Heterogeneous Photocatalytic C(sp2)-H Activation of Formate for Hydrocarboxylation of Alkenes

Light-driven carboxylation offers a promising approach for synthesizing valuable fine chemicals under mild conditions. Here we disclose a heterogeneous photocatalytic strategy of C(sp2)-H activation of formate for hydrocarboxylation of alkenes over zinc indium sulfide (ZnIn2S4) under visible light. This protocol functions well with a variety of substituted styrenes with good to excellent yields; it also works for unactivated alkenes albeit with lower yields. Mechanistic studies confirm the existence of CO2⋅- as a key intermediate. It was found that C(sp2)-H activation of formate is induced by S⋅ species on the surface of ZnIn2S4 via hydrogen atom transfer (HAT) instead of a photogenerated hole oxidation mechanism. Moreover, both cleavage of the C(sp2)-H of HCOO- and formation of a benzylic anion were found to be involved in the rate-determining step for the hydrocarboxylation of styrene.

Surprising Radiolytic Stability of 8-Thiomethyladenine in an Aqueous Solution

8-Thiomethyladenine (ASCH3), a potentially radiosensitizing modified nucleobase, has been synthesized in a reaction between 8-thioadenine and methyl iodide. Despite favorable dissociative electron attachment (DEA) characteristics, the radiolysis of an aqueous solution of ASCH3 with a dose of X-ray amounting to as much as 300 Gy leads to no effects. Nevertheless, crossed electron-molecule beam experiments in the gas phase on ASCH3 confirm the theoretical findings regarding the stability of its radical anion, namely, the most abundant reaction channel is related to the dissociation of the S-CH3 bond in the respective anion. Furthermore, electron-induced degradation of ASCH3 has been observed in aprotic acetonitrile, which is strong evidence for the involvement of proton transfer (PT) in stabilizing the radical anion in an aqueous solution. These findings demonstrate that PT in water can be the main player in deciding the radiosensitizing properties of modified nucleobases/nucleosides.

Single electron reduction of NHC-CO2-borane compounds

The carbon dioxide radical anion [CO2˙-] is a highly reactive species of fundamental and synthetic interest. However, the direct one-electron reduction of CO2 to generate [CO2˙-] occurs at very negative reduction potentials, which is often a limiting factor for applications. Here, we show that NHC-CO2-BR3 species - generated from the Frustrated Lewis Pair (FLP)-type activation of CO2 by N-heterocyclic carbenes (NHCs) and boranes (BR3) - undergo single electron reduction at a less negative potential than free CO2. A net gain of more than one volt was notably measured with a CAAC-CO2-B(C6F5)3 adduct, which was chemically reduced to afford [CAAC-CO2-B(C6F5)3˙-]. This room temperature stable radical anion was characterized by EPR spectroscopy and by single-crystal X-ray diffraction analysis. Of particular interest, DFT calculations showed that, thanks to the electron withdrawing properties of the Lewis acid, significant unpaired spin density is localised on the carbon atom of the CO2 moiety. Finally, these species were shown to exhibit analogous reactivity to the carbon dioxide radical anion [CO2˙-] toward DMPO. This work demonstrates the advantage provided by FLP systems in the generation and stabilization of [CO2˙-]-like species.

Photoredox-Catalyzed Defluorinative Carboxylation of gem-Difluorostyrenes with Formate Salt

Herein, we present a transition-metal-free, easy handling protocol for regioselective carboxylation of gem-difluorostyrenes with sodium formate as the C1 source. 30 examples of α-fluoracrylates were obtained in yields of 30 to 80% under these conditions. A defluorinative monofluorovinyl intermediate and consecutive photoinduced electron transfer mechanism were proposed after mechanism investigation.

Reactivity of radiolytically and photochemically generated tertiary amine radicals towards a CO2 reduction catalyst

Homogeneous solar fuels photocatalytic systems often require several additives in solution with the catalyst to operate, such as a photosensitizer (PS), Brønsted acid/base, and a sacrificial electron donor (SED). Tertiary amines, in particular triethylamine (TEA) and triethanolamine (TEOA), are ubiquitously deployed in photocatalysis applications as SEDs and are capable of reductively quenching the PS's excited state. Upon oxidation, TEA and TEOA form TEA•+ and TEOA•+ radical cations, respectively, which decay by proton transfer to generate redox non-innocent transient radicals, TEA• and TEOA•, respectively, with redox potentials that allow them to participate in an additional electron transfer step, thus resulting in net one-photon/two-electron donation. However, the properties of the TEA• and TEOA• radicals are not well understood, including their reducing powers and kinetics of electron transfer to catalysts. Herein, we have used both pulse radiolysis and laser flash photolysis to generate TEA• and TEOA• radicals in CH3CN, and combined with UV/Vis transient absorption and time-resolved mid-infrared spectroscopies, we have probed the kinetics of reduction of the well-established CO2 reduction photocatalyst, fac-ReCl(bpy)(CO)3 (bpy = 2,2'-bipyridine), by these radicals [kTEA• = (4.4 ± 0.3) × 109 M-1 s-1 and kTEOA• = (9.3 ± 0.6) × 107 M-1 s-1]. The ∼50× smaller rate constant for TEOA• indicates, that in contrast to a previous assumption, TEA• is a more potent reductant than TEOA• (by ∼0.2 V, as estimated using the Marcus cross relation). This knowledge will aid in the design of photocatalytic systems involving SEDs. We also show that TEA can be a useful radiolytic solvent radical scavenger for pulse radiolysis experiments in CH3CN, effectively converting unwanted oxidizing radicals into useful reducing equivalents in the form of TEA• radicals.

The Mechanism of Inhibition of Pyruvate Formate Lyase by Methacrylate

Pyruvate Formate Lyase (PFL) catalyzes acetyl transfer from pyruvate to coenzyme a by a mechanism involving multiple amino acid radicals. A post-translationally installed glycyl radical (G734· in Escherichia coli) is essential for enzyme activity and two cysteines (C418 and C419) are proposed to form thiyl radicals during turnover, yet their unique roles in catalysis have not been directly demonstrated with both structural and electronic resolution. Methacrylate is an isostructural analog of pyruvate and an informative irreversible inhibitor of pfl. Here we demonstrate the mechanism of inhibition of pfl by methacrylate. Treatment of activated pfl with methacrylate results in the conversion of the G734· to a new radical species, concomitant with enzyme inhibition, centered at g = 2.0033. Spectral simulations, reactions with methacrylate isotopologues, and Density Functional Theory (DFT) calculations support our assignment of the radical to a C2 tertiary methacryl radical. The reaction is specific for C418, as evidenced by mass spectrometry. The methacryl radical decays over time, reforming G734·, and the decay exhibits a H/D solvent isotope effect of 3.4, consistent with H-atom transfer from an ionizable donor, presumably the C419 sulfhydryl group. Acrylate also inhibits PFL irreversibly, and alkylates C418, but we did not observe an acryl secondary radical in H2O or in D2O within 10 s, consistent with our DFT calculations and the expected reactivity of a secondary versus tertiary carbon-centered radical. Together, the results support unique roles of the two active site cysteines of PFL and a C419 S-H bond dissociation energy between that of a secondary and tertiary C-H bond.

Dearomatization of (Hetero)arenes through Photodriven Interplay between Polysulfide Anions and Formate

The facile construction of C(sp3 )-rich carbo- and heterocyclic compounds is a pivotal synthetic strategy to foster contemporary drug discovery programs. The downstream dearomatization of readily accessible two-dimensional (2D) planar arenes represents a direct pathway towards accessing three-dimensional (3D) aliphatic scaffolds. Here, we demonstrate that polysulfide anions are capable of catalyzing a dearomatization process of substituted naphthalenes, indoles, and other related heteroaromatic compounds in the presence of potassium formate and methanol under visible light irradiation. The developed protocol exhibits broad functional group tolerance, operational simplicity, scalability, and cost-effectiveness, representing a practical and sustainable synthetic tool for the arene dearomatization.

Combined Effects of Hemicolligation and Ion Pairing on Reduction Potentials of Biphenyl Radical Cations

Formal reduction potentials of highly oxidizing and short-lived radical cations of substituted biphenyls generated by pulse radiolysis in 1,2-dichloroethane (DCE) were measured using a redox equilibrium ladder method. The effect of halide ion-radical interactions on reduction potentials of biphenyls was examined by utilizing the ability of DCE to release Cl- in the vicinity of the radical cation. The Hammett correlation of measured potentials across a range of over 700 mV shows saturation at high Hammett sigma values. This effect has been explained by both ion-pairing and hemicolligation interactions between biphenyl radical cations and Cl- and appears to modulate reduction potentials by as much as 400 mV. This finding offers a convenient way to manipulate the energetics of electron transfer involving organic redox species.

Recent Advances in C-H Functionalisation through Indirect Hydrogen Atom Transfer

The functionalisation of C-H bonds has been an enormous achievement in synthetic methodology, enabling new retrosynthetic disconnections and affording simple synthetic equivalents for synthons. Hydrogen atom transfer (HAT) is a key method for forming alkyl radicals from C-H substrates. Classic reactions, including the Barton nitrite ester reaction and Hofmann-Löffler-Freytag reaction, among others, provided early examples of HAT. However, recent developments in photoredox catalysis and electrochemistry have made HAT a powerful synthetic tool capable of introducing a wide range of functional groups into C-H bonds. Moreover, greater mechanistic insights into HAT have stimulated the development of increasingly site-selective protocols. Site-selectivity can be achieved through the tuning of electron density at certain C-H bonds using additives, a judicious choice of HAT reagent, and a solvent system. Herein, we describe the latest methods for functionalizing C-H/Si-H/Ge-H bonds using indirect HAT between 2018-2023, as well as a critical discussion of new HAT reagents, mechanistic aspects, substrate scopes, and background contexts of the protocols.

Radical Hydrocarboxylation of Unactivated Alkenes via Photocatalytic Formate Activation

Herein we disclose a strategy to promote the hydrocarboxylation of unactivated alkenes using photochemical activation of formate salts. We illustrate that an alternative initiation mechanism circumvents the limitations of prior approaches and enables hydrocarboxylation of this challenging substrate class. Specifically, we found that accessing the requisite thiyl radical initiator without an exogenous chromophore eliminates major byproducts that have plagued attempts to exploit similar reactivity for unactivated alkene substrates. This redox-neutral method is technically simple to execute and effective across a broad range of alkene substrates. Feedstock alkenes, such as ethylene, are hydrocarboxylated at ambient temperature and pressure. A series of radical cyclization experiments indicate how the reactivity described in this report can be diverted by more complex radical processes.

Mechanistic roles of metal- and ligand-protonated species in hydrogen evolution with [Cp*Rh] complexes

Protonation reactions involving organometallic complexes are ubiquitous in redox chemistry and often result in the generation of reactive metal hydrides. However, some organometallic species supported by η5-pentamethylcyclopentadienyl (Cp*) ligands have recently been shown to undergo ligand-centered protonation by direct proton transfer from acids or tautomerization of metal hydrides, resulting in the generation of complexes bearing the uncommon η4-pentamethylcyclopentadiene (Cp*H) ligand. Here, time-resolved pulse radiolysis (PR) and stopped-flow spectroscopic studies have been applied to examine the kinetics and atomistic details involved in the elementary electron- and proton-transfer steps leading to complexes ligated by Cp*H, using Cp*Rh(bpy) as a molecular model (where bpy is 2,2'-bipyridyl). Stopped-flow measurements coupled with infrared and UV-visible detection reveal that the sole product of initial protonation of Cp*Rh(bpy) is [Cp*Rh(H)(bpy)]+, an elusive hydride complex that has been spectroscopically and kinetically characterized here. Tautomerization of the hydride leads to the clean formation of [(Cp*H)Rh(bpy)]+. Variable-temperature and isotopic labeling experiments further confirm this assignment, providing experimental activation parameters and mechanistic insight into metal-mediated hydride-to-proton tautomerism. Spectroscopic monitoring of the second proton transfer event reveals that both the hydride and related Cp*H complex can be involved in further reactivity, showing that [(Cp*H)Rh] is not necessarily an off-cycle intermediate, but, instead, depending on the strength of the acid used to drive catalysis, an active participant in hydrogen evolution. Identification of the mechanistic roles of the protonated intermediates in the catalysis studied here could inform design of optimized catalytic systems supported by noninnocent cyclopentadienyl-type ligands.

Hydrogen Production from Formic Acid by In Situ Generated Ni/CdS Photocatalytic System under Visible Light Irradiation

Simple and practical noble-metal-free catalyzed hydrogen production from sustainable resources, such as renewable formic acid, is highly desirable. Herein, the development of an efficient photocatalytic hydrogen production from aqueous solution of formic acid using in situ generated Ni/CdS photocatalytic system was described. CdS-Cys (Cys=l-cysteine) quantum dots (QDs) acting as photocatalyst with Ni(OAc)₂ as H₂ production catalyst precursor, a 94 % yield was obtained within 5 h under visible light irradiation at 50 °C. The average rate of H₂ production reached up to 282 μmol mg^-1  h^-1 with 99.8 % H₂ selectivity. Mechanistic studies indicate cooperation of dynamic quenching and static quenching of CdS-Cys QDs by Ni(OAc)₂ . Especially, Ni⁰ , generated in the dynamic quenching, accelerated the electron transfer by acting as an electron outlet and enhancing the stability of CdS to slow down the photocorrosion distinctly, delivering efficient H₂ production with high selectivity. Our study will inspire exploration of various efficient non-noble-metal catalysts for practical H₂ production from bio-based formic acid.

Practical and General Alcohol Deoxygenation Protocol

Herein, we describe a practical protocol for the removal of alcohol functional groups through reductive cleavage of their benzoate ester analogs. This transformation requires a strong single electron transfer (SET) reductant and a means to accelerate slow fragmentation following substrate reduction. To accomplish this, we developed a photocatalytic system that generates a potent reductant from formate salts alongside Brønsted or Lewis acids that promote fragmentation of the reduced intermediate. This deoxygenation procedure is effective across structurally and electronically diverse alcohols and enables a variety of difficult net transformations. This protocol requires no precautions to exclude air or moisture and remains efficient on multigram scale. Finally, the system can be adapted to a one-pot benzoylation-deoxygenation sequence to enable direct alcohol deletion. Mechanistic studies validate that the role of acidic additives is to promote the key C(sp3 )-O bond fragmentation step.

Steric and Lewis Basicity Influence of the Second Coordination Sphere on Electrocatalytic CO2 Reduction by Manganese Bipyridyl Complexes

This study aims to provide a greater insight into the balance between steric (bpy vs (Ph)₂bpy vs mes₂bpy ligands) and Lewis basic ((Ph)₂bpy vs (MeOPh)₂bpy vs (MeSPh)₂bpy ligands) influence on the efficiencies of the protonation-first vs reduction-first CO₂ reduction mechanisms with [Mn^I(R₂bpy)(CO)₃(CH₃CN)]⁺ precatalysts, and on their respective transition-state geometries/energies for rate-determining C-OH bond cleavage toward CO evolution. The presence of only modest steric bulk at the 6,6'-diphenyl-2,2'-bipyridyl ((Ph)₂bpy) ligand has here allowed unique insight into the mechanism of catalyst activation and CO₂ binding by navigating a perfect medium between the nonsterically encumbered bpy-based and the highly sterically encumbered mes₂bpy-based precatalysts. Cyclic voltammetry conducted in CO₂-saturated electrolyte for the (Ph)₂bpy-based precatalyst [2-CH₃CN]⁺ confirms that CO₂ binding occurs at the two-electron-reduced activated catalyst [2]^- in the absence of an excess proton source, in contrast to prior assumptions that all manganese catalysts require a strong acid for CO₂ binding. This observation is supported by computed free energies of the parent-child reaction for [Mn-Mn]⁰ dimer formation, where increased steric hindrance relative to the bpy-based precatalyst correlates with favorable CO₂ binding. A critical balance must be adhered to, however, as the absence of steric bulk in the bpy-based precatalyst [1-CH₃CN]⁺ maintains a lower overpotential than [2-CH₃CN]⁺ at the protonation-first pathway with comparable kinetic performance, whereas an ∼2-fold greater TOF_max is observed at its reduction-first pathway with an almost identical overpotential as [2-CH₃CN]⁺. Notably, excessive steric bulk in the mes₂bpy-based precatalyst [3-CH₃CN]⁺ results in increased activation free energies of the C-OH bond cleavage transition states for both the protonation-first and the reduction-first pathways relative to both [1-CH₃CN]⁺ and [2-CH₃CN]⁺. In fact, [3-CH₃CN]⁺ requires a 1 V window beyond its onset potential to reach its peak catalytic current, which is in contrast to the narrower (<0.30 V) potential response window of the remaining catalysts here studied. Voltammetry recorded under 1 atm of CO₂ with 2.8 M (5%) H₂O establishes [2-CH₃CN]⁺ to have the lowest overpotential (η = 0.75 V) in the series here studied, attributed to its ability to lie "on the fence" when providing sufficient steric bulk to hinder (but not prevent) [Mn-Mn]⁰ dimerization, while simultaneously having a limited steric impact on the free energy of activation for the rate-determining C-OH bond cleavage transition state. While the methoxyphenyl bpy-based precatalyst [4-CH₃CN]⁺ possesses an increased steric presence relative to [2-CH₃CN]⁺, this is offset by its capacity to stabilize the C-OH bond cleavage transition states of both the protonation-first and the reduction-first pathways by facilitating second coordination sphere H-bonding stabilization.

Coupling Pulse Radiolysis with Nanosecond Time-Resolved Step-Scan Fourier Transform Infrared Spectroscopy: Broadband Mid-Infrared Detection of Radiolytically Generated Transients

We describe the first implementation of broadband, nanosecond time-resolved step-scan Fourier transform infrared (S²-FT-IR) spectroscopy at a pulse radiolysis facility. This new technique allows the rapid acquisition of nano- to microsecond time-resolved infrared (TRIR) spectra of transient species generated by pulse radiolysis of liquid samples at a pulsed electron accelerator. Wide regions of the mid-infrared can be probed in a single experiment, which often takes < 20-30 min to complete. It is therefore a powerful method for rapidly locating the IR absorptions of short-lived, radiation-induced species in solution, and for directly monitoring their subsequent reactions. Time-resolved step-scan FT-IR detection for pulse radiolysis thus complements our existing narrowband quantum cascade laser-based pulse radiolysis-TRIR detection system, which is more suitable for acquiring single-shot kinetics and narrowband TRIR spectra on small-volume samples and in strongly absorbing solvents, such as water. We have demonstrated the application of time-resolved step-scan FT-IR spectroscopy to pulse radiolysis by probing the metal carbonyl and organic carbonyl vibrations of the one-electron-reduced forms of two Re-based CO₂ reduction catalysts in acetonitrile solution. Transient IR absorption bands with amplitudes on the order of 1 × 10^-3 are easily detected on the sub-microsecond timescale using electron pulses as short as 250 ns.

CO2 Electroreduction in Organic Aprotic Solvents: A Mini Review

An annual increase of CO2 concentrations in the atmosphere causes global environmental problems, addressed by systematic research to develop effective technologies for capturing and utilizing carbon dioxide. Electrochemical catalytic reduction is one of the effective directions of CO2 conversion into valuable chemicals and fuels. The electrochemical conversion of CO2 at catalytically active electrodes in aqueous solutions is the most studied. However, the problems of low selectivity for target products and hydrogen evolution are unresolved. Literature sources on CO2 reduction at catalytically active cathodes in nonaqueous mediums, particularly in organic aprotic solvents, are analyzed in this article. Two directions of cathodic reduction of CO2 are considered—nonaqueous organic aprotic solvents and organic aprotic solvents containing water. The current interpretation of the cathodic conversion mechanism of carbon (IV) oxide into CO and organic products and the main factors influencing the rate of CO2 reduction, Faradaic efficiency of conversion products, and the ratio of direct cathodic reduction of CO2 are given. The influence of the nature of organic aprotic solvent is analyzed, including the topography of the catalytically active cathode, values of cathode potential, and temperature. Emphasis is placed on the role of water impurities in reducing CO2 electroreduction overpotentials and the formation of new CO2 conversion products, including formate and H2.

Solvated Electron in Acetonitrile: Radiation Yield, Absorption Spectrum, and Equilibrium between Cavity- and Solvent-Localized States

The equilibrium between a solvent cavity-localized electron, e_cav^-, and a dimeric solvent anion, (CH₃CN)₂^•-, which are the two lowest energy states of the solvated electron in acetonitrile, has been investigated by pulse radiolysis at 233-353 K. The enthalpy and entropy for the e_cav^- to (CH₃CN)₂^•- conversion amount to -11.2 ± 0.3 kcal/mol and -39.3 ± 1.2 cal/(mol K), corresponding to a 0.44 ± 0.35 equilibrium constant at 25 °C. The radiation yield of the solvated electron has been quantified using a Co(II) macrocycle that scavenges electrons with a 1.55 × 10¹¹ M^-1 s^-1 rate constant. The apparent yield increases without saturation over the attainable scavenger concentration range, reaching 2.8 per 100 eV; this value represents the lower limit for the acetonitrile ionization yield in pulse radiolysis. The apparent molar absorption coefficient of (20.8 ± 1.5) × 10³ M^-1 cm^-1 at 1450 nm and 20 °C for the solvated electron and individual vis-near-infrared (NIR) absorption spectra of e_cav^- and (CH₃CN)₂^•- are derived from the data. Variances with previous reports are thoroughly discussed. Collectively, these results resolve several controversies concerning the solvated electron properties in acetonitrile and furnish requisite data for quantitative pulse radiolysis investigations in this commonly used solvent.

The energetics of electron and proton transfer to CO2 in aqueous solution

The electrocatalytic reduction of CO₂ is considered an effective method to reduce CO₂ emissions and achieve electrical/chemical energy conversion. It is crucial to determine the reaction mechanism so that the key reaction intermediates can be targeted and the overpotential lowered. The process involves the interaction with the electrode surface and with species, including the solvent, at the electrode-electrolyte interface, and it is therefore not easy to separate catalytic contributions of the electrode from those of the electrolyte. We have used density functional theory-based molecular dynamics to calculate the Gibbs free energy of the proton and electron transfer reactions corresponding to each step in the electroreduction of CO₂ to HCOOH in aqueous media. The results show thermodynamic pathways consistent with the mechanism proposed by Hori. Since electrodes are not included in this work, differences between the calculated results and the experimental observations can help determine the catalytic contribution of the electrode surface.

Photoinduced Hydrocarboxylation via Thiol-Catalyzed Delivery of Formate Across Activated Alkenes

Herein we disclose a new photochemical process to prepare carboxylic acids from formate salts and alkenes. This redox-neutral hydrocarboxylation proceeds in high yields across diverse functionalized alkene substrates with excellent regioselectivity. This operationally simple procedure can be readily scaled in batch at low photocatalyst loading (0.01% photocatalyst). Furthermore, this new reaction can leverage commercially available formate carbon isotologues to enable the direct synthesis of isotopically labeled carboxylic acids. Mechanistic studies support the working model involving a thiol-catalyzed radical chain process wherein the atoms from formate are delivered across the alkene substrate via CO₂^•- as a key reactive intermediate.

Integration of aprotic CO2 reduction to oxalate at a Pb catalyst into a GDE flow cell configuration

Electrochemical CO2 reduction to oxalic acid in aprotic solvents could be a potential pathway to produce carbon-neutral oxalic acid. One of the challenges in aprotic CO2 reduction are the limited achievable current densities under standard conditions, despite the increased CO2 solubility compared to aqueous applications. The application of aprotic solvents can reduce CO2 rather selectively to oxalate, and faradaic efficiencies (FEs) of up to 80% were achieved in this study with a Pb catalyst in acetonitrile, the FE being mainly dictated by the local CO2 concentration at the electrode. This process was integrated into a flow cell employing a two-layered carbon-free lead (Pb) gas diffusion electrode (GDE) and a sacrificial zinc (Zn) anode. With the application of this GDE the applicable current densities could be improved up to a current density of j = 80 mA cm-2 at a FE(oxalate) = 53%, which is within the range of the highest j reported in the literature. In addition, we provide an explanation for the deactivation mechanism of metal catalysts observed in the aprotic CO2 reduction literature. The deactivation is not related to a mass transport limitation but to cathodic corrosion observed at highly negative potential when employing quaternary ammonium supporting electrolyte cations, promoting catalyst leaching.

Non-innocent Radical Ion Intermediates in Photoredox Catalysis: Parallel Reduction Modes Enable Coupling of Diverse Aryl Chlorides

We describe a photocatalytic system that elicits potent photoreductant activity from conventional photocatalysts by leveraging radical anion intermediates generated in situ. The combination of an isophthalonitrile photocatalyst and sodium formate promotes diverse aryl radical coupling reactions from abundant but difficult to reduce aryl chloride substrates. Mechanistic studies reveal two parallel pathways for substrate reduction both enabled by a key terminal reductant byproduct, carbon dioxide radical anion.

Radiolytic Approach for Efficient, Selective and Catalyst-free CO2 Conversion at Room Temperature

The present study proposes a new approach for direct CO₂ conversion using primary radicals from water irradiation. In order to ensure reduction of CO₂ into CO₂ ^-. by all the primary radiation-induced water radicals, we use formate ions to scavenge simultaneously the parent oxidizing radicals H^. and OH^. producing the same transient CO₂ ^-. radicals. Conditions are optimized to obtain the highest conversion yield of CO₂ . The goal is achieved under mild conditions of room temperature, neutral pH and 1 atm of CO₂ pressure. All the available radicals are exploited for selectively converting CO₂ into oxalate that is accompanied by H₂ evolution. The mechanism presented accounts for the results and also sheds light on the data in the literature. The radiolytic approach is a mild and scalable route of direct CO₂ capture at the source in industry and the products, oxalate salt and H₂ , can be easily separated.