Showing papers in "Chemistry: A European Journal in 2012"

Supramolecular Binding Thermodynamics by Dispersion-Corrected Density Functional Theory

Abstract: The equilibrium association free enthalpies ΔG(a) for typical supramolecular complexes in solution are calculated by ab initio quantum chemical methods. Ten neutral and three positively charged complexes with experimental ΔG(a) values in the range 0 to -21 kcal mol(-1) (on average -6 kcal mol(-1)) are investigated. The theoretical approach employs a (nondynamic) single-structure model, but computes the various energy terms accurately without any special empirical adjustments. Dispersion corrected density functional theory (DFT-D3) with extended basis sets (triple-ζ and quadruple-ζ quality) is used to determine structures and gas-phase interaction energies (ΔE), the COSMO-RS continuum solvation model (based on DFT data) provides solvation free enthalpies and the remaining ro-vibrational enthalpic/entropic contributions are obtained from harmonic frequency calculations. Low-lying vibrational modes are treated by a free-rotor approximation. The accurate account of London dispersion interactions is mandatory with contributions in the range -5 to -60 kcal mol(-1) (up to 200% of ΔE). Inclusion of three-body dispersion effects improves the results considerably. A semilocal (TPSS) and a hybrid density functional (PW6B95) have been tested. Although the ΔG(a) values result as a sum of individually large terms with opposite sign (ΔE vs. solvation and entropy change), the approach provides unprecedented accuracy for ΔG(a) values with errors of only 2 kcal mol(-1) on average. Relative affinities for different guests inside the same host are always obtained correctly. The procedure is suggested as a predictive tool in supramolecular chemistry and can be applied routinely to semirigid systems with 300-400 atoms. The various contributions to binding and enthalpy-entropy compensations are discussed.

C-H activation: a complementary tool in the total synthesis of complex natural products.

Abstract: The recent advent of transition-metal mediated CH activation is revolutionizing the synthetic field and gradually infusing a “CH activation mind-set” in both students and practitioners of organic synthesis. As a powerful testament of this emerging synthetic tool, applications of CH activation in the context of total synthesis of complex natural products are beginning to blossom. Herein, recently completed total syntheses showcasing creative and ingenious incorporation of CH activation as a strategic manoeuver are compared with their “non-CH activation” counterparts, illuminating a new paradigm in strategic synthetic design.

Direct α-functionalization of saturated cyclic amines.

Abstract: Recent advances in synthetic methods for the direct α-functionalization of saturated cyclic amines are described. Methods are categorized according to the in situ formed reactive intermediate (α-amino cation, α-amino anion, and α-amino radical). Transition-metal-catalyzed reactions involving other intermediates have been treated as a separate and fourth class.

Nitrogen‐Doped Carbon Monolith for Alkaline Supercapacitors and Understanding Nitrogen‐Induced Redox Transitions

Abstract: A nitrogen-doped porous carbon monolith was synthesized as a pseudo-capacitive electrode for use in alkaline supercapacitors. Ammonia-assisted carbonization was used to dope the surface with nitrogen heteroatoms in a way that replaced carbon atoms but kept the oxygen content constant. Ammonia treatment expanded the micropore size-distributions and increased the specific surface area from 383 m2?g-1 to 679 m2?g-1. The nitrogen-containing porous carbon material showed a higher capacitance (246 F?g-1) in comparison with the nitrogen-free one (186 F?g-1). Ex situ electrochemical spectroscopy was used to investigate the evolution of the nitrogen-containing functional groups on the surface of the N-doped carbon electrodes in a three-electrode cell. In addition, first-principles calculations were explored regarding the electronic structures of different nitrogen groups to determine their relative redox potentials. We proposed possible redox reaction pathways based on the calculated redox affinity of different groups and surface analysis, which involved the reversible attachment/detachment of hydroxy groups between pyridone and pyridine. The oxidation of nitrogen atoms in pyridine was also suggested as a possible reaction pathway.

Electrochemical Preparation of Luminescent Graphene Quantum Dots from Multiwalled Carbon Nanotubes

Abstract: Green luminescent, graphene quantum dots (GQDs) with a uniform size of 3, 5, and 8.2(±0.3) nm in diameter were prepared electrochemically from MWCNTs in propylene carbonate by using LiClO4 at 90 °C, whereas similar particles of 23(±2) nm were obtained at 30 °C under identical conditions. Both these sets of GQDs displayed a remarkable quantum efficiency of 6.3 and 5.1 %, respectively. This method offers a novel strategy to synthesise size-tunable GQDs as evidenced by multiple characterisation techniques like transmission and scanning electron microscopy, atomic force microscopy, Raman spectroscopy and X-ray diffraction (XRD). Photoluminescence of these GQDs can be tailored by size variation through a systematic change in key process parameters, like diameter of carbon nanotube, electric field, concentration of supporting electrolyte and temperature. GQDs are promising candidates for a variety of applications, such as biomarkers, nanoelectronic devices and chemosensors due to their unique features, like high photostability, biocompatibility, nontoxicity and tunable solubility in water.

ortho‐Quinone Methides in Natural Product Synthesis

Abstract: ortho-Quinone methides (o-QMs) are emerging as highly useful intermediates, the inherent reactivity of which can be used in linchpin reactions for the construction of complex natural products. This review encompasses the major contributions in this field, exemplifying the major strategies and reactivity modes which can be applied.

[Cu(dap) 2Cl] as an efficient visible-light-driven photoredox catalyst in carbon-carbon bond-forming reactions

Abstract: Copper sees the light of day: [Cu(dap)(2)Cl] proved to be an excellent photoredox catalyst for atom-transfer radical addition reactions, as well as for allylation reactions (see scheme), providing an attractive alternative to commonly used iridium- and ruthenium-based catalysts.

Recent Developments in the Synthesis of Five‐ and Six‐Membered Heterocycles Using Molecular Iodine

Abstract: Heterocyclic scaffolds represent the key structural subunits of many biologically active compounds. Over the last few years iodine-mediated reactions have been extensively studied due to their low cost and eco-friendliness. This Review covers advances in the field of iodine-mediated synthesis of heterocyclic compounds since 2006, especially with an emphasis on mechanisms of ring formation. In this article, syntheses of different heterocycles are classified based on the manipulation of functional groups.

Hydrogen Bonds: A Structural Insight into Ionic Liquids

Abstract: Ionic liquids (ILs) have attracted intensive attention in academia and industry due to their unique properties and potential applications. Nowadays, much interest is focused on finding out what is the main force that determines the properties of ionic liquids. Intuitively like NaCl, in high-temperature molten salt (HTMS) the electrostatic Coulomb force is regarded as the dominant factor that determines the behaviors of ILs. However, a large amount of evidence indicates that such a molten-salt-based simplified explanation is not consistent with the corresponding experimental results. Besides the Coulomb force, the hydrogen bond is another important noncovalent interaction in the IL and is closely related to some important properties and applications, as suggested in some new research results. Therefore in this review, we present results concerning the hydrogen bond in ILs, from the perspective of experiment and calculation, to shed light on its effects and roles. The deep insights into structure, in particular the hydrogen bonds, can provide us with a rational design for the new ILs to fulfill the demands in some complicated chemical processes.

Reactivity and Mechanistic Insight into Visible-Light-Induced Aerobic Cross-Dehydrogenative Coupling Reaction by Organophotocatalysts

Abstract: With visible-light irradiation, a mild, simple, and efficient metal-free photocatalytic system for the facile construction of sp(3)-sp(3) C-C bonds between tertiary amines and activated C-H bonds has been achieved. Spectroscopic study and product analysis demonstrate for the first time that photoinduced electron transfer from N-aryl tetrahydroisoquinolines to eosin Y bis(tetrabutylammonium salt) (TBA-eosin Y) takes place to generate TBA-eosin Y radical anion, which can subsequently react with nucleophiles and molecular oxygen. More strikingly, electron spin resonance (ESR) measurements provide direct evidence for the formation of superoxide radical anions (O(2)(-.)) rather than singlet oxygen ((1)O(2)) during visible-light irradiation. This active species is therefore believed to be responsible for the large rate of acceleration of the aerobic photocatalytic reactions.

New insight into daylight photocatalysis of AgBr@Ag: synergistic effect between semiconductor photocatalysis and plasmonic photocatalysis.

Abstract: Noble metal nanoparticles (NPs) are often used as electron scavengers in conventional semiconductor photocatalysis to suppress electron-hole (e(-)-h(+) ) recombination and promote interfacial charge transfer, and thus enhance photocatalytic activity of semiconductors. In this contribution, it is demonstrated that noble metal NPs such as Ag NPs function as visible-light harvesting and electron-generating centers during the daylight photocatalysis of AgBr@Ag. Novel Ag plasmonic photocatalysis could cooperate with the conventional AgBr semiconductor photocatalysis to enhance the overall daylight activity of AgBr@Ag greatly because of an interesting synergistic effect. After a systematic investigation of the daylight photocatalysis mechanism of AgBr@Ag, the synergistic effect was attributed to surface plasmon resonance induced local electric field enhancement on Ag, which can accelerate the generation of e(-)-h(+) pairs in AgBr, so that more electrons are produced in the conduction band of AgBr under daylight irradiation. This study provides new insight into the photocatalytic mechanism of noble metal/semiconductor systems as well as the design and fabrication of novel plasmonic photocatalysts.

Catalytic hydrogenation of carbon dioxide and bicarbonates with a well-defined cobalt dihydrogen complex.

Abstract: the potential to replace the use of the more toxic carbon monoxide, which is currently utilised in industry on a million-ton scale. In the last 20 years, significant improvements in catalyst development have been made in this area, starting from ruthenium complexes by Leitner and progressing to the recent work of Nozaki and co-workers that uses highly efficient pincer-type Ir catalysts. So far, mainly noble metal complexes based on ruthenium, rhodium and iridium have been studied for this transformation and impressive catalyst productivities have been achieved. On the other hand, non-precious-metal catalysts based on iron, manganese or zinc have scarcely been investigated and the obtained catalytic activities are low (turnover numbers (TONs)< 120). In addition to the hydrogenation of carbon dioxide, the catalytic reduction of bicarbonates and carbonates also provides an interesting route for the synthesis of formates. To date, relatively few transition-metal catalysts have been developed for this biologically relevant reduction (Scheme 2). For several years, we have been exploring the use of iron catalysts for various redox reactions. For example, we were recently able to show that the hydrogenation of CO2 and bicarbonates is possible by using iron complexes with the socalled tetraphos ligand (PP3: P(CH2CH2PPh2)3). [10] The turnover numbers with this iron system (600–700) are still much lower than those of the best precious-metal catalysts, but it was the first real step forward for the use of non-precious metals for the benign reduction of CO2. Herein, we describe the synthesis and behaviour of novel cobalt dihydrogen complexes that show improved catalyst performance for the catalytic hydrogenation of CO2. To the best of our knowledge, homogeneous cobalt complexes have scarcely been reported for this type of transformation. However, the use of a cobalt foil at high temperature (250 8C) has been reported to produce some activity. In addition, CoACHTUNGTRENNUNG(OAc)2 has been used for hydrogenation in the presence of phosphane ligands. This limited data is somewhat surprising considering the recent interest in cobalt dihydrogen complexes. Based on our previous work on iron complexes, we started to investigate the hydrogenation of sodium bicarbonate by using in situ generated catalysts. Initially, we used a sodium bicarbonate solution containing cationic CoACHTUNGTRENNUNG(BF4)2·6H2O and PP3 at 80 8C. To our delight, after 20 h, sodium formate was obtained in 94 % yield, and a turnover number (TON) of 3877 when the reaction temperature was increased to 120 8C (Table 1, entries 1 and 2). This catalytic productivity is six times as high as the best TON described in the literature for any non-precious-metal catalyst, and twice that of the best precious-metal system described. Notably, the catalytic activity is uniquely dependent on the PP3 ligand. In tests with various other ligands, such as triphenylphosphine, xantphos, 1,2-bisdiphenylphosphinoethane, [18]crown-6 and 1,1,1-tris(diphenylphosphinomethyl)ethane, no activity was observed. However, variation of the cobalt precursor is possible and several cobalt species, for example, CoACHTUNGTRENNUNG(acac)2 (acac=acetylacetonate), CoACHTUNGTRENNUNG(acac)3 and CoCl2, in the presence of the tetraphos ligand showed similar activity to the cationic cobalt salts. Utilising the in situ generated active cobalt complex also made it possible to hydrogenate sodium bicarbonate at a lower pressure of hydrogen (5 bar; Table 1, entry 3). [a] C. Federsel, C. Ziebart, Dr. R. Jackstell, Dr. W. Baumann, Prof. Dr. M. Beller Leibniz-Institut f r Katalyse e.V. an der Universit t Rostock Albert Einstein Str. 29a, 18059 Rostock (Germany) Fax: (+49) 381-1281-51113 E-mail : matthias.beller@catalysis.de Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201101343. Scheme 1. Catalytic hydrogenation of CO2 to form alkyl formates and formamides. Scheme 2. Cobalt-catalysed hydrogenation of bicarbonates to form formates.

Porous, Conductive Metal‐Triazolates and Their Structural Elucidation by the Charge‐Flipping Method

Abstract: A new family of porous crys- tals was prepared by combining 1H- 1,2,3-triazole and divalent metal ions (Mg, Mn, Fe, Co, Cu, and Zn) to give six isostructural metal-triazolates (termed MET-1 to 6). These materials are prepared as microcrystalline pow- ders, which give intense X-ray diffrac- tion lines. Without previous knowledge of the expected structure, it was possi- ble to apply the newly developed charge-flipping method to solve the complex crystal structure of METs: all the metal ions are octahedrally coordi- nated to the nitrogen atoms of triazo- late such that five metal centers are joined through bridging triazolate ions to form super-tetrahedral units that lie at the vertexes of a diamond-type structure. The variation in the size of metal ions across the series provides for precise control of pore apertures to a fraction of an Angstrom in the range 4.5 to 6.1 �. MET frameworks have permanent porosity and display surface areas as high as some of the most porous zeolites, with one member of this family, MET-3, exhibiting signifi- cant electrical conductivity.

Fabrication based on the Kirkendall effect of Co3O4 porous nanocages with extraordinarily high capacity for lithium storage.

Abstract: Herein we report a novel facile strategy for the fabrication of Co(3)O(4) porous nanocages based on the Kirkendall effect, which involves the thermal decomposition of Prussian blue analogue (PBA) Co(3)[Co(CN)(6)](2) truncated nanocubes at 400 °C. Owing to the volume loss and release of internally generated CO(2) and N(x) O(y) in the process of interdiffusion, Co(3)O(4) nanocages with porous shells and containing nanoparticles were finally obtained. When evaluated as electrode materials for lithium-ion batteries, the as-prepared Co(3)O(4) porous nanocages displayed superior battery performance. Most importantly, capacities of up to 1465 mA h g(-1) are attained after 50 cycles at a current density of 300 mA g(-1). Moreover, this simple synthetic strategy is potentially competitive for scaling-up industrial production.

Triazole-based one-dimensional spin-crossover coordination polymers.

Abstract: One-dimensional coordination Fe(II) polymers constructed through triple N(1),N(2)-1,2,4-triazole bridges form a unique class of spin-crossover materials, the synthetic versatility of which allows tuning the spin-crossover properties, the design of gels, films, liquid crystals, and nanoparticles and single-particle addressing. This Minireview provides the first complete overview of these very attractive switchable materials and their most recent developments.

A microporous metal-organic framework for highly selective separation of acetylene, ethylene, and ethane from methane at room temperature.

Abstract: A novel three-dimensional microporous metal-organic framework Zn4L(DMA)4 (UTSA-33, H8L=1,2,4,5-tetra(5-isophthalic acid)benzene, DMA=N,N′-dimethylacetamide) with small pores of about 4.8 to 6.5 A was synthesized and structurally characterized as a non-interpenetrated (4,8)-connected network with the flu topology (Schlafli symbol: (41261284)(46)2). The activated UTSA-33 a exhibits highly selective separation of acetylene, ethylene, and ethane from methane with the adsorption selectivities of 12 to 20 at 296 K, which has been established exclusively by the sorption isotherms and simulated breakthrough experiments, thus methane can be readily separated from their binary and even ternary mixtures at room temperature.

Dual catalysis: combination of photocatalytic aerobic oxidation and metal catalyzed alkynylation reactions--C-C bond formation using visible light.

Abstract: A new dual catalytic system for efficient C[BOND]H functionalization was developed. The appropriate choice of two metal catalysts allows the oxidative alkynylation of tertiary amines under mild and sustainable reaction conditions.

Light-Mediated Heterogeneous Cross Dehydrogenative Coupling Reactions: Metal Oxides as Efficient, Recyclable, Photoredox Catalysts in CC Bond- Forming Reactions

Abstract: Let there be light: A heterogeneous photocatalytic system based on easily recyclable TiO(2) or ZnO allows cross dehydrogenative coupling reactions of tertiary amines. The newly developed protocols have successfully been applied to various C-C and C-P bond-forming reactions to provide nitro amines as well as amino ketones, nitriles and phosphonates.

One‐Pot Synthesis, Characterization, and Enhanced Photocatalytic Activity of a BiOBr–Graphene Composite

Abstract: Herein, a chemically bonded BiOBr–graphene composite (BiOBr–RG) was prepared through a facile in situ solvothermal method in the presence of graphene oxide. Graphene oxide could be easily reduced to graphene under solvothermal conditions, and simultaneously BiOBr nanoplates with pure tetragonal phase were grown uniformly on the graphene surface. The structure and photoelectrochemical properties of the resulting materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and impedance and photocurrent action measurements. The combination of BiOBr and graphene introduces some properties of graphene into the photocatalysis reaction, such as excellent conductivity, adsorptivity, and controllability. A remarkable threefold enhancement in the degradation of rhodamine B (RhB) was observed with as-prepared BiOBr–RG as compared with pure BiOBr under visible light (λ>420 nm). The enhanced photocatalytic activity could be attributed to the great adsorptivity of dyes, the extended photoresponse range, the negative shift in the Fermi level of BiOBr–RG, and the high migration efficiency of photoinduced electrons, which may effectively suppress the charge recombination.

Addressing challenges in palladium-catalyzed cross-coupling reactions through ligand design.

Abstract: The development of palladium-catalyzed cross-coupling reactions has revolutionized the synthesis of organic molecules on both bench-top and industrial scales. While significant research effort has been directed toward evaluating how modifying various reaction parameters can influence the outcome of a given cross-coupling reaction, the design and implementation of novel ancillary ligand frameworks has played a particularly important role in advancing the state-of-the-art. This Review seeks to highlight notable examples from the recent chemical literature, in which newly developed ancillary ligands have enabled more challenging substrate transformations to be addressed with greater selectivity and/or under increasingly mild conditions. Throughout, the importance and subtlety of ligand effects in palladium-catalyzed cross-coupling reactions are described, in an effort to inspire further development and understanding within the field of ancillary ligand design.

Bimetallic catalysis using transition and Group 11 metals: an emerging tool for C-C coupling and other reactions.

Abstract: Bimetallic catalysis refers to homogeneous processes in which either two transition metals (TM), or one TM and one Group 11 (G11) element (occasionally Hg also), cooperate in a synthetic process (often a CC coupling) and their actions are connected by a transmetalation step. This is an emerging research area that differs from the isolated or tandem applications of the now classic processes (Stille, Negishi, Suzuki, Hiyama, Heck). Most of the reactions used so far combine Pd with a second metal, often Cu or Au, but syntheses involving very different TM couples (e.g., Cr/Ni in the catalyzed vinylation of aldehydes) have also been developed. Further development of the topic will soon demand a good knowledge of the mechanisms involved in bimetallic catalysis, but this knowledge is very limited for catalytic processes. However, there is much information available, dispersed in the literature, coming from basic research on exchange reactions occurring out of any catalytic cycle, in polynuclear complexes. These are essentially the same processes expected to operate in the heart of the catalytic process. This Review gathers together these two usually isolated topics in order to stimulate synergy between the bimetallic research coming from more basic organometallic studies and the more synthetic organic approaches to this chemistry.

Rare‐Earth Nanoparticles with Enhanced Upconversion Emission and Suppressed Rare‐Earth‐Ion Leakage

Abstract: Upconversion emissions from rare-earth nanoparticles have attracted much interest as potential biolabels, for which small particle size and high emission intensity are both desired. Herein we report a facile way to achieve NaYF(4):Yb,Er@CaF(2) nanoparticles (NPs) with a small size (10-13 nm) and highly enhanced (ca. 300 times) upconversion emission compared with the pristine NPs. The CaF(2) shell protects the rare-earth ions from leaking, when the nanoparticles are exposed to buffer solution, and ensures biological safety for the potential bioprobe applications. With the upconversion emission from NaYF(4):Yb,Er@CaF(2) NPs, HeLa cells were imaged with low background interference.

Merging organocatalysis and gold catalysis--a critical evaluation of the underlying concepts.

Abstract: While both organocatalysis and gold catalysis have their roots deeply entrenched in the landscape of modern organic chemistry, an exciting trend in the complementary merging of organocatalysis and especially Au(I) catalysis has emerged in the last four years. This niche area has been developing rapidly and this minireview serves to pin-point the fundamental concepts guiding reaction design in these binary catalytic systems. Moreover, the proven synthetic utility of organo/Au(I) multicatalytic systems in accessing molecular frameworks, previously a challenge to single catalytic systems, has resulted in this new concept permeating numerous areas of organocatalysis, such as primary/secondary amine, Bronsted acid, hydrogen-bonding as well as N-heterocyclic carbene (NHC) catalysis. The first detailed account of these recent developments is systematically presented.

Tuning the Physicochemical Properties of Diverse Phenolic Ionic Liquids for Equimolar CO2 Capture by the Substituent on the Anion

Abstract: Phenolic ionic liquids for the efficient and reversible capture of CO{sub 2} were designed and prepared from phosphonium hydroxide and substituted phenols. The electron-withdrawing or electron-donating ability, position, and number of the substituents on the anion of these ionic liquids were correlated with the physicochemical properties of the ionic liquids. The results show that the stability, viscosity, and CO{sub 2}-capturing ability of these ionic liquids were significantly affected by the substituents. Furthermore, the relationship between the decomposition temperature, the CO{sub 2}-absorption capacity, and the basicity of these ionic liquids was quantitatively correlated and further rationalized by theoretical calculation. Indeed, these ionic liquids showed good stability, high absorption capacity, and low absorption enthalpy for CO{sub 2} capture. This method, which tunes the physicochemical properties by making use of substituent effects in the anion of the ionic liquid, is important for the design of highly efficient and reversible methods for CO{sub 2}-capture. This CO{sub 2} capture process using diverse phenolic ionic liquids is a promising potential method for CO{sub 2} absorption with both high absorption capacity and good reversibility.

Synthesis of Ni–Ru Alloy Nanoparticles and Their High Catalytic Activity in Dehydrogenation of Ammonia Borane

Abstract: We report the synthesis and characterization of new Ni(x)Ru(1-x) (x = 0.56-0.74) alloy nanoparticles (NPs) and their catalytic activity for hydrogen release in the ammonia borane hydrolysis process. The alloy NPs were obtained by wet-chemistry method using a rapid lithium triethylborohydride reduction of Ni(2+) and Ru(3+) precursors in oleylamine. The nature of each alloy sample was fully characterized by TEM, XRD, energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). We found that the as-prepared Ni-Ru alloy NPs exhibited exceptional catalytic activity for the ammonia borane hydrolysis reaction for hydrogen release. All Ni-Ru alloy NPs, and in particular the Ni(0.74)Ru(0.26) sample, outperform the activity of similar size monometallic Ni and Ru NPs, and even of Ni@Ru core-shell NPs. The hydrolysis activation energy for the Ni(0.74)Ru(0.26) alloy catalyst was measured to be approximately 37 kJ mol(-1). This value is considerably lower than the values measured for monometallic Ni (≈70 kJ mol(-1)) and Ru NPs (≈49 kJ mol(-1)), and for Ni@Ru (≈44 kJ mol(-1)), and is also lower than the values of most noble-metal-containing bimetallic NPs reported in the literature. Thus, a remarkable improvement of catalytic activity of Ru in the dehydrogenation of ammonia borane was obtained by alloying Ru with a Ni, which is a relatively cheap metal.

The First Catalytic Synthesis of an Acrylate from CO2 and an Alkene—A Rational Approach

Abstract: For more than three decades the catalytic synthesis of acrylates from the cheap and abundantly available C1 building block carbon dioxide and alkenes has been an unsolved problem in catalysis research, both in academia and industry. Herein, we describe a homogeneous catalyst based on nickel that permits the catalytic synthesis of the industrially highly relevant acrylate sodium acrylate from CO2, ethylene, and a base, as demonstrated, at this stage, by a turnover number of greater than 10 with respect to the metal.

Scaffold‐Inspired Enantioselective Synthesis of Biologically Important Spiro[pyrrolidin‐3,2′‐oxindoles] with Structural Diversity through Catalytic Isatin‐Derived 1,3‐Dipolar Cycloadditions

Abstract: Catalytic asymmetric construction of the biologically important spiro[pyrrolidin-3,2'-oxindole] scaffold with contiguous quaternary stereogenic centers in excellent stereoselectivities (up to >99:1 d.r., 98% ee) has been established by using an organocatalytic 1,3-dipolar cycloaddition of isatin-based azomethine ylides. This protocol represents the first example of catalytic asymmetric 1,3-dipolar cycloadditions involving azomethine ylides generated in situ from unsymmetrical cyclic ketones. In addition, theoretical calculations were performed on the transition state of the reaction to understand the stereochemistry. Preliminary bioassays with these spiro[pyrrolidin-3,2'-oxindole] revealed that several compounds showed moderate cytotoxicity to SW116 cells.