Access to Polyhydroxyalkanoates with Diverse Syndiotacticity via Polymerization by Spiro-Salen Complexes and Insights into the Stereocontrol Mechanism.

Polyhydroxyalkanoates (PHAs) have attracted broad interest as promising sustainable materials to address plastic pollution and resource scarcity. However, the chemical synthesis of stereoregular PHAs via ring-opening polymerization (ROP) has long been an elusive endeavor. In this contribution, we exploited a robust spiro-salen yttrium complex (Y3) as the catalyst to successfully prepare syndiotactic PHAs with diverse pendent groups.

Mechanism-Inspired Synthesis of Poly(alkyl malonates) via Alternating Copolymerization of Epoxides and Meldrum's Acid Derivatives.

Direct incorporation of malonate units into polymer backbones is a synthetic challenge. Herein, we report the alternating and controlled anionic copolymerization of epoxides and Meldrum's acid (MA) derivatives to access poly(alkyl malonates) using (-bis(salicylidene)phenylenediamine)AlCl and a tris(dialkylamino)cyclopropenium chloride cocatalyst. This unique copolymerization yields a malonate-containing repeat unit while releasing a small molecule upon MA-derivative ring-opening.

Scalable Nickel Catalysts for Carbonylative Terpolymerization of Ethylene/α-Olefin with High Efficiency.

The carbonylative polymerization of olefin yields aliphatic polyketones, which are used as engineering plastics in the market due to their excellent mechanical strength, chemical resistance, and surface and barrier properties. However, the usage of precious palladium catalysts has restricted their extensive application as commodity materials. Herein, we present a series of phosphine-sulfonate Ni catalysts with a wide spectrum of electronic and steric substituents on the phosphorus moiety for the carbonylative polymerization of ethylene.

Electron-rich Phosphines Catalyzed Head-to-Tail Dimerization of Renewable Alkyl Crotonates.

Herein, a facile head-to-tail dimerization of alkyl crotonates using electron-rich N,N'-bis(imidazolyl) guanidinylphosphines (BIG-Ps) as organocatalysts was firstly developed. This reaction proceeded smoothly under mild reaction conditions, effectively generating a series of functionalized 2-ethylidene-3-methylpentanedioates in excellent yields and stereoselectivity. Furthermore, this method was successfully applied for the synthesis of unsaturated polyesters by employing alkyl dicotonates as monomers.

Chemical Recycling of Poly(cyclohexene carbonate)s via Synergistic Catalysis.

Chemical recycling of polymers to the corresponding monomers offers a valuable solution to address the current plastics crisis for creating an ideal and circular polymer economy. Here, we present a bimetallic synergistic depolymerization of the widely studied CO-based polycarbonates, poly(cyclohexene carbonate)s, to epoxide monomers efficiently. The bimetallic Cr-complex-mediated highly selective depolymerization and repolymerization was achieved via the regulation of reaction temperature, thus closing the circular loop of poly(cyclohexene carbonate)s .

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

Electroreductive ring-opening carboxylation of styrene carbonates with CO to achieve dicarboxylic acids and/or -hydroxy acids has been developed the selective cleavage of the C(sp)-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.

Stereoregular poly(2-phenylthiirane) 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.

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.

Iron-catalyzed selective construction of indole derivatives oxidative C(sp)-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(sp)-H functionalization of indolin-2-ones. Selective transformations displayed excellent activity and chemoselectivity using FeCl 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.

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.

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

Electrocarboxylation of the C(sp)-O bond in 1,3-oxazolidin-2-ones with CO to achieve β-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 CO  intermediate under additive-free conditions. A great diversity of β-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 (S).

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 (T ) 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.

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

The statistical terpolymerization of epoxides, CO and cyclic anhydrides remains challenging, mainly because epoxide/CO 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 CO 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.

Eletrocarboxylation Reactions Using CO Both as Promoter and Carboxylative Reagent.

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

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.

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 () 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.

Preparation of Poly(β-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) and pyridine derivatives are employed for direct carbonylative polymerization of benzyl glycidate (BG) for poly(β-malic acid) production.

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.

Direct and Selective Electrocarboxylation of Styrene Oxides with CO for Accessing β-Hydroxy Acids.

Highly selective and direct electroreductive ring-opening carboxylation of epoxides with CO 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 β-hydroxy acids. Mechanistic studies show that CO 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.

Efficient and Selective Chemical Recycling of CO -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 CO -based alicyclic polycarbonates to epoxide monomers in solvent-free conditions by a simple Cr -Salen complex mediated catalytic pyrolysis process. The chemical recycling of the widely studied poly(cyclohexene carbonate) exhibits excellent reactivity (TOF up to 3000 h , 0.

A sustainable approach for the synthesis of recyclable cyclic CO-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 CO and epoxides have attracted much attention since they can enable CO-fixation and furnish biorenewable and degradable polymeric materials. So far, only linear CO-based polycarbonates have been reported and typically degraded to cyclic carbonates.

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 10  g polymer (g Ni) , which represents a rare discovery that a Ni complex could operate with such exceptional efficiency in comparison with Pd catalysts.

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

Direct electrocarboxylation of various -acylimines with atmospheric CO 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 -radical carbanion as the key intermediate.