Copper-Substituted Polyoxotungstates as Catalysts for the Electrocatalytic Oxygenation of Light Alkanes.

The low-temperature oxidation of alkanes and arenes using molecular oxygen under ambient conditions is still one of the grand challenges of catalysis. Inspired by the alkane hydroxylation activity of the copper-based metalloenzyme, particulate methane monooxygenase, a tetra-copper polyoxometalate, [Cu(HO)(PWO)], was investigated as an electrocatalyst for the cathodic (reductive) oxidation of hydrocarbons with emphasis on oxidation of ethane. Controlled potential electrolysis (CPE) in water at -0.

Heterometallic Transition Metal Oxides Containing Lewis Acids as Molecular Catalysts for the Reduction of Carbon Dioxide to Carbon Monoxide with Bimodal Activity.

Electrocatalytic CO reduction (e-CORR) to CO is replete with challenges including the need to carry out e-CORR at low overpotentials. Previously, a tricopper-substituted polyoxometalate was shown to reduce CO to CO with a very high faradaic efficiency albeit at -2.5 V versus Fc/Fc.

Electrocatalytic Reduction of Dinitrogen to Ammonia with Water as Proton and Electron Donor Catalyzed by a Combination of a Tri-ironoxotungstate and an Alkali Metal Cation.

The electrification of ammonia synthesis is a key target for its decentralization and lowering impact on atmospheric CO concentrations. The lithium metal electrochemical reduction of nitrogen to ammonia using alcohols as proton/electron donors is an important advance, but requires rather negative potentials, and anhydrous conditions. Organometallic electrocatalysts using redox mediators have also been reported.

Residue analysis evidence for wine enriched with vanilla consumed in Jerusalem on the eve of the Babylonian destruction in 586 BCE.

The article presents results of residue analysis, based on Gas Chromatograph Mass Spectrometer (GC-MS) measurements, conducted on 13 ceramic storage jars unearthed in the Babylonian destruction layer (586 BCE) in Jerusalem. Five of the jars bear rosette stamp impressions on their handles, indicating that their content was related to the kingdom of Judah's royal economy. The identification of the original contents remains is significant for the understanding of many aspects related to the nutrition, economy and international trade in the ancient Levant.

Molecular Transition Metal Oxide Electrocatalysts for the Reversible Carbon Dioxide-Carbon Monoxide Transformation.

Carbon monoxide dehydrogenase (CODH) enzymes are active for the reversible CO oxidation-CO reduction reaction and are of interest in the context of CO abatement and carbon-neutral solar fuels. Bioinspired by the active-site composition of the CODHs, polyoxometalates triply substituted with first-row transition metals were modularly synthesized. The polyanions, in short, {SiM W } and {SiM' M''W }, M, M', M''=Cu , Ni , Fe are shown to be electrocatalysts for reversible CO oxidation-CO reduction.

Photoelectrochemical Reduction of Carbon Dioxide with a Copper Graphitic Carbon Nitride Photocathode.

Research on the photoreduction of CO often has been dominated by the use of sacrificial reducing agents. A pathway that avoids this problem would be the development of photocathodes for CO reduction that could then be coupled to a photoanodic oxygen evolution reaction. Here, we present the use of copper-substituted graphitic carbon nitride (Cu-CN) on a fluorinated tin oxide (FTO) electrode for the photoelectrochemical two-electron reduction of CO to CO as a major product (>95 %) and formic acid (<5 %).

The formyloxyl radical: electrophilicity, C-H bond activation and anti-Markovnikov selectivity in the oxidation of aliphatic alkenes.

In the past the formyloxyl radical, HC(O)O˙, had only been rarely experimentally observed, and those studies were theoretical-spectroscopic in the context of electronic structure. The absence of a convenient method for the preparation of the formyloxyl radical has precluded investigations into its reactivity towards organic substrates. Very recently, we discovered that HC(O)O˙ is formed in the anodic electrochemical oxidation of formic acid/lithium formate.

Guest Transition Metals in Host Inorganic Nanocapsules: Single Sites, Discrete Electron Transfer, and Atomic Scale Structure.

Host-guest solution chemistry with a wide range of organic hosts is an important and established research area, while the use of inorganic hosts is a more nascent area of research. In the recent past in a few cases, Keplerate-type molybdenum oxide-based porous, spherical clusters, shorthand notation {Mo}, have been used as hosts for organic guests. Here, we demonstrate the synthetically controlled encapsulation of first-row transition metals (M = Mn, Fe, and Co) within a Keplerate cluster that was lined on the inner core with phosphate anions, {MoPO}.

Selective Oxidation by H[PVMoO] in a Highly Acidic Medium.

Dissolution of the polyoxometalate (POM) cluster anion H[PVMoO] (; a mixture of positional isomers) in 50% aq HSO dramatically enhances its ability to oxidize methylarenes, while fully retaining the high selectivities typical of this versatile oxidant. To better understand this impressive reactivity, we now provide new information regarding the nature of (115 mM) in 50% (9.4 M) HSO.

Visible-Light Photochemical Reduction of CO to CO Coupled to Hydrocarbon Dehydrogenation.

Research on the photochemical reduction of CO , initiated already 40 years ago, has with few exceptions been performed by using amines as sacrificial reductants. Hydrocarbons are high-volume chemicals whose dehydrogenation is of interest, so the coupling of a CO photoreduction to a hydrocarbon-photodehydrogenation reaction seems a worthwhile concept to explore. A three-component construct was prepared including graphitic carbon nitride (g-CN) as a visible-light photoactive semiconductor, a polyoxometalate (POM) that functions as an electron acceptor to improve hole-electron charge separation, and an electron donor to a rhenium-based CO reduction catalyst.

Aerobic oxygenation catalyzed by first row transition metal complexes coordinated by tetradentate mono-carbon bridged bis-phenanthroline ligands: intra- versus intermolecular carbon-hydrogen bond activation.

Commonly, iron(ii) and copper(i) complexes bind dioxygen (O2) and then activate O2 through a reductive reaction pathway. There is, however, significant interest in low temperature oxygenation with O2 without the use of a sacrificial reductant. Here, earth-abundant metal complexes (FeII, CoII, NiII and CuII) coordinated by two different tetra-dentate mono-carbon bridged bis-phenanthroline ligands, (1,10-Phen)2-2,2'-CR1R2, where R1 = n-butyl and R2 = n-butyl or H were synthesized.

A Thiourea Tether in the Second Coordination Sphere as a Binding Site for CO and a Proton Donor Promotes the Electrochemical Reduction of CO to CO Catalyzed by a Rhenium Bipyridine-Type Complex.

The electrochemical reduction of CO has been extensively investigated in recent years, with the expectation that a detailed mechanistic understanding could achieve the goal of finding a stable catalyst with high turnover frequencies and low reduction potentials. In the catalytic cycle of the carbon dioxide hydrogenase enzyme, it has been suggested that the reduced metal center reacts with CO to form a carboxylate intermediate that is stabilized by hydrogen bonding using a histidine moiety in the second coordination sphere. Using the well-known fac-Re(I)bipyridine(CO)Cl complex as a starting point, the bipyridine ligand was modified in the second coordination sphere with a thiourea tether that is known to form hydrogen bonds with carbonyl moieties.

Electrochemical Hydroxylation of Arenes Catalyzed by a Keggin Polyoxometalate with a Cobalt(IV) Heteroatom.

The sustainable, selective direct hydroxylation of arenes, such as benzene to phenol, is an important research challenge. An electrocatalytic transformation using formic acid to oxidize benzene and its halogenated derivatives to selectively yield aryl formates, which are easily hydrolyzed by water to yield the corresponding phenols, is presented. The formylation reaction occurs on a Pt anode in the presence of [Co W O ] as a catalyst and lithium formate as an electrolyte via formation of a formyloxyl radical as the reactive species, which was trapped by a BMPO spin trap and identified by EPR.

The kinetics and mechanism of oxidation of reduced phosphovanadomolybdates by molecular oxygen: theory and experiment in concert.

The reactivity of the HPVMoO polyoxometalate and its analogues as an electron transfer and electron transfer-oxygen transfer oxidant has been extensively studied in the past and has been shown to be useful in many transformations. One of the hallmarks of this oxidant is the possibility of its re-oxidation with molecular oxygen, thus enabling aerobic catalytic cycles. Although the re-oxidation reaction was known, the kinetics and mechanism of this reaction have not been studied in any detail.

Hydrogen-Atom Transfer Oxidation with HO Catalyzed by [FeII(1,2-bis(2,2'-bipyridyl-6-yl)ethane(HO)]: Likely Involvement of a (μ-Hydroxo)(μ-1,2-peroxo)diiron(III) Intermediate.

The iron(II) triflate complex () of 1,2-bis(2,2'-bipyridyl-6-yl)ethane, with two bipyridine moieties connected by an ethane bridge, was prepared. Addition of aqueous 30% HO to an acetonitrile solution of yielded , a green compound with λ=710 nm. Moessbauer measurements on showed a doublet with an isomer shift (δ) of 0.

Dioxygen in Polyoxometalate Mediated Reactions.

In this review article, we consider the use of molecular oxygen in reactions mediated by polyoxometalates. Polyoxometalates are anionic metal oxide clusters of a variety of structures that are soluble in liquid phases and therefore amenable to homogeneous catalytic transformations. Often, they are active for electron transfer oxidations of a myriad of substrates and upon reduction can be reoxidized by molecular oxygen.

Self-Assembly through Noncovalent Preorganization of Reactants: Explaining the Formation of a Polyfluoroxometalate.

High-order elementary reactions in homogeneous solutions involving more than two molecules are statistically improbable and very slow to proceed. They are not generally considered in classical transition-state or collision theories. Yet, rather selective, high-yield product formation is common in self-assembly processes that require many reaction steps.

Real-time molecular scale observation of crystal formation.

How molecules in solution form crystal nuclei, which then grow into large crystals, is a poorly understood phenomenon. The classical mechanism of homogeneous crystal nucleation proceeds via the spontaneous random aggregation of species from liquid or solution. However, a non-classical mechanism suggests the formation of an amorphous dense phase that reorders to form stable crystal nuclei.

Photochemical Reduction of CO with Visible Light Using a Polyoxometalate as Photoreductant.

The photochemical reduction of CO to CO requires two electrons and two protons that, in the past, have been derived from sacrificial amine donors that are also non-innocent in the catalytic cycle. Towards the realization of a water-splitting reaction as the source of electrons and protons for CO reduction, we have found that a reduced acidic polyoxometalate, H PW W O , is a photoactive electron and proton donor with visible light through excitation of the intervalence charge-transfer band. Upon linking the polyoxometalate to a dirhenium molecular catalyst, a cascade of transformations occurs where the polyoxometalate is electrochemically reduced at a relatively low negative potential of 1.

Encapsulation of Arenes within a Porous Molybdenum Oxide {Mo } Nanocapsule.

The use of confined space to modulate chemical reactivity and to sequester organic compounds spans significant disciplines in chemistry and biology. Here, the inclusion and assembly of arenes into a water-soluble porous metal oxide nanocapsule [{(Mo )Mo O (H O) } {Mo O (CH COO)} ] (Mo ) is reported. The uptake of benzene, halobenzenes, alkylbenzenes, phenols, and other derivatives was studied by NMR, where it was possible to follow the encapsulation process from the outside of the capsule through its pores and then into the interior.

On the effect of ion pairing of Keggin type polyanions with quaternary ammonium cations on redox potentials in organic solvents.

The electrochemical properties of Keggin type polyoxometalates Qn[XW12O40] (X = P, Si, B; Q = n-tetraoctylammonium and n-trioctylmethylammonium) in organic solvents were investigated in order to understand the interrelation between the redox potentials, solvents and ion pairing. A logarithmic correlation between the dielectric constant of the solvent (ε ranged from 4.8 to 46.

Aerobic epoxidation catalysed by transition metal substituted polyfluorooxometalates.

First row transition metal substituted polyfluorooxmetalates with quasi Wells-Dawson structures and a nitro terminal ligand, [NaH2M(NO2)W17F6O55](q-), were used as catalysts for the aerobic epoxidation of cyclic alkenes. The Cu(NO2) analog combined the best traits of conversion and selectivity. Some C-C bond cleavage was also observed and cis isomers reacted preferentially without stereochemical inversion indicating an oxygen atom to double bond concerted reaction.

Reactivity and O2 Formation by Mn(IV)- and Mn(V)-Hydroxo Species Stabilized within a Polyfluoroxometalate Framework.

Manganese(IV,V)-hydroxo and oxo complexes are often implicated in both catalytic oxygenation and water oxidation reactions. Much of the research in this area is designed to structurally and/or functionally mimic enzymes. On the other hand, the tendency of such mimics to decompose under strong oxidizing conditions makes the use of molecular inorganic oxide clusters an enticing alternative for practical applications.

Oxygenation of methylarenes to benzaldehyde derivatives by a polyoxometalate mediated electron transfer-oxygen transfer reaction in aqueous sulfuric Acid.

The synthesis of benzaldehyde derivatives by oxygenation of methylarenes is of significant conceptual and practical interest because these compounds are important chemical intermediates whose synthesis is still carried out by nonsustainable methods with very low atom economy and formation of copious amounts of waste. Now an oxygenation reaction with a 100% theoretical atom economy using a polyoxometalate oxygen donor has been found. The product yield is typically above 95% with no "overoxidation" to benzoic acids; H2 is released by electrolysis, enabling additional reaction cycles.

Sodium periodate mediated oxidative transformations in organic synthesis.

The investigation of new oxidative transformations for the synthesis of carbon-heteroatom and heteroatom-heteroatom bonds is of fundamental importance in the synthesis of numerous bioactive molecules and fine chemicals. In this context, NaIO4, an exciting reagent, has attracted increasing attention enabling the development of these unprecedented oxidative transformations that are difficult to achieve otherwise. Thus, NaIO4 has been successfully explored as a versatile oxidant for a variety of fundamental organic transformations such as C-H activation, oxidative functionalization of alkenes and other interesting oxidative transformations and its application in the synthesis of bioactive natural products.