Terminal Epoxides Research Articles

CO2 conversion into carbonate using pyridinium-based ionic liquids under mild conditions

A sequence of pyridinium-based acidic-ionic liquids (PyAILs) as dual-functional ILs were synthesized and applied as metal-free, stable and homogeneous catalysts to convert economical, renewable, sustainable and inert CO2 into carbonates. These PyAILs were used to synthesize high-efficiency terminal carbonate from epoxide and greenhouse CO2. Various factors that affected the conversion and selectivity of the reaction including the amount of catalyst, chain length of acidic pendant, anion type, reaction temperature, solvent and reaction time were investigated. The special design of the dual acid-functionalized PyAILs, activated CO2 and epoxide, and the reaction was carried out under mild conditions, solvent-free, low pressure with great TOF and excellent conversion and selectivity above 99% for different types of terminal epoxides. A conceivable reaction mechanism was proposed and it was signified that the carboxylic group and halide ions had a synergetic effect on cyclic carbonates synthesis. In addition, PyAILs can be easily separated by simple extraction from the reaction medium.

Covalent Conjugate of Ser-Pro-Cys Tripeptide with PEGylated Comb-Like Polymer as Novel Killer of Human Tumor Cells.

Recently, we detected a previously unknown Ser-Pro-Cys (SPC) tripeptide in the blood serum of multiple sclerosis patients. Its role as a biomarker of the autoimmune disease was suggested, although its origin and real biological activity remained unclear. Here, we created a biocompatible PEGylated comb-like polymer that was used as a platform for covalent immobilization of the SPC, which provided a possibility to explore the biological activity of this tripeptide. This macromolecular conjugate was synthesized via a reaction of the terminal epoxide group of the biocompatible copolymer of dimethyl maleate (DMM) and polyethylene glycol methyl ether methacrylate (PEGMA) with the amino group of the SPC tripeptide. Unexpectedly, the resulting conjugate containing SPC demonstrated anticancer activity in vitro. It possessed pro-apoptotic action toward human tumor cells, while there was no cytotoxic effect of that conjugate toward normal lymphocytes of human peripheral blood. The detected biological effects of the created conjugate inspired us to carry out a thorough study of structural and colloidal-chemical characteristics of this surface-active copolymer containing side PEG chains and a terminal nontoxic synthetic fragment. The copolymer composition, in particular, the content of the peptide fragment, was determined via elemental analysis and NMR spectroscopy. At CMC, it formed polymeric micelle-like structures with a hydrodynamic diameter of 180 ± 60 nm. The conjugation of the peptide fragment to the initial comb-like copolymer caused a change of zeta-potential of the formed micelle-like structures from -0.15 to 0.32 mV. Additional structural modification of the created polymeric nanoplatform was performed via attachment of fluorescein isothiocianate (FITC) dye that permitted monitoring of the behavior of the bioactive SPC-functionalized conjugate in the treated tumor cells. Its penetration into those cells and localization in their cytoplasm were revealed. The principal novelty of this study consists in finding that covalent conjugation of two nontoxic compounds-SPC tripeptide and comb-like PEGylated polymer-led to an unexpected synergy which appeared in the distinct cytotoxic action of the macromolecular complex toward human tumor cells. A potential role of peculiarities of the colloidal-chemical properties of the novel conjugate in its cytotoxic effect are discussed. Thus, synthesized comb-like PEGylated polymers can provide a prospective nanoplatform for drug delivery in anticancer chemotherapy.

New dinuclear chromium complexes supported by thioether-triphenolate ligands as active catalysts for the cycloaddition of CO2 to epoxides

A new family of dinuclear chromium complexes bearing thioether-triphenolate ligands has been developed for the cycloaddition of CO2 with epoxides. The catalytic systems resulting from the combination of complexes 1–3 with tetrabutylammonium chloride (TBAC) show high activity and selectivity for the synthesis of cyclic carbonates with a broad range of substrates including terminal and internal epoxides. Notably, in the case of epichlorohydrin, a TOF up to 4650 h-1 (120 °C, 2 MPa) was recorded, showing one of the highest activity for chromium complexes. In the case of internal epoxides, the reaction proceeds with the retention of the substrate configuration highlighting that the mechanism proceeds through two consecutive SN2 reactions.

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.

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.

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.

Metal-Free N-Doped Carbons for Solvent-Less CO2 Fixation Reactions: A Shrimp Shell Valorization Opportunity.

High anthropogenic CO2 emissions are among the main causes of climate change. Herein, we investigate the use of CO2 for the synthesis of organic cyclic carbonates on metal-free nitrogen-doped carbon catalysts obtained from chitosan, chitin, and shrimp shell wastes, both in batch and in continuous flow (CF). The catalysts were characterized by N2 physisorption, CO2-temperature-programmed desorption, X-ray photoelectron spectroscopy, scanning electron microscopy, and CNHS elemental analysis, and all reactivity tests were run in the absence of solvents. Under batch conditions, the catalyst obtained by calcination of chitin exhibited excellent performance in the conversion of epichlorohydrin (selected as a model epoxide), resulting in the corresponding cyclic carbonate with 96% selectivity at complete conversion, at 150 °C and 30 bar CO2, for 4 h. On the other hand, in a CF regime, a quantitative conversion and a carbonate selectivity >99% were achieved at 150 °C, by using the catalyst obtained from shrimp waste. Remarkably, the material displayed an outstanding stability over a reaction run time of 180 min. The robustness of the synthetized catalysts was confirmed by their good operational stability and reusability: ca. (75 ± 3)% of the initial conversion was achieved/retained by all systems, after six recycles. Also, additional batch experiments proved that the catalysts were successful on different terminal and internal epoxides.

A new nitrogen rich porous organic polymer for ultra-high CO2 uptake and as an excellent organocatalyst for CO2 fixation reactions

The steady increase in the carbon dioxide (CO2) concentration in the atmosphere is causing serious environmental threats like global warming and climate change. Thus to mitigate this issue, suitable adsorbent cum catalyst for high CO2 capture and its fixation to reactive organics is very much essential. In this context, we have synthesized a new porous cross-linked organic polymer DAT-1 through the radical polymerization of divinylbenzene, triallylamine and 2,4,6-tris(allyloxy)− 1,3,5-triazine. DAT-1 possesses high degree of flexibility, with exceptionally large BET surface area (1105 m2g−1) along with bimodal porosity. Furthermore, due to the presence of triazine unit along with tertiary amine moieties inside the porous architecture of DAT-1 with very rich in basic N-sites could make it as an excellent adsorbent for the unprecedented CO2 capture (73.3 mmol g−1 at 30 bar pressure / 273 K). Further, it exhibits excellent catalytic activity for the conversion of simple terminal epoxides to bio-derived sterically hindered epoxides to cyclic carbonate by utilizing carbon dioxide as C1 resource. Basicity associated with N-rich sites at the surface of the high surface area porous organic polymer is responsible for record CO2 capture and its excellent catalytic activity for the CO2 fixation on epoxides for the synthesis of value added cyclic carbonates.

Tetra-Coordinated Boron-Functionalized Phenanthroimidazole-Based Zinc Salen as a Photocatalyst for the Cycloaddition of CO2 and Epoxides.

A unique B-N coordinated phenanthroimidazole-based zinc salen was synthesized. The zinc salen thus synthesized acts as a photocatalyst for the cycloaddition of carbon dioxide with terminal epoxides under ambient conditions. DFT study of the cycloaddition of carbon dioxide with terminal epoxide indicates the preference of the reaction pathway when photocatalyzed by zinc salen. We anticipate that this strategy will help to design new photocatalysts for CO2 fixation.

Ammonium zincates as suitable catalyst for the room temperature cycloaddition of CO2 to epoxides

We have recently shown that simple ammonium ferrates are competent catalyst for the cycloaddition reaction of CO2 to epoxides under moderate reaction conditions (T = 100°C, P(CO2) = 0.8 MPa). We report here that ammonium zincates of general formulae [TBA]2 [ZnX4] (TBA = tetrabutylammonium), simply obtained by treating an ethanolic solution of an appropriate zinc(II) salt with two equivalents of tetrabutylammonium halides, outperform ammonium ferrates in the synthesis of cyclic carbonates under milder reaction conditions (room temperature and atmospheric CO2 pressure). Using [TBA]2[ZnBr4] complex as homogeneous catalyst at 100°C and P(CO2) = 0.8 MPa a 52% conversion of styrene oxide with complete selectivity in styrene carbonate in just 15 min was observed, corresponding to a Turnover frequency (TOF) of 416 h−1. The same catalyst proved to be very active even at room temperature and atmospheric or very moderate CO2 pressures (0.2 MPa), with a quite broad range of substrates, especially in the case of terminal epoxides, with high selectivity towards cyclic carbonate products. The difference in reactivity of terminal and internal epoxides could be exploited using 4-vinylcyclohexene dioxide, where the endocyclic epoxide remained untouched when reacted at room temperature and the formation of the di-carbonate product was observed only at harsher conditions. A multigram scale conversion of propylene oxide was achieved (46 mmol) and the catalyst also proved to be recyclable (3 cycles) by distillation of the product and subsequent addition of fresh reagent, maintaining high conversion values and complete selectivity for propylene carbonate. This simple zinc-based catalytic system, which outperform the recently reported iron-based one by working at much milder conditions, could represent a valuable prospect in both laboratory and industrial scale, combining an inherent cheapness and synthetic easiness that should be deeply considered when the goal is to give value to a waste product as CO2.

Asymmetric Synthesis of Methoxylated Ether Lipids: A Glyceryl Glycidyl Ether Key Building Block Design, Preparation, and Synthetic Application.

The report describes the preparation and use of a double-C3 building block intended as a head group synthon in the synthesis of saturated, mono-, and polyunsaturated 1-O-alkyl-sn-glycerol type methoxylated ether lipids (MELs). The resulting head piece, an enantiopure isopropylidene-protected glyceryl glycidyl ether diastereomer, was accomplished in 49% yield (max 50%) from a 1:1 diastereomeric mixture obtained from R-solketal and racemic epichlorohydrin after treatment with the Jacobsen (S,S)-Co(III)salen catalyst for the hydrolytic kinetic resolution of terminal epoxides. The diol hydrolytic product obtained in 47% yield from the unwanted diastereomer was reconverted into epoxide with an inversion of configuration in a three-step operation involving a highly regioselective lipase. This enabled the recovery of a substantial amount of diastereopure material after a subsequent treatment with the Jacobsen catalyst to furnish the oxirane head piece in altogether 72% yield of higher than 99% diastereomeric purity. A modified synthesis of a monounsaturated 16:1 MEL confirmed the correct stereochemistry and excellent enantiopurity of the head piece and resulted in a dramatic improvement in yields, efficiency, and economy of the synthesis.

Nicotinamide onium halide bidentate hybrid H–bond donor organocatalyst for CO2 fixation

H-bond donor (HBD) and nucleophilic halide cooperating catalysis was well developed in cycloaddition of CO2 with epoxide (CCE) reactions where common strong HBD was prevalent. Here a type of onium halide organocatalyst featured weak C–H and N–H HBD was proposed, designed and evaluated in CCE reactions. Based on biobased nicotinamide, nicotinamidium halide catalyst was prepared by simple alkylation on pyridyl N and/or on amide NH. A mono-alkylated on pyridyl N, 1-octyl nicotinamidium iodide, was screened an optimal catalyst that achieved 96 % yield of carbonate under 1 mol% catalyst loading, 1 atm pressure of CO2, 80 °C, by 24 h. Terminal epoxides were converted successfully into their corresponding cyclic carbonates by 84–99 % yields with 99 % selectivity. Scale-up preparation of styrene carbonate with 100 g of styrene epoxide (by 88 % yield and 98 % selectivity), and preparation of bis(cyclic carbonate) of a commercial diglycidyl ether of bisphenol A (by 79 % yield and 98 % selectivity) showed practical utility. The H-bonding activation between C–H and N–H HBDs with epoxide was validated by 1H NMR titrations. Designed analog catalysts to 1-octyl nicotinamidium iodide with blocked C–H or blocked N–H revealed the bidentate HBDs worked synergistically. The observations of the beneficial outcome of weak pyridium α-C–H and amide N–H H-bond donors proposed a protocol for simple yet efficient biobased H-bond donor organocatalyst development for CCE reactions.

Synthesis of Enantiomeric ω-Substituted Hydroxy Acids from Terminal Epoxides and Alkenes: Functional Building Blocks for Discrete and Sequence-Defined Polyesters

Synthesis of Enantiomeric ω-Substituted Hydroxy Acids from Terminal Epoxides and Alkenes: Functional Building Blocks for Discrete and Sequence-Defined Polyesters

The Use of Sustainable Transition Metals for the Cycloaddition of Epoxides and CO2 under Mild Reaction Conditions

AbstractFollowing green chemistry principles, we present a one pot synthesis of zinc curcumin complex as a homogeneous, sustainable catalyst for cyclic carbonate (CC) synthesis from CO2 and a variety of terminal and internal epoxides under 1 bar CO2 at 60 °C using DMSO as a solvent. Zinc curcumin (Zn‐Cur) complex was identified via 1H/13C NMR and ATR‐FTIR spectroscopies, elemental analysis, ionic conductivity, and quantitative silver nitrate test to confirm a 1 : 1 molar ratio of metal to the ligand. Interestingly, Zn‐Cur showed an outstanding performance in catalysing the synthesis of renewable CCs including dimeric pinene and limonene carbonates. In this context, other metal complexes, including magnesium (MgII), calcium (CaII), and nickel (NiII) complexes showed good to excellent catalytic activity. Furthermore, a plausible reaction mechanism was investigated by density functional theory (DFT) calculations. The reaction was found to be overall exergonic by 39 kJ/mol and the rate determining step was CO2 insertion, which is in good agreement with the experimental findings.

ONSN]-type chromium complexes catalyzed coupling of CO2 with epoxides

A new family of [ONSN]-type chromium complexes bearing hybrid coordination site (O, N, S) have been developed for the coupling of epoxides with CO2. The catalytic system resulting from the complex C2 in combination with TBAB shows the high activity for the cycloaddition of epoxides with CO2 with a broad range of substrates including terminal epoxides and internal epoxides. When catalytic system is switched from complex C2 and TBAB to complex C3 and PPNCl as well as regulation of the reaction conditions, which causes the variation of chemo-selectivity and allows the highly selective synthesis of poly(cyclohexene carbonate) by employing cyclohexene oxide as substrate. The spectroscopic analysis, including UV–vis, FT-IR, and ESIMS, pointed to the formation of new chromium complex, which may be an active species in the reaction.

Bifunctional Rare‐Earth Metal Catalysts for Conversion of CO2 and Epoxides into Cyclic Carbonates

AbstractA series of bifunctional rare‐earth metal complexes bearing zwitterionic amino‐bis(phenolato) ligands were synthesized and structurally characterized. These complexes were applied as catalysts for the synthesis of cyclic carbonates from epoxides and CO2. Lanthanum complex 1La was most active, converting terminal epoxides into the cyclic carbonates in moderate to excellent yields at 40 °C in the presence of 1 bar CO2. The catalyst was also recycled five runs without loss of catalytic activity. The kinetics of the cycloaddition of CO2 and epichlorohydrin (ECH) catalyzed by complex 1La were investigated. According to the Arrhenius equation, the activation barrier for cyclic carbonate formation is determined to be 8.29±0.68 kcal/mol.

Experimental and theoretical insight into the mechanism of CO2 cycloaddition to epoxides catalyzed by ammonium ferrates

Soluble tetrabutylammonium ferrates, [TBA][FeX3Y] (TBA = nBu4N) were synthetized by treating ferric salts (FeX3) with tetrabuthylammoniom halides. Their activity as a stand-alone catalyst in CO2 cycloaddition reactions to epoxides was assessed under solvent free and quite mild reaction conditions (CO2 pressures between 0.4 and 0.8 MPa) and TOF up to 428 h-1 (T = 150 °C) were observed. Good yields of cyclic organic carbonates were obtained, especially with terminal epoxides, without the need of any Lewis base as co-catalyst, with a broad reaction scope. A scale-up reaction on 5 mL of styrene oxide was performed and the robustness of the catalyst was proved up to three recycles in the case of propylene oxide (TON = 594). To shed light on the reaction mechanism, an extensive set of theoretical calculations has been carried out. Iron salts almost annihilate the barrier for the epoxide ring opening and stabilize the first reaction intermediate. Along the same reaction path, chloride proved to be more effective as nucleophile than bromide, and preferentially attacks on the more hindered carbon atom. On the other hand, when no Lewis acid (LA) is present, the rate determining step of the reaction becomes the ring opening of the epoxide. A tight correlation with experimental results was observed.

Catalytic Hydrogenation of Epoxides to Alcohols.

Atom-economical catalytic reactions are a highly enticing strategy because all atoms of the starting materials are incorporated into the products. Catalytic hydrogenation of epoxides to alcohols is an attractive and alternative protocol to other synthetic methodologies for the synthesis of alcohols from alkenes. In the last two decades, catalytic hydrogenation of epoxides to alcohols has made remarkable progress in chemical synthesis. In this review, an overview of the catalytic hydrogenation of both terminal and internal epoxides to the corresponding alcohols is presented. An outline of both homogeneous and heterogeneous hydrogenation of epoxides to the corresponding alcohols is provided. Moreover, the selectivity, efficiency, and the reaction mechanisms of these epoxide hydrogenation reactions are highlighted.

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Preparation of Sequence-Controlled Polyester and Polycarbonate Materials via Epoxide Copolymerization Mediated by Trinuclear Co(III) Complexes

In this study, we design various bi- and trimetallic CoIII complexes as catalysts for the ring-opening copolymerization of phthalic anhydride or CO2 (A) with terminal epoxides (B). A trimetallic catalyst with flexible linking groups prefers consecutive epoxide insertion and the formation of ABn ether sequences. Sequence-controlled polymers with evenly distributed backbone ether groups are produced with a broad substrate scope, resulting in a single-glass transition and tunable properties. This new class of polymers featuring controlled ABn sequences cannot be obtained using traditional catalysts, which tend to favor alternating AB structures. Further, copolymer chains possessing both alternating AB and nonalternating ABn structures could have potential applications as miscibility-promoting agents in mixed polyether/polyester systems.