Ring Opening Of Epoxides Research Articles

Post-synthetic modification of NH2-MIL88B(Fe) with sulfonic acid groups for acid-catalyzed epoxide ring-opening reaction

A new metal–organic framework-based solid acid catalyst was successfully prepared and exploited in the catalytic ring-opening of epoxides.

Ruthenium-Catalyzed Reductive Coupling of Epoxides with Primary Alcohols via Hydrogen Transfer Catalysis

Herein, we report the ruthenium-catalyzed synthesis of β-alkylated secondary alcohols via the regioselective ring-opening of epoxides with feedstock primary alcohols. The reaction utilized alcohol as the carbon source and the terminal reductant. Kinetic and labeling experiments elucidate the hydrogen transfer catalysis that operates via tandem Markovnikov selective transfer hydrogenation of terminal epoxides and hydrogen transfer-mediated cross-coupling of the resulting alcohol with primary alcohol substrates. A broad scope (40 examples including drugs/natural product derivatives) and excellent regioselectivity for a variety of substrates were shown.

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.

A Biomass‐Ligand‐Based Ru(III) Complex as a Catalyst for Cycloaddition of CO2 and Epoxides to Cyclic Carbonates and a Study of the Mechanism

AbstractAiming highly efficient conversion of greenhouse gas CO2 to cyclic carbonates, a biomass Ru(III) Schiff base complex catalyst (SalRu) was constructed by employing a derivative of Lignin degradation (5‐aldehyde vanillin). The SalRu catalyst had a remarkable conversion for epoxides into corresponding cyclic carbonates even at atmospheric pressure of CO2 without the presence of co‐catalyst. As the condition at 120 °C and 2 MPa CO2 the conversion reached to 94 % with selectivity at 99 % after 8 h. 32 % cyclic carbonate production was obtained even under 0.2 MPa CO2 pressure. The epoxide activation and ring opening, CO2 insertion and cyclic carbonate formation were illuminated explicitly through the of characteristic absorption peaks changing, which further providing direct and visual evidence for the mechanism proposing. This study has important theoretical significance for the comprehensive utilization of environmental pollutants and energy.

Calcium(II)‐Catalyzed Chemoselective and Regioselective Epoxide Ring Opening with NH Sulfoximines

AbstractWe describe herein a versatile methodology for the synthesis of 1,2‐sulfoximidoyl ethanols thanks to a Ca(NTf2)2‐catalyzed epoxide ring‐opening with NH sulfoximines in 2‐MeTHF at 90 °C. The reaction is regioselective by an attack on the less hindered position of the epoxides. The chemoselectivity is assessed by competition reactions with other nucleophiles.

Chemical fixation of CO2 with epoxides catalyzed by DBO as activator for the LiI promoted system: A theoretical study

Chemical fixation of carbon dioxide into value-added products is a promising idea. However, its conversion to valuable organic compounds requires highly efficient and safe catalytic system. In this work, the catalytic efficiency of the nontoxic organic base 1, 4‑Diazabicyclo Oct-4-ene (DBO) and its improved result after it has been cooperated with LiI salt have been studied. We gained more insight into the catalytic effects of DBO/LiI on the fixation of CO2 by means of density functional theory calculations using exchange–correlation functional B3LYP through basis sets of LANL2DZ for iodine and 6–31 + G(d,p) for non-iodine atoms. The calculations were carried out in both gas phase and in the presence of water as a solvent. Two reaction mechanisms were proposed and their respective energy was investigated to identify the favorable path for DBO/LiI system catalyzed reaction. Mechanism I is more favorable, in which the ring-opening of epoxide is the rate-limiting step which demands 32.20 kcal mol−1 Gibbs free energy of activation in the gas phase and 20.60 kcal mol-1in water. Lastly, this work validates that DBO in the presence of LiI displayed better catalytic activity for the title reaction and water is a good solvent for DBO/LiI catalyzed cycloaddition of CO2 with an epoxide.

Preparation of miniaturized hydrophilic affinity monoliths: Towards a reduction of non-specific interactions and an increased target protein density

In affinity chromatography, non-specific interactions between the ligands and the affinity column may affect the results, leading to misinterpretations during the investigation of protein-ligand interactions (detection of false positives in ligand screening, lack of specificity in purification). Such non-specific interactions may arise both from the underlying support or from the target protein itself. If the second ones are protein-dependent (and cannot be studied in a general framework), the first ones occur in the same way regardless of the immobilized target. We propose a methodology to identify the origin of such non-specific interactions with the underlying material of the affinity column. This methodology relies on the systematic investigation of the retention behavior of a set of 41 low-molecular weight compounds covering a wide chemical space (net charge, log D, functionality). We first demonstrate that the main source of non-specific interactions on the most commonly used GMA-co-EDMA monolith comes from hydrophobic effects. To reduce such non-specific interactions, we developed a new hydrophilic glycidyl methacrylate-based monolith by replacing the EDMA crosslinker by the more hydrophilic NN’ Methylenebisacrylamide (MBA). Optimization of the synthesis parameters (monomer content, initiation type, temperature) has focused on the reduction of non-specific interaction with the monolithic support while maximizing the amount of protein that can be grafted onto the monolith at the issue of its synthesis. The retention data of the 41 test solutes on the new poly(GMA-co-MBA) monolith shows a drastic reduction of non-specific interactions except for cationic compounds. The particular behavior of cationic compounds is due to their electrostatic interactions with carboxylic groups resulting from the partial acidic hydrolysis of amide groups of MBA during the epoxide ring opening step. So, the ring opening step in acidic media was replaced by a hot water treatment to avoid side reaction on MBA. The new monolith poly(GMA-co-MBA) not only has improved hydrophilic surface properties but also a higher protein density (16 ± 0.8 pmol cm−1 instead of 8 ± 0.3 pmol cm−1). To highlight the benefits of this new hydrophilic monolith for affinity chromatographic studies, frontal affinity chromatography experiments were conducted on these monoliths grafted with con A.

Tuning the Properties of Ester-Based Degradable Polymers by Inserting Epoxides into Poly(ϵ-caprolactone).

A series of ester-ether copolymers were obtained via the reaction between α,ω-dihydroxyl poly(ϵ-caprolactone) (PCL) and ethylene oxide (EO) or monosubstituted epoxides catalyzed by strong phosphazene bases. The two types of monomeric units were distributed in highly random manners due to the concurrence of epoxide ring-opening and fast transesterification reactions. The substituent of epoxide showed an interesting bidirectional effect on the enzymatic degradability of the copolymer. Compared with PCL, copolymers derived from EO exhibited enhanced hydrophilicity and decreased crystallinity which then resulted in higher degradability. For the copolymers derived from propylene oxide and 1,2-butylene oxide, the hydrophobic alkyl pendant groups also allowed lower crystallinity of the copolymers thus higher degradation rates. However, further enlarging the pendant groups by using styrene oxide or 2-ethylhexyl glycidyl ether caused a decrease in the degradation rate, which might be ascribed to the higher bulkiness hindering the contact of ester groups with lipase.

Highly uniform Fe-based MOFs fabricated by mixed-linker strategy for ring-opening of epoxides with alcohols

Highly uniform nano-/micro-rods with a hexagonal shape of Fe-based MOFs (named as Mill-88-hmta) has been synthesized by using mixed-linker method towards the reaction between organic linkers (fumaric acid and hexamethylenetetramine) and Fe(NO3)3 via a solvothermal method. The as-prepared Mill-88-hmta MOFs exhibits excellent performance for ring-opening of epoxides with alcohols, which could be a promising candidate for other ring-opening reactions.

Robust salen-typed Ce-MOFs supported Fe(III) catalyst fabricated by metalloligand strategy for catalytic epoxides with alcohols

A salen-based Ce-MOFs contained rich uncoordinated imine (−CH=N−) groups (termed as N-Ce-salen) has been synthesized by using solution-diffusion method. Furthermore, the as-synthesized N-Ce-salen MOFs served as a “metalloligand” could coordinate with Fe(III) ions forming a MOFs supported Fe(III) ions catalyst via a coordination assisted preparation strategy (named as Fe-N@Ce-salen-CAP). The coordination between the uncoordinated imine (−CH=N−) and Fe(III) ions was characterized by 13C solid-state NMR, N 1s XPS, FT-IR and UV-Vis techniques. The developed Fe-N@Ce-salen-CAP catalyst delivers excellent performance for ring-opening of epoxides with alcohols reaction in comparison with that Ce-salen MOFs (using the same organic linker) without containing uncoordinated imine groups supported Fe(III) catalyst (named as Fe/Ce-salen-IWI) prepared by classic incipient wetness impregnation (IWI) method. Various characterization techniques, e.g. XPS, TEM, HADDF-STEM, were employed to reveal the origin of enhanced performance of Fe-N@Ce-salen-CAP catalyst for ring-opening of epoxides with alcohols. We anticipate that this coordination-assisted preparation strategy may provide a new avenue for synthesis of other highly efficient MOFs supported catalysts for other heterogeneous catalytic reactions.

One-pot non-covalent heterogenization and aromatization of poly(ionic liquids) for metal-/cocatalyst-free and atmospheric CO2 conversion

The intensification of Lewis acidity/basicity of a given heterogeneous catalyst at a molecular level is an advanced approach for boosting CO2 activation and conversion under extremely mild conditions, which, yet remains a great challenge. This work proposes a one-pot strategy for heterogenization and aromatization of homopolymerized ionic liquids (HpolyILs) through dynamic imine assembly with aromatic spacers for boosting CO2 conversion into cyclic carbonates. The aromatization of HpolyILs can be controllably achieved at room temperature, and has been proven to enhance the Lewis acidity of C-2 proton on imidazolium IL for promoting ring-opening of epoxides and facilitate CO2 bending synchronously. The resultant dynamic covalent polyILs exhibit superior catalytic activity and outstanding recyclability for a variety of epoxides under extremely mild conditions (1 atm, 50–90 ºC) without metal/co-catalyst consumption. This work offers a feasible to scale-up approach for tailor-made designing high-efficiency heterogeneous catalysts for CO2 utilization, guiding the precise regulation of acid-base catalysis.

Manganese porphyrins/mesoporous amberlyst 15 nanocomposites: Robust biomimetic catalysts for aqueous oxidation of olefins

In this study, the manganese complexes of N‐methylated meso‐tetra(2‐, 3‐, or 4 pyridyl)porphyrins, immobilized into the pores of the sodium salt of mesoporous amberlyst 15 nanoparticles (nanoAmbSO3Na), nanoAmbSO3@MnT(2‐MePy)P (OAc), nanoAmbSO3@MnT(3‐MePy)P (OAc), and nanoAmbSO3@MnT(4‐MePy)P (OAc), were synthesized and characterized by field‐emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectroscopy (EDX), thermal gravimetric analysis (TGA), nitrogen adsorption/desorption porosimetry analysis, and diffuse reflectance UV–vis spectroscopy. FESEM images revealed a particle size less than ~40 nm for the nanocomposites. The results of BET are in accord with the occupation of the larger pores of the polymer matrix in the case of MnT(2‐MePy)P (OAc) as the most sterically demanding metalloporphyrin of the series, and the smaller pores in the case of the other ones. The immobilized manganese porphyrins were used as catalysts for the oxidation of olefins with sodium periodate in the presence of imidazole (ImH) as the co‐catalyst. The negligible oxidative destructions of the immobilized manganese porphyrins under the oxidative conditions allowed the comparison of the inherent catalytic activity of the metalloporphyrins, decreased as nanoAmbSO3@MnT(4‐MePy)P (OAc) > nanoAmbSO3@MnT(3‐MePy)P (OAc) ≫ nanoAmbSO3@MnT(2‐MePy)P (OAc). Contrary to the general belief that electron‐deficient metalloporphyrins are more efficient catalysts than the electron‐rich ones, the most electron‐deficient metalloporphyrin of the series, that is, nanoAmbSO3@MnT(2‐MePy)P (OAc), showed the lowest catalytic activity. Due to the high oxidative stability of the immobilized manganese porphyrins, ring opening of epoxide competes with the epoxidation reaction to decrease the yield of epoxide at longer reaction times than the optimized one.

Sequence-Reversible Construction of Oxygen-Rich Block Copolymers from Epoxide Mixtures by Organoboron Catalysts.

Switchable catalysis, in combination with epoxide-involved ring-opening (co)polymerization, is a powerful technique that can be used to synthesize various oxygen-rich block copolymers. Despite intense research in this field, the sequence-controlled polymerization from epoxide congeners has never been realized due to their similar ring-strain which exerts a decisive influence on the reaction process. Recently, quaternary ammonium (or phosphonium)-containing bifunctional organoboron catalysts have been developed by our group, showing high efficiency for various epoxide conversions. Herein, we, for the first time, report an operationally simple pathway to access well-defined polyether-block-polycarbonate copolymers from mixtures of epoxides by switchable catalysis, which was enabled through thermodynamically and kinetically preferential ring-opening of terminal epoxides or internal epoxides under different atmospheres (CO2 or N2) using one representative bifunctional organoboron catalyst. This strategy shows a broad substrate scope as it is suitable for various combinations of terminal epoxides and internal epoxides, delivering corresponding well-defined block copolymers. NMR, MALDI-TOF, and gel permeation chromatography analyses confirmed the successful construction of polyether-block-polycarbonate copolymers. Kinetic studies and density functional theory calculations elucidate the reversible selectivity between different epoxides in the presence/absence of CO2. Moreover, by replacing comonomer CO2 with cyclic anhydride, the well-defined polyether-block-polyester copolymers can also be synthesized. This work provides a rare example of sequence-controlled polymerization from epoxide mixtures, broadening the arsenal of switchable catalysis that can produce oxygen-rich polymers in a controlled manner.

Stabilized Lignin Nanoparticles for Versatile Hybrid and Functional Nanomaterials.

Spherical lignin nanoparticles are emerging biobased nanomaterials, but instability and dissolution in organic solvents and aqueous alkali restrict their applicability. Here, we report the synthesis of hydroxymethylated lignin nanoparticles and their hydrothermal curing to stabilize the particles by internal cross-linking reactions. These colloidally stable particles contain a high biobased content of 97% with a tunable particle size distribution and structural stability in aqueous media (pH 3 to 12) and organic solvents such as acetone, ethanol, dimethylformamide, and tetrahydrofuran. We demonstrate that the free phenolic hydroxyl groups that are preserved in the cured particles function as efficient reducing sites for silver ions, giving rise to hybrid lignin-silver nanoparticles that can be used for quick and facile sensing of hydrogen peroxide. The stabilized lignin particles can also be directly modified using base-catalyzed reactions such as the ring-opening of cationic epoxides that render the particles with pH-dependent agglomeration and redispersion properties. Combining scalable synthesis, solvent stability, and reusability, this new class of lignin nanoparticles shows potential for its use in circular biobased nanomaterials.

Mechanochemical synthesis of unsymmetrical salens for the preparation of Co-salen complexes and their evaluation as catalysts for the synthesis of α-aryloxy alcohols via asymmetric phenolic kinetic resolution of terminal epoxides.

In this paper, we report the mechanochemical synthesis of unsymmetrical salens using grinding and ball milling technologies, respectively, both of which were afforded in good yield. The chelating effect of the unsymmetrical salens with zinc, copper, and cobalt was studied and the chiral Co–salen complex 2f was obtained in 98% yield. Hydrolytic kinetic resolution (HKR) of epichlorohydrin with water catalyzed by complex 2f (0.5 mol %) was explored and resulted in 98% ee, suggesting complex 2f could serve as an enantioselective catalyst for the asymmetric ring opening of terminal epoxides by phenols. A library of α-aryloxy alcohols 3 was thereafter synthesized in good yield and high ee using 2f via the phenolic KR of epichlorohydrin.

Esters from castor oil functionalized with aromatic amines as a potential lubricant

AbstractVegetable oils are very promising alternatives to fossil lubricants due to their abundance, low cost, excellent performance, and environmental friendliness. Due to its multifunctional structure, castor oil is an excellent precursor in the synthesis of new biolubricants. However, it showed poor thermal‐oxidative stability and a higher pour point. This study used castor oil fatty acids prepared by transesterification (EHRO), epoxidation (TEPO), and oxirane ring opening with the aromatic amines aniline (ANIL) andp‐anisidine (ANIS). The chemical structure of these oils was verified by1H and13C NMR analysis, and mass spectrometry. Measurements show that the presence of an aromatic amine increases the viscosity resulting in 172 (ANIL) and 199 (ANIS) cSt at 40°C, but reduces viscosity index to 16 and 1, respectively. In addition, the amine groups can scavenge radicals increasing their thermal and oxidative stability. These products do not oxidize copper, and tribological analysis reveals that ANIS has the lowest torque with wear equivalent to commercial mineral lubricant NH‐140.

Simple Trivalent Cobalt Complex-Mediated Copolymerization of Epoxides with Isocyanate: Combining High Activity and Selectivity

Controlled ring-opening copolymerization involving epoxides represents a valuable strategy for the synthesis of oxygenated polymers with unique biodegradability and biocompatibility. In this study, simple trivalent metal complexes, salenM(III)X (salen = N,N′-bis(salicylidine) diamine derivatives, M = Al, Cr, and Co), are employed for copolymerizing p-tosyl isocyanate (TSI) with epoxides, generating perfectly alternating polyurethanes with various structures and tunable properties. The trivalent cobalt acetate complex of N,N′-bis(salicylidine)-o-phenylenediamine bearing 3- and 3′-, 5- and 5′-tert-butyl groups exhibited the highest activity of up to 41,400 h–1 under mild conditions. This single-site catalyst also showed excellent activity and selectivity for copolymer formation even at an extremely low loading of 0.002 mol % without any cocatalyst activator and operated efficiently for various terminal epoxides, affording completely alternating polyurethanes with high molecular weights and narrow polydispersities. Also, this catalyst was tolerant of large quantities of chain transfer agents, thereby allowing control of the molecular weight. Notably, the ring opening of terminal epoxides predominantly occurring at the methylene C–O bond resulted in the formation of stereoregular polyurethanes with more than 96% head-to-tail content.

Strong Electronic Metal-Support Interaction between Iridium Single Atoms and a WO3 Support Promotes Highly Efficient and Robust CO2 Cycloaddition.

The carbon dioxide (CO2 ) cycloaddition of epoxides to cyclic carbonates is of great industrial importance owing to the high economical values of its products. Single-atom catalysts (SACs) have great potential in CO2 cycloaddition by virtue of their high atom utilization efficiency and desired activity, but they generally suffer from poor reaction stability and catalytic activity arising from the weak interaction between the active centers and the supports. In this work, Ir single atoms stably anchored on the WO3 support (Ir1 -WO3 ) are developed with a strong electronic metal-support interaction (EMSI). Superior CO2 cycloaddition is realized in the Ir1 -WO3 catalyst via the EMSI effect: 100% conversion efficiency for the CO2 cycloaddition of styrene oxide to styrene carbonate after 15h at 40 °C and excellent stability with no degradation even after ten reaction cycles for a total of more than 150h. Density functional theory calculations reveal that the EMSI effect results in significant charge redistribution between the Ir single atoms and the WO3 support, and consequently lowers the energy barrier associated with epoxide ring opening. This work furnishes new insights into the catalytic mechanism of CO2 cycloaddition and would guide the design of stable SACs for efficient CO2 cycloaddition reactions.

Mechanistic Basis for the High Enantioselectivity and Activity in the Multichiral Bimetallic Complex-Mediated Enantioselective Copolymerization of meso-Epoxides

The desymmetric ring-opening copolymerization of meso-epoxides with cyclic anhydrides or carbon dioxide (CO2) constitutes a straightforward route to diverse isotactic polymers with two contiguous stereogenic centers. Both high enantioselectivity and excellent activity have been observed in catalyst systems based on biaryl-linked bimetallic complexes with multiple chiralities. In this study, we analyzed the basis for the high enantioselectivity and activity of multichiral bimetallic catalysts by combining experimental observations and theoretical calculations. More specifically, density functional theory calculations of the entire catalytic cycles for the copolymerization of cyclohexene oxide (CHO) and phthalic anhydride (PA) or CO2 demonstrated that ligand exchange was required for CHO coordination, while the ring-opening stage was the rate-determining step. Notably, the M···M separation and the endo dihedral angle of the bimetallic complex changed continuously during copolymer propagation, wherein the cleft opened and closed alternately, demonstrating that a flexible phenol–phenol (biphenol) axis is essential. The carboxylate anion coordinated simultaneously with both metal ions in the dinuclear catalyst reduces the reaction energy barrier during the ligand exchange process significantly. Calculation of the optimal routes for the coordination of CHO to Al(III) or Co(III) ions indicated three possible states. The energy barriers for CHO ring-opening mediated by the (R,R,Ra,R,R)- and (R,R,Sa,R,R)-isomers were calculated in each state, and it was found that epoxide ring-opening was sensitive to the absolute stereochemistries of the biphenol linker and the cyclohexyl diamine skeletons, as well as the phenolate ortho-substituents. The two diastereoisomers have opposite stereoselectivities in the epoxide ring-opening stage, wherein the (R,R,Ra,R,R)-isomer-mediated CHO ring-opening process at the (S)-C–O bond in the most stable CHO coordination state exhibited the lowest energy barrier, therefore determining the enantiomer preference and the copolymerization rate.

Insights into the Mechanism of Carbon Dioxide and Propylene Oxide Ring-Opening Copolymerization Using a Co(III)/K(I) Heterodinuclear Catalyst.

A combined computational and experimental investigation into the catalytic cycle of carbon dioxide and propylene oxide ring-opening copolymerization is presented using a Co(III)K(I) heterodinuclear complex (DeacyA. C.Co(III)/Alkali-Metal(I) Heterodinuclear Catalysts for the Ring-Opening Copolymerization of CO2 and Propylene Oxide. J. Am. Chem. Soc.2020, 142( (45), ), 19150−1916033108736). The complex is a rare example of a dinuclear catalyst, which is active for the copolymerization of CO2 and propylene oxide, a large-scale commercial product. Understanding the mechanisms for both product and byproduct formation is essential for rational catalyst improvements, but there are very few other mechanistic studies using these monomers. The investigation suggests that cobalt serves both to activate propylene oxide and to stabilize the catalytic intermediates, while potassium provides a transient carbonate nucleophile that ring-opens the activated propylene oxide. Density functional theory (DFT) calculations indicate that reverse roles for the metals have inaccessibly high energy barriers and are unlikely to occur under experimental conditions. The rate-determining step is calculated as the ring opening of the propylene oxide (ΔGcalc† = +22.2 kcal mol–1); consistent with experimental measurements (ΔGexp† = +22.1 kcal mol–1, 50 °C). The calculated barrier to the selectivity limiting step, i.e., backbiting from the alkoxide intermediate to form propylene carbonate (ΔGcalc† = +21.4 kcal mol–1), is competitive with the barrier to epoxide ring opening (ΔGcalc† = +22.2 kcal mol–1) implicating an equilibrium between alkoxide and carbonate intermediates. This idea is tested experimentally and is controlled by carbon dioxide pressure or temperature to moderate selectivity. The catalytic mechanism, supported by theoretical and experimental investigations, should help to guide future catalyst design and optimization.