Carboxylate Catalysts Research Articles

SiO2-Coated Ag Nanoparticles for Conversion of Terminal Alkynes to Propolic Acids via CO2 Insertion

Integration of adequate activity, stability, and productivity in a catalyst is of strategical importance to achieve high performance, particularly for inactive reactants, e.g., CO2. Here, using a reversed microemulsion method, ultrafine metallic Ag nanoparticles coated with porous SiO2 can be facilely obtained using micelles as separated nanoreactors for the preparation. Such architectures allowed the rigid SiO2 matrices to act as physical spacers, so that aggregation of the Ag particles could be avoided. Meanwhile, due to the templating effect from the surfactant, large mesopores could be induced in the SiO2 shell, and thus the diffusion barrier of reactants could be minimized. When used as a heterogeneous catalyst for carboxylation of terminal alkynes by CO2 under mild conditions, the prepared x[email protected]2 catalysts showed extraordinary performance in terms of excellent activity, stability, productivity, and wide substrate scope. The knowledge developed here may also enrich the toolbox for performance promotion of metal catalysts via specially fabricated structures.

Mechanism and kinetics of epoxide ring-opening with carboxylic acids catalyzed by the corresponding carboxylates

The ring-opening reactions of epoxides with carboxylic acids have great applications in the coating and polymer industry. However, the systematical study on the structure-activity relation of catalysts is still scarce. In this work, the carboxylate catalysts were directly prepared rather than using the traditional catalysts like amines or quaternary ammonium salts, thus removing the induction period and making the kinetic results more accurate and rigorous. The reaction orders of reactants and catalyst were obtained by kinetic experiments, and based on that, the kinetic equation and mechanism were put forward. The influences of solvent environment, as well as the structure and properties of catalysts on their activity were further studied. It was found that the alkalinity of the carboxylate ions and the electrostatic interaction are the key factors to affect the nucleophilicity of catalysts. Generally, the nucleophilicity is enhanced with the increase of cation radius and anion branches.

An efficient Ag/MIL-100(Fe) catalyst for photothermal conversion of CO2 at ambient temperature

The conversion of CO2 under mild condition is of great importance because these reactions involving CO2 can not only produce value-added chemicals from abundant and inexpensive CO2 feedstock but also close the carbon cycle. However, the chemical inertness of CO2 requires the development of high-performance catalysts. Herein, Ag nanoparticles/MIL-100(Fe) composites were synthesized by simple impregnation-reduction method and employed as catalysts for the photothermal carboxylation of terminal alkynes with CO2. MIL-100(Fe) could stabilize Ag nanoparticles and prevent them from aggregation during catalytic process. Taking the advantages of photothermal effects and catalytic activities of both Ag nanoparticles and MIL-100(Fe), various aromatic alkynes could be converted to corresponding carboxylic acid products (86%–92% yields) with 1 atm CO2 at room temperature under visible light irradiation when using Ag nanoparticles/MIL-100(Fe) as photothermal catalysts. The catalysts also showed good recyclability with almost no loss of catalytic activity for three consecutive runs. More importantly, the catalytic performance of Ag nanoparticles/MIL-100(Fe) under visible light irradiation at room temperature was comparable to that upon heating, showing that the light source could replace conventional heating method to drive the reaction. This work provided a promising strategy of utilizing solar energy for achieving efficient CO2 conversion to value-added chemicals under mild condition.

Nickel-phenanthroline Complex Supported on Mesoporous Carbon as a Catalyst for Carboxylation under CO2 Atmosphere

Carbon dioxide is a highly potential renewable C1 source for synthesis of fine chemicals. Utilization of CO2 in carboxylation reactions requires catalysts, such as: nickel complex for CO2 activation. However, the use of homogeneous catalysts in the reaction is still less efficient due to the difficulty of separating the product and catalyst from reaction mixture. Therefore, it is necessary to heterogenize the nickel complex in a solid support such as mesoporous carbon. In this report, mesoporous carbon (MC) prepared from phloroglucinol and formaldehyde through soft template method was used as a solid support for Ni-phenanthroline complex (Ni-phen). The catalyst was characterized by Fourier Transform Infra Red (FT-IR), X-Ray Diffraction (XRD), Scanning Electron Microscope - Energy Dispersive X-Ray (SEM-EDX), and Surface Area Analyzer (SAA). The result of SAA characterization showed that the pore diameter of MC was 6.7 nm and Ni-phen/MC was 5.1 nm which indicates that the materials have meso-size pores. Ni-phen/MC material was then used as a heterogeneous catalyst in the carboxylation reaction of phenylacetylene under an ambient CO2 pressure. The reactions were carried out in several variations of conditions such as temperature, time and catalyst types. Based on the results of the reaction, the best conditions were obtained at 25 °C for 8 h of reaction time using Ni-phen/MC catalyst. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Synthesis of Polysiloxanes with Functional Groups by Using Organometallic Carboxylate Catalysts

Abstract Linear polysiloxanes were synthesized by using organometallic carboxylic acid catalysts containing tin, zinc, or iron. By optimizing the amount of catalyst and the reaction temperature, polysiloxanes could be synthesized from dialkoxysilanes linked with vinyl monomers by the thiol–ene reaction. Furthermore, cross-linked polysiloxanes could be formed through interactions between the catalyst and the carboxylic acid in the monomer side chain.

Conformational Control in Dirhodium(II) Paddlewheel Catalysts Supported by Chalcogen-Bonding Interactions for Stereoselective Intramolecular C–H Insertion Reactions

D2-symmetric dirhodium(II) carboxylate catalysts that bear axially chiral binaphthothiophene δ-amino acid derivatives have been developed. Conformational control is supported through chalcogen-bond...

Asymmetric C–H Functionalization in Flow by an Immobilized Rhodium Carboxylate Catalyst

Key words C–H functionalization - rhodium catalysis - diazo compounds - asymmetric catalysis

Postmetalation of a new porphyrin ligand-based metal–organic framework for catalytic oxidative carboxylation of olefins

Heterogeneous catalytic reactions based on single metal–organic framework (MOF) material for the oxidative carboxylation of olefins following a tandem process, which involves the epoxidation of olefins and subsequent epoxide–CO2 cycloaddition, are highly desirable and economical for CO2 chemical fixation. In this work, a new trans-A2B2-type porphyrin ligand, 5,15-di(m-benzoato)-porphyrin (H2DMBP), was successfully synthesized and utilized for constructing a novel, highly porous, and stable Nd-porphyrin MOF, named CSUST-2. (CSUST stands for Changsha University of Science and Technology.) Furthermore, the coordinatively unsaturated Co(II) ions were implanted into the MOF by exploiting the innate non-metallated porphyrin ligands to generate Co(II)@CSUST-2 framework, which was evidenced to act as an efficient recyclable catalyst for oxidative carboxylation of olefins in the presence of tert-butyl hydroperoxide (TBHP) as an oxidant and tetrabutylammonium bromide (n-Bu4NBr) as a co-catalyst under mild conditions (1 atm CO2, 75 °C, and without solvent).

Theoretical research on the direct carboxylation of benzene with CO2 catalyzed by different carbene‐CuOH compounds

AbstractThe direct carboxylation between the benzene C–H and CO2 is a long‐standing challenge in catalysis. Based on the known experimental process for the direct carboxylation of fluorobenzene, herein, a theoretical design of efficient carbene‐copper catalysts for the direct carboxylation of benzene was reported. It was found that the reaction included two steps: C–H bond breaking and CO2 insertion into Cu‐phenyl. C–H breaking is the rate‐determining step. To find out a more effective catalyst, totally, 16 carbene‐copper compounds with different electronic and steric structures were investigated. The energy barriers for the C–H bond breaking range from 104.2 to 153.7 kJ/mol. Two effective methods are proposed for improving the catalytic reactivity: reducing the electronically active substituent on carbene and introducing interaction to stabilize the transition state (TS). Based on these findings, adopting a well‐known (amino)(silyl)carbene modified by a –NH2 group gives the most effective catalyst for the direct carboxylation of benzene. Using –NH2 group can introduce two strong interactions (OOH···HNH2 and NNH2···Cu) during the formation of TS, which can greatly stabilize the structure of TS and dramatically reduce the energy barrier. The catalytic reactivity of the most effective carbene‐copper catalyst is comparable with the noble metal‐based ruthenium pincer carboxylate complexes.

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.

Optimized Immobilization Strategy for Dirhodium(II) Carboxylate Catalysts for C-H Functionalization and Their Implementation in a Packed Bed Flow Reactor.

Herein we demonstrate a packed bed flow reactor capable of achieving highly regio- and stereoselective C-H functionalization reactions using a newly developed Rh2 (S-2-Cl-5-CF3 TPCP)4 catalyst. To optimize the immobilized dirhodium catalyst employed in the flow reactor, we systematically study both (i) the effects of ligand immobilization position, demonstrating the critical factor that the catalyst-support attachment location can have on the catalyst performance, and (ii) silica support mesopore length, demonstrating that decreasing diffusional limitations leads to increased accessibility of the active site and higher catalyst turnover frequency. We employ the immobilized dirhodium catalyst in a simple packed bed flow reactor achieving comparable yields and levels of enantioselectivity to the homogeneous catalyst employed in batch and maintain this performance over ten catalyst recycles.

Optimized Immobilization Strategy for Dirhodium(II) Carboxylate Catalysts for C−H Functionalization and Their Implementation in a Packed Bed Flow Reactor

AbstractHerein we demonstrate a packed bed flow reactor capable of achieving highly regio‐ and stereoselective C−H functionalization reactions using a newly developed Rh2(S‐2‐Cl‐5‐CF3TPCP)4 catalyst. To optimize the immobilized dirhodium catalyst employed in the flow reactor, we systematically study both (i) the effects of ligand immobilization position, demonstrating the critical factor that the catalyst‐support attachment location can have on the catalyst performance, and (ii) silica support mesopore length, demonstrating that decreasing diffusional limitations leads to increased accessibility of the active site and higher catalyst turnover frequency. We employ the immobilized dirhodium catalyst in a simple packed bed flow reactor achieving comparable yields and levels of enantioselectivity to the homogeneous catalyst employed in batch and maintain this performance over ten catalyst recycles.

Highly Efficient Fixation of Carbon Dioxide at RT and Atmospheric Pressure Conditions: Influence of Polar Functionality on Selective Capture and Conversion of CO2.

The rapid increase in the concentration of atmospheric carbon dioxide (CO2) has resulted in undesirable environmental issues. Hence, selective CO2 capture and utilization as C1 feedstock for the preparation of high-value chemicals and fuels has been considered as a promising step toward mitigating the growing concentration of atmospheric CO2. In this direction, herein we report rational construction of a Ag(I)-anchored sulfonate-functionalized UiO-66 MOF named as MOF-SO3Ag composed of CO2-philic sulfonate functionality and catalytically active alkynophilic Ag(I) sites for chemical fixation of carbon dioxide. The MOF-SO3Ag exhibits selective as well as recyclable adsorption of CO2 with a high heat of adsorption energy (Qst) of 37.8 kJ/mol. On the other hand, the analogous MOF, UiO-66 doped with Ag(I), showed a lower Qst value of 30 kJ/mol, highlighting the importance of the sulfonate group for stronger interaction with CO2. Furthermore, the MOF-SO3Ag acts as an efficient heterogeneous catalyst for cyclic carboxylation of propargylic alcohols to generate α-alkylidene cyclic carbonates in >99% yield at mild conditions of RT and 1 bar CO2. More importantly, one-pot synthesis of oxazolidinones by a three-component reaction between CO2, propargylic alcohol, and primary amine has also been achieved using MOF-SO3Ag catalyst under the mild conditions. The MOF is highly recyclable and retains its superior catalytic activity even after several cycles. To the best of our knowledge, MOF-SO3Ag is the first example of MOF reported for RT chemical fixation of CO2 to oxazolidinones by aminolysis of α-alkylidene cyclic carbonates under the environment-friendly mild conditions.

A novel fiber-supported cooperative catalyst for the carboxylation of terminal alkynes through CO2 utilization

Herein, a novel fiber-supported N-heterocyclic carbene (NHC) precursor and copper(I) composite (EIMBr-PANFTA@CuI), capable of acting as a cooperative catalyst for cleaner carboxylation of terminal alkynes from CO2, is presented. The EIMBr-PANFTA@CuI was synthesized systematically, and the resulting fiber samples from preparation and utilization processes were characterized detailedly. Moreover, the unique fiber-supported composite structure as a cooperative catalyst exhibited the synergistic effect on the activation of CO2 and terminal alkyne, which corporately contributed to the high catalytic performance on carboxylation for producing a series of alkyl 2-alkynoates in acetonitrile under ambient conditions. Furthermore, EIMBr-PANFTA@CuI was stable to air and moisture, and could be easily recovered with a tiny pair of tweezers and recycled with good activity over 10 runs. In addition, this protocol was convenient and effective for gram-scale experiments and thereby was prospective in practical applications.

Supported Ruthenium and Tetrapropylammonium Bromide Catalysts for Oxidative Carboxylation of 1-Decene

Cyclic carbonate compounds are valuable for a range of applications and can be synthesized by a one-pot reaction involving epoxidation of olefin followed by reaction of the epoxide with CO2. This study used supported ruthenium catalysts for the epoxidation step (first step), where a combination of tetrapropylammonium bromide and zinc bromide was used for the cycloaddition of carbon dioxide. The supported ruthenium catalyst, prepared by a sol-immobilization method, allowed the effective epoxidation of 1-decene in air (using oxygen as the main oxidant) at 90 ºC in the presence of a catalytic quantity of radical initiator. This approach was applied to the one-pot multi-step oxidative carboxylation of 1-decene in the presence of 1 % Ru/support-Pr4NBr/ZnBr2 catalyst

Discovery of very active catalysts for methanol carboxylation into DMC by screening of a large and diverse catalyst library

The direct synthesis of dimethyl carbonate from methanol and CO2 is particularly attractive as it provides a green alternative to other routes while allowing CO2 conversion.

Quantum chemical descriptors based QSAR modeling of neodymium carboxylate catalysts for coordination polymerization of isoprene

Abstract Based on the quantum chemical descriptors and the activities for isoprene polymerization of 12 neodymium carboxylates obtained by authors' earlier work, statistical analysis of data was made and a QSAR model correlating the quantum chemical descriptors and the activity was built with the partial least square (PLS) approach. The model is: A = 51,602 eHOMO + 6 σ + 12,546, which indicates that the catalytic activity A is positively correlated with the HOMO energy eHOMO and the ligand polarizability σ, with the contribution of σ being larger, eHOMO smaller. The model's coefficient of determination r2 = 0.96 and that of cross validation q2 = 0.94, both being close to 1, which means that its quality is well and its predictive power is strong. Analysis of the modeling process and the resulted QSAR model, together with the interpretation of the model's mechanism, also shows that the model obtained from this study is valid and reliable. According to the QSAR model, the mechanism of catalyst activity can be interpreted as that neodymium carboxylates with higher HOMO energy and larger ligand polarizability are easier to react with the co-catalysts so as to produce more active and stable centers of catalyst, resulting in a higher activity.

Electrophilic Iron Catalyst Paired with a Lithium Cation Enables Selective Functionalization of Non-Activated Aliphatic C-H Bonds via Metallocarbene Intermediates.

Combining an electrophilic iron complex [Fe(F pda)(THF)]2 (3) [F pda=N,N'-bis(pentafluorophenyl)-o-phenylenediamide] with the pre-activation of α-alkyl-substituted α-diazoesters reagents by LiAl(ORF )4 [ORF =(OC(CF3 )3 ] provides unprecedented access to selective iron-catalyzed intramolecular functionalization of strong alkyl C(sp3 )-H bonds. Reactions occur at 25 °C via α-alkyl-metallocarbene intermediates, and with activity/selectivity levels similar to those of rhodium carboxylate catalysts. Mechanistic investigations reveal a crucial role of the lithium cation in the rate-determining formation of the electrophilic iron-carbene intermediate, which then proceeds by concerted insertion into the C-H bond.

Electrophilic Iron Catalyst Paired with a Lithium Cation Enables Selective Functionalization of Non‐Activated Aliphatic C−H Bonds via Metallocarbene Intermediates

AbstractCombining an electrophilic iron complex [Fe(Fpda)(THF)]2 (3) [Fpda=N,N′‐bis(pentafluorophenyl)‐o‐phenylenediamide] with the pre‐activation of α‐alkyl‐substituted α‐diazoesters reagents by LiAl(ORF)4 [ORF=(OC(CF3)3] provides unprecedented access to selective iron‐catalyzed intramolecular functionalization of strong alkyl C(sp3)−H bonds. Reactions occur at 25 °C via α‐alkyl‐metallocarbene intermediates, and with activity/selectivity levels similar to those of rhodium carboxylate catalysts. Mechanistic investigations reveal a crucial role of the lithium cation in the rate‐determining formation of the electrophilic iron‐carbene intermediate, which then proceeds by concerted insertion into the C−H bond.

Facile and Rapid Preparation of Ag@ZIF-8 for Carboxylation of Terminal Alkynes with CO2 in Mild Conditions.

Metal-organic frameworks (MOFs) are promising hosts for catalytic active sites due to their adjustable porosity and framework chemistry. Strategies to improve synergistic effects between the installed sites and the parent MOF are highly desired. Herein, a facile and rapid method for the preparation of xAg@ZIF-8 materials was reported. The materials were systematically characterized and used as catalysts for carboxylation of terminal alkynes via direct insertion of CO2 to the C(sp)-H bond (CTACO2). It was found that the integrity of the ZIF-8 structure could be retained upon Ag loading, but short-range crystalline ordering was modified. Two types Ag species could be installed, namely, highly dispersed Ag(I) in the backbone (AgHD) and aggregated Ag(0) nanoparticles on the outer surface (AgNP). The AgNP sites are highly effective for the activation of terminal alkynes due to its high accessibility, while the AgHD-modified ZIF-8 framework worked as a CO2 reservoir with enhanced affinity. Combination of these factors translated to high activity in the CTACO2 process, the measured turnover frequency and time yield are among the highest among most heterogeneous catalysts.