DFT mechanistic study of the chemical fixation of CO2 by aziridine derivatives

Using density functional theory (DFT), we treat the reaction of coupling of CO2 with aziridine in gas phase, in the presence of water and of a green catalyst (NaBr). Computations show that, in gas phase, this ring-opening conversions to oxazolidinones initiates by coordinating a CO2 molecule to the nitrogen atom of the aziridine. Then, a nucleophilic interaction between one oxygen atom of the coordinated CO2 and the carbon atom of the aziridine occurs. For methyl substituted aziridine, two pathways are proposed leading either to 4-oxazolidinone or to 5-oxazolidinone. Besides, we show that the activation energy of this reaction reduces in aqueous solution, in the presence of a water molecule explicitly or NaBr catalyst. In addition, the corresponding reaction mechanisms and regioselectivity associated with this ring-opening conversions to oxazolidinones, in the presence of carbon dioxide are found to be influenced by solvent and catalyst. The present findings should allow better designing regioisomer oxazolidinones relevant for organic chemistry, medicinal and pharmacological applications.

Self-assembled mononuclear complexes: open metal sites and inverse dimension-dependent catalytic activity for the Knoevenagel condensation and CO2 cycloaddition

To lessen the greenhouse effect, measures such as improving the recovery of crude oil and converting carbon dioxide (CO₂) into valuable chemicals are necessary to create a sustainable low-carbon future. To this end, the development of efficient new oil-displacing agents and CO₂ conversion has aroused great interest in both academia and industry. The Knoevenagel condensation and CO₂ cycloaddition are the key reactions to solve the above problems. Four Cu- or Zn-based molecular complexes built from different ligands possessing hydrophilic-hydrophobic layers and different dimensionalities were chosen as solid catalysts for this study. Structural analysis revealed the presence of hydrophilic-hydrophobic layers and open metal sites in the low-dimensional complexes. To obtain deep insight into the reaction mechanism, first-principles density functional theory (DFT) calculations were carried out. These calculations confirmed that in the Knoevenagel condensation reaction, the final formation of benzylidenemalononitrile is the rate-determining step (an energy barrier (ΔE) value of 73.2 kJ mol^-1). The zero-dimensional (0D) Cu molecular complex with unsaturated metal centers, hydrophilic and hydrophobic layers, exhibited higher catalytic activity (yield: 100%, temperature: room temperature, and time: 2 h) compared with one- and two-dimensional Cu complexes. In the presence of a 0D Zn complex co-catalyzed with Br^- in the CO₂ cycloaddition reaction, the ΔE value reduces to 35.5 kJ mol^-1 for the ring opening of styrene oxide (SO), which is significantly lower than Br^- catalyzed (80.9 kJ mol^-1) reactions. The roles of unsaturated metal centers, hydrophilic-hydrophobic layers and dimensionality in the Knoevenagel condensation and CO₂ cycloaddition were explained in the results of structure-activity relationships.

An yttrium-organic framework based on a hexagonal prism second building unit for luminescent sensing of antibiotics and highly effective CO2 fixation

An yttrium-organic framework based on a hexagonal prism second building unit was constructed from nonanuclear yttrium(iii) and 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine for the luminescent sensing of antibiotics and highly effective CO2 fixation.

Green Conversion of CO2 and Propargylamines Triggered by Triply Synergistic Catalytic Effects in Metal-Organic Frameworks

Cyclization of propargylamines with CO₂ to obtain 2-oxazolidone heterocyclic compounds is an essential reaction in industry but it is usually catalyzed by noble-metal catalysts with organic bases as co-catalysts under harsh conditions. We have synthesized a unique Cu^I /Cu^II mixed valence copper-based framework {[(Cu^I ₆ I₅ )Cu₃ ^II L₆ (DMA)₃ ](NO₃ )⋅9DMA}_n (1) with good solvent and thermal stability, as well as a high density of uncoordinated amino groups evenly distributed in the large nanoscopic channels. Catalytic experiments show that 1 can effectively catalyze the reaction of propargylamines with CO₂ , and the yield can reach 99 %. The turnover frequency (TOF) reaches a record value of 230 h^-1 , which is much higher than that of reported noble-metal catalysts. Importantly, this is the first report of heterogeneously catalyzed green conversion of propargylamines with CO₂ without solvents and co-catalysts under low temperature and atmospheric pressure. A mechanistic study reveals that a triply synergistic catalytic effect between Cu^I /Cu^II and uncoordinated amino groups promotes highly efficient and green conversion of CO₂ . Furthermore, 1 directly catalyzes this reaction with high efficiency when using simulated flue gas as a CO₂ source.

Rational Stepwise Construction of Different Heterometallic-Organic Frameworks (HMOFs) for Highly Efficient CO2 Conversion

The coordination preference of different metal ions and ligands have an immense influence on the constructions of functional MOF materials. In this work, two new monometallic complexes, namely [Ag(HL)(bipy)_0.5 ] (1) and {[Tb(L)_1.5 (H₂ O)]⋅4 H₂ O}_n (2) (bipy=4,4-bipyridine), have been synthesized successfully by employing a bifunctional 2-(imidazol-1-yl)terephthalic acid (H₂ L) ligand. After that, two new different heterometallic-organic frameworks (HMOFs), namely {[TbAg(L)₂ (H₂ O)₃ ]⋅H₂ O}_n (3) and [TbAg(L)₂ (H₂ O)]_n (4), were obtained from complexes 1 and 2 as the precursors based on a rational stepwise construction strategy and the theory of hard and soft acids and bases (HSAB principle), respectively. The HMOFs bearing dual metallic catalytic sites (Tb and Ag) can be used as heterogeneous catalysts without losing performance for the chemical fixation of CO₂ with epoxides including the sterically hindered epoxides, demonstrating some of the highest reported catalytic activity values. This work may provide a new synthetic route toward tailoring new HMOFs with excellent catalytic activity.

The fixation of CO2 by epoxides over nickel-pyrazolate-based metal–organic frameworks

Ni-based MOFs with Lewis acid sites was developed for CO₂ fixation with epoxides into cyclic carbonates, and a comparative study shows that the density and accessibility of the Lewis acid sites in the MOFs greatly influence the catalytic performance.

Formation of CX Bonds in CO2 Chemical Fixation Catalyzed by Metal-Organic Frameworks

Transformation of CO₂ based on metal-organic framework (MOF) catalysts is becoming a hot research topic, not only because it will help to reduce greenhouse gas emission, but also because it will allow for the production of valuable chemicals. In addition, a large number of impressive products have been synthesized by utilizing CO₂ . In fact, it is the formation of new covalent bonds between CO₂ and substrate molecules that successfully result in CO₂ solidly inserting into the products, and only four types of new CX bonds, including CH, CC, CN, and CO bonds, are observed in this exploration. An overview of recent progress in constructing CX bonds for CO₂ conversion catalyzed by various MOF catalysts is provided. The catalytic mechanism of generating different CX bonds is further discussed according to both structural features of MOFs and the interactions among CO₂ , substrates, as well as MOFs. The future opportunities and challenges in this field are also tentatively covered.

Highly efficient synergistic CO2 conversion with epoxide using copper polyhedron-based MOFs with Lewis acid and base sites

The catalytic performances and effect of LASs and LBSs of four isomorphous Cu-PMOFs in CO₂ cycloaddition reaction were systematically studied. JLU-Liu21 exhibited significant catalytic efficiency, remarkable recyclability and catalytic stability.