Functionalization of Intramolecular Frustrated Lewis Pairs by 1,1‐Carboboration with Conjugated Enynes

The vicinal P/B frustrated Lewis pair (FLP) Mes₂PCH₂CH₂B(C₆F₅)₂ undergoes 1,1‐carboboration reactions with the Me₃Si‐substituted enynes to give ring‐enlarged functionalized C₃‐bridged P/B FLPs. These serve as active FLPs in the activation of dihydrogen to give the respective zwitterionic [P]H⁺/[B]H^? products. One such product shows activity as a metal‐free catalyst for the hydrogenation of enamines or a bulky imine. The ring‐enlarged FLPs contain dienylborane functionalities that undergo “bora‐Nazarov”‐type ring‐closing rearrangements upon photolysis. A DFT study had shown that the dienylborane cyclization of such systems itself is endothermic, but a subsequent C₆F₅ migration is very favorable. Furthermore, substituted 2,5‐dihydroborole products are derived from cyclization and C₆F₅ migration from the photolysis reaction. In the case of the six‐membered annulation product, a subsequent stereoisomerization reaction takes place and the resultant compound undergoes a P/B FLP 1,2‐addition reaction with a terminal alkyne with rearrangement.     

Synthesis of High‐Surface‐Area Nitrogen‐Doped Porous Carbon Microflowers and Their Efficient Carbon Dioxide Capture Performance

Sustainable carbon materials have received particular attention in CO₂ capture and storage owing to their abundant pore structures and controllable pore parameters. Here, we report high‐surface‐area hierarchically porous N‐doped carbon microflowers, which were assembled from porous nanosheets by a three‐step route: soft‐template‐assisted self‐assembly, thermal decomposition, and KOH activation. The hydrazine hydrate used in our experiment serves as not only a nitrogen source, but also a structure‐directing agent. The activation process was carried out under low (KOH/carbon=2), mild (KOH/carbon=4) and severe (KOH/carbon=6) activation conditions. The mild activated N‐doped carbon microflowers (A‐NCF‐4) have a hierarchically porous structure, high specific surface area (2309 m² g^?1), desirable micropore size below 1 nm, and importantly large micropore volume (0.95 cm³ g^?1). The remarkably high CO₂ adsorption capacities of 6.52 and 19.32 mmol g^?1 were achieved with this sample at 0 °C (273 K) and two pressures, 1 bar and 20 bar, respectively. Furthermore, this sample also exhibits excellent stability during cyclic operations and good separation selectivity for CO₂ over N₂.     

CO2‐Cross‐Linked Frustrated Lewis Networks as Gas‐Regulated Dynamic Covalent Materials

The design of structurally dynamic molecular networks can offer strategies for fabricating stimuli‐responsive adaptive materials. Herein we first report a gas‐responsive dynamic gel system based on frustrated Lewis pair (FLP) chemistry. Two trefoil‐like molecules with bulky triphenylborane and triphenylphosphine groups are synthesized as complementary Lewis acid and base with trivalent sites. They can together bind CO₂ gas molecules and further form a cross‐linked network via the bonding interactions between FLPs and CO₂. Such CO₂‐bridged dative linkages are shown to be dynamic covalent bonds, which endow the frustrated Lewis network with adaptable behaviors and unprecedented gas‐regulated viscoelastic, mechanical, and self‐healing performance. This study is an initial attempt to apply the FLP concept in materials chemistry, but we believe that this strategy will open a promising future for gas‐sensitive smart materials.     

Enhanced CO2 Adsorption Affinity in a NbO‐type MOF Constructed from a Low‐Cost Diisophthalate Ligand with a Piperazine‐Ring Bridge

A metal–organic framework (NPC‐6) with an NbO topology based on a piperazine ring‐bridged diisophthalate ligand was synthesized and characterized. The incorporated piperazine group leads to an enhanced adsorption affinity for CO₂ in NPC‐6, in which the CO₂ uptake is 4.83 mmol g^?1 at 293 K and 1 bar, ranking among the top values of CO₂ uptake on MOF materials. At 0.15 bar and 293 K, the NPC‐6 adsorbs 1.07 mmol g^?1 of CO₂, which is about 55.1 % higher than that of the analogue MOF NOTT‐101 under the same conditions. The enhanced CO₂ uptake combined with comparable uptakes for CH₄ and N₂ leads to much higher selectivities for CO₂/CH₄ and CO₂/N₂ gas mixtures on NPC‐6 than on NOTT‐101. Furthermore, an N‐alkylation is used in the synthesis of the PDIA ligand, leading to a much lower cost compared with that in the synthesis of ligands in the NOTT series, as the former does not require a palladium‐based catalyst and borate esters. Thus, we conclude that NPC‐6 is a promising candidate for CO₂ capture applications.     

In Situ Formation of Frustrated Lewis Pairs in a Water‐Tolerant Metal‐Organic Framework for the Transformation of CO2

Frustrated Lewis pairs (FLPs) consist of sterically hindered Lewis acids and Lewis bases, which provide high catalytic activity towards non‐metal‐mediated activation of “inert” small molecules, including CO₂ among others. One critical issue of homogeneous FLPs, however, is their instability upon recycling, leading to catalytic deactivation. Herein, we provide a solution to this issue by incorporating a bulky Lewis acid‐functionalized ligand into a water‐tolerant metal‐organic framework (MOF), named SION‐105 , and employing Lewis basic diamine substrates for the in situ formation of FLPs within the MOF. Using CO₂ as a C1‐feedstock, this combination allows for the efficient transformation of a variety of diamine substrates into benzimidazoles. SION‐105 can be easily recycled by washing with MeOH and reused multiple times without losing its identity and catalytic activity, highlighting the advantage of the MOF approach in FLP chemistry.     

Flexible and Rigid Amine‐Functionalized Microporous Frameworks Based on Different Secondary Building Units: Supramolecular Isomerism,Selective CO2 Capture,and Catalysis

We report the synthesis, structural characterization, and porous properties of two isomeric supramolecular complexes of ([Cd(NH₂?bdc)(bphz)_0.5]?DMF?H₂O}_n (NH₂?bdc=2‐aminobenzenedicarboxylic acid, bphz=1,2‐bis(4‐pyridylmethylene)hydrazine) composed of a mixed‐ligand system. The first isomer, with a paddle‐wheel‐type Cd₂(COO)₄ secondary building unit (SBU), is flexible in nature, whereas the other isomer has a rigid framework based on a μ‐oxo‐bridged Cd₂(μ‐OCO)₂ SBU. Both frameworks are two‐fold interpenetrated and the pore surface is decorated with pendant ?NH₂ and ?N?N? functional groups. Both the frameworks are nonporous to N₂, revealed by the type II adsorption profiles. However, at 195 K, the first isomer shows an unusual double‐step hysteretic CO₂ adsorption profile, whereas the second isomer shows a typical type I CO₂ profile. Moreover, at 195 K, both frameworks show excellent selectivity for CO₂ among other gases (N₂, O₂, H₂, and Ar), which has been correlated to the specific interaction of CO₂ with the ?NH₂ and ?N?N? functionalized pore surface. DFT calculations for the oxo‐bridged isomer unveiled that the ?NH₂ group is the primary binding site for CO₂. The high heat of CO₂ adsorption (ΔH_ads=37.7 kJ mol^?1) in the oxo‐bridged isomer is realized by NH₂???CO₂/aromatic π???CO₂ and cooperative CO₂???CO₂ interactions. Further, postsynthetic modification of the ?NH₂ group into ?NHCOCH₃ in the second isomer leads to a reduced CO₂ uptake with lower binding energy, which establishes the critical role of the ?NH₂ group for CO₂ capture. The presence of basic ?NH₂ sites in the oxo‐bridged isomer was further exploited for efficient catalytic activity in a Knoevenagel condensation reaction.     

Boron‐Functionalized Graphene Oxide‐Organic Frameworks for Highly Efficient CO2 Capture

The capture and storage of CO₂ have been suggested as an effective strategy to reduce the global emissions of greenhouse gases. Hence, in recent years, many studies have been carried out to develop highly efficient materials for capturing CO₂. Until today, different types of porous materials, such as zeolites, porous carbons, N/B‐doped porous carbons or metal‐organic frameworks (MOFs), have been studied for CO₂ capture. Herein, the CO₂ capture performance of new hybrid materials, graphene‐organic frameworks (GOFs) is described. The GOFs were synthesized under mild conditions through a solvothermal process using graphene oxide (GO) as a starting material and benzene 1,4‐diboronic acid as an organic linker. Interestingly, the obtained GOF shows a high surface area (506 m² g⁻¹) which is around 11 times higher than that of GO (46 m² g⁻¹), indicating that the organic modification on the GO surface is an effective way of preparing a porous structure using GO. Our synthetic approach is quite simple, facile, and fast, compared with many other approaches reported previously. The synthesized GOF exhibits a very large CO₂ capacity of 4.95 mmol g⁻¹ at 298 K (1 bar), which is higher those of other porous materials or carbon‐based materials, along with an excellent CO₂/N₂ selectivity of 48.8.     

A Comparative Study of CO Oxidation on Nitrogen‐ and Phosphorus‐Doped Graphene

The geometry, electronic structure, and catalytic properties of nitrogen‐ and phosphorus‐doped graphene (N‐/P‐graphene) are investigated by density functional theory calculations. The reaction between adsorbed O₂ and CO molecules on N‐ and P‐graphene is comparably studied via Langmuir–Hinshelwood (LH) and Eley–Rideal (ER) mechanisms. The results indicate that a two‐step process can occur, namely, CO+O₂→CO₂+O_ads and CO+O_ads→CO₂. The calculated energy barriers of the first step are 15.8 and 12.4 kcal mol^?1 for N‐ and P‐graphene, respectively. The second step of the oxidation reaction on N‐graphene proceeds with an energy barrier of about 4 kcal mol^?1. It is noteworthy that this reaction step was not observed on P‐graphene because of the strong binding of O_ads species on the P atoms. Thus, it can be concluded that low‐cost N‐graphene can be used as a promising green catalyst for low‐temperature CO oxidation.     

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.     

Mechanism and Kinetics of Carbon Dioxide Capture Using Activated 2‐Amino‐2‐methyl‐1,3‐propanediol

The continued use of fossil fuels as primary sources of energy in industry and other applications stands the test of time, due to their availability and relatively lower cost than alternative sources of energy. In view of this perspective, obtaining an advanced bulk carbon dioxide (CO₂) capture medium becomes an urgent necessity so as to mitigate their effect, especially in global warming, as the use of fossil fuels produces a high rate of CO₂. In this work, the mechanism and kinetics of CO₂ capture using aqueous piperazine (PZ) as an activator to 2‐amino‐2‐methyl‐1,3‐propanediol (AMPD) were investigated. The termolecular mechanism was used to model the kinetics of the system. Reaction kinetics of the single pure amines was first obtained. The reaction rate constant, the k value of AMPD, was 77.2 m³/kmol·s, with a reaction order, n, of 1.25 at 298 K. while that of PZ was equal to 11,059 m³/kmol·s and n as 1.49 at 298 K. Blending of 0.05 kmol/m³ of PZ with 0.5 kmol/m³ of AMPD gave a rate constant, k, value of 23,319 m³/kmol·s and n equal to 1.23 at 298 K. The result obtained for the blended system is more than twice the value of the summation of the corresponding pure amines; in addition, it is comparably higher than the rate constant of monoethanolamine (MEA) in use as a commercial solvent for CO₂ capture. Therefore, an aqueous blend of PZ with AMPD deserves more comprehensive study as a solvent for commercial CO₂ capture. AMPD like other sterically hindered amines absorbs CO₂ in an equimolar ratio that is significantly higher than that of MEA. PZ serves as a promoter in the amine mixture and is required in a very small proportion.     

Computer‐Assisted Design of Imidazolate‐Based Ionic Liquids for Improving Sulfur Dioxide Capture,Carbon Dioxide Capture,and Sulfur Dioxide/Carbon Dioxide Selectivity

A new strategy involving the computer‐assisted design of substituted imidazolate‐based ionic liquids (ILs) through tuning the absorption enthalpy as well as the basicity of the ILs to improve SO₂ capture, CO₂ capture, and SO₂/CO₂ selectivity was explored. The best substituted imidazolate‐based ILs as absorbents for different applications were first predicted. During absorption, high SO₂ capacities up to ≈5.3 and 2.4 mol mol_IL⁻¹ could be achieved by ILs with the methylimidazolate anions under 1.0 and 0.1 bar (1 bar=0.1 MPa), respectively, through tuning multiple N ⋅⋅⋅ S interactions between SO₂ and the N atoms in the imidazolate anion with different substituents. In addition, CO₂ capture by the imidazolate‐based ILs could also be easily tuned through changing the substituents of the ILs, and 4‐bromoimidazolate IL showed a high CO₂ capacity but a low absorption enthalpy. Furthermore, a high selectivity for SO₂/CO₂ could be reached by IL with 4,5‐dicyanoimidazolate anion owing to its high SO₂ capacity but low CO₂ capacity. The results put forward in this work are in good agreement with the predictions. Quantum‐chemical calculations and FTIR and NMR spectroscopy analysis methods were used to discuss the SO₂ and CO₂ absorption mechanisms.     

Water‐stable Adenine‐based MOFs with Polar Pores for Selective CO2 Capture

Here, we report two novel water‐stable amine‐functionalized MOFs, namely IISERP‐MOF26 ([NH₂(CH₃)₂][Cu₂O(Ad)(BDC)]?(H₂O)₂(DMA), 1 ) and IISERP‐MOF27 ([NH₂(CH₃)₂]_1/2[Zn₄O(Ad)₃(BDC)₂]?(H₂O)₂(DMF)_1/2, 2 ), which show selective CO₂ capture capabilities. They are made by combining inexpensive and readily available terephthalic acid and N‐rich adenine with Cu and Zn, respectively. They possess 1D channels decorated by the free amine group from the adenine and the polarizing oxygen atoms from the terephthalate units. Even more, there are dimethyl ammonium (DMA⁺) cations in the pore rendering an electrostatic environment within the channels. The activated Cu‐ and Zn‐MOFs physisorb about 2.7 and 2.2 mmol g^?1 of CO₂, respectively, with high CO₂/N₂ and moderate CO₂/CH₄ selectivity. The calculated heat of adsorption (HOA=21–23 kJ mol^?1) for the CO₂ in both MOFs suggest optimal physical interactions which corroborate well with their facile on‐off cycling of CO₂. Notably, both MOFs retain their crystallinity and porosity even after soaking in water for 24 hours as well as upon exposure to steam over 24 hours. The exceptional thermal and chemical stability, favorable CO₂ uptakes and selectivity and low HOA make these MOFs promising sorbents for selective CO₂ capture applications. However, the MOF′s low heat of adsorption despite having a highly CO₂‐loving groups lined walls is quite intriguing.     

One‐stage Template‐free KOH Activation for Mesopore‐enriched Carbons and Their Application in CO2 Capture

Activated carbons with a high mesoporous structure were prepared by a one‐stage KOH activation process without the assistance of templates and further used as adsorbents for CO₂ capture. The physical and chemical properties as well as the pore structures of the resulting mesoporous carbons were characterized by N₂ adsorption isotherms, scanning electron microscopy (SEM ), X‐ray diffraction (XRD ), Raman spectroscopy, and Fourier transform infrared (FTIR ) spectroscopy. The activated carbon showed greater specific surface area and mesopore volume as the activation temperature was increased up to 600°C, showing a uniform pore structure, great surface area (up to ~815 m²/g), and high mesopore ratio (~55%). The activated sample exhibited competitive CO₂ adsorption capacities at 1 atm pressure, reaching 2.29 and 3.4 mmol/g at 25 and 0°C, respectively. This study highlights the potential of well‐designed mesoporous carbon as an adsorbent for CO₂ removal and widespread gas adsorption applications.     

Boosting CO2 Electroreduction on N,P‐Co‐doped Carbon Aerogels

Electroreduction of CO₂ to CO powered by renewable electricity is a possible alternative to synthesizing CO from fossil fuel. However, it is very hard to achieve high current density at high faradaic efficiency (FE). Here, the first use of N,P‐co‐doped carbon aerogels (NPCA) to boost CO₂ reduction to CO is presented. The FE of CO could reach 99.1 % with a partial current density of ?143.6 mA cm^?2, which is one of the highest current densities to date. NPCA has higher electrochemical active area and overall electronic conductivity than that of N‐ or P‐doped carbon aerogels, which favors electron transfer from CO₂ to its radical anion or other key intermediates. By control experiments and theoretical calculations, it is found that the pyridinic N was very active for CO₂ reduction to CO, and co‐doping of P with N hinder the hydrogen evolution reaction (HER) significantly, and thus the both current density and FE are very high.     

Kinetics of Carbon Dioxide Reaction with Aqueous Mixture of Piperazine and 2‐Amino‐2‐ethyl‐1,3‐propanediol

Current researchers from environmental and industrial fields are focusing on advanced means of carbon dioxide (CO₂) capture to limit its consequences in process industries. They also intend to enhance the mitigation of environmental impart by CO₂ especially its greenhouse effect. In this study, the kinetics of CO₂ reaction with an aqueous blend of piperazine (PZ) and 2‐amino‐2‐ethyl‐1,3‐propanediol (AEPD) were investigated. It was found that blending of AEPD with a little percentage of PZ generated the observed rate constant, k_o, values that were more than twice the direct summation of the k_o values of the aqueous pure amines at the corresponding concentration and temperature. The kinetic study of the system was modeled using a termolecular mechanism. Blending 0.05 kmol/m³ of PZ with 0.5 kmol/m³ of AEPD gives an observed rate constant k_o value of 2397.9 s^?1 at 298 K. This result is comparable to rate constants of other amine mixtures. Thus, the aqueous blend of AEPD with PZ is an attractive solvent for CO₂ capture that has good advantages. The PZ that serves as the promoter in the reaction is needed in small fraction, whereas AEPD, which is a sterically hindered amine, increases CO₂ absorption capacity of the system. AEPD can be produced from renewable materials. © 2013 Wiley Periodicals, Inc. Int J Chem Kinet 45: 161–167, 2013     

Carbene‐9‐BBN Ring Expansions as a Route to Intramolecular Frustrated Lewis Pairs for CO2 Reduction

Reactions of phosphine‐derived carbenes with 9‐borabicyclo[3.3.1]nonane (9‐BBN) result in ring‐expansion reactions to generate novel intramolecular frustrated Lewis pairs (FLPs). These FLPs effect the catalytic reduction of CO₂ in the presence of boranes to give BOB and methoxy‐borate species.     

An Ethylene‐Bridged Phosphane/Borane Frustrated Lewis Pair Featuring the ‐B(Fxyl)2 Lewis Acid Component

Hydroboration of dimesitylvinylphosphane with bis[3,5‐bis(trifluoromethyl)phenyl]borane [HB(Fxyl)₂] gave the intramolecular ethylene‐bridged P/B frustrated Lewis pair (FLP) Mes₂PCH₂CH₂B(Fxyl)₂. The new compound underwent a variety of typical FLP reactions such as P/B‐addition to the carbonyl group of p‐chloro‐benzaldehyde. Cooperative N,N‐addition to nitric oxide gave the respective persistent P/B FLPNO^. radical, which readily reacted with 1,4‐cyclohexadiene by H‐atom abstraction to yield the corresponding P/B FLPNOH product. The B(Fxyl)₂‐containing FLP reacted as a template for the HB(C₆F₅)₂ reduction of carbon monoxide to the formyl stage to give the respective FLP(η²‐formylborane) product. Most products were characterized by single‐crystal X‐ray crystal structure analysis.     

Nucleophilic Reactivity of a Nitride‐Bridged Diuranium(IV) Complex: CO2 and CS2 Functionalization

Thermolysis of the nitride‐bridged diuranium(IV) complex Cs{(μ‐N)[U(OSi(O^tBu)₃)₃]₂} ( 1 ) showed that the bridging nitride behaves as a strong nucleophile, promoting N?C bond formation by siloxide ligand fragmentation to yield an imido‐bridged siloxide/silanediolate diuranium(IV) complex, Cs{(μ‐N^tBu)(μ‐O₂Si(O^tBu)₂)U₂(OSi(O^tBu)₃)₅}. Complex 1 displayed reactivity towards CS₂ and CO₂ at room temperature that is unprecedented in f‐element chemistry, affording diverse N‐functionalized products depending on the reaction stoichiometry. The reaction of 1 with two equivalents of CS₂ yielded the thiocyanate/thiocarbonate complex Cs{(μ‐NCS)(μ‐CS₃)[U(OSi(O^tBu)₃)₃]₂} via a putative NCS^?/S^2? intermediate. The reaction of 1 with one equivalent of CO₂ resulted in deoxygenation and N?C bond formation, yielding the cyanate/oxo complex Cs{(μ‐NCO)(μ‐O)[U(OSi(O^tBu)₃)₃]₂}. Addition of excess CO₂ to 1 led to the unprecedented dicarbamate product Cs{(μ‐NC₂O₄)[U(OSi(O^tBu)₃)₃]₂}.     

Palladium‐, Platin‐ und Dieisenkomplexe mit Isocyanacetat: Ringschluß, säureinduzierte Ringöffnung,Diprotonierung

Palladium, Platinum, and Diiron Complexes with Isocyanoacetate: Ring Closure, Acid‐Induced Ring Opening, Diprotonation Substitution by isocyanoacetate (CNCH₂CO₂^?) of one chloro ligand in trans‐[MCl₂(PPh₃)₂] (M = Pd, Pt) results in the Δ²‐oxazolin‐5‐on‐2‐ato complexes 4a , b , i.e. immediate cyclization occurs in contact with these metal(II) species. In contrast, the open‐chain form of the functional isocyanide is retained in [K(18‐crown‐6][Fe₂Cp₂(CNCH₂CO₂)(CO)₃] ( 16 ) in which it occupies a terminal position. Protonation (alkylation) of the platinum complex 4b proceeds with ring cleavage and formation of isocyano acetic acid 11 (ethyl isocyanoacetate 12 ) stabilized by metal ion coordination. Protonation of 16 requires two equivalents of acid to yield the aminocarbyne‐bridged complex [{μ‐C=N(H)CH₂CO₂H}Fe₂Cp₂(CO)₃](BF₄) ( 17 ) as the only isolable product. Here isocyanoacetate displays a third kind of reactivity pattern in addition to that at Pd^II/Pt^II and that at Cr⁰/W⁰ where the primary species [M(CO)₅CNCH₂CO₂]^? and [M(CO)₅CNCH₂CO₂H] proved to be the most stable. All of the proposed structures are substantiated by analytical and the usual spectroscopic (IR, NMR{¹H, ¹³C, ³¹P}, FAB‐MS) data, that of 4b also by an X‐ray structure determination which reveals a practically perpendicular arrangement of the coordination and the ring plane, and a long C2‐O bond as the predetermined breaking point of the heterocycle.     

Synthesis,Structure and Magnetic Properties of a Novel N‐Benzenesulfonyl‐L‐glutamic Acid‐bridged Manganese(II) Polymer with Double‐Chain Structure

First N‐benzenesulfonyl‐L‐glutamic acid‐bridged manganese(II) coordination polymer [Mn(bipy)(bs‐glu)]_n (bs‐glu = N‐benzenesulfonyl‐L‐glutamic acid dianion, bipy = 2, 2′‐bipyridine) has been synthesized and characterized structurally and magnetically. It crystallizes in the orthorhombic space group P2₁2₁2₁. The γ‐carboxyl group coordinates to the Mn^II atom in a chelating mode, while the α‐carboxyl group coordinates in a bidentate‐bridging mode. The complex displays a one‐dimensional double‐chain polymer. Magnetic measurements show that there are weak antiferromagnetic interactions between the adjacent Mn^II ions in the compound.