Simple Copper Salt Research Articles

Unsymmetrical Pyrazoly‐Pyridinyl‐Triazole Promoted High Active Copper Composites on Mesoporous Materials and Catalytic Applications

AbstractHigh active ligand usually plays an important role during catalysis and organic synthesis area. Unsymmetrical tridentate pyrazoly‐pyridinyl‐triazole ligand bridged copper composite supported on the ordered mesoporous material was synthesized from the designed ligand, simple copper salt and commercially available SBA‐15. The resulting copper composite was fully characterized by X‐ray photoelectron spectrometry, scanning electron microscopy and transmission electron microscopy and X‐ray power diffraction. Compared to traditional noble Ir, Ru, Rh and Pd complexes, this economical and stable heterogeneous copper revealed high catalytic selectivity for the reaction of hydronaphthalenones and alcohols with good recyclability. Mechanism explorations disclosed that oxidation, condensation and hydrogenation processes were all involved during this process and this provided an efficient method to the synthesis of 2‐benzyl‐3,4‐dihydronaphthalen‐1(2H)‐onederivatives with good recyclability through the green borrowing hydrogen strategy.

Electrocatalytic Cross-Coupling Reactions Assisted By Redox-Active Mediators

The seminar will detail electrocatalytic C–C and C–N bond-forming methodologies enabled by redox-active mediators and shuttles. Here, we will demonstrate a symbiotic relationship between energy storage and metal-catalyzed organic synthesis. Two research initiatives will be discussed that highlight the use of a mediator to (i) protect a coupling catalyst from overreduction through a degenerate shuttling of electrons and (ii) assist in oxidation of complexes with slow ET kinetics under electrochemical conditions.The concept of protecting catalyst from degradation using shuttles will be discussed in the context of cross-electrophile coupling (XEC). Couplings of alkyl and aryl halides promoted by electrochemistry represents an attractive alternative to conventional methods that require stoichiometric quantities of high-energy reductants. Most importantly, electroreduction can readily exceed the reducing potentials of chemical reductants to activate catalysts with improved reactivities and selectivities that are otherwise incompatible with conventional reductants. This work details the mechanistically-driven development of an electrochemical methodology for XEC that utilizes redox-active shuttles developed by the energy-storage community to protect reactive coupling catalysts from overreduction. The resulting electrocatalytic system is practical, scalable, and broadly applicable to the reductive coupling of a wide range of aryl, heteroaryl, or vinyl bromides with primary or secondary alkyl bromides. The impact of overcharge protection as a strategy for electrosynthetic methodologies is underscored by the dramatic differences in yields from coupling reactions with added redox shuttles (generally >80%) and those without (generally <20%). In addition to excellent yields for a wide range of substrates, reactions protected from overreduction can be performed at high currents and on multigram scalesThe second half of the talk will demonstrate the use of mediators to protect ligandless complexes that are susceptible to electroplating on a cathode and to facilitate oxidation of the electrochemically-inactive catalysts to the active form. This strategy is applied to an electrochemically driven, scalable Chan-Lam-Evans reaction that utilizes simple copper salts to promote C-N bond formation under an inert atmosphere. This work represents a rare example of air-free CLE coupling. This oxidative reaction is performed in an undivided cell with a simple Cu salt that would otherwise rapidly plate out of solution. Mediator-assisted CLE coupling provides access to a broad range of amine products that are otherwise challenging to form even in air. The methodology seeks to eliminate the need for O2 on scale and provide an attractive alternative for process groups in industry.

Mediator-Enabled Electrocatalysis with Ligandless Copper for Anaerobic Chan-Lam Coupling Reactions.

Simple copper salts serve as catalysts to effect C-X bond-forming reactions in some of the most utilized transformations in synthesis, including the oxidative coupling of aryl boronic acids and amines. However, these Chan-Lam coupling reactions have historically relied on chemical oxidants that limit their applicability beyond small-scale synthesis. Despite the success of replacing strong chemical oxidants with electrochemistry for a variety of metal-catalyzed processes, electrooxidative reactions with ligandless copper catalysts are plagued by slow electron-transfer kinetics, irreversible copper plating, and competitive substrate oxidation. Herein, we report the implementation of substoichiometric quantities of redox mediators to address limitations to Cu-catalyzed electrosynthesis. Mechanistic studies reveal that mediators serve multiple roles by (i) rapidly oxidizing low-valent Cu intermediates, (ii) stripping Cu metal from the cathode to regenerate the catalyst and reveal the active Pt surface for proton reduction, and (iii) providing anodic overcharge protection to prevent substrate oxidation. This strategy is applied to Chan-Lam coupling of aryl-, heteroaryl-, and alkylamines with arylboronic acids in the absence of chemical oxidants. Couplings under these electrochemical conditions occur with higher yields and shorter reaction times than conventional reactions in air and provide complementary substrate reactivity.

Synthesis and structural characterisation of some mononuclear 1:1:1 complexes of coinage metal(I) compounds with tertiary phosphines (arsines) and 1,2-diamines, [MX(EPh3)(N,N'-1,2-diamine)

Crystallization of adducts of simple copper(I) and silver(I) salts (MX) with triphenylphosphine from 'N,N,N′,N'-tetramethylethylenediamine', 'tmeda', has yielded adducts of 1:1:1 MX:PPh3:tmeda stoichiometry, all of which have been characterized by room temperature single crystal X-ray structure determinations. In all adducts, the complex is mononuclear [M(PPh3)(N,N′-tmeda)X] with four-coordinate N2PMX metal atom environments (M = Cu, X = Cl, Br, I; M = Ag, X = Cl or NO3). The tricyclohexylphosphine species [Ag(Pcy3)(N,N′-tmeda)(ONO2)], also in a N2PAgX metal environment, has been defined. A number of similar silver(I) adducts are obtained by using 1,2-diaminopropane, 'pn' as solvent. The chloride, bromide and iodide complexes are isomorphous, the complexes being mononuclear, [Ag(PPh3)(pn)X], with four-coordinate N2PAgX environments, the pn ligand chelating. An isomorphous arsenic analogue of the bromide has also been isolated. All complexes have been characterized by IR and NMR (1H and 31P) spectroscopy.

Copper Oxide/Hydroxide Nanomaterial Synthesized from Simple Copper Salt

The copper oxide, CuO, and copper hydroxide, Cu(OH)2 nanomaterials have been prepared by a simple copper salt aqueous solution reaction. The powder X-ray diffraction (XRD) analysis showed the successful formation of Cu(OH)2 and CuO nanoparticles. The average crystallite size of these Cu(OH)2 and CuO nanoparticles was estimated and found to be around 17[Formula: see text]nm (Cu(OH)2) and 10[Formula: see text]nm (CuO). The surface morphology and size of the CuO particles were confirmed by Scanning Electron Microscope (SEM) and High-resolution transmission electron microscope (HRTEM). The Raman analysis, dielectric and conductivity of CuO nanoparticles have been performed. The frequency variation of the capacitance (real dielectric constant) and dielectric loss was studied. The capacitance of the CuO nanoparticles is high at low frequencies and decreases rapidly when the frequency is increased. The frequency dependent ac conductivity follows Johnscher’s power law.

Alkylation–peroxidation of α-carbonyl imines or ketones catalyzed by a copper salt via radical-mediated Csp3–H functionalization

The catalytic alkylation–peroxidation of α-carbonyl imines or ketones was enabled by a simple copper salt via radical-mediated Csp3–H functionalization.

Stereospecific Nickel-Catalyzed Borylation of Secondary Benzyl Pivalates

A stereoselective nickel-catalyzed direct borylation of enantioenriched secondary benzyl pivalates is described. This methodology is characterized by an intriguing cooperativity of simple nickel and copper salts to promote the targeted C–B bond formation under mild reaction conditions. Unlike classical SN2-type processes, this protocol occurs with a neat retention of configuration, resulting in synthetically versatile benzyl boronic esters with excellent stereochemical fidelity.

Copper‐Catalyzed Carboxylation of Aryl‐ and Alkenyltrialkoxysilanes

AbstractThe use of a simple copper salt as a catalyst, in conjunction with CsF as an activator, enabled a wide range of aryl‐ and alkenyltrialkoxysilanes to undergo carboxylation under atmospheric pressure of CO2, affording the corresponding carboxylic acids in good to high yields.

A Boron Protecting Group Strategy for 1,2-Azaborines

Upon reaction with either molecular oxygen or di-tert-butylperoxide in the presence of a simple copper(I) salt and an alcohol, a range of 1,2-azaborines readily exchange B-alkyl or B-aryl moieties for B-alkoxide fragments. This transformation allows alkyl and aryl groups to serve for the first time as removable protecting groups for the boron position of 1,2-azaborines during reactions that are not compatible with the easily modifiable B-alkoxide moiety. This reaction can be applied to synthesize a previously inaccessible BN isostere of ethylbenzene, a compound of interest in biomedical research. A sequence of epoxide ring opening using N-deprotonated 1,2-azaborines followed by an intramolecular version of the boron deprotection reaction can be applied to access the first examples of BN isosteres of dihydrobenzofurans and benzofurans, classes of compounds that are important to medicinal chemistry and natural product synthesis.

Copper-catalyzed Selective Oxygenation of Methyl and Benzyl Substituents in Pyridine with O2

A selective oxygenation of picolines and their derivatives has been achieved by using a simple copper salt as a catalyst and molecular oxygen as an oxidant, where the α-position of the alkyl substituent is selectively oxidized to give the corresponding aldehydes or ketones. Addition of a catalytic amount of water enhances the catalytic activity, which could be attributed to the role of the proton donor to activate the substrates.

Copper-Catalyzed Carbenoid Insertion Reactions of α-Diazoesters and α-Diazoketones into Si-H and S-H Bonds.

An efficient copper-catalyzed carbenoid insertion reaction of α-diazo carbonyl compounds into Si-H and S-H bonds was developed. A wide range of α-silylesters and α-thioesters was obtained in high yields (up to 98%) from α-diazoesters using 5 mol% of a simple copper(I) salt as catalyst. Using 0.05 mol% of the same catalyst, α-diazoketones led to α-silylketones in low to good yields (up to 70%).

Reactions Catalysed by a Binuclear Copper Complex: Aerobic Cross Dehydrogenative Coupling of N-Aryl Tetrahydroisoquinolines.

Binuclear copper complex [{Cu(Sal)2 (NCMe)}2 ] (Sal=salicylate) was found to be an active catalyst for the aerobic oxidation of N-aryl tetrahydroisoquinolines to the corresponding iminium ions, which could be trapped by a wide range of nucleophiles to form coupled products. The reactions took place under 1 bar of O2 at room temperature with 1 mol % of the copper catalyst being sufficient in most cases, and are considerably accelerated by catalytic chloride anions. Mechanistic studies show that the CuII dimer oxidizes the amine to the iminium ion, and this two-electron process requires O2 , whereby the resulting CuI is concomitantly reoxidised back to CuII . Various lines of evidence suggest that the oxidative coupling reaction is turnover-limited by the step of iminium formation, and it is this step that is promoted by the chloride anion. Since it is more efficient than and mechanistically distinct from the well-studied simple copper salts such as CuBr and CuCl2 , the binuclear copper catalyst provides a new tool for oxidative coupling reactions.

Chemoselective synthesis and cytotoxic activity of a series of novel benzo[1,4]oxazin-3-one derivatives

That tetraacetonitrile copper perchlorate catalyzes intramolecular amidation of arenes was found to be a new strategy for construction of nitrogen-containing heterocycles and resulted in the formation of a series of novel benzo[1,4]oxazin-3-one derivatives from N-(1,3-diphenyl-1H-1,2,4-triazol-5-yl)-2-phenoxyacetamides. This approach of heterocyclic construction proceeds in a chemoselective manner in which only benzo[1,4]oxazin-3-one derivatives were obtained by CN bonds formation with cheap and simple copper salt catalyst under mild conditions in moderate to good yields. The biological assay of some of benzo[1,4]oxazin-3-one derivatives showed that they had moderate antiproliferative activity toward MDA-MB231 and HeLa cancer cell lines.

Dehydrogenative Cross-Coupling Reactions of N-Aryl α-Amino Acid Esters with Nitroalkanes for the Synthesis of β-Nitro α-Amino Acid Esters

A novel copper-catalyzed dehydrogenative cross-coupling reaction of N -aryl α-amino acid esters with nitroalkanes to give β-nitro α-amino acid esters was developed. Various N -aryl α-amino acid esters reacted smoothly with nitroalkanes to give the desired coupling products in moderate to good yields. The method uses a cheap and simple copper salt as a catalyst and molecular oxygen as an environmentally benign oxidant. A possible mechanism for the dehydrogenative cross-coupling reaction is proposed.

ChemInform Abstract: Copper Mediated Decarboxylative Direct C—H Arylation of Heteroarenes with Benzoic Acids.

Decarboxylative coupling reactions to date require a stoichiometric oxidant (such as copper and silver salts) for decarboxylation purposes along with a metal catalyst (e.g. palladium) for cross-coupling. In this communication, an economic and sustainable approach by using a simple copper salt was developed in the presence of molecular oxygen as the sole oxidant. A wide range of 5-membered heteroarenes undergo aryl–heteroaryl cross-coupling with electron deficient aryl carboxylic acids.

Noble Metal-Free Copper Hydroxide as an Active and Robust Electrocatalyst for Water Oxidation at Weakly Basic pH

Copper hydroxide (Cu(OH)2) is a quite inexpensive and abundant material, but the literature contains no reports of using it as a stable water oxidation catalyst (WOC). In this study, we report for the first time that Cu(OH)2 material synthesized from a simple copper salt can be used as a WOC with good activity and stability. Under optimal conditions using Cu(OH)2 as the electrocatalyst, a catalytic current density of 0.1 mA/cm2 can be achieved under an applied potential of ∼1.05 V relative to Ag/AgCl at pH 9.2. The slope of the Tafel plot is 78 mV/dec. The Tafel plot indicates that a current density of ∼0.1 mA/cm2 requires an overpotential of 550 mV. The Faradaic efficiency was measured to be ∼95%. The as-synthesized Cu(OH)2 material was characterized by X-ray powder diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy.

Copper-Catalyzed Intramolecular Oxidative Amination of Unactivated Internal Alkenes.

A copper-catalyzed oxidative amination of unactivated internal alkenes has been developed. The Wacker-type oxidative alkene amination reaction is traditionally catalyzed by a palladium through a mechanism involving aminopalladation and β-hydride elimination. Replacing the precious and scarce palladium with a cheap and abundant copper for this transformation has been challenging because of the difficulty associated with the aminocupration of internal alkenes. The combination of a simple copper salt, without additional ligand, as the catalyst and Dess-Martin periodinane as the oxidant, promotes efficiently the oxidative amination of allylic carbamates and ureas bearing di- and trisubstituted alkenes leading to oxazolidinones and imidazolidinones. Preliminary mechanistic studies suggested a hybrid radical-organometallic mechanism involving an amidyl radical cyclization to form the key C-N bond.

Copper-catalyzed tandem A3-coupling–isomerization–hydrolysis reactions of aldehydes and terminal alkynes leading to chalcones

A3 coupling is not the end: catalyzed by a simple copper salt, the reaction of aldehyde, alkyne, and amine can afford chalcone.

Cuprous oxide thin film directly electrodeposited from a simple copper salt on conductive electrode for efficient oxygen evolution reaction

Catalysts made of earth-abundant elements for water splitting have attracted increasing attention in recent years. Herein we report that inexpensive cheap copper oxide thin film material can be used as an excellent electrocatalyst precursor for the oxygen evolution reaction (OER). Cuprous oxide (Cu2O) thin films were facilely electrodeposited on conductive fluorine doped tin oxide (FTO) substrates from a simple Cu(II) salt solution under a very low applied potential (-0.17V or -0.23V). Two kinds of morphologies (dendritic branching and cluster-like) of Cu2O were obtained just by altering the deposition potentials. Both Cu2O films can be used for OER, and the dendritic branching Cu2O material exhibits better performance. Under optimal conditions, OER was achieved under an onset potential at ∼0.92V (vs. Ag/AgCl) in 0.1M borate solution at pH 9.2. A catalytic current density of ∼0.1mA/cm2 required a low overpotential of ∼430mV using the electrodeposited Cu2O material under an optimal condition. The slope of the Tafel plot is ∼59.9mV/dec and the Faradaic efficiency was close to 93%. The samples were well characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS).

ChemInform Abstract: Condensation versus Hydroamination for the Direct, Catalytic Synthesis of Tetrasubstituted Propargylamines

AbstractReview: [24 refs.