Unprecedented Reaction Research Articles

A Zintl Cluster for Transition Metal-Free Catalysis: C═O Bond Reductions.

The first fully characterized boron-functionalized heptaphosphide Zintl cluster, [(BBN)P7]2- ([1]2-), is synthesized by dehydrocoupling [HP7]2-. Dehydrocoupling is a previously unprecedented reaction pathway to functionalize Zintl clusters. [Na(18-c-6)]2[1] was employed as a transition metal-free catalyst for the hydroboration of aldehydes and ketones. Moreover, the greenhouse gas carbon dioxide (CO2) was efficiently and selectively reduced to methoxyborane. This work represents the first examples of Zintl catalysis where the transformation is transition metal-free and where the cluster is noninnocent.

Switchable Reactivity of Cyclopropane Diesters toward (3 + 3) and (3 + 2) Cycloadditions with Benzoquinone Esters.

Herein, we describe an unprecedented (3 + 3) cycloaddition reaction of the donor-acceptor cyclopropanes with quinone esters toward the construction of chroman scaffolds in moderate to good yields. Interestingly, the strategy is also adjustable toward a (3 + 2) cycloaddition by just switching the Lewis acid to furnish benzofuran scaffolds. Based on the choice of Lewis acid used, the same set of precursors has been used to deliver the benzopyran and benzofuran derivatives.

Does US Infectious Disease Equity Market Volatility Index Predict G7 Stock Returns? Evidence Beyond Symmetry

During the COVID-19 pandemic, Baker et al. (2020) [The unprecedented stock market reaction to COVID-19. The Review of Asset Pricing Studies, 10, 742–758.] proposed the infectious disease equity market volatility (ID-EMV) index, which tracks US equity market volatility caused by infectious diseases. We extended the literature by using this newly developed ID-EMV index to examine its asymmetric effect on the share market returns of the G7 countries, which include the United Kingdom, Italy, Japan, Germany, France, Canada, and the United States of America. Moreover, we used novel techniques like the quantile-on-quantile regression test, quantile cointegration test, and quantile unit root test. The quantile cointegration test indicates that the infectious disease EMV index is cointegrated with G7 stock returns. Moreover, the quantile-on-quantile regression technique reveals that the infectious disease index positively affects stock returns during bullish states of the stock markets. In contrast, it negatively affects stock returns during bearish states of the stock market returns. The negative effect of the bearish states implies that investors may discourage investments during the downturns of the economy, whereas they need to boost their investments during economic booms.

Ultimate Localization

We report approaches to grow directly noble-metal-(NM)-decorated nanotubes by self-organized anodization. Key to obtain highly defined tubes is an optimized and controlled anodization of Ti-Pt (or other NM) alloys in fluoride containing solutions. In general, the morphology of porous TiO2 and of the tubular layers is affected strongly by the electrochemical growth parameters. NM-decorated titanium-dioxide is a highly functional material that has numerous interesting properties, for example, in solar energy conversion, catalysis of the decomposition of organic compounds (self-cleaning). Therefore this simple approach to produce this highly defined nanoscopic form of NM-TiO2 bears a high potential for technological exploitation. Over the years numerous efforts have been devoted to the shrinkage of the NM-particles to enhance the usage of the noble metal. Evidently the most extreme case of shrinkage is the use of an isolated single atoms of Pt. The use of single atoms as a co-catalyst in photocatalysis has in recent years attracted strong interest, not only because the single atom state represents a maximized surface to volume efficiency, but also because single atom reactivity allows for unprecedented reaction pathways.In the presentation we discuss the formation of Pt dispersed and anchored as single atoms on TiO2 nanotubes and the use of such tubes in highly effective photocatalysis.

(Invited) Single Atom Co-Catalysts in Photocatalytic H2 Generation

Photocatalytic H2 generation has been a highly investigated topic ever since Fujishima und Honda (1972) reported on the use of TiO2 as a solar-illuminated semiconductor for the splitting of water into H2 and O2. Generally, in a fully photocatalytic setting (when photogenerated electron and hole are transferred from a solution-suspended TiO2 nanoparticle to an aqueous electrolyte), a reasonable electron transfer rate can only be established when a noble metal co-catalyst is attached to the TiO2. Mostly this is a Pt nanoparticle that is deposited onto the TiO2 by various reductive treatments.Over the years numerous efforts have been devoted to the shrinkage of the particle to enhance the usage of the noble metal. Evidently the most extreme case shrinkage is the use of an insulated single atom of Pt. The use of such isolated atoms as a co-catalyst in photocatalysis has in recent years attracted strong interest, not only because the single atom state represents a maximized surface to volume efficiency, but also because single atom reactivity allows for unprecedented reaction pathways.In the presentation we discuss the use of Pt dispersed and anchored as single atoms on TiO2 nanocrystallites, powders and nanotubes as a co-catalyst in photocatalytic H2 generation.We discuss various trapping and stabilization approaches of SAs on photocatalysts and report on a SA-Pt photocatalyst with a higher photocatalytic activity than observed for classic arrangements of co-catalyst on the semiconductive substrate. Moreover, we show that a small fraction of the totally deposited Pt that is stably trapped SAs provides virtually all photocatalytic reactivity of a Pt decorated catalyst.

Unexpected Copper-Catalyzed Cascade Reaction of 1,6-Enynes with Sulfoxonium Ylides.

An unprecedented copper-catalyzed cascade reaction of 1,6-enynes with sulfoxonium ylides is reported, providing a series of structurally intriguing 2,3-disubstituted indolines bearing a conjugated dienone functionality at the 3-position in moderate to excellent yields with good chemo-, regio-, and diastereoselectivities under mild reaction conditions. Importantly, sulfoxonium-ylide-derived copper-carbene herein exhibits quite different reactivity from that of diazo copper-carbene. A rational mechanism, an initial ammonium ylide rather than allene formation, is proposed.

X-ray Diffraction, Micro-Raman and X-ray Photoemission Spectroscopic Investigations for Hydrothermally Obtained Hybrid Compounds of Delafossite CuGaO2 and Wurtzite ZnO

P-type delafossite CuGaO2 is a wide-bandgap semiconductor for optoelectronic applications, and its lattice parameters are very similar to those of n-type semiconductor wurtzite ZnO. Accordingly, the investigation of crystalline heterostructures of CuGaO2 and ZnO has attracted significant attention. In this study, interfacial CuGaO2/ZnO hetero-compounds were examined through X-ray diffraction (XRD) analysis, confocal micro-Raman spectroscopy, and X-ray photo-electron spectroscopy (XPS). XRD and Raman analysis revealed that the hydrothermal deposition of ZnO on hexagonal platelet CuGaO2 base crystals was successful, and the subsequent reduction process could induce a unique, unprecedented reaction between CuGaO2 and ZnO, depending on the deposition parameters. XPS allowed the comparison of the binding energies (peak position and width) of the core level electrons of the constituents (Cu, Ga, Zn, and O) of the pristine CuGaO2 single crystallites and interfacial CuGaO2/ZnO hybrids. The presences of Cu2+ ions and strained GaO6 octahedra were the main characteristics of the CuGaO2/ZnO hybrid interface. The XPS and modified Auger parameter analysis gave an insight into a specific polarization of the interface, promising for further development of CuGaO2/ZnO hybrids.

Inner Co Synergizing Outer Ru Supported on Carbon Nanotubes for Efficient pH-Universal Hydrogen Evolution Catalysis

HighlightsA multicomponent Co@CNTs|Ru catalyst has been rationally designed, in which Co nanoparticles are in-situ confined inside CNTs while trace Ru loading is uniformly deposited on their exterior walls.Co and Ru nanoparticles spatially confined by the inner and outer surface of CNTs, respectively, would induce charge redistribution and a synergistic electron coupling.Co@CNTs|Ru catalyst exhibits an unprecedented hydrogen evolution reaction (HER) activity in all pH-range, representing a new record among all the previously reported HER catalysts.

Optimization of Methyl Anthranilate Synthesis Process by Response Surface Methodology and Its Reaction Mechanism

AbstractIn this paper, a unique process for the production of methyl anthranilate (MA) was investigated. The factors of the phthalimide/sodium hypochlorite/methanol molar ratio, reaction temperature, hydrolysis temperature, and water consumption on the yield and purity of MA were analyzed. Response surface methodology (RSM) was used to optimize conditions for the semi-batch synthesis process of MA. The best synthetic conditions for the formation of MA were reaction temperature 0.5 °C, hydrolysis temperature 70 °C and n(phthalimide)/n(sodium hypochlorite)/n(methanol) = 1:2.03:5.87, and water consumption m(H2O)/m(phthalimide) = 7.16:1. The yield of MA could reach 90% under the optimal conditions, which is more than 10% higher than that of the previous semi-batch process. Furthermore, the reaction mechanism was investigated by infrared spectroscopy analysis, and the mechanism of ester group formation and the structure of intermediate products are proposed. The byproduct of the reaction was studied by GC-MS analysis, a byproduct called 2-cyanobenzoic acid has been discovered. Therefore, an unprecedented reaction mechanism of the whole synthesis process is proposed.

Fluoroacetate distribution, response to fluoridation, and synthesis in juvenile Gastrolobium bilobum plants

Like angiosperms from several other families, the leguminous shrub Gastrolobium bilobum R.Br. produces and accumulates fluoroacetate, indicating that it performs the difficult chemistry needed to make a C–F bond. Bioinformatic analyses indicate that plants lack homologs of the only enzymes known to make a C–F bond, i.e., the Actinomycete flurorinases that form 5′-fluoro-5′-deoxyadenosine from S-adenosylmethionine and fluoride ion. To probe the origin of fluoroacetate in G. bilobum we first showed that fluoroacetate accumulates to millimolar levels in young leaves but not older leaves, stems or roots, that leaf fluoroacetate levels vary >20-fold between individual plants and are not markedly raised by sodium fluoride treatment. Young leaves were fed adenosine-13C-ribose, 13C-serine, or 13C-acetate to test plausible biosynthetic routes to fluoroacetate from S-adenosylmethionine, a C3-pyridoxal phosphate complex, or acetyl-CoA, respectively. Incorporation of 13C into expected metabolites confirmed that all three precursors were taken up and metabolized. Consistent with the bioinformatic evidence against an Actinomycete-type pathway, no adenosine-13C-ribose was converted to 13C-fluoroacetate; nor was the characteristic 4-fluorothreonine product of the Actinomycete pathway detected. Similarly, no 13C from acetate or serine was incorporated into fluoroacetate. While not fully excluding the hypothetical pathways that were tested, these negative labeling data imply that G. bilobum creates the C–F bond by an unprecedented biochemical reaction. Enzyme(s) that mediate such a reaction could be of great value in pharmaceutical and agrochemical manufacturing.

Cross Dehydrogenative Coupling of Chloro‐ and Fluoroalkanes with Methylarenes

Cross dehydrogenative coupling reactions (CDCs) are considerably more step- and atom efficient compared to classical cross coupling methods. In this context, the photochemical CDCs of hydrochlorocarbons and hydrofluorocarbons with methylarenes are herein described. This unprecedented CDC reaction concept enables a new retrosynthetic cut for the selective construction of valuable chlorinated and fluorinated organic skeletons, from industrially important dichloromethane, dichloroethane, difluoromethane (HFC-32), and 1,1,1,2-tetrafluoroethane (HFC-134a).

Angstrom-confined catalytic water purification within Co-TiOx laminar membrane nanochannels

The freshwater scarcity and inadequate access to clean water globally have rallied tremendous efforts in developing robust technologies for water purification and decontamination, and heterogeneous catalysis is a highly-promising solution. Sub-nanometer-confined reaction is the ultimate frontier of catalytic chemistry, yet it is challenging to form the angstrom channels with distributed atomic catalytic centers within, and to match the internal mass transfer and the reactive species’ lifetimes. Here, we resolve these issues by applying the concept of the angstrom-confined catalytic water contaminant degradation to achieve unprecedented reaction rates within 4.6 Å channels of two-dimensional laminate membrane assembled from monolayer cobalt-doped titanium oxide nanosheets. The demonstrated degradation rate constant of the target pollutant ranitidine (1.06 ms−1) is 5–7 orders of magnitude faster compared with the state-of-the-art, achieving the 100% degradation over 100 h continuous operation. This approach is also ~100% effective against diverse water contaminates with a retention time of <30 ms, and the strategy developed can be also extended to other two-dimensional material-assembled membranes. This work paves the way towards the generic angstrom-confined catalysis and unravels the importance of utilizing angstrom-confinement strategy in the design of efficient catalysts for water purification.

Ammonia Synthesis Via Electrochemical Atomic Hydrogen Permeation between 25 and 100 C

Ammonia is an energy-rich molecule, primarily used as fertiliser and produced at large scale via the intensive Haber-Bosh process, which is responsible for 1-2% of the CO2 emitted globally.1 In recent years, the electroreduction of N2 to ammonia registered a bursting interest, motivated by the urgent necessity to meet the fast-growing demand for carbon neutral fertilisers and sustainable fuels. However, ammonia synthesis in conventional electrochemical aqueous electrolyte systems is facing serious challenges, such as the competing hydrogen evolution reaction that regularly prevails during electrocatalysis.Herein we propose a strategy to decouple the hydrogen generation from the activation and hydrogenation of nitrogen (Figure 1). Atomic hydrogen is electrochemically generated from water reduction and inserted in the nickel electrode/membrane lattice. The dense metallic electrode provides a selective and controlled access of protons and electrons to the nitrogen active site, while ensuring a complete separation from the electrolyte. Our results demonstrate the unprecedented hydrogenation reaction of activated surface nitrogen to ammonia by electrochemical permeating atomic hydrogen. Ammonia synthesis and quantification were carried out following rigorous protocols and control experiments, including careful check of contamination level, purification of feed gases and 15N2 experiments. A gas chromatography method was developed to continuously detect in situ the produced ammonia, with a limit of quantification of 150 ppb.2 Quantitative 15N labelling experiments confirm that ammonia is produced directly in the gas phase at room temperature and atmospheric pressure from gaseous N2. Experimental observations reveal that the presence of N-vacancies, formed upon the hydrogenation of surface nitrides, plays a key role in the catalytic process facilitating gaseous nitrogen adsorption via a Mars-van Krevelen mechanism. This work provides an alternative pathway for the development of an efficient direct electrolytic ammonia production at ambient conditions from water, nitrogen and renewable electricity.We are currently extending our knowledge on the reaction mechanisms and considerably improving the systems performances. Preliminary results reveal that the formation of nitrogen vacancies via electrochemical hydrogen permeation at 100 C and atmospheric pressure enables a direct hydrogenation process, in which H2, N2 and N-vacancies react to form NH3 at conditions otherwise not favourable to ammonia synthesis.In this talk our latest progress on ammonia synthesis via electrochemical permeating hydrogen will be reviewed.References D. R. MacFarlane, P. V. Cherepanov, J. Choi, B. H. R. Suryanto, R. Y. Hodgetts, J. M. Bakker, F. M. Ferrero Vallana and A. N. Simonov, Joule, 2020, 4, 1186-1205.R. Zaffaroni, D. Ripepi, J. Middelkoop and F. M. Mulder, ACS Energy Letters, 2020, 5, 3773-3777.D. Ripepi, R. Zaffaroni, H. Schreuders, B. Boshuizen and F. M. Mulder, ACS Energy Letters, 2021, DOI: 10.1021/acsenergylett.1c01568, 3817-3823. Figure 1

Metallosupramolecular Assemblies of Phthalocyanines, Subphthalocyanines and Bodipys: Photosensitizers for Visible-Light Induced Processes

Molecular self-assembly provides limitless possibilities to obtain stable and structurally well-defined supramolecules with different physicochemical properties than those of precursor building blocks. From all supramolecular interactions, strong and directional coordination-driven self-assembly allows a fine control over the rational design of two- and three-dimensional architectures with multiple potential applications. The preparation of cutting-edge metallo-supramolecular assemblies based on phthalocyanines, subphthalocyanines and BODIPYs is herein described. These ensembles have been applied for different purposes: i) as molecular receptors showing electronic interactions between the chromophore panels of the host and electroactive guests such as fullerenes and perylenediimides; ii) as hollow molecular containers able to influence a chemical reaction by providing an isolated cavity of particular size and shape, demonstrating, for example, the ability to induce unprecedented photoredox reaction with guest fullerenes, triggered by the porphyrinoid excited state; and iii) as metallosupramolecular amphiphilic systems, able to yield nanostructures via self-organization in aqueous media. Figure 1

Synthesis of α-Ketoamides via Gold(I) Carbene Intermediates.

α-Ketoamides have been found to be an important functional group in a broad spectrum of inhibitors such as the Corona virus and other viruses. Here we report an unprecedented gold-catalyzed 2-fold reaction of a bromoalkyne with anthranils. Hydrolysis of the initial product then directly leads to α-ketoamides. Water addition to the intermediate α-iminoimidoyl halides delivered α-ketoamides from a broad range of bromoalkynes.

Transition-Metal-Free Domino Reaction of [60]Fullerene, Indole, and DMSO/HCl: One-Pot Access to Diverse N-Substituted [60]Fulleroindole Derivatives.

An unprecedented multicomponent domino reaction of [60]fullerene, indole, and DMSO/HCl has been developed for the one-pot efficient synthesis of diverse N-substituted [60]fulleroindole derivatives. This methodology features simple operation, low cost, and transition-metal-circumvented and good functional group tolerance in indole.

Dewar Metallabenzenes from Reactions of Metallacyclobutadienes with Alkynes

AbstractDewar benzenes, the metastable valence isomers of benzenes, have been extensively studied both experimentally and theoretically. In contrast, little is known about Dewar metallabenzenes having a transition metal in the skeletal framework, despite the recent intensive interest in the development of chemistry of metallabenzenes. Herein, we report the isolation and characterization of the first examples of structurally characterized Dewar metallabenzenes. These compounds were generated via unprecedented reactions of metallacyclobutadienes with aminoalkynes.

Dewar Metallabenzenes from Reactions of Metallacyclobutadienes with Alkynes.

Dewar benzenes, the metastable valence isomers of benzenes, have been extensively studied both experimentally and theoretically. In contrast, little is known about Dewar metallabenzenes having a transition metal in the skeletal framework, despite the recent intensive interest in the development of chemistry of metallabenzenes. Herein, we report the isolation and characterization of the first examples of structurally characterized Dewar metallabenzenes. These compounds were generated via unprecedented reactions of metallacyclobutadienes with aminoalkynes.

Cascade of C(sp2)-H Addition to Carbonyl and C(sp2)-CN/C(sp2)-H Coupling Enabled by Brønsted Acid: Construction of Benzo[a]carbazole Frameworks.

Herein, we report an unprecedented cascade reaction of C(sp2)-H addition to carbonyl and the C(sp2)-CN/C(sp2)-H coupling of 2-(2-oxo-2-arylethyl)benzonitriles with indoles enabled by commercially available TsOH·H2O. The protocol represents the first metal-free C(sp2)-CN/C(sp2)-H coupling, affording a new route for the synthesis of various benzo[a]carbazole derivatives with a broad substrate scope, high yields, and simple conditions.

Synthesis, Characterization, and Reactivity of a Hydrido- and Imido-Bridged Dinuclear Ytterbium(III) Complex.

The trivalent rare-earth metal hydrido and imido complexes are of versatile reactivity, and many such complexes have been synthesized. However, no example of a rare-earth metal complex bearing both hydrido- and imido-ligands has been reported. Herein, we report the first rare-earth metal complex bearing both hydrido- and imido-ligands, namely a hydrido- and imido-bridged dinuclear ytterbium(III) complex. The complex was synthesized via an unprecedented redox reaction of divalent rare-earth metal hydrido complex with azido compound. DFT calculation indicated that the N2 release from azido compound in the presence of ytterbium(II) is a kinetically facile process because of the cooperative effects of the two metal centers. The reactivity of the hydrido- and imido-bridged dinuclear ytterbium(III) complex was also explored, which showed the redox, addition and σ-bond metathesis reactivities.