Iron-Mediated Coupling of Carbon Dioxide and Ethylene: Macrocyclic Metallalactones Enable Access to Various Carboxylates

Tortajada A., Juliá‐Hernández F., Börjesson M., Moragas T., Martin R.

AbstractDriven by the inherent synthetic potential of CO2 as an abundant, inexpensive and renewable C1 chemical feedstock, the recent years have witnessed renewed interest in devising catalytic CO2 fixations into organic matter. Although the formation of C−C bonds via catalytic CO2 fixation remained rather limited for a long period of time, a close look into the recent literature data indicates that catalytic carboxylation reactions have entered a new era of exponential growth, evolving into a mature discipline that allows for streamlining the synthesis of carboxylic acids, building blocks of utmost relevance in industrial endeavors. These strategies have generally proven broadly applicability and convenient to perform. However, substantial challenges still need to be addressed reinforcing the need to cover metal‐catalyzed carboxylation area in a conceptual and concise manner, delineating the underlying new principles that are slowly emerging in this vibrant area of expertise.

Schmidt V.A., Kennedy C.R., Bezdek M.J., Chirik P.J.

The selective, intermolecular [1,4]-hydrovinylation of conjugated dienes with unactivated α-olefins catalyzed by α-diimine iron complexes is described. Value-added "skipped" diene products were obtained with exclusive [1,4]-selectivity, and the formation of branched, ( Z)-olefin products was observed with no evidence for alkene isomerization. Mechanistic studies conducted with the well-defined, single-component iron precatalyst (MesDI)Fe(COD) (MesDI = [2,4,6-Me3-C6H2-N═CMe]2); COD = 1,5-cyclooctadiene) provided insights into the origin of the high selectivity. An iron diene complex was identified as the catalyst resting state, and one such isoprene complex, (iPrDI)Fe(η4-C5H8), was isolated and characterized. A combination of single crystal X-ray diffraction, Mößbauer spectroscopy, magnetic measurements, and DFT calculations established that the complex is best described as a high-spin Fe(I) center ( SFe = 3/2) engaged in antiferromagnetic coupling to an α-diimine radical anion ( SDI = -1/2), giving rise to the observed S = 1 ground state. Deuterium-labeling experiments and kinetic analyses of the catalytic reaction provided support for a pathway involving oxidative cyclization of an alkene with the diene complex to generate an iron metallacycle. The observed selectivity can be understood in terms of competing steric interactions in the transition states for oxidative cyclization and subsequent β-hydrogen elimination.

Wang X., Wang H., Sun Y.

Summary The synthesis of acrylic acid and its derivatives with the use of CO 2 and ethylene feedstock is an exciting yet extremely challenging reaction. In addition to the inherent stability of CO 2 , other challenges arise, such as the elimination of β-hydride from metallalactone to release free acrylate. Since the ground-breaking work more than three decades ago, tremendous efforts have been made to realize an effective catalytic system. From historical findings to recent progress, this review gives a comprehensive overview of this reaction. Reactions mediated by different transition-metal complexes and mechanistic details are discussed in depth.

Hoyt J.M., Schmidt V.A., Tondreau A.M., Chirik P.J.

Iron plays matchmaker to pair up olefins In theory, shining the right wavelength of light onto carbon-carbon double bonds should pair them up into four-membered cyclobutane rings. In practice, however, this route can prove finicky and inefficient, particularly if the necessary wavelength lies deep in the ultraviolet region. Hoyt et al. report an iron catalyst that coaxes a wide variety of simple olefins into such rings without the need for photoexcitation (see the Perspective by Smith and Baran). Systematic optimization of the ligand coordinated to iron effectively eliminated competing pathways to alternative products. Science, this issue p. 960; see also p. 925 A carefully optimized catalyst offers a general route to four-membered carbon rings. [Also see Perspective by Smith and Baran] Cycloadditions, such as the [4+2] Diels-Alder reaction to form six-membered rings, are among the most powerful and widely used methods in synthetic chemistry. The analogous [2+2] alkene cycloaddition to synthesize cyclobutanes is kinetically accessible by photochemical methods, but the substrate scope and functional group tolerance are limited. Here, we report iron-catalyzed intermolecular [2+2] cycloaddition of unactivated alkenes and cross cycloaddition of alkenes and dienes as regio- and stereoselective routes to cyclobutanes. Through rational ligand design, development of this base metal–catalyzed method expands the chemical space accessible from abundant hydrocarbon feedstocks.

Stieber S.C., Huguet N., Kageyama T., Jevtovikj I., Ariyananda P., Gordillo A., Schunk S.A., Rominger F., Hofmann P., Limbach M.

We report the first catalyst based on palladium for the reaction of CO2, alkene and a base to form sodium acrylate and derivatives. A mechanism similar to a previously reported Ni(0)-catalyst is proposed based on stoichiometric in situ NMR experiments, isolated intermediates and a parent palladalactone. Our palladium catalyst was applied to the coupling of CO2 with conjugated alkenes.

Kraus S., Rieger B.

The story of nickelalactones finally ends well. Over three decades after their discovery, catalytic processes have been successfully established to synthesize acrylate derivatives from ethylene and abundantly available carbon dioxide. The performed research during this time in the CO2 utilization via C–C bond formation with olefins is presented within this review. It gives detailed insights starting from the initial milestones in the 1980s up to modern strategies through cleavage auxiliaries. Different approaches are examined from an experimental and theoretical point of view as the choice of cleavage agent and the corresponding ligand is crucial for the reaction control and suppression of undesired pathways. Methylation of the lactone species led to a first successful liberation of methyl acrylate in stoichiometric amounts. These results led to a vast progress in research with auxiliaries afterward. Upon addition of Lewis acids or strong sodium bases, finally the first two different catalytic routes have been established which are discussed in detail.

Huguet N., Jevtovikj I., Gordillo A., Lejkowski M.L., Lindner R., Bru M., Khalimon A.Y., Rominger F., Schunk S.A., Hofmann P., Limbach M.

The nickel-catalyzed direct carboxylation of alkenes with the cheap and abundantly available C1 building block carbon dioxide (CO2 ) in the presence of a base has been achieved. The one-pot reaction allows for the direct and selective synthesis of a wide range of α,β-unsaturated carboxylates (TON>100, TOF up to 6 h(-1) , TON=turnover number, TOF=turnover frequency). Thus, it is possible, in one step, to synthesize sodium acrylate from ethylene, CO2 , and a sodium salt. Acrylates are industrially important products, the synthesis of which has hitherto required multiple steps.

Hendriksen C., Pidko E.A., Yang G., Schäffner B., Vogt D.

With regard to sustainability, carbon dioxide (CO2) is an attractive C1 building block. However, due to thermodynamic restrictions, reactions incorporating CO2 are relatively limited so far. One of the so-called "dream reactions" in this field is the catalytic oxidative coupling of CO2 and ethene and subsequent β-H elimination to form acrylic acid. This reaction has been studied intensely for decades. However up to this date no suitable catalytic process has been established. Here we show that the catalytic conversion of ethene and CO2 to acrylate is possible in the presence of a homogeneous nickel catalyst in combination with a "hard" Lewis acid. For the first time, catalytic conversion of CO2 and ethene to acrylate with turnover numbers (TON) of up to 21 was demonstrated.

Plessow P.N., Schäfer A., Limbach M., Hofmann P.

The first step of the nickel-mediated synthesis of acrylates from carbon dioxide (CO2) and ethylene is the formation of nickelalactones. Nickelalactones could then react to give complexes containing acrylic acid moieties. Such a spontaneous reaction, however, is usually not observed and most progress has recently been made by cleaving the lactones with auxiliaries such as Lewis acids and strong bases. Here we investigate in detail the coupling of CO2 and ethylene and further reactivity in absence of auxiliaries mediated by nickel complexes bearing bidentate ligands. We have found a new mechanism for lactone formation which, for some bidentate ligands, is favored over the mechanism described in the literature. Furthermore, we found that β-H elimination leading to ring contraction of the lactone is almost feasible at room temperature. Importantly, however, all investigated mechanisms for formation of acrylic acid complexes require higher activation free energies of ca. 130 kJ/mol and are not accessible at a...

Jin D., Williard P.G., Hazari N., Bernskoetter W.H.

A sodium scramble: Sodium cations can be used to facilitate a β-hydride elimination reaction in CO2-derived nickelalactones, which is key to the production of acrylates. A related isomerization reaction can also occur without Lewis acid to produce rare unstabilized γ-nickelalactones, but with a higher activation energy and less favorable thermodynamics than the sodium-containing counterpart (see scheme).

Aresta M., Dibenedetto A., Angelini A.

Jin D., Schmeier T.J., Williard P.G., Hazari N., Bernskoetter W.H.

The Lewis acid tris(pentafluorophenyl)borane was found to rapidly promote ring-opening β-hydride elimination in a 1,1′-bis(diphenylphosphino)ferrocene (dppf) nickelalactone complex under ambient conditions. The thermodynamic product of nickelalactone ring-opening was characterized as (dppf)Ni(CH(CH3)CO2BArf3), the result of β-hydride elimination and subsequent 2,1-insertion from a transient nickel(II) acrylate hydride intermediate. Treatment of (dppf)Ni(CH(CH3)CO2BArf3) with a nitrogen-containing base afforded a diphosphine nickel(0) η2-acryl borate adduct. Formation of the diphosphine nickel(0) η2-acryl borate adduct completes a net conversion of nickelalactone to acrylate species, a significant obstacle to catalytic acrylate production from CO2 and ethylene. Displacement of the η2-acrylate fragment from the nickel center was accomplished by addition of ethylene to yield a free acrylate salt and (dppf)Ni(CH2═CH2).

Hoyt J.M., Sylvester K.T., Semproni S.P., Chirik P.J.

The bis(imino)pyridine iron dinitrogen compound, ((iPr(TB))PDI)Fe(N2)2 ((iPr(TB))PDI = 2,6-(2,6-(i)Pr2-C6H3-N═C-(CH2)3)2(C5H1N)) is an effective precatalyst for the [2π + 2π] cycloaddition of diallyl amines as well as the hydrogenative cyclization of N-tosylated enynes and diynes. Addition of stoichiometric quantities of amino-substituted enyne and diyne substrates to ((iPr(TB))PDI)Fe(N2)2 resulted in isolation of catalytically competent bis(imino)pyridine iron metallacycle intermediates. A combination of magnetochemistry, X-ray diffraction, and Mössbauer spectroscopic and computational studies established S = 1 iron compounds that are best described as intermediate-spin iron(III) (SFe = 3/2) antiferromagnetically coupled to a chelate radical anion (SPDI = 1/2). Catalytically competent bis(imino)pyridine iron diene and metallacycles relevant to the [2π + 2π] cycloaddition were also isolated and structurally characterized. The combined magnetic, structural, spectroscopic, and computational data support an Fe(I)-Fe(III) catalytic cycle where the bis(imino)pyridine chelate remains in its one-electron reduced radical anion form. These studies revise a previous mechanistic proposal involving exclusively ferrous intermediates and highlight the importance of the redox-active bis(imino)pyridine chelate for enabling catalytic cyclization chemistry with iron.

Lejkowski M.L., Lindner R., Kageyama T., Bódizs G.É., Plessow P.N., Müller I.B., Schäfer A., Rominger F., Hofmann P., Futter C., Schunk S.A., Limbach M.

A dream come true: For over three decades the catalytic synthesis of acrylates from the cheap and abundantly available C1 building block CO2 and alkenes has been an unsolved problem in catalysis research. A homogeneous catalyst system based on a Ni complex has now been developed that permits the catalytic synthesis of Na acrylate from CO2, ethylene, and a base (see scheme), as shown by a turnover number of greater than 10 with respect to the metal.

Cokoja M., Bruckmeier C., Rieger B., Herrmann W.A., Kühn F.E.

A plethora of methods have been developed over the years so that carbon dioxide can be used as a reactant in organic synthesis. Given the abundance of this compound, its utilization in synthetic chemistry, particularly on an industrial scale, is still at a rather low level. In the last 35 years, considerable research has been performed to find catalytic routes to transform CO(2) into carboxylic acids, esters, lactones, and polymers in an economic way. This Review presents an overview of the available homogeneous catalytic routes that use carbon dioxide as a C(1) carbon source for the synthesis of industrial products as well as fine chemicals.

Nguyen D.T., Mondal R., Evans M.J., Parr J.M., Jones C.

AbstractReactions of 1,2‐dimagnesioethane compound [{K(TCHPNON)Mg}2(μ‐C2H4)] (TCHPNON = 4,5‐bis(2,4,6‐tricyclohexylanilido)‐2,7‐diethyl‐9,9‐dimethyl‐xanthene), formed by the two‐electron reduction of ethene with a dimagnesium/dipotassium complex of reduced N2, viz. [{K(TCHPNON)Mg}2(μ‐N2)], with CO and CO2 have been explored. In the case of the reaction with CO, cross‐coupling of the reduced ethene fragment with two molecules of CO gave a heterobimetallic complex of the parent cyclobutenediolate dianion, [{K(TCHPNON)Mg}2(μ‐O2C4H4)], which when exposed to THF gave adduct [{K(TCHPNON)Mg}2(μ‐O2C4H4)(THF)]. Treating [{K(TCHPNON)Mg}2(μ‐C2H4)] with CO2 led to the insertion of CO2 into both Mg─C bonds and all Mg─N bonds, yielding a magnesium succinate complex, [{K(TCHPNON‐C2O4)Mg}2(μ‐O4C4H4)], in which the diamide ligands have been converted to xanthene bridged dicarbamates. The reaction of [{K(TCHPNON)Mg}2(μ‐N2)] with CO2, proceeded via reductive coupling of the heterocumulene to give the oxalate dianion, in addition to the insertion of CO2 into all Mg─N bonds of the magnesium‐dinitrogen complex, forming dimeric [{K(TCHPNON‐C2O4)Mg}2(μ‐O4C2)]2. When treated with THF this yields monomeric [{K(THF)(TCHPNON‐C2O4)Mg(THF)}2(μ‐O4C2)]. Related chemistry results from the reaction of a dianionic magnesium(I) compound with CO2. In contrast, C─C bond formation was not observed in the reaction of [{K(TCHPNON)Mg}2(μ‐N2)] with a CO2 analog, i.e., the carbodiimide CyNCNCy (Cy = cyclohexyl). Instead, H abstraction by a proposed radical intermediate gave polymeric formamidinate complex [K(TCHPNON)Mg{(CyN)2CH}]∞. Reaction of CO2 with the magnesium hydride complex [{K(TCHPNON)Mg(μ‐H)}2] gave the unusual trimeric magnesium formate complex [{K(TCHPNON‐CO2)Mg}(μ‐O2CH)]3 in which CO2 has inserted into only one Mg─N bond of each TCHPNON ligand. This study highlights the capacity of [{K(TCHPNON)Mg}2(μ‐N2)] to act as a masked dimagnesium(I) diradical in reductive coupling or cross‐coupling of the simple gaseous reagents, C2H4, CO, CO2 and H2, to give value‐added organic fragments.

Nguyen D.T., Mondal R., Evans M.J., Parr J.M., Jones C.

AbstractReactions of 1,2‐dimagnesioethane compound [{K(TCHPNON)Mg}2(μ‐C2H4)] (TCHPNON = 4,5‐bis(2,4,6‐tricyclohexylanilido)‐2,7‐diethyl‐9,9‐dimethyl‐xanthene), formed by the two‐electron reduction of ethene with a dimagnesium/dipotassium complex of reduced N2, viz. [{K(TCHPNON)Mg}2(μ‐N2)], with CO and CO2 have been explored. In the case of the reaction with CO, cross‐coupling of the reduced ethene fragment with two molecules of CO gave a heterobimetallic complex of the parent cyclobutenediolate dianion, [{K(TCHPNON)Mg}2(μ‐O2C4H4)], which when exposed to THF gave adduct [{K(TCHPNON)Mg}2(μ‐O2C4H4)(THF)]. Treating [{K(TCHPNON)Mg}2(μ‐C2H4)] with CO2 led to the insertion of CO2 into both Mg─C bonds and all Mg─N bonds, yielding a magnesium succinate complex, [{K(TCHPNON‐C2O4)Mg}2(μ‐O4C4H4)], in which the diamide ligands have been converted to xanthene bridged dicarbamates. The reaction of [{K(TCHPNON)Mg}2(μ‐N2)] with CO2, proceeded via reductive coupling of the heterocumulene to give the oxalate dianion, in addition to the insertion of CO2 into all Mg─N bonds of the magnesium‐dinitrogen complex, forming dimeric [{K(TCHPNON‐C2O4)Mg}2(μ‐O4C2)]2. When treated with THF this yields monomeric [{K(THF)(TCHPNON‐C2O4)Mg(THF)}2(μ‐O4C2)]. Related chemistry results from the reaction of a dianionic magnesium(I) compound with CO2. In contrast, C─C bond formation was not observed in the reaction of [{K(TCHPNON)Mg}2(μ‐N2)] with a CO2 analog, i.e., the carbodiimide CyNCNCy (Cy = cyclohexyl). Instead, H abstraction by a proposed radical intermediate gave polymeric formamidinate complex [K(TCHPNON)Mg{(CyN)2CH}]∞. Reaction of CO2 with the magnesium hydride complex [{K(TCHPNON)Mg(μ‐H)}2] gave the unusual trimeric magnesium formate complex [{K(TCHPNON‐CO2)Mg}(μ‐O2CH)]3 in which CO2 has inserted into only one Mg─N bond of each TCHPNON ligand. This study highlights the capacity of [{K(TCHPNON)Mg}2(μ‐N2)] to act as a masked dimagnesium(I) diradical in reductive coupling or cross‐coupling of the simple gaseous reagents, C2H4, CO, CO2 and H2, to give value‐added organic fragments.

Zhang X., Zhao Y., Wang C., Tang S.

Adamson T.T., Reeder L.G., Kelley S.P., Bernskoetter W.H.

Kunihiro K., Rajeshkumar T., Maron L., Heyte S., Paul S., Roisnel T., Carpentier J., Kirillov E.

Andre C.M., Szymczak N.K.

We report low-valent iron complexes containing bis-NHC and bis-phosphine donor ligands that coordinate and strongly activate N2 and CO.

Zhang J., Jiang L., Liu S., Shen J., Braunstein P., Shen Y., Kang X., Li Z.

When aiming at the direct use of CO2 for the preparation of advanced/value-added materials, the synthesis of CO2/olefin copolymers is very appealing but challenging. The δ-lactone 3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVP), synthesized by telomerization of CO2 with 1,3-butadiene, is a promising monomer. However, its chemoselective ring-opening polymerization (ROP) is hampered by unfavorable thermodynamics and the competitive polymerization of highly reactive C=C double bonds under usual conditions. Herein, we report the chemoselective ROP of EVP using a phosphazene/urea binary catalyst, affording exclusively a linear unsaturated polyester poly(EVP)ROP, with a molar mass (Mn) up to 16.1 kg·mol−1 and a narrow distribution (Ð < 1.6), which can be fully recycled back to the pristine monomer, thus establishing a monomer-polymer-monomer closed-loop life cycle. In these polyesters, the CO2 content reaches 33 mol% (29 wt%). The reasons for the unexpected chemoselectivity were investigated by Density-functional theory (DFT) calculations. The poly(EVP)ROP features two pendent C=C double bonds per repeating unit, which show distinct reactivity and thus can be properly engaged in sequential functionalizations towards the synthesis of bifunctional polyesters. We disclose here a methodology providing a facile access to bifunctional and recyclable polyesters from readily available feedstocks. The δ-lactone 3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVP), synthesized by telomerization of CO2 with 1,3-butadiene, is a promising monomer for the direct use of CO2 in the synthesis of polymers, but its ring-opening polymerization (ROP) remains challenging. Here the authors report its chemoselective ROP using a phosphazene/urea binary catalyst, affording exclusively a linear unsaturated polyester which can be recycled back to the pristine monomer.

Kuznetsov Nikolai Yu., Maximov Anton L., Beletskaya Irina P.

The development of atom-economical and efficient processes for obtaining a variety of chemical products using CO2 as C1-synthon plays an increasingly important role in modern scientific and technological research. Due to the inertness of CO2 many extremely attractive routes to valuable chemical products turn out to be impossible to implement, particularly for thermodynamic reasons, leaving one only dreaming about them as something unattainable. This review demonstrates how the catalytic coupling of ethylene and CO2 into acrylic acid, once considered a "dream reaction" has not only become a reality, but has also evolved into the category of technological processes. The key stages of the long-term development of this unique reaction from the discovery of metal activation of CO2 and stoichiometric preparation of metallalactones to catalytic synthesis using a variety of metal-catalysts (Ni, Pd, Ru, Rh) showcase the ingenuity and skill of researchers as well as an example of consistent development in this field of chemistry. We believe that this remarkably successful example will inspire scientists to tackle any "impossible" problems.The bibliography includes 117 references.

Zhu Y., Sun L., Zeng Z., Liu Z.

Maity N., Garcia N., Jaseer E.A., Barman S., Aitani A.M., Tijani M.M., Al-Yassir N.

Catalytic CO2 conversion has always been a fascinating area of research in chemistry. CO2 being a highly abundant and commercially cheap carbon feedstock, it is immensely appealing if such conversion could be advanced to novel economical and sustainable routes to take over the existing industrial processes for accessing highly demanding organic products. Acrylic acid is produced industrially by two-step catalytic processes involving partial oxidation of propylene. Catalytic acrylic acid production by a direct oxidative C–C coupling between olefin and CO2 has remained a great challenge for the research community due to unfavorable thermodynamics. However, reactions conducted in the presence of a suitable base leading to the acrylate product were envisaged to shed some light on this end. Indeed, this domain of exploration has gained significant interest, especially towards achieving a direct catalytic carboxylation of ethylene by CO2. While several earlier reviews probed into catalyst systems associated with this research, the recently surfaced promising catalysts remained unaddressed. These developments provide vital insights for designing high-performance materials in intentional applications and commercial technologies for catalytic acrylate production. Examining these developments creates an opportunity for more sustainable processes, utilizing CO2 as a C1 feedstock, contributing significantly to the circular carbon economy. This review explores the latest advancements, offering a comprehensive overview of the gradual evolution of catalyst systems, and identifying optimal candidates for intentional applications. Special attention is given to proposed reaction mechanisms supported by theoretical studies, enhancing understanding of reaction cycles and suggesting new strategies for better catalyst systems.

Kumar N., Gupta P.

Masood Z., Nguyen Q.P., Wang B.

Tang S., Lin B., Tonks I., Eagan J.M., Ni X., Nozaki K.

O'Reilly A., Gardiner M., McMullin C.L., Fulton J.R., Coles M.P.

The aluminacyclopropane K[Al(NON)(η-C2H4)] ([NON]2– = [O(SiMe2NDipp)2]2–, Dipp = 2,6-iPr2C6H3) reacts with CO2 and iPrN=C=NiPr to afford ring-expanded products of C–C bond formation. The latter system undergoes a 1,3-silyl retro-Brook rearrangement...

Kamal, Khatua M., Rani S., Goswami B., Samanta S.