Showing papers on "Lewis acids and bases published in 2021"
TL;DR: In this article, the authors reveal the extraordinary role and mechanism of surface-adsorbed carboxylate ligands on bi/trimetallic layered double hydroxides (LDHs)/MOFs for oxygen evolution reaction (OER) electrocatalytic activity enhancement.
Abstract: Metal-organic frameworks (MOFs) with carboxylate ligands as co-catalysts are very efficient for the oxygen evolution reaction (OER) However, the role of local adsorbed carboxylate ligands around the in-situ-transformed metal (oxy)hydroxides during OER is often overlooked We reveal the extraordinary role and mechanism of surface-adsorbed carboxylate ligands on bi/trimetallic layered double hydroxides (LDHs)/MOFs for OER electrocatalytic activity enhancement The results of X-ray photoelectron spectroscopy (XPS), synchrotron X-ray absorption spectroscopy, and density functional theory (DFT) calculations show that the carboxylic groups around metal (oxy)hydroxides can efficiently induce interfacial electron redistribution, facilitate an abundant high-valence state of nickel species with a partially distorted octahedral structure, and optimize the d-band center together with the beneficial Gibbs free energy of the intermediate Furthermore, the results of in situ Raman and FTIR spectra reveal that the surface-adsorbed carboxylate ligands as Lewis base can promote sluggish OER kinetics by accelerating proton transfer and facilitating adsorption, activation, and dissociation of hydroxyl ions (OH- )
125 citations
TL;DR: This Outlook gives an overview of phosphorus-based organocatalysis and highlights key advances in three topics: nucleophilic phosphine catalysis, organophosphorus catalysis to bypass phosphine oxide waste, and organoph phosphorus compound-mediated single electron transfer processes.
Abstract: Phosphorus-based organocatalysis encompasses several subfields that have undergone rapid growth in recent years. This Outlook gives an overview of its various aspects. In particular, we highlight key advances in three topics: nucleophilic phosphine catalysis, organophosphorus catalysis to bypass phosphine oxide waste, and organophosphorus compound-mediated single electron transfer processes. We briefly summarize five additional topics: chiral phosphoric acid catalysis, phosphine oxide Lewis base catalysis, iminophosphorane super base catalysis, phosphonium salt phase transfer catalysis, and frustrated Lewis pair catalysis. Although it is not catalytic in nature, we also discuss novel discoveries that are emerging in phosphorus(V) ligand coupling. We conclude with some ideas about the future of organophosphorus catalysis.
98 citations
TL;DR: In this paper, a series of boron carbonitride (BCN) materials were designed and synthesized and the Lewis acid catalysis sites were tuned easily by adjusting the relative contents of BORON and nitrogen atoms.
Abstract: From a thermodynamic point of view, electrocatalytic nitrogen reduction reaction (NRR) is possible for the carbon-based metal-free catalysts, which are gradually becoming a class of potential alternatives to metal-based catalysts. However, the clarification of true active sites and corresponding exact catalytic mechanism of metal-free catalysts is urgently required. Taking full advantage of boron “Lewis acid”, a series of boron carbonitride (BCN) materials were designed and synthesized and the “Lewis acid catalysis” sites were tuned easily by adjusting the relative contents of boron and nitrogen atoms. Boron-enriched BCN exhibited outstanding NRR performance with an ammonia yield of −8.39 μg h−1.cm−2cat. (−41.9 μg h−1.mg−1cat.) and Faradaic efficiency of −9.87 %, together with excellent stability. Density functional theory calculations indicate that the boron sites of BCN enable the low energy barrier of the NRR rate-determining steps and the spontaneity of nitrogen adsorption. Our philosophy opens a new possible avenue to explore high-performance metal-free materials for nitrogen activation.
92 citations
TL;DR: In this article, a single-atomic-site Cu catalyst supported by a Lewis acid for electrocatalytic CO2 reduction to CH4 was proposed, which achieved a faradaic efficiency of 62% at -1.2 V (vs RHE) with a corresponding current density of 153.0 mA cm-2 for CH4 formation.
Abstract: Developing an efficient catalyst for the electrocatalytic CO2 reduction reaction (CO2RR) is highly desired because of environmental and energy issues. Herein, we report a single-atomic-site Cu catalyst supported by a Lewis acid for electrocatalytic CO2 reduction to CH4. Theoretical calculations suggested that Lewis acid sites in metal oxides (e.g., Al2O3, Cr2O3) can regulate the electronic structure of Cu atoms by optimizing intermediate absorption to promote CO2 methanation. Based on these theoretical results, ultrathin porous Al2O3 with enriched Lewis acid sites was explored as an anchor for Cu single atoms; this modification achieved a faradaic efficiency (FE) of 62% at -1.2 V (vs RHE) with a corresponding current density of 153.0 mA cm-2 for CH4 formation. This work demonstrates an effective strategy for tailoring the electronic structure of Cu single atoms for the highly efficient reduction of CO2 into CH4.
90 citations
TL;DR: The concept of frustrated Lewis pairs (FLP) was introduced in this paper, where the authors focus on the new directions and developments that are emerging from FLP chemistry involving hydrogen, including new applications and approaches to FLP reductions, the reductions of small molecules, and the advances in heterogeneous FLP systems.
Abstract: The articulation of the notion of "frustrated Lewis pairs" (FLPs) emerged from the discovery that H2 can be reversibly activated by combinations of sterically encumbered main group Lewis acids and bases. This has prompted numerous studies focused on various perturbations of the Lewis acid/base combinations and the applications to organic reductions. This Perspective focuses on the new directions and developments that are emerging from this FLP chemistry involving hydrogen. Three areas are discussed including new applications and approaches to FLP reductions, the reductions of small molecules, and the advances in heterogeneous FLP systems. These foci serve to illustrate that despite having its roots in main group chemistry, this simple concept of FLPs is being applied across the discipline.
77 citations
TL;DR: For traditional cycloaddition reaction between CO2 and epoxide, high temperature and high pressure are usually needed In as mentioned in this paper, the authors introduce Lewis acid Bi atom into the porphyrin ring of a met.
Abstract: For traditional cycloaddition reaction between CO2 and epoxide, high temperature and high pressure are usually needed In this work, we introduce Lewis acid Bi atom into the porphyrin ring of a met
75 citations
TL;DR: In this article, the authors reported a simple strategy to tune the Lewis acidity of iron-based MOFs by substituting Fe centers with Ce atoms in the node (a.k.a., Ce doping).
69 citations
TL;DR: The first application of a bidentate bis(iodolium) salt as organocatalyst in a Michael and a nitro‐Michael addition reaction as well as in a Diels–Alder reaction that had not been activated by noncovalent organoc atalysts before.
Abstract: In contrast to iodine(I)-based halogen bond donors, iodine(III)-derived ones have only been used as Lewis acidic organocatalysts in a handful of examples, and in all cases they acted in a monodentate fashion. Herein, we report the first application of a bidentate bis(iodolium) salt as organocatalyst in a Michael and a nitro-Michael addition reaction as well as in a Diels-Alder reaction that had not been activated by noncovalent organocatalysts before. In all cases, the performance of this bidentate XB donor distinctly surpassed the one of arguably the currently strongest iodine(I)-based organocatalyst. Bidentate coordination to the substrate was corroborated by a structural analysis and by DFT calculations of the transition states. Overall, the catalytic activity of the bis(iodolium) system approaches that of strong Lewis acids like BF 3 .
63 citations
TL;DR: In this article, unique frustrated Lewis pairs (FLPs) were precisely designed in flower-like nickel borate [Ni3(BO3)2], where the surface hydroxyl and neighboring Ni site serve as a Lewis base and acid, respectively.
Abstract: The simultaneous electrocatalytic conversion of N2 and CO2 into value-added urea is highly anticipated but suffers from the predicament of the poor chemisorption, activation, and coupling activity of reactant molecules. Herein, unique frustrated Lewis pairs (FLPs) were precisely designed in flower-like nickel borate [Ni3(BO3)2], where the surface hydroxyl and neighboring Ni site serve as a Lewis base and acid, respectively. Comprehensive investigations endorsed that the Lewis basic and acidic sites in FLPs acted synergistically in the targeted capture of inert CO2 and N2 by orbital interaction. Subsequently, the bonding and antibonding orbitals of the inert gas interacted with the empty orbitals of the Lewis acid and nonbonding orbitals of the Lewis base, respectively, achieving molecule activation by FLPs. Afterward, the *NN* and CO intermediates underwent electrocatalytic C–N coupling by the σ orbital carbonylation strategy to produce *NCON* precursors. Thus, the prepared Ni3(BO3)2-150 nanocrystal delivered the record-highest urea yield rate of 9.70 mmol h−1 gcat−1 and a Faradaic efficiency of 20.36% at −0.5 V vs. RHE.
63 citations
TL;DR: In this article, the authors show that the 3.5-mol% W-substituted vanadium oxide exhibits higher NOx removal ability than the TiO2 supported vanadia catalyst in the presence of water.
Abstract: NH3-SCR (selective catalytic reduction) is important process for removal of NOx. However, water vapor included in exhaust gases critically inhibits the reaction in a low temperature range. Here, we report bulk W-substituted vanadium oxide catalysts for NH3-SCR at a low temperature (100–150 °C) and in the presence of water (~20 vol%). The 3.5 mol% W-substituted vanadium oxide shows >99% (dry) and ~93% (wet, 5–20 vol% water) NO conversion at 150 °C (250 ppm NO, 250 ppm NH3, 4% O2, SV = 40000 mL h−1 gcat−1). Lewis acid sites of W-substituted vanadium oxide are converted to Bronsted acid sites under a wet condition while the distribution of Bronsted and Lewis acid sites does not change without tungsten. NH4+ species adsorbed on Bronsted acid sites react with NO accompanied by the reduction of V5+ sites at 150 °C. The high redox ability and reactivity of Bronsted acid sites are observed for bulk W-substituted vanadium oxide at a low temperature in the presence of water, and thus the catalytic cycle is less affected by water vapor. NH3 selective catalytic reduction is an important technique for NOx removal but water vapor critically inhibits the reaction at a low temperature. Here the authors show bulk W-substituted VOx exhibits higher NOx removal ability than the TiO2 supported vanadia catalyst in the presence of water.
61 citations
TL;DR: In this paper, a new Fenton-like catalyst of CUMSs/MIL-101(Fe,Cu), i.e., MIL-101 (MIL, Material Institute Lavoisier) with mixed valence of Fe(II)/Fe(III) and Cu(I)/Cu(II) as coordinatively unsaturated metal sites (CUMSs).
TL;DR: In this paper, a bifunctional heterogeneous catalyst was synthesized by modifying ZIF-67 with phosphotungstic acid (HPW) for biodiesel production.
TL;DR: In this article, a stereodivergent method for the Michael addition of aryl acetic acid esters to α,β-unsaturated aldehydes catalyzed by a combination of chiral pyrrolidine and a chiral Lewis base is presented.
Abstract: We report here a stereodivergent method for the Michael addition of aryl acetic acid esters to α,β-unsaturated aldehydes catalyzed by a combination of a chiral pyrrolidine and a chiral Lewis base. This reaction proceeds through a synergistic catalytic cycle which consists of one cycle leading to a chiral iminium electrophile and a second cycle generating a nucleophilic chiral enolate for the construction of a carbon-carbon bond. By varying the combinations of catalyst enantiomers, all four stereoisomers of the products with two vicinal stereocenters are accessible with high enantio- and diastereoselectivity. The products of the Michael addition, 1,5-aldehyde esters, can be readily transformed into a variety of other valuable enantioenriched structures, including those bearing three contiguous stereocenters in an acyclic system, thus providing an efficient route to an array of structural and stereochemical diversity.
12 Sep 2021
TL;DR: In this article, the authors proposed the construction of highly efficient tandem catalytic reactions, which have attracted extensive interest because of their ability to reduce reaction steps, energy consumption, and waste.
Abstract: Tandem catalytic reactions have attracted extensive interest because of their ability to reduce reaction steps, energy consumption, and waste. However, the construction of highly efficient tandem c...
TL;DR: In this paper, the authors reported a new kind of organic diradicaloids containing boron atoms, and they synthesized two isomeric B-containing PHs composed of indenofluorene π-skeletons and two dioxa-bridged triphenylborane moieties.
Abstract: Organic diradicaloids have unique open-shell structures and properties and promising applications in organic electronics and spintronics. Incorporation of heteroatoms is an effective strategy to alter the electronic structures of organic diradicaloids. However, B-containing organic diradicaloids are very challenging due to their high reactivities, which are caused by not only diradical nature but also the B atom. In this article, we report a new kind of organic diradicaloids containing boron atoms. Our strategy is to incorporate planarized triarylboranes to antiaromatic polycyclic hydrocarbons (PHs). We synthesized two isomeric B-containing PHs composed of indenofluorene π-skeletons and two dioxa-bridged triphenylborane moieties. As proved by theoretical and experimental results, both of them have excellent ambient stability and open-shell singlet diradical structures, as well as intriguing magnetic and optoelectronic properties, such as thermally accessible triplet species, reversible multiredox ability, and narrow energy gaps. Notably, they possess sufficient Lewis acidity, which has never been observed for organic diradicaloids. In addition, they can coordinate with Lewis bases to form Lewis adducts, achieving unprecedented dynamic modulations of (anti)aromaticity and thus diradical character of organic diradicaloids.
TL;DR: In this paper, an anti-solvent-free adduct approach using 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU) as a Lewis base additive was proposed.
Abstract: High-quality large-area perovskite films are realized by an anti-solvent-free adduct approach using 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU) as a Lewis base additive. Perovskite crystallization kinetics was found to depend on the latent heat of vaporization, associated with vapor pressure, and donor number of the Lewis base under force convection in air-knife-assisted D-bar coating. The conventionally used dimethyl sulfoxide (DMSO) or N-methyl-2-pyrrolidone (NMP) Lewis base is inappropriate for high-quality perovskite films because of rapid co-evaporation with solvents by argon gas blowing generated under 1.5 MPa, while the DMPU-containing precursor solution induces the formation of a stable adduct intermediate in the as-deposited film due to the low vapor pressure and high donor number of DMPU. Upon addition of DMPU into the precursor solution, the concentration of DMPU is found to affect the morphology and photo-excited carrier lifetime of the resulting perovskite film. A piece of the (FAPbI3)0.95(CsPbBr3)0.05 perovskite film coated on a 4.8 × 9.6 cm2-substrate was used for testing the photovoltaic performance, where the power conversion efficiency (PCE) significantly improved from 3.21% to 20.08% (best PCE is 20.56%) when 0.5 M DMPU (with respect to 1 M of perovskite) was added into the precursor solution. A monolithic perovskite solar module with an active area of 19.69 cm2, employing the perovskite film formed from the 0.5 M DMPU-containing solution, demonstrates a PCE of 17.94%.
TL;DR: In this paper, highly efficient selective capacitive removal of heavy metal ions from complex wastewater over Lewis base sites of S-doped Fe-N-C cathodes was originally performed via an electro-adsorption process.
Abstract: The pollution of toxic heavy metals is becoming an increasingly important issue in environmental remediation because these metals are harmful to the ecological environment and human health. Highly efficient selective removal of heavy metal ions is a huge challenge for wastewater purification. Here, highly efficient selective capacitive removal (SCR) of heavy metal ions from complex wastewater over Lewis base sites of S-doped Fe-N-C cathodes was originally performed via an electro-adsorption process. The SCR efficiency of heavy metal ions can reach 99% in a binary mixed solution [NaCl (100 ppm) and metal nitrate (10 ppm)]. Even the SCR efficiency of heavy metal ions in a mixed solution containing NaCl (100 ppm) and multicomponent metal nitrates (10 ppm for each) can approach 99%. Meanwhile, the electrode also demonstrated excellent cycle performance. It has been demonstrated that the doping of S can not only enhance the activity of Fe-N sites and improve the removal ability of heavy metal ions but also combine with heavy metal ions by forming covalent bonds of S- clusters on Lewis bases. This work demonstrates a prospective way for the selective removal of heavy metal ions in wastewater.
TL;DR: In this article, both oxygen vacancies and Con+ Lewis acid sites were purposely introduced on ordered macroporous La0.8Sr0.2CoO3 monolithic catalysts by one-step reduction and selective etching in oxalic acid, and their synergistic effect on methane combustion was investigated.
Abstract: An in-depth understanding of the surface properties-activity relationship could provide a fundamental guidance for the design of highly efficient perovskite-based catalysts for the control of anthropogenic methane emission. Herein, both oxygen vacancies and Con+ Lewis acid sites were purposely introduced on ordered macroporous La0.8Sr0.2CoO3 monolithic catalysts by one-step reduction and selective etching in oxalic acid, and their synergistic effect on methane combustion was investigated. Combined with experimental and theoretical investigations, we revealed that the positively charged Con+ Lewis acid sites and single-electron-trapped oxygen vacancies (Vo·) formed an active pair, which enabled an effective localized electron cloud shift from Vo· to Con+. The characteristic electronic effect modulates surface electronic properties and coordination structures, thus resulting in superior oxygen activation capacity, lattice oxygen mobility, and reducibility, as well as favorable CH4 interaction and oxidation. Our work not only gives insights into surface properties-activity relationships on perovskite for hydrocarbon combustion but also sheds substantial light on future environmental catalyst design and modulation for hydrocarbon pollutants elimination.
TL;DR: By reverting the octahedrally coordinated aluminum back to a tetrahedral geometry, the corresponding Brønsted acid sites are restored with a concomitant loss in the ability to form Lewis acid sites.
Abstract: Lewis acidic aluminum in zeolites, particularly acidity that is inherent to the framework, is an indeterminate concept. A fraction of framework aluminum changes geometry to octahedral coordination in the proton form of zeolite mordenite. Such octahedrally coordinated aluminum is the precursor of a Lewis acid site and its formation is accompanied by a loss in Bronsted acidity. Herein, we show that such Lewis acid sites have a preferred location in the pore structure of mordenite. A greater proportion of these Lewis acid sites resides in the side-pockets than in the main channel. By reverting the octahedrally coordinated aluminum back to a tetrahedral geometry, the corresponding Bronsted acid sites are restored with a concomitant loss in the ability to form Lewis acid sites. Thereby, reversible octahedral–tetrahedral aluminum coordination provides a means to indirectly switch between Lewis and Bronsted acidity. This phenomenon is unique to Lewis acidity that is inherent to the framework, thereby distinguishing it from Lewis acidity originating from extra-framework species. Furthermore, the transformation of framework aluminum into octahedral coordination is decoupled from the generation of distorted tetrahedrally coordinated aluminum, where the latter gives rise to the IR band at 3660 cm−1 in the OH stretching region.
TL;DR: A promotion effect of support on the alkali and sulfur resistance is unraveled, which could promote the adsorption of SO2 on the TiO2 and reduce the toxicity of the active component (MnO2).
TL;DR: Zr6OTf-BTB is a two-dimensional metal-organic framework with 96% accessible Lewis acid sites as probed by the bulky Lewis base pivalonitrile as mentioned in this paper.
Abstract: Owing to hindered diffusions, the application of porous catalytic materials has been limited to relatively simple organic transformations with small substrates. Herein we report a dimensional reduction strategy to construct a two-dimensional metal-organic framework (MOF), Zr6OTf-BTB, with 96% accessible Lewis acidic sites as probed by the bulky Lewis base pivalonitrile. With nearly free substrate accessibility, Zr6OTf-BTB outperformed two three-dimensional MOF counterparts of similar Lewis acidity (Zr6OTf-BPDC and Zr6OTf-BTC) in catalyzing sterically hindered multicomponent reactions (MCRs) for the construction of tetrahydroquinoline and aziridine carboxylate derivatives with high turnover numbers (TONs). Zr6OTf-BTB was also superior to the homogeneous benchmark Sc(OTf)3 with nearly 14 times higher TON and 9 times longer catalyst lifetime. Furthermore, the topology-activity relationships in these Zr-based Lewis acidic MOFs were rationalized by comparing their Lewis acidity, numbers of Lewis acidic sites, and sterically accessible Lewis acidic sites. Zr6OTf-BTB was successfully used to construct several bioactive molecules via MCRs with excellent efficiency. This dimensional reduction strategy should allow the development of other MOF catalysts for synthetically useful and complicated organic transformations.
TL;DR: In this paper, the inorganic CsPbI2Br based perovskite solar cells with thioacetamide additive exhibit the best performance of 15.87% (AM 1.5, 1 sun) and good ambient stability compared with the control device and device with acetamide.
TL;DR: A metal-free heterogeneous catalyst, boron-doped graphitic carbon nitride for effective conversion of CO2 to cyclic carbonates at atmospheric pressure under solvent-free conditions is reported in this article.
Abstract: Conversion of carbon dioxide (CO2) to value-added products is imperative to combat global warming. In this regard, herein we report a metal-free heterogeneous catalyst, boron-doped graphitic carbon nitride for effective conversion of CO2 to cyclic carbonates at atmospheric pressure under solvent-free conditions. The developed catalyst possesses acid-base dual functionality as active sites, which activate both epoxides as well as CO2 simultaneously to carry out the cycloaddition reaction. The catalyst showed a maximum yield up to 99 % with a turnover number of 173. Detailed optimization studies have been performed to find out the best doping content of boron and best conditions by varying the reaction time, temperature and catalysts amount. Furthermore, the ease of catalyst recovery and excellent recyclability demonstrate the sustainability and versatility of the catalyst for selective and efficient conversion of CO2 to cyclic carbonates at mild conditions.
TL;DR: C(1)‐Ammonium enolates are powerful, catalytically generated synthetic intermediates applied in the enantioselective α‐functionalisation of carboxylic acid derivatives using isothiourea Lewis base organocatalysts using two distinct catalyst turnover approaches.
Abstract: C(1)-Ammonium enolates are powerful, catalytically generated synthetic intermediates applied in the enantioselective α-functionalisation of carboxylic acid derivatives This minireview describes the recent developments in the generation and application of C(1)-ammonium enolates from various precursors (carboxylic acids, anhydrides, acyl imidazoles, aryl esters, α-diazoketones, alkyl halides) using isothiourea Lewis base organocatalysts Their synthetic utility in intra- and intermolecular enantioselective C-C and C-X bond forming processes on reaction with various electrophiles will be showcased utilising two distinct catalyst turnover approaches
TL;DR: In this article, rare-earth-based complexes were synthesized and applied for the first time as homogeneous Lewis acids for the cycloaddition of CO2 to epoxides in the presence of quaternary ammonium salts.
01 Jan 2021
TL;DR: In this article, the volcano curves have proven to be particularly useful in new catalyst design in the field of heterogeneous catalysis, and the further enhancement of the performance of the optimal catalysis was further enhanced.
Abstract: Volcano curves have proven to be particularly useful in new catalyst design in the field of heterogeneous catalysis. On the other hand, the further enhancement of the performance of the optimal cat...
TL;DR: A review of the role of tris(pentafluorophenyl)borane (BCF) in metal-free catalysis can be found in this article, which mainly focuses on recent reports from 2018 onwards and provides a concise knowledge to the readers.
Abstract: A series of boron based Lewis acids have been reported to date, but among them, tris(pentafluorophenyl)borane (BCF) has gained the most significant attention in the synthetic chemistry community. The viability of BCF as a potential Lewis acid catalyst has been vastly explored in organic and materials chemistry due to its thermal stability and commercial availability. Most explorations of BCF chemistry in organic synthesis has occurred in the last two decades and many new catalytic reactivities are currently under investigation. This review mainly focuses on recent reports from 2018 onwards and provides a concise knowledge to the readers about the role of BCF in metal-free catalysis. The review has mainly been categorized by different types of organic transformation mediated through BCF catalysis for the C-C and C-heteroatom bond formation.