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The use of CO 2 as a C1 building block will be of essential importance in the future. In this context the synthesis of cyclic carbonates from epoxides and CO 2 gained great attention recently. These products are valuable compounds in a variety of chemical fields. The development of new catalysts and catalytic systems for this atom-economic, scalable, and industrially relevant reaction is a highly active research field. Over the past 17 years great advances have been made in this area of research. This chapter covers the survey of the important known classes of homogeneous catalysts for the addition of CO 2 to epoxides. Besides pioneering work, recent developments and procedures that allow this transformation under mild reaction conditions (reaction temperatures of ≤100 °C and/or CO 2 pressures of 0.1 MPa) are especially emphasized.

New neutral and zwitterionic chiral NNO-donor scorpionate ligands 1 and 2 were designed to obtain new mononuclear and dinuclear NNO-heteroscorpionate aluminum complexes. Reaction of 1 with [AlR 3 ] (R=Me, Et) in a 1:1 or 1:2 molar ratio afforded the neutral mononuclear alkyl complexes [AlR 2 (κ 2 -bpzappe)] {R=Me (3), Et (4); bpzappeH=2,2-bis(3,5-dimethylpyrazol-1-yl)-1-[4-(dimethylamino)phenyl]-1-phenylethanol} and bimetallic complexes [{AlR 2 (κ 2 -bpzappe)}(μ-O){AlR 3 }] [R=Me (5), Et (6)]. By reaction of complexes 3-6 with PhCH 2 Br, mononuclear and dinuclear cationic aluminum complexes [AlR 2 (κ 2 -bbpzappe)]Br {R=Me (7), Et (8); bbpzappeH=N-benzyl-4-[2,2-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1-hydroxy-1-phenylethyl]-N,N-dimethylbenzenaminium bromide} and [{AlR 2 (κ 2 -bbpzappe)}(μ-O){AlR 3 }]Br [R=Me (9), Et (10)] were synthesized. Both neutral aluminum complexes in the presence of Bu 4 NBr and cationic aluminum complexes were investigated as catalysts for cyclic carbonate formation from epoxides and carbon dioxide. Amongst them, complex 10 was found to be an efficient one-component catalyst for the synthesis of cyclic carbonates from both monosubstituted and internal epoxides and was shown to have broad substrate scope., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The synthesis of cyclic carbonates through coupling of carbon dioxide with epoxides is 100 % atom economical and is already performed on an industrial scale. Its impact regarding the use of carbon dioxide as a renewable carbon source is expected to grow significantly in the near future, so that the development of efficient catalysts is of high interest in academia and industry. To improve the carbon footprint and sustainability of the cycloaddition reaction, the use of organocatalytic methods is a promising approach. Herein, available metal-free catalysts for the preparation of cyclic carbonates are described and elaborated concerning the overall sustainability of the process. Therefore, the required reaction conditions, as well as the activity of the catalysts and their reusability, are compared and evaluated. In addition to ammonium-, phosphonium-, or imidazolium-based single-component catalysts and their supported analogues, the growing field of research concerning dual catalysts are also discussed in detail., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A bifunctional ammonium salt covalently bound to a polystyrene or silica support proved to be an efficient and recyclable catalyst for the solvent-free synthesis of cyclic carbonates from epoxides and CO2 . The catalyst can be easily recovered by simple filtration after the reaction and reused in up to 13 consecutive runs with retention of high activity and selectivity even at 90 °C. The scope and limitations of the reaction has been evaluated in terms of reaction conditions and substrate scope., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The synthesis of bio‐derived cyclic carbonates is attracting a lot of attention as the incorporation of bio‐derived functionality into these compounds provides the opportunity to prepare previously unknown structures, whilst also improving their sustainability profiles. This study presents a facile preparation of diastereomerically pure bio‐derived cyclic carbonates displaying a range of optical rotation values. These compounds are obtained from glycidol, amino acids and CO2 in a facile two‐step approach. Initially, the diastereomerically pure amino acid functionalised epoxides are prepared through a robust Steglich esterification of enantiopure glycidol (R or S) and an amino acid (D or L). Thereafter, in a second step, cycloaddition of the epoxide with CO2 results in the retention of the initial stereochemistry of the epoxide, furnishing novel diastereomerically pure and optically active cyclic carbonate products. A DFT study has explained the basis of this observed retention of configuration for these compounds. Further, results from this DFT study also provide new mechanistic information concerning a co‐catalyst‐free cycloaddition reaction starting from glycidol when using the gallium‐catalyst, which is found to operate through metal‐ligand cooperativity. [ABSTRACT FROM AUTHOR]

The design of molecular scaffolds bearing multiple functional groups for the activation and ring‐opening of epoxides is a crucial challenge for the synthesis of efficient homogeneous and heterogeneous catalysts that are used for the cycloaddition reaction of CO2 to epoxides. Traditional approaches to prepare such multifunctional catalysts often imply multistep synthetic procedures and expensive building blocks. In this work we show that bifunctional catalysts for the cycloaddition of CO2 to epoxides bearing a Lewis acid metal and a quaternary ammonium halide group can be prepared in just two steps starting from an opportunely designed epoxide precursor by using inexpensive substrates. Such a readily accessible catalyst was applied for the cycloaddition of CO2 to a series of epoxides under atmospheric conditions generally leading to quantitative substrate conversion and high carbonate selectivities. Importantly, we also show that the epoxide‐driven concept developed for the preparation of the molecular catalyst, could be applied to prepare recyclable heterogeneous systems for the target cycloaddition reaction. [ABSTRACT FROM AUTHOR]

The cycloaddition of CO2 to epoxides to afford versatile and useful cyclic carbonate compounds is a highly investigated method for the nonreductive upcycling of CO2. One of the main focuses of the current research in this area is the discovery of readily available, sustainable, and inexpensive catalysts, and of catalytic methodologies that allow their seamless solvent-free recycling. Water, often regarded as an undesirable pollutant in the cycloaddition process, is progressively emerging as a helpful reaction component. On the one hand, it serves as an inexpensive hydrogen bond donor (HBD) to enhance the performance of ionic compounds; on the other hand, aqueous media allow the development of diverse catalytic protocols that can boost catalytic performance or ease the recycling of molecular catalysts. An overview of the advances in the use of aqueous and biphasic aqueous systems for the cycloaddition of CO2 to epoxides is provided in this work along with recommendations for possible future developments. [ABSTRACT FROM AUTHOR]

Polyoxometalates can be tuned for specific catalytic property by substituting transition metal ions. We report the synthesis of hybrid materials of Cu2+, Co2+ and Ni2+ substituted phosphotungstates and poly(diallyldimethylammonium) chloride polymer (PDDA) for CO2 fixation. The in situ generated transition metal substituted polyoxometalates (TMS-POMs) are analyzed by FTIR, powder XRD, 31P NMR and SEM techniques. The hybrid TMS-POM materials are found to be good catalysts for converting epoxides to cyclic carbonates. Among these, PDDA-PWCo is the most efficient catalyst for cycloaddition of CO2 under solvent-free conditions at room temperature in shortest reaction time. Only 0.2 mol% of PDDA-PWCo is enough to deliver 100% conversion and selectivity to cyclic carbonates. This catalytic approach is employed for conversion of other cyclic, acyclic, and aromatic epoxides without using column purifications. Overall, the method of obtaining cyclic carbonates under green conditions using TMS-POMs-PDDA hybrid materials appears suitable for industrial applications. [ABSTRACT FROM AUTHOR]

The fixation of CO2 into valuable chemicals under mild conditions is of great importance. Here, we reported an efficient and mild method for the cycloaddition of CO2 to cyclic carbonates. Iodized salt of DBU was used as hydrogen-bonding acceptor, 4-methoxyphenol was employed as hydrogen-bonding donor, and deep eutectic solvent was synthesized and characterized by NMR, FI-IR and thermogravimetric analysis. Optimization of the reaction conditions catalyzed by the deep eutectic solvent was performed, a series of epoxides have been converted to the corresponding products with excellent yields under the optimized conditions. The reaction kinetics for the synthesis of cyclic carbonates was investigated, in addition, excellent recovery performance of the catalyst was obtained after recycling for 5 times. Comparing with the literature reported, the method was much milder and efficient simultaneously. This work provides a promising way to the fixation of CO2. [ABSTRACT FROM AUTHOR]

In this work, two ionic liquids (ILs) immobilized metal‐organic frameworks (MOFs), Fe‐MIL‐101‐3N(BuBr) and Fe‐MIL‐101‐N(Bnme2)Br, were obtained by modifying amino groups in Fe‐MIL‐101‐NH2 with bromobutane and quaternary ammonium salt. The ionic liquid immobilized MOFs have Lewis acid sites (Fe3+) and nucleophilic sites (Br−), which can synergistically catalyze the cycloaddition reaction of CO2 and epoxides. Various cyclic carbonate derivatives were obtained in excellent yields under the optimal conditions. Additionally, we found that Fe‐MIL‐101‐N(Bnme2)Br exhibited the highest catalytic activity and it can be easily recovered and reused for at least 5 times without loss of catalytic activity. Our method of preparing bifunctional catalysts provides a new approach to design catalysts for the chemical conversion of CO2. [ABSTRACT FROM AUTHOR]

The fixation of carbon dioxide with epoxides is one of the most attractive methods for the green utilisation of this greenhouse gas and leads to many valuable chemicals. This process is characterised by 100% atom efficiency; however, an efficient catalyst is required to achieve satisfactory yields. Metal–organic frameworks (MOFs) are recognised as being extremely promising for this purpose. Nevertheless, many of the proposed catalysts are based on ions of rare elements or elements not entirely safe for the environment; this is notable with commercially unavailable ligands. In an effort to develop novel catalysts for CO2 fixation on an industrial scale, we propose novel MOFs, which consist of aluminium ions coordinated with commercially available 1,4-naphthalene dicarboxylic acid (Al@NDC) and their nanocomposites with gold nanoparticles entrapped inside their structure (AlAu@NDC). Due to the application of 4-amino triazole and 5-amino tetrazole as crystallization mediators, the morphology of the synthesised materials can be modified. The introduction of gold nanoparticles (AuNPs) into the structure of the synthesised Al-based MOFs causes the change in morphology from nano cuboids to nanoflakes, simultaneously decreasing their porosity. However, the homogeneity of the nanostructures in the system is preserved. All synthesised MOF materials are highly crystalline, and the simulation of PXRD patterns suggests the same tetragonal crystallographic system for all fabricated nanomaterials. The fabricated materials are proven to be highly efficient catalysts for carbon dioxide cycloaddition with a series of model epoxides: epichlorohydrin; glycidol; styrene oxide; and propylene oxide. Applying the synthesised catalysts enables the reactions to be performed under mild conditions (90 °C; 1 MPa CO2) within a short time and with high conversion and yield (90% conversion of glycidol towards glycerol carbonate with 89% product yield within 2 h). The developed nanocatalysts can be easily separated from the reaction mixture and reused several times (both conversion and yield do not change after five cycles). The excellent performance of the fabricated catalytic materials might be explained by their high microporosity (from 421 m2 g−1 to 735 m2 g−1); many catalytic centres in the structure exhibit Lewis acids' behaviour, increased capacity for CO2 adsorption, and high stability. The presence of AuNPs in the synthesised nanocatalysts (0.8% w/w) enables the reaction to be performed with a higher yield within a shorter time; this is especially important for less-active epoxides such as propylene oxide (two times higher yield was obtained using a nanocomposite, in comparison with Al-MOF without nanoparticles). [ABSTRACT FROM AUTHOR]

2–(1H–1,2,4–Triazol–3–yl)phenol (CAT–1) was used as an organocatalyst for the coupling reaction of CO2 and epoxides at an ambient temperature and atmospheric CO2 pressure (1 bar). This compound has a structure in which a hydrogen bond donor, a hydrogen bond acceptor, and another hydrogen bond donor are adjacent in sequence in a molecule. The binary catalytic system of CAT–1/nBu4NI showed TON = 19.2 and TOF = 1.60 h−1 under 1 bar CO2 at room temperature within 12 h using 2–butyloxirane. Surprisingly, the activity of CAT–1, in which phenol and 1H–1,2,4–triazole are chemically linked, showed a much greater synergistic effect than when simply mixing the same amount of phenol and 1H–1,2,4–triazole under the same reaction conditions. In addition, our system showed a broad terminal and internal epoxide substrate scope. [ABSTRACT FROM AUTHOR]

Carbon dioxide is a cheap, easily available, and practically inexhaustible source of synthetic carbon (C1-synthon). Among various transformations of CO2, the synthesis of cyclic carbonates from epoxides and cyclic carbamates from aziridines can be referred to as priority areas in the development of contemporary chemical synthesis and catalysis. Cyclic carbonates found wide application in modern industry (electrolytes, solvents, reagents, polymers) and their use and production will be constantly increased. The development of effective catalytic processes that would allow the synthesis of carbonates under mild conditions (atmospheric pressure of CO2 or lower, temperature 25°C) and low loads of durable and affordable catalysts is at the forefront of research. In the present review we analyze the existing directions of research on the catalytic systems based earth-abundant metals Al3+, Fe2+(3+), and Zn2+ for the synthesis of cyclic carbonates from epoxides and cyclic carbamates from aziridines. [ABSTRACT FROM AUTHOR]

Development of an effective catalytic system for the cycloaddition of carbon dioxide to epoxides for the preparation of cyclic carbonates under mild conditions is of great importance. Herein, a mixture of zinc iodide, metal chlorides, and strong organic bases is demonstrated to be a useful catalytic system that works at room temperature under atmospheric pressure. The most efficient combination, zinc iodide-niobium chloride-7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (1.2-0.3-3.0 mol%), gave styrene carbonate (95%) from styrene oxide and CO2 (balloon) at 25 °C for 24 h. Another combination, zinc iodide-zinc chloride-1,8-diazabicyclo[5.4.0]undec-7-ene (1.2-0.8-4.0 mol%), kept the catalytic activity for the preparation of propylene carbonate until the fourth run. Therefore, the reaction system was operationally simple, highly efficient, and proceeded under ambient conditions. The catalyst is composed of readily available reagents and is reusable. Thus, the method presented is a powerful tool for utilizing CO2 as the starting material for the production of valuable chemicals. [ABSTRACT FROM AUTHOR]

A type of MCM-41 supported dual imidazolium ionic liquids have been synthesized and efficiently used as catalysts in the sustainable chemical conversion of CO2 and epoxides into cyclic carbonates. It was shown that the highest efficiency was achieved in the cycloaddition of a variety of epoxides and CO2 in the presence of the MCM-41@DILSCN solid catalyst under mild conditions. More interestingly, the catalyst was stable, very active, robust, and displayed good recyclability without significant loss of catalytic activity after six consecutive cycles during the process. Overall, the present protocol of synthesizing cyclic carbonates under solvent free conditions using MCM-41@DILSCN is promising for industrial applications. [ABSTRACT FROM AUTHOR]

The utilization of CO2 as building block for the production of cyclic carbonate is a promising route to simultaneously mitigate the global warming issue and obtain valuable commercial chemicals. In this work, the activity of nicotinamidium halide catalysts towards the CO2 conversion into cyclic carbonate has been explored by means of density functional theory (DFT) calculations. DFT calculations support the ability, suggested experimentally, of the pyridium α‐C−H proton of the catalysts to activate the epoxide ring via a hydrogen bond. Interestingly, DFT calculations underline the involvement of the n‐octyl substituent of the pyridyl ring in the epoxide activation, while the hydrogen atom of the amide group N−H is rather involved in the stabilization of the iodide trough electrostatic interactions. Moreover, the replacement of the pyridium α‐C−H proton with the bulkier methyl group leads to a different reaction mechanism. The calculated energy barriers well reproduce the experimental trends of the studied catalysts, and the computed activation barrier of 29.0 kcal/mol, relative to the ring opening step of the most active catalyst, is in line with the experimental working temperature of 80 °C. Those results shed light on the CO2 fixation reaction contributing to the development of more efficient catalytic systems. [ABSTRACT FROM AUTHOR]

The development of efficient bifunctional organocatalysts for the catalytic conversion of CO2 under mild conditions remains particularly challenging. Inspired by the synergistic mechanism of intramolecular Lewis acid‐base active sites, we report a series of bifunctional cross‐linked epoxy resin organocatalysts containing multiple active sites for the cycloaddition reaction of dilute CO2 with epoxides. These catalysts exhibit high reactivity and product selectivity (10 examples, >99 %) for the cycloaddition reactions of a variety of epoxides and CO2, and surprisingly, epichlorohydrin (ECH), can be converted under ambient temperature and pressure (25 °C, 1.0 bar) without co‐catalysts. 1H NMR, 13C NMR, 19F NMR and in situ IR studies suggest that the simultaneous and efficient activation of CO2 and epoxides is responsible for the improved catalytic activity. Upon an insightful investigation of the catalytic mechanism, this protocol will contribute to the development of efficient and environmentally friendly metal‐free catalysts. [ABSTRACT FROM AUTHOR]

Novel polyhydroxylated ammonium, imidazolium, and pyridinium salt organocatalysts were prepared through N-alkylation sequences using glycidol as the key precursor. The most active pyridinium iodide catalyst effectively promoted the carbonation of a set of terminal epoxides (80 to >95% yields) at a low catalyst loading (5 mol%), ambient pressure of CO2, and moderate temperature (75 °C) in batch operations, also demonstrating high recyclability and simple downstream separation from the reaction mixture. Moving from batch to segmented flow conditions with the operation of thermostated (75 °C) and pressurized (8.5 atm) home-made reactors significantly reduced the process time (from hours to seconds), increasing the process productivity up to 20.1 mmol(product) h−1 mmol(cat)−1, a value ~17 times higher than that in batch mode. [ABSTRACT FROM AUTHOR]

Aiming highly efficient conversion of greenhouse gas CO2 to cyclic carbonates, a biomass Ru(III) Schiff base complex catalyst (SalRu) was constructed by employing a derivative of Lignin degradation (5‐aldehyde vanillin). The SalRu catalyst had a remarkable conversion for epoxides into corresponding cyclic carbonates even at atmospheric pressure of CO2 without the presence of co‐catalyst. As the condition at 120 °C and 2 MPa CO2 the conversion reached to 94 % with selectivity at 99 % after 8 h. 32 % cyclic carbonate production was obtained even under 0.2 MPa CO2 pressure. The epoxide activation and ring opening, CO2 insertion and cyclic carbonate formation were illuminated explicitly through the of characteristic absorption peaks changing, which further providing direct and visual evidence for the mechanism proposing. This study has important theoretical significance for the comprehensive utilization of environmental pollutants and energy. [ABSTRACT FROM AUTHOR]

In recent years, the chemical industry has put emphasis on designing or modifying chemical processes that would increasingly meet the requirements of the adopted proecological sustainable development strategy and the principles of green chemistry. The development of cyclic carbonate synthesis from CO2 and epoxides undoubtedly follows this trend. First, it represents a significant improvement over the older glycol phosgenation method. Second, it uses renewable and naturally abundant carbon dioxide as a raw material. Third, the process is most often solvent-free. However, due to the low reactivity of carbon dioxide, the process of synthesising cyclic carbonates requires the use of a catalyst. The efforts of researchers are mainly focused on the search for new, effective catalysts that will enable this reaction to be carried out under mild conditions with high efficiency and selectivity. Recently, deep eutectic solvents (DES) have become the subject of interest as potential effective, cheap, and biodegradable catalysts for this process. The work presents an up-to-date overview of the method of cyclic carbonate synthesis from CO2 and epoxides with the use of DES as catalysts. [ABSTRACT FROM AUTHOR]

Transforming CO2 into value-added chemicals has been an important subject in recent years. The development of a novel heterogeneous catalyst for highly effective CO2 conversion still remains a great challenge. As an emerging class of porous organic polymers, covalent organic frameworks (COFs) have exhibited superior potential as catalysts for various chemical reactions, due to their unique structure and properties. In this study, a layered two-dimensional (2D) COF, IM4F-Py-COF, was prepared through a three-component condensation reaction. Benzimidazole moiety, as an ionic liquid precursor, was integrated onto the skeleton of the COF using a benzimidazole-containing building unit. Ionization of the benzimidazole framework was then achieved through quaternization with 1-bromobutane to produce an ionic liquid-immobilized COF, i.e., BMIM4F-Py-COF. The resulting ionic COF shows excellent catalytic activity in promoting the chemical fixation of CO2 via reaction with epoxides under solvent-free and co-catalyst-free conditions. High porosity, the one-dimensional (1D) open-channel structure of the COF and the high catalytic activity of ionic liquid may contribute to the excellent catalytic performance. Moreover, the COF catalyst could be reused at least five times without significant loss of its catalytic activity. [ABSTRACT FROM AUTHOR]

A novel cobalt-based MOF nanoribbon with high catalytic activity and selectivity in the CO 2 cycloaddition reaction. [Display omitted] Chemical fixation of CO 2 with epoxides is an effective option to achieve sustainable synthesis of cyclic organic carbonates. Although metal–organic frameworks (MOFs) are promising catalysts for this reaction, their low stability in aqueous solutions makes this application infeasible. In an effort to overcome this limitation, cobalt-based metal–organic framework (Co(II)MOF) nanoribbons have been prepared by coordinating the Co(II) ions with a new ligand (C 16 H 12 N 4 O 4) full of oxygen and nitrogen moieties. Strong chemical interactions occur between the adsorbed CO 2 and oxygen/nitrogen atoms in this porous MOF structure. Co(II)-MOF nanoribbons with tetra- n -butylammonium bromide acted as cocatalysts with ∼97% yield of cyclic carbonate (reaction kinetic rate of 14.7 × 106 µmol g-1 h−1) upon the cycloaddition of epichlorohydrin (ECH) to CO 2 (>99% reaction selectivity under solvent-free reaction condition at 80 °C, 3 h and 1 MPa CO 2 pressure). This work may open a new avenue for chemical fixation of CO 2 by rational design of the components and morphology of MOF-based catalysts. [ABSTRACT FROM AUTHOR]

The development of an efficient, easily prepared, and environmentally friendly catalyst is important for the coupling reaction between CO2 and epoxides. Herein, novel TBAB‐based (tetrabutylammonium bromide, TBAB) deep eutectic solvents (DESs) have been applied in the transformation of CO2 and epoxides into cyclic carbonates with exhibit high activity and selectivity under mild conditions (25 °C, 8 bar CO2), The excellent activity and versatility of the TBAB‐based DESs can be attributed to the hydrogen‐bond interaction between the TBAB and citric acid. Due to hydrogen‐bond interaction between −OH and Br−, the Br− becomes more flexible and facilitates the nucleophilic ring‐opening process. The density functional theory (DFT) method has been used to explore the mechanism governing the CO2 cycloaddition reaction. DFT results imply that intramolecular hydrogen bonding and the flexible nucleophilic Br− anion can significantly accelerate the ring‐opening process. Hence, the ring‐closure reaction may be the rate‐determining step in the CO2 cycloaddition reaction catalyzed by TBAB‐based DESs. Both the experimental and computational results have demonstrated that the synergistic effect between the −OH and Br− in the TBAB‐based DESs play a significant role in the acceleration of the ring‐opening process of the CO2 cycloaddition reaction. [ABSTRACT FROM AUTHOR]

The synthesis of three bifunctional phosphonium salts bearing perfluorinated side chains is reported. These compounds were employed as catalysts for the synthesis of cyclic carbonates from epoxides and CO2. The most efficient catalyst comprised a phenolic substructure and allowed the synthesis of various carbonates at room temperature and a CO2 pressure as low as 0.1 MPa. The reaction could be performed in perfluorodecalin which in some cases led to improved yields and facilitated the separation of the catalyst. Furthermore, the isolation from the reaction mixture and recyclability of two catalysts was evaluated. However, the activity of the recycled catalysts gradually decreases due to partial decomposition. In total 16 cyclic carbonates were prepared in yields up to 97%. [ABSTRACT FROM AUTHOR]

Wehave recently shown that simple ammonium ferrates are competent catalyst for the cycloaddition reaction of CO2 to epoxides under moderate reaction conditions (T = 100°C, P(CO2) = 0.8 MPa). We report here that ammonium zincates of general formulae [TBA]2 [ZnX4] (TBA = tetrabutylammonium), simply obtained by treating an ethanolic solution of an appropriate zinc(II) salt with two equivalents of tetrabutylammonium halides, outperform ammonium ferrates in the synthesis of cyclic carbonates under milder reaction conditions (room temperature and atmospheric CO2 pressure). Using [TBA]2[ZnBr4] complex as homogeneous catalyst at 100°C and P(CO2) = 0.8 MPa a 52% conversion of styrene oxide with complete selectivity in styrene carbonate in just 15 min was observed, corresponding to a Turnover frequency (TOF) of 416 h-1. The same catalyst proved to be very active even at room temperature and atmospheric or very moderate CO2 pressures (0.2 MPa), with a quite broad range of substrates, especially in the case of terminal epoxides, with high selectivity towards cyclic carbonate products. The difference in reactivity of terminal and internal epoxides could be exploited using 4-vinylcyclohexene dioxide, where the endocyclic epoxide remained untouched when reacted at room temperature and the formation of the di-carbonate product was observed only at harsher conditions. A multigram scale conversion of propylene oxide was achieved (46 mmol) and the catalyst also proved to be recyclable (3 cycles) by distillation of the product and subsequent addition of fresh reagent, maintaining high conversion values and complete selectivity for propylene carbonate. This simple zinc-based catalytic system, which outperform the recently reported iron-based one by working at much milder conditions, could represent a valuable prospect in both laboratory and industrial scale, combining an inherent cheapness and synthetic easiness that should be deeply considered when the goal is to give value to a waste product as CO2. [ABSTRACT FROM AUTHOR]

A series of bifunctional rare‐earth metal complexes bearing zwitterionic amino‐bis(phenolato) ligands were synthesized and structurally characterized. These complexes were applied as catalysts for the synthesis of cyclic carbonates from epoxides and CO2. Lanthanum complex 1La was most active, converting terminal epoxides into the cyclic carbonates in moderate to excellent yields at 40 °C in the presence of 1 bar CO2. The catalyst was also recycled five runs without loss of catalytic activity. The kinetics of the cycloaddition of CO2 and epichlorohydrin (ECH) catalyzed by complex 1La were investigated. According to the Arrhenius equation, the activation barrier for cyclic carbonate formation is determined to be 8.29±0.68 kcal/mol. [ABSTRACT FROM AUTHOR]

For the production of cyclic carbonates from the cycloaddition of CO2 with epoxides, halogen pollution and product purity are two of the most common problems due to the usage of homogeneous halogen-containing catalysts such as ammonium salt and alkali metal halide. Hence, the development of a novel, halogen-free and efficient catalyst for the synthesis of high-purity cyclic carbonates is significant. Here, a series of acid–base bifunctional Ce1-xZrxO2 nanorods were successfully prepared. The Ce1-xZrxO2 nanorods could catalyze the cycloaddition of CO2 with epoxides efficiently without any halogen addition. Especially for the Ce0.7Zr0.3O2 catalyst, a conversion of 96% with 100% 1,2-butylene carbonate selectivity was achieved. The excellent catalytic performance of Ce1-xZrxO2 nanorods is attributed to the formation of the CeO2-ZrO2 solid solution, which contributes to abundant moderate acidic–basic active sites on the catalyst surface. It is the synergistic effect of moderate acidic–basic sites that dominates the conversion of CO2 with epoxides, which will supply important references for the synthesis of efficient metal oxide catalyst for the cycloaddition of CO2 with epoxides. [ABSTRACT FROM AUTHOR]

Haloazaphosphatranes are the halogenated parents of proazaphosphatranes, also known as Verkade's superbase. While the synthesis of iodo‐, bromo‐ and chloroazaphosphatranes was reported more than thirty years ago by J. G. Verkade, the first synthesis of fluoroazaphosphatranes was only described in 2018 by Stephan et al. Currently, no common and versatile procedure exists to access fluoroazaphosphatranes platform with different structural characteristics. In this report, a new and simple synthesis of this class of compounds was developed based on the nucleophilic attack of the fluoride anion on chloroazaphosphatrane derivatives with good to high isolated yields for the corresponding fluoroazaphosphatranes (70–92%). The scope of the reaction was widened to fluoroazaphosphatranes bearing various substituents and X‐ray molecular structures of two of them are reported. The stability of fluoroazaphosphatranes toward nucleophilic solvents like water has been investigated. As they revealed much more robust cations than their chloroazaphosphatrane parents, their chloride salts were tested as organocatalysts for the formation of cyclic carbonates from epoxides and CO2. Fluoroazaphosphatranes proved to be both efficient and stable catalytic systems for CO2 conversion with catalytic activities similar to those of azaphosphatranes, and no decomposition of the cation was observed at the end of reaction. [ABSTRACT FROM AUTHOR]

A series of mesoporous KIT-6 supported ionic liquids were prepared and tested as effective and practical catalysts for the synthesis of cyclic carbonates by the cycloaddition of CO2 with epoxides. The effects of type of catalysts, catalyst amount, CO2 pressure, reaction temperature and catalyst stability have also been investigated in detail, the catalyst KIT-6@ILCH3CH(OH)COO(0.6) exhibited excellent activity in good to excellent yields, may be attributed to the synergetic effect between hydroxyl groups and lactate anion of the ionic liquid. In addition, the supported catalyst can be easily recovered and reused for six times still with satisfactory catalytic activity. Moreover, a general synergetic catalytic mechanism for the reaction was proposed. This work introduces a new and highly efficient pathway to explore the supported ionic liquids for the chemical fixation of carbon dioxide. [ABSTRACT FROM AUTHOR]

The involvement of CO2 as a renewable and abundant feedstock toward a carbon balanced future has led to production of several value-added products. The primary focus in the current effort is to assess fixation of CO2 and epoxides into cyclic carbonates by employing state-of-the-art metal complexes as promising catalytic systems. Our attention is restricted to Earth-abundant metals such as aluminum, cobalt, iron, zinc and few transition metals in association with different ligand skeletons used for the structural construction of the respective complexes. This review sequentially categorizes these complexes and provides a panoramic overview of their selective catalytic activities and mechanistic understandings based on experimental and theoretical evidences. [ABSTRACT FROM AUTHOR]

Supramolecular catalysis can provide distinct advantages for the catalytic conversion of CO2 into carbonates by cycloaddition to epoxides. For example, the absence of metals in the catalytic site, and the easy design for optimization. The incorporation of multiple functionalities in pseudopeptidic macrocycles with a pendant arm allows catalytic systems to be obtained where halide anions (nucleophilic activating agents for epoxides), hydrogen bond acceptor sites (activating agents for epoxides and stabilizing sites for anionic intermediates), and amine groups (Lewis basic sites for activating CO2) are in proximity. This allows a high activity in the cycloaddition of CO2 to styrene oxide under mild conditions (turnover number (TON) = 900, CO2 balloon, 100 °C, 5 h). The primary amino groups in the arm facilitate the immobilization of these macrocyclic structures in cross‐linked polymeric matrices containing ammonium halide fragments. Such multifunctional insoluble polymers afford excellent catalytic results with high TON and turnover frequency values and remarkable productivities (>10 gprod gresin−1 h−1). This activity is maintained for a variety of epoxides and is retained after several catalytic runs. Their performance is significantly higher than those reported for most heterogenous supramolecular catalytic systems for CO2 transformation into carbonates. [ABSTRACT FROM AUTHOR]

The current production of organic cyclic carbonates involves the reaction of appropriate alcohols with toxic phosgene. But an alternative route for obtaining these valuable products is the cycloaddition reaction of CO2 with appropriative epoxides. The development of new catalytic systems for this reaction is a highly active field of research works. For this purpose, were developed many effective catalytic systems, such as organocatalysts, metal–organic frameworks, homogeneous metal-based catalysts, and ionic liquid catalysts. Among them, zinc-containing and ionic liquid catalysts are highly active systems, resulting in the increase in selectivity and the beneficial effect on the reaction rate under mild reaction conditions: reaction temperatures of below 100 °C at a low CO2 concentration and pressure at 0.1 MPa, if possible, without solvents and co-catalysts. This review article summarizes and discusses the results of research works over the last 10–15 years on the study of the homogeneous zinc-containing and ionic liquid catalysts for the cycloaddition reaction of CO2 with epoxides. We hope that it can be stimulated for further development in this area and will be useful for understanding the potential commercialization of these catalysts. [ABSTRACT FROM AUTHOR]

Ammonium derivatives of triethanolamine have been effectively used as catalysts for the addition of CO2 to epoxides. The iodine additive was found to exert a positive effect on the catalytic activity of these polyhydroxy-containing salts. [ABSTRACT FROM AUTHOR]

Chemical fixation of CO2 as C1 source at ambient temperature and low pressure is an energy‐saving way to make use of the green‐house gas, but it still remains a challenge since efficient catalyst with high catalytic active sites is required. Here, a novel monoclinic azo‐functionalized Zr‐based metal−organic polyhedron (Zr‐AZDA) has been prepared and applied in CO2 fixation with epoxides. The inherent azo groups not only endow Zr‐AZDA with good solubilization, but also act as basic sites to enrich CO2 showing efficient synergistic catalysis as confirmed by TPD‐CO2 analysis. XPS results demonstrate that the Zr active sites in Zr‐AZDA possess suitable Lewis acidity, which satisfies both substrates activation and products desorption. DFT calculation indicates the energy barrier of the rate‐determining step in CO2 cycloaddition could be reduced remarkably (by ca. 60.9 %) in the presence of Zr‐AZDA, which may rationalize the mild and efficient reaction condition employed (80 °C and 1 atm of CO2). The work provides an effective multi‐functional cooperative method for improvement of CO2 cycloaddition. [ABSTRACT FROM AUTHOR]

A series of dopamine‐based mono‐ and dinuclear boronate esters are studied as stable, efficient, and green metal‐free catalysts for coupling CO2 with epoxides under suitable and solvent‐free conditions. Under the optimized reaction conditions, dinuclear boronate esters compared with those with mononuclear compounds display high catalytic activity and selectivity for the chemical conversion of CO2 into cyclic organic carbonates as a valuable product. Ferrocene group containing boronate ester (B4a) display the highest activity for the carboxylation of epichlorohydrin at 100 °C and 1.6 MPa of CO2 pressure, obtaining 96.3% conversion after just 2 h. After seeing a high catalytic performance of trigonal‐planar boronate ester (B1–B5) and tetrahedral boronate ester (B1a–B5a) catalysts, the effect of ionic liquid, epoxide, base, temperature, CO2 pressure, reaction time, and amount of catalyst/substrate/cocatalyst is investigated for these catalysts. The newly synthesized dopamine‐based trigonal‐planar and tetrahedral boronate esters are entirely characterized by melting point, elemental analysis, NMR (1H, 13C, and 11B NMR) spectroscopy, FT‐IR spectroscopy, UV–vis spectroscopy, and LC–MS/MS spectrometry. [ABSTRACT FROM AUTHOR]

A group of available catalysts based on polyethylenimine quaternized with p-xylylene dichloride followed by subsequent exchange of anions was developed. The influence of the nature of halide ions and electronic and steric factors of the substituents in epoxides on the reaction rate of carbon dioxide addition to epoxides was studied. The catalytic capabilities of the adduct of polyethylenimine with iodine were considered. [ABSTRACT FROM AUTHOR]

Sodium and potassium halides in combination with molecular iodine are efficient catalysts for the solvent-free addition of CO2 (10–56 atm) to epoxides giving organic carbonates. [ABSTRACT FROM AUTHOR]

The reaction between epoxides and CO2 to yield cyclic carbonates is efficiently promoted under solvent‐free and relatively mild reaction conditions (0.5 mol % catalyst loading, 0.8 MPa, 125 °C) by zinc(II) complexes of pyridine containing macrocyclic ligands (Pc−L pyridinophanes). The zinc complexes have been fully characterized, including X‐ray structural determination. The [Zn(II)X(Pc−L)]X complexes showed good solubility in several polar solvents, including cyclic carbonates. The scope of the reaction under solvent‐free conditions has been studied and good to quantitative conversions with excellent selectivities have been obtained, starting from terminal epoxides. When solvent‐free conditions were not possible (solid epoxides or low solubility of the catalyst in the oxirane) the use of cyclic carbonates as solvents has been successfully investigated. The remarkable stability of the catalytic system has been demonstrated by a series of consecutive runs. [ABSTRACT FROM AUTHOR]

CO2 insertion reactions on terminal epoxides (styrene oxide, 1,2‐epoxyhexane and butyl glycidyl ether) were performed in a binary homogeneous mixture comprising NaBr as the nucleophilic catalyst and diethylene glycol (DEG) as both solvent and catalyst activator (cation coordinating agent). The reaction protocol was initially studied under batch conditions either in autoclaves and glass reactors: quantitative formation of the cyclic organic carbonate products (COCs) were achieved at T=100 °C and p0(CO2)=1–40 bar. The process was then transferred to continuous‐flow (CF) mode. The effects of the reaction parameters (T, p(CO2), catalyst loading, and flow rates) were studied using microfluidic reactors of capacities variable from 7.85 ⋅ 10−2 to 0.157 cm3. Albeit the CF reaction took place at T=220 °C and 120 bar, CF improved the productivity and allowed catalyst recycle through a semi‐continuous extraction procedure. For the model case of 1,2‐epoxyhexane, the (non‐optimized) rate of formation of the corresponding carbonate, 4‐butyl‐1,3‐dioxolan‐2‐one, was increased up to 27.6 mmol h−1 equiv.−1, a value 2.5 higher than in the batch mode. Moreover, the NaBr/DEG mixture was reusable without loss of performance for at least 4 subsequent CF‐tests. [ABSTRACT FROM AUTHOR]

• A series of deep eutectic solvents (DESs) catalysts with varying ratios were successfully synthesized. • The DES with a composition of [TEA-12][OH]:[Q-COOH]- 0.9: 0.1 had the lowest melting point of 100.17 °C. • The efficiency of the catalysts for CO 2 fixation was evaluated and [TEA-12][OH]:[Q-COOH]−0.9:0.1 proved to be the most effective catalyst with a TOF of 1466 h−1. • Exceptional conversions were observed for epoxides with electron-withdrawing function groups, while electron-donating functional groups showed lower activity. The accumulation of greenhouse gases (GHG) in the atmosphere, with carbon dioxide being the most significant contributor, is a major environmental problem as it impacts significantly on climate change. The development of new catalysts and chemical reactions that incorporate CO 2 are needed to reduce its further emission significantly. Deep eutectic solvents (DES) have garnered increasing attention as environmentally friendly catalysts in the cycloaddition of carbon dioxide (CO 2) with epoxide substrates to produce cyclic carbonates. Their appeal stems from their facile synthesis, cost-effectiveness, low vapour pressure, and thermal stability. In this study, we present a convenient solvent-free synthesis method for nine deep eutectic solvents (DES), utilizing varying compositions of quaternary amine salts (N,N,N -triethyldodecan-1-aminium hydroxide, [TEA-12][OH]) and quinaldic acid [Q-COOH]. These deep eutectic solvents were thoroughly characterized using several techniques, including FTIR, NMR, DSC, and TGA. Moreover, their efficacy for the solvent-free fixation of CO 2 to cyclic carbonates were evaluated. Among the tested compositions, [TEA-12]:[Q-COOH] (0.9:0.1) exhibited the lowest melting point (100.17 °C) and highest catalytic activity, showcasing an optimized Turn-Over Frequency (TOF) of 1466 h−1. This remarkable result represents a significant advancement in the application of DES for CO 2 fixation, exceeding the previous highest catalytic activity observed with TBAB:Citric acid (2.5:1) by more than tenfold. [Display omitted] [ABSTRACT FROM AUTHOR]

The coupling reaction of carbon dioxide and highly-substituted epoxides derived from renewable resources such as fatty acids and waste vegetable oils (cooking oils derived from olive and sunflower) leads to the synthesis of new bio-derived cyclic carbonates using efficient metal-free bifunctional organocatalysts under mild and solvent-free reaction conditions. Once cyclic carbonates derived from biobased sources were synthesized, the design of non-isocyanate polyurethanes (NIPUs) with different chemical structures was investigated by their reaction with a broad substrate scope of diamines. The NIPUs materials were characterized by spectroscopic techniques (NMR and IR) and their molecular weights and polydispersities were determined by GPC studies. Finally, thermal properties of the polymers were studied by DSC and TGA analyses. [Display omitted] ● Valorization of cooking vegetable oils for the preparation of polymers such as non-isocyanate polyurethanes (NIPUs). ● Highly active metal-free catalysts for the carboxylation of epoxides with CO 2 under solvent-free conditions. ● The catalyst is efficient, inexpensive, and recyclable. [ABSTRACT FROM AUTHOR]

A series of hydroxy‐functionalized phosphonium salts were studied as bifunctional catalysts for the conversion of CO2 with epoxides under mild and solvent‐free conditions. The reaction in the presence of a phenol‐based phosphonium iodide proceeded via a first order rection kinetic with respect to the substrate. Notably, in contrast to the aliphatic analogue, the phenol‐based catalyst showed no product inhibition. The temperature dependence of the reaction rate was investigated, and the activation energy for the model reaction was determined from an Arrhenius‐plot (Ea=39.6 kJ mol−1). The substrate scope was also evaluated. Under the optimized reaction conditions, 20 terminal epoxides were converted at room temperature to the corresponding cyclic carbonates, which were isolated in yields up to 99 %. The reaction is easily scalable and was performed on a scale up to 50 g substrate. Moreover, this method was applied in the synthesis of the antitussive agent dropropizine starting from epichlorohydrin and phenylpiperazine. Furthermore, DFT calculations were performed to rationalize the mechanism and the high efficiency of the phenol‐based phosphonium iodide catalyst. The calculation confirmed the activation of the epoxide via hydrogen bonding for the iodide salt, which facilitates the ring‐opening step. Notably, the effective Gibbs energy barrier regarding this step is 97 kJ mol−1 for the bromide and 72 kJ mol−1 for the iodide salt, which explains the difference in activity. [ABSTRACT FROM AUTHOR]

The development of efficient heterogeneous catalysts suitable for carbon capture and utilization (CCU) under mild conditions is a promising step towards mitigating the growing concentration of CO2 in the atmosphere. Herein, we report the construction of a hydrogen‐bonded 3D framework, {[Zn(hfipbba)(MA)]⋅3 DMF}n (hfipbba=4,4′‐(hexaflouroisopropylene)bis(benzoic acid)) (HbMOF1) utilizing ZnII center, a partially fluorinated, long‐chain dicarboxylate ligand (hfipbba), and an amine‐rich melamine (MA) co‐ligand. Interestingly, the framework possesses two types of 1D channels decorated with CO2‐philic (−NH2 and −CF3) groups that promote the highly selective CO2 adsorption by the framework, which was supported by computational simulations. Further, the synergistic involvement of both Lewis acidic and basic sites exposed in the confined 1D channels along with high thermal and chemical stability rendered HbMOF1 a good heterogeneous catalyst for the highly efficient fixation of CO2 in a reaction with terminal/internal epoxides at mild conditions (RT and 1 bar CO2). Moreover, in‐depth theoretical studies were carried out using periodic DFT to obtain the relative energies for each stage involved in the catalytic reaction and an insight mechanistic details of the reaction is presented. Overall, this work represents a rare demonstration of rational design of a porous ZnII MOF incorporating multiple functional sites suitable for highly efficient fixation of CO2 with terminal/internal epoxides at mild conditions supported by comprehensive theoretical studies. [ABSTRACT FROM AUTHOR]

A molecular cage consisting of two free‐base porphyrins connected by four flexible linkers was metalated with Co(III) to afford in good yield a bimetallic catalyst. The catalytic activity of the bis‐Co(III) porphyrin molecular cage (CoCl)2‐1 was studied for the formation of cyclic carbonates from CO2 and propylene oxide (PO) or styrene oxide (SO) with pyridine as cocatalyst. Various reaction parameters such as the molar ratio of the catalyst and the co‐catalyst, the time of reaction, the temperature and CO2 pressure were investigated. The molecular cage was shown to be a catalyst of high selectivity for the studied reactions and much more efficient to convert the epoxides to the corresponding cyclic carbonates than the monomeric Co(III)Cl meso‐tetraphenylporphyrin (CoCl‐TPP) model. When quantitative conversion of PO into propylene carbonate (PC) was reached (0.1 mol% catalyst, 1.2 mol% pyridine, 120 °C, 30 bar of CO2) only 23 % of PC was obtained with CoCl‐TPP (0.2 mol%). This enhanced catalytic activity is attributed to the synergistic effect of the two metal sites incorporated in the framework of the molecular cage. [ABSTRACT FROM AUTHOR]

In the present research, the synthesis, spectroscopic characterization, and structural investigations of a unique ZnII complex of imine‐functionalized polyhedral oligomeric silsesquioxane (POSS) is designed, and hereby described, as a catalyst for the synthesis of cyclic carbonates from epoxides and CO2. The uncommon features of the designed catalytic system is the elimination of the need for a high pressure of CO2 and the significant shortening of reaction times commonly associated with such difficult transformations like that of styrene oxide to styrene carbonate. Our studies have shown that imine‐POSS is able to chelate metal ions like ZnII to form a unique coordination complex. The silsesquioxane core and the hindrance of the side arms (their steric effect) influence the construction process of the homoleptic Zn4@POSS‐1 complex. The compound was characterized in solution by NMR (1H, 13C, 29Si), ESI‐MS, UV/Vis spectroscopy and in the solid state by thermogravimetric/differential thermal analysis (TG‐DTA), elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), cross‐polarization magic angle spinning (CP MAS) NMR (13C, 29Si) spectroscopy, and X‐ray crystallography. [ABSTRACT FROM AUTHOR]

In the present research, the synthesis, spectroscopic characterization, and structural investigations of a unique ZnII complex of imine‐functionalized polyhedral oligomeric silsesquioxane (POSS) is designed, and hereby described, as a catalyst for the synthesis of cyclic carbonates from epoxides and CO2. The uncommon features of the designed catalytic system is the elimination of the need for a high pressure of CO2 and the significant shortening of reaction times commonly associated with such difficult transformations like that of styrene oxide to styrene carbonate. Our studies have shown that imine‐POSS is able to chelate metal ions like ZnII to form a unique coordination complex. The silsesquioxane core and the hindrance of the side arms (their steric effect) influence the construction process of the homoleptic Zn4@POSS‐1 complex. The compound was characterized in solution by NMR (1H, 13C, 29Si), ESI‐MS, UV/Vis spectroscopy and in the solid state by thermogravimetric/differential thermal analysis (TG‐DTA), elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), cross‐polarization magic angle spinning (CP MAS) NMR (13C, 29Si) spectroscopy, and X‐ray crystallography. [ABSTRACT FROM AUTHOR]

• Luffa sponge-supported dendritic imidazolium ionic liquid heterogeneous catalysts with high ionic density were prepared. • A series of cyclic carbonates have been efficiently synthesized in high yields (84–99 %) under mild reaction conditions. • There was a positive dendritic effect on the yields of cyclic carbonates. • Cyclic carbonates could be prepared on a multigram scale. Efficient using of green heterogeneous catalysts from renewable natural sources through chemical modification for the cycloaddition of terminal epoxides with CO 2 is attractive but still challenging. Luffa sponge is a cheap, biodegradable, abundant and renewable source with netting-like three-dimensional porous structure. Herein, we report a simple and facile approach to the preparation of a series of novel luffa sponge-supported dendritic imidazolium ILs heterogeneous catalysts LS-DIL-(G1-G3) with high ionic density from natural luffa sponge fibers. LS-DIL-(G1-G3) were properly characterized by FT-IR spectroscopy, TGA, elemental analysis, and SEM. Among them, LS-DIL-G3 was found to exhibit the highest catalytic activity for the synthesis of cyclic carbonates under metal-free and solvent-free conditions. It was clearly observed that there was a positive dendritic effect on the yields of cyclic carbonates. Furthermore, a wide range of terminal epoxides was converted smoothly to the corresponding cyclic carbonates with high yields (84–99 %). LS-DIL-G3 could be reused for up to six consecutive runs without any obvious decline in catalytic activity. Importantly, the desired cyclic carbonates could be prepared on a multigram scale by using LS-DIL-G3 as a green heterogeneous catalyst. [ABSTRACT FROM AUTHOR]

An imidazolium catalyst supported on thermomorphic polyethylene (PE) was prepared from 1‐methylimidazole and polyethylene iodide (PE−I). The catalyst was characterized by 1H and 13C NMR, SEC and MALDI‐ToF mass spectrometry. Its catalytic activity was evaluated in the ring‐opening of epoxides with carbon dioxide to give cyclic carbonates under solvent‐free conditions. The catalyst proved to be active at low catalyst loading (down to 0.1 mol%) and allows the reaction to occur at low CO2 pressure (1–5 bar) and moderate temperature (100 °C). A range of terminal and internal epoxides was converted to the corresponding cyclic carbonates with high yields and selectivities. The recyclability of the catalyst was studied and no significant loss of activity was observed after 5 runs. [ABSTRACT FROM AUTHOR]

Cheap and readily available 2-aminopyridine and related compounds can be used as organocatalysts for the conversion of epoxides into cyclic carbonates. This reaction gives high conversions under solvent-free conditions and is amenable to a kilogram-scale conversion under mild conditions. [ABSTRACT FROM AUTHOR]

We have studied the synthesis of five-membered cyclic carbonates through the cycloaddition of CO2 to epoxides by using acyclic guanidinium salts. We have found that the cycloaddition reactions proceed smoothly at ordinary temperatures and pressures and result in good yields when acyclic guanidinium iodides are employed as catalysts. Both cation moiety and anion moiety of the guanidinium salts play important roles in their catalytic activity. It is essential to have active hydrogens on the cation moiety as well as an iodide ion as the anion moiety so as to achieve good catalytic activity. Guanidinium iodides with three or more active hydrogens give cyclic carbonates in high yields in polar solvents such as 1-methylpyrrolidin-2-one, whereas the guanidinium iodides with one or two active hydrogens show good catalytic activity in less polar solvents such as 2-methyltetrahydrofuran. [ABSTRACT FROM AUTHOR]