Showing papers on "Epoxide published in 2022"

Controlling covalent chemistry on graphene oxide

Abstract: Graphene has attracted intensive research interest in many fields, owing to its remarkable physicochemical properties. Nevertheless, its low dispersibility in most organic solvents and in water, and its tendency to aggregate, prevent full exploitation of its properties. Graphene oxide (GO) is an alternative material that exhibits high dispersibility in polar solvents. GO contains abundant oxygen-containing groups, mainly epoxide and hydroxy groups, which can be further chemically derivatized. However, because of GO’s high reactivity, several reactions may occur simultaneously, often leading to uncontrolled GO derivatives. Moreover, because GO can be easily reduced, functionalization should be performed under mild conditions. In this Review, we discuss the chemical reactivity of GO and explore issues that hamper precise control of its functionalization, such as its instability, the lack of a well-defined chemical structure and the presence of impurities. We focus on strategies for the selective derivatization of the oxygenated groups and C=C bonds, along with the challenges for unambiguous characterization of the resulting structures. We briefly review applications of GO materials, relating their chemistry and nanostructure to desired physical properties and function, and chart future directions for improving the control of GO chemistry. Graphene oxide (GO) has attracted intensive research interest, owing to remarkable physicochemical properties. Nevertheless, its high chemical reactivity and low stability may lead to uncontrolled GO derivatives. The chemistry of GO can be controlled by selective derivatization of the oxygenated groups and C=C bonds and by appropriate characterization.

One-step synthesis of sequence-controlled multiblock polymers with up to 11 segments from monomer mixture

Abstract: Switchable polymerization holds considerable potential for the synthesis of highly sequence-controlled multiblock. To date, this method has been limited to three-component systems, which enables the straightforward synthesis of multiblock polymers with less than five blocks. Herein, we report a self-switchable polymerization enabled by simple alkali metal carboxylate catalysts that directly polymerize six-component mixtures into multiblock polymers consisting of up to 11 blocks. Without an external trigger, the catalyst polymerization spontaneously connects five catalytic cycles in an orderly manner, involving four anhydride/epoxide ring-opening copolymerizations and one L-lactide ring-opening polymerization, creating a one-step synthetic pathway. Following this autotandem catalysis, reasonable combinations of different catalytic cycles allow the direct preparation of diverse, sequence-controlled, multiblock copolymers even containing various hyperbranched architectures. This method shows considerable promise in the synthesis of sequentially and architecturally complex polymers, with high monomer sequence control that provides the potential for designing materials.

One-step synthesis of sequence-controlled multiblock polymers with up to 11 segments from monomer mixture

Abstract: Switchable polymerization holds considerable potential for the synthesis of highly sequence-controlled multiblock. To date, this method has been limited to three-component systems, which enables the straightforward synthesis of multiblock polymers with less than five blocks. Herein, we report a self-switchable polymerization enabled by simple alkali metal carboxylate catalysts that directly polymerize six-component mixtures into multiblock polymers consisting of up to 11 blocks. Without an external trigger, the catalyst polymerization spontaneously connects five catalytic cycles in an orderly manner, involving four anhydride/epoxide ring-opening copolymerizations and one L-lactide ring-opening polymerization, creating a one-step synthetic pathway. Following this autotandem catalysis, reasonable combinations of different catalytic cycles allow the direct preparation of diverse, sequence-controlled, multiblock copolymers even containing various hyperbranched architectures. This method shows considerable promise in the synthesis of sequentially and architecturally complex polymers, with high monomer sequence control that provides the potential for designing materials.

Chemical Recycling of Poly(Cyclohexene Carbonate) Using a Di‐MgII Catalyst

Abstract: Abstract Chemical recycling of polymers to true monomers is pivotal for a circular plastics economy. Here, the first catalyzed chemical recycling of the widely investigated carbon dioxide derived polymer, poly(cyclohexene carbonate), to cyclohexene oxide and carbon dioxide is reported. The reaction requires dinuclear catalysis, with the di‐MgII catalyst showing both high monomer selectivity (>98 %) and activity (TOF=150 h−1, 0.33 mol %, 120 °C). The depolymerization occurs via a chain‐end catalyzed depolymerization mechanism and DFT calculations indicate the high selectivity arises from Mg‐alkoxide catalyzed epoxide extrusion being kinetically favorable compared to cyclic carbonate formation.

Cooperative Activation of CO2 and Epoxide by a Heterobinuclear Al-Fe Complex via Radical Pair Mechanisms.

Abstract: Activation of inert molecules like CO2 is often mediated by cooperative chemistry between two reactive sites within a catalytic assembly, the most common form of which is Lewis acid/base bifunctionality observed in both natural metalloenzymes and synthetic systems. Here, we disclose a heterobinuclear complex with an Al-Fe bond that instead activates CO2 and other substrates through cooperative behavior of two radical intermediates. The complex Ldipp(Me)AlFp (2, Ldipp = HC{(CMe)(2,6-iPr2C6H3N)}2, Fp = FeCp(CO)2, Cp = η5-C5H5) was found to insert CO2 and cyclohexene oxide, producing LdippAl(Me)(μ:κ2-O2C)Fp (3) and LdippAl(Me)(μ-OC6H10)Fp (4), respectively. Detailed mechanistic studies indicate unusual pathways in which (i) the Al-Fe bond dissociates homolytically to generate formally AlII and FeI metalloradicals, then (ii) the metalloradicals add to substrate in a pairwise fashion initiated by O-coordination to Al. The accessibility of this unusual mechanism is aided, in part, by the redox noninnocent nature of Ldipp that stabilizes the formally AlII intermediates, instead giving them predominantly AlIII-like physical character. The redox noninnocent nature of the radical intermediates was elucidated through direct observation of LdippAl(Me)(OCPh2) (22), a metalloradical species generated by addition of benzophenone to 2. Complex 22 was characterized by X-band EPR, Q-band EPR, and ENDOR spectroscopies as well as computational modeling. The "radical pair" pathway represents an unprecedented mechanism for CO2 activation.

Conversion of CO2 with epoxides to cyclic carbonates catalyzed by amino acid ionic liquids at room temperature

Abstract: CO2 utilization plays an important role in rational use of carbon resources and reduction of carbon emissions. It is still a challenge to achieve efficient CO2 utilization by amino acid ionic liquids (AAILs) under room temperature and atmospheric pressure with cocatalyst- and solvent-free conditions. Herein, the newly developed AAILs including 1,1,3,3-tetramethylguanidine cation ([HTMG]+) together with both amino acid and halogen as anions, were simply synthesized by neutralization reaction. Under mild conditions (30 °C, 20 h and 1 MPa CO2), the cycloaddition reaction of CO2 and propylene oxide could be efficiently catalyzed by [HTMG][His][I] with 99 % propylene carbonate yield and selectivity in the absence of additional solvent and cocatalyst. Notably, even at room temperature and atmospheric pressure for 72 h, [HTMG][His][I] also displayed 96 % yield and 99 % selectivity due to the cooperation of [HTMG]+, [His]2– and [I]–. Meanwhile, [HTMG][His][I] performed excellent universality of various epoxides and reusability. Based on the characterization results of 1H and 13C NMR, it was verified that propylene oxide and CO2 were simultaneously activated by the functional groups in [HTMG][His][I]. Hence, the reaction mechanism for CO2 cycloaddition with epoxide catalyzed by [HTMG][His][I] was proposed. This work provided a simple strategy to prepare sustainable AAILs for efficient CO2 utilization under very mild conditions of room temperature and atmospheric pressure (even the low CO2 concentration at simulated flue gases).

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

Abstract: 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 15 h at 40 °C and excellent stability with no degradation even after ten reaction cycles for a total of more than 150 h. 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.

A review of fatty epoxide ring opening reactions: Chemistry, recent advances, and applications

Abstract: Fatty epoxides are produced from the corresponding alkenes by oxidation in the presence of peracids or other oxidants. The classic method is the Prilezhaev epoxidation in which peracids are generated by in situ oxidation of formic or acetic acids with hydrogen peroxide. Epoxidized vegetable oils and esters are used directly as biobased plasticizers and stabilizers for poly(vinyl chloride) or as important platform chemicals for the oleochemical industry. Nucleophilic attack at the oxirane moiety affords a variety of ring opened monomeric or polymeric products, which in many cases undergo further synthetic modification to yield finished products. The most common nucleophiles include water, alcohols, carboxylic acids, acid anhydrides, and amines, although numerous others can also lead to valuable functionalized fatty derivatives. This review summarizes the chemistry of fatty epoxide ring opening reactions as well as applications of the resultant products. Literature from the last 20 years will be emphasized, although older publications of particular significance will be included. Important applications include biobased lubricants as well as polyols for subsequent production of polyurethanes. In addition, ring-opening reactions hitherto unreported on fatty oxiranes will be suggested to facilitate further advancements in the chemistry and utility of fatty epoxides. Finally, interest in fatty epoxides and their consequent products will continue to grow due to the simplicity, efficiency, and versatility of oxirane formation and ring opening as well as the continued societal transition away from petroleum to a sustainable, circular, low-carbon, and biobased economy.

Efficient and Selective Chemical Recycling of CO2-based Alicyclic Polycarbonates via Catalytic Pyrolysis.

Abstract: Chemical recycling of polymers to their constituent monomers is the foremost challenge in building a sustainable circular plastics economy. Here, we reported a strategy for highly efficient depolymerization of various CO 2 -based alicyclic polycarbonates to epoxide monomers in solvent free condition by a simple Cr III -Salen complex mediated catalytic pyrolysis process. The chemical recycling of the widely studied poly(cyclohexene carbonate) exhibits excellent reactivity (TOF up to 3000 h -1 , 0.1 mol% catalyst loading) and high epoxide monomer selectivity (>99%). Mechanistic investigation reveals that the process proceeds in a sequential fashion via a trans -carbonate intermediate.

Synergic Heterodinuclear Catalysts for the Ring-Opening Copolymerization (ROCOP) of Epoxides, Carbon Dioxide, and Anhydrides

Abstract: Conspectus The development of sustainable plastic materials is an essential target of chemistry in the 21st century. Key objectives toward this goal include utilizing sustainable monomers and the development of polymers that can be chemically recycled/degraded. Polycarbonates synthesized from the ring-opening copolymerization (ROCOP) of epoxides and CO2, and polyesters synthesized from the ROCOP of epoxides and anhydrides, meet these criteria. Despite this, designing efficient catalysts for these processes remains challenging. Typical issues include the requirement for high catalyst loading; low catalytic activities in comparison with other commercialized polymerizations; and the requirement of costly, toxic cocatalysts. The development of efficient catalysts for both types of ROCOP is highly desirable. This Account details our work on the development of catalysts for these two related polymerizations and, in particular, focuses on dinuclear complexes, which are typically applied without any cocatalyst. We have developed mechanistic hypotheses in tandem with our catalysts, and throughout the Account, we describe the kinetic, computational, and structure–activity studies that underpin the performance of these catalysts. Our initial research on homodinuclear M(II)M(II) complexes for cyclohexene oxide (CHO)/CO2 ROCOP provided data to support a chain shuttling catalytic mechanism, which implied different roles for the two metals in the catalysis. This mechanistic hypothesis inspired the development of mixed-metal, heterodinuclear catalysts. The first of this class of catalysts was a heterodinuclear Zn(II)Mg(II) complex, which showed higher rates than either of the homodinuclear [Zn(II)Zn(II) and Mg(II)Mg(II)] analogues for CHO/CO2 ROCOP. Expanding on this finding, we subsequently developed a Co(II)Mg(II) complex that showed field leading rates for CHO/CO2 ROCOP and allowed for unique insight into the role of the two metals in this complex, where it was established that the Mg(II) center reduced transition state entropy and the Co(II) center reduced transition state enthalpy. Following these discoveries, we subsequently developed a range of heterodinuclear M(III)M(I) catalysts that were capable of catalyzing a broad range of copolymerizations, including the ring-opening copolymerization of CHO/CO2, propylene oxide (PO)/CO2, and CHO/phthalic anhydride (PA). Catalysts featuring Co(III)K(I) and Al(III)K(I) were found to be exceptionally effective for PO/CO2 and CHO/PA ROCOP, respectively. Such M(III)M(I) complexes operate through a dinuclear metalate mechanism, where the M(III) binds and activates monomers while the M(I) species binds the polymer change in close proximity to allow for insertion into the activated monomer. Our research illustrates how careful catalyst design can yield highly efficient systems and how the development of mechanistic understanding aids this process. Avenues of future research are also discussed, including the applicability of these heterodinuclear catalysts in the synthesis of sustainable materials.

Enhancing the Catalytic Performance of Group I, II Metal Halides in the Cycloaddition of CO2 to Epoxides under Atmospheric Conditions by Cooperation with Homogeneous and Heterogeneous Highly Nucleophilic Aminopyridines: Experimental and Theoretical Study.

Abstract: Compared to metal-organic complexes and transition-metal halides, group I metal halides are attractive catalysts for the crucial cycloaddition reaction of CO2 to epoxides as they are ubiquitously available and inexpensive, have a low molecular weight, and are not based on (potentially) endangered metals, especially for the case of sodium and potassium. Nevertheless, given their low intrinsic catalytic efficiency, they require the assistance of additional catalytic moieties. In this work, we show that by exploiting the high nucleophilicity of opportunely designed aminopyridines, catalytic systems based on alkaline metals can be formed, which allow the cycloaddition of CO2 to epoxides to proceed under atmospheric pressure at moderate temperatures. Importantly, the aminopyridine nucleophiles can be applied in their heterogenized form, leading to a recyclable catalytic system. An investigation of the reaction mechanism by density functional theory calculations shows that metal halide complexes and nucleophilic pyridines can work as a dual cooperative catalytic system where the use of aminopyridines leads to lower energy barriers for the opening of the epoxide ring, and halide-adducts are involved in the subsequent steps of CO2 insertion and ring closure.

Mechanism-Inspired Upgradation of Phosphonium-Containing Organoboron Catalysts for Epoxide-Involved Copolymerization and Homopolymerization

Abstract: The dynamic Lewis multicore system (DLMCS) which integrates the Lewis acidic boron center(s) and an ammonium salt in one molecule has shown good catalytic performance in polymer synthesis. Inspired by the insightful intramolecular ammonium cation assisted mechanism, herein, we communicated a superior organoboron system by replacing a nitrogen atom with a phosphorus atom. The upgraded mono-, di-, and trinuclear organoboron catalysts show significantly improved catalytic performance and heat resistance for versatile epoxide-involved transformations, including ring-opening copolymerization of epoxides and cyclic anhydrides, copolymerization of CO2 and epoxides, and ring-opening polymerization of epoxides. 11B NMR, single-crystal X-ray diffraction, and DFT results imply that the replacing nitrogen with phosphorus in an onium cation led to an effective epoxide activation and nucleophilic attack of the counterion on the activated epoxide, which remarkably shortened the initiation period and accelerated chain expansion, resulting in the obvious improvement of the activity. The upgraded phosphonium-containing organoboron system combined with the mechanism study and insightful understanding would be instructive in designing advanced metal-free catalysts.

Switchable Polymerization Organocatalysis: From Monomer Mixtures to Block Copolymers.

Abstract: One-pot production of sequence-controlled block copolymer from mixed monomers is a crucial but rarely reached goal. Using a switchable Lewis-Pair organocatalyst, we have accomplished sequence-selective polymerization from a mixture of O -carboxyanhydride (OCA) and epoxide. Polymerization of OCA monomer occurs first and exclusively because of its exceedingly high polymerizability. When OCA is fully consumed, alternating copolymerization of epoxide and CO 2 liberated in OCA polymerization is triggered from the termini of the first block. The two polymerizations thus occur tandemly, both in chemoselective fashions, so that sequence-controlled block polymer with up to 99% CO 2 conversion is furnished in this one-pot protocol. Calculations and experimental results demonstrate a chemoselective and cooperative mechanism, where the high polymerizability of OCA monomers guarantees exquisite sequence selectivity and the cooperative decarboxylation partly arose from the stabilization effect by triethylborane, facilitates the smooth transformation of the chain end from carbonate to alkoxide.

Direct Propylene Epoxidation with Molecular Oxygen over Cobalt-Containing Zeolites.

Abstract: Direct propylene epoxidation with molecular oxygen is a dream reaction with 100% atom economy, but aerobic epoxidation is challenging because of the undesired over-oxidation and isomerization of epoxide products. Herein, we report the construction of uniform cobalt ions confined in faujasite zeolite, namely, Co@Y, which exhibits unprecedented catalytic performance in the aerobic epoxidation of propylene. Propylene conversion of 24.6% is achieved at propylene oxide selectivity of 57% at 773 K, giving a state-of-the-art propylene oxide production rate of 4.7 mmol/gcat/h. The catalytic performance of Co@Y is very stable, and no activity loss can be observed for over 200 h. Spectroscopic analyses reveal the details of molecular oxygen activation on isolated cobalt ions, followed by interaction with propylene to produce epoxide, in which the Co2+-Coδ+-Co2+ (2 < δ < 3) redox cycle is involved. The reaction pathway of propylene oxide and byproduct acrolein formation from propylene epoxidation is investigated by density functional theory calculations, and the unique catalytic performance of Co@Y is interpreted. This work presents an explicit example of constructing specific transition-metal ions within the zeolite matrix toward selective catalytic oxidations.

Heterodinuclear Mg(II)M(II) (M=Cr, Mn, Fe, Co, Ni, Cu and Zn) Complexes for the Ring Opening Copolymerization of Carbon Dioxide/Epoxide and Anhydride/Epoxide

Abstract: Abstract The catalysed ring opening copolymerizations (ROCOP) of carbon dioxide/epoxide or anhydride/epoxide are controlled polymerizations that access useful polycarbonates and polyesters. Here, a systematic investigation of a series of heterodinuclear Mg(II)M(II) complexes reveals which metal combinations are most effective. The complexes combine different first row transition metals (M(II)) from Cr(II) to Zn(II), with Mg(II); all complexes are coordinated by the same macrocyclic ancillary ligand and by two acetate co‐ligands. The complex syntheses and characterization data, as well as the polymerization data, for both carbon dioxide/cyclohexene oxide (CHO) and endo‐norbornene anhydride (NA)/cyclohexene oxide, are reported. The fastest catalyst for both polymerizations is Mg(II)Co(II) which shows propagation rate constants (k p) of 34.7 mM−1 s−1 (CO2) and 75.3 mM−1 s−1 (NA) (100 °C). The Mg(II)Fe(II) catalyst also shows excellent performances with equivalent rates for CO2/CHO ROCOP (k p=34.7 mM−1 s−1) and may be preferable in terms of metallic abundance, low cost and low toxicity. Polymerization kinetics analyses reveal that the two lead catalysts show overall second order rate laws, with zeroth order dependencies in CO2 or anhydride concentrations and first order dependencies in both catalyst and epoxide concentrations. Compared to the homodinuclear Mg(II)Mg(II) complex, nearly all the transition metal heterodinuclear complexes show synergic rate enhancements whilst maintaining high selectivity and polymerization control. These findings are relevant to the future design and optimization of copolymerization catalysts and should stimulate broader investigations of synergic heterodinuclear main group/transition metal catalysts.

Poly(ionic liquid) materials tailored by carboxyl groups for the gas phase-conversion of epoxide and CO2 into cyclic carbonates

Abstract: Carbon dioxide (CO 2 ) is an important C1 resource, and the preparation of cyclocarbonate by catalyzing CO 2 and epoxides is a nature-friendly route to utilize. In this study, polymer ionic liquid materials (PILMs) were prepared by copolymerizing the vinylimidazole-based ionic liquids (ILs) as monomer with carbonyl-rich copolymer monomer methyl methacrylate (MMA) and crosslinking agent ethylene glycol dimethacrylate (EGDMA), to enhance the affinity of PILMs for CO 2 and PO. Then, epoxides and CO 2 were converted to cyclic carbonates using PILMs by the gas-liquid reaction (GLR) and the gas phase-conversion progress (GCP). Amongst those polymer ionic liquid materials, the PILM containing carboxypropyl group (PILM-VCPImBr) exhibited the performance with the propylene carbonate (PC) yield of 96.7% (at 130 °C, 3 MPa CO 2 , reaction time 3 h) by GLR. And the yield of PC reached 94.2% (at 130 °C, 2 MPa CO 2 , reaction time 3 h) by GCP, which was the same as that of GLR. The excellent catalytic activity can be attributed to the fact that the PILMs fully dispersed the active sites and were rich in pores, which could effectively catalyze propylene oxide (PO) and CO 2 to generate PC. Finally, 1 H NMR spectra showed that VCPImBr and PO formed strong hydrogen bonds to participate the ring-opening process of epoxides, and a possible catalytic mechanism of H-bond synergistic effect was proposed. This article provides a novel strategy for designing both stable and nature-friendly catalysts in the CO 2 transformation, and proposes a new method for cyclic carbonate conversion. • Polymeric ionic liquid materials containing high active sites were prepared by photoinitiated polymerization. • The catalytic effect was satisfactory, due to the synergistic effect of carboxyl group and Br - . • The catalytic material had good effect in the gas phase-conversion process (GCP). • The H-bond synergistic effect was verified by 1 H NMR. • A possible catalytic mechanism was proposed.

Surface science approach to the heterogeneous cycloaddition of CO2 to epoxides catalyzed by site-isolated metal complexes and single atoms: A review

Abstract: The cycloaddition of CO2 to epoxides to afford cyclic organic carbonates is an increasingly relevant non-reductive strategy to convert CO2 to useful products able to serve as high-boiling solvents, chemical intermediates, and monomers for the preparation of more sustainable polymers. The development of efficient and robust heterogeneous catalysts for such transformation is, therefore, crucial and can be carried out by several strategies that often require the preparation of sophisticated and/or expensive organic networks, linkers, or compounds. A different approach to the preparation of heterogeneous catalysts for CO2-epoxide coupling is by applying surface science methodologies to graft molecular fragments or single atoms on various supports leading to well-defined active sites. In this context, surface organometallic chemistry (SOMC), along with comparable methodologies, is a valuable approach for the preparation of efficient, single-site Lewis acids and catalysts for the target cycloaddition reaction on metal oxides, whereas, other grafting methodologies, can be applied to prepare analogous catalysts on different kinds of surfaces. Finally, we discuss very recent advances in the application of surface methodologies for the preparation of single atom catalysts as an increasingly relevant approach towards highly active Lewis acids for the cycloaddition of CO2 to epoxides. Overall, we show that Lewis acids and catalysts prepared by facile surface methodologies hold significant potential for future application in the synthesis of cyclic carbonates from CO2.

Chiral Phosphoric Acid Catalyzed Conversion of Epoxides into Thiiranes: Mechanism, Stereochemical Model, and New Catalyst Design

Abstract: Computations and experiments leading to new chiral phosphoric acids (CPAs) for epoxide thionations are reported. Density functional theory calculations reveal the mechanism and origin of the enantioselectivity of such CPA-catalyzed epoxide thionations. The calculated mechanistic information was used to design new efficient CPAs that were tested experimentally and found to be highly effective. Bulky ortho-substituents on the 3,3'-aryl groups of the CPA are important to restrict the position of the epoxide in the key transition states for the enantioselectivity-determining step. Larger para-substituents significantly improve the enantioselectivity of the reaction.

One-Pot Synthesis of Strain-Release Reagents from Methyl Sulfones.

Abstract: Sulfone-substituted bicyclo[1.1.0]butanes and housanes have found widespread application in organic synthesis due to their bench stability and high reactivity in strain-releasing processes in the presence of nucleophiles or radical species. Despite their increasing utility, their preparation typically requires multiple steps in low overall yield. In this work, we report an expedient and general one-pot procedure for the synthesis of 1-sulfonylbicyclo[1.1.0]butanes from readily available methyl sulfones and inexpensive epichlorohydrin via the dialkylmagnesium-mediated formation of 3-sulfonylcyclobutanol intermediates. Furthermore, the process was extended to the formation of 1-sulfonylbicyclo[2.1.0]pentane (housane) analogues when 4-chloro-1,2-epoxybutane was used as the electrophile instead of epichlorohydrin. Both procedures could be applied on a gram scale with similar efficiency and are shown to be fully stereospecific in the case of housanes when an enantiopure epoxide was employed, leading to a streamlined access to highly valuable optically active strain-release reagents.

Guanidyl-implanted UiO-66 as efficient catalysts for enhanced conversion of carbon dioxide into cyclic carbonates

Abstract: The development of heterogeneous catalysts for promoting epoxide cycloaddition with carbon dioxide is highly desirable for recycling CO2 and achieving the goal of carbon neutrality. Herein, we designed and synthesized...

Total Syntheses of Scabrolide A and Nominal Scabrolide B

Abstract: The marine natural product scabrolide A was obtained by isomerization of the vinylogous 1,4-diketone entity of nominal scabrolide B as the purported pivot point of the biosynthesis of these polycyclic norcembranoids. Despite the success of this maneuver, the latter compound itself turned out not to be identical with the natural product of that name. The key steps en route to the carbocyclic core of these targets were a [2,3]-sigmatropic rearrangement of an allylic sulfur ylide to forge the overcrowded C12–C13 bond, an RCM reaction to close the congested central six-membered ring, and a hydroxy-directed epoxidation/epoxide opening/isomerization sequence to set the “umpoled” 1,4-dicarbonyl motif and the correct angular configuration at C12.

Solid-State Chemical Recycling of Polycarbonates to Epoxides and Carbon Dioxide Using a Heterodinuclear Mg(II)Co(II) Catalyst

Abstract: Polymer chemical recycling to monomers (CRM) could help improve polymer sustainability, but its implementation requires much better understanding of depolymerization catalysis, ensuring high rates and selectivity. Here, a heterodinuclear [Mg(II)Co(II)] catalyst is applied for CRM of aliphatic polycarbonates, including poly(cyclohexene carbonate) (PCHC), to epoxides and carbon dioxide using solid-state conditions, in contrast with many other CRM strategies that rely on high dilution. The depolymerizations are performed in the solid state giving very high activity and selectivity (PCHC, TOF = 25700 h–1, CHO selectivity >99 %, 0.02 mol %, 140 °C). Reactions may also be performed in air without impacting on the rate or selectivity of epoxide formation. The depolymerization can be performed on a 2 g scale to isolate the epoxides in up to 95 % yield with >99 % selectivity. In addition, the catalyst can be re-used four times without compromising its productivity or selectivity.

Near-Infrared Photothermal Catalysis for Enhanced Conversion of Carbon Dioxide under Mild Conditions.

Abstract: Enhanced conversion of carbon dioxide (CO2) for cycloaddition with epoxide derivatives is highly desired in organic synthesis and green chemistry, yet it is still a challenge to obtain satisfactory activity under mild reaction conditions of temperature and pressure. For this purpose, an unexploited strategy is proposed here by incorporating near-infrared (NIR) photothermal properties into multicomponent catalysts. Through the electrostatic adsorption of Co- or Ce-substituted polyoxometalate (POM) clusters on the surface of graphene oxide (GO) with covalently grafted polyethyleneimine (PEI), a series of composite catalysts POMs@GO-PEI are prepared. The structural and property characterizations demonstrate the synergistic advantages of the catalysts bearing Lewis acids and bases and local NIR photothermal heating from the GO matrix for dramatically enhanced CO2 cycloaddition. Noticeably, while the turnover frequency increases up to 2718 h-1, the heterogeneous catalysts exhibit photothermal stability and recyclability. With this method, the onsite NIR photothermal transformation becomes extendable to more green reaction processes.