CO2 Adduct Research Articles

Towards green polyurethane foams via renewable castor oil-derived polyol and carbon dioxide releasing blowing agents from alkylated polyethylenimines

Alternatives to climate changing blowing agents (e.g. chlorofluorocarbons) and petroleum sourced raw materials (e.g. polyether polyols) are very attractive in the polyurethane (PU) foam industry. We explore a series of CO2 adducts from a branched polyethylenimine (bPEI) alkylated with C4 to C16 alkyl glycidyl ethers. These adducts can serve as CO2 releasing blowing agents during the exothermic polymerisation of PUs. A 13% alkylation of the bPEI amine groups enhances the dispersibility of the resultant CO2 adducts into the PU foaming mixtures containing a castor oil-derived polyol. In particular, the CO2 adduct with a C8 alkyl (2-ethylhexyl) side chain possesses the best dispersibility and is among the most effective in decreasing the foam density. It generates PU foams whose density and compressive strength are almost suitable for thermal insulation of underground steel pipes. This is the first report showing that PU foams from biomass polyols can be blown by CO2 adducts that are environmentally neutral.

Direct Synthesis of Dimethyl Carbonate from Carbon Dioxide and Methanol at Room Temperature Using Imidazolium Hydrogen Carbonate Ionic Liquid as a Recyclable Catalyst and Dehydrant.

The direct synthesis of dimethyl carbonate (DMC) from CO2 and CH3 OH was achieved at room temperature with 74 % CH3 OH conversion in the presence of an imidazolium hydrogen carbonate ionic liquid ([Cn Cm Im][HCO3 ]). Experimental and theoretical results reveal that [Cn Cm Im][HCO3 ] can transform quickly into a CO2 adduct, which serves as an effective catalyst and dehydrant. Its dehydration ability is reversible. The energy barrier of the rate-determining step for the DMC synthesis is only 21.7 kcal mol-1 . The ionic liquid can be reused easily without a significant loss of its catalytic and dehydrating ability.

Carboxylation of Terminal Alkynes with Carbon Dioxide Catalyzed by an In Situ Ag2O/N‐Heterocyclic Carbene Precursor System

AbstractA carboxylation of terminal alkynes with carbon dioxide (CO2) at ambient conditions was developed in situ using a series of N‐heterocyclic carbene (NHC) precursors and Ag2O. The unique structure of NHCs largely increases the solubility of active Ag species and meanwhile activates CO2 by forming the NHC–CO2 adduct. This novel catalytic system demonstrated quite low Ag loading, very high activities, wide substrate generality and excellent tolerance for a variety of functionalities. In addition, avoiding cumbersome synthesis procedures, processing, and reserving of the photosensitive Ag complex, this system could be stored and operated as straightforward as the inorganic Ag salt catalysts.

Electrochemical Capture and Release of Carbon Dioxide

Understanding the chemistry of carbon dioxide is key to affecting changes in atmospheric concentrations. One area of intense interest is CO2 capture in chemically reversible cycles relevant to carbon capture technologies. Most CO2 capture methods involve thermal cycles in which a nucleophilic agent captures CO2 from impure gas streams (e.g., flue gas), followed by a thermal process in which pure CO2 is released. Several reviews have detailed progress in these approaches. A less explored strategy uses electrochemical cycles to capture CO2 and release it in pure form. These cycles typically rely on electrochemical generation of nucleophiles that attack CO2 at the electrophilic carbon atom, forming a CO2 adduct. Then, CO2 is released in pure form via a subsequent electrochemical step. In this Perspective, we describe electrochemical cycles for CO2 capture and release, emphasizing electrogenerated nucleophiles. We also discuss some advantages and disadvantages inherent in this general approach.

Electrochemical Capture and Release of Carbon Dioxide Using a Disulfide-Thiocarbonate Redox Cycle.

We describe a new electrochemical cycle that enables capture and release of carbon dioxide. The capture agent is benzylthiolate (RS-), generated electrochemically by reduction of benzyldisulfide (RSSR). Reaction of RS- with CO2 produces a terminal, sulfur-bound monothiocarbonate, RSCO2-, which acts as the CO2 carrier species, much the same as a carbamate serves as the CO2 carrier for amine-based capture strategies. Oxidation of the thiocarbonate releases CO2 and regenerates RSSR. The newly reported S-benzylthiocarbonate (IUPAC name benzylsulfanylformate) is characterized by 1H and 13C NMR, FTIR, and electrochemical analysis. The capture-release cycle is studied in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP TFSI) and dimethylformamide. Quantum chemical calculations give a binding energy of CO2 to benzyl thiolate of -66.3 kJ mol-1, consistent with the experimental observation of formation of a stable CO2 adduct. The data described here represent the first report of electrochemical behavior of a sulfur-bound terminal thiocarbonate.

Facile synthesis of NHC-stabilized Ni nanoparticles and their catalytic application in the Z-selective hydrogenation of alkynes.

Well defined Ni nanoparticles (NiNPs) stabilized with N-heterocyclic carbenes (NHCs) have been synthesized through a new methodology involving the decarboxylation of a zwitterionic CO2 adduct. Their catalytic performance was tested in the partial hydrogenation of alkynes into (Z)-alkenes under very mild reaction conditions (50 °C and 5 bar H2 pressure), providing excellent activities and selectivities.

Structure of Chemisorbed CO(2) Species in Amine-Functionalized Mesoporous Silicas Studied by Solid-State NMR and Computer Modeling.

Two-dimensional (2D) solid-state nuclear magnetic resonance (SSNMR) experiments on samples loaded with 13C-labeled CO2, "under controlled partial pressures", have been performed in this work, revealing unprecedented structural details about the formation of CO2 adducts from its reaction with various amine-functionalized SBA-15 containing amines having distinct steric hindrances (e.g., primary, secondary) and similar loadings. Three chemisorbed CO2 species were identified by NMR from distinct carbonyl environments resonating at δC ≈ 153, 160, and 164 ppm. The newly reported chemisorbed CO2 species at δC ≈ 153 ppm was found to be extremely moisture dependent. A comprehensive 1H-based SSNMR study [1D 1H and 2D 1H-X heteronuclear correlation (HETCOR, X = 13C, 29Si) experiments] was performed on samples subjected to different treatments. It was found that all chemisorbed CO2 species are involved in hydrogen bonds (HBs) with either surface silanols or neighboring alkylamines. 1H chemical shifts up to 11.8 ppm revealed that certain chemisorbed CO2 species are engaged in very strong HBs. We effectively demonstrate that NMR may help in discriminating among free and hydrogen-bonded functional groups. 13C{14N} dipolar-recoupling NMR showed that the formation of carbonate or bicarbonate is excluded. Density functional theory calculations on models of alkylamines grafted into the silica surface assisted the 1H/13C assignments and validated various HB arrangements that may occur upon formation of carbamic acid. This work extends the understanding of the chemisorbed CO2 structures that are formed upon bonding of CO2 with surface amines and readily released from the surface by pressure swing.

DFT study of N-Heterocyclic Olefins-catalyzed carboxylative cyclization of CO2with alkynol: A CO2-promoted hydrogen abstraction mechanism

DFT calculations have been carried out to study the detailed mechanisms of the carboxylative cyclization reaction between propargylic alcohols and CO2catalyzed by N-Heterocyclic Olefins (NHO), as well as the molecular orbital theory. Results indicated that this type of reaction prefers a three steps mechanism controlled by free NHO rather than to be catalyzed by the NHO–CO2adducts. For the first step, CO2promotes the hydrogen transfer from alkynol to NHO to form the carboxylate, in which propargylic alcohols was deprotonated by the free NHO acted as the catalyst precursor to form the alkynol anion; meanwhile, alkynol anion captures carbon dioxide to form the carboxylate. We found this CO2promoting Hydrogen abstraction mechanism would decrease the reaction energy barrier and increase releasing heat of this reaction. Secondly, a five-membered-ring intermediate is easily formed to generate carboxylate via an intramolecular ring-closing reaction. Finally, the production generated through a protonating process.

N-Heterocyclic Olefin-Carbon Dioxide and -Sulfur Dioxide Adducts: Structures and Interesting Reactivity Patterns.

Depending on the amount of methanol present in solution, CO2 adducts of N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs) have been found to be in fully reversible equilibrium with the corresponding methyl carbonate salts [EMIm][OCO2 Me] and [EMMIm][OCO2 Me]. The reactivity pattern of representative 1-ethyl-3-methyl-NHO-CO2 adduct 4 has been investigated and compared with the corresponding NHC-CO2 zwitterion: The protonation of 4 with HX led to the imidazolium salts [NHO-CO2 H][X], which underwent decarboxylation to [EMMIm][X] in the presence of nucleophilic catalysts. NHO-CO2 zwitterion 4 can act as an efficient carboxylating agent towards CH acids such as acetonitrile. The [EMMIm] cyanoacetate and [EMMIm]2 cyanomalonate salts formed exemplify the first C-C bond-forming carboxylation reactions with NHO-activated CO2 . The reaction of the free NHO with dimethyl carbonate selectively led to methoxycarbonylated NHO, which is a perfect precursor for the synthesis of functionalized ILs [NHO-CO2 Me][X]. The first NHO-SO2 adduct was synthesized and structurally characterized; it showed a similar reactivity pattern, which allowed the synthesis of imidazolium methyl sulfites upon reaction with methanol.

Direct Observation by Rapid-Scan FT-IR Spectroscopy of Two-Electron-Reduced Intermediate of Tetraaza Catalyst [Co(II)N4H(MeCN)](2+) Converting CO2 to CO.

In the search for the two-electron-reduced intermediate of the tetraaza catalyst [Co(II)N4H(MeCN)](2+) (N4H = 2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentaene) for CO2 reduction and elementary steps that result in the formation of CO product, rapid-scan FT-IR spectroscopy of the visible-light-sensitized catalysis, using Ir(ppy)3 in wet acetonitrile (CD3CN) solution, led to the observation of two sequential intermediates. The initially formed one-electron-reduced [Co(I)N4H](+)-CO2 adduct was converted by the second electron to a transient [Co(I)N4H](+)-CO2(-) complex that spontaneously converted CO2 to CO in a rate-limiting step on the second time scale in the dark under regeneration of the catalyst (room temperature). The macrocycle IR spectra of the [Co(I)N4H](+)-CO2(-) complex and the preceding one-electron [Co(I)N4H](+)-CO2 intermediate show close similarity but distinct differences in the carboxylate modes, indicating that the second electron resides mainly on the CO2 ligand. Vibrational assignments are corroborated by (13)C isotopic labeling. The structure and stability of the two-electron-reduced intermediate derived from the time-resolved IR study are in good agreement with recent predictions by DFT electronic structure calculations. This is the first observation of an intermediate of a molecular catalyst for CO2 reduction during the bond-breaking step producing CO. The reaction pathway for the Co tetraaza catalyst uncovered here suggests that the competition between CO2 reduction and proton reduction of a macrocyclic multi-electron catalyst is steered toward CO2 activation if the second electron is directly captured by an adduct of CO2 and the one-electron-reduced catalyst intermediate.

Climate‐friendly polyurethane blowing agent based on a carbon dioxide adduct from palmitic acid grafted polyethyleneimine

ABSTRACTTo explore a new blowing agent for polyurethanes (PUs), palmitic acid was grafted onto a branched polyethyleneimine (bPEI; weight‐average molecular weight = 25,000 Da) via N,N′‐carbonyldiimidazole condensation to form a hydrophobically modified bPEI [palmitic acid grafted branched polyethyleneimine (C16–bPEI)] with a grafting rate of 12%. A CO2 adduct of C16–bPEI, which trapped 16.8% CO2 in it, was synthesized from C16–bPEI. The long alkyl chain grafting improved the dispersibility of the CO2 adduct in the PU raw materials and favored a homogeneous release of CO2 to blow PUs during the exothermic foaming process. The preliminary results show that the foams possessed a density of 72.0 kg/m3 and a compressive strength of 246 kPa; this matched the required values of foams for the thermal insulation of underground steel pipes. This new blowing agent emitted nothing but CO2 to the atmosphere, so it will not promote ozone depletion and will avoid global warming problems that are associated with traditional blowing agents such as chlorofluorocarbons and hydrochloroflourocarbons. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43874.

ChemInform Abstract: Efficient Domino Hydroformylation/Benzoin Condensation: Highly Selective Synthesis of α‐Hydroxy Ketones.

AbstractOlefins are smoothly and with excellent regioselectivity converted into the corresponding α‐hydroxy ketones using a specific catalytic system consisting of a rhodium/phosphine complex and the CO2 adduct of a N‐heterocyclic carbene.

A Significant but Constrained Geometry Pt→Al Interaction: Fixation of CO2 and CS2, Activation of H2 and PhCONH2.

Reaction of the geminal PAl ligand [Mes2PC(═CHPh)AltBu2] (1) with [Pt(PPh3)2(ethylene)] affords the T-shape Pt complex [(1)Pt(PPh3)] (2). X-ray diffraction analysis and DFT calculations reveal the presence of a significant Pt→Al interaction in 2, despite the strain associated with the four-membered cyclic structure. The Pt···Al distance is short [2.561(1) Å], the Al center is in a pyramidal environment [Σ(C-Al-C) = 346.6°], and the PCAl framework is strongly bent (98.3°). Release of the ring strain and formation of X→Al interactions (X = O, S, H) impart rich reactivity. Complex 2 reacts with CO2 to give the T-shape adduct 3 stabilized by an O→Al interaction, which is a rare example of a CO2 adduct of a group 10 metal and actually the first with η(1)-CO2 coordination. Reaction of 2 with CS2 affords the crystalline complex 4, in which the PPtP framework is bent, the CS2 molecule is η(2)-coordinated to Pt, and one S atom interacts with Al. The Pt complex 2 also smoothly reacts with H2 and benzamide PhCONH2 via oxidative addition of H-H and H-N bonds, respectively. The ensuing complexes 5 and 7 are stabilized by Pt-H→Al and Pt-NH-C(Ph) = O→Al bridging interactions, resulting in 5- and 7-membered metallacycles, respectively. DFT calculations have been performed in parallel with the experimental work. In particular, the mechanism of reaction of 2 with H2 has been thoroughly analyzed, and the role of the Lewis acid moiety has been delineated. These results generalize the concept of constrained geometry TM→LA interactions and demonstrate the ability of Al-based ambiphilic ligands to participate in TM/LA cooperative reactivity. They extend the scope of small molecule substrates prone to such cooperative activation and contribute to improve our knowledge of the underlying factors.

Reversible Carbon Dioxide Binding by Simple Lewis Base Adducts with Electron-Rich Phosphines.

For the efficient utilization of carbon dioxide as feedstock in chemical synthesis, low-energy-barrier CO2 activation is a valuable tool. We report a metal-free approach to reversible CO2 binding under mild conditions based on simple Lewis base adducts with electron-rich phosphines. Variable-temperature NMR studies and DFT calculations reveal almost thermoneutral CO2 binding with low-energy barriers or stable CO2 adduct formation depending on the phosphines donor ability. The most basic phosphine forms an air-stable CO2 adduct that was used as phosphine transfer agent, providing a convenient access to transition-metal complexes with highly electron-rich phosphine ligands relevant to catalysis.

A Frustrated Lewis Pair Based on a Cationic Aluminum Complex and Triphenylphosphine

The highly Lewis acidic, cationic aluminum species [DIPP-nacnacAlMe]+[B(C6F5)4]− (1, DIPP-nacnac = [HC{C(Me)N(2,6-iPr2C6H3)}2]−) has been shown to undergo reactions with a wide variety of small molecules, in both the presence and absence of an external weak phosphine base, PPh3. Cycloaddition reactions of unsaturated C–C bonds across the aluminum diketiminate framework are reported, and the first structural confirmation of this type of cycloaddition product is presented. Addition of PPh3 to 1 produces the cationic aluminum phosphine complex [DIPP-nacnacAl(Me)PPh3]+[B(C6F5)4]−, which undergoes fluxional dissociation/coordination of the phosphine in solution. This weak Al–P interaction can be utilized in frustrated Lewis pair type reactions to activate alkenes, alkynes, CO2, propylene oxide, and the C–Cl bonds of CH2Cl2. The CO2 adduct [DIPP-nacnacAl(Me)OC(PPh3)O]+[B(C6F5)4]− undergoes further stoichiometric reduction with Et3SiH to produce an aluminum formate species.

A family of polypropylene glycol-grafted polyethyleneimines reversibly absorb and release carbon dioxide to blow polyurethanes

The chemical structure of CO2 adducts from polypropylene glycol grafted polyethyleneimines has been optimised to blow polyurethanes.

ChemInform Abstract: Boron‐Mediated Activation of Carbon Dioxide

AbstractReview: 103 refs.

Convenient preparation of high molecular weight poly(dimethylsiloxane) using thermally latent NHC-catalysis: a structure-activity correlation.

The polymerization of octamethylcyclotetrasiloxane (D4) is investigated using several five-, six- and seven-membered N-heterocyclic carbenes (NHCs). The catalysts are delivered in situ from thermally susceptible CO2 adducts. It is demonstrated that the polymerization can be triggered from a latent state by mild heating, using the highly nucleophilic 1,3,4,5-tetramethylimidazol-2-ylidene as organocatalyst. This way, high molecular weight PDMS is prepared (up to >400 000 g/mol, 1.6 < ÐM < 2.5) in yields >95%, using low catalyst loadings (0.2–0.1 mol %). Furthermore, the results suggest that a nucleophilic, zwitterionic mechanism is in operation, in preference to purely anionic polymerization.

Efficient Domino Hydroformylation/Benzoin Condensation: Highly Selective Synthesis of α-Hydroxy Ketones.

An improved domino hydroformylation/benzoin condensation to give α-hydroxy ketones has been developed. Easily available olefins are smoothly converted into the corresponding α-hydroxy ketones in high yields with excellent regioselectivities. Key to success is the use of a specific catalytic system consisting of a rhodium/phosphine complex and the CO2 adduct of an N-heterocyclic carbene.

CO2 Adducts of Phosphorus Ylides: Highly Active Organocatalysts for Carbon Dioxide Transformation

A series of phosphorus ylide (P-ylide) CO2 adducts were synthesized and first used as organocatalysts for CO2 transformation. Detailed studies on the cycloaddition reaction of CO2 with terminal epoxides show that P-ylide CO2 adducts are efficient metal-free and halogen-free organocatalysts to mediate this reaction under ambient conditions (25 °C, 1 atm of CO2). More importantly, the reactions proceeded with a broad scope, high efficiency, and good functional group tolerance and the corresponding cyclic carbonate products were obtained in good to excellent yields (46–99%). Meanwhile, the kinetic study by in situ FTIR methods suggested an intermolecular cooperation effect for effectively accelerating the ring opening of terminal epoxides. Furthermore, from an investigation of the catalytic diversity of P-ylide CO2 adducts, CO2 also could be converted to functionalized cyclic α-alkylidene carbonates, oxazolidinone, and N-methylated and N-formylated amines by organocatalytic reactions.