Are There Carbenes in N‐Heterocyclic Carbene Organocatalysis?

Azolium cations are widely employed in organocatalysis to catalyse highly valuable synthetic processes in the presence of a base. These reactions are called “N‐heterocyclic carbene catalysis”, based on the assumption that they are initiated by the formation of a free carbene through deprotonation, which can then react with the substrates and thereby affect their reactivity to obtain the desired products. However, we herein provide evidence that an electrophilic aromatic substitution mechanism is energetically more favourable, in which the azolium cation reacts directly with the substrate, avoiding the formation of the free carbene in solution.     

New Chiral Substituted 8-Quinolinyl-oxazolines as Ligands for Copper(I)-catalyzed Asymmetric Cyclopropanation

ＩｎｔｒｏｄｕｃｔｉｏｎＡｓｙｍｍｅｔｒｉｃｃａｔａｌｙｔｉｃｃｙｃｌｏｐｒｏｐａｎａｔｉｏｎｏｆｏｌｅｆｉｎｓｗｉｔｈｄｉａｚｏｃｏｍｐｏｕｎｄｓｉｓｏｎｅｏｆｔｈｅｍｏｓｔｕｓｅｆｕｌｍｅｔｈｏｄｓｆｏｒｔｈｅｓｙｎｔｈｅｓｉｓｏｆｃｈｉｒａｌｃｙｃｌｏｐｒｏｐａｎｅｓ .1Ａｎｕｍｂｅｒｏｆｅｆｆｉｃｉｅｎｔｃｈｉｒａｌｌｉｇａｎｄｓ ,ｐａｒｔｉｃｕｌａｒｌｙｂｉｓｎｉｔｒｏｇｅｎｌｉｇａｎｄｓ ,ｈａｖｅｂｅｅｎｄｅｖｅｌｏｐｅｄ ,ａｎｄｅｘｃｅｌｌｅｎｔｅｎａｎｔｉｏｓｅｌｅｃｔｉｖｉｔｉ…     

Syntheses of Binuclear Copper(I) Complexes Containing Benzimidazole

1 INTRODUCTION Procedures to synthesize copper(I) complexes are of great interest due to the diversity of products resulting from almost the same methodology. It has been long known that four-electron-donordipho- sphine compounds Ph2P(CH2)nPPh2 are excellent bi- dentate ligands[1, 2]. The chelating tendency of bis- (diphenylphosphino) methane is one of the dipho- sphine ligands most suitable to lock two metal atoms together in close proximity[3]. Many examples of bi- or polynuclear com…     

Copper (I) Iodide-Catalyzed Solvent-Free Synthesis of α-Aminophosphonates

Abstract

A method for the synthesis of α-aminophosphonates through the three-component coupling reaction of aldehydes, amines, and diisopropyl phosphite using copper (I) iodide salt catalyst is demonstrated, The reaction is highly efficient, economic, and also environment friendly.

[Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental resource: Table S1, Figures S1–S9.]

GRAPHICAL ABSTRACT      

The Ternary Coppersilver Selenide—A New Homogeneous Solid State Ion-Selective Electrode for Copper (II)

Abstract

The performance characteristics of a copper (II) ion-selective electrode, based on pressed-pellet membrane of ternary CuAgSe, are reported. The sensing material is isostructural with the natural mineral β -eucairite and shows high corrosion resistivity which results in stable and reproducible electrode performance upon ageing. The electrodes exhibit a linear Nernstian response dawn to 5.10^?8 M in non buffered medium and down to 10^?13M in copper-glycine ion buffer. Data on the electrode stability for a period of two and a half years, on the electrode response time, pH-dependence, selectivity etc. are also presented.     

Synthesis and Structure of the Copper(I) Complex Containing Bis(diphenylphosphino)ethane

1 INTRODUCTION Procedures to synthesize copper(I) complexes are of great interest because of the diversity of products resulting from almost the same methodology. It has long been known that four-electron-donor diphosphine compounds Ph2P(CH2)nPPh2 are excellent bidentate ligands[1]. The chelating tendency decreases as the chain length increases, so that for the ligands Ph2P(CH2)nPPh2, the tendency to chelation is the greatest for bis(diphenylphosphino)ethane. Copper(I) displays wide…     

2,2′-Biimidazole as an Efficient Ligand for Copper(I)-Catalyzed C‒N Coupling Reactions

An efficient copper(I)-catalyzed system using 2,2′-biimidazole as the ligand was applied to N-arylation of a broad spectrum of nitrogen nucleophiles with aryl halides. The reactions were carried out in relatively mild conditions with good to excellent yields.     

Trapping a Silicon(I) Radical with Carbenes: A Cationic cAAC–Silicon(I) Radical and an NHC–Parent-Silyliumylidene Cation

The trapping of a silicon(I) radical with N-heterocyclic carbenes is described. The reaction of the cyclic (alkyl)(amino) carbene [cAAC_Me] (cAAC_Me=:C(CMe₂)₂(CH₂)NAr, Ar=2,6-iPr₂C₆H₃) with H₂SiI₂ in a 3:1 molar ratio in DME afforded a mixture of the separated ion pair [(cAAC_Me)₂Si:^.]⁺I⁻ ( 1 ), which features a cationic cAAC–silicon(I) radical, and [cAAC_Me−H]⁺I⁻. In addition, the reaction of the NHC–iodosilicon(I) dimer [I_Ar(I)Si:]₂ (I_Ar=:C{N(Ar)CH}₂) with 4 equiv of I_Me (:C{N(Me)CMe}₂), which proceeded through the formation of a silicon(I) radical intermediate, afforded [(I_Me)₂SiH]⁺I⁻ ( 2 ) comprising the first NHC–parent-silyliumylidene cation. Its further reaction with fluorobenzene afforded the C_Ar−H bond activation product [1-F-2-I_Me-C₆H₄]⁺I⁻ ( 3 ). The isolation of 2 and 3 confirmed the reaction mechanism for the formation of 1 . Compounds 1 – 3 were analyzed by EPR and NMR spectroscopy, DFT calculations, and X-ray crystallography.     

Copper (I) and silver (I) complexes of dithiomalonamide,NN′-dimethyl- and NN′-diphenyl-dithiomalonamide.

Some copper (I) and silver (I) complexes with dithiomalonamide (Hdtma), NN′-dimethyl-(HMe₂dtma) and NN′-diphenyl-dithiomalonamide (HPh₂dtma) were prepared: Cu(Hdtma)X (X² = Cl, Br, I(H₂O), ClO₄); Cu(HL)₂X (HMe₂dtma: X = Cl, Br, I, ClO₄; HPh₂dtma: X = Cl, Br, I); Ag(HL)X (Hdtma: X = Cl; HMe₂dtma: X = Br, ClO₄, BF₄; HPh₂dtma: X = Br, I); Ag₂(HL)₃X₂ (Hdtma: X = ClO₄, BF₄; HMe₂dtma: X = Cl; HPh₂-dtma: X = Cl, ClO₄); Ag₂(HMe₂dtma)I₂ and Ag₃(Hdtma)₂Br₃. Molar conductivities in DMF show that the complexes behave: M₂(HL)₃(ClO₄)₂ as 1:2 electrolytes, M(HL) (ClO₄ of BF₄) as 1:1 electrolytes; those of the halides Cu(HL)X and Cu(HL)₂X, are almost equal and intermediate between values for non-electrolytes and 1:1 electrolites. Infrared spectra indicate an S,N-coordination for all the complexes: ν(MN) bands in the region of 400–500 cm⁻¹ and ν(MS) bands in the region of 300–400 cm⁻¹ (for Hdtma), 300–320 cm⁻¹ (for HMe₂dtma) and 260–280 cm⁻¹ (for HPh₂dtma) are observed. No ν(MX) bands were identified in the halide complexes indicating that a mental—halide coordination, if present in the solid complexes, should be very weak.     

Thiolate Bridged Gold(I)–NHC Catalysts: New Approach for Catalyst Design and its Application to Trapping Catalytic Intermediates

New dinuclear N-heterocyclic gold complexes with bridging thiolate ligands have been designed as catalytic precursors with desired properties such as stability, recyclability and that do not require additives. The dinuclear compound [(AuNHC)₂(μ-SC₆F₅)]OTf could slowly release the active catalytic species [Au(NHC)]⁺ and the precursor [Au(SC₆F₅)(NHC)] in solution, which means that both species would remain stable throughout the catalytic cycle and the pre-catalyst could easily be recovered. The properties exhibited by the complexes have been taken advantage of to gain new insights on the gold-catalyzed hydroalkoxylation of alkynes, with the aim of clarifying all the steps of the catalytic cycle, together with the characterization of intermediates and final products. Isolation and characterization of the pure final spiroketals and the thermodynamic intermediate have been achieved for the first time. Moreover, the kinetic intermediate has also been detected for the first time.     

13C NMR Spectroscopy of N-Heterocyclic Carbenes Can Selectively Probe σ Donation in Gold(I) Complexes

The Dewar–Chatt–Duncanson (DCD) model provides a successful theoretical framework to describe the nature of the chemical bond in transition-metal compounds and is especially useful in structural chemistry and catalysis. However, how to actually measure its constituents (substrate-to-metal donation and metal-to-substrate back-donation) is yet uncertain. Recently, we demonstrated that the DCD components can be neatly disentangled and the π back-donation component put in strict correlation with some experimental observables. In the present work we make a further crucial step forward, showing that, in a large set of charged and neutral N-heterocyclic carbene complexes of gold(I), a specific component of the NMR chemical shift tensor of the carbenic carbon provides a selective measure of the σ donation. This work opens the possibility of 1) to characterize unambiguously the electronic structure of a metal fragment (LAu(I)^n+/0 in this case) by actually measuring its σ-withdrawing ability, 2) to quickly establish a comparative trend for the ligand trans effect, and 3) to achieve a more rigorous control of the ligand electronic effect, which is a key aspect for the design of new catalysts and metal complexes.     

Mechanically Activated Solid-Phase Reaction of Copper(I) Chloride with Sodium β-Diketonates: Formation of Metallic Copper Nanoparticles

Russian Journal of General Chemistry - Solid-phase reaction of copper(I) chloride with sodium β-diketonates under mechanical activation in a vibration ball mill involves disproportionation of...     

Copper(I) 3-Methylsalicylate Mediates the Chan–Lam N-Arylation of Heterocycles

Copper(I) 3-methylsalicylate (CuMeSal) mediates N-arylation reactions between aryl boronic acids and aromatic heterocycles (Chan–Lam coupling) under moderate reaction conditions (K₂CO₃, methanol, 65 °C, in air, 3–5 h). Both electron-rich and electron-deficient aryl boronic acids and a diverse set of N-heterocycles were allowed to react and gave N-arylation products in reasonable yields, which demonstrate the utility of this catalyst.     

Natriummetaphosphat (I) in Metaphosphors?ure (II)

Ohne Zusammenfassung     

Intramolecular Reactions of Metal Carbenoids with Allylic Ethers: Is a Free Ylide Involved in Every Case?

Rhodium‐, copper‐ and iridium‐catalyzed reactions of the ¹³C‐labelled diazo carbonyl substrates 18* and 19* were performed. Results obtained from copper‐ and iridium‐catalyzed reactions of the ¹³C‐labelled α‐diazo β‐keto ester 19* indicate that either or both of these reactions do not proceed via a free oxonium ylide but instead follow a competing non‐ylide route that delivers apparent [2,3]‐sigmatropic rearrangement products. In the case of the iridium‐catalyzed reaction of α‐diazo β‐keto ester 19* , results obtained from crossover experiments indicate that the initially formed metal‐bound ylide dissociates to give an iridium enolate and an allyl cation, which recombine to form the C?C bond.     

Thionyl Chloride-pyridine Mediated Rearrangement. Synthesis of Potential Intermediates for (+) and (±)-Occidol

Thionyl chloride-pyridine mediated rearrangement of cylohexadienyl alcohols (2) and (8) has provided hyposantonin (3) and tetrahydronaphthalene (9), respectively, which in turn have served as potential intermediates for the synthesis of optically active and racemic occidol (6), respectively.     

Copper(I) and copper(II) inhibit Aβ peptides proteolysis by insulin-degrading enzyme differently: implications for metallostasis alteration in Alzheimer's disease

Accumulation of neurotoxic amyloid-β peptide (Aβ) and alteration of metal homeostasis (metallostasis) in the brain are two main factors that have been very often associated with neurodegenerative diseases, such as Alzheimer's disease (AD). Aβ is constantly produced from the amyloidprecursor-protein APP precursor and immediately catabolized under normal conditions, whereas dysmetabolism of Aβ and/or metal ions seems to lead to a pathological deposition. Although insulin-degrading enzyme (IDE) is the main metalloprotease involved in Aβ degradation in the brain being up-regulated in some areas of AD brains, the role of IDE for the onset and development of AD is far from being understood. Moreover, the biomolecular mechanisms involved in the recognition and interaction between IDE and its substrates are still obscure. In spite of the important role of metals (such as copper, aluminum, and zinc), which has brought us to propose a "metal hypothesis of AD", a targeted study of the effect of metallostasis on IDE activity has never been carried out. In this work, we have investigated the role that various metal ions (i.e., Cu(2+), Cu(+), Zn(2+), Ag(+), and Al(3+)) play in modulating the interaction between IDE and two Aβ peptide fragments, namely Aβ(1-16) and Aβ(16-28). It was therefore possible to identify the direct effect that such metal ions have on IDE structure and enzymatic activity without interferences caused by metal-induced substrate modifications. Mass spectrometry and kinetic studies revealed that, among all the metal ions tested, only Cu(2+), Cu(+), and Ag(+) have an inhibitory effect on IDE activity. Moreover, the inhibition of copper(II) is reversed by adding zinc(II), whereas the monovalent cations affect the enzyme activity irreversibly. The molecular basis of their action on the enzyme is also discussed on the basis of computational investigations.     

Luminescence of cesium dicyanoaurate(I). Evidence for extended Au(I)Au(I) interactions in two dimensions

The luminescence of microcrystalline samples of Cs[Au(CN)₂] is reported and ascribed to planar AuAu interactions. Low-temperature measurements from 1.6 to 100 K of the luminescence decay rate of Cs[Au(CN)₂] for the band centered at 458 nm reveal the presence of at least two emitting levels separated by 46 cm⁻¹. A simple orbital model is proposed to account for the luminescence, and spin—orbit coupling is invoked to explain the splitting of the two lowest states. The analogies and differences between this luminescence and that observed for salts of Pt(CN)₄²⁻ are briefly discussed.