Cycloaddition Reaction Of Epoxides Research Articles

Green Conversion of Epoxides to Cyclic Carbonates by Copper Nanocrystals Fabricated on Jute Tartaric Acid Composite Surface

AbstractThe synthesis of copper nanocrystals on tartaric acid jute composite surface is reported. The formation of nanocrystals is detected by FT IR, Powder X‐ray diffraction, SEM, and TEM analysis. The average size of the nanocrystals is found to be 500 nm. The reaction of the copper nanocrystals with CO2 resulted in a decrease in the size of the nanoparticles. Cycloaddition reaction of epoxides to cyclic carbonate is efficiently carried out by the copper nanocrystals on tartaric acid jute composite surface (CUNPJT) without using any cocatalyst and solvent. To the best of author's knowledge, this is the first example of copper nanocrystals catalyzing the cycloaddition of CO2 and epoxide.

Biomass-based ionic liquids efficiently catalyzed the cycloaddition reaction of epoxides with CO2 by hydrogen-bonding and the anion cooperative effect

Several novel biomass-based ionic liquids derived from 5-hydroxymethylfurfural were used as single-component, recyclable and efficient catalysts for transformation of CO2.

Metal–organic frameworks with Lewis acid-base sites as highly efficient catalyst for the cycloaddition of carbon dioxide

The chemical fixation of carbon dioxide (CO2) into high value-added chemicals like cyclic carbonates is an effective strategy to solve the energy and ecological issues. Metal-organic frameworks (MOFs) can efficiently catalyze the reaction due to their diverse structures and accessible active sites, herein, two novel MOFs have been successfully constructed based on bi-functional ligand 4-(2, 4-dicarboxylphenyl)-4, 2’: 6′, 4″-terpyridine) (H2dcptpy). The Fourier-transform infrared (FT-IR) spectra data indicated complete de-protonation of the H2dcptpy ligand, their structures have been refined and formulated as [Co(dcptpy)]∙DMF∙6H2O (MOF 1) with a large BET surface areas of 3.4 m2/g and [Cu(dcptpy)(H2O)2] (MOF 2). They both exhibit a three-dimensional network structure with microporosity and contain Lewis acid-base sites located on the surface of the pores. The good purity and stability of the as-synthesized samples were adequately characterized by powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA). Remarkably, a series of cycloaddition reactions of epoxides with CO2 show that MOF 1 has excellent heterogeneous catalytic activity for cyclic carbonate of epibromohydrin and butyl glycidyl ether, and almost complete conversion can be achieved even under mild conditions (1 bar CO2, 80 °C, 12 h and solvent-free). Therefore, MOF 1 has the potential to be a catalyst material for CO2 conversion.

Monodentate H-bond donor bifunctional catalyst in fixation of atmospheric pressure carbon dioxide into cyclic carbonates

The efficient conversion of epoxides and CO2 into cyclic carbonates by employing H-bond donor (HBD) and nucleophilic halide cooperating catalysis under mild conditions is an attractive research topic. Herein, we report a new onium halide bearing a CON(H) moiety as a weak HBD catalyst to facilitate the cycloaddition reaction of epoxides and CO2 under mild conditions. The structural influences on the catalytic activity were scrutinized, which included tunable substituents, the distance between functional groups, and counter anions. The result indicated that the catalyst of the bis-meta-substitutions on an aromatic ring exhibited excellent activity for converting epichlorohydrin into cyclic carbonate under atmospheric pressure at 25–70 °C. Twelve terminal epoxides were converted into corresponding cyclic carbonates in 72–99 % isolated yield. A reasonable activation mechanism was proposed and validated by using control experiments and NMR titrations. In addition, the good recyclability proves that the onium halide is a sustainable green organocatalyst.

Fixing CO2 under Atmospheric Conditions and Dual Functional Heterogeneous Catalysis Employing Cu MOFs: Polymorphism, Single-Crystal-to-Single-Crystal (SCSC) Transformation and Magnetic Studies.

New copper compounds, [Cu(C14H8O6)(C10H8N2)(H2O)] (1), [Cu(C14H8O6)(C10H8N2)(H2O)]·(C3H7ON)2 (2), [Cu(C14H8O6)(C10H8N2)(H2O)2]·(C3H7ON) (3), [Cu(C14H8O6)(C10H8N4)] (4), and [Cu(C14H8O6)(C10H8N4)]·(H2O) (5), were prepared employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as the primary ligand and 4,4'-bipyridine (1-3) and 4,4'-azopyridine (4-5) as the secondary ligands. Single-crystal studies indicated that compounds 1-4 have two-dimensional layer structures and compound 5 has a three-dimensional structure. Compounds 1-3 were isolated from the same reaction mixture but by varying the time of reaction. The framework structures of compounds 1-3 are similar and may be considered as polymorphic structures. Compounds 4 and 5 can also be considered polymorphic with a change in dimensionality of the structure. Compounds 1-3 can be formed through a single-crystal-to-single-crystal transformation under a suitable solvent mixture. The Cu center was explored for the Lewis acid-catalyzed cycloaddition reaction of epoxide and CO2 under ambient conditions in a solventless condition and also for the synthesis of propargylamine derivatives by three-component coupling reactions (A3 coupling) in a DCM medium. The Lewis basic functionality of the MOF (-N═N- group) has been explored for the Henry reaction (aldol condensation) in a solventless condition. In all of the catalytic reactions, good yields and recyclability were observed. The magnetic studies indicated that compounds 1 and 4 have antiferromagnetic interactions and compound 5 has ferromagnetic interactions. The present studies illustrated the rich diversity that the copper-containing compounds exhibit in extended framework structures.

A highly robust {ZnTb}n-Organic framework for excellent catalytic performance on cycloaddition reaction of epoxides with CO2

Effective chemical fixation of CO2 into high value-added industrial raw materials, recognized as an effective strategy to alleviate energy crisis and environmental pollution, makes the research of innovative catalysts a hot topic. Herein, a robust {ZnTb}n-chain-based framework of {[ZnTb(CPPDP)(H2O)]·5DMF·H2O}n (NUC-62) achieved from the solvothermal condition was reported. In NUC-62, nanoporous channels (aperture ca. 10.5 Å) are shaped by six rows of {ZnTb(CO2)5(H2O)}n chains, which is the first reported 3d-4f heterometallic chain with the staggered arrangement of Zn2+ and Tb3+. As for the activated NUC-62a with the removal of lattice and coordinated DMF and H2O, the host framework characterizes the merits of exposed Lewis-acidic metal sites, high specific surface, large void volume and stable chemical property. Furthermore, NUC-62a was tested as a heterogenous catalyst for the two organic reactions of cycloaddition of CO2 with epoxides and Knoevenagel condensation of aldehydes and malononitrile, in which NUC-62a display the high catalytic performance along with high selectivity and excellent recyclability. Hence, this work provides an effective synthesis strategy for MOFs-based catalysts.

Heterometallic YbCo–Organic Framework for Efficiently Catalyzing Cycloaddition of CO2 with Epoxides and Knoevenagel Condensation

Due to the excellent catalytic performance of Co-MOFs and Ln-MOFs on the chemical fixation of CO2, the self-assembly of microporous heterometallic compounds with the aid of designed functional ligands is carried out in our group. Herein, the solvothermal self-assembly of Co2+, Yb3+, and 2,6-bis(2,4-dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine (H5BDCP) generated a rarely reported {CoYb}n-chain-based framework of {[CoYb(BDCP)(H2O)]·3DMF·3H2O}n (NUC-70) with quasi-nanoporous channels (aperture ca. 11.4 Å) shaped by six rows of {CoYb(CO2)5(H2O)}n nodes. To the best of our knowledge, this is a rare 3d-4f heterometallic chain of {CoYb(CO2)5(H2O)}n with a staggered arrangement of Co2+ and Yb3+. After removing the associated water molecules, NUC-70a possesses the excellent characteristics of a large specific surface area, unsaturated open metal sites of Co2+ and Yb3+ as Lewis acid sites, and high heat/water-resistant physicochemical properties. Catalytic experiments showed that NUC-70a possessed a high catalytic activity on the cycloaddition reactions of epoxides with CO2 under mild conditions. Furthermore, the experiments performed confirmed that the Knoevenagel condensation reactions of aldehydes and malononitrile could be efficiently catalyzed by NUC-70a. This work illustrates that characteristic ligand design plays a key role in the self-assembly of MOFs with specific functions.

Fabrication of Carboxylic Acid and Imidazolium Ionic Liquid Functionalized Porous Cellulosic Materials for the Efficient Conversion of Carbon Dioxide into Cyclic Carbonates

Cellulosic poly(ionic liquid)s ([Cellmim][Br]) with a degree of substitution (DS) in the range of 0.32–0.89 were synthesized successfully via the homogeneous transesterification reaction of cellulose with 1-(2-methoxyacetyl)-3-methyl imidazole bromide IL ([Mmim][Br]) in a DBU/DMSO/CO2 solvent system. The structure and properties of these novel materials have been fully characterized. Cellulosic poly(ionic liquid) POF polymers (POF-[Cellmim][Br]) were then obtained by an in situ crosslinking reaction without adding an exterior catalyst. The porosity and properties of the POF-[Cellmim][Br] materials can be modulated. The POF-[Cellmim][Br] materials functioned as green, efficient, and highly active catalysts for cycloaddition reactions of epoxides and carbon dioxide under solvent-free and co-catalyst-free conditions. These reactions gave high yields (up to 97%), and the catalyst can be easily separated with excellent reusability and no significant change to its structure. A plausible reaction mechanism for the cycloaddition reaction of epoxide and carbon dioxide by the POF-[Cellmim][Br] catalyst is proposed based on the experimental results. This work provided a new strategy to prepare cellulosic-PIL POF materials and offered a platform to understand the cooperative effects of porous properties and nucleophilic anions on the cycloaddition reaction of carbon dioxide and epoxides.

Benzimidazolium‐Decorated Metalloporphyrin Molecule and Polymer: a Reliable Preparation Method and Application in Catalyzing the Cycloaddition Reaction of CO2and Epoxides

AbstractDue to the synergistic effect of central metal and halide anion, cationic metalloporphyrins and derivatives exhibit outstanding catalytic activities for the cycloaddition reaction of epoxides and carbon dioxide. Herein, a generic strategy was developed to synthesize the benzimidazolium‐containing metalloporphyrin molecule and polymer. To demonstrate the method feasibility, we firstly synthesized the molecule1H, in which the benzimidazole groups were in‐site constructed by the cyclization of 5,10,15,20‐(4‐carboxyphenyl)‐porphyrin (H2TCPP) witho‐diaminobenzene (PEA). After post‐synthetic ionization and metallization, I−and Zn2+were introduced as the nucleophile and Lewis acid, respectively. The structure of1ZnILwas confirmed by single crystal X‐ray diffraction analysis. By using the similar conditions of model reaction,H2TCPPwas copolymerized with 1,2,4,5‐tetraaminobenzene (BTA) to prepare the polymerP‐1ZnIL. The prepared cationic molecule1ZnILand polymerP‐1ZnILshowed comparable activities in catalyzing the cycloaddition of carbon dioxide with epoxides to cyclic carbonates compared to the reported bifunctional catalysts based on metalloporphyrins.

N-heterocyclic carbene-pyridine ligand coordinated Mo(II) complexes catalyzed synthesis of cyclic carbonates from carbon dioxide and epoxides

A variety of zero-valent molybdenum complexes and divalent molybdenum complexes with N-heterocyclic carbenes (NHC)-pyridine ligands were synthesized, and their catalytic activities and performances in the cycloaddition reaction of epoxides and carbon dioxide (CO2) were investigated. It was found that the divalent molybdenum complexes show high catalytic activity in the synthesis of cyclic carbonates from epoxide and CO2 in comparison with zero-valent molybdenum complexes. The divalent molybdenum complexes combined with tetrabutylammonium iodide (TBAI) can effectively transform various terminal epoxides and internal epoxides under 30–80 ℃ and 5–10 bar of CO2 pressure. The mechanic experiments by FT-IR and HRMS spectrometry reveal the reaction pathway of binary system in combination of divalent molybdenum complexes with TBAI.

A highly robust cluster-based indium(III)-organic framework with efficient catalytic activity in cycloaddition of CO2 and Knoevenagel condensation.

The efficient catalytic performance displayed by MOFs is decided by an appropriate charge/radius ratio of defect metal sites, large enough solvent-accessible channels and Lewis base sites capable of polarizing substrate molecules. Herein, the solvothermal self-assembly led to a highly robust nanochannel-based framework of {[In4(CPDD)2(μ3-OH)2(DMF)(H2O)2]·2DMF·5H2O}n (NUC-66) with a 56.8% void volume, which is a combination of a tetranuclear cluster [In4(μ3-OH)2(COO)10(DMF)(H2O)2] (abbreviated as {In4}) and a conjugated tetracyclic pentacarboxylic acid ligand of 4,4'-(4-(4-carboxyphenyl)pyridine-2,6-diyl)diisophthalic acid (H5CPDD). To the best of our knowledge, NUC-66 is a rarely reported {In4}-based 3D framework with embedded hierarchical triangular-microporous (2.9 Å) and hexagonal-nanoporous (12.0 Å) channels, which are shaped by six rows of {In4} clusters. After solvent exchange and vacuum drying, the surface of nanochannels in desolvated NUC-66a is modified by unsaturated In3+ ions, Npyridine atoms and μ3-OH groups, all of which display polarization ability towards polar molecules due to their Lewis acidity or basicity. The catalytic experiments performed showed that NUC-66a had high catalytic activity in the cycloaddition reactions of epoxides with CO2 under mild conditions, which should be ascribed to its structural advantages including nanoscale channels, rich bifunctional active sites, large surface areas and chemical stability. Moreover, NUC-66a, as a heterogeneous catalyst, could greatly accelerate the Knoevenagel condensation reactions of aldehydes and malononitrile. Hence, this work confirms that the development of rigid nanoporous cluster-based MOFs built on metal ions with a high charge and large radius ratio will be more likely to realize practical applications, such as catalysis, adsorption and separation of gas, etc.

A stable nanotubular metal–organic framework as heterogeneous catalyst for efficient chemical fixation of CO2

The incorporation of high-density and easily accessible Lewis acid sites is of great significance to obtain high catalytic activity in the CO2cycloaddition reaction of epoxides.

POSS-based polyionic liquids for efficient CO2 cycloaddition reactions under solvent- and cocatalyst-free conditions at ambient pressure.

The conversion of CO2 into value-added chemicals has become an imminent research topic and the cycloaddition of CO2 with a C1 resource to produce cyclic carbonates is a promising pathway for CO2 utilization. Herein, a series of POSS-based polyionic liquids (PILs) were synthesized by the copolymerization of octavinyl polyhedral oligomeric silsesquioxane (POSS) with an imidazolium ion linker. The prepared PILs have the characteristics of hydrogen bond donors, halogen atom sites, stable pore structures, and thermal stability, and are used as heterogeneous catalysts for the cycloaddition of epoxides with carbon dioxide. The effect of linkers on the cycloaddition is investigated by tuning the ratio of POSS units to imidazolium ions. Under the optimized conditions, the conversion of epichlorohydrin can reach 99.18% at atmospheric pressure with neither co-catalysts nor solvents. It is concluded that the reaction of the cycloaddition of epoxides with carbon dioxide follows pseudo-first-order kinetics. Moreover, the presence of the catalysis of PILs leads to a significant decrease in the activation energy barrier for cycloaddition. The catalyst can be facilely recovered due to its high stability, and only a slight decrease in conversion was observed after five successive runs. In addition, the mechanism of PILs catalyzing the cycloaddition reaction of epoxides with CO2 is proposed. This work not only provides a sustainable and green process for CO2 cycloaddition, but also highlights the potential of using PILs for CO2 utilization.

Construction of stable MOFs integrated with open metal sites and amine groups for CO2 capture and conversion

CO2 is deemed as the major greenhouse gas causing global warming over the past several decades. Developing porous solid materials to achieve the capture and utilization of CO2, in this work, two metal–organic frameworks, [Ni2(5H-Ade)(TCPE)(H2O)3]·3DMF·6H2O (Ni-Ade-TCPE), and [Co4.5(HCOO)3(4H-Ade)2(TCPE)(H2O)5]·5DMF·7H2O (Co-Ade-TCPE) have been synthesized by employing mixed adenine and tetrakis(4-carboxyphenyl)ethylene (H4TCPE). The structural analysis demonstrates they are 3D frameworks possessing 1D open channels with –NH2 groups and open metal sites modified surfaces. They display impressive chemical stability in acidic and basic water solutions and high adsorption capacity for CO2. At 70 ​°C and 1 ​bar, Ni-Ade-TCPE exhibits outstanding activity, selectivity, and recyclability in the cycloaddition reaction of epoxides with CO2 due to Lewis acid–base bifunctional sites. Moreover, a reasonable catalytic reaction mechanism has been proposed.

Hexagonal Cages and Lewis Acid-Base Sites in a Metal-Organic Framework for Synergistic CO2 Capture and Conversion under Mild Conditions.

The cycloaddition reaction of carbon dioxide (CO2) is a highly economic solution to becoming carbon-neutral. Herein, we have designed and synthesized a robust zinc(II)-organic framework (Zn-Ade-TCPE) by a function-directed strategy. Zn-Ade-TCPE possesses uncommon hexagonal cages with Lewis acid-base bifunctional sites and displays a high adsorption capacity for CO2. At room temperature and atmospheric pressure, Zn-Ade-TCPE exhibits outstanding activity, selectivity, and recyclability in the cycloaddition reaction of epoxides with CO2 because of the synergistic effect of multiple active sites and confined cavities.

Nanochannel-Based Heterometallic {CoIITbIII}-Organic Framework for Fluorescence Recognition of Tryptophan and Catalytic Cycloaddition of Epoxides with CO2

To pave the way for the salient application of metal–organic frameworks (MOFs) as realistic sensors, it is critical to screen or design the customized functional structure with specified prominent synergistic effects provided by its constituents, voids, specific surfaces, functional sites, etc. This prompts us to study the sensing performance of a honeycomb nanochannel of heterometallic MOFs previously invented. This structure has excellent physical and chemical properties of high specific surface area, good chemical stability, and highly open coexistence of Lewis acid–base sites. In this work, the highly robust sky-blue [CoTb(CO2)6(OH2)]-based heterometallic framework of {[(CH3)2NH2][CoTb(TDP)(H2O)]·3H2O·4DMF}n (NUC-31; H6TDP = 2,4,6-tri(2′,4′-dicarboxyphenyl)pyridine) was synthesized. The results of the fluorescence recognition experiment show that, compared with other amino acids, NUC-31 has an ultrastrong fluorescence quenching for tryptophan with a detection limit as low as 0.11 mM, which means that NUC-31 can be used as a potential fluorescence probe for the targeted detection of tryptophan of ecosystems. In addition, the catalytic experiment results indicated that NUC-31 has high activity for catalyzing the cycloaddition reaction of epoxides with CO2 under 75 °C and 1 atm. It is precisely due to NUC-31 having extremely unsaturated tetracoordinated Co(II) and hepta-coordinated Tb(III) metal ions as well as a high pore volume (65.1%), which makes the catalytic reaction conditions relatively mild. Therefore, this work certificated that nanoporous MOFs assembled from a multifunctional ligand with the highly open coexistent Lewis acid–base sites had a potential application not only in monitoring tryptophan in clinical scenarios but also as an effective heterogeneous catalyst.

Effective Dual-Functional Metal-Organic Framework (DF-MOF) as a Catalyst for the Solvent-Free Cycloaddition Reaction.

A new porous metal-organic framework, [Co (oba) (bpdh)]·(DMF) (TMU-63), containing accessible nitrogen-rich diazahexadiene groups was successfully prepared with the solvothermal assembly of 5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (4-bpdh), 4,4'-oxybis(benzoic) acid (oba), and Co(II) ions. The combination of Lewis basic functional groups and porosity leads to high performance in CO2 adsorption and conversion in the cycloaddition reaction of epoxides under solvent-free conditions. To further enhance the catalytic efficiency of TMU-63, we introduced a highly acidic malonamide ligand into the structure via solvent-assisted ligand exchange (SALE) as a postsynthesis method. Incorporating different percentages of N1,N3-di(pyridine-4-yl) malonamide linker (4-dpm) into TMU-63 created a new porous structure. Powder X-ray diffraction (PXRD) and NMR spectroscopy confirmed that 4-bpdh was successfully replaced with 4-dpm in the daughter MOF, TMU-63S. The catalytic activity of both MOFs was confirmed by significant amounts of CO2 cycloaddition of epoxides under solvent-free conditions. The catalytic cycloaddition activities were found to be well-correlated with the Lewis base/Brønsted acid distributions of the materials examined in the TMU-63S series, showing that the concurrent presence of both acid and base sites was desirable for high catalytic activity. Furthermore, the heterogeneous catalysts could easily be separated out from the reaction mixtures and reused four times without loss of catalytic activity and with no structural deterioration.

Nanoporous {Y2}-Organic Frameworks for Excellent Catalytic Performance on the Cycloaddition Reaction of Epoxides with CO2 and Deacetalization-Knoevenagel Condensation.

Stable metal-organic frameworks containing periodically arranged nanosized pores and active Lewis acid-base active sites are considered as ideal candidates for efficient heterogeneous catalysis. Herein, the exquisite combination of [Y2(CO2)7(H2O)2] cluster (abbreviated as {Y2}) and multifunctional linker of 2,4,6-tri(2,4-dicarboxyphenyl)pyridine (H6TDP) led to a nanoporous framework of {[Y2(TDP)(H2O)2]·5H2O·4DMF}n (NUC-53, NUC = North University of China), which is a rarely reported binuclear three-dimensional (3D) framework with hierarchical tetragonal-microporous (0.78 nm) and octagonal-nanoporous (1.75 nm) channels. The inner walls of these channels are aligned by {Y2} clusters and plentifully coexisted Lewis acid-base sites of YIII ions and Npyridine atoms. Furthermore, NUC-53 has a quite large void volume of ∼65.2%, which is significantly higher than most documented 3D rare-earth-based MOFs. The performed catalytic experiments exhibited that activated NUC-53 showed a high catalytic activity on the cycloaddition reactions of CO2 with styrene oxide under mild conditions with excellent turnover number (TON: 1980) and turnover frequency (TOF: 495 h-1). Moreover, the deacetalization-Knoevenagel condensation reactions of benzaldehyde dimethyl acetal and malononitrile could be efficiently prompted by the heterogeneous catalyst of NUC-53. These findings not only pave the way for the construction of nanoporous MOF based on rare-earth clusters with a variety of catalytic activities but also provide some new insights into the catalytic mechanism.

A nanocaged cadmium-organic framework with high catalytic activity on the chemical fixation of CO2 and deacetalization-knoevenagel condensation

Heterogeneous MOFs catalysts have attracted great attention due to the efficient combination of heterogeneity (easy post-reaction separation and recyclability) and homogeneity (active sites and porosity), which inspire us to explore functional MOFs materials with higher catalytic activity on the chemical fixation of CO2 and deacetalization-Knoevenagel condensation. Herein, the self-assembly of Cd2+ and H6TDP under acidic solvothermal condition generated one cadmium-organic framework of {[(CH3)2NH2]2 [Cd2 (TDP) (H2O)2]⋅3DMF⋅2H2O}n (NUC-29, H6TDP = 2,4,6-tris(2,4-dicarboxyphenyl)pyridine) with nano-caged voids and hierarchical microporous channels, which were built on the combination of two kinds of mononuclear units of [Cd (1) (COO)3(H2O)] and [Cd (2) (COO)3(H2O)]. After the removal of solvent molecules by activation, NUC-29 possesses the coexistence of Lewis acid-base sites on the inner surface of channels including all exposed Cd2+ sites and Npyridine sites, which render it an excellent recyclable heterogeneous catalyst to facilitate the cycloaddition reaction of epoxides with CO2 and deacetalization-Knoevenagel condensation under mild conditions.

4‐(2‐Hydroxyphenyl)imidazolium Salts as Organocatalysts for Cycloaddition of Isocyanates and Epoxides to Yield Oxazolidin‐2‐ones

AbstractNovel salts based on 1,3‐dibutyl‐4‐(2‐hydroxyphenyl)‐1H‐imidazolium bromide or iodide have been developed as bifunctional organocatalysts for the cycloaddition reaction of epoxides and isocyanates to form 3,4‐ and 3,5‐disubstituted oxazolidin‐2‐ones. The molecular structure of these compounds was determined spectroscopically and confirmed by X‐ray diffraction analysis. Imidazolium compounds were screened as catalysts to produce a range of oxazolidinones. The influence of the substituents on the aromatic ring and the counterion of the catalysts on the catalytic activity have been studied, showing that 1,3‐dibutyl‐4‐(5‐fluro‐2‐hydroxyphenyl)‐1H‐imidazolium iodide (4 d) was the most active catalyst for this process in the absence of a cocatalyst.