Electrochemical ring-opening carboxylation of cyclic carbonate with carbon dioxide.

Electroreductive ring-opening carboxylation of styrene carbonates with CO2 to achieve dicarboxylic acids and/or ß-hydroxy acids has been developed via the selective cleavage of the C(sp3)-O bond in cyclic carbonates. The product selectivity is probably determined by the stability and reactivity of the key benzylic radical and carbanion intermediate.

Innovative Approach to Chiral Polyurethanes: Asymmetric Copolymerization with Isocyanates.

The introduction of nitrogen-containing functional groups to chiral polymer backbones enables the tailoring of physical properties and offers opportunities for further post-polymerization modification. However, the substrate scope of such polymers is extremely limited because monomers having nitrogen-containing groups can change coordination state with respect to the metal centers, thus decreasing the activity and enantioselectivity and even poisoning the catalyst completely. In this paper, we report our attempts to carry out the asymmetric copolymerization of meso-epoxide with highly reactive isocyanates. In particular, we found that biphenol-linked bimetallic Co(III) complexes with multiple chiral centers are very efficient in catalyzing this asymmetric copolymerization reaction, affording optically active polyurethanes with a completely alternating nature and a high enantioselectivity of up to 94 % ee. Crucially, we identified that the steric hindrance at the phenolate ortho position of the ligand strongly influences the catalytic activity and product enantioselectivity. In addition, density functional theory calculations revealed that the highly sterically bulky substituents change the mechanism from bimetallic to monometallic, and result in the unexpected inversion of the chiral induction direction. Moreover, the high stereoregularity of the produced polyurethanes enhances their thermal stability, and they can be selectively decomposed into oxazolidinones. This study offers a versatile methodology for the synthesis of chiral polymers containing nitrogen functionalities.

Stereoregular poly(2-phenylthiirane) via cationic ring-opening polymerization.

Herein, we describe an effective strategy for synthesizing polythioethers with a well-defined structure through the cationic polymerization of thiirane with electron-withdrawing substituents. This strategy allows for precisely controlling the regio- and stereochemistry of the ring-opening polymerization of 2-phenylthiirane, thus allowing for producing poly(2-phenylthiirane) with high stereoregularity using enantiomeric pure thiirane.

Iron-catalyzed selective construction of indole derivatives via oxidative C(sp3)-H functionalization of indolin-2-ones.

Considering the importance of developing powerful catalysts and the pharmacophore characteristics of indole derivatives, we describe a switchable approach for the iron-catalyzed oxidative C(sp3)-H functionalization of indolin-2-ones. Selective transformations displayed excellent activity and chemoselectivity using FeCl2 as the catalyst, air as the oxidant, and alcohol as the solvent. By manipulating the reaction conditions, particularly the choice of solvent, catalyst loading, and reaction sequence, a series of valuable indole derivatives, including isatins and symmetrical and nonsymmetrical isoindigos, were selectively synthesized in good to excellent yields. Furthermore, the gram-scale synthesis of compounds with biological anticancer activity under simple conditions highlights their great potential in practical applications.

Closed-loop recycling of sulfur-rich polymers with tunable properties spanning thermoplastics, elastomers, and vitrimers.

The development of closed-loop recycling polymers that exhibit excellent performance is of great significance. Sulfur-rich polymers possessing excellent optical, thermal, and mechanical properties are promising candidates for chemical recycling but lack efficient synthetic strategies for achieving diverse structures. Herein, we report a universal synthetic strategy for producing polytrithiocarbonates, a class of sulfur-rich polymers, via the polycondensation of dithiols and dimethyl trithiocarbonate. This strategy has excellent compatibility with a wide range of monomers, including aliphatic, heteroatomic, and aromatic dithiols enabling the synthesis of polytrithiocarbonates with diverse structures. The present synthesis strategy offers a versatile platform for the construction of thermoplastics, elastomers, and vitrimers. Notably, these polytrithiocarbonates can be easily depolymerized via solvolysis into the corresponding monomers, which can be repolymerized to virgin polymers without changing the material properties.

A Powerful Strategy for Synthesizing Block Copolymers via Bimetallic Synergistic Catalysis.

Block copolymers, comprising polyether and polyolefin segments, are an important and promising category of functional materials. However, the lack of efficient strategies for the construction of polyether-b-polyolefin block copolymers have hindered the development of these materials. Herein, we propose a simple and efficient method to obtain various block copolymers through the copolymerization of epoxides and acrylates via bimetallic synergistic catalysis. The copolymerization of epoxides and acrylates proceeds in a sequence-controlled manner, where the epoxides-involved homo- or copolymerization occurs first, followed by the homopolymerization of acrylates initiated by the alkoxide species from the propagating polymer chain, thus yielding copolymers with a block structure. Notably, the high monomer compatibility of this powerful strategy provides a platform for synthesizing various polyacrylate-based block copolymers comprising polyether, polycarbonate, polythiocarbonate, polyester, and polyurethane segments, respectively.

Electroreductive Ring-Opening Carboxylation of 1,3-Oxazolidin-2-ones with CO2 for Accessing ß-Amino Acids.

Electrocarboxylation of the C(sp3)-O bond in 1,3-oxazolidin-2-ones with CO2 to achieve ß-amino acids is developed. The C-O bond in substrates can be selectively cleaved via the single electron transfer on the surface of a cathode or through a CO2• - intermediate under additive-free conditions. A great diversity of ß-amino acids can be obtained in a moderate to excellent yield and readily converted to various biologically active compounds.

Copolymerization Involving Sulfur-Containing Monomers.

Incorporating sulfur (S) atoms into polymer main chains endows these materials with many attractive features, including a high refractive index, mechanical properties, electrochemical properties, and adhesive ability to heavy metal ions. The copolymerization involving S-containing monomers constitutes a facile method for effectively constructing S-containing polymers with diverse structures, readily tunable sequences, and topological structures. In this review, we describe the recent advances in the synthesis of S-containing polymers via copolymerization or multicomponent polymerization techniques concerning a variety of S-containing monomers, such as dithiols, carbon disulfide, carbonyl sulfide, cyclic thioanhydrides, episulfides and elemental sulfur (S8). Particularly, significant focus is paid to precise control of the main-chain sequence, stereochemistry, and topological structure for achieving high-value applications.

Azopolyesters with Intrinsic Crystallinity and Photoswitchable Reversible Solid-to-Liquid Transitions.

Herein, we introduce a variety of azopolyesters (azobenzene-based polyesters) with remarkable intrinsic crystallinity and photoinduced reversible solid-to-liquid transition abilities from copolymerization of azobenzene-based epoxides with cyclic anhydrides. The length of the soft alkyl side-chain inlaid with azobenzenes and stereoregularity of main-chain of azopolymers have tremendous effects on crystallization properties of the resulting polyesters with melting temperature (Tm ) in the range of 51-251 °C. Moreover, some of azopolyesters possess excellently photoinduced reversible solid-to-liquid transition performance thanks to trans-cis photoisomerization of azobenzenes. Trans-azopolyesters are yellow solids with Tm s or glass transition temperatures (Tg s) above room temperature, whereas cis-polymers are red liquids with Tg s below -20 °C. These azopolyesters could be applied as novel light-switchable adhesives for quartz/quartz, wood/wood and quartz/wood adhesion, with the strength in the range of 0.73-0.89 MPa for trans-polymers. Conversely, the adhesion strength of liquefied cis-azopolyesters generated from the irradiation of trans-polymers by UV light was about 0.1 MPa, which shows light enable to control the adhesion process with high spatiotemporal resolution.

Sequence Control in Asymmetric Terpolymerizations of meso-Epoxides, CO2 , and Phthalic Anhydride: Unprecedented Statistical Ester-Carbonate Distributions.

The statistical terpolymerization of epoxides, CO2 and cyclic anhydrides remains challenging, mainly because epoxide/CO2 and epoxide/anhydride copolymerizations typically proceed at considerably different rates. Herein, we report the syntheses of novel chiral terpolymers with unprecedented statistical distributions of carbonate and ester units (up to 50 % junction units) via the one-pot reaction of cyclohexene oxide, phthalic anhydride, and CO2 under mild conditions using enantiopure bimetallic aluminum-complex-based catalyst systems. Notably, all resulting terpolymers exhibited excellent enantioselectivities (≥96 % ee) that were independent of the carbonate-ester distribution. The statistical compositions of the carbonate and ester units in the resulting terpolymers were determined via 1 H and 13 C NMR spectroscopies. Furthermore, thermal properties were tuned by altering the ester content of the chiral terpolymer without influencing the enantioselective ring-opening step involving the meso-epoxide. This asymmetric terpolymerization methodology is also compatible with a variety of meso-epoxides to afford the corresponding terpolymers with 17 %-25 % junction units and excellent enantioselectivities (94 %-99 % ee). The present study is expected to provide new guidelines for preparing a broad range of biodegradable polymers with excellent enantioselectivities and adjustable properties.

Eletrocarboxylation Reactions Using CO2 Both as Promoter and Carboxylative Reagent.

Electrocarboxylation reaction, which employs organic electrosynthesis to achieve the utilization of CO2 as a carboxylative reagent, provides a powerful and efficient tool for the preparation of organic carboxylic acid. In some electrocarboxylation reactions, CO2 also acts as a promoter to facilitate the desired reaction. This concept mainly highlights recent CO2 -promoted electrocarboxylation reactions via CO2 ⋅- intermediate or transiently protective carboxylation of active intermediate with CO2 .

Emerging Trends in Closed-Loop Recycling Polymers: Monomer Design and Catalytic Bulk Depolymerization.

Plastics are indispensable materials in modern society; however, their extensive use has contributed to the depletion of finite natural resources and caused severe environmental issues. One end-of-use solution for plastics involves the chemical recycling of polymers back to monomers for repolymerization to virgin polymers without changing the material properties, allowing the establishment of a circular material economy. This concept focuses on the critical advantages of chemically recyclable polymers in terms of monomer design, material properties, and the feasibility of bulk depolymerization. The recyclability via bulk thermolysis of various polyesters, CO2 -based polycarbonates, and polyacetals produced via ring-opening polymerization is highlighted through discussions regarding rational monomer design and efficient catalyst development. An outlook and perspective are provided to delineate the future challenges in the rational design of monomer and polymer structures that deliver the desired materials performance while being suitable for bulk thermolysis with high (de)polymerization activity and selectivity.

Favorable Propylene-Incorporated Terpolymerization of Ethylene with CO Mediated by Cationic [P,O]-Pd and Ni Complexes.

Commercial polyketone materials are generally produced by palladium-catalyzed terpolymerization of ethylene and α-olefin with carbon monoxide (CO), and rare examples were reported regarding the incorporation of propylene into an ethylene/CO copolymer chain using a cost-effective nickel catalyst. In this study, we have developed a series of [P,O]-type cationic Pd and Ni complexes supported by a diphosphazane monoxide (PNPO) platform, and the electronic and steric effect on phosphine, amine, and phosphine oxide moieties is systematically investigated for terpolymerization in terms of activity, propylene/CO (C3) incorporation, and molecular weight control. It is observed that the melting temperature (Tm) is proportional to the number of C3 incorporations present in the polymer chain, and the incorporated propylene does not affect the degradation temperature substantially, thus broadening the processing temperature window of the resultant polyketones. Notably, in comparison with dppp-type catalysts, PNPO catalysts exhibited a higher preference for propylene consumption, which is of great importance for making more efficient use of α-olefin resources.

Electroreductive Ring-Opening Carboxylation of Cycloketone Oxime Esters with Carbon Dioxide.

Electroreductive ring-opening carboxylation of cycloketone oxime esters with atmospheric carbon dioxide is reported. This reaction proceeded under simple constant current conditions in an undivided cell using glassy carbon as the cathode and magnesium as the sacrificial anode, providing substituted γ- and δ-cyanocarboxylic acids in moderate to good yields. Electrochemically generated cyanoalkyl radicals and cyanoalkyl anion are proposed as the key intermediates.

Preparation of Poly(ß-malic acid) via Direct Carbonylative Polymerization of Benzyl Glycidate.

Poly(malic acid) (PMLA) is a water-soluble, biodegradable, biocompatible, and nontoxic polyester in the poly(hydroxyalkanoate) (PHA) family. it features various applications in pharmaceutical field. Herein, NaCo(CO)4 and pyridine derivatives are employed for direct carbonylative polymerization of benzyl glycidate (BG) for poly(ß-malic acid) production. Further investigation on reaction mechanism reveals that this polymerization undergoes a direct chain growth, rather than a sequential process involving ß-lactone intermediate. The low cost and facile preparation of epoxide substrate render this methodology extremely appealing that avoids the rather tedious procedures for ß-malolactonate synthesis required toward ring opening polymerization. This study also represents an alternative strategy over traditional methods for poly(ß-malic acid) production using step growth polycondensation of malic acid.

Direct and Selective Electrocarboxylation of Styrene Oxides with CO2 for Accessing ß-Hydroxy Acids.

Highly selective and direct electroreductive ring-opening carboxylation of epoxides with CO2 in an undivided cell is reported. This reaction shows broad substrate scopes within styrene oxides under mild conditions, providing practical and scalable access to important synthetic intermediate ß-hydroxy acids. Mechanistic studies show that CO2 functions not only as a carboxylative reagent in this reaction but also as a promoter to enable efficient and chemoselective transformation of epoxides under additive-free electrochemical conditions. Cathodically generated α-radical and α-carbanion intermediates lead to the regioselective formation of α-carboxylation products.

A sustainable approach for the synthesis of recyclable cyclic CO2-based polycarbonates.

It is highly desirable to reduce the environmental pollution related to the disposal of end-of-life plastics. Polycarbonates derived from the copolymerization of CO2 and epoxides have attracted much attention since they can enable CO2-fixation and furnish biorenewable and degradable polymeric materials. So far, only linear CO2-based polycarbonates have been reported and typically degraded to cyclic carbonates. Here we synthesize a homogeneous dinuclear methyl zinc catalyst ((BDI-ZnMe)2, 1) to rapidly copolymerize meso-CHO and CO2 into poly(cyclohexene carbonate) (PCHC) with an unprecedentedly cyclic structure. Moreover, in the presence of trace amounts of water, a heterogeneous multi-nuclear zinc catalyst ((BDI-(ZnMe2·xH2O)) n , 2) is prepared and shows up to 99% selectivity towards the degradation of PCHC back to meso-CHO and CO2. This strategy not only achieves the first case of cyclic CO2-based polycarbonate but also realizes the complete chemical recycling of PCHC back to its monomers, representing closed-loop recycling of CO2-based polycarbonates.

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

Chemical recycling of polymers to their constituent monomers is the foremost challenge in building a sustainable circular plastics economy. Here, we report a strategy for highly efficient depolymerization of various CO2 -based alicyclic polycarbonates to epoxide monomers in solvent-free conditions by a simple CrIII -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.

Cationic P,O-Coordinated Nickel(II) Catalysts for Carbonylative Polymerization of Ethylene: Unexpected Productivity via Subtle Electronic Variation.

Transition-metal-catalyzed copolymerization of ethylene with carbon monoxide affords polyketones materials with excellent mechanical strength, photodegradability, surface and barrier properties. Unlike the widely used and rather expensive Pd catalysts, Ni-catalyzed carbonylative polymerization is very difficult since the strong binding affinity of CO to Ni deactivates the highly electrophilic metal center easily. In this study, various cationic P,O-coordinated Ni complexes were synthesized using the electronic modulation strategy, and the catalyst with strong electron-donating substituents exhibits an excellent productivity of 104  g polymer (g Ni)-1 , which represents a rare discovery that a Ni complex could operate with such exceptional efficiency in comparison with Pd catalysts. Notably, those Ni catalysts were also efficient for terpolymerization of ethylene, propylene with CO for producing commercial polyketone materials with low melting temperatures and easy processibility.

Electrocarboxylation of N-Acylimines with Carbon Dioxide: Access to Substituted α-Amino Acids.

Direct electrocarboxylation of various N-acylimines with atmospheric CO2 is achieved in an undivided cell under mild conditions, affording substituted α-amino acids in yields of 62-95%. This reaction is conducted with high efficiency using triethanolamine as an external reductant under nonsacrificial anode conditions, and can be facilely performed on gram scale. Preliminary mechanistic studies including cyclic voltammetry and control experiments support N-radical carbanion as the key intermediate.