Α-alkylidene Cyclic Carbonates Research Articles

Two Sustainable Pathways of MOF-Catalyzed Room Temperature Chemical Fixation of CO2 inside Alkynes under Atmospheric Pressure.

The rising atmospheric CO2 levels necessitate the development of effective materials for its mitigation. Utilization of adsorbent materials for the reversible physisorption of CO2 has a significantly less impact. Recognizing this need, herein, we present a nitrogen-rich, aqua-stable, Ag(0)-nanoparticle-doped metal-organic framework (MOF) designed for the irreversible chemical conversion of CO2 into valuable fine chemicals. We demonstrate two sustainable pathways for CO2 fixation, utilizing the catalyst, 1'@Ag NPs. The designed catalyst facilitates the cyclization of propargylic amines and alcohols under ambient temperature and pressure conditions. Remarkably, this is the first MOF-based catalyst that allows for quantitative conversion of propargylic amines into 2-oxazolidinones at room temperature with atmospheric CO2 pressure. The process successfully transforms various propargylic amines and alcohols into 2-oxazolidinones and α-alkylidene cyclic carbonates under the CO2 atmosphere. Additionally, the catalyst shows excellent recyclability, maintaining its activity and structural integrity across multiple reuse cycles. Control experiments revealed that the catalytic efficiency of 1'@Ag NPs is attributed to the highly exposed alkynophilic Ag(0) sites on its pore walls. Computational studies further elucidate the mechanistic pathway for CO2 fixation. This work highlights the potential of 1'@Ag NPs to enhance environmental sustainability by converting CO2 into valuable bioactive chemicals under mild conditions.

Non-Noble Metal Anchored 2D Covalent Organic Framework for Ambient CO2 Fixation to High-Value Compounds.

The catalytic functionalization of CO2 into high-value compounds comprises a promising approach to mitigate its atmospheric content and sustainable generation of fine chemicals. Herein, we report application of a crystalline, nano-porous 2D COF (ET-BP-COF) for utilization of CO2. The ET-BP-COF features a unique 2D kagome (kgm) topology composed of hexagonal and triangular 1D channels decorated with bipyridine sites, which were exploited for covalent anchoring of eco-friendly Cu(I) by post-synthetic method. The Cu(I) engrafted COF was applied as a recyclable catalyst for coupling CO2 with alkynes to generate two high-value compounds, α-alkylidene cyclic carbonates (α-ACCs) and 2-oxazolidinones. Notably, Cu(I)@ET-BP-COF demonstrated excellent catalytic performance for transforming propargylic amine and CO2 to 2-oxazolidinone, an essential building block for antibiotics. Besides, an efficient transformation of propargylic alcohols to generate α-ACCs, valuable commodity chemicals, has been achieved by utilizing carbon dioxide. Further, detailed theoretical simulations disclosed the insight mechanistic path of Cu(I) catalyzed coupling of CO2 with alkynes to produce 2-oxazolidinones and α-ACCs. Significantly, Cu(I)@COF was reusable for multiple cycles without losing framework rigidity and catalytic performance. This study showcases the potential application of ET-BP-COF for stable anchoring of eco-friendly metals as catalytic sites for effective utilization of CO2 to produce two high-value products.

Novel and reusable magnetic MOF nanocomposite coupled ionic liquid- promoted efficient chemical fixation of CO2 into α-alkylidene cyclic carbonates

Carbon dioxide as a C1 building block to synthesize α-alkylidene cyclic carbonates is an environmental and sustainable approach. In this work, we designed and synthesized a type of multifunctional magnetic MOF nanocomposite catalysts, which could realize the carboxylic cyclization of CO2 and propargylic alcohols into α-alkylidene cyclic carbonates under solvent-free conditions. Among all the prepared nanocomposites, the MnFe2O4@SiO2@Cu-MOF nanocomposite is the best in catalytic activity combined with the tetrabutylphosphonium acetate ([Bu4P]OAc) ionic liquid cocatalyst. The catalytic system MnFe2O4@SiO2@Cu-MOF/[Bu4P]OAc displayed excellent performance in catalyzing the carboxylic cyclization of CO2 and different propargylic alcohols, and a series of α-alkylidene cyclic carbonates were obtained in high to excellent yields (88 ∼ 98 %) under mild reaction conditions (0.2 MPa, 35 °C). In addition, the two-component catalytic system had high stability and reusability, and can be easily separated and reused up to six consecutive cycles without considerable decrease in catalytic activity. Moreover, using the ionic liquid [Bu4P]OAc as the cocatalyst, the nanocomposite had good substrate adaptability for the catalytic carboxylic cyclization, which opens interesting prospects for the development of new magnetic MOF nanocomposites as efficient heterogeneous catalysts for the chemical transformation of CO2 into value-added chemicals.

In Situ Anchoring of Small-Sized Silver Nanoparticles on Porphyrinic Triazine-Based Frameworks for the Conversion of CO2 into α-Alkylidene Cyclic Carbonates with Outstanding Catalytic Activities under Ambient Conditions.

The preparation of catalytic hybrid materials by introducing highly dispersed metallic nanoparticles into porous organic polymers (POPs) may be an ideal and promising strategy for integrated CO2 capture and conversion. In terms of the carboxylative cyclization of propargyl alcohols with CO2, the anchoring of silver nanoparticles (AgNPs) on functional POPs to fabricate efficient heterogeneous catalysts is considered to be quite intriguing but remains challenging. In the contribution, well-dispersed AgNPs were successfully anchored onto the porphyrinic triazine-based frameworks by a simple "liquid impregnation and in situ reduction" strategy. The presence of N-rich dual active sites, porphyrin and triazine, which acted as the electron donor and acceptor, respectively, offered a huge opportunity for the nucleation and growth of metal nanoparticles. Significantly, the as-prepared catalyst Ag/TPP-CTF shows excellent catalytic activity (up to 99%) toward the carboxylative cyclization of propargyl alcohols with CO2 at room temperature, achieving record-breaking activities (TOF up to 615 h-1 at 1 bar and 3077 h-1 at 10 bar). Moreover, the catalyst can be easily recovered and reused at least 10 times with retention of high catalytic activity. The possible mechanism involves small-sized AgNP-mediated alkyne activation, which may promote highly efficient and green conversion of CO2. This work paves the way for immobilizing metal nanoparticles onto functional POPs by surface structure changes for enhanced CO2 catalysis.

AgNPs Embedded in Porous Polymeric Framework: A Reusable Catalytic System for the Synthesis of α-Alkylidene Cyclic Carbonates and Oxazolidinones via Chemical Fixation of CO2

AgNPs Embedded in Porous Polymeric Framework: A Reusable Catalytic System for the Synthesis of α-Alkylidene Cyclic Carbonates and Oxazolidinones via Chemical Fixation of CO2

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.

Carboxylative cyclization of propargyl alcohols with carbon dioxide for the synthesis of α-alkylidene cyclic carbonates in presence of Co(III) schiff base complex catalyst

A cobalt(III) complex, [Co(L)3](DMF) (1) of Schiff base ligand HL, 2-((E)-(benzylimino)methyl)-4-bromophenol is prepared and single crystal X-ray structural analysis have also been performed. The structures of complex 1 showed hexa-coordinated mononuclear systems that adopt octahedral geometry. The complex has also exhibited the supramolecular networks through non-covalent interactions like H-bonding, C–Hπ stacking. Moreover, the complex 1 is very effective in the catalytic fixation of carbon dioxide in propergyl alcohols to produce α-alkylidene cyclic carbonates. The catalytic production of α-alkylidene cyclic carbonates have been carried out through carboxylative cyclization of propargyl alcohols using CO2 balloon of 1 atm pressure at 80 °C. Solvent free condition (green synthesis) made this catalytic protocol eco-friendly towards the environment. Utilizing various substrates of propargyl alcohols moderate to high percentage yield (62–95%) of respective α-alkylidene cyclic carbonates product have been isolated over this catalytic reaction. Besides, the theoretical calculations (DFT) was performed for the prediction of probable mechanism of the catalytic reaction.

Amino-functionalized organic polymer loaded with highly dispersed CuI for efficient catalytic conversion of CO2 with PA

The conversion of CO2 into high value-added chemicals through efficient catalysis is an ideal strategy to reduce atmospheric CO2 pollution and achieve carbon neutrality. Therefore, amino-functionalized organic polymer Cu@Co-PIL-N4 loaded with highly dispersed CuI as a novel catalyst was developed. The functionalization of the surface and the high dispersion of the active phase integrate CO2 capture and conversion into one catalytic system. The locally enriched CO2 is converted to the easily activated carbon-oxygen negative ion by the action of primary or secondary amines. Thus, it is easier to achieve efficient preparation of α-alkylidene cyclic carbonates (STY = 20.8 h−1) by CO2 carboxylative cyclization under mild conditions (25 °C, CO2 pressure of 1 bar). The addition of a small amount of water to the cyclization system boosted domino reaction to convert the α-alkylidene cyclic carbonates to α-hydroxy ketones. The domino reaction also exhibited efficient catalytic activity and outstanding regioselectivity. In addition, the Cu@Co-PIL-N4 catalyst exhibited excellent substrate expansion and cyclic regeneration for both reactions. This work promises great significance for further developing cost-effective and high-performance catalysts for the chemical conversion of CO2.

Rational construction of noble metal-free Cu(I) anchored Zr-MOF for efficient fixation of CO2 from dilute gas at ambient conditions

The utilization of carbon dioxide (CO2) from dilute gas as C1 feedstock for synthesis of high-value chemicals such as α-alkylidene cyclic carbonates is one of the promising approaches towards mitigating the increasing atmospheric CO2 concentration. Consequently, herein, we demonstrate the application of UiO-MOF functionalized with bipyridine sites for facile anchoring of catalytically active noble metal-free copper (I) sites by post-synthetic treatment. The Cu(I) anchored UiO-MOF exhibits an excellent catalytic activity for coupling CO2 with propargylic alcohols affording α-alkylidene cyclic carbonates, valuable commodity chemicals at mild conditions of 1 atm of CO2 (balloon). Furthermore, the MOF catalyst showed good activity for fixation carbon dioxide from dilute gas (CO2:N2 = 13:87%) condition. The superior catalytic performance of Cu(I)@UiO-MOF over the homogeneous counterpart has been attributed to a synergistic effect of high CO2-philicity of MOF and catalytic activity of copper (I) sites exposed in the 1D channels of the MOF. The catalyst can be recycled up to five cycles with retention of catalytic efficiency and its heterogeneity enjoyed over the reaction period. This work demonstrates the rational integration of non-noble metal catalytic sites in functionalized frameworks for the efficient fixation of CO2 from dilute gas into fine chemicals.

AgNPs supported over porous organic polymers for the fixation of CO2 on propargyl alcohols and amines under solvent-free conditions

Silver nanoparticle embedded POP was synthesized and used as a heterogeneous catalyst for the synthesis of α-alkylidene cyclic carbonates and acyclic carbamates via CO2 fixation under mild conditions.

The effect of metal silver(I) salt on CO2 conversion to α-alkylidene cyclic carbonates: A DFT study

The cycloaddition of CO2 with propargylic alcohol (PA) catalyzed by ILs has evoked great interest in the past few decades. Recent research found that metal-assisted catalytic system can achieve higher CO2 conversion and product yield than pure IL. However, the microscopic mechanisms of different catalytic systems have not been investigated in detail. In this study, considering activation sequences of the reactants, various reaction routes of PA-activated mechanism and CO2-activated mechanism in the catalytic system with or without metal participation were simulated respectively. The PA-activated mechanism was found to be the optimal path for the carboxylative cyclization of PA with CO2, and intramolecular cyclization was the rate-determining step. Due to the synergistic catalytic effect of [Ch][Triz] and AgNO3 in the reaction, the activation Gibbs free energy of 14.2 kcal/mol in metal-assisted system is lower than that in pure IL (24.9 kcal/mol). [Ch][Triz] promotes deprotonation of the hydroxyl and elimination of metal electrophile by providing hydrogen protons, while Ag salts facilitate the intramolecular cyclization step by activating CC triple bond of the substrate. Simultaneously, the influence of cations in ionic liquids is analyzed, and it is found that the weak interaction between CO2 and cations can indirectly affect the active center through electronic effects.

Pyrrolidine-2,5-dione-derived ionic liquids promoted efficient transformation of flue gas CO2 into α-alkylidene cyclic carbonates at room temperature

The combination of pyrrolidine-2,5-dione-derived ionic liquids with silver acetate (AgOAc) were developed as binary catalysts for conversion of simulated flue gas CO2 and propargylic alcohols to α-alkylidene cyclic carbonates. By tuning different catalyst components, the [HTMG][Pyrro]/AgOAc system was confirmed to be the most efficient and exhibited an excellent synergistic action in facilitating the carboxylic cyclization under room temperature and solvent-free conditions. The influence of reaction parameters on carboxylic cyclization of CO2 with 2-methylbut-3-yn-2-ol were optimized. Under the determined conditions, the [HTMG][Pyrro]/AgOAc system was stable enough to show durable high activity in eight recycles, and also versatile in carboxylic cyclization of flue gas CO2 with other propargylic alcohols. Moreover, a thorough comparison of [HTMG][Pyrro]/AgOAc with the reported catalysts was provided and evaluated, the results suggested that the developed catalytic system has significant advantages in practical application. Finally, the mechanistic details for the conversion of CO2 into α-alkylidene cyclic carbonates catalyzed by [HTMG][Pyrro]/AgOAc was also elucidated on the basis of reactants activation.

Rational design of Cu(I)-anchored porous covalent triazine framework (CTF) for simultaneous capture and conversion of CO2 at ambient conditions

The selective carbon capture and utilization (CCU) as a C1 source is sought to be an important step towards environmental remediation and sustainable production of useful chemicals. In this context, herein, we report the strategic integration of noble metal-free Cu(I) catalytic sites with a nitrogen-rich, CO2-philic, bipyridine functionalized covalent triazine framework (bipy-CTF) by a post-synthetic approach. The Cu(I)@bipy-CTF showed very good performance for simultaneous capture and fixation of CO2 into α-alkylidene cyclic carbonates (α-aCCs), high-value commodity chemicals at ambient conditions. Further, the Cu(I) anchored bipy-CTF showed high CO2 affinity with the interaction energy of 44.09 kJ/mol attributed to the presence of CO2-philic, basic nitrogen sites. The presence of both CO2-philic nitrogen and alkynophilic Cu(I) sites decorated in the 1D channels of bipy-CTF provided a good catalytic activity for the chemical fixation of carbon dioxide from dilute gas (13 % CO2) to yield α-aCCs at atmospheric pressure (balloon) of CO2. Notably, Cu(I)@bipy-CTF showed high recyclability and chemical stability for multiple catalytic cycles. Overall, the present work represents a rare example of a COF-based recyclable catalyst for CO2 fixation from dilute gas into valuable chemicals under mild conditions.

Highly Efficient Conversion of Propargylic Alcohols and Propargylic Amines with CO2 Activated by Noble-Metal-Free Catalyst Cu2 O@ZIF-8.

The cyclization reactions of propargylic alcohols and propargylic amines with CO2 are important in industrial applications, but it was a great challenge that non-noble-metal catalysts catalyzed both reactions under mild conditions. Herein, the catalyst Cu2 O@ZIF-8 was prepared by encapsulating Cu2 O nanoparticles into robust ZIF-8, and it can effectively catalyze the cyclization of both propargylic alcohols and propargylic amines with CO2 into valuable α-alkylidene cyclic carbonates and oxazolidinones with turnover numbers (TONs) of 12.1 and 19.6, which can be recycled at least five times. The mechanisms were further uncovered by NMR, FTIR, 13 C isotope-labeling experiments and DFT calculations, in which Cu2 O and DBU can synergistically activate the C≡C bond and the hydroxy/amino group of substrates. Importantly, it is the first example of a noble-metal-free catalyst that can catalyze both propargylic alcohols and propargylic amines with CO2 simultaneously.

Tandem Reactions Based on the Cyclization of Carbon Dioxide and Propargylic Alcohols: Derivative Applications of α-Alkylidene Carbonates

As a well-known greenhouse gas, carbon dioxide (CO2) has attracted increasing levels of attention in areas of energy, environment, climate, etc. Notably, CO2 is an abundant, nonflammable, and renewable C1 feedstock in view of chemistry. Therefore, the transformation of CO2 into organic compounds is an extremely attractive research topic in modern green and sustainable chemistry. Among the numerous CO2 utilization methods, carboxylative cycloaddition of CO2 into propargylic alcohols is an ideal route due to the corresponding products, α-alkylidene cyclic carbonates, which are a series of highly functionalized compounds that supply numerous potential methods for the construction of various synthetically and biologically valuable agents. This cyclization reaction has been intensively studied and systematically summarized, in the past years. Therefore, attention has been gradually transferred to produce more derivative compounds. Herein, the tandem reactions of this cyclization with hydration, amination, alcoholysis, and isomerization to synthesize α-hydroxyl ketones, oxazolidinones, carbamates, unsymmetrical carbonates, tetronic acids, ethylene carbonates, etc. were systematically reviewed.

Synthesis of α-alkylidene cyclic carbonates via CO2 fixation under ambient conditions promoted by an easily available silver carbamate

A series of α-alkylidene cyclic carbonates has been synthesized under mild conditions using silver carbamate Ag(O2CNEt2) in combination with PPh3.

Copper-catalysed synthesis of α-alkylidene cyclic carbonates from propargylic alcohols and CO2

A sterically encumbered, nine-membered NHC-copper(i) complex was shown to be an effective catalyst for the chemical fixation of CO2 by propargylic alcohols for the diastereoselective synthesis of α-alkylidene cyclic carbonates.

The carboxylative cyclization of propargyl alcohol and carbon dioxide catalyzed by organocatalysts

Carbon dioxide (CO2), as a cheap, non-toxic, and abundant C1 resource, can be transformed into high value-added chemicals by constructing C−C, C−O, C−N, and C−S bonds, which is in agreement with the requirements of green chemistry and sustainable development. For example, CO2 can not only be transformed into fuel-related formic acid, methanol etc., but also serves as raw materials for the synthesis of fine chemicals such as carbonates, carbamates and salicylic acid. However, CO2 has the disadvantage of thermodynamic stability and chemical inertness, which can hinder its chemical conversion and utilization. It has become one of the research hotspots to develop efficient catalysts of activating CO2 and reducing the reaction energy barrier in the field of CO2 conversion. Under the continuing efforts of chemists, a series of highly efficient catalysts have been developed and applied in the catalytic conversion of CO2. The carboxylative cyclization of propargyl alcohol to prepare α-alkylidene cyclic carbonates is one of desired chemical reaction in CO2 fixation, which presents 100% atomic utilization and meets the requirements of green chemistry. Now, investigations on the carboxylative cyclization of propargyl alcohol and CO2 have been developing rapidly, and a series of novel reaction systems have been reported. In the carboxylative cyclization, transition metals are extensively studied. Various transition-metal catalytic systems, including silver (AgI), copper (CuI), zinc (ZnII), are closely investigated in the carboxylative cyclization. The transition-metal salts can effectively activate the carbon-carbon triple bond in the propargyl alcohol structure, facilitating the subsequent attack of carbon-carbon triple bonds by alkyl carbonate anions to generate the target products. Although the transition metals are efficient catalysts in this cyclization reaction, their disadvantages, such as high cost and transition-metal residues, are not favourable. Recently, transition metal-free organocatalysts have been becoming one hotspot in the catalysis field, and found wide applications in the field of CO2 conversion, burgeoning in the literature. A series of organocatalysts, such as ionic liquids (ILs), organic strong bases, phosphines and CO2 adducts, have been reported in this carboxylation cyclization reaction. Herein, an overview about the research progresses of organocatalyst-catalyzed carboxylative cyclization is provided, with a particular emphasis on the application of ionic liquids, CO2 adducts and phosphines, and their corresponding mechanisms. Rationally designed CO2-reactive site-containing ILs could activate CO2 effectively, in which the anion is the main contributor, while the cations make a lower contribution. By introducing one or more CO2-reactive sites into the anion structure of ILs, linear CO2 molecules can transformed into active carbonate anions and carbamate anions, thereby achieving the effect of activating CO2. In virtue of CO2-reactive sites, ILs-catalyzed carboxylation cyclization is realized under mild conditions. Strong nucleophiles are found to easily react with CO2 molecule to generate CO2 adducts, such as N -heterocyclic carbenes-CO2 adducts (NHC-CO2), N-heterocyclic olefins-CO2 adducts, alkylated N -heterocyclic olefins CO2-adducts (ANHO-CO2), carbodicarbenes-CO2 adducts (CDCs-CO2), alkoxide-functionalized imidazolium betaines CO2-adducts(AFIB-CO2) and so on, which can serve as efficient organocatalysts in the carboxylative cyclization reaction. Phosphines also present strong nucleophilicity, can activate CO2 and propargyl alcohol molecules by nucleophilic addition to CO2 and carbon-carbon triple bonds of propargyl alcohols. Furthermore, chiral phosphines can act as chiral organocatalysts to afford optically active functionalized cyclic carbonates. Taken together, these rationally designed organocatalysts exhibited excellent performance, obtaining a series of α-alkylidene cyclic carbonates in good yields. In this paper, the mechanisms of the carboxylative cyclization promoted by organocatalysts are closely discussed, hoping to pave a way for the design of more efficient and green organocatalysts.

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 highly stable polyoxovanadate-based Cu(i)–MOF for the carboxylative cyclization of CO2with propargylic alcohols at room temperature

A POVs-based Cu(i)–MOF was synthesized and utilized as a heterogeneous catalyst for the cyclization of CO2with propargylic alcohols to obtain value-added α-alkylidene cyclic carbonates, exhibiting high catalytic activity and sustainability.