Direct Copolymerization of CO2 and Diols

Sustainable Copolymer Synthesis from Carbon Dioxide and Butadiene

Carbon dioxide (CO2) has long been recognized as an ideal C1 feedstock comonomer for producing sustainable materials because it is renewable, abundant, and cost-effective. However, activating CO2 presents a significant challenge because it is highly oxidized and stable. A CO2/butadiene-derived δ-valerolactone (EVP), generated via palladium-catalyzed telomerization between CO2 and butadiene, has emerged as an attractive intermediate for producing sustainable copolymers from CO2 and butadiene. Owing to the presence of two active carbon-carbon double bonds and a lactone unit, EVP serves as a versatile intermediate for creating sustainable copolymers with a CO2 content of up to 29 wt % (33 mol %). In this Review, advances in the synthesis of copolymers from CO2 and butadiene with divergent structures through various polymerization protocols have been summarized. Achievements made in homo- and copolymerization of EVP or its derivatives are comprehensively reviewed, while the postmodification of the obtained copolymers to access new polymers are also discussed. Meanwhile, potential applications of the obtained copolymers are also discussed. The literature references were sorted into sections based on polymerization strategies and mechanisms, facilitating readers in gaining a comprehensive view of the present chemistry landscape and inspiring innovative approaches to synthesizing novel CO2-derived copolymers.

Direct Esterification of Alkylcarbamic Acids with Alcohols over CeO2 Catalyst

Alkylcarbamic acids, which are easily produced via chemical absorption of CO2 into amines, have a great potential to be substrates for producing value-added chemicals. In this research, the esterification of various alkylcarbamic acids with alcohols into alkyl N-alkylcarbamates was demonstrated by using a heterogeneous catalyst as well as the corresponding amine additives. In the model reaction, the esterification of benzylcarbamic acid (BZA-CA) and methanol (MeOH), the target product of methyl N-benzylcarbamate was obtained in 64 % CO2 -based yield at 413 K in 12 h over a CeO2 catalyst, which also exhibited good reusability. In this catalytic system, the corresponding amine additive (i. e., benzylamine for BZA-CA) had the important role in the improvement of CO2 -moiety-based balance, allowing the precise kinetic study, in contrast to the cases without such additive. The detailed kinetic study on the target catalytic system and control systems suggested that BZA-CA underwent the esterification by MeOH directly. The current catalytic system using the combination of CeO2 catalyst and corresponding amine additive was also demonstrated to be applicable to the synthesis of alkyl N-alkylcarbamates from alkylcarbamic acids and alcohols with short, linear alkyl chains (≤C3 ).

Comparative Study between 2-Furonitrile and 2-Cyanopyridine as Dehydrants in Direct Synthesis of Dialkyl Carbonates from CO2 and Alcohols over Cerium Oxide Catalyst

The shift of equilibrium by removing water with nitrile dehydrants is crucial for CeO2 -catalyzed synthesis of dialkyl carbonates from CO2 and alcohols. Two nitriles - 2-cyanopyridine and 2-furonitrile - were previously found as effective dehydrants, yet their detailed comparison as well as exploration of potential of 2-furonitrile remain insufficient. Herein, the performance of 2-cyanopyridine and 2-furonitrile was compared in the synthesis of various dialkyl carbonates. 2-furonitrile was found to be superior to 2-cyanopyridine in the synthesis of dialkyl carbonates from CO2 and bulky or long-chain (≥C3) alcohols. Namely, the yield of diisopropyl carbonate (up to 50 %) achieved using CeO2 and 2-furonitrile is comparable to or even higher than previously reported ones. Meanwhile, 2-cyanopyridine acted as a better dehydrant than 2-furonitrile in the synthesis of dimethyl carbonate and diethyl carbonate. The adsorption experiments and density functional theory calculations have indicated that the better performance of 2-furonitrile compared to 2-cyanopyridine in the synthesis of dialkyl carbonates from bulky or long-chain alcohols is due to the weaker interaction of 2-furonitrile with the CeO2 surface. Such weak interaction of 2-furonitrile offers a larger reaction field on the catalyst surface for both CO2 and alcohols.

Advances in the Synthesis of Copolymers from Carbon Dioxide, Dienes, and Olefins

ConspectusCarbon dioxide (CO₂) has long been considered a sustainable comonomer for polymer synthesis due to its abundance, easy availability, and low toxicity. Polymer synthesis from CO₂ is highly attractive and has received continuous interest from synthetic chemists. In this regard, alternating copolymerization of CO₂ and epoxides is one of the most well-established methods to synthesize aliphatic polycarbonates. Moreover, binucleophiles including diols, diamines, amino alcohols, and diynes have been reported to copolymerize with CO₂ to give polycarbonates, polyureas, polyurethanes, and polyesters, respectively. Nevertheless, little success has been made for incorporating CO₂ into the most widely used polyolefin materials.Although extensive studies have been focused on the copolymerization of olefins and CO₂, most of the attempted reactions resulted in olefin homopolymerization owing to the endothermic property and high energy barriers of CO₂ insertion during the chain propagation process. In this Account, we show how this challenge is addressed by taking advantage of a metastable lactone intermediate, 3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVP), which is produced from CO₂ and butadiene via palladium catalysis. Homopolymerization of EVP furnishes CO₂/butadiene copolymers with up to 29 wt % of CO₂ content. This reaction strategy represents a breakthrough for the long-standing challenge of inherent kinetic and thermodynamically unfavorable CO₂/olefin copolymerization. A new class of polymeric materials bearing repeating bicyclic lactone and unsaturated lactone units can be obtained. Importantly, one-pot copolymerization of CO₂/butadiene or terpolymerization of CO₂/butadiene/diene can be achieved to afford copolymers through a two-step reaction protocol. Interestingly, the bicyclic lactone units in the polymer chain can undergo ring-opening through hydrolysis and aminolysis, while reversible ring-closing of the hydrolyzed or aminolyzed units was also achieved simply by heating.Over the past few years, more and more studies have utilized EVP as an intermediate to synthesize copolymers from olefins, butadiene, and CO₂. Recently, we successfully incorporated CO₂ into the most widely used polyethylene materials via the direct copolymerization of EVP and ethylene. Taking advantage of the bifunctional reactivity of EVP, we were able to access two types of main-chain-functionalized polyethylenes through palladium-catalyzed coordination/insertion copolymerization and radical copolymerization. Besides polyethylenes, CO₂ was also incorporated into poly(methyl methacrylate), poly(methyl acrylate), polystyrene, polymethyl acrylate, polyvinylchloroacetate, and poly(vinyl acetate) materials via radical copolymerization of EVP and olefin monomers. The EVP/olefin copolymerization strategy provides a novel avenue for the synthesis of highly versatile copolymers from an olefin, CO₂, and butadiene.

Sr[C2O5] is an Inorganic Pyrocarbonate Salt with [C2O5]2- Complex Anions

The synthesis of a novel type of carbonate, namely of the inorganic pyrocarbonate salt Sr[C₂O₅], which contains isolated [C₂O₅]^2--groups, significantly extends the crystal chemistry of inorganic carbonates beyond the established sp²- and sp³-carbonates. We synthesized Sr[C₂O₅] in a laser-heated diamond anvil cell by reacting Sr[CO₃] with CO₂. By single crystal synchrotron diffraction, Raman spectroscopy, and density functional theory (DFT) calculations, we show that it is a pyrocarbonate salt. Sr[C₂O₅] is the first member of a novel family of inorganic carbonates. We predict, based on DFT calculations, that further inorganic pyrocarbonates can be obtained and that these will be relevant to geoscience and may provide a better understanding of reactions converting CO₂ into useful inorganic compounds.

En Route to CO2-Based (a)Cyclic Carbonates and Polycarbonates from Alcohols Substrates by Direct and Indirect Approaches

This review is dedicated to the state-of-the art routes used for the synthesis of CO2-based (a)cyclic carbonates and polycarbonates from alcohol substrates, with an emphasis on their respective main advantages and limitations. The first section reviews the synthesis of organic carbonates such as dialkyl carbonates or cyclic carbonates from the carbonation of alcohols. Many different synthetic strategies have been reported (dehydrative condensation, the alkylation route, the “leaving group” strategy, the carbodiimide route, the protected alcohols route, etc.) with various substrates (mono-alcohols, diols, allyl alcohols, halohydrins, propargylic alcohols, etc.). The second section reviews the formation of polycarbonates via the direct copolymerization of CO2 with diols, as well as the ring-opening polymerization route. Finally, polycondensation processes involving CO2-based dimethyl and diphenyl carbonates with aliphatic and aromatic diols are described.

No competitive inhibition of bicarbonate or carbonate for formate dehydrogenase from Candida boidinii -catalyzed CO2 reduction

Formate dehydrogenase from Candida boidinii (CbFDH) reversibly catalyzes the formate to CO2 with the redox coupling NAD+/NADH. While many studies on CbFDH-catalyzed formate oxidation in the presence of NAD+ are...

Facile synthesis, structure and properties of CO2-sourced poly(thioether-co-carbonate)s containing acetyl pendants via thio-ene click polymerization

Synthetic transformation of CO2 into di- and trivinyl carbonates allows for photo-initiated thio-ene polymerization leading to sequence controlled poly(thioether-carbonate)s.

Systematic Variation of 3d Metal Centers in a Redox-Innocent Ligand Environment: Structures, Electrochemical Properties, and Carbon Dioxide Activation

Coordination compounds of earth-abundant 3d transition metals are among the most effective catalysts for the electrochemical reduction of carbon dioxide (CO₂). While the properties of the metal center are crucial for the ability of the complexes to electrochemically activate CO₂, systematic variations of the metal within an identical, redox-innocent ligand backbone remain insufficiently investigated. Here, we report on the synthesis, structural and spectroscopic characterization, and electrochemical investigation of a series of 3d transition-metal complexes [M = Mn(I), Fe(II), Co(II), Ni(II), Cu(I), and Zn(II)] coordinated by a new redox-innocent PNP pincer ligand system. Only the Fe, Co, and Ni complexes reveal distinct metal-centered electrochemical reductions from M(II) down to M(0) and show indications for interaction with CO₂ in their reduced states. The Ni(0) d¹⁰ species associates with CO₂ to form a putative Aresta-type Ni-η²-CO₂ complex, where electron transfer to CO₂ through back-bonding is insufficient to enable electrocatalytic activity. By contrast, the Co(0) d⁹ intermediate binding CO₂ can undergo additional electron uptake into a formal cobalt(I) metallacarboxylate complex able to promote turnover. Our data, together with the few literature precedents, single out that an unsaturated coordination sphere (coordination number = 4 or 5) and a d⁷-to-d⁹ configuration in the reduced low oxidation state (+I or 0) are characteristics that foster electrochemical CO₂ activation for complexes based on redox-innocent ligands.

A series of 3d transition-metal complexes (M = Mn, Fe, Co, Ni, Cu, and Zn) coordinated by a new redox-innocent PNP pincer ligand system were synthesized and structurally as well as electrochemically analyzed to illuminate the role of the metal center in molecular electrochemical carbon dioxide (CO₂) activation.

Self-Healable and Recyclable Biomass-Derived Polyurethane Networks through Carbon Dioxide Immobilization

Due to growing environmental issues, research on carbon dioxide (CO2) use is widely conducted and efforts are being made to produce useful materials from biomass-derived resources. However, polymer materials developed by a combined strategy (i.e., both CO2-immobilized and biomass-derived) are rare. In this study, we synthesized biomass-derived poly(carbonate-co-urethane) (PCU) networks using CO2-immobilized furan carbonate diols (FCDs) via an ecofriendly method. The synthesis of FCDs was performed by directly introducing CO2 into a biomass-derived 2,5-bis(hydroxymethyl)furan. Using mechanochemical synthesis (ball-milling), the PCU networks were effortlessly prepared from FCDs, erythritol, and diisocyanate, which were then hot-pressed into films. The thermal and thermomechanical properties of the PCU networks were thoroughly characterized by thermogravimetric analysis, differential scanning calorimetry, dynamic (thermal) mechanical analysis, and using a rheometer. The self-healing and recyclable properties of the PCU films were successfully demonstrated using dynamic covalent bonds. Interestingly, transcarbamoylation (urethane exchange) occurred preferentially as opposed to transcarbonation (carbonate exchange). We believe our approach presents an efficient means for producing sustainable polyurethane copolymers using biomass-derived and CO2-immobilized diols.

2,2-Bis(hydroxymethyl) propionic acid based cyclic carbonate monomers and their (co)polymers as advanced materials for biomedical applications

Designing grafted biodegradable polymers with tailored multi-functional properties is one of the most researched fields with extensive biomedical applications. Among many biodegradable polymers, polycarbonates have gained much attention due to their ease of synthesis, high drug loading, and excellent biocompatibility profiles. Among various monomers, 2,2-bis(hydroxymethyl) propionic acid (bis-MPA) derived cyclic carbonate monomers have been extensively explored in terms of their synthesis as well as their polymerization. Since the late 90s, significant advancements have been made in the design of bis-MPA derived cyclic carbonate monomers as well as in their reaction schemes. Currently, bis-MPA derived polycarbonates have taken a form of an entire platform with a multitude of applications, the latest being in the field of nanotechnology, targeted drug, and nucleic acid delivery. The present review outlines an up to date developments that have taken place in the last two decades in the design, synthesis, and biomedical applications of bis-MPA derived cyclic carbonates and their (co)polymers.

Catalytic CO2 esterification with ethanol for the production of diethyl carbonate using optimized CeO2 as catalyst

The direct conversion of (bio)ethanol and CO₂ is a promising route to diethyl carbonate (DEC) using CeO₂ from optimized catalyst synthesis procedure and cheap reactants originating from renewable resources in bioethanol production.

Recycling of CO2 by Hydrogenation of Carbonate Derivatives to Methanol: Tuning Copper-Oxide Promotion Effects in Supported Catalysts

The selective hydrogenation of organic carbonates to methanol is a relevant transformation to realize flexible processes for the recycling of waste CO₂ with renewable H₂ mediated by condensed carbon dioxide surrogates. Oxide-supported copper nanoparticles are promising solid catalysts for this selective hydrogenation. However, essential for their optimization is to rationalize the prominent impact of the oxide support on performance. Herein, the role of Lewis acid centers, exposed on the oxide support at the periphery of the Cu nanoparticles, was systematically assessed. For the hydrogenation of propylene carbonate, as a model cyclic carbonate, the conversion rate, the apparent activation energy, and the selectivity to methanol correlate with the Lewis acidity of the coordinatively unsaturated cationic sites exposed on the oxide support. Lewis sites of markedly low and high electron-withdrawing character promote unselective decarbonylation and decarboxylation reaction pathways, respectively. Supports exposing Lewis sites of intermediate acidity maximize the selectivity to methanol while inhibiting acid-catalyzed secondary reactions of the propanediol product, and thus enable its recovery in cyclic processes of CO₂ hydrogenation mediated by condensed carbonate derivatives. These findings help rationalize metal-support promotion effects that determine the performance of supported metal nanoparticles in this and other selective hydrogenation reactions of significance in the context of sustainable chemistry.

Synthesis of Fluorinated Dialkyl Carbonates from Carbon Dioxide as a Carbonyl Source

Fluorinated dialkyl carbonates (DACs), which serve as environmentally benign phosgene substitutes, were produced successfully from carbon dioxide either directly or indirectly. Nucleophilic addition of 2,2,2-trifluoroethanol to carbon dioxide and subsequent reaction with 2,2,2-trifluoroethyltriflate (3 a) afforded bis(2,2,2-trifluoroethyl) carbonate (1) in up to 79 % yield. Additionally, carbonate 1 was obtained through the stoichiometric reaction of 3 a and cesium carbonate. Although bis(1,1,1,3,3,3-hexafluoro-2-propyl) carbonate (4) was difficult to obtain by either of the above two methods, it could be synthesized through the transesterification of carbonate 1.

Update and Challenges in Carbon Dioxide-Based Polycarbonate Synthesis

The utilization of carbon dioxide as a comonomer to produce polycarbonates has attracted a great deal of attention from both industrial and academic communities because it promises to replace petroleum-derived plastics and supports a sustainable environment. Significant progress in the copolymerization of cyclic ethers (e.g., epoxide, oxetane) and carbon dioxide has been made in recent decades, owing to the rapid development of catalysts. In this Review, the focus is to summarize and discuss recent advances in the development of homogeneous catalysts, including metal- and organo-based complexes, as well as the preparation of carbon dioxide-based block copolymer and functional polycarbonates.

Theoretical study on CO2 reduction catalyzed by formate dehydrogenase using the cation radical of a bipyridinium salt with an ionic substituent as a co-enzyme

Mechanism for formate dehydrogenase from Candida boidinii catalyzed CO₂ reduction to formate with the cation radical of a 4,4′-bipyridinium salt with an ionic substituent as a co-enzyme was clarified by theoretical studies.

Artificial co-enzyme based on carbamoyl-modified viologen derivative cation radical for formate dehydrogenase in the catalytic CO2 reduction to formate

The interaction between the single-electron reduced carbamoyl-modified-4,4-bipyridinium salt and CbFDH in the CO₂ reduction to formate is elucidated by enzymatic kinetic analysis, the docking simulation and density functional theory calculation.

Trivalent metal ions promote the malic enzyme-catalyzed building of carbon–carbon bonds from CO2and pyruvate

ME is an attractive biocatalyst for building carbon–carbon bonds through carboxylation of pyruvate with CO₂. The carboxylation of pyruvate with CO₂was promoted by adding a trivalent metal ion. In particular, Al³⁺accelerates ME-catalyzed carboxylation of pyruvate with CO₂.

Advances in the use of CO2 as a renewable feedstock for the synthesis of polymers

Carbon dioxide offers an accessible, cheap and renewable carbon feedstock for synthesis. Current interest in the area of carbon dioxide valorisation aims at new, emerging technologies that are able to provide new opportunities to turn a waste into value. Polymers are among the most widely produced chemicals in the world greatly affecting the quality of life. However, there are growing concerns about the lack of reuse of the majority of the consumer plastics and their after-life disposal resulting in an increasing demand for sustainable alternatives. New monomers and polymers that can address these issues are therefore warranted, and merging polymer synthesis with the recycling of carbon dioxide offers a tangible route to transition towards a circular economy. Here, an overview of the most relevant and recent approaches to CO2-based monomers and polymers are highlighted with particular emphasis on the transformation routes used and their involved manifolds.

Catalytic Hydrogenation of Cyclic Carbonates using Manganese Complexes

Catalytic hydrogenation of cyclic carbonates to diols and methanol was achieved using a molecular catalyst based on earth-abundant manganese. The complex [Mn(CO)2 (Br)[HN(C2 H4 Pi Pr2 )2 ] 1 comprising commercially available MACHO ligand is an effective pre-catalyst operating under relatively mild conditions (T=120 °C, p(H2 )=30-60 bar). Upon activation with NaOt Bu, the formation of coordinatively unsaturated complex [Mn(CO)2 [N(C2 H4 Pi Pr2 )2 )] 5 was spectroscopically verified, which confirmed a kinetically competent intermediate. With the pre-activated complex, turnover numbers up to 620 and 400 were achieved for the formation of the diol and methanol, respectively. Stoichiometric reactions under catalytically relevant conditions provide insight into the stepwise reduction form the CO2 level in carbonates to methanol as final product.

Ring-opening polymerization of trimethylene carbonate to poly(trimethylene carbonate) diol over a heterogeneous high-temperature calcined CeO2 catalyst

CeO₂ calcined at 1273 K was an effective reusable heterogeneous catalyst for the synthesis of poly(trimethylene carbonate) diol by ring-opening polymerization of trimethylene carbonate under neat conditions without any additives.

Synthesis of dimethyl carbonate from CO2 and methanol over a hydrophobic Ce/SBA-15 catalyst

A series of Ce/SBA-15 catalysts with different degrees of hydrophobicities were prepared via a post-grafting method and used for the direct synthesis of dimethyl carbonate (DMC) from CO₂ and methanol. The Ce/SBA-15-6 catalyst exhibited the highest DMC yield of 0.2%, which was close to the equilibrium value under the reaction conditions of 130 °C, 12 h and 12 MPa. The catalysts were characterized via XRD, BET, FT-IR, solid-state ²⁹Si MAS NMR, CA, TEM, XPS and NH₃/CO₂-TPD; the results indicated that the hydrophobicity of the catalysts facilitated the creation of oxygen vacancies, which could act as Lewis acids to activate methanol. Higher amounts of moderate acid sites led to higher yields of DMC. In addition, the hydrophobicity of the catalysts could also reduce the adsorbed water on their surface and increase the DMC yield while shortening the reaction time.

A series of Ce/SBA-15 catalysts with different degrees of hydrophobicities were prepared via a post-grafting method and used for the direct synthesis of dimethyl carbonate (DMC) from CO₂ and methanol.

Direct Synthesis of Dimethyl Carbonate from Carbon Dioxide and Methanol at Room Temperature Using Imidazolium Hydrogen Carbonate Ionic Liquid as a Recyclable Catalyst and Dehydrant

The direct synthesis of dimethyl carbonate (DMC) from CO₂ and CH₃ OH was achieved at room temperature with 74 % CH₃ OH conversion in the presence of an imidazolium hydrogen carbonate ionic liquid ([C_n C_m Im][HCO₃ ]). Experimental and theoretical results reveal that [C_n C_m Im][HCO₃ ] can transform quickly into a CO₂ adduct, which serves as an effective catalyst and dehydrant. Its dehydration ability is reversible. The energy barrier of the rate-determining step for the DMC synthesis is only 21.7 kcal mol^-1 . The ionic liquid can be reused easily without a significant loss of its catalytic and dehydrating ability.