Coupling Of Alkynes Research Articles

Selective hydrogenation of acetylene on carbon-encapsulated Ni-Co-Cu trimetallic nanoparticles: Synergizing electronic effects and spatial confinement

Achieving high ethylene selectivity and activity simultaneously for acetylene selective hydrogenation still remains challenging. Here, the challenge of the trade-off between activity and selectivity was solved by synergizing electronic effects and spatial confinement, which was achieved by confining the Ni-Co-Cu trimetallic nanoparticles in a carbon layer (NixCuyCoz@C/Al2O3). Compared to the catalyst without carbon encapsulation (NixCuyCoz/Al2O3), NixCuyCoz@C/Al2O3 showed superior catalytic performance in terms of enhanced activity, selectivity and stability. Under optimal conditions, acetylene conversion of 100% and ethylene selectivity of 89% were achieved, whereas NixCuyCoz/Al2O3 exhibited lower acetylene conversion (92%) and ethylene selectivity (21%). Detailed characterizations reveal that the electronic structure can be regulated flexibly by controlling the composition of Ni-Co-Cu nanoparticles. The enhanced activity and selectivity were attributed to the weakened adsorption of acetylene and ethylene on the electron-rich Ni. The improved stability was related to the carbon layer, which suppressed the acetylene coupling by the acidic sites on the Al2O3 surface.

Synergistic effects of CuZnMg-based catalysts for enhanced catalysis in alkyne-aldehyde coupling reactions

The coupling of acetylene and formaldehyde provides an atomic economy and a green feasible strategy for the synthesis of high value-added chemicals, but the development of efficient catalysts remains a challenge. In this work, we present the construction of CuZnxMgyAl-LDO multicenter catalysts using layered double hydroxide derivatives. By optimizing the Zn/Mg ratio, the CuZn3Mg1Al-LDO catalyst has a 78.1% yield of 1,4-butynediol and a turnover frequency of 5.36 h−1. The characterization and density functional theory results demonstrated that the synergistic effects of CuO-(ZnMgAl)Ox multicenter structure can adjust the chemical environment of Cu species, change its electronic structure, allowing them to be rapidly converted into copper acetylide active species, as well as to a higher electrophilicity and better anti-reduction ability. Importantly, such extraordinary efficacy of the multicenters catalyst is attributed to the Cu species-MgO and ZnO units, which work synergistically to generate the active acetylene species and activate the carbonyl bonds of formaldehyde, respectively. The results reported herein provide a new strategy for constructing multicenter and offer insights into the structure–property relationship of catalysts.

Oxidative addition of an alkyl halide to form a stable Cu(III) product.

The step that cleaves the carbon-halogen bond in copper-catalyzed cross-coupling reactions remains ill defined because of the multiple redox manifolds available to copper and the instability of the high-valent copper product formed. We report the oxidative addition of α-haloacetonitrile to ionic and neutral copper(I) complexes to form previously elusive but here fully characterized copper(III) complexes. The stability of these complexes stems from the strong Cu-CF3 bond and the high barrier for C(CF3)-C(CH2CN) bond-forming reductive elimination. The mechanistic studies we performed suggest that oxidative addition to ionic and neutral copper(I) complexes proceeds by means of two different pathways: an SN2-type substitution to the ionic complex and a halogen-atom transfer to the neutral complex. We observed a pronounced ligand acceleration of the oxidative addition, which correlates with that observed in the copper-catalyzed couplings of azoles, amines, or alkynes with alkyl electrophiles.

Coupling of alkynes and aryl halides with nickel-catalyzed Sonogashira reactions

Coupling of alkynes and aryl halides with nickel-catalyzed Sonogashira reactions

TfOH‐Catalyzed Highly Regioselective Synthesis of Conjugated Enones by Coupling of Alkynes and Aldehydes

AbstractTriflic acid‐catalyzed regioselective enone synthesis from intermolecular coupling of aldehydes and alkynes has been developed. The present reaction is very efficient, effective, simple in nature and mild. The substrate scope is very diverse. This metathesis reaction exclusively provided trans product using aryl and aliphatic aldehydes and internal and terminal alkynes.

A green protocol for the base, ligand, and phase transfer catalyst free coupling of terminal acetylenes in water

A green protocol for the base, ligand, and phase transfer catalyst free coupling of terminal acetylenes in water

A Simple and Practical Bis-N-Heterocyclic Carbene as an Efficient Ligand in Cu-Catalyzed Glaser Reaction.

Conjugated diyne derivatives are important scaffolds in modern organic synthetic chemistry. Using the Glaser reaction involves the coupling of terminal alkynes which can efficiently produce conjugated diyne derivatives, while the use of a stoichiometric amount of copper salts, strong inorganic base, and excess oxidants is generally needed. Developing an environmentally friendly and effective method for the construction of symmetrical 1,3-diynes compounds by Glaser coupling is still highly desirable. In this study, we present an economical method for the production of symmetric diynes starting from various terminal acetylenes in a Glaser reaction. A simple and practical bis-N-heterocyclic carbene ligand has been introduced as efficient ligands for the Cu-catalyzed Glaser reaction. High product yields were obtained at 100 °C for a variety of substrates including aliphatic and aromatic terminal alkynes and differently substituted terminal alkynes including the highly sterically hindered substrate 2-methoxy ethynylbenzene or 2-trifluoromethyl ethynylbenzene and a series of functional groups, such as trifluoromethyl group, ester group, carboxyl group, and nitrile group. The established protocol is carried out in air under base-free condition and is operationally simple. These research work suggest that bis-N-heterocyclic carbene could also an appealing ligand for Glaser reaction and provide a reference for the preparation of symmetric 1,3-diynes in industrial filed.

C(sp3)–C(sp2) Reductive Elimination versus β-Hydride Elimination from Cobalt(III) Intermediates in Catalytic C–H Functionalization

The cationic bis(phosphine) cobalt(I) arene complex, [(depe)Co(η6-C7H8)][BAr4F] (depe = 1,2-bis(diethylphosphino)ethane; BAr4F = B[(3,5-(CF3)2)C6H3]4), was investigated as a precatalyst for three-component coupling of arenes, alkenes, and alkynes. Although a sterically attenuated catalyst was targeted with the goal of accelerating C–H functionalization, hydrovinylation derived from the alkene and alkyne was favored over three-component coupling. Remarkably, no catalytic hydrovinylation was observed in the absence of arene, demonstrating the role of C–H activation in the hydrovinylation process and ruling out a mechanism that involves β-H elimination from a cobalt(III) metallacycle. Deuterium labeling supported β-H elimination from a putative cobalt(III)–alkyl,aryl intermediate that forms after C–H activation by a cobalt(III) metallacycle. By varying the arene and alkene coupling partners, factors affecting the selectivity of C(sp3)–C(sp2) reductive elimination versus β-H elimination from the cobalt(III)–alkyl,aryl intermediate were determined.

Oxidation coupling of terminal alkynes over CuPd bimetallic alloy enhanced by optimized charge transfer and alloy structure

Homocoupling of terminal alkynes is an effective approach for the synthesis of 1,3-diyne, which is an important building block for numerous fine chemicals and pharmaceuticals. However, this reaction frequently encounters difficulties in catalyst recovery, and requires the addition of base or organic ligands, limiting their practical applications. Herein, we developed an efficient and recyclable CuPd bimetallic nanoalloy catalyst, which exhibited superior activity and selectivity in the homocoupling of terminal alkynes under mild conditions without any additives. In contrast to the low activity of monometallic Cu or Pd catalysts, a full conversion with a 100% selectivity for 1,3-diyne was achieved on bimetallic Cu2Pd1-400 nanoalloy with an extremely high activity. The comprehensive characterizations clearly evidenced that the alloying Cu with Pd was found to perturb the Cu electronic structure, and the positively charged Cu on the step and edge sites of CuPd nanoalloy catalyzed the homocoupling reaction via Cu-acetylide intermediates, and the density functional theory calculations revealed that the desorption of 1,3-diyne on CuPd nanoalloy was the rate-determining step for the whole reaction. This work provides a viable strategy for the rational design and fabrication of other nanoalloy catalysts for the green synthesis related to terminal alkyne oxidation.

Micelle-Mediated Sonogashira Coupling for DNA-Encoded Library Synthesis.

DNA-Encoded Libraries (DELs) are becoming widely established as a hit identification strategy for drug discovery campaigns. Their successful application relies on the availability and efficiency of the reactions that can be carried out on DNA. These reactions should proceed with high conversion to the desired product and have a broad substrate scope to synthesise chemically diverse and drug-like DELs. The Sonogashira coupling provides a unique means of coupling an sp-hybridized carbon centre to an aryl halide and methods to achieve this reaction on DNA are highly desirable. We report the application of our micellar technology for on-DNA chemistry to the Sonogashira reaction. This method gives highly efficient conversions for the coupling of (hetero)aromatic and aliphatic alkynes to (hetero)aryl iodides and bromides allowing the preparation of highly diverse DELs.

One-pot synthesis of heteroaryl diketoalkynyl C-glycoside and dialkynyl di-C-glycoside analogues by three-component successive coupling reaction

The synthesis of heteroaryl diketoalkynyl C-glycoside and dialkynyl di-C-glycoside analogues has been accomplished by successive coupling of heteroaromatics, oxalyl chloride and terminal sugar alkynes in one pot. The three-component coupling reaction catalyzed by CuI gives heteroaryl diketoalkynyl C-glycosides. The same three-component coupling in the presence of n-BuLi produces dialkynyl di-C-glycosides, and the 1:1 of molar ratio of heteroaromatics to terminal sugar alkynes affords the corresponding esters of dialkynyl di-C-glycosides. The desired products have been obtained in good to excellent yields. This sequential one-pot method is mild and efficient, suitable for different heteroaromatics and terminal sugar alkynes. The sugar alkynes include furanosides, pyranosides, and acyclic sugars. Twenty-seven examples have been given. The mechanism for the formation of the desired products has been elucidated.

Ruthenium‐Catalyzed C−C Coupling of Terminal Alkynes with Primary Alcohols or Aldehydes: α,β‐Acetylenic Ketones (Ynones) via Oxidative Alkynylation

AbstractThe first metal‐catalyzed oxidative alkynylations of primary alcohols or aldehydes to form α,β‐acetylenic ketones (ynones) are described. Deuterium labelling studies corroborate a novel reaction mechanism in which alkyne hydroruthenation forms a transient vinylruthenium complex that deprotonates the terminal alkyne to form the active alkynylruthenium nucleophile.

Ruthenium-Catalyzed C-C Coupling of Terminal Alkynes with Primary Alcohols or Aldehydes: α,β-Acetylenic Ketones (Ynones) via Oxidative Alkynylation.

The first metal-catalyzed oxidative alkynylations of primary alcohols or aldehydes to form α,β-acetylenic ketones (ynones) are described. Deuterium labelling studies corroborate a novel reaction mechanism in which alkyne hydroruthenation forms a transient vinylruthenium complex that deprotonates the terminal alkyne to form the active alkynylruthenium nucleophile.

Total Synthesis of Okaspirodiol

AbstractThe asymmetric total synthesis of okaspirodiol was achieved following Sharpless asymmetric epoxidation, Gilman reaction, Wittig reaction, Horner–Wadsworth–Emmons olefination, and coupling of alkyne with the aldehyde, and acid‐catalyzed spiroketalization as key reactions.

Carbon-confined Cu-Pd alloy nanoparticles as high-performance catalysts for acetylene selective hydrogenation

A catalyst with high selectivity for acetylene selective hydrogenation is highly desirable, yet ideal selectivity often comes at the price of activity loss. Here, a carbon confined Cu15Pd catalyst (Cu15Pd@C) was fabricated through an eco-friendly and efficient approach, which improves ethylene selectivity while at the same time, maintains high activity. Under optimized conditions, acetylene conversion of 100% and ethylene selectivity of 91% were simultaneously achieved. Comprehensive characterization and DFT reveal that the carbon layer not only promotes the formation of smaller nanoparticles, but effectively inhibits the production of green oil, which is associated to the confined spatial microenvironment by the carbon layer, posing steric hindrance to chain growth from acetylene coupling. A series of carbon confined Cu and Ag-based bimetal catalysts were fabricated through the same method, proving the facilitation of carbon layer on such selective hydrogenation universal, and also showed great potential of our method and catalysts in practical application.

Multicomponent Reaction: Pd/Cu-Catalyzed Coupling and Boration of Acyl Chlorides and Alkynes to β-Boryl Ketones

An unprecedented and challenging multicomponent reaction has been developed that allows for the direct transformation of acyl chlorides with alkynes into the corresponding saturated β-boryl ketones via Pd/Cu-catalyzed coupling and boration with ethyl acetate as the hydrogen sources. Various β-boryl ketones were synthesized in good to excellent yields with broad functional group tolerance. In addition, the introduction of boron groups into the products provides substantial opportunities for further conversions.

Coupling of Amino Acid Terminal Alkyne with in situ Iminium Ion to Access Nε‑Substituted Lysine Mimetics

Key words copper catalysis - lysine mimetics - A3 coupling reaction - terminal alkynes - amino acids

Silica-grafted DBU-supported NiCl2: a sustainable heterogeneous catalyst for A3 coupling

Silica-grafted DBU-supported NiCl2 complex, 1-(3-((3-(silica-trioxysilyl) propyl) amino) propyl) azepan-2-one nickel chloride (SiO2@DBU-NiCl2), has been designed and synthesized by multistep approach and characterized by FT-IR, XRD, EDS, FE-SEM, TGA and XPS. Catalytic activity of SiO2@DBU-NiCl2 has been explored for A3 coupling of terminal alkynes, aldehydes and secondary amines resulting in excellent yields (up to 97%). Special features of present protocol are high TONs (625–1212) and TOFs (52–404), low catalyst loading (0.08 mol %), solvent-free conditions, facile recyclability and reusability of the catalyst (up to 5 times).

Synthesis of gem-Difluorinated 1,4-Dienes via Nickel-Catalyzed Three-Component Coupling of (Trifluoromethyl)alkenes, Alkynes, and Organoboronic Acids.

Herein, a nickel-catalyzed defluorinative three-component coupling of trifluoromethyl alkenes, internal alkynes, and organoboronic acids is presented. The protocol provides a highly efficient and selective route for the synthesis of structurally diverse gem-difluorinated 1,4-dienes under mild conditions. Mechanistic studies suggest that C-F bond activation proceeds probably through the oxidative cyclization of trifluoromethyl alkenes with Ni(0) species, sequential addition to alkynes, and β-fluorine elimination.

Serendipitous discovery of Pd-catalyzed intramolecular cyclization of ortho-bromo(hetero)aryl-substituted (hetero)aryl-1,2-diketones: Applications in the synthesis of carba- and heterocyclic benzoin derivatives

Carbaand heterocyclic benzoin derivatives were prepared by Sonogashira coupling of alkynes with 1,2-dihaloalkenes and subsequent oxidation of the alkyne to a 1,2-diketone. The Pd-catalyzed reaction of the product with (2-bromophenyl)boronic acid in the presence of phenylacetylene resulted in formation of cyclic benzoin derivatives by Suzuki-Miyaura reaction and subsequent Pd catalyzed nucleophilic addition to the carbonyl group. Hitherto unprecedented 5-hydroxy-5-phenylbenzo[b]naphtho[1,2-d]thiophene-6(5H)-ones and their regioisomers were prepared from 2,3-dibromobenzothiophene. Phenanthrene benzoin derivatives were prepared from 2-bromo-1-iodobenzene.