Oxo Compounds Research Articles

Probing tungsten-alkylidyne cyclic polymer initiator decomposition pathways with oxidants

An OCO-pincer supported tungsten(VI) alkylidyne exhibits diverse reactivity depending on the identity of the oxidizing agent and the stoichiometry of the reaction. Oxidation reactions are studied with azo, nitroso, and oxo compounds. Benzo(c)cinnoline facilitates migratory insertion of the alkylidyne carbon in the pincer backbone forming a tethered tungsten (VI) alkylidene complex. Analogous azobenzene activates a CC bond in the tert—butyl group of the alkylidyne and results in a tungsten di-imido complex. Nitrosobenzene and pyridine N-oxide undergo oxygen atom transfer (OAT) reactions and result in tungsten oxo complexes. Reactions with nitrosobenzene are sensitive to stoichiometry; CC bond activation is observed in stoichiometric reactions, while only OAT occurs with excess nitrosobenzene.

Применение прогрессивных окислительных процессов для деградации диклофенака в водных растворах

The photocatalytic activity of iron-containing metal-ceramic composites based on silicon nitride modified with semiconductor tantalum oxo compounds in the process of oxidative degradation of diclofenac (DCF) was investigated. The composites were synthesized by autowave combustion in nitrogen atmosphere of ferrosilicoaluminum with different additives (5, 10, 15 wt%) of metallic tantalum. The phase composition was determined by X-ray diffraction and IR-spectroscopy, and the content of elements in local surface areas was quantitatively evaluated by X-ray spectral microanalysis. The activity of composites under conditions of heterogeneous photocatalysis, combined heterogeneous photocatalysis with photo-Fenton and "Peroxone" processes under UV irradiation, catalytic ozonation under UV and visible light irradiation was studied. The combination of heterogeneous photocatalysis and "Peroxone" process is the most effective. The Langmuir-Hinshelwood scheme was applied to establish the mechanism of DCF photocatalytic degradation process.

Nanostructured porous WO3 for photoelectrochemical splitting of seawater

Seawater, due to its salinity, can serve as an electrolyte in photoelectrochemical (PEC) systems, which have the potential to enable solar-driven production of hydrogen and oxidizing species. In this study several micrometer thick and highly porous nanostructured WO3 films were formed and their performance in photoanodic oxidation of chloride and sulfate ions, the most abundant anionic species in seawater, was investigated. Layers were characterized using scanning electron microscopy, X-ray diffraction, diffuse reflectance spectroscopy, and BET surface area measurements. The study demonstrates that efficient PEC performance is achieved through optimal light absorption by sufficiently thick WO3 layers (3–5 μm), a highly porous structure that facilitates electrolyte permeation and ionic transport and provides a large electrochemically active interfacial area, and a nanosheet morphology where the sheet thickness is shorter than the hole diffusion length in WO3. The Faradaic efficiency of ClO- + ClO2- generation in neutral chloride-based electrolytes was found to be close to 100 %, but decreased significantly with photoelectrolysis time, presumably, due to the formation of higher chlorine oxo compounds. In addition, photocurrent stability and dissolution of WO3 photoanodes in acidic sulfate and neutral chloride media was compared. Though dissolution of WO3 in 0.5 M NaCl was found to be up to 3 times higher, photocurrent decay was more significant in 0.5 M H2SO4. The phenomenon was attributed to effective hole scavenging by surface-adsorbed Cl- ions, which prevents passivation of the photoelectrode surface due to formation of W(VI) peroxospecies.

The Last Decade of Optically Active α-Aminophosphonates.

α-Aminophosphonates and related compounds are important due to their real and potential biological activity. α-Aminophosphonates may be prepared by the Kabachnik-Fields condensation of oxo compounds, amines and dialkyl phosphites, or by the aza-Pudovik addition of the same P-reagents to imines. In this review, the methods that allow for the synthesis of α-aminophosphonates with optical activity are surveyed. On the one hand, optically active catalysts or ligands may induce enantioselectivity during the Kabachnik-Fields reaction. On the other hand, asymmetric catalysis during the aza-Pudovik reaction, or hydrogenations of iminophosphonates, may prove to be a useful tool. Lastly yet importantly, it is possible to start from optically active reagents that may be associated with diastereoselectivity. The "green" aspects of the different syntheses are also considered.

Biosynthetic flexibility of Pseudomonas aeruginosa leads to hydroxylated 2-alkylquinolones with proinflammatory host response

The human pathogen Pseudomonas aeruginosa produces various 4(1H)-quinolones with diverse functions. Among these, 2-nonyl-4(1H)-quinolone (NQ) and its N-oxide (NQNO) belong to the main metabolites. Their biosynthesis involves substrates from the fatty acid metabolism and we hypothesized that oxidized fatty acids could be responsible for a so far undetected class of metabolites. We developed a divergent synthesis strategy for 2′-hydroxy (2′-OH) and 2′-oxo- substituted quinolones and N-oxides and demonstrated for the first time that 2′-OH-NQ and 2′-OH-NQNO but not the corresponding 2′-oxo compounds are naturally produced by PAO1 and PA14 strains of P. aeruginosa. The main metabolite 2′-OH-NQ is produced even in concentrations comparable to NQ. Exogenous availability of β-hydroxydecanoic acid can further increase the production of 2′-OH-NQ. In contrast to NQ, 2′-OH-NQ potently induced the cytokine IL-8 in a human cell line at 100 nм, suggesting a potential role in host immune modulation.

Design and Synthesis of Al7Ni2 Heterometallic Clusters Based on Metal Substitution and Ligands Protection Strategies†

Comprehensive SummaryThe synthesis of heterometallic aluminum‐based materials is challenging yet attractive, due to their potential applications in optics, catalysis, magnetism and semiconductor device. We have now successfully synthesized two Al7Ni2 heterometallic clusters bearing different peripheral alkoxide ligands through a heterometal substitution strategy. Single crystal structure analysis shows that they are isostructural, only with slight differences in the number of OH and guests. We found that benzyl alkoxides protected Al7Ni2 cluster compound is more stable in H2O and various organic solvents when compared with ethoxides coordinated one. Moreover, it can be used as a reliable catalyst in aldol condensation reactions with higher activity. This work provides a new method for the design of stable crystalline heterometallic aluminum oxo compounds and reveals their excellent catalysis performance.

К вопросу о термоокислительном старении нефтяных битумов и гудронов

The dependences of the adhesive properties and pH of bitumen of various oxidation depths and tar, raw materials of bitumen production, depending on the aging time are investigated. It is shown that in bitumen, with an increase in the depth of oxidation during CBT, a change in the type of oxo compounds formed and, as a consequence, adhesive properties occurs. In high-melting bitumen, during aging, there is an intensive formation of asphaltenes, resins and asphaltogenic acids, which allow to improvethe adhesive properties of the binder. Low-melting bitumen is characterized by intensive formation of carboxyl and hydroxyl groups of compounds that reduce adhesion to alkaline mineral materials. It is established that the rate of tar aging increases, and for oxidized bitumen it is extreme, where the maximum values are observed in the first hours of aging. It is proposed to use the adhesion index and acidity in combination with the standard quality indicator - the softening temperature after aging to select the component composition of bitumen obtained using the "oxidation-compounding" technology, as well as to develop methods to reduce the aging rate of bitumen in the initial period of operation of asphalt concrete coatings and to improve their quality and durability.

Electronic Structure and Reactivity of Dioxygen-Derived Aliphatic Thiolate-Ligated Fe-Peroxo and Fe(IV) Oxo Compounds.

Herein, we examine the electronic and geometric structural properties of O2-derived aliphatic thiolate-ligated Fe-peroxo, Fe-hydroxo, and Fe(IV) oxo compounds. The latter cleaves strong C-H bonds (96 kcal mol-1) on par with the valine C-H bond cleaved by isopencillin N synthase (IPNS). Stopped-flow kinetics studies indicate that the barrier to O2 binding to [FeII(SMe2N4(tren))]+ (3) is extremely low (Ea = 36(2) kJ mol-1), as theoretically predicted for IPNS. Dioxygen binding to 3 is shown to be reversible, and a superoxo intermediate, [FeIII(SMe2N4(tren))(O2)]+ (6), forms in the first 25 ms of the reaction at -40 °C prior to the rate-determining (Ea = 46(2) kJ mol-1) formation of peroxo-bridged [(SMe2N4(tren))Fe(III)]2(μ-O2)2+ (7). A log(kobs) vs log([Fe]) plot for the formation of 7 is consistent with the second-order dependence on iron, and H2O2 assays are consistent with a 2:1 ratio of Fe/H2O2. Peroxo 7 is shown to convert to ferric-hydroxo [FeIII(SMe2N(tren))(OH)]+ (9, g⊥ = 2.24, g∥ = 1.96), the identity of which was determined via its independent synthesis. Rates of the conversion 7 → 9 are shown to be dependent on the X-H bond strength of the H-atom donor, with a kH/kD = 4 when CD3OD is used in place of CH3OH as a solvent. A crystallographically characterized cis thiolate-ligated high-valent iron oxo, [FeIV(O)(SMe2N4(tren))]+ (11), is shown to form en route to hydroxo 9. Electronic structure calculations were shown to be consistent with 11 being an S = 1 Fe(IV)═O with an unusually high νFe-O stretching frequency at 918 cm-1 in line with the extremely short Fe-O bond (1.603(7) Å).

Olefin Metathesis Catalysts Generated In Situ from Molybdenum(VI)-Oxo Complexes by Tuning Pendant Ligands.

Tailored molybdenum(VI)‐oxo complexes of the form MoOCl2(OR)2(OEt2) catalyse olefin metathesis upon reaction with an organosilicon reducing agent at 70 °C, in the presence of olefins. While this reactivity parallels what has recently been observed for the corresponding classical heterogeneous catalysts based on supported metal oxide under similar conditions, the well‐defined nature of our starting molecular systems allows us to understand the influence of structural, spectroscopic and electronic characteristics of the catalytic precursor on the initiation and catalytic proficiency of the final species. The catalytic performances of the pre‐catalysts are determined by the highly electron withdrawing (σ‐donation) character of alkoxide ligands, OtBuF9 being the best. This activity correlates with both the 95Mo chemical shift and the reduction potential that follows the same trend: OtBuF9>OtBuF6>OtBuF3.

Structural Effects on Dioxygen Evolution from Ru(V)−Oxo Complexes

AbstractA series of ruthenium(V)−oxo compounds, LRu(V)O(n) [L=bipyridinedicarboxylate (BDA), alpha‐hydroxycarboxylate (AHA), porphyrin (POR), dimethylglyoximate (DMG), and nitrilotriacetate (NTA); n=+1,0, −1] are evaluated by Density Functional Theory for their ability to produce dioxygen through coupling of Ru(V)−oxo species, bimetallic peroxides (LRu(IV)‐O−O−Ru(IV)L), and dioxygen (LRu(IV)‐O2) complexes. Anionic Ru−oxo complexes (AHA)2RuO− (2) and (NTA)Ru(O)Cl− (5 e) have prohibitively large free energies of coupling, while neutral and monocationic species (1 b, 3–5 a–d) show small to moderate free energies of coupling. Transition states for O−O coupling were found for (NTA)RuO (5 a), (NTA)RuO(NH3) (5 c), (NTA)RuO(Pyr) (5 d), (DMG)2ClRu(O) (8) and (POR)RuO(Cl) (9), yielding moderate activation energies in the range of 18–22 kcal/mol. The overall oxygen evolution reaction (OER) free energies decrease in favourability as the coordination number of LRuO decreases, i. e. 7>6>5. The modest activation energies and free energies along the reaction coordinate for (NTA)(L)RuO and (POR)ClRu(O) suggest that these species would undergo kinetically and thermodynamically favorable oxygen evolution.

Synthesis of α-Aminophosphonates and Related Derivatives; the Last Decade of the Kabachnik-Fields Reaction.

The Kabachnik–Fields reaction, comprising the condensation of an amine, oxo compound and a P-reagent (generally a >P(O)H species or trialkyl phosphite), still attracts interest due to the challenging synthetic procedures and the potential biological activity of the resulting α-aminophosphonic derivatives. Following the success of the first part (Molecules 2012, 17, 12821), here we summarize the synthetic developments in this field accumulated in the last decade. The procedures compiled include catalytic accomplishments as well as catalyst-free and/or solvent-free “greener” protocols. The products embrace α-aminophosphonates, α-aminophosphinates, and α-aminophosphine oxides along with different bis derivatives from the double phospha-Mannich approach. The newer developments of the aza-Pudovik reactions are also included.

Molecular oxofluorides OMFnof nickel, palladium and platinum: oxyl radicals with moderate ligand field inversion

High-valent late transition metal oxo compounds attracted attention because of their peculiar metal–oxygen bond. Their oxo ligands exhibit an electrophilic and distinct radical oxyl (O˙−) rather than the more common nucleophilic (O2−) character.

Beyond CO2 Reduction: Vistas on Electrochemical Reduction of Heavy Non-metal Oxides with Very Strong E-O Bonds (E = Si, P, S).

The carbon dioxide reduction reaction (CO2RR), in particular electrochemically, to produce carbonaceous fuels is considered as a viable approach to store energy and to enable a CO2-neutral carbon management. Besides CO2RR, there is an additional strong demand for benign electrochemical reduction of other important heavy non-metal oxo species (e.g., SiO2, phosphine oxides, SO2) with thermodynamically stable E-O bonds, which accrue in large quantities in industry. In this respect, the energy-intense deoxygenation of oxo compounds of silicon, phosphorus, and sulfur is of particular technological importance because they represent some of the main feedstocks to produce important molecules and functional materials. For example, the release of elemental silicon, phosphorus (P4), and sulfur (S8) from naturally occurring minerals (e.g., silicate, phosphate, sulfate) follows energy-intensive chemical routes. Thus, the established chemical reduction routes to deoxygenate such oxo precursors produce tons of reagent waste or, in the case of carbothermal treatment of minerals, afford a lot of CO2. On the contrary, electrochemical strategies developed for the selective deoxygenation of E-O compounds remain as a feasible alternative powered by renewable electricity instead of fossil energy. Moderate reaction conditions, a large scope in experiment design for selective reactions, easy product isolation, and zero reagent waste by applying electrochemical methods offer a promising solution to overcome the drawbacks of chemical reduction routes. This Perspective summarizes the emergence of electrochemical strategies developed for the reduction of selected examples of E-O/E═O compounds with E = silicon, phosphorus, and sulfur in the past few decades and highlights opportunities and future challenges.

Atomic-Level Topological Indices for Prediction of the Infinite Dilution Activity Coefficients of Oxo Compounds in Water

The atomic-level AI topological indices and the modified Xu (mXu) index were utilized for quantitative structure–property relationship (QSPR) modeling of the infinite dilution activity coefficients of 108 oxo compounds in water at 298.15 K. Stepwise multiple linear regression (SMLR) analysis using the topological descriptors resulted in a model with R2 = $${\mathrm{R}}_{\mathrm{a}\mathrm{d}\mathrm{j}}^{2}$$= 0.9904, SE = 0.3769, F = 1267.1 and an average relative error of 4.89%. The selected descriptors were then used to develop an artificial neural network (ANN) model for the activity coefficients. Findings of the study indicated that a 7–8-1 ANN trained by Levenberg–Marquardt algorithm results in the improved predictions, especially in view of a decrease as large as 47.24% in the average relative error compared to the SMLR model. The AI indices with a total contribution of 81.43% showed the dominant role of the atomic groups of the oxo compounds in determination of their activity coefficients at infinite dilution in water.

Redox chemistry and H-atom abstraction reactivity of a terminal zirconium(iv) oxo compound mediated by an appended cobalt(i) center.

The reactivity of the terminal zirconium(iv) oxo complex, O Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> Zr(MesNPiPr2)3CoCNtBu (2), is explored, revealing unique redox activity imparted by the pendent redox active cobalt(i) center. Oxo complex 2 can be chemically reduced using Na/Hg or Ph3C• to afford the ZrIV/Co0 complexes [(μ-Na)OZr(MesNPiPr2)3CoCNtBu]2 (3) and Ph3COZr(MesNPiPr2)3CoCNtBu (4), respectively. Based on the cyclic voltammogram of 2, Ph3˙ should not be sufficiently reducing to achieve the chemical reduction of 2, but sufficient driving force for the reaction is provided by the nucleophilicity of the terminal oxo fragment and its affinity to bind Ph3C+. Accordingly, 2 reacts readily with [Ph3C][BPh4] and Ph3CCl to afford [Ph3COZr(MesNPiPr2)3CoCNtBu][BPh4] ([5][BPh4]) and Ph3COZr(MesNPiPr2)3CoCl (6), respectively. The chemical oxidation of 2 is also investigated, revealing that oxidation of 2 is accompanied by immediate hydrogen atom abstraction to afford the hydroxide complex [HOZr(MesNPiPr2)3CoCNtBu]+ ([9]+). Thus it is posited that the transient [OZr(MesNPiPr2)3CoCNtBu]+ [2]+ cation generated upon oxidation combines the basicity of a nucleophilic early metal oxo fragment with the oxidizing power of the appended cobalt center to facilitate H-atom abstraction.

Activation and Photoinduced Release of Alkynes on a Biomimetic Tungsten Center: The Photochemical Behavior of the W-S-Phoz System.

The synthesis and structural determination of four tungsten alkyne complexes coordinated by the bio‐inspired S,N‐donor ligand 2‐(4′,4′‐dimethyloxazoline‐2′‐yl)thiophenolate (S‐Phoz) is presented. A previously established protocol that involved the reaction of the respective alkyne with the bis‐carbonyl precursor [W(CO)2(S‐Phoz)2] was used for the complexes [W(CO)(C2R2)(S‐Phoz)2] (R=H, 1 a; Me, 1 b; Ph, 1 c). Oxidation with pyridine‐N‐oxide gave the corresponding W‐oxo species [WO(C2R2)(S‐Phoz)2] (R=H, 2 a; Me, 2 b; Ph, 2 c). All W‐oxo‐alkyne complexes (2 a, b, c) were found to be capable of alkyne release upon light irradiation to afford five‐coordinate [WO(S‐Phoz)2] (3). The photoinduced release of the alkyne ligand was studied in detail by in situ 1H NMR measurements, which revealed correlation of the photodissociation rate constant (2 b>2 a>2 c) with the elongation of the alkyne C≡C bond in the molecular structures. Oxidation of [WO(S‐Phoz)2] (3) with pyridine‐N‐oxide yielded [WO2(S‐Phoz)2] (4), which shows highly fluxional behavior in solution. Variable‐temperature 1H NMR spectroscopy revealed three isomeric forms with respect to the ligand arrangement versus each other. Furthermore, compound 4 rearranges to tetranuclear oxo compound [W4O4(μ‐O)6(S‐Phoz)4] (5) and dinuclear [{WO(μ‐O)(S‐Phoz)}2] (6) over time. The latter two were identified by single‐crystal X‐ray diffraction analyses.

Trapping Iron(III)-Oxo Species at the Boundary of the "Oxo Wall": Insights into the Nature of the Fe(III)-O Bond.

Terminal non-heme iron(IV)-oxo compounds are among the most powerful and best studied oxidants of strong C-H bonds. In contrast to the increasing number of such complexes (>80 thus far), corresponding one-electron-reduced derivatives are much rarer and presumably less stable, and only two iron(III)-oxo complexes have been characterized to date, both of which are stabilized by hydrogen-bonding interactions. Herein we have employed gas-phase techniques to generate and identify a series of terminal iron(III)-oxo complexes, all without built-in hydrogen bonding. Some of these complexes exhibit ∼70 cm-1 decrease in ν(Fe-O) frequencies expected for a half-order decrease in bond order upon one-electron reduction to an S = 5/2 center, while others have ν(Fe-O) frequencies essentially unchanged from those of their parent iron(IV)-oxo complexes. The latter result suggests that the added electron does not occupy a d orbital with Fe═O antibonding character, requiring an S = 3/2 spin assignment for the nascent FeIII-O- species. In the latter cases, water is found to hydrogen bond to the FeIII-O- unit, resulting in a change from quartet to sextet spin state. Reactivity studies also demonstrate the extraordinary basicity of these iron(III)-oxo complexes. Our observations show that metal-oxo species at the boundary of the "Oxo Wall" are accessible, and the data provide a lead to detect iron(III)-oxo intermediates in biological and biomimetic reactions.

Characterization of Oxo-Bridged Iron Amino-bis(phenolate) Complexes Formed Intentionally or in Situ: Mechanistic Insight into Epoxide Deoxygenation during the Coupling of CO2 and Epoxides.

A series of iron(III) chloride and iron(III) μ-oxo compounds supported by tetradentate amino-bis(phenolate) ligands containing a homopiperazinyl backbone were prepared and characterized by electronic absorption spectroscopy, magnetic moment measurement, and MALDI-TOF mass spectrometry. The solid-state structures of three iron(III) μ-oxo compounds were determined by single crystal X-ray diffraction and revealed oxo-bridged bimetallic species with Fe-O-Fe angles between 171.7 and 180°, with the iron centers in distorted square pyramidal environments. Variable temperature magnetic measurements show the oxo complexes exhibit strong antiferromagnetic coupling between two high-spin S = 5/2 iron(III) centers. The oxo complexes exhibit poor activity for the reaction of carbon dioxide and epoxides in the presence of a cocatalyst, under solvent free conditions to yield cyclic carbonates. The least active iron oxo compound bears tert-butyl groups on the phenolate donors, and we propose that steric congestion around the iron center reduces catalytic activity in this case. We provide evidence that an epoxide deoxygenation step occurs when employing monometallic iron(III) chlorido species as catalysts. This affords the corresponding μ-oxo compounds which can then enter their own catalytic cycle. Deoxygenation of epoxides during their catalytic reactions with carbon dioxide is frequently overlooked and should be considered as an additional mechanistic pathway when investigating catalysts.

New Perspectives for Aminotroponiminates: Coordination Chemistry, Redox Behavior, Cooperativity, and Catalysis

Aminotroponiminates (ATIs) are monoanionic ligands with an N,N‐binding pocket and a rigid, planar, unsaturated, C7‐ring as a ligand backbone. Recent findings show that this ligand backbone can play an active role in coordination chemistry, redox reactions, and ligand‐centered reactivity of ATI complexes. Based on these results, ATIs have been recognized as redox‐active and cooperative ligands, which has implications for existing and potential future applications of ATI compounds in synthesis, catalysis, and materials science. The catalytic applications of ATI complexes are summarized in this Microreview, including results from the fields of hydroamination, epoxidation, cyanosilylation, ε‐caprolactone‐, olefin‐, epoxide‐, and epoxide/CO2 (co‐)polymerization as well as electron transfer catalysis. Furthermore, recent advances in the use of ATI ligands for stabilizing heavy analogs of carbon oxo compounds are showcased.

The History and the Current Revival of the Oxo Chemistry of Iron in its Highest Oxidation States: FeVI – FeVIII

The history of the oxo compounds of iron in its highest oxidation states is reviewed and modern activities in this long neglected area of inorganic chemistry are highlighted. The chemistry of ferrates(VI) is the most rapidly advancing branch owing to several potential applications in diverse fields such as environmental chemistry and energy storage. Convenient and high‐yield preparations of ferrates(VI) in high purity are presented, followed by a coverage of the analytical, spectroscopic, and structural characterization in the solid and in solution, with a focus on the stability of these compounds, which had long been under‐estimated. Particular attention has been paid to the fascinating mechanisms that have been proposed for the intriguing “self‐decay” of the [FeO4]2– dianion. Redox processes with inorganic and organic substrates are summarized including fresh and waste water treatment on the one hand and “super‐iron batteries” on the other. Recent advances in the experimental and computational approach to ferrates(VII) [FeO4]– and the elusive “iron tetroxide” [FeO4] are described.