Basic ionic liquids promoted chemical transformation of CO2 to organic carbonates

Ionic-Liquid-Assisted One-Step Construction of Mesoporous Metal-Organic Frameworks

The synthesis of ionic-mesoporous-metal-organic frameworks (ionic-meso-MOFs) has received considerable interest in the fields of macromolecular adsorption, acid-base catalysis, ionic conductivity, etc.; yet, their synthesis still presents significant difficulties. In this study, functionalized mesoporous MIL-101-ILs (Cr) was facilely constructed via an in situ self-assembly method by using aromatic-anion-functionalized ionic liquids (ILs) as competitive ligands. It has been demonstrated that the inclusion of an aromatic moiety into an IL improves the coordination ability and is advantageous for the anchoring of ILs on Cr³⁺ via amino-metal coordination. Thus, ionic-meso-MOFs with a specific surface area of 441.9-624.9 cm²/g and an average pore diameter of 5.5 to 8.4 nm were successfully synthesized. Because of the presence of open Lewis acidic metal sites on the MOFs and basic active sites on the ILs, the resulting ionic-meso-MOFs demonstrated both an acid-base cooperative effect and a mesoporous structure, indicating a high potential for acid-base catalysis. This in situ synthesis procedure for ionic mesoporous MOFs offers a simple method for developing and fabricating multifunctional mesoporous materials.

Quasi-square-shaped cadmium hydroxide nanocatalysts for electrochemical CO2 reduction with high efficiency

Powered by a renewable electricity source, electrochemical CO2 reduction reaction is a promising solution to facilitate the carbon balance. However, it is still a challenge to achieve a desired product with commercial current density and high efficiency. Herein we designed quasi-square-shaped cadmium hydroxide nanocatalysts for CO2 electroreduction to CO. It was discovered that the catalyst is very active and selective for the reaction. The current density could be as high as 200 mA cm-2 with a nearly 100% selectivity in a commonly used H-type cell using the ionic liquid-based electrolyte. In addition, the faradaic efficiency of CO could reach 90% at a very low overpotential of 100 mV. Density functional theory studies and control experiments reveal that the outstanding performance of the catalyst was attributed to its unique structure. It not only provides low Cd-O coordination, but also exposes high activity (002) facet, which requires lower energy for the formation of CO. Besides, the high concentration of CO can be achieved from the low concentration CO2 via an adsorption-electrolysis device.

Ionic-Liquid-Catalyzed Approaches under Metal-Free Conditions

ConspectusMetal-free catalysis is a promising protocol to access chemicals without metal contamination. Ionic liquids (ILs) that are entirely composed of organic cations and inorganic/organic anions have emerged as promising alternatives to molecular solvents and metal catalysts due to their unique properties such as structural tunability, the coexistence of multiple interactions among ions (e.g., electrostatic interaction, hydrogen bonding, van de Waals forces, acid/base interactions, hydrophilic/hydrophobic interactions, etc.), unique affinity for a wide range of chemicals, good chemical and thermal stability, and quite low volatility. ILs have shown potential applications in various chemical processes.In this Account, we systematically described our most recent work on IL-catalyzed approaches under metal-free conditions. The first section presents the IL-catalyzed strategies toward the transformation of CO2 to value-added chemicals, focusing on the CO2-reactive IL-catalyzed CO2 transformation to various heterocycles and the IL-catalyzed reductive transformation of CO2 to chemicals. In these approaches, we designed task-specific ILs that are able to chemically capture and activate CO2 via forming anion-based carbonate/carbamate or cation-based carboxylate/carbamate intermediates, thus further accomplishing its transformation to a series of heterocycles including quinazoline-2,4(1H,3H)-diones, cyclic carbonates, 2-oxazolidinones, oxazolones, and benzimidazolones under metal-free conditions. For the IL-catalyzed approaches to reducing CO2 with hydrosilanes to chemicals, we employed ILs capable of activating the Si-H bond in hydrosilanes and the N-H bond in amine substrates via H-bonding, thus achieving the reductive transformation of CO2 to formamides, benzimidazoles, and benzothiazoles via cooperative catalysis. The second section describes our finding on the IL-catalyzed hydration of the C≡C bond in propargylic alcohols. Azolate anion-based ILs that can chemically capture CO2 via the formation of carbamates could serve as robust nucleophiles to attack the C≡C bond in propargylic alcohols and then efficiently catalyze the hydration of propargylic alcohols to produce α-hydroxy ketones with the assistance of atmospheric CO2 gas under metal-free conditions. The third section unveils the cooperative catalysis strategy of hydrogen bond donors and acceptors of ILs for chemical reactions. In the hydrogen-bonding catalysis protocols, cations of the ILs act as H-bond donors and anions, as acceptors, forming H-bonds with the reactant molecules, respectively, in opposite ways, which can cooperatively catalyze the ring-closing C-O/C-O bond metathesis reactions of aliphatic diethers to O-heterocycles, the dehydrative etherification of alcohols to ethers, and direct oxidative esterification of alcohols to esters. We believe that these IL-catalyzed metal-free processes and strategies display promising practical applications, and their commercialization would bring great benefits to the production of the as-afforded value-added chemicals.

Basic ionic liquids for catalysis: the road to greater stability

Homogeneous and heterogenized basic ionic liquids as reaction catalysts have been highlighted, particularly where they are used to promote reactions that could form the basis of more sustainable energy and chemical production.

Ionic liquid [DBUH][BO2]: an excellent catalyst for chemical fixation of CO2 under mild conditions

The basic IL [DBUH][BO2] was easily synthesized and used for the chemical fixation of CO₂ at atmospheric pressure and room temperature.

CO2 = CO + [O]: recent advances in carbonylation of C–H bonds with CO2

Carbon dioxide (CO₂) is an ideal one-carbon source owing to its nontoxicity, abundance, availability, and recyclability.

Molecular design and experimental study on synergistic catalysts for the synthesis of cyclocarbonate from styrene oxide and CO2

Taking the reaction between styrene oxide and CO₂ to yield cyclocarbonate as the target, the activities of synergistic catalysts, which are composed of Br⁻ and alcohol compounds serving as hydrogen bond donors (HBDs), were predicted by DFT calculations and confirmed by subsequent experiments.

Efficient transformation of CO2 into quinazoline-2,4(1H,3H)-diones at room temperature catalyzed by a ZnI2/NEt3 system

The readily available ZnI₂/NEt₃ system promotes the efficient transformation of CO₂ and 2-aminobenzonitriles into quinazoline-2,4(1H,3H)-diones at room temperature and low CO₂ pressure.