Triethanolamine/KI: A Multifunctional Catalyst for CO2 Activation and Conversion with Epoxides into Cyclic Carbonates

A catalytic system of triethanolamine/potassium iodide (KI) was proved to be efficient for the chemical fixation of CO₂ with epoxide. It was found that triethanolamine with dual function could activate both CO₂ and epoxides. Effects of parameters such as catalyst molar ratio and amount, reaction time, pressure, and temperature were studied systematically. As a result, 99% propylene oxide conversion as well as 99% propylene carbonate selectivity could be obtained under the optimal reaction condition. Furthermore, the catalyst was found to be applicable to a variety of terminal epoxides, providing the corresponding cyclic carbonates in good yields and selectivity. Moreover, the catalyst could be reused five times without loss of activity. This work presents an example of a cheap and efficient catalyst for the chemical fixation of CO₂ to high-value chemicals, which could help to improve the catalytic efficiency and decrease cost of products for larger applications.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource: Full experimental and spectral details.]     

Zinc Imine Polyhedral Oligomeric Silsesquioxane as a Quattro-Site Catalyst for the Synthesis of Cyclic Carbonates from Epoxides and Low-Pressure CO2

In the present research, the synthesis, spectroscopic characterization, and structural investigations of a unique Zn^II 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 Zn^II 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.     

Deep Eutectic Solvents as Catalysts for Cyclic Carbonates Synthesis from CO2 and Epoxides

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.     

Bifunctional Boron Phosphate as an Efficient Catalyst for Epoxide Activation to Synthesize Cyclic Carbonates with CO2

Development of inexpensive, easily prepared, non‐toxic, and efficient catalysts for the cycloaddition of CO₂ with epoxides to synthesize five‐membered cyclic carbonates is a very attractive topic in the field of CO₂ transformation. In this work, we conducted the first work on the cycloaddition of CO₂ with epoxides to produce cyclic carbonates catalyzed by a binary catalyst system consisting of KI and boron phosphate (BPO₄), which are both inexpensive and non‐toxic, and various corresponding cyclic carbonates could be produced with high yields (93–99 %) at 110 °C with a CO₂ pressure of 4 MPa under solvent‐free conditions. In the BPO₄/KI catalyst system, BPO₄, a Brønsted and Lewis acid hybrid, played the role of activating the epoxy ring through the formation of hydrogen bonds with Brønsted acidic sites and the interaction with Lewis acidic sites simultaneously, and thus enhanced the activity of KI for the cycloaddition of CO₂ with epoxides significantly. Additionally, the activity of the BPO₄/KI catalyst system showed no noticeable decrease after being reused five times, indicating that the BPO₄ was stable under the reaction conditions.     

二氧化碳与环氧化合物共聚催化剂研究进展

二氧化碳是一种廉价、低毒、资源丰富的可用于有机合成的理想原料。由二氧化碳和环氧化合物共聚合成的脂肪族聚碳酸酯具有生物可降解性。自1969年井上祥平等发现二氧化碳和环氧化合物通过共聚反应合成脂肪族聚碳酸酯以来,利用二氧化碳制备高分子材料一直备受人们注目。该过程的关键是寻找具有高选择性的高效催化剂,三十余年来通过各国科学家的不懈努力已取得了不少成果,本文对其研究的最新进展进行了综述。     

新型氮杂环卡宾锌化合物催化CO2和环氧化物高效合成环状碳酸酯

合成了一系列新型的芘标记含溴亲核阴离子的氮杂环卡宾前驱体化合物,接枝卤化锌后获得具有CO2捕获能力以及路易斯酸碱位点的NHC-PDBI-ZnX2(X=Cl、Br、I)催化剂,通过1H NMR、13C NMR 、XPS、FT-IR、13C CP-MAS NMR和ICP-AES表征技术对该类催化剂结构和化学性质进行了表征。氮杂卡宾锌配合物被证明是有效的单组分多功能催化剂,对环氧丙烷和CO2的环加成反应显示出较高的催化活性和选择性。最佳活性的NHC-PDBI-ZnI2催化剂在120℃、3.0MPa、2.0h较温和条件下,取得98%以上碳酸丙烯酯收率。该催化剂还具有优异的底物普适性和循环使用稳定性,归因于路易斯酸性Zn 2 与NHC-PBDI主链形成的强共价键。此外,结合FTIR等表征推测了反应机理,其中NHC-PDBI-ZnX2的卡宾位吸附活化CO2以及路易斯酸碱位点开环的协同效应促进了环加成反应在无溶剂和助催化剂的条件下有效地进行。     

负载型钌/铝钛复合载体上的二氧化碳甲烷化反应

用浸渍法制备了铝钛复合载体担载的钌催化剂，考察了它们对二氧化碳甲烷化反应的催化性能，结果表明，高TiO2含量载体制备的催化剂的活性和选择性较高，同时考察了反应温度、空速、金属担载量以及添加第二金属组分等对催化剂性能的影响．     

A Pyridinium-Pyridinium Zinc(II) Porphyrin Ion Porous Organic Polymer as Efficient Heterogeneous Catalyst for Cycloaddition of Epoxides with CO2

A zinc(II)porphyrin-based ion porous organic polymer (ZnTPyPBr₄-iPOP) is successfully synthesized from newly designed pyridinium-functionalized cationic Zn-porphyrin monomer (ZnTPyPBr₄) by free radical self-polymerization, and is employed as an efficient bifunctional heterogeneous catalyst for CO₂ cycloaddition reaction with epoxides. The ZnTPyPBr₄-iPOP exhibits excellent catalytic performance and good substrate expansion in CO₂ cycloaddition reaction under solvent-free and cocatalyst-free conditions with a TOF as high as 15,500 h⁻¹ for the cycloaddition of CO₂ and epichlorohydrin. The synergistic effect of zinc(II)porphyrin as the Lewis acidic site and the Br⁻ anion as the nucleophile in ZnTPyPBr₄-iPOP responds to the high catalytic activity. Moreover, ZnTPyPBr₄-iPOP can easily be recovered and reused at least seven times without the loss of activity. This work provides a valuable approach for the synthesis of novel and efficient heterogeneous catalyst for CO₂ cycloaddition.     

Functionalized Ionic (Poly)Styrenes and their Application as Catalysts in the Cycloaddition of CO2 to Epoxides

Valorization of CO₂, an abundant C(1) synthon, into platform chemicals is of growing interest. In this context, a key reaction is the cycloaddition of CO₂ to epoxides to form carbonates (CCE). A series of organocatalysts for this reaction, based on imidazolium salts modified with a styrene functional group and a second variable functional group, were prepared and characterized. Both the ionic salts and ionic polymers derived from the salts were evaluated in this reaction. In general, the monomers perform slightly better than the polymers; however, the latter are considerably more convenient to use. Of the catalysts studied, the ionic polystyrene imidazolium salt with an ammonium functionality shows highest activity, tolerates a range of epoxides, and can be recycled multiple times without loss of activity.     

双功能金属卟啉催化环氧化合物与 CO2 偶联反应合成环碳酸酯

 合成了新颖的双功能水溶性金属卟啉 催化剂 M(TTMAPP)I4(X) (M = Co, Fe, Mn 和 Cr; X = OAc, CF3COO, CCl3COO, OTs, Cl, Br 和 I), 研究了它们催化 CO2 与末端环氧化合物合成环碳酸酯的偶联反应. 分别考察了反应温度、不同金属的 Lewis 酸中心、抗衡离子和催化剂重复使用次数对反应性能的影响. 当以 Co(III)(TTMAPP)I4(OAc) 为催化剂, 底物与催化剂摩尔比为 1 000, 温度为 353 K, CO2 压力为 667 kPa 和无溶剂条件下, 反应 5 h 时丙烯环碳酸酯收率为 95.4%. 在 298 K, 底物与催化剂之比为 2 000 时, 加入 1 ml 甲醇, 反应 24 h 丙烯环碳酸酯收率为 19.4%. 催化剂可以用乙醚回收, 循环使用 5 次后催化剂活性没有明显降低.     

Synthesis of Cyclic Carbonates from CO2 and Epoxides Catalyzed by Hexaalkylguanidinium Halides

Hexaalkylguanidinium halides exhibit an efficient catalytic activity in the synthesis of cyclic carbonates from epoxides and carbon dioxide. By this method cyclic carbonates can be obtained in a high yield and a high selectivity at a low temperature and atmospheric pressure. This procedure is easy for the product isolation and recycling of the catalyst.     

Immobilization of Ionic Liquid on a Covalent Organic Framework for Effectively Catalyzing Cycloaddition of CO2 to Epoxides

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.     

Mg(OH)Cl/KI as a Highly Active Heterogeneous Catalyst for the Synthesis of Cyclic Carbonates from CO2 and Epoxides under Solvent‐Free Conditions

The combination of magnesium hydroxyl chloride [Mg(OH)Cl] with KI could efficiently catalyze the coupling reaction of carbon dioxide with epoxides to give the corresponding cyclic carbonates in good to excellent yields (75.0% –98.3%) and high selectivity (99.6%) in the absence of organic solvents. The heterogeneous catalyst Mg(OH)Cl/KI could be reused at least six times almost without loss of the catalytic activity. The influence of some key factors (such as molar ratio of Mg(OH)Cl to KI, temperature, reaction time and CO₂ pressure) on the reaction was also discussed.     

A DFT Study on the Mechanism of the Cycloaddition Reaction of CO2 to Epoxides Catalyzed by Zn(Salphen) Complexes

The reaction mechanism for the Zn(salphen)/NBu₄X (X=Br, I) mediated cycloaddition of CO₂ to a series of epoxides, affording five‐membered cyclic carbonate products has been investigated in detail by using DFT methods. The ring‐opening step of the process was examined and the preference for opening at the methylene (C_β) or methine carbon (C_α) was established. Furthermore, calculations were performed to clarify the reasons for the lethargic behavior of internal epoxides in the presence of the binary catalyst. Also, the CO₂ insertion and the ring‐closing steps have been explored for six differently substituted epoxides and proved to be significantly more challenging compared with the ring‐opening step. The computational findings should allow the design and application of more efficient catalysts for organic carbonate formation.     

水合碱金属卤化物催化 CO2 与环氧化物合成环状碳酸酯

 在不添加任何助剂及溶剂的条件下, 考察了水合碱金属卤化物催化 CO2 与环氧丙烷合成碳酸丙烯酯的反应性能. 结果表明, 水合碱金属卤化物表现出远高于无水碱金属卤化物的催化活性, 其中, 以 NaI2H2O 的催化性能最好, 在 120 C, 1 MPa 的条件下反应 1.5 h, 碳酸丙烯酯收率达 97%. 此外, NaI2H2O 在 CO2 与其它环氧化物合成相应环状碳酸酯反应中也表现出较高的催化活性.     

Aluminosilicate-Supported Catalysts for the Synthesis of Cyclic Carbonates by Reaction of CO2 with the Corresponding Epoxides

Functionalized aluminosilicate materials were studied as catalysts for the conversion of different cyclic carbonates to the corresponding epoxides by the addition of CO₂. Aluminum was incorporated in the mesostructured SBA-15 silica network. Thereafter, functionalization with imidazolium chloride or magnesium oxide was performed on the Al_SBA-15 supports. The isomorphic substitution of Si with Al and the resulting acidity of the supports were investigated via ²⁷Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and NH₃ adsorption microcalorimetry. The Al content and the amount of MgO were quantified via inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis. The anchoring of the imidazolium salt was assessed by ²⁹Si and ¹³C MAS NMR spectroscopy and quantified by combustion chemical analysis. Textural and structural properties of supports and catalysts were studied by N₂ physisorption and X-ray diffraction (XRD). The functionalized systems were then tested as catalysts for the conversion of CO₂ and epoxides to cyclic carbonates in a batch reactor at 100 or 125 °C, with an initial CO₂ pressure (at room temperature) of 25 bar. Whereas the activity of the MgO/xAl_SBA-15 systems was moderate for the conversion of glycidol to the corresponding cyclic carbonate, the Al_SBA-15-supported imidazolium chloride catalysts gave excellent results over different epoxides (conversion of glycidol, epichlorohydrin, and styrene oxide up to 89%, 78%, and 18%, respectively). Reusability tests were also performed. Even when some deactivation from one run to the other was observed, a comparison with the literature showed the Al-containing imidazolium systems to be promising catalysts. The fully heterogeneous nature of the present catalysts, where the inorganic support on which the imidazolium species are immobilized also contains the Lewis acid sites, gives them a further advantage with respect to most of the catalytic systems reported in the literature so far.     

Highly Active and Robust Metalloporphyrin Catalysts for the Synthesis of Cyclic Carbonates from a Broad Range of Epoxides and Carbon Dioxide

Bifunctional metalloporphyrins with quaternary ammonium bromides (nucleophiles) at the meta, para, or ortho positions of meso‐phenyl groups were synthesized as catalysts for the formation of cyclic carbonates from epoxides and carbon dioxide under solvent‐free conditions. The meta‐substituted catalysts exhibited high catalytic performance, whereas the para‐ and ortho‐substituted catalysts showed moderate and low activity, respectively. DFT calculations revealed the origin of the advantage of the meta‐substituted catalyst, which could use the flexible quaternary ammonium cation at the meta position to stabilize various anionic species generated during catalysis. A zinc(II) porphyrin with eight nucleophiles at the meta positions showed very high catalytic activity (turnover number (TON)=240 000 at 120 °C, turnover frequency (TOF)=31 500 h^?1 at 170 °C) at an initial CO₂ pressure of 1.7 MPa; catalyzed the reaction even at atmospheric CO₂ pressure (balloon) at ambient temperature (20 °C); and was applicable to a broad range of substrates, including terminal and internal epoxides.     

Efficient and Reusable Iron Catalyst to Convert CO2 into Valuable Cyclic Carbonates

The production of cyclic carbonates from CO₂ cycloaddition to epoxides, using the C-scorpionate iron(II) complex [FeCl₂{κ³-HC(pz)₃}] (pz = 1H-pyrazol-1-yl) as a catalyst, is achieved in excellent yields (up to 98%) in a tailor-made ionic liquid (IL) medium under mild conditions (80 °C; 1–8 bar). A favorable synergistic catalytic effect was found in the [FeCl₂{κ³-HC(pz)₃}]/IL system. Notably, in addition to exhibiting remarkable activity, the catalyst is stable during ten consecutive cycles, the first decrease (11%) on the cyclic carbonate yield being observed during the 11th cycle. The use of C-scorpionate complexes in ionic liquids to afford cyclic carbonates is presented herein for the first time.     

Mechanism of Cyclic Carbonate Synthesis from Epoxides and CO2

Three interconnected catalytic cycles account for the title reaction catalyzed by a bimetallic aluminum(salen) complex and Bu₄NBr. In the first, Bu₄NBr acts as a nucleophile to activate the epoxide. In the second, Bu₃N generated in situ serves to activate CO₂. In the third, the aluminum(salen) complex brings the two activated species together so that the key bonds can be formed intramolecularly.