Cyclic Carbonate Formation from Epoxides and CO2 Catalyzed by Sustainable Alkali Halide-Glycol Complexes: A DFT Study to Elucidate Reaction Mechanism and Catalytic Activity

Multifunctional Magnetic Chiral HKUST MOF Decorated by Triazine, Fe3O4, and Cu(l-Proline)2 Complex for Green and Mild Asymmetric Catalysis

A multifunctional magnetic chiral metal-organic framework (MOF) was developed for asymmetric applications by utilizing strategies of chiralization and multifunctionalization. Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 was employed as a chiral secondary agent to synthesize a chiral hybrid nanocomposite within a MOF. The use of a chiral secondary agent efficiently induces chirality in an achiral MOF structure that cannot be directly chiralized. The HKUST-1@Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 nanocomposite was afforded by first anchoring chiral Cu(l-proline)2 on the Triazine/Fe3O4@SiO2-NH2 surface and then encapsulating the Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 nanoparticles with HKUST-1 via in situ ultrasonication synthesis. In the synthesis of the HKUST-1@Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 nanocomposite, Cu(l-proline)2 was used as a chiral complex due to its Lewis acidic/basic hydroxyl groups, carboxylate carbonyl functional groups acting as Lewis bases, an active Cu site functioning as a Lewis acid center, and azine groups of TCT acting as Lewis bases, all synergistically interacting with the Lewis acidity of the Cu centers in HKUST-1. To assess these synergic effects, HKUST-1@Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 was used in the formation of an asymmetric C-C bond in nitroaldol condensation and asymmetric cycloaddition of CO2 to epoxides. The findings demonstrated that under mild and green conditions, in both the asymmetric nitroalcohol condensation and the asymmetric cycloaddition of CO2, HKUST-1@Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 had better enantioselectivity than the Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 nanoparticles and a higher selectivity toward β-nitroalcohol and cyclic carbonate over the pure HKUST-1. Despite its simple and easy synthesis, HKUST-1@Cu(l-proline)2-Triazine/Fe3O4@SiO2-NH2 exhibited exceptional performance in the asymmetric nitroaldol condensation and asymmetric cycloaddition of CO2 to epoxides. Additionally, the mechanism of the reactions was depicted with reference to the total energy of the reactants, intermediates, and products.

Mixed-Linker Zr-Metal-Organic Framework with Improved Lewis Acidic Sites for CO2 Fixation Reaction Catalysis

Applying the mixed-linker strategy in synthesizing metal-organic frameworks (MOFs) has drawn considerable attention as a heterogeneous catalyst owing to their easy synthesis and different functional ligands in their frameworks. Following this strategy, we have developed a mixed linker Zr(IV)-based MOF, [Zr6O4(OH)4(FUM)n(PZDC-NO2)6-n] (PZDC-NO2 = 4-nitro-3,5-pyrazoledicarboxylic acid, FUM = fumaric acid) denoted as MOF-801(PZDC-NO2) synthesized via this strategy which possess an electron-withdrawing group (-NO2) on secondary linkers. The MOF-801(PZDC-NO2) has been fully characterized via various analyses, such as Fourier transform infrared, powder X-ray diffraction, 13C/1H nuclear magnetic resonance, XPS, TGA, and N2 adsorption/desorption, SEM, EDX, etc. By considering the concurrent existence of acid-base active sites and the synergistic role of these sites, this mixed-linker MOF was used as a catalyst for the cycloaddition reaction of CO2 and epoxides under mild without-solvent conditions. MOF-801(PZDC-NO2) displays significant catalytic performance by producing the highest catalytic conversion of epoxide to cyclic carbonate (93%) with a turnover number of 130.7 in 8 h reaction time and 100 °C temperature under low-pressure CO2 pressure. The mixed-linker Zr-MOF exhibits exceptional stability and reusability, maintaining its structure and functionality after consecutive cycles of utilization. Finally, the reaction mechanism was further investigated by density functional theory calculations. The total energy of the reactants, intermediates, and products involved in the process.

Density functional theory methods applied to homogeneous and heterogeneous catalysis: a short review and a practical user guide

The application of density functional theory (DFT) methods in catalysis has been growing fast in the last few decades thanks to both the availability of more powerful high computing resources and the development of new efficient approximations and approaches. DFT calculations allow for the understanding of crucial catalytic aspects that are difficult or even impossible to access by experiments, thus contributing to faster development of more efficient and selective catalysts. Depending on the catalytic system and properties under investigation, different approaches should be used. Moreover, the reliability of the obtained results deeply depends on the approximations involved in both the selected method and model. This review addresses chemists, physicists and materials scientists whose interest deals with the application of DFT-based computational tools in both homogeneous catalysis and heterogeneous catalysis. First, a brief introduction to DFT is presented. Then, the main approaches based on atomic centered basis sets and plane waves are discussed, underlining the main differences, advantages and limitations. Eventually, guidance towards the selection of the catalytic model is given, with a final focus on the evaluation of the energy barriers, which represents a crucial step in all catalytic processes. Overall, the review represents a rational and practical guide for both beginners and more experienced users involved in the wide field of catalysis.

Bifunctional Onium and Potassium Iodides as Nucleophilic Catalysts for the Solvent-Free Syntheses of Carbonates, Thiocarbonates, and Oxazolidinones from Epoxides

The catalytic potential of organo-onium iodides as nucleophilic catalysts is aptly demonstrated in the synthesis of cyclic carbonates from epoxides and carbon dioxide (CO2 ), as a representative CO2 utilization reaction. Although organo-onium iodide nucleophilic catalysts are metal-free environmentally benign catalysts, harsh reaction conditions are generally required to efficiently promote the coupling reactions of epoxides and CO2 . To solve this problem and accomplish efficient CO2 utilization reactions under mild conditions, bifunctional onium iodide nucleophilic catalysts bearing a hydrogen bond donor moiety were developed by our research group. Based on the successful bifunctional design of the onium iodide catalysts, nucleophilic catalysis using a potassium iodide (KI)-tetraethylene glycol complex was also investigated in coupling reactions of epoxides and CO2 under mild reaction conditions. These effective bifunctional onium and potassium iodide nucleophilic catalysts were applied to the solvent-free syntheses of 2-oxazolidinones and cyclic thiocarbonates from epoxides.

Functionalized β-Cyclodextrins Catalyzed Environment-Friendly Cycloaddition of Carbon Dioxide and Epoxides

Ammonium, imidazole, or pyridinium functionalized β-cyclodextrins (β-CDs) were used as efficient one-component bifunctional catalysts for the coupling reaction of carbon dioxide (CO₂) and epoxide without the addition of solvent and metal. The influence of different catalysts and reaction parameters on the catalytic performance were examined in detail. Under optimal conditions, Im-CD1-I catalysts functionalized with imidazole groups were able to convert various epoxides into target products with high selectivity and good conversion rates. The one-component bifunctional catalysts can also be recovered easily by filtration and reused at least for five times with only slight decrease in catalytic performance. Finally, a possible process for hydroxyl group-assisted ring-opening of epoxide and functionalized group- induced activation of CO₂ was presented.

Basically, nucleophilicity matters little: towards unravelling the supramolecular driving forces in enzyme-like CO2 conversion

The reaction mechanism for the cycloaddition of CO₂ to styrene oxide in the presence of macrocyclic pseudopeptides has been studied using DFT methods. Computational calculations indicate that the unprecedented catalytic behaviour previously observed experimentally, in which the most reactive species was not the most nucleophilic but the most basic one, can be associated to the tight cooperativity between several supramolecular interactions promoted by simple peptidomimetics able to display a synzymatic behaviour. This bizarre catalytic performance afforded remarkable conversions of a sluggish substrate like styrene oxide into the desired cyclic carbonate, even under relatively mild reaction conditions, opening the way for the practical use of CO₂ as a raw material in the preparation of valuable chemicals. Furthermore, the remote modification of essential structural features of the macrocycle (synzyme engineering) permitted the driving forces of the synzymatic system to be analyzed, stressing the crucial synergic effect between an elegantly preorganized oxyanion hole and additional aromatic interactions.

Efficient synthesis of cyclic carbonates from CO2 under ambient conditions over Zn(betaine)2Br2: experimental and theoretical studies

It is very interesting to synthesize high value-added chemicals from CO₂ under mild conditions with low energy consumption. Here, we report that a novel catalyst, Zn(betaine)₂Br₂, can efficiently promote the cycloaddition of CO₂ with epoxides to synthesize cyclic carbonates under ambient conditions (30 °C, 1 atm). DFT calculations provide important insights into the mechanism, particularly the unusual synergistic catalytic action of Zn²⁺, Br^- and NR⁴⁺, which is the critical factor for the outstanding performance of Zn(betaine)₂Br₂. The unique features of the catalyst are that it is cheap, green and very easy to prepare.

Insights into the effect of hydroxyl-, epoxy-, and carboxyl-pores on the desolvation of K+with water as a solvent: a first-principles study

The oxygen-containing functional group is particularly effective at the capacity and cycle performance of porous carbon, but there are few reports on the influence of ionic desolvation. The desolvated behavior in porous carbon could be availably simulated through the bilayer graphene with the interlayer spacings of 4-10 Å as the flat pore model by a first-principles calculation. The desolvated behavior of hydrated potassium ion ([K(H₂O)]⁺) is calculated in AA- and AB-stacking hydroxyl-, epoxy-, carboxyl-flat pores. The results show that the fully desolvated sizes of [K(H₂O)]⁺in hydroxyl-, epoxy-, carboxyl-pores are 4.6 Å, 4.7 Å, and 4.2 Å, respectively. The fully desolvated pore size increases under the modification of hydroxyl- and epoxy-groups in pores and the size slightly reduces in carboxyl-pores compared with the fully desolvated size of (4.4 Å) [K(H₂O)]⁺in flat pores without oxygen-containing functional group. Electron density difference and Hirshfeld charge analysis show that K⁺primarily interacts with the oxygen-containing functional groups of pores. Our present results are helpful to improve the capacity of supercapacitors by adjusting the types of oxygen-containing functional groups on the pore walls of porous carbon materials.

Hydrogenation of CO2 to methanol by the diphosphine–ruthenium(ii) cationic complex: a DFT investigation to shed light on the decisive role of carboxylic acids as promoters

We present a quantum-chemical investigation of the CO₂ hydrogenation to methanol catalyzed by the recently proposed diphosphine–ruthenium(ii) cationic complex, Ru2, in presence of carboxylic acids.