Efficient and selective Palladium-catalyzed Telomerization of 1,3-Butadiene with Carbon Dioxide

Sustainable Copolymer Synthesis from Carbon Dioxide and Butadiene

Carbon dioxide (CO2) has long been recognized as an ideal C1 feedstock comonomer for producing sustainable materials because it is renewable, abundant, and cost-effective. However, activating CO2 presents a significant challenge because it is highly oxidized and stable. A CO2/butadiene-derived δ-valerolactone (EVP), generated via palladium-catalyzed telomerization between CO2 and butadiene, has emerged as an attractive intermediate for producing sustainable copolymers from CO2 and butadiene. Owing to the presence of two active carbon-carbon double bonds and a lactone unit, EVP serves as a versatile intermediate for creating sustainable copolymers with a CO2 content of up to 29 wt % (33 mol %). In this Review, advances in the synthesis of copolymers from CO2 and butadiene with divergent structures through various polymerization protocols have been summarized. Achievements made in homo- and copolymerization of EVP or its derivatives are comprehensively reviewed, while the postmodification of the obtained copolymers to access new polymers are also discussed. Meanwhile, potential applications of the obtained copolymers are also discussed. The literature references were sorted into sections based on polymerization strategies and mechanisms, facilitating readers in gaining a comprehensive view of the present chemistry landscape and inspiring innovative approaches to synthesizing novel CO2-derived copolymers.

Functional and Degradable Polyester-co-polyethers from CO2, Butadiene, and Epoxides

Carbon dioxide (CO2), as a renewable and nontoxic C1 feedstock, has been recognized as an ideal comonomer to prepare sustainable materials. In this regard, substantial focus has been dedicated to the ring-opening copolymerization of CO2 and epoxides, which results in the creation of aliphatic polycarbonates in most cases. Here, we report an unprecedented strategy to synthesize functional and degradable polyester-co-polyethers from CO2, butadiene, and epoxides via a CO2/butadiene-derived δ-valerolactone intermediate (EVP). Utilizing a chromium salen complex as the catalyst, the copolymerization of EVP and epoxides was successfully achieved to produce CO2/butadiene/epoxide terpolymers. The obtained polyester-co-polyethers with varied 39-93 mol % EVP content (equal to 18-28 wt % CO2 incorporation) show high thermal stability, tunable glass-transition temperatures, on-demand functionality, and good chemical degradability. This method extends the potential to access functional CO2-based polymers.

The Divergent Reactivity of Lactones Derived from Butadiene and Carbon Dioxide in Macromolecular Synthesis

The catalytic conversion of carbon dioxide and 1,3-butadiene into unsaturated lactone monomers provides an efficient route for converting sustainable carbon feedstocks into novel macromolecules. The chemical reactivity of this monomer is reviewed in order to highlight the many viable mechanistic pathways. Polymerization strategies, monomer alterations, and post-polymerization modifications are covered. The polymerization methods include radical, coordination, conjugate addition, ring-opening, olefin metathesis, and thiol-ene chemistries. Materials derived from these processes possess a wide range of function including responsiveness, degradability, adhesion, recyclability, and self-assembly. These aspects along with the advances in polymer chemistry that make them possible are discussed, along with a perspective on the future directions of the field.

3-Ethyl-6-vinyltetrahydro-2H-pyran-2-one (EVP): a versatile CO2-derived lactone platform for polymer synthesis

3-Ethyl-6-vinyltetrahydro-2H-pyran-2-one (EVP) is a CO₂-derived lactone synthesized via Pd-catalyzed telomerization of butadiene. As EVP is 28.9% by weight CO₂, it has received significant recent attention as an intermediary for the synthesis of high CO₂-content polymers. This article provides an overview of strategies for the polymerization of EVP to a wide variety of polymer structures, ranging from radical polymerizations to ring-opening polymerizations, that each take unique advantage of the highly functionalized lactone.

Tunable and recyclable polyesters from CO2 and butadiene

Carbon dioxide is inexpensive and abundant, and its prevalence as waste makes it attractive as a sustainable chemical feedstock. Although there are examples of copolymerizations of CO₂ with high-energy monomers, the direct copolymerization of CO₂ with olefins has not been reported. Here an alternative route to functionalizable, recyclable polyesters derived from CO₂, butadiene and hydrogen via an intermediary lactone, 3-ethyl-6-vinyltetrahydro-2H-pyran-2-one, is described. Catalytic ring-opening polymerization of the lactone by 1,5,7-triazabicyclo[4.4.0]dec-5-ene yields polyesters with molar masses up to 13.6 kg mol^-1 and pendent vinyl side chains that can undergo post-polymerization functionalization. The polymer has a low ceiling temperature of 138 °C, allowing for facile chemical recycling, and is inherently biodegradable under aerobic aqueous conditions (OECD-301B protocol). These results show that a well-defined polyester can be derived from CO₂, olefins and hydrogen, expanding access to new polymer feedstocks that were once considered unfeasible.

Advances in the Synthesis of Copolymers from Carbon Dioxide, Dienes, and Olefins

ConspectusCarbon dioxide (CO₂) has long been considered a sustainable comonomer for polymer synthesis due to its abundance, easy availability, and low toxicity. Polymer synthesis from CO₂ is highly attractive and has received continuous interest from synthetic chemists. In this regard, alternating copolymerization of CO₂ and epoxides is one of the most well-established methods to synthesize aliphatic polycarbonates. Moreover, binucleophiles including diols, diamines, amino alcohols, and diynes have been reported to copolymerize with CO₂ to give polycarbonates, polyureas, polyurethanes, and polyesters, respectively. Nevertheless, little success has been made for incorporating CO₂ into the most widely used polyolefin materials.Although extensive studies have been focused on the copolymerization of olefins and CO₂, most of the attempted reactions resulted in olefin homopolymerization owing to the endothermic property and high energy barriers of CO₂ insertion during the chain propagation process. In this Account, we show how this challenge is addressed by taking advantage of a metastable lactone intermediate, 3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVP), which is produced from CO₂ and butadiene via palladium catalysis. Homopolymerization of EVP furnishes CO₂/butadiene copolymers with up to 29 wt % of CO₂ content. This reaction strategy represents a breakthrough for the long-standing challenge of inherent kinetic and thermodynamically unfavorable CO₂/olefin copolymerization. A new class of polymeric materials bearing repeating bicyclic lactone and unsaturated lactone units can be obtained. Importantly, one-pot copolymerization of CO₂/butadiene or terpolymerization of CO₂/butadiene/diene can be achieved to afford copolymers through a two-step reaction protocol. Interestingly, the bicyclic lactone units in the polymer chain can undergo ring-opening through hydrolysis and aminolysis, while reversible ring-closing of the hydrolyzed or aminolyzed units was also achieved simply by heating.Over the past few years, more and more studies have utilized EVP as an intermediate to synthesize copolymers from olefins, butadiene, and CO₂. Recently, we successfully incorporated CO₂ into the most widely used polyethylene materials via the direct copolymerization of EVP and ethylene. Taking advantage of the bifunctional reactivity of EVP, we were able to access two types of main-chain-functionalized polyethylenes through palladium-catalyzed coordination/insertion copolymerization and radical copolymerization. Besides polyethylenes, CO₂ was also incorporated into poly(methyl methacrylate), poly(methyl acrylate), polystyrene, polymethyl acrylate, polyvinylchloroacetate, and poly(vinyl acetate) materials via radical copolymerization of EVP and olefin monomers. The EVP/olefin copolymerization strategy provides a novel avenue for the synthesis of highly versatile copolymers from an olefin, CO₂, and butadiene.

Chemically Recyclable Polyesters from CO2, H2 and 1,3-Butadiene

Chemically recyclable solid polymeric materials with commercializable properties only using CO₂ and inexpensive bulk chemicals as chemical feedstock can open a brand-new avenue to economically viable, large-scale fixation of CO₂ over a long period of time. Despite previous great advancements, development of such a kind of CO₂-based polymers remains a long-term unsolved research challenge of great significance. Herein, we reported the first methodology to polymerize six-membered lactone with two substituents vicinal to the ester group (HL), a compound previously found to be non-polymerizable. The present methodology enables the first synthesis of chemically recyclable solid polyesters (polyHL) with a high CO₂ content (28 wt %) and large molecular weights (M_n up to 613.8 kg mol⁻¹). Transparent membranes with promising pressure-sensitive adhesive (PSA) properties comparable with their commercial counterparts can be conveniently fabricated from the polyesters. Mechanistic studies indicate that rigorous removal of water impurity is the key to the successful polymerization of the relatively inert disubstituted six-membered lactone. A complete monomer recovery from polyHL was also successfully achieved under mild catalytic conditions. The synthesis of polyHL only requires CO₂ and two inexpensive bulk chemicals, H₂ and 1,3-butadiene, as the starting materials, thus providing a new strategy for potential scalable chemical utilization of CO₂ with desirable economic values and concomitant mitigation of CO₂ emissions. This work should inspire future research to make useful new solid CO₂-based polymers that can meaningfully increase the scale of chemical utilization of CO₂ and promote the contribution of chemical utilization of CO₂ to global mitigation of CO₂ emissions.

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CO₂-based recyclable polymers are promising in reducing CO₂ emission and pollution

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Disubstituted δ-lactone, a previously non-polymerizable monomer, was polymerized

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Complete monomer recovery was successfully achieved via chemical recycling process

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CO₂ constitutes 28% of the weight of newly designed chemically recyclable polymers

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The polymers show pressure-sensitive adhesive property comparable to commercial tapes

Advances in Palladium-Catalyzed Carboxylation Reactions

In this short review, we highlight the advancements in the field of palladium-catalyzed carbon dioxide utilization for the synthesis of high value added organic molecules. The review is structured on the basis of the kind of substrate undergoing the Pd-catalyzed carboxylation process. Accordingly, after the introductory section, the main sections of the review will illustrate Pd-catalyzed carboxylation of olefinic substrates, acetylenic substrates, and other substrates (aryl halides and triflates).

Accessing Divergent Main-Chain-Functionalized Polyethylenes via Copolymerization of Ethylene with a CO2/Butadiene-Derived Lactone

Carbon dioxide (CO₂) has been used as a sustainable comonomer in the synthesis of different functional polymers including polycarbonates, polyurea, and polyurethane. Until today, despite the great interest, little success has been made for incorporating CO₂ into the most widely used polyethylene materials. Herein, we report the incorporation of CO₂ to polyethylenes through the copolymerization of ethylene with a CO₂/butadiene-derived lactone, 3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVP). Two-types of main-chain-functionalized polyethylenes can be synthesized through different copolymerization strategies. Palladium-catalyzed coordination/insertion copolymerization furnished polyethylenes bearing unsaturated lactones, while radical copolymerization afforded polyethylenes bearing bicyclic lactones. Modification of the polyethylene chains was successfully accomplished through Michael addition or aminolysis. This highly versatile copolymerization protocol provides access to a diverse range of polyethylene materials made from ethylene, CO₂, and 1,3-butadiene.

Nickel-Catalyzed Reductive Carboxylation and Amidation Reactions

The ubiquity and importance of carboxylic acids and amides in peptides, pharmaceuticals, agrochemicals, and synthetic materials has challenged chemists to design de novo catalytic carboxylation and amidation protocols. They represent a powerful alternative to canonical oxidation of alcohols and aldehydes, hydrolysis of nitriles, transamidation reactions, or condensation techniques for the synthesis of these functional groups. Among various scenarios, the recent years have witnessed considerable advances in Ni-catalyzed reductive carboxylation and amidation reactions utilizing carbon dioxide and isocyanate counterparts. This Account aims to highlight the progress made in this arena with a historical perspective, with particular emphasis on the methodologies that have emanated from our laboratories without losing sight of the underlying principles by which these reactions operate, with the ultimate goal of allowing the transition from comprehension to prediction in this exciting field.Unlike the utilization of conventional polar yet highly reactive organometallic reagents in carboxylation or amidation reactions, the utilization of nickel catalysts has allowed the use of carbon dioxide and isocyanates with less reactive and less-polarized counterparts for the formations of carboxylic acids and amides. These less reactive groups include organic halides and pseudohalides (i.e., alkyl bromides and chlorides, esters, alcohols, and ammonium salts), unsaturated hydrocarbons (i.e., alkynes, styrenes, unactivated alkenes, and dienes) or even C-H bonds, where forging the targeted C-C bond at previously unfunctionalized C-H linkages was possible, thus giving access to densely functionalized compounds that would be difficult to access otherwise. The C-H functionalization includes chain-walking scenarios, where subtle changes in the ligand and reaction conditions marked the selectivity of the transformations, and reactions via a [1,4]-Ni shift, where selective carboxylation in aromatic rings could be achieved. Conceptuality and practicality aside, these transformations have even offered the possibility of modulating and dictating the site-selectivity pattern, thus providing not only new vistas when controlling the selectivity of bond-forming reactions at specific sites within the side chain but also new knowledge in retrosynthetic analysis when accessing carboxylic acids and amide backbones. Importantly, these techniques have shown to be particularly suited for the preparation of isotopically labeled molecules when using ¹³CO₂ or even ¹⁴CO₂, thus becoming a useful endeavor in the drug discovery pipeline. Although mechanistic understanding at the molecular level still constitutes the "Achilles heel" of these transformations, the recent empirical discoveries and the rapid adoption of these protocols by the community augurs well for the widespread utilization of reductive carboxylation and amidation reactions in both academic and industrial laboratories.

Progress Toward Sustainable Reversible Deactivation Radical Polymerization

The recent focus of media and governments on renewability, green chemistry, and circular economy has led to a surge in the synthesis of renewable monomers and polymers. In this review, focussing on renewable monomers for reversible deactivation radical polymerizations (RDRP), it is highlighted that for the majority of the monomers and polymers reported, the claim to renewability is not always accurate. By closely examining the sustainability of synthetic routes and the renewability of starting materials, fully renewable monomers are identified and discussed in terms of sustainability, polymerization behavior, and properties obtained after polymerization. The holistic discussion considering the overall preparation process of polymers, that is, monomer syntheses, origin of starting materials, solvents used, the type of RDRP technique utilized, and the purification method, allows to highlight certain topics which need to be addressed in order to progress toward not only (partially) renewable, but sustainable monomers and polymers using RDRPs.

Advances in the use of CO2 as a renewable feedstock for the synthesis of polymers

Carbon dioxide offers an accessible, cheap and renewable carbon feedstock for synthesis. Current interest in the area of carbon dioxide valorisation aims at new, emerging technologies that are able to provide new opportunities to turn a waste into value. Polymers are among the most widely produced chemicals in the world greatly affecting the quality of life. However, there are growing concerns about the lack of reuse of the majority of the consumer plastics and their after-life disposal resulting in an increasing demand for sustainable alternatives. New monomers and polymers that can address these issues are therefore warranted, and merging polymer synthesis with the recycling of carbon dioxide offers a tangible route to transition towards a circular economy. Here, an overview of the most relevant and recent approaches to CO2-based monomers and polymers are highlighted with particular emphasis on the transformation routes used and their involved manifolds.