Hydrogenation of CO2 to Formate with H2: Transition Metal Free Catalyst Based on a Lewis Pair

Hydrogenation of CO₂ to formate with H₂ in the absence of transition metal is a long‐standing challenge in catalysis. The reactions between tris(pentafluorophenyl)borane (BCF) and K₂CO₃ (or KHCO₃) are found to form a Lewis pair (K₂[(BCF)₂?CO₃]) which can react with both H₂ and CO₂ to produce formate. Based on these stoichiometric reactions, the first catalytic hydrogenation process of CO₂ to formate using transition metal free catalyst (BCF/M₂CO₃, M=Na, K, and Cs) is reported. The highest TON value of this catalytic process is up to 3941. Further research revealed the reaction mechanism in which the Lewis pair enables the splitting of H₂ and the insertion of CO₂ into the B?H bond.     

Pyridinium-functionalized metalloporphyrins as bifunctional catalysts for cycloaddition of epoxides and carbon dioxide

New pyridinium-functionalized metalloporphyrins MEtPpBr₄ (M = Zn²⁺, Co²⁺, Ni²⁺, Cu²⁺; EtPp = 5, 10, 15, 20-tetra(4-(3-(N-ethyl-4-pyridyl)pyrazolyl)phenyl)porphyrin) were synthesized as bifunctional catalysts for the cycloaddition reactions of epoxides and CO₂. The effects of catalyst loading, CO₂ pressure, reaction temperature and time on catalytic activity were investigated. ZnEtPpBr₄ ( 1 ) and CoEtPpBr₄ ( 2 ) exhibited efficient activities in the cycloaddition reactions of various epoxides with CO₂ as at 120 °C under 2 MPa of CO₂ pressure without solvent. Most of corresponding cyclic carbonates could be obtained in almost quantitative yields and > 99.9% selectivity with molar ratio of epoxide/catalyst 2222 after 8 hr of reaction.     

Reversible Addition of Carbon Dioxide to Main Group Metal Complexes at Temperatures about 0 °C

The reaction of dialane [LAl-AlL] ( 1 ; L=dianion of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene, dpp-bian) with carbon dioxide results in two different products depending on solvent. In toluene at temperatures of about 0 °C, the reaction gives cycloadduct [L(CO₂)Al-Al(O₂C)L] ( 2 ), whereas in diethyl ether, the reaction affords oxo-bridged carbamato derivative [L(CO₂)(Et₂O)Al(μ-O)AlL] ( 3 ). The DFT and QTAIM calculations provide reasonable explanations for the reversible formation of complex 2 in the course of two subsequent (2+4) cycloaddition reactions. Consecutive transition states with low activation barriers were revealed. Also, the DFT study demonstrated a crucial effect of diethyl ether coordination to aluminium on the reaction of dialane 1 with CO₂. The optimized structures of key intermediates were obtained for the reactions in the presence of Et₂O; calculated thermodynamic parameters unambiguously testify the irreversible formation of the product 3 .     

Rate constants for the reactions of Cl atoms with HCOOH and with HOCO radicals

Rate constants have been measured at room temperature for the reactions of Cl atoms with formic acid and with the HOCO radical: Cl + HCOOH → HCl + HOCO (R1) Cl + HOCO → HCl + CO₂ (R2) Cl atoms were generated by flash photolysis of Cl₂ and the progress of reaction was followed by time‐resolved infrared absorption measurements using tunable diode lasers on the CO₂ that was formed either in the pair of reactions ( R1 ) plus ( R2 ), or in reaction ( R1 ) followed by O₂ + HOCO → HO₂ + CO₂ (R3) In a separate series of experiments, conditions were chosen so that the kinetics of CO₂ formation were dominated either by the rate of reaction ( R1 ) or by that of reactions ( R1 ) and ( R2 ) combined. The results of our analysis of these experiments yielded: k₁ = (1.8₃ ± 0.12) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ k₂ = (4.8 ± 1.0) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 85–91, 2000     

Hochdrucksynthesen einiger Carbonate mit überkritischem CO2

Syntheses of Some Carbonates with CO₂ under High Pressures Carbonates of the alkali metals and of some transition metals are prepared from their solutions, hydroxides, or oxides by reactions with CO₂ using pressures of 600–4500 at and temperatures of 100– 400°C. The carbonates MnCO₃, FeCO₃, CoCO₃, NiCO₃, ZrCO₃ · 2H₂O, Th(CO₃)₂ · 0.5 H₂O and the carbonates of the alkali metals are characterized by infrared spectroscopy and X-ray investigations. The structures of Rb₂CO₃ (1) and Cs₂CO₃ (2) are presented. They are both monoclinic, space group P 2_1/c (No. 14) with a = 5.87 (1), 6.13 (2); b = 10.13 (1), 10.28 (2); c = 7.33 (1), 8.15 Å (2), β = 97.65° (1), 95.85° (2) and Z = 4.     

Reaction of Amino-Terminated PAMAM Dendrimers with Carbon Dioxide in Aqueous and Methanol Solutions

Polyamines have been used as active materials to capture carbon dioxide gas based on its well-known reaction with amines to form carbamates. This work investigates the reactions between three amino-terminated poly(amidoamine) (PAMAM) dendrimers (G1, G3 and G5) and CO₂(g) in aqueous (D₂O) and methanolic (CD₃OD) solutions. The reactions were monitored using ¹H NMR spectroscopy, and yielded dendrimers with a combination of terminal carbamate and terminal ammonium groups. In aqueous media the reaction was complicated by the generation of soluble carbonate and bicarbonate ions. The reaction was cleaner in CD₃OD, where the larger G5 dendrimer solution formed a gel upon exposure to CO₂(g). All reactions were reversible, and the trapped CO₂ could be released by treatment with N₂(g) and mild heating. These results highlight the importance of the polyamine dendrimer size in terms of driving changes to the solution’s physical properties (viscosity, gel formation) generated by exposure to CO₂(g).     

Abiotic C?C bond formation under environmental conditions: Kinetics of the aldol condensation of acetaldehyde in water catalyzed by carbonate ions (CO32−)

The role of C? C bond‐forming reactions such as aldol condensation in the degradation of organic matter in natural environments is receiving a renewed interest because naturally occurring ions, ammonium ions, NH⁺₄, and carbonate ions, CO₃^2?, have recently been reported to catalyze these reactions. While the catalysis of aldol condensation by OH^? has been widely studied, the catalytic properties of carbonate ions, CO₃^2?, have been little studied, especially under environmental conditions. This work presents a study of the catalysis of the aldol condensation of acetaldehyde in aqueous solutions of sodium carbonate (0.1–50 mM) at T = 295 ± 2 K. By monitoring the absorbance of the main product, crotonaldehyde, instead of that of acetaldehyde, interferences from other reaction products and from side reactions, in particular a known Cannizzaro reaction, were avoided. The rate constant was found to be first order in acetaldehyde in the presence of both CO₃^2? and OH^?, suggesting that previous studies reporting a second order for this base‐catalyzed reaction were flawed. Comparisons between the rate constants in carbonate solutions and in sodium hydroxide solutions ([NaOH] = 0.3–50 mM) showed that, among the three bases present in carbonate solutions, CO₃^2?, HCO₃^?, and OH^?, OH^? was the main catalyst for pH ≤ 11. CO₃^2? became the main catalyst at higher pH, whereas the catalytic contribution of HCO₃^? was negligible over the range of conditions studied (pH 10.3–11.3). Carbonate‐catalyzed condensation reactions could contribute significantly to the degradation of organic matter in hyperalkaline natural environments (pH ≥ 11) and be at the origin of the macromolecular matter found in these environments. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 676–686, 2010     

Fundamentals in CO_2 capture of Na_2CO_3 under a moist condition

Capacity and kinetics of CO_2 capture of Na_2CO_3 were studied to determine the mechanism for CO_2 sequestration under ambient conditions. Bicarbonate formation of Na_2CO_3 was examined by a thermogravimetric analysis(TGA) under various CO_2 and water vapor concentrations and the accompanying structural changes of Na_2CO_3 were demonstrated by X-ray diffraction(XRD). Morphological variations were observed during the reaction of CO_2 capture through scanning electron microscope(SEM). Structural changes and morphological variations, which occurred during the course of the reaction, were then connected to the kinetic and exothermic properties of the CO_2 capture process from the XRD and SEM measurements. The results showed that the bicarbonate formation of Na_2CO_3 has two different pathways.For higher CO_2 and H_2O concentrations, the bicarbonate formation proceeded effectively. However, for lower CO_2 and H_2O concentrations, the reactions were more complicated. The formation of Na_2CO_3·H_2O from Na_2CO_3 as the first step, followed by the subsequent formation of Na_5H_3(CO_3)_4, and then the bicarbonate formation proceeds. To understand such fundamental properties in CO_2 capture of Na_2CO_3 is very important for utilization of Na_2CO_3 as a sorbent for CO_2 capture.     

Thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O: II. Identification of the gaseous products

The main goal of the presented work was to verify the previously assumed decomposition stages of [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O (HACOT) [Thermochim. Acta 354 (2000) 45] under different atmospheres (inert, oxidising and reducing). The gaseous products of the decomposition were qualitatively and quantitatively analysed by mass spectrometry (MS) and Fourier-transformed infrared spectroscopy (FT-IR). It was confirmed that the gaseous products of HACOT decomposition under studied atmospheres there were H₂O (stage I) and NH₃, CO₂ (stage II). The main gaseous products in the third stage in argon and hydrogen (20 vol.% H₂/Ar) were CO and CO₂, whereas in air (20 vol.% O₂/Ar) only CO₂ was identified. Under the oxidising as well as reducing atmospheres the influence of secondary reactions on the composition of both, solid and gaseous products was found particularly strong during the third stage of the process. The studies of the multistage decomposition of HACOT, additionally complicated by many secondary reactions, required application of the hyphenated TA-MS or TA-FT-IR techniques combined with the pulse thermal analysis PTA^® allowing quantification of the spectroscopic signals and investigation of gas-solid and gas-gas reactions in situ.     

BNN-1,3-dipoles: isolation and intramolecular cycloaddition with unactivated arenes

The mono-base-stabilized 1,2-diboranylidenehydrazine derivatives featuring a 1,3-dipolar BNN skeleton are obtained by dehydrobromination of [ArB(Br)NH]₂ (Ar = 2,6-diphenylphenyl (Dpp), Ar = 2,6-bis(2,4,6-trimethylphenyl)phenyl (Dmp) or Ar = 2,4,6-tri-tert-butylphenyl (Mes*)) with N-heterocyclic carbenes (NHCs). Depending on the Ar substituents, such species can be isolated as a crystalline solid (Ar = Mes*) or generated as reactive intermediates undergoing spontaneous intramolecular aminoboration of the proximal arene rings via [3 + 2] cycloaddition (Ar = Dpp or Dmp). The latter reactions showcase the 1,3-dipolar reactivity toward unactivated arenes at ambient temperature. In addition, double cycloaddition of the isolable BNN species with two CO₂ molecules affords a bicyclic species consisting of two fused five-membered BN₂CO rings. The electronic structures of these BNN species and the mechanisms of these cascade reactions are interrogated through density functional theory (DFT) calculations.

The mono-base-coordinated 1,2-diboranylidenehydrazine derivatives exhibiting the BNN-1,3-dipolar reactivity toward unactivated arenes and CO₂ are reported.     

Highly selective hydrohalogenation reaction of substituted 2,3-allenoates

The hydrohalogenation reaction of 1-alkyl substituted 1,2-allenyl carboxylic acid esters (1) with MX (M= Na, or Li, X= Cl, Br, I) afforded a mixture of (5,7-unsaturated 3-halo-3-alkenoates (2) and α,β-unsaturated 3-halo-2-alkenoates (3) in HOAc, while using a mkture of HOAc-CF3CO2H (1:1) or CF3CO2H as the reaction medium the corresponding reaction cleanly produced β,γ-unsaturated 3-halo-3-alkenoates (2) as the sole products in high yields. The subsequent coupling reactions were studied.     

Hydrogenation of CO2 Promoted by Silicon-Activated H2S: Origin and Implications

Unlike the usual method of CO_x (x = 1, 2) hydrogenation using H₂ directly, H₂S and HSiSH (silicon-activated H₂S) were selected as alternative hydrogen sources in this study for the CO_x hydrogenation reactions. Our results suggest that it is kinetically infeasible for hydrogen in the form of H₂S to transfer to CO_x at low temperatures. However, when HSiSH is employed instead, the title reaction can be achieved. For this approach, the activation of CO₂ is initiated by its interaction with the HSiSH molecule, a reactive species with both a hydridic H^δ− and protonic H^δ+. These active hydrogens are responsible for the successive C-end and O-end activations of CO₂ and hence the final product (HCOOH). This finding represents a good example of an indirect hydrogen source used in CO₂ hydrogenation through reactivity tuned by silicon incorporation, and thus the underlying mechanism will be valuable for the design of similar reactions.     

The CO_2 laser-induced radical-chain reactions between CH_3CF_2H and chlorine-atom donors CF_2ClCFCl_2, CF_3CCl_3 CFCl_3 or CF_2Cl_2

The CO_2 laser induced room temperature reactions of CH_3CF_2H or another protium-donorCH_3CHClCH_3 with chlorine-atom donors (Z--Cl) CFCl_2CF_2Cl, CF_3CCl_3, CFCl_3 or CF_2Cl_2, havebeen investigated. Some of these reactions can yield two important monomers (CF_2=CH_2 andCF_2=CFCl) for fluoropolymers simultaneously. The yield dependence of these two alkenes on experi-mental conditions has been studied. A laser-initiated chain process is supported by identifica-tion of Z--H intermediates in these reactions.     

Carbonyl‐Komplexe von Chrom,Molybdän und Wolfram mit Isocyanacetat. Reaktionen am koordinierten Isocyanacetat. Stabilisierung von Isocyanessigsäure und Isocyanacetylchlorid am Metall. Isocyanopeptide [1]

Carbonyl Complexes of Chromium, Molybdenum and Tungsten with Isocyano Acetate. Reactions of Coordinated Isocyanoacetate. Stabilization of Isocyanoacetic Acid and Isocyanoacetyl Chloride at the Metal Atom. Isocyanopeptides The reactions of [(OC)₅MCNCH₂CO₂Et] (M = Cr, W) with Na[N(SiMe₃)₂] or with KOH afford the isocyanoacetate complexes [(OC)₅MCNCH₂CO₂]^? ( 1,2 ). Similarly, the complex [(OC)₃Mo(CNCH₂CO₂^?Li⁺)₃] ( 4 ) was obtained from [(OC)₃Mo(CNCH₂CO₂Et)₃] ( 3 ) and LiOH. Protonation of 1 and 2 affords the sublimable isocyanoacetic acid complexes [(OC)₅MCNCH₂CO₂H] ( 5 , 6 ; M = Cr, W) in which the functional isocyanide is stabilized at the metal atom. Reactions of [(OC)₅WCNCH₂CO₂^?K⁺] and of [(OC)₃Mo(CNCH₂CO₂^?Li⁺)₃] with oxalyl dichloride give the isocyanoacetyl chloride compounds [(OC)₅WCNCH₂COCl] ( 9 ) (sublimable) and [(OC)₃Mo(CNCH₂COCl)₃] ( 10 ); the latter ( 10 ) was not isolated. Complexes 9 and 10 were reacted in situ with β‐alanine, glycine, phenylalanine and methionine esters as well as the peptide esters GlyGlyOEt, PhePheOMe, Phe‐β‐AlaOMe, and GlyGlyGlyOMe to form the isocyanoacetyl amino acid esters ( 11 ‐ 14 ) and the isocyanoacetyl peptide esters ( 15 ‐ 18 ) which are stabilized at the molybdenum atom.     

Hochdrucksynthesen von Carbonaten. V. Carbonatdarstellungen durch Schmelzreaktionen unter hohen CO2-Drücken

High Pressure Syntheses of Carbonates. V. Syntheses of Carbonates by Melt Reactions under High CO₂ Pressure Binary compounds of transition metals react in melts of Tl₂CO₃ under CO₂ pressure from 1 000 to 5 000 bar by giving ternary carbonates. By this the compounds Tl₂Cu(CO₃)₂, TlCr(CO₃)₂, Tl₃Cr(CO₃)₃, and Tl₃V(CO₂)₃ could be prepared. The structure of Tl₂Cu(CO₃)₂ contains Cu₂ groups (a₀ = 7.583 Å, b₀ = 9.799 Å, c₀ = 9.119 Å, β 111.51°, Z = 4, space group P2₁/c Nr. 14). The space group of TlCr(CO₃)₂ is also P2₁/c Nr. 14 (a₀ = 19.917 Å, b₀ = 8.605 Å, c₀ = 19.138 Å, β = 104.79°, Z = 24). The compounds too were characterized by infrared spectroscopy.     

Synthesis,Crystal Structure,and Spectroscopic Characterization of Na5[NiO2][CO3], containing the Linear [NiO2]3– Group with Monovalent Nickel

For the first time ruby‐red single crystals and powder samples of Na₅[NiO₂][CO₃] were obtained via a redox reaction between nickel metal and CdO in the presence of Na₂O and Na₂CO₃ (molar ratios of CdO : Na₂O : Na₂CO₃ equal 1 : 3 : 2). The crystal structure has been refined from single crystal X‐ray diffraction data at 170 K (tetragonal, P4/mmm, a = 462.7(1) pm, c = 830.5(2) pm) and at 293 K (a = 462.35(7) pm, c = 830.9(1) pm). Na₅[NiO₂][CO₃] is the first example of an alkaline‐rich transition metal oxide with two different oxoanions, [NiO₂]^3– and [CO₃]^2–, coexisting in one compound. The electronic spectrum of Na₅[NiO₂][CO₃] has been measured between 4000 and 25000 cm^–1. Two d‐d‐transitions of the linear [NiO₂]^3– complex (d⁹) are observed at 5870 cm^–1 and 11850 cm^–1 and analysed using the angular overlap model. MIR and FIR spectra give evidence for the [CO₃]^2– anion present in the structure.     

Die ersten Hydrogencarbonate mit einer trimeren [H2(CO3)3]4−-Baugruppe: Zur Darstellung und Kristallstruktur von Rb4H2(CO3)3 · H2O und K4H2(CO3)3 · 1,5 H2O

The First Hydrogencarbonates with a Trimeric [H₂(CO₃)₃]^4? Group: Preparation and Crystal Structure of Rb₄H₂(CO₃)₃ · H₂O and K₄H₂(CO₃)₃ · 1.5 H₂O Rb₄H₂(CO₃)₃ · H₂O and K₄H₂(CO₃)₃ · 1,5 H₂O were prepared by means of the reaction of (CH₃)₂CO₃ with RbOH resp. KOH in aqueous methanole. Trimer [H₂(CO₃)₃]^4?-anions were found in the crystal structure of Rb₄H₂(CO₃)₃ · H₂O (orthorhombic, Pnma (no. 62), a = 1 218.0(1) pm, b = 1 572.3(6) pm, c = 615.9(1) pm, V_EZ = 1 179.5(5) · 10⁶ pm³, Z = 4, R1(I ≥ 2σ(I)) = 0.027, wR2(I ≥ 2σ(I)) = 0.055). K₄H₂(CO₃)₃ · 1,5 H₂O crystallizes in an OD-structure. The determined superposition structure (orthorhombic, Pbam (no. 55), a = 1 161.8(1) pm, b = 597.0(1) pm, c = 383.85(3) pm, V_EZ = 266.3(1) · 10⁶ pm³, Z = 1, R1(I ≥ 2σ(I)) = 0.035, wR2(I ≥ 2σ(I)) = 0.074) can be derived from the structure of the rubidium compound. The thermal decomposition of the substances is discussed.     

The influence of spatial limits on the modeling chemical reactivity: The example of CO2 hydration in MeX zeolites (Me = K,Rb, Cs)

Zeolite cell size variations upon cationic exchange are frequently disregarded while calculating chemical reactions with rather bulky reagents. An example of the reaction between the small reagents (H₂O and CO₂) illustrates a necessity to check this assumption for faujasite (FAU) zeolites with large porous space. The interplay of the space for the reaction center and the mobility of alkali cations forces lattice parameters to play a crucial role for the accurate computation of activation barrier of CO₂ hydration. While the CO₂ hydration is modeled in the MeX forms (Me = Rb, or Cs) with a fixed volume of NaX one, barrierless reactions were predicted that is not confirmed by experimental data. When the RbX and CsX cell parameters were optimized with Vienna Ab-initio Simulation Package (VASP), activation energies were obtained in agreement with the experimental data that CO₂ hydration in CsX occurs at room temperature.     

CO2 capture properties of M-C-O-H (M=Li, Na, K) systems: A combined density functional theory and lattice phonon dynamics study

We have computed the phase diagrams for multi-component M-C-O-H (M=Li, Na, K) systems using first-principles density functional theory complemented with lattice phonon calculations. We have identified all CO₂ capture reactions that lie on the Gibbs free energy convex hull as a function of temperature and the partial pressures of CO₂ and H₂O. Our predicted phase diagrams for CO₂ capture reactions are in qualitative and in some instances quantitative agreement with experimental data. The Na₂CO₃/NaHCO₃ and K₂CO₃/KHCO₃ systems were found to be the most promising candidates of all those we investigated for both pre- and post-combustion CO₂ capture. Overall, we show that our calculation approach can be used to screen promising materials for CO₂ capture under different conditions of temperature and pressure.