Mechanism Of Cycloaddition Reaction Research Articles

Multi-amino functionalized triazine-based polymers as the catalyst for cycloaddition of CO2 to epoxides

Designing efficient catalysts for CO2 cycloaddition to reduce CO2 emission is one of crucial for environmental issues technology. Herein, the multiple-amino functionalized triazine-based polymer (MAFTP) was prepared through the nucleophilic reaction of cyanuric chloride with melamine and ethylenediamine by a conventional heating method, which are favorable for CO2 adsorption due to their nitrogen-rich structure. MAFTP was characterized entirely, the CO2 adsorption capacity of MAFTP showed the CO2 uptake performance with the values of 5.73 cm3g−1 at 273 K and 1 bar. MAFTP/KI catalyst exhibited efficient catalytic activity for CO2 fixation to epoxides. 99 % propylene carbonate yield and 99 % selectivity were obtained under 120 °C, 2.0 MPa for 2.0 h without organic solvent. Additionally, the catalysts could be recycled easily from the products after reaction by centrifugation and then reused 5 times efficiently. Meanwhile, the catalytic activity of MAFTP/KI to other substituted epoxides was discussed. Moreover, DFT calculation was adopted to analyze the possible cycloaddition reaction mechanism. The MAFTP/KI system is a promising candidate for CO2 chemical fixation attributing to the low cost, abundant availability, easy separation and high catalytic activity for CO2 chemical fixation.

The Synthesis of 1,3,4-Thiadiazoles, 1,3,4-Selenadiazoles and Pyrazolo[3,4-d]pyrimidine Derivatives: Utility of hydrazonoyl bromide and DFT study

1,3,4-Selenadiazoles and 1,3,4-thiadiazolese, were synthesized from the reaction of hydrazonoyl bromide with potassium thiocyanate and potassium selenocyanate, respectively. Also, treatment of hydrazonoyl bromide with malononitrile gave pyrazole-4-carbonitrile derivatives which reacted with formic acid, and formamide to produce the respective pyrazolo[3,4-d]pyrimidines. Elemental analyses, alternative synthesis procedures, and spectrum data were used to confirm the structures of the novel compounds. We studied the 1,3-dipolar cycloaddition reaction mechanism of these reactions using the density functional theory (DFT) method at the B3LYP/6–311++G** level of theory. The product formation was explained experimentally by calculations involving natural bond orbitals (NBO) and frontier molecular orbitals (FMO).The results of this study are consistent with the proposed experimental mechanism.

Two coordination polymers based on imidazopyridine carboxylic acid ligand for efficient catalytic cycloaddition of CO2 with epoxides and cyanosilylation

Two coordination polymers (CPs){[M(L)2(H2O)2]·2H2O}n (M=Co (1) and Mn (2), HL=4-(3H-imidazo[4,5-b]pyridin-2-yl) benzoic acid) have been prepared under hydrothermal method and systematically characterized. The catalytic properties of the two CPs were investigated, the results showed that CP 1 could be used to catalyze CO2 cycloaddition reactions efficiently under eco-friendly, solvent-free conditions. The influencing factors and catalytic mechanism of cycloaddition reaction were discussed. Moreover, CP 2 exhibited catalytic performance for cyanosilylation reaction. The recycling experiments showed that the CPs 1 and 2 could be recovered and reused at least 5 reaction cycles without an obvious decrease of catalytic activity.

Boosting catalytic performance for CO2 cycloaddition under mild condition via amine grafting on MIL-101-SO3H catalyst

The efforts to achieve sustainable chemical conversion and efficient CO2 utilization are critical to addressing climate change and environmental sustainability, and therefore the development of effective CO2 conversion catalysts is crucial. In this study, novel acid-base bifunctional catalysts, MIL-101-SO3H@Atz and MIL-101-SO3H@DAtz, were successfully synthesized using MIL-101-SO3H as an acid support material through post-synthetic modification with 3-amino-1,2,4-triazole (Atz) and 3,5-diamino-1,2,4-triazole (DAtz) for CO2 conversion reaction. The incorporation of the amine species into MIL-101-SO3H created unique synergistic effects with dual acid-base catalytic sites, facilitating the efficient conversion of CO2 and epoxides into cyclic carbonates. Among the catalysts, MIL-101- SO3H@DAtz demonstrated superior catalytic performance with achieving 100% epichlorohydrin (ECH) conversion with over 99% selectivity to cyclic carbonate with high selectivity of > 99% under the ambient condition of 1 bar CO2 without any co-catalyst or solvent. The elucidated CO2 cycloaddition reaction mechanism highlights the synergistic effects of acid-base functionalities and CO2-philic Lewis bases as well as hydrogen bonding donor groups, providing valuable insights into the factors contributing to superior catalytic performance. The simulated flue gas (15% CO2/85% N2, v/v) was also conducted using MIL-101-SO3H@DAtz catalyst. Additionally, the MIL-101-SO3H@DAtz catalyst exhibited remarkably robust structural stability and recyclability, maintaining its activity over multiple cycles.

Ionic liquids bonded in mesoporous HAP serve as efficient catalysts for CO2 fixation

In this study, hydroxyapatite (HAP) with abundant surface hydroxyl and large pores was used as the ionic liquid ([DMCA]X) immobilization carrier, where the surface hydroxyl groups of HAP were used as binding sites and the n-halogen-acids were used as bonding agents. The supported ionic liquid catalysts [DMCA]X-n-HAP were characterized by XRD, TEM, TG and FTIR, proving that the ionic liquids were successfully bonded onto the surface of HAP. The utilization of hydroxyl sites on the surface of HAP was as high as 90%. The above catalysts were used to catalyze the cycloaddition reaction of CO2 and propylene oxide (PO), and the yield and selectivity of propylene carbonate (PC) were up to 98.7% and 100%, respectively. The length effect of the bonding agents on the catalyst performance was also studied, and found that n-chlorine-butyric acid was the most suitable chemical for channel structure of HAP and spatial freedom of ionic liquid. In addition, the effects of halogen anion and hydroxyl hydrogen on the performance of the reaction were also studied. Importantly, autocatalysis was discovered in the reaction. Finally, the reaction intermediates and reaction mechanism of CO2 cycloaddition were investigated by in situ-DRIFTS, revealing that ring-open of PO is rate-determining step.

Two Ln-MOFs containing abundant Lewis acid sites as the efficient and heterogeneous catalyst to activate epoxides for cycloaddition of CO2

The burning of a large number of fossil fuels leads to the increase of CO2 content in the air, causing environmental problems such as greenhouse effect and ocean acidification, which has attracted wide attention. It is of great significance to utilize microporous metal-organic frameworks (MOFs) for carbon dioxide conversion and utilization. Herein, two MOFs {[Ln(dppa)(H2O)2·2H2O]·dima·H2O·0.5O} (1: Sm-MOF; 2: Gd-MOF; H4dppa = 5-(3′ 4′-dicar- boxylphenoxy) isophthalic acid, dima = dimethylamine, which is decomposed by DMF hydrothermal reaction), and its structural characterization and CO2 catalytic conversion performance were studied. The BET test of MOFs 1–2 shows that it has good microporosity. At 273 K and 298 K, MOFs 1–2 showed lower adsorption capacity for CH4, but higher adsorption capacity for CO2. The adsorption enthalpy of CO2 was calculated by Virial equation, and the adsorption selectivity of CO2 at different separation ratios was discussed respectively. The heterogeneity of MOFs 1–2 was proved by thermal filtration experiments. The reproducibility test shows that the catalyst structure is still intact after five cycles, indicating that the catalyst still has good repeatability. In addition, the catalytic mechanism of cycloaddition reaction was discussed.

The role of sulfur cycle in new particle formation: Cycloaddition reaction of SO3 to H2S

The chemistry of sulfur cycle contributes significantly to the atmospheric nucleation process, which is the first step of new particle formation (NPF). In the present study, cycloaddition reaction mechanism of sulfur trioxide (SO3) to hydrogen sulfide (H2S) which is a typical air pollutant and toxic gas detrimental to the environment were comprehensively investigate through theoretical calculations and Atmospheric Cluster Dynamic Code simulations. Gas-phase stability and nucleation potential of the product thiosulfuric acid (H2S2O3, TSA) were further analyzed to evaluate its atmospheric impact. Without any catalysts, the H2S + SO3 reaction is infeasible with a barrier of 24.2 kcal/mol. Atmospheric nucleation precursors formic acid (FA), sulfuric acid (SA), and water (H2O) could effectively lower the reaction barriers as catalysts, even to a barrierless reaction with the efficiency of cis-SA > trans-FA > trans-SA > H2O. Subsequently, the gas-phase stability of TSA was investigated. A hydrolysis reaction barrier of up to 61.4 kcal/mol alone with an endothermic isomerization reaction barrier of 5.1 kcal/mol under the catalytic effect of SA demonstrates the sufficient stability of TSA. Furthermore, topological and kinetic analysis were conducted to determine the nucleation potential of TSA. Atmospheric clusters formed by TSA and atmospheric nucleation precursors (SA, ammonia NH3, and dimethylamine DMA) were thermodynamically stable. Moreover, the gradually decreasing evaporation coefficients for TSA-base clusters, particularly for TSA-DMA, suggests that TSA may participate in NPF where the concentration of base molecules are relatively higher. The present new reaction mechanism may contributes to a better understanding of atmospheric sulfur cycle and NPF.

Structural design of core-shell zeolitic imidazolate frameworks as an efficient catalyst for CO2 cycloaddition to epoxides

Size-controlled hybrid ZIFs (core-shell ZIF-67@ZIF-8, ZIF-8@ZIF-67, and bimetallic Zn/Co-ZIF-8) with the same particle size were synthesized by a seed-mediated methodology by adjusting the particle size of core ZIFs. The synthesized hybrid ZIFs was tested as heterogeneous catalysts for the CO2 cycloaddition to epoxides using pure CO2 gas and mixed gas (85 % CO2/15% N2) without any co-catalyst and solvent. The effect of the composition of shell and core ZIFs on the catalytic performance of CO2 cycloaddition reaction to epoxides were investigated. Furthermore, the correlation between structural defects and catalytic activity in ZIF catalysts along with their particle sizes was investigated by calculating the ratio of DXRD/DSEM. Both core-shell type ZIF-67@ZIF-8 and ZIF-8@ZIF-67 exhibited better catalyst performance of CO2 cycloaddition reaction than other ZIF catalysts. Among the ZIF catalysts, ZIF-67@ZIF-8 exhibited the highest catalytic performance for epoxide conversion owing to its abundant Lewis acid-base properties and relatively large window size of ZIF-8 shell with appropriate binding force between epoxide and CO2. It showed good recyclability for CO2 cycloaddition reaction without a structural collapse during ten recycles. The structural stability of ZIF-67@ZIF-8 was examined in detail by a hot filtering test, leaching test, and TGA analysis. The mechanism of CO2 cycloaddition reaction was proposed and the effect of the shell composition in core-shell type ZIFs on the binding energy with epoxide substrate also was studied based on DFT calculations.

Triazolato Pd(II) and Pt(II) complexes of 2,6-bis(1-ethylbenzimidazol-2′-yl)pyridine formed via catalyst-free [3 + 2] click reactions

At the ambient temperature and under catalyst-free conditions, reactions between [MN3(LET)]PF6 (M = Pd(II) and Pt(II); LET = 2,6-bis(1-ethylbenzimidazol-2′-yl)pyridine) and substituted alkynes (dimethyl acetylene-dicarboxylate and 4,4,4-trifluoro-2‑butynoic acid ethyl ester) afforded the corresponding triazolate complexes. These reactions produced a mixture of triazolate bound isomers. The N1 triazolate isomer of the Pt(II) complexes, which first appeared in the [3 + 2] coupling, eventually isomerized to the N2-analogue during the incubation in DMSO. The reactions of [MN3(LET)]PF6 with asymmetric alkyne, 4,4,4-trifluoro-2‑butynoic acid ethyl ester, produced a mixture of the three anticipated triazolate isomers, according to 19F NMR spectroscopy. The stability of the triazolate complexes was investigated, along with the cycloaddition reaction's mechanism and the nature of the intermediates, using NMR spectroscopy.

Mechanistic insight into cobalt-mediated [2 + 2 + 2]-cycloaddition reactions with γ-alkylidenebutenolide and γ-alkylidenebuterolactam as 2π partners.

The molecular complexity of recently reported cobalt(III) polycyclic complexes, resulting from an intramolecular formal (2 + 2 + 3) cycloaddition reaction on an enediyne containing a lactone moiety, has prompted us to computationally review the mechanisms of cobalt cycloaddition reactions with γ-alkylidenebutenolide or γ-alkylidenebuterolactam as 2π partners. Computed mechanisms are compared, leading to either cobalt(III)- or cobalt(I)-spiro complexes depending of both the nature of the reaction (intra- vs. intermolecular pathway) and the nature of the 2π partner (γ-alkylidenebutenolide vs. γ-alkylidenebuterolactam). These proposed mechanisms are supported by experiments, allowing us to report the synthesis and characterization of the predicted compounds.

DFT Study on the Molecular Mechanism, Thermodynamic and Kinetic Parameters of Cycloaddition Reaction of Aziridine with CO2 in the Presence of Organocatalysts (TBD and 7-Azaindole)

The catalytic conversions of CO2 into value added chemicals have attracted the interest of many visionary researchers. In this work, the coupling reaction of aziridine with CO2 has been investigated in the absence and presence of organocatalysts (TBD and 7-azaindole) computationally using density functional theory method. The kinetic and thermodynamic parameters of each mechanism were calculated at B3LYP/6-31G (d) level. The results show that, the TBD and 7-azaindole catalyzed reactions of aziridine with CO2 have significantly lower the energy barrier compared to a single step concerted non-catalyzed one. In TBD catalyzed reaction, mechanism I in which the TBD catalyst first interact with CO2 to form TBD-CO2 adduct (zwitterion) and then the zwitterion formed facilitated the ring opening of aziridine to form intermediate is the favorable path. In the case of 7-azaindole catalyzed reaction, mechanism 1 is the most favorable pathway in both gas phase and water phase. However, these parameters were significantly affected in the presence of water using Solvent Model Density (SMD).

Theoretical study on the cycloaddition reaction of phosphenium cation and formaldehyde

The mechanism of cycloaddition reaction between phosphenium cation and phosphindene with formaldehyde has been systematically investigated at the B3LYP/6-311++G(d,p) level of theory in order to better understand the reactivity for the valence isoelectronic of carbene. Phosphenium cation acts as an electrophilic reagent and accepts σ electrons of formaldehyde to form a complex in the first addition step. The greater the positive charge on phosphorus atom in phosphenium cation, the more stable the formed complex is. Introduction of substituents will decrease positive charge on phosphorus atom in phosphenium cation. The order of positive charge on phosphorus atom is HP+–F > HP+–OH > HP+–NH2, which is consistent with their Lewis acidities. The complex transforms to a three-membered ring product via a transition state in the second cyclization step. The product is less stable than the complex due to its tension of small ring.

Catalytic performance of MOFs containing trinuclear lanthanides clusters in the cycladdition reaction of CO2 and epoxide

With the rapid development of global industrialization, global warming and ocean acidification caused by the accumulation of greenhouse gases (such as CO2) have attracted widespread attention. It is of great significance to use microporous metal-organic frameworks (MOFs) to adsorb carbon dioxide and further convert it into valuable chemical products. Herein, two kinds of isomorphic (MOFs): {[Ln3(deta)2(DMF)2(COOH)·2H2O]·DMF·H2O}n (LnDy(1), Tb(2), DMF = N-N-dimethyl formamide) based on 4-(3,5-dicarboxyphenoxy)phthalic acid (H4deta) ligands were successfully synthesized by the solvothermal synthesis method. Interestingly, MOFs 1–2 is based on a trinuclear Dy/Tb unit connected to six adjacent trinuclear Dy/Tb units via a (deta)4- ligand, extending to a 3D microporous network structure. MOFs 1–2 not only has good thermal stability, chemical stability and excellent water resistance, but also has abundant active sites of Lewis acid due to the fact that the metal center of MOFs 1–2 is lanthanides metal. The results show that MOFs 1–2 has a good catalytic activity for the chemical fixation of carbon dioxide with epoxides under moderate conditions. Moreover, they can be recycled at least 5 times without affecting their activity, showing excellent chemical stability and reusability. In addition, the reaction mechanism of CO2 cycloaddition to PO catalyzed by MOF 1–2 was also discussed.

Insights into reaction mechanisms of phosphenium cation and methyleneimine: a theoretical study

The mechanism of cycloaddition reaction between phosphenium cation and phosphindene with methyleneimine has been systematically investigated at the B3LYP/6-311++G(d,p) level of theory in order to better understand the reactivity for the valence isoelectronic of carbene. Phosphenium cation acts as an electrophilic reagent and accepts σ electrons of methyleneimine to form a complex in the first addition step. The greater the positive charge at phosphorus atom in phosphenium cation, the more stable the formed complex is. Introduction of substituents will decrease positive charge on phosphorus atom in phosphenium cation. The order of positive charge on phosphorus atom is HP+-F > HP+-OH > HP+-NH2, which is consistent with their Lewis acidities. The complex transforms to a three-membered ring product via a transition state in the second cyclization step. The product is less stable than the complex due to its tension of small ring.

Theoretical study on mechanism of cycloaddition reaction between o-alkynylbenzaldoximes and hexynol catalyzed by silver(I)

• A detailed description of the reaction mechanism of AgOTf-catalyzed synthesis of 2-(3-cyclopropylisoquinolin-1-yl)-1,1-diphenylhexen-3-one using DFT calculations. • Parr function analysis showed that the generation of Ag-π complexes could influence the electrophilicity of reaction species. • During intramolecular dehydration, AgOTf acts as a dehydration medium. Lewis acid metal-catalyzed cyclizations to construct quinoline ring compounds have made breakthroughs in the more recent years. Understanding the specific mechanism of this kind of reactions remains a challenging issue in this field. In this work, the mechanism of the silver(I)-catalyzed cyclization of o-alkynylbenzaldoxime with propargyl alcohol to construct 2-(3-cyclopropylisoquinolin-1-yl)-1,1-diphenylhex-1-en-3-one was investigated using density functional theory (DFT). The calculated results indicated that the 1,3-dipole cycloaddition process is the rate-determined step of the whole reaction process. The Ag-π complex formed by AgOTf with o-alkynylbenzaldehyde oxime increased the electrophilicity of the γ-C of the alkyne group prompting the intramolecular 6-endo cyclization. In addition, the Ag-π complex formed by AgOTf with alkynyl alcohol enhances the nucleophilicity of α-C atom and the electrophilicity of β-C atom of o-alkynylbenzaldehyde oxime, thus promoting the 1,3-dipole cycloaddition reaction with isoquinoline-N-oxide. The revealed mechanism will provide valuable a clue for the design of the Ag-based novel catalyst. Abstract

Mechanism of diethylamine/DBU-catalyzed cycloaddition of azides to unsaturated aldehydes: A quantum mechanical investigation

Density functional theory (DFT) methods have been used to investigate the mechanism of diethylamine-catalyzed cycloaddition reaction of phenyl azide and pentanal. The single point energies have been computed at M06-2X/6-311+G(d,p)//M06-2X /6-31+G(d,p) levels of theory in the presence of DMSO as a solvent. The computational results indicate that the catalyzed cycloaddition reaction is carried out via two one-step transition states that lead to 1,4- and 1,5-regioisomers, and favors the generation of the 1,4-regioisomer. In the absence of a catalyst, the 32CA reactions of azide and alkyne lack poor regioselectivity. Finally, distortion/interaction analysis along the reaction pathways was used to explain the 1,5-regioselectivity.

Accurate computed singlet-triplet energy differences for cobalt systems: implication for two-state reactivity.

Accurate singlet-triplet energy differences for cobalt and rhodium complexes were calculated by using several wave function methods, such as MRCISD, CASPT2, CCSD(T) and BCCD(T). Relaxed energy differences were obtained by considering the singlet and triplet complexes, each at the minimum of their potential energy surfaces. Active spaces for multireference calculations were carefully checked to provide accurate results. The considered systems are built by increasing progressively the first coordination sphere around the metal. We included in our set two CpCoX complexes (Cp = cyclopentadienyl, X = alkenyl ligand), which have been suggested as intermediates in cycloaddition reactions. Indeed, cobalt systems have been used for more than a decade as active species in this kind of transformations, for which a two-state reactivity has been proposed. Most of the considered systems display a triplet ground state. However, in the case of a reaction intermediate, while a triplet ground state was predicted on the basis of Density Functional Theory results, our calculations suggest a singlet ground state. This stems from the competition between the exchange term (stabilising the triplet) and the accessibility of an intramolecular coordination (stabilising the singlet). This finding has an impact on the general mechanism of the cycloaddition reaction. Analogous rhodium systems were also studied and, as expected, they have a larger tendency to electron pairing than cobalt species.

Cobalt Porphyrin-Cross-Linked Poly(Ionic Liquid)s as Efficient Heterogeneous Catalysts for Carbon Dioxide Conversion under Mild Conditions

The cycloaddition reaction of CO2 and epoxides to form cyclic carbonates is a promising strategy to alleviate the climate change caused by CO2 in view of its high atomic economic efficiency and solvent-free and mild conditions. Inspired by the mechanism of cycloaddition reactions catalyzed by Lewis acid/Lewis base binary systems, we explored a series of heterogeneous catalysts functionalized by cobalt porphyrin cross-linked phosphonium salt poly(ionic liquid)s. Specifically, poly(4-vinylbenzyl chloride) (PVBnCl) was used as the polymer backbone. Then, PVBnCl was cross-linked by 5,10,15,20-tetra(4-pyridyl) porphyrin (TPyP) and quaternized by triphenylphosphine (PPh3). After complexing with CoCl2 and anion exchange, the as-prepared polymers CoTPyP-c-PVBnPPh3X were characterized using FTIR, SEM, TEM, XPS, TGA, ICP, and solid-state 13C NMR measurements. The results demonstrated that CoTPyP-c-PVBnPPh3X were efficient catalysts for the cycloaddition of CO2 and epoxides under mild conditions. Almost quantitative conversion of epoxides could be achieved at 80 °C and 1 atm CO2, and CoTPyP-c-PVBnPPh3X could be easily separated and reused for four cycles only with a little decrease in the catalysis activity. The synergistic catalysis of the Lewis acid metal center and nucleophilic halogen ion addressed the excellent performance of CoTPyP-c-PVBnPPh3X. Therefore, our findings provided a new solution for the development of efficient heterogeneous catalysts with multi-centers for CO2 conversion.

On the Question of Stepwise [4+2] Cycloaddition Reactions and Their Stereochemical Aspects

Even at the end of the twentieth century, the view of the one-step [4+2] cycloaddition (Diels-Alder) reaction mechanism was widely accepted as the only possible one, regardless of the nature of the reaction components. Much has changed in the way these reactions are perceived since then. In particular, multi-step mechanisms with zwitterionic or diradical intermediates have been proposed for a number of processes. This review provided a critical analysis of such cases.

Task-specific ionic liquid-grafted mesoporous alumina for chemical fixation of carbon dioxide into cyclic carbonate

In this paper, task-specific ionic liquid-grafted mesoporous alumina (MA) was synthesized and applied for CO2 chemical fixation. First, task-specific ionic liquid 1-(2-carboxymethyl)-3-methylimidazolium bromide ([CmMim][Br]) with high thermal stability was successfully prepared. Then [CmMim][Br]-MA material was fabricated via chemical grafting. The crystal structure of the grafted material maintains well compared to the support and its morphology keeps honeycomb with wrinkled surface. The specific surface area of grafted materials varies from 130 to 12 m2/g depending on the grafting degree of [CmMim][Br]. Finally, cycloaddition reaction of CO2 with epichlorohydrin was studied without any solvent and co-catalyst. The yield of 4-(chloromethyl)-1,3-dioxolan-2-one reaches 96.6% with 1.0 wt% [CmMim][Br]-grafted MA-0.2 relative to epichlorohydrin as catalyst at 110 °C, 2 MPa for 6 h . The catalyst can be reused at least 16 cycles with above 90% yield of 4-(chloromethyl)-1,3-dioxolan-2-one and its microstructure keeps well. The mechanism of cycloaddition reaction is also discussed.