CO2‐Induced Spin‐State Switching at Room Temperature in a Monomeric Cobalt(II) Complex with the Porous Nature

CO₂‐responsive spin‐state conversion between high‐spin (HS) and low‐spin (LS) states at room temperature was achieved in a monomeric cobalt(II) complex. A neutral cobalt(II) complex, [Co^II(COO‐terpy)₂]?4 H₂O ( 1?4 H₂O ), stably formed cavities generated via π–π stacking motifs and hydrogen bond networks, resulting in the accommodation of four water molecules. Crystalline 1?4 H₂O transformed to solvent‐free 1 without loss of porosity by heating to 420 K. Compound 1 exhibited a selective CO₂ adsorption via a gate‐open type of the structural modification. Furthermore, the HS/LS transition temperature (T_1/2) was able to be tuned by the CO₂ pressure over a wide temperature range. Unlike 1 exhibits the HS state at 290 K, the CO₂‐accomodated form 1?CO₂ (P =110 kPa) was stabilized in the LS state at 290 K, probably caused by a chemical pressure effect by CO₂ accommodation, which provides reversible spin‐state conversion by introducing/evacuating CO₂ gas into/from 1 .     

Adsorption of CO2 and Coadsorption of H and CO2 on Potassium‐Promoted Cu(115)

The influence of potassium, in the submonolayer regime, on the adsorption and coadsorption of CO₂ and H on a stepped copper surface, Cu(115), has been studied by photoelectron spectroscopy, temperature‐programmed desorption, and work‐function measurements. Based on the fast recording of C 1s and O 1s core‐level spectra, the uptake of CO₂ on K/Cu(115) surfaces at 120 K has been followed in real time, and the different reaction products have been identified. The K 2p_3/2 peak exhibits a chemical shift of ?0.4 eV with CO₂ saturation, the C 1s peaks of the CO₃ and the CO species show shifts of ?0.8 and ?0.5 eV, respectively, and the C 1s peak of the physisorbed CO₂ exhibits no shift. The effects of gradually heating the CO₂/K/Cu(115) surface include the desorption of physisorbed CO₂ at 143 K; the desorption of CO at 193 K; the ordering of the CO₃ species, and subsequently the dissociation of the carbonate with desorption at 520–700 K. Formate, HCOO^?, was synthesized by the coadsorption of H and CO₂ on the K/Cu(115) surface at 125 K. Formate formed exclusively for potassium coverages of less than 0.4 monolayer, whereas both formate and carbonate were formed at higher coverages. The desorption of formate‐derived CO₂ took place in the temperature range 410–425 K and carbonate‐derived CO₂ desorbed at 645–660 K, depending on the potassium coverage.     

A Noble‐Metal‐Free Metal–Organic Framework (MOF) Catalyst for the Highly Efficient Conversion of CO2 with Propargylic Alcohols

Cyclization of propargylic alcohols with CO₂ is an important reaction in industry, and noble‐metal catalysts are often employed to ensure the high product yields under environmentally friendly conditions. Herein a porous noble‐metal‐free framework 1 with large 1D channels of 1.66 nm diameter was synthesized for this reaction. Compound 1 exhibits excellent acid/base stability, and is even stable in corrosive triethylamine for one month. Catalytic studies indicate that 1 is an effective catalyst for the cyclization of propargylic alcohols and CO₂ without any solvents under mild conditions, and the turnover number (TON) can reach to a record value of 14 400. Furthermore, this MOF catalyst also has rarely seen catalytic activity when the biological macromolecule ethisterone was used as a substrate. Mechanistic studies reveal that the synergistic catalytic effect between Cu^I and In^III plays a key role in the conversion of CO₂.     

High yield synthesis of biodegradable poly(propylene carbonate) from carbon dioxide and propylene oxide

A novel SalenCo^III (2,4‐dinitrophenoxy) (Salen = N,N'‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediamino) and 1,10‐phenanthroline monohydrate catalyst system was designed and employed for the copolymerization of CO₂ and propylene oxide (PO). The perfectly alternating copolymerization of CO₂ and PO proceeds effectively under middle temperature and pressure to yield poly(propylene carbonate) with a high yield and a high number average molecular weight of polymer. The structure of polymer was characterized by the IR and NMR measurements. The perfectly alternating copolymer was confirmed. The MALDI‐TOF spectrum insinuates that the copolymerization of CO₂ and PO was initiated by H₂O. Copyright © 2016 John Wiley & Sons, Ltd.     

Stable,Hydroxyl Functional Polycarbonates With Glycerol Side Chains Synthesized From CO2 and Isopropylidene(glyceryl glycidyl ether)

A series of functional polycarbonates, poly((isopropylidene glyceryl glycidyl ether)‐co‐(glycidyl methyl ether) carbonate) (P((IGG‐co‐GME) C)) random copolymers with different fractions of 1,2‐isopropylidene glyceryl glycidyl ether (IGG) units, is synthesized. After acidic hydrolysis of the acetal protecting groups, a new type of functional polycarbonate prepared directly from CO₂ and glycerol is obtained, namely poly((glyceryl glycerol)‐co‐(glycidyl methyl ether) carbonate) (P((GG‐co‐GME) C)). All hydroxyl functional samples exhibit monomodal molecular weight distributions with PDIs between 2.5 and 3.3 and M _n between 12 000 and 25 000 g mol⁻¹. Thermal properties reflect the amorphous structure of the polymers. The materials are stable in bulk and solution.     

Design and Syntheses of Three Novel Carbonate Halides: Cs3Pb2(CO3)3I,KBa2(CO3)2F,and RbBa2(CO3)2F

Three new carbonate halides, Cs₃Pb₂(CO₃)₃I, KBa₂(CO₃)₂F and RbBa₂(CO₃)₂F have been synthesized with hydrothermal and solid‐state methods. Cs₃Pb₂(CO₃)₃I is the first product in the lead carbonate iodides family; KBa₂(CO₃)₂F and RbBa₂(CO₃)₂F are the first two centrosymmetric compounds found in the alkaline–alkaline earth carbonate fluorides family. Cs₃Pb₂(CO₃)₃I crystallizes in a centrosymmetric space group C2/m, and exhibits a two‐ dimensional layered structure which is formed by [Cs₄Pb₄(CO₃)₆I₂]_∞ double‐layers consisting of [Pb₂(CO₃)₃I]_∞ single‐layers bridged by the Cs atoms. KBa₂(CO₃)₂F and RbBa₂(CO₃)₂F, which are isostructural, crystallize in a trigonal crystal system with a centric space group of R featuring a honeycomb‐like framework. First principle calculations indicate that Cs₃Pb₂(CO₃)₃I has a moderate birefringence and explain the difference between the band gaps of the title compounds from electron structures. The effects of cations and halogens on the structures and properties of the title compounds are also discussed.     

Palladium‐catalyzed carbonylative cyclization of 3‐bromoallyl alcohols leading to furan‐2(5H)‐ones

3‐Bromoallyl alcohols are carbonylatively cyclized under carbon monoxide pressure in toluene in the presence of a catalytic amount of Pd(OAc)₂ and PPh₃ along with Na₂CO₃ to give furan‐2(5H)‐ones in good yields. Copyright © 2012 John Wiley & Sons, Ltd.     

A comparative study of two polymorphs of bis(1‐hydroxy‐2‐methylpropan‐2‐aminium) carbonate

Alkanolamines have been known for their high CO₂ absorption for over 60 years and are used widely in the natural gas industry for reversible CO₂ capture. In an attempt to crystallize a salt of (RS)‐2‐(3‐benzoylphenyl)propionic acid with 2‐amino‐2‐methylpropan‐1‐ol, we obtained instead a polymorph (denoted polymorph II) of bis(1‐hydroxy‐2‐methylpropan‐2‐aminium) carbonate, 2C₄H₁₂NO⁺·CO₃²⁻, (I), suggesting that the amine group of the former compound captured CO₂ from the atmosphere forming the aminium carbonate salt. This new polymorph was characterized by single‐crystal X‐ray diffraction analysis at low temperature (100 K). The salt crystallizes in the monoclinic system (space group C2/c, Z = 4), while a previously reported form of the same salt (denoted polymorph I) crystallizes in the triclinic system (space group P, Z = 2) [Barzagli et al. (2012). ChemSusChem, 5 , 1724–1731]. The asymmetric unit of polymorph II contains one 1‐hydroxy‐2‐methylpropan‐2‐aminium cation and half a carbonate anion, located on a twofold axis, while the asymmetric unit of polymorph I contains two cations and one anion. These polymorphs exhibit similar structural features in their three‐dimensional packing. Indeed, similar layers of an alternating cation–anion–cation neutral structure are observed in their molecular arrangements. Within each layer, carbonate anions and 1‐hydroxy‐2‐methylpropan‐2‐aminium cations form planes bound to each other through N—H…O and O—H…O hydrogen bonds. In both polymorphs, the layers are linked to each other via van der Waals interactions and C—H…O contacts. In polymorph II, a highly directional C—H…O contact (C—H…O = 156°) shows as a hydrogen‐bonding interaction. Periodic theoretical density functional theory (DFT) calculations indicate that both polymorphs present very similar stabilities.     

Calorimetric investigation of reaction Ca(NO3)2 + Na3PO4 in water and microemulsions saturated with CO2

The reactions of Ca(NO₃)₂ + Na₃PO₄ in water and water/sodium bis(2‐ethylhexyl) sulfosuccinate (AOT)/hydrocarbon microemulsions saturated CO₂ with various molar ratios of water to surfactant R, oil phases, and surfactant concentrations were investigated by isothermal titration calorimetry. The product of the reaction was confirmed to be sodium‐and‐carbonate‐substituted hydroxyapatite (NaCO₃HAP) by Fourier transform infrared spectra (FTIR), energy dispersive spectrometry (EDS), and X‐ray diffraction (XRD). From calorimetric measurements, the molar enthalpies of solution of water in the AOT/n‐dodecane system, and the molar enthalpies, the rate constants, and the activation energies of the reactions were determined. It was found that the enthalpy of solution of water in AOT/n‐dodecane micells and the molar enthalpy of the reaction in the microemulsions increased with the decreases of R until R = 7; below that they kept almost constant. It may be attributed to the increase of the ratio of the bound water to the free water with the decrease of R until there was no free water when R < 7. However, the reaction rate constant k₁ was affected by the ionic strength of the medium and log k₁ showed a linear dependence on 1/R in the whole range of R we investigated. It was also observed that the rate constant and the enthalpy of the reaction remained almost unchanged when the surfactant concentration and the nature of oil phase varied. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 322–330, 2011     

A vibrational-spectroscopic study of the species present in the CO2−H2O system

Raman and infrared spectra have been recorded of water and heavy-water solutions of carbon dioxide, potassium bicarbonate, and potassium carbonate. The structures of the carbonate and bicarbonate ions and CO₂ (aqueous solution) have been determined from a consideration of Raman and infrared data. The results reveal the presence of solvent effects in the carbonate and CO₂ water solutions. No bands characteristic of H₂CO₃ were observed in the Raman spectrum of aqueous solutions of CO₂.     

Silver(I)‐Catalyzed Three‐Component Reaction of Propargylic Alcohols,Carbon Dioxide and Monohydric Alcohols: Thermodynamically Feasible Access to β‐Oxopropyl Carbonates

A silver(I)‐catalyzed three‐component reaction of propargylic alcohols, CO₂, and monohydric alcohols was successfully developed for the synthesis of β‐oxopropyl carbonates. As such, a series of β‐oxopropyl carbonates were exclusively produced in excellent yields (up to 98 %), even under atmospheric pressure of CO₂. The silver catalyst works efficiently for both the carboxylative cyclization of propargylic alcohols with CO₂ and subsequent transesterification of α‐alkylidene cyclic carbonates with monohydric alcohols; thus this tandem process performs smoothly under mild conditions. This work provides a versatile and thermodynamically favorable approach to dissymmetric dialkyl carbonates.     

A Biomass-Ligand-Based Ru(III) Complex as a Catalyst for Cycloaddition of CO2 and Epoxides to Cyclic Carbonates and a Study of the Mechanism

Aiming highly efficient conversion of greenhouse gas CO₂ to cyclic carbonates, a biomass Ru(III) Schiff base complex catalyst ( SalRu ) was constructed by employing a derivative of Lignin degradation (5-aldehyde vanillin). The SalRu catalyst had a remarkable conversion for epoxides into corresponding cyclic carbonates even at atmospheric pressure of CO₂ without the presence of co-catalyst. As the condition at 120 °C and 2 MPa CO₂ the conversion reached to 94 % with selectivity at 99 % after 8 h. 32 % cyclic carbonate production was obtained even under 0.2 MPa CO₂ pressure. The epoxide activation and ring opening, CO₂ insertion and cyclic carbonate formation were illuminated explicitly through the of characteristic absorption peaks changing, which further providing direct and visual evidence for the mechanism proposing. This study has important theoretical significance for the comprehensive utilization of environmental pollutants and energy.     

Poly(ionic liquid)s based on imidazolium hydrogen carbonate monomer units as recyclable polymer‐supported N‐heterocyclic carbenes: Use in organocatalysis

Synthesis of novel poly(ionic liquid)s, namely, poly(1‐vinyl‐3‐alkylimidazolium hydrogen carbonate)s, denoted as poly([NHC(H)][HCO₃])s or PVRImHCO₃, where R is an alkyl group (R = ethyl, butyl, phenylethyl, dodecyl), is described. Two distinct synthetic routes were explored. The first method is based on the free‐radical polymerization (FRP) of 1‐vinyl‐3‐alkylimidazolium monomers featuring a hydrogen carbonate counter anion (HCO₃^?), denoted as VRImHCO₃. The latter monomers were readily synthesized by alkylation of 1‐vinylimidazole (VIm), followed by direct anion exchange of 1‐vinyl‐3‐alkylimidazolium bromide monomers (VRImBr), using potassium hydrogen carbonate (KHCO₃) in methanol at room temperature. Alternatively, the same anion exchange method could be applied onto FRP‐derived poly(1‐vinyl‐3‐alkylimidazolium bromide) precursors (PVRImBr). All PVRImHCO₃ salts proved air stable and could be manipulated without any particular precautions. They could serve as polymer‐supported precatalysts to generate polymer‐supported N‐heterocyclic carbenes, referred to as poly(NHC)s, formally by a loss of “H₂CO₃” (H₂O +CO₂) in solution. This was demonstrated through selected organocatalyzed reactions of molecular chemistry, known as being efficiently mediated by molecular NHC catalysts, including benzoin condensation, transesterification and cyanosilylation of aldehyde. Of particular interest, recycling of the polymer‐supported precatalysts was possible by re‐carboxylation of in situ generated poly(NHC)s. Organocatalyzed reactions could be performed with excellent yields, even after five catalytic cycles. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4530–4540     

Carbon Dioxide Activation at Metal Centers: Evolution of Charge Transfer from Mg .+ to CO2 in [MgCO2(H2O)n].+, n=0–8

We investigate activation of carbon dioxide by singly charged hydrated magnesium cations Mg ^.+(H₂O)_n, through infrared multiple photon dissociation (IRMPD) spectroscopy combined with quantum chemical calculations. The spectra of [MgCO₂(H₂O)_n]^.+ in the 1250–4000 cm^?1 region show a sharp transition from n=2 to n=3 for the position of the CO₂ antisymmetric stretching mode. This is evidence for the activation of CO₂ via charge transfer from Mg ^.+ to CO₂ for n≥3, while smaller clusters feature linear CO₂ coordinated end‐on to the metal center. Starting with n=5, we see a further conformational change, with CO₂^.? coordination to Mg²⁺ gradually shifting from bidentate to monodentate, consistent with preferential hexa‐coordination of Mg²⁺. Our results reveal in detail how hydration promotes CO₂ activation by charge transfer at metal centers.     

Synthesis,Characterization, and Properties of a Carbonate‐Bridged Dinuclear Rhodium(III) Complex via Fixation of Atmospheric CO2

A carbonate‐bridged rhodium(III) dimeric complex of formula μ‐CO₃‐[(ppy)₂Rh]₂, (ppy = 2‐phenylpyridine) was synthesized and characterized by IR and ¹H NMR spectroscopy as well as X‐ray diffraction. The bridging carbonate ion presumably originates from the capture of CO₂ in air deduced on a series of control experiments, which may have valuable implications for the study of fixation of CO₂. The luminescent and thermal properties of this complex were also investigated.     

Synthesis of poly[(2‐oxo‐1,3‐dioxolane‐ 4‐yl)methyl methacrylate‐co‐styrene] by addition reaction of carbon dioxide and its compatibility with poly(methyl methacrylate) or poly(vinyl chloride)

We investigated the chemical fixation of carbon dioxide (CO ₂) to a copolymer bearing epoxide and the application of the cyclic carbonate group containing copolymer to polymer blends. In the synthesis of poly[(2‐oxo‐1,3‐dioxolane‐4‐yl)methyl methacrylate‐co‐styrene] [poly(DOMA‐co‐St)] from the addition of CO ₂ to poly(glycidyl methacrylate‐co‐styrene) [poly(GMA‐co‐St)], quaternary ammonium salts showed good catalytic activity at mild reaction conditions. The CO ₂ addition reaction followed pseudo first‐order kinetics with the concentration of poly(GMA‐co‐St). In order to expand the applications of the CO ₂ fixed copolymer, polymer blends of this copolymer with poly(methyl methacrylate) (PMMA) or poly(vinyl chloride) (PVC) were cast from N,N′‐dimethylformamide (DMF) solution. Miscibility of blends of poly(DOMA‐co‐St) with PMMA or PVC have been investigated both by differential scanning calorimetry (DSC) and visual inspection of the blends, and the blends were miscible over the whole composition ranges. The miscibility behaviors were also discussed in terms of FT‐IR spectra. Copyright © 2002 John Wiley & Sons, Ltd.     

Sur les carbonates basiques de fer (III): III. Préparation,radiocristallographie et spectres IR. du (NH4)4Fe2(OH)4(CO3)3·3H2O

The obtention of the crystalline basic carbonate of iron (III) and ammonium, (NH₄)₄Fe₂(OH)₄(CO₃)₃ · 3 H₂O, is described, and its formula is established by chemical analysis and infrared spectroscopy. The compound is probably monoclinic, but it was not possible to index with certainty all X-ray reflections. The compound is similar to (NH₄)₂Fe₂(OH)₄(CO₃)₂ · H₂O and its infrared spectrum leads to the assumption that in both the CO group is linked in the same fashion.     

Stereoregular polycarbonate synthesis: Alternating copolymerization of CO2 with aliphatic terminal epoxides catalyzed by multichiral cobalt(III) complexes

Completely stereoregular polycarbonate synthesis was achieved with the use of unsymmetric multichiral cobalt‐based complexes bearing a derived chiral BINOL and an appended 1,5,7‐triabicyclo[4.4.0] dec‐5‐ene as catalyst for the copolymerization of CO₂ and aliphatic terminal epoxides at mild conditions. The (S,S,S)‐Co(III) complex 1c with sterically hindered substituent group is more stereoregular catalyst for the copolymerization of CO₂ and racemic propylene oxide to afford a perfectly regioregular poly(propylene carbonate) (PPC), with >99% head‐to‐tail linkages, >99% carbonate linkages, and a K_rel of 24.4 for the enchainment of (R)‐epoxide over (S)‐epoxide. The isotactic PPC exhibits an enhanced glass transition temperature of 47 °C, which is 10–12 °C higher than that of the corresponding irregular polycarbonate. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Mechanistic study of photocatalytic CO2 reduction using a Ru(ii)–Re(i) supramolecular photocatalyst

Supramolecular photocatalysts comprising [Ru(diimine)₃]²⁺ photosensitiser and fac-[Re(diimine)(CO)₃{OC(O)OC₂H₄NR₂}] catalyst units can be used to reduce CO₂ to CO with high selectivity, durability and efficiency. In the presence of triethanolamine, the Re catalyst unit efficiently takes up CO₂ to form a carbonate ester complex, and then direct photocatalytic reduction of a low concentration of CO₂, e.g., 10% CO₂, can be achieved using this type of supramolecular photocatalyst. In this work, the mechanism of the photocatalytic reduction of CO₂ was investigated applying such a supramolecular photocatalyst, RuC2Re with a carbonate ester ligand, using time-resolved visible and infrared spectroscopies and electrochemical methods. Using time-resolved spectroscopic measurements, the kinetics of the photochemical formation processes of the one-electron-reduced species RuC2(Re)−, which is an essential intermediate in the photocatalytic reaction, were clarified in detail and its electronic structure was elucidated. These studies also showed that RuC2(Re)− is stable for 10 ms in the reaction solution. Cyclic voltammograms measured at various scan rates besides temperature and kinetic analyses of RuC2(Re)− produced by steady-state irradiation indicated that the subsequent reaction of RuC2(Re)− proceeds with an observed first-order rate constant of approximately 1.8 s⁻¹ at 298 K and is a unimolecular reaction, independent of the concentrations of both CO₂ and RuC2(Re)−.

Formation processes and reactivity of an important intermediate of photocatalytic CO₂ reduction, one-electron reduced species of a Ru(ii)–Re(i) supramolecular photocatalyst with a carbonate ester ligand, were investigated in detail.     

CO2 Capture from Ambient Air by Crystallization with a Guanidine Sorbent

Carbon capture and storage is an important strategy for stabilizing the increasing concentration of atmospheric CO₂ and the global temperature. A possible approach toward reversing this trend and decreasing the atmospheric CO₂ concentration is to remove the CO₂ directly from air (direct air capture). Herein we report a simple aqueous guanidine sorbent that captures CO₂ from ambient air and binds it as a crystalline carbonate salt by guanidinium hydrogen bonding. The resulting solid has very low aqueous solubility (K _sp=1.0(4)×10⁻⁸), which facilitates its separation from solution by filtration. The bound CO₂ can be released by relatively mild heating of the crystals at 80–120 °C, which regenerates the guanidine sorbent quantitatively. Thus, this crystallization‐based approach to CO₂ separation from air requires minimal energy and chemical input, and offers the prospect for low‐cost direct air capture technologies.