Carboxylative Coupling Research Articles

Silver-Catalyzed Coupling of Unreactive Carboxylates: Synthesis of α-Fluorinated O-Aryl Esters.

α-Fluorinated aryl esters pose a challenge in synthesis via O-arylation of α-fluorinated carboxylates owing to their low reactivities. This limitation has been addressed by combining a silver catalyst with aryl(trimethoxyphenyl)iodonium tosylates to access α-fluorinated aryl esters. We envision that the catalytic system involves high-valent aryl silver species generated via the oxidation of silver(I) salt. The present method provided a synthetic protocol for various α-fluorinated aryl esters including fluorinated analogs of drug derivatives.

Transformation of CO2 into α-alkylidene cyclic carbonates at room temperature and atmospheric pressure by phthalimide based ionic liquids with inert cation and moderate basicity

The carboxylative coupling of carbon dioxide (CO2) with propargyl alcohols is an important pathway to accomplish the reusability of CO2. Moreover, the α-methylene cyclic carbonates are the critical intermediate to generate the fine chemicals and pharmaceuticals. However, the robust catalyst is still limited to perform this reaction under the mild conditions, especially to obtain the equilibrium among several reaction conditions including reaction time, reaction temperature, and catalyst amount. The novel ionic liquid, [Pth][BTMA], is synthesized in this work to be catalyst for the title reaction along with AgOAc as the co-catalyst. To explore the influence of cation, anion, and Ag salt, other four ionic liquids are utilized to catalyze the reaction along with five different Ag salts. Under the atmospheric pressure and 30 °C, the 98.7 % product yield is achieved by [Pth][BTMA]/AgOAc within 9 h, which are better than most of catalysts in literature. More important, the role of cation and anion in the catalysis is elucidated by the 1H NMR, 13C NMR, and density functional theory (DFT) calculations. Both the moderate basicity and inert cation of [Pth][BTMA] contribute the excellent catalytic activity.

Construction of covalent organic framework functionalized with carbene dual active sites for enhancing CO2 carboxylation conversion

It is challenging to drive the integral insertion of linear CO2 with thermodynamic stability and kinetic inertness as carboxylation reagents into C-H, O-H, and other chemical bonds. The known strategies mainly focus on unilaterally activating substrates as nucleophilic reagents, and the CO2 insertion process has to overcome high reaction energy barriers. Herein, this work reports copper carbene NHC-CuCl and CO2 adduct NHC-CO2 as dual active sites are introduced into the porous crystal covalent organic framework to effectively drive the simultaneous activation of substrate and CO2. The catalyst COF@NHC-CuCl/CO2 exhibited high space–time yield (STY = 71.9 h−1 at 40 °C and 36.7 h−1 at 25 °C, ambient pressure) in the carboxylative coupling of propargylic alcohols, which is superior to most of the cutting-edge heterogeneous catalysts. Experimental data and density functional theory calculation revealed that the carboxylation reaction involving NHC-CO2 and ordinary CO2 source follows different reaction mechanisms. The free energy barrier of the CO2 insertion process (TS:35.9 kcal/mol → 17.4 kcal/mol) is effectively reduced by NHC modulation of the CO2 bond energy parameters to facilitate the reaction. Due to the unique structural design, COF@NHC-CuCl/CO2 exhibited outstanding diffusion mass transfer, catalytic diversity and reusability. This work proposes a novel construction strategy of heterogeneous dual activation catalyst to provide a sustainable solution for efficiently producing value-added chemicals from CO2 under mild conditions.

Boosting CO2 Conversion with Terminal Alkynes by Molecular Architecture of Graphene Oxide-Supported Ag Nanoparticles

Summary Carboxylation of terminal alkynes with CO2 via direct C–H bond activation is a highly appealing way to capture and convert CO2 but faces great challenges and difficulty. Here, we report an efficient catalyst that is prepared simply through introduction of p-tert-butylaniline into graphite oxide powders followed by localized growth of Ag nanoparticles (NPs). The bulky nature of p-tert-butylaniline facilitates the powder exfoliation, giving rise to mass production of uniform modified graphene oxide (tert-GO) nanosheets of 4 nm in thickness. Notably, Ag/tert-GO shows excellent catalytic activity for converting alkynes regardless of containing electron-donating or electron-withdrawing groups under mild reaction conditions. The synergy of the amide linkages on tert-GO nanosheets and the supported small-sized Ag NPs is recognized as the vital role in promoting adsorption of CO2 and subsequent conversion.

Size-Controlled Growth of Silver Nanoparticles onto Functionalized Ordered Mesoporous Polymers for Efficient CO2 Upgrading.

Highly dispersed metallic silver nanoparticles (AgNPs) are promising heterogeneous catalysts for carboxylative coupling of terminal alkynes with CO2 under mild conditions. Yet, their size-controlled synthesis is very challenging because of the high surface energy. Here, we prepared a series of amino-functionalized ordered mesoporous polymers as hosts for anchoring AgNPs. Control experiments and computations showed that electron-rich amines were confined in mesochannels with varying electron density and steric hindrance, creating "localized active zones (LAZ)" to control the growth of AgNPs. The particle size of AgNPs grows along with the increased volume of LAZ around nitrogen species. We also revealed that the catalytic activity of Ag-based catalysts is size-dependent and increases with decreasing particle size. Building on these findings, we report a facile one-pot synthesis strategy for preparing an amine-incorporated ordered mesoporous polymer (NOMP) with a high specific surface area, small LAZ volume, and uniform amine sites with controllable loading. These features result in the formation of ultrasmall and monodispersed Ag nanoparticles. Remarkably, Ag@NOMP gave a quantitative target yield under the conditions of 1 atm CO2 pressure and 50 °C, showing superior catalytic activity in CO2 carboxylation compared to other mesoporous analogues.

Cover Feature: Ordered Mesoporous CeO2‐supported Ag as an Effective Catalyst for Carboxylative Coupling Reaction Using CO2 (ChemCatChem 8/2019)

The Cover Feature shows that Ag/Mesoporous CeO2 could be used in the carboxylative coupling of terminal alkynes, chloride compounds and CO2. In their Full Paper, X. Zhang et al. demonstrate that Ag/M-CeO2 catalysts synthesized through the gas bubbling-assisted membrane reduction (GBMR) method contain uniform mesoporous structure, large surface area and oxygen vacancies, which promote the dispersion of Ag nanoparticles. Density functional theory (DFT) calculations indicate that Ag nanoparticles supported on M-CeO2 could facilitate the formation of oxygen vacancies, which result in higher CO2 adsorption capacity. A wide range of functionalized 2-alkynoates could be synthesized by Ag(3.12%)/M-CeO2 catalyst in good yield. More information can be found in the Full Paper by X. Zhang et al. on page 2089 in Issue 8, 2019 (DOI: 10.1002/cctc.201900039).

Ordered Mesoporous CeO2‐supported Ag as an Effective Catalyst for Carboxylative Coupling Reaction Using CO2

AbstractAg/Mesoporous CeO2 (Ag/M−CeO2) catalysts were synthesized through the gas bubbling‐assisted membrane reduction (GBMR) method and characterized by XRD, ICP‐OES, N2 adsorption‐desorption, XPS, Raman spectroscopy, TEM, HRTEM, HAADF‐STEM and CO2‐TPD. Ag/M−CeO2 catalysts contain uniform mesoporous structure, large surface area and oxygen vacancies, which promote the dispersion of Ag nanoparticles. Density functional theory (DFT) calculations indicate that Ag nanoparticles supported on M−CeO2 could facilitate the formation of oxygen vacancies, which result in higher CO2 adsorption capacity. With the most oxygen vacancies and the well‐dispersed Ag active species, Ag (3.12 %)/M−CeO2 exhibits high efficiency for the carboxylative coupling of terminal alkynes, chloride compounds and CO2 under mild reaction conditions (60 °C, 0.5 MPa), affording a wide range of functionalized 2‐alkynoates in good yields.

Effect of the types of stabilizers and size distribution on catalytic activity of palladium nanoparticles in the carboxylative coupling reaction

Palladium nanoparticles (Pd NPs) generated in situ and stabilized by quaternary ammonium salts were used in three-component coupling reaction as the catalyst. Cations and anions of quaternary ammonium salts influenced the catalytic activity of Pd NPs, and tetrabutyl-ammonium bromide (TBAB) proved to be the best stabilizer. (2.23 ± 0.58) nm-sized Pd NPs showed the best catalytic activity under the molar ratio 1/30 [Pd(acac)2/TBAB]. The mercury poisoning test demonstrated the reaction occurred on the surface of Pd NPs. Pd NPs could be recycled for four times without significant loss in catalytic activity. The mercury poisoning tests demonstrated carboxylative coupling reaction occurred on the surface of Pd NPs which generated in situ, the types and additive amount of stabilizers influenced the catalytic activity of this catalytic system which could be recycled.

CO2‐Sourced Non‐Isocyanate Poly(Urethane)s with pH‐Sensitive Imine Linkages

AbstractCarbon dioxide is a renewable C1‐feedstock that is exploited for the production of polymers. In this work, we report on the conversion of CO2 into novel bis(oxo‐carbamate)s that are then exploited for the synthesis of degradable non‐isocyanate polyurethanes (NIPUs) bearing acid‐sensitive imine functions within the polymer backbone. Two CO2‐sourced bis(oxo‐carbamate)s were first prepared by the facile catalyst‐free and regioselective aminolysis of an α‐alkylidene cyclic carbonate (prepared by carboxylative coupling of CO2 with a propargylic alcohol) with two secondary diamines, piperazine and N,N’‐dimethyl‐1,6‐hexanediamine. A large diversity of poly(urethane‐co‐imine)s (PUIs) with molar masses ranging from 4500 to 8500 g/mol were then prepared by polycondensation of bis(oxo‐carbamate)s with various primary diamines, and by using Ti(OEt)4 as catalyst and drying agent. Finally, the pH‐responsiveness of PUIs was demonstrated by immersing a representative polymer in aqueous solutions at different pH. This work illustrates that hydrolytically degradable NIPUs can be constructed by polycondensation of novel CO2‐sourced monomers with diamines.magnified image

Nickel-Catalyzed Decarboxylative Coupling of Alkynyl Carboxylates with Aryl Tosylates and Mesylates

A method for the nickel-catalyzed coupling of alkynyl carboxylates or acids with aryl tosylates and mesylates is described. Electronically varied carboxylates and aryl electrophiles participate in these transformations to afford the desired diarylalkyne products. In general, electrophiles bearing an extended π-system lead to products in higher yields than sulfonates with only one aromatic ring.

Boosting the Catalytic Performance of Organic Salts for the Fast and Selective Synthesis of α‐Alkylidene Cyclic Carbonates from Carbon Dioxide and Propargylic Alcohols

AbstractThe synthesis of α‐alkylidene cyclic carbonates (αCCs) by the carboxylative coupling of CO2 with propargylic alcohols is receiving increasing interest but requires the use of catalysts that are most often added in large quantities and/or lack selectivity. Herein, we describe the fine‐tuning of the structure of organocatalysts of the ammonium‐type that enables us to identify the important structural parameters that dictate their catalytic performance. Tetrabutylammonium oxalate was revealed to be one of the most attractive organocatalysts with a remarkably fast, complete and selective production of αCCs at a low catalyst loading (2.5 mol %) under solvent‐free conditions. This study opens new avenues for the facile and selective synthesis of libraries of αCCs from CO2 and propargylic alcohol by using simple organocatalysts.

Metal Catalyzed Carboxylative Coupling of Terminal Alkynes, Organohalides and Carbon Dioxide: A Novel and Promising Synthetic Strategy Toward 2-Alkynoates (A Review)

Metal Catalyzed Carboxylative Coupling of Terminal Alkynes, Organohalides and Carbon Dioxide: A Novel and Promising Synthetic Strategy Toward 2-Alkynoates (A Review)

Mechanism of the chemical fixation of carbon dioxide with 2-aminobenzonitrile catalyzed by cesium carbonate: A computational study

A series of density functional theory (DFT) calculations have been carried out to unravel the mechanism for Cs2CO3-catalyzed reaction between carbon dioxide with 2-aminobenzonitrile. Two kinds of reaction mechanisms involving either the 2-aminobenzonitrile coordinating to Cs2CO3 or CO2 as the first step are examined. The preferred mechanism mainly includes carboxylative coupling and intramolecular rearrangement, each of which consists of different steps. The calculations show that the lactone ring compound 5a is a key active species, which is attributed to the regioselectivity of Cs2CO3, resulting in the CO bond activation and facilitating the later intramolecular rearrangement to give the final product. The rate-determining step of the catalytic cycle is the process from 4 to TS5a-6. As the pivotal catalyst, the multiple roles of Cs2CO3 have been elucidated.

1,3-Bis(4-methylbenzyl)imidazol-2-ylidene silver(I) chloride catalyzed carboxylative coupling of terminal alkynes, butyl iodide and carbon dioxide

The N-heterocyclic carbene silver(I) complex 1,3-bis(4-methylbenzyl)imidazol-2-ylidene silver chloride was applied as the effective catalyst for the three-component carboxylative coupling of terminal alkynes, butyl iodide and carbon dioxide. The reaction proved to be highly efficient when using 2mol% of 1,3-bis(4-methylbenzyl)imidazol-2-ylidene silver(I) chloride as the catalyst in the presence of 1.5 equiv. of Cs2CO3 as the base in DMF. This reaction shows good selectivity and substituent-loading capability, in which various functionalized 2-alkynoates were obtained in good yields under very mild conditions.

Inside Cover: Carboxylative Coupling of Chloromethyl(hetero)arenes with Allyltrimethoxysilane Catalyzed by Palladium Nanoparticles (Asian J. Org. Chem. 2/2017)

Inside Cover: Carboxylative Coupling of Chloromethyl(hetero)arenes with Allyltrimethoxysilane Catalyzed by Palladium Nanoparticles (Asian J. Org. Chem. 2/2017)

Silver-catalyzed one-pot synthesis of benzyl 2-alkynoates under ambient pressure of CO2 and ligand-free conditions

The carboxylative coupling of aryl/alkyl terminal alkynes, CO2 and benzyl halides was investigated using silver iodide as the catalyst and Cs2CO3 as the base in CH3CN under ligand-free conditions. This reaction protocol shows a wide substrate scope and high functional group tolerance ability for benzyl halides, in which various functionalized benzyl 2-alkynoates were achieved in good yields. This one-pot, ligand-free and CH3CN mediated reaction proved to be easy to handle and could be facilitated under atmospheric CO2 pressure.

Carboxylative Coupling of Chloromethyl(hetero)arenes with Allyltrimethoxysilane Catalyzed by Palladium Nanoparticles

AbstractThe palladium‐catalyzed three‐component coupling of either (chloromethyl)arenes or (chloromethyl)heteroarenes with allyltrimethoxysilane and carbon dioxide (i.e., a carboxylative Hiyama coupling reaction) successfully produced α,β‐unsaturated esters in satisfactory to good yields. This reaction proceeded smoothly under mild conditions in the presence of palladium nanoparticles (NPs). A reaction mechanism, which includes the formation of an π‐allylpalladium chloride intermediate, has been proposed.

ChemInform Abstract: Carboxylative Coupling Reaction of Five‐Membered (Chloromethyl)heteroarenes with Allyltributylstannane Catalyzed by Palladium Nanoparticles.

AbstractThe precatalyst Pd(acac)2 reacts with stannane (II) in the presence of the stabilizer Bu4NBr to furnish palladium nanoparticles which catalyze the three‐component coupling to afford β,γ‐unsaturated esters.

Synthesis of Peptides by Silver-Promoted Coupling of Carboxylates and Thioamides: Mechanistic Insight from Computational Studies.

The mechanism of the recently described N→C direction peptide synthesis through silver-promoted coupling of N-protected amino acids with thioacetylated amino esters was explored by using density functional theory. Calculation of the potential energy surfaces for various pathways revealed that the reaction proceeds through silver-assisted addition of the carboxylate to the thioamide, which is followed by deprotonation and silver-mediated extrusion of sulfur as Ag2 S. The resulting isoimide is the key intermediate, which subsequently rearranges to an imide through a concerted pericyclic [1,3]-acyl shift (O-sp(2) N 1,3-acyl migration). The proposed mechanism clearly emphasises the requirement of two equivalents of Ag(I) and basic reaction conditions, which is in full agreement with the experimental findings. Alternative rearrangement pathways involving only one equivalent of Ag(I) or through O-sp(3) N 1,3-acyl migration can be excluded. The computations further revealed that peptide couplings involving thioformamides require significant conformational changes in the intermediate isoformimide, which slow down the rearrangement process.

Carboxylative coupling reaction of five-membered (chloromethyl)heteroarenes with allyltributylstannane catalyzed by palladium nanoparticles

The palladium-catalyzed three-component coupling reaction of five-membered (chloromethyl)heteroarenes, allyltributylstannane, and carbon dioxide (carboxylative Stille coupling reaction) was successfully conducted to produce β,γ-unsaturated esters in satisfactory to good yields. The carboxylative Stille coupling reaction occurred smoothly under mild conditions in the presence of palladium nanoparticles through the formation of π-allylpalladium chloride intermediates.