sinensis</i> Leaves Extract

In the present work, nanoparticles of Al2O3, Cu-Al2O3, and Ni-Al2O3 were prepared using Hibiscus rosa-sinensis plant leaf extract through co-precipitation method. The prepared nanomaterials were characterized through TGA, EDX, SEM, UV-Vis, XRD, and FTIR instruments. The electrochemical behavior of Al2O3, Cu-Al2O3, and Ni-Al2O3 has been studied in DMF solution in the potential ranges from −1.5 to 1.5 V. The nanoparticles are thermally stable, according to the TGA, and the XRD patterns revealed that all the Al2O3, Cu-Al2O3, and Ni-Al2O3 particles were crystalline, with the mean sizes of 12.44, 34.61, and 31.63 nm, respectively. The cyclic voltammogram showed a cathodic peak (Epc) at 0.49 V with an anodic counterpart (Epa) at 0.49 V [E1/2 = 1.748 V]. The optical band gaps of Al2O3, Cu-Al2O3, and Ni-Al2O3 were 3.8, 3.2 and 3.65 eV, owed a cathode. It is observed that the electrochemical behavior of Ni-Al2O3 was identical to that of Al2O3 and Cu-Al2O3. The anodic and cathodic peak values rise with the scan rate. The one-electron oxidation and reduction processes are reversible, as seen by the shifting cathodic peak value toward higher negative values. All cycles exhibit absorption has a constant anodic current. This result indicated the diffusion-based redox process.

Highly efficient activation of sulfite by p-type S-doped g-C3N4 under visible light for emerging contaminants degradation

The photocatalytic activation of sulfite is a one-electron oxidation process of SO32− or HSO3−, and therefore the property of photo-generated holes is essential in determining the activation performance. The n-type g-C3N4 (pCN) was successfully converted to p-type by substituting N2C positions by S (SCN), which not only increased the hole density but also positively shifted the valence band (VB). Whereafter, the SCNs were for the first time applied in sulfite activation under visible light irradiation to degrade diclofenac (DCF). The 1:1SCN showed the highest VB potential of 2.45 V, which exhibited the best performance in activating S(IV). Moreover, the 1:1SCN also demonstrated improved photoelectric properties and enhanced adaptability to complex water qualities (pH, different emerging contaminants, high pollutant concentration and water matrices). The density functional theory (DFT) calculations implied that the doping of S improved the sulfite adsorption capability of 1:1SCN, favorably producing SO3•− as the primary active species. Diverse reactive oxidation species including h+, •OH, SO3•− and SO5•− were present, and h+ and SO5•− were identified as the dominant contributors to DCF degradation. Based on DFT calculations and LC/MS analysis, four pathways were proposed for DCF degradation. This work provides new insights into the sulfite activation technologies and a promising alternative for efficient degradation of emerging contaminants in water.

Electrochemical and in-situ spectroelectrochemical properties of novel (5-(tert-butyl)-2-((3,4-dicyanophenoxy)methyl)phenyl)methanolate substituted mononuclear metal phthalocyanines

This work involves the synthesis and characterization of metallic (Co, Fe, Mn, Ni, Zn) ball-type phthalocyanine precursors by using novel 4,4′-(((4-(tert-butyl)-1,2-phenylene)bis-(methylene))bis(oxy))diphthalonitrile starting compound. The classical oxo-bridge in phthalocyanines was altered with the -OCH2- bridge first time for these ball-type phthalocyanine precursors, and the effects of this change on the chemical, physical and spectral features of phthalocyanine complexes were investigated, in the study. The redox properties of phthalocyanines were researched by electrochemical and in situ spectroelectrochemical measurements on a Pt working electrode in non-aqueous medium. The color changes involved in the redox processes were observed via in situ electrocolorimetric techniques. Electrochemical and UV–Vis spectral measurements exhibited that the compounds had reversible and serial one-electron reduction and oxidation processes. Furthermore, they also had nitrile reduction processes because of opened nitrile groups located at peripheral tails of the phthalocyanine complexes. The plentiful redox conducts of the complexes such as Pc ring based and/or central redox active metal-based reduction and oxidation reactions at low potentials showed that these complexes can be used as functional materials. Because of the apparent spectral and net color changes, the complexes are suitable for utilization in electrochromic devices. Moreover, their rich redox features are a sign of their high electrocatalytic activity for oxygen reduction.

The Speciation of Americium Cations in Neat Water Implicated from DFT Studies.

The recent observed manipulatable redox potential of trivalent americium ion in the aqueous phase by modifying an electrode offers an alternative to accomplish the separation. In order to understand extensively the speciation of Am, which is the prerequisite to understanding the mechanism of the oxidation of Am, we conducted a density functional study to identify the potential species of Am in its tri-, tetra-, and pentavalent states in aqueous phase. Based on the speciation analysis, the calculations implicate a stepwise mechanism for the oxidation of hydrated Am(III), which predominantly exists in its hydrated monatomic cationic form (Am3+(aq)). The two sequential one-electron oxidation processes first produce AmO2+(aq), which may establish an equilibrium with Am4+(aq), and the AmO2+(aq) may then evolve to the dioxo americyl(V) ion. These results suggest the copresence of Am4+(aq) and AmO2+(aq), which builds a bridge for the conversion of americium ion from a monatomic ion to dioxo americyl(V).

S-Shaped Fused Azacorannulene Dimer: Structural and Redox Properties

S-Shaped Fused Azacorannulene Dimer: Structural and Redox Properties

A near-infrared absorbing ring-fused quinoid-bisboron pyrrole dye with double BF2 chelation

Ring-fused quinoid-bisboron pyrrole dyes with double BF2 chelation (QBBP) were prepared for the first time. According to X-ray crystallographic analysis, the centrosymmetric structure of QBBP was confirmed. The core of the central quinone moiety and two ring-fused pyrroles is almost planar, and the arrangement of aggregates involve J-type packing. Bisboron dye QBBP underwent two successive one-electron reduction and two successive one-electron oxidation processes. QBBP absorbs in the near-infrared (NIR) with a high molar extinction coefficient. Although QBBP shows no fluorescence and low intersystem crossing (ISC) efficiency, it has considerable photothermal conversion efficiency and is desirable for a photothermal-photodynamic therapy agent.

Transformations of Main-Group Organometallics Induced by Transition Metals

AbstractThe oxidative dehydrometallation of silyl or boron enolates is induced by palladium(II) catalyst to result in the versatile introduction of α,β-unsaturated carbon–carbon double bonds via palladium enolates. Selective oxidative cross- and homo-coupling reactions of silyl or boron enolates induced by vanadium(V) oxidant provide a selective synthetic method for accessing 1,4-dicarbonyl compounds in a nucleo­phile-nucleophile coupling mode. The ligand coupling reaction of main-group organometallic compounds induced by vanadium(V) oxi­dant provides a unique method for intramolecular carbon–carbon bond formation of nucleophiles. The last two reactions are a complementary strategy for the nucleophile-electrophile coupling reaction. The dehydrometallation and coupling reactions probably proceed through two- and one-electron oxidation processes, respectively.1 Introduction2 Palladium-Catalyzed Dehydrometallation3 Homo- and Cross-Coupling of Main-Group Organometallic Compounds4 Oxidative Ligand Coupling of Main-Group Organometallic Compounds5 Conclusion

Electrochemical, spectrochemical and catalytical properties of cobalt(II) phthalocyanine regioisomers studies

Two regioisomers of tetrasubstituted cobalt(II) phthalocyanine bearing L-menthol moieties in the periphery, were synthesized through remetallation reaction of metal-free phthalocyanines as substrates. Mass spectrometry and UV-Vis spectrophotometry were employed for characteristics. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) studies indicate three one-electron ring-based oxidation processes, oxidation/reduction of cobalt center (Co(II)/Co(I)) and one ring-based reduction. The comparative studies of catalytic activity of the two phthalocyanines were investigated. Cyclohexene oxidation using tert-butylhydroperoxide (TBHP) and cobalt(II) phthalocyanines results in formation of 2-cyclohexen-1-one, 2-cyclohexen-1-ol, cyclohexanol, cyclohexene epoxide. Formation of 2-cyclohexen-1-one were favored.

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence {Fe III 4 Fe II 4 } Cubes

Thermally Induced Reversible Metal-to-Metal Charge Transfer in Mixed-Valence {Fe ^III ₄ Fe ^II ₄ } Cubes

NHC-Stabilized 1,2-Dihalodiborenes: Synthesis, Characterization, and Reactivity Toward Elemental Chalcogens.

The 2-fold reduction of B2X4(NHC)2 (X = Cl, Br, I; NHC = (un)saturated N-heterocyclic carbene) yields the corresponding green-colored 1,2-dihalodiborenes B2X2(NHC)2, the 11B NMR resonances of which are strongly upfield-shifted upon descending the halide group. The diborenes crystallize as the trans isomers, with relatively short B═B double bonds (1.513(9) to 1.568(4) Å). Cyclic voltammetric experiments with these diborenes reveal reversible one-electron oxidation processes to the corresponding diboron radical cation (E1/2 = -1.16 to -1.50 V); the reducing power of B2X2(NHC)2 increasing with the electronegativity of the halide and for the less π-accepting unsaturated NHCs. The main UV-vis absorption (393-463 nm), which corresponds mainly to a highest occupied molecular orbital (HOMO) → lowest unoccupied molecular orbital (LUMO) transition, undergoes a blueshift upon descending the halide group and shows some dependence on the stereoelectronics of the NHC ligands. Computational analyses show that the HOMO of B2X2(NHC)2 is mostly localized on the B═B π bond, with the contribution from halide p orbitals decreasing down the group, and the saturated NHCs affording some π-bonding delocalization over the B-CNHC bonds. The calculated HOMO and LUMO energies decrease upon descending the halide group, while the HOMO-LUMO gap also decreases, correlating well with the cyclovoltammetry and UV-vis data. The reactions of B2Br2(NHC)2 with elemental sulfur and red selenium lead to the formation of the corresponding diborathiiranes and seleniranes, respectively, which were characterized by NMR and UV-vis spectroscopy, cyclic voltammetry, and X-ray diffraction analyses. In one case, an additional one-electron oxidation yields a unique cyclic B2Se radical cation. Computational analyses show that the localization of the HOMO and HOMO - 1 of the diboraseleniranes is inverted compared to the diborathiiranes.

Intrinsic stability of the antiviral drug umifenovir by stress testing and DFT studies

Umifenovir is an antiviral drug approved in China and Russia for the treatment of influenza. The available dosage form consists of capsules marketed under the brand name Arbidol®. Due to its broad spectrum, umifenovir may also be used in other viral contexts, alone or combined with other antiviral drugs. Although knowledge of umifenovir intrinsic stability may be useful for any potential development of other pharmaceutical forms for other routes of administration and for quality risk management, no data regarding this matter is available to date. In this study, the exploration of the molecule's behaviour under hydrolytic, oxidative and photolytic conditions was carried out experimentally and supported by density functional theory (DFT) studies. It comes out that umifenovir is sensitive to these stress conditions giving rise to 6 structurally characterized degradation products. The one-electron oxidation process produced on the sulphur atom is probably the main cause of umifenovir degradation with reference to the structures of the degradation products formed and the DFT data.

Rutheniumethynyl-Triarylamine Organic-Inorganic Mixed-Valence Systems: Regulating Ru-N Electronic Coupling by Different Aryl Bridge Cores.

Four rutheniumethynyl-triarylamine complexes 1-4 with different aryl bridge cores were prepared. The solid structures of complexes 2-4 were fully confirmed by X-ray single-crystal diffraction analysis. Two consecutive one-electron oxidation processes of complexes 1-4 were attributed to the ruthenium and nitrogen centers, as revealed by cyclic voltammetry and square-wave voltammogram. Results also showed decreasing potential difference ΔE of complexes 1, 3, and 4, with the largest value for 2. Upon chemical oxidation of complexes 1-4 by 1.0 eq oxidation reagents FcPF6 or AgSbF6 , the mixed-valence complexes, except for 2+ , show characteristic broad NIR absorptions in the UV-vis-NIR spectroscopic experiments. NIR multiple absorptions were assigned to NAr2 →RuCp*(dppe) intervalence charge transfer (IVCT) and metal-to-ligand charge transfer transitions by TDDFT calculations. Coupling parameter (Hab ) from Hush theory revealed that increasing electronic communication in 1+ , 3+ , and 4+ . Electron density distribution of the HOMO for neutral molecules (1, 3, and 4) and spin density distribution of the corresponding single-oxidized states (1+ , 3+ , and 4+ ) increases progressively on the bridge as the size of the aromatic system increases, proving incremental contributions from bridge cores during oxidation.

Protolytic behavior of water-soluble zinc(II) porphyrin and the electrocatalytic two-electron water oxidation to form hydrogen peroxide

Two-electron water oxidation is an energy-efficient way for solar energy conversion and one of the promising candidates to get through the bottleneck of artificial photosynthesis, photon- flux density problem. In light of renewable energy factor (REF) that is defined by Energy output/Energy input, for the realization of practical systems, the energy input for catalyst preparation have much importance. Herein, we report a facile, cost-effective and environment benign synthesis of zinc (II) 5, 10, 15, 20-tetrakis(N-methylpyridinium-4′-yl)porphyrin (ZnTMPyP) in water at room temperature. We observed coordination of water molecules to the central Zn(II) ion of ZnTMPyP and four-step protolytic equilibria among five axially ligated species. Electrochemical and controlled potential electrolysis experiments, as well as theoretical DFT calculation, showed that ZnTMPyP(OH)(O−) exhibits the two-electron water oxidation to form hydrogen peroxide as the primary product initiated by one-electron oxidation process of the catalyst with a moderate turnover frequency (96.4 s-1) and a small overpotential (∼60 mV). Isotope-labeled studies clearly showed that water molecule served as an oxygen atom source in the formation of hydrogen peroxide.

Synthesis, DFT, electrochemical, biological and DNA-interaction studies of a novel copper(II) complex of salicylic acid and N-tosyl substituted benzimidazole

Sulfonylbenzimidazoles and their copper complexes have tremendous applications in drug development. In the present work, bis(2-hydroxylbenzoato-κ2O,O′)bis(2-methyl-1-(toluene-4-sulfonyl)-1H-benzimidazole) copper(II) complex [Cu(L1)(L2)] has been synthesized and structurally characterized by Fourier-transformed infrared spectroscopy (FTIR) and single-crystal X-ray diffraction (XRD). The complex formed a distorted octahedral geometry with the benzimidazole ligands occupying the axial position and the hydroxylbenzoato ligands in the equatorial positions. The latter ligands coordinated in an isobidentate manner with a Cu–Odeprotenated bond length of 1.955(18) Å and a long range Cu–Ocarbonyl of 2.574(2) Å. An excellent correlation was found between bond lengths and bond angles obtained experimentally from single-crystal XRD analysis and that obtained from density functional theory. Electrochemical behavior of [Cu(L1)(L2)] has been probed by cyclic voltammetry (CV). CV studies revealed that it undergoes one-electron reduction followed by one-electron oxidation process. In vitro tyrosinase inhibitory activity of the complex was evaluated and it was observed that it exhibited good inhibitory potential with IC50 value 56.8 ± 11.4 μM. Complex-DNA-interaction studies were performed by CV, electronic and florescence spectroscopic titrations and it has been inferred that the [Cu(L1)(L2)] binds with DNA through intercalation and the value of binding constant was 3.6 × 104 M−1.