Lewis Acid Research Articles

Tuning Secondary-Sphere Lewis Acidity via Late-Stage Modification of an Appended Borane

Tuning Secondary-Sphere Lewis Acidity via Late-Stage Modification of an Appended Borane

Copper(I)‐Catalyzed Asymmetric 1,4‐Hydroarsination of α,β‐Unsaturated Compounds

Herein, a copper(I)‐catalyzed asymmetric 1,4‐hydroarsination of β‐substituted α,β‐unsaturated esters is achieved in moderate to excellent yields with high to excellent enantioselectivity, based on the proposed nucleophilic [Cu]‐AsPh2 species. As for α‐substituted α,β‐unsaturated esters, a 1,4‐hydroarsination/enantioselective protonation event occurs smoothly in satisfying results. Furthermore, β‐substituted α,β‐unsaturated ketone, α,β‐unsaturated amide, and α,β‐unsaturated phosphine sulfide are well applied in the present catalytic system. Finally, some control experiments show that HAsPh2 is activated through coordination with the copper(I) catalyst and HAsPh2 exhibits inferior soft Lewis basicity to HPPh2 in the presence of a copper(I)‐bisphosphine complex.

Copper(I)‐Catalyzed Asymmetric 1,4‐Hydroarsination of α,β‐Unsaturated Compounds

Herein, a copper(I)‐catalyzed asymmetric 1,4‐hydroarsination of β‐substituted α,β‐unsaturated esters is achieved in moderate to excellent yields with high to excellent enantioselectivity, based on the proposed nucleophilic [Cu]‐AsPh2 species. As for α‐substituted α,β‐unsaturated esters, a 1,4‐hydroarsination/enantioselective protonation event occurs smoothly in satisfying results. Furthermore, β‐substituted α,β‐unsaturated ketone, α,β‐unsaturated amide, and α,β‐unsaturated phosphine sulfide are well applied in the present catalytic system. Finally, some control experiments show that HAsPh2 is activated through coordination with the copper(I) catalyst and HAsPh2 exhibits inferior soft Lewis basicity to HPPh2 in the presence of a copper(I)‐bisphosphine complex.

PnictogenIII Dications Supported by BZIMPY Ligands.

Two homologous series of pnictogen(III) dications, stabilized by 2,6-bis(benzimidazole-2-yl)pyridine ligands have been prepared. Both series contain PnIII-X moieties (Pn = P, As, Sb, Bi; X = Cl or Ph) and have been fully characterized using spectroscopic methods including X-ray crystallography. The Lewis acidity of these compounds has also been probed by computational methods; the results suggest that the dictations are strong Lewis acids, with the PnCl2+ compounds being more acidic than the PnPh2+ compounds, and with Lewis acidity increasing from P to Bi, in both series. The PhP2+-containing compound was also found to be a versatile PIII transfer reagent, leading to new synthetic routes for various PhP-containing compounds. The redox chemistry of all compounds has also been probed using cyclic voltammetry and chemical reductions. In some cases the resulting PnI moieties could be trapped using diazabutadienes.

Stereocatalytic Effect of CeO2 for the Synthesis of trans‐3‐Penten‐2‐ol

AbstractThe transformation of biobased alkanediols over heterogeneous catalysts is a major object. Here, a series of catalysts were prepared for 2,4‐pentanediol dehydration to 3‐penten‐2‐ol. Ceria‐based catalysts had a unique property of showing high efficiency. More importantly, a stereocatalytic effect was observed for CeO2, yielding trans‐3‐penten‐2‐ol with a high selectivity. Raman, XPS, TPD, and TPR were carried out to clarify the catalyst structure, and the relationship between the catalyst structure and catalytic performance were studied. The amount of Lewis acid sites can hardly be correlated with the total concentrations of the oxygen vacancies. It was suggested that the geometry structure of the active sites played a crucial role in trans‐3‐penten‐2‐ol production. The oxygen vacancies originating from CeO2 consisted of active sites with a geometrical structure, which were different from those created by Pr doping CeO2. In addition, the Pr doping enhanced the oxygen migration, which resulted in side reactions, consequently, giving a lower selectivity to trans‐3‐penten‐2‐ol.

Lewis Acid Promotes Three-Component Cyclization to Construct Dithioxazole Derivatives.

A simple and effective strategy for the construction of disulfide-substituted oxazole derivatives from amides, ynals, and acetyl disulfides via a Lewis acid-promoted three-component reaction has been reported. In addition, this reaction possesses other unique advantages, such as transition-metal-free catalysis, the production of disulfides, good functional group tolerance, and good regioselectivity.

Fabrication of novel PVA loaded ZnO nanoparticles for anti-renal failure.

X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the structural, surface and particles properties of a series of zinc oxides (ZnO) doped with polyvinyl alcohol (PVA) that were prepared using the sol-gel method. The results demonstrated that the crystallinity of the catalysts decreased as the PVA content increased beyond 5 PVA/ZnO. However, on raising the calcination temperature up to 500°C, the average crystal size of the PVA/ZnO nanoparticles increased. Next Pyridine adsorption was used to measure the surface acidity of the catalysts, and the results showed that doping ZnO with PVA and raising the calcination temperature to 500°C increased the catalyst's surface acidity. Furthermore, the data indicates that raising the ratio of the Brønsted to Lewis acid sites enhanced the catalytic activity for the synthesis of coumarin derivatives. We concluded that the structural and acidity characteristics of the catalysts under study had a significant impact on the catalytic activity. Furthermore, a study examining the biological activity of ZnO/PVA and pure ZnO revealed that 5PVA/ZnO performed the best in terms of improving the kidney functions of diabetic rats.

Tailoring of Novel Ru (III) and Cr (III) Salen Complexes as Catalysts for a Sustainable and Green Synthesis of Dihydro‐tetrazolo [1,5‐a] thiazolo [4,5‐d] pyrimidin‐6‐yl morpholine: Experimental and Theoretical Approaches

ABSTRACTTwo novel Cr (III) and Ru (III) salen complexes based on {3,4‐Bis‐[(5‐chloro‐2‐hydroxy‐benzylidene)‐amino]‐phenyl}‐phenyl‐methanone ligand (CSAB) were synthesized. The complexes were characterized using various spectral and analytical methods. The catalytic performance of the CSAB complexes was investigated via a four‐component condensation reaction involving aromatic aldehydes, rhodamine, morpholine, and 5‐aminotetrazole under mild, environmentally friendly conditions. Different Lewis acids, bases, ionic liquid catalysts, solvents, and catalyst amounts were assessed to optimize the reaction parameters. Both catalyst systems demonstrated robust catalytic activity under strictly managed conditions, with the heterogeneous catalyst CSAB‐Ru showing superior efficacy compared to the homogeneous CSAB‐Cr catalyst. The study confirmed the catalytic capabilities of both complexes and evaluated their recyclability and reusability. The heterogeneous catalyst (CSAB‐Ru) could be reused seven times, whereas the homogeneous catalyst (CSAB‐Cr) could be recycled four times. Both complexes demonstrated strong catalytic activity and selectivity, resulting in high product yields. The study provides insights into the synthetic applications of novel CSAB complexes, highlighting their potential in organic transformations. It emphasizes their ease of use, safety, stability, component availability, quick reaction times, and high yields, making them promising for future industrial applications.

Steering Acid-base Site Distribution and Hydrophobicity of Bioresourced Bifunctional Hybrid Materials for Direct Synthesis of γ-Valerolactone from Biomass-based Furfural.

The direct production of value-added chemicals from biomass via multiple conversion processes with a sole renewable solid catalyst is promising for carbon-neutral development while challenging. Herein, a series of novel bioresourced organic-inorganic hybrid materials were synthesized from bio-based ascorbic acid (Vc), zirconium chloride (ZrCl4) and p-toluenesulfonic acid (p-TSA) through a facile solvothermal process. The as-prepared Zr-Vc-3 catalyst with Vc, ZrCl4, and p-TSA in the 1:1:0.5 molar ratio displayed outstanding performance in direct furfural-to-γ-valerolactone (GVL) transformation, giving an ultrahigh GVL yield of 76.2%, with an ideal activation energy (55.46 kJ mol-1), outperforming state-of-the-art catalysts. The superior performance of Zr-Vc-3 could be ascribed to its good reusability, relatively large pore size, suitable amount of acid-base sites, and good hydrophobicity. Mechanistic studies unveiled that Lewis acid-base sites facilitate the conversion of furfural to furfuryl alcohol and isopropyl levulinate (IPL) to 4-hydroxypentanoate via transfer hydrogenation process, while Brønsted acid sites are instrumental in the ring-opening of furfuryl alcohol to IPL and the lactonization of 4-hydroxypentanoate to GVL, overall contributing to the multi-step conversion of furfural to GVL in a single pot. This work provides a valuable reference for precisely constructing bio-based OIHMs with tailored functionalities forone-pot valorization of biomass feedstocks via tandem reactions.

Electric‐Field Catalysis on Carbon Nanotubes in Electromicrofluidic Reactors: Monoterpene Cyclizations

AbstractThe control over the movement of electrons during chemical reactions with oriented external electric fields (OEEFs) has been predicted to offer a general approach to catalysis. Recently, we suggested that many problems to realize electric‐field catalysis in practice under scalable bulk conditions could possibly be solved on multiwalled carbon nanotubes in electromicrofluidic reactors. Here, we selected monoterpene cyclizations to assess the scope of our system in organic synthesis. We report that electric‐field catalysis can function by stabilizing both anionic and cationic transition states, depending on the orientation of the applied field. Moreover, electric‐field catalysis can promote reactions which are barely accessible by general Brønsted and Lewis acids and field‐free anion‐π and cation‐π interactions, and drive chemoselectivity toward intrinsically disfavored products without the need for pyrene interfacers attached to the substrate to prolong binding to the carbon nanotubes. Finally, interfacing with chiral organocatalysts is explored and evidence against contributions from redox chemistry is provided.

Public Preparedness for Agricultural Investment and its Contribution to Sustainable Economic Growth in Nigeria

Purpose: The study investigated public preparedness for agricultural investment and its contribution to and economic growth in Nigeria. The study was guided by the following objectives; to assess the level of individuals' awareness on the current condition of the agriculture industry in Nigeria, public's perspective of the substantial influence of agricultural on Nigeria's overall economic growth, the preparedness of citizens to invest in the agriculture sector for the enhancement of Nigeria's economic growth and delineate the agriculture sector's contribution to GDP. Theoretical Framework: The study was anchored on Lewis (1979) theory of impacting economic growth. Method: The study utilized a descriptive research approach involving 133 respondents across the 36 states, including the federal capital territory, whose major vocation is food production. The samples were selected by a convenience sampling method, considering the respondent geographic closeness and included only those present throughout the survey. Closed-ended questionnaire was utilized as a data-collecting instrument to assess the variables under study; the data on the contribution of agricultural practices to GDP was access from Nigeria Bureau of Statistics (2022-2023). To ensure content validity, the survey instrument was validated utilizing the Lawshe's template. A threshold of 0.99 was noted, signifying that the questionnaire was both representative and comprehensible. The Cronbach alpha technique yielded a reliability coefficient of 0.83, affirming the instrument's homogeneity. The data was analyzed using frequency counts (f) and percentages (%) while the results was presented in graphs. Findings: The survey revealed that most respondents are aware of the current state of agriculture in Nigeria. The heightened awareness has impacted public perception of agriculture's significant role in national economic growth, as the majority of respondents acknowledged that agriculture not only provides food for the populace but also improves farmers' living standards by reducing poverty and hunger, thus promoting economic development. They are willing to invest in agriculture despite a decline in production and a reduced contribution to the national GDP. Conclusion: Although the agricultural sector's contribution to GDP has diminished, individuals are inclined to invest in agriculture therefore, enhanced engagement in agriculture, along with Nigeria's extensive arable land and various people and material resources, and the implementation of sustainable agricultural innovations, will result in significant economic growth.

Controllable p-type doping and improved conductance of few-layer WSe2 via Lewis acid

Manipulation of the electronic properties of layered transition-metal dichalcogenides (TMDs) is of fundamental significance for a wide range of electronic and optoelectronic applications. Surface charge transfer doping is considered to be a powerful technique to regulate the carrier density of TMDs. Herein, the controllable p-type surface modification of few-layer WSe2by FeCl3Lewis acid with different doping concentrations have been achieved. Effective hole doping of WSe2has been demonstrated using Raman spectra and XPS. Transport properties indicated the p-type FeCl3surface functionalization significantly increased the hole concentration with 1.2 × 1013cm-2, resulting in 6 orders of magnitude improvement for the conductance of FeCl3-modified WSe2compared with pristine WSe2. This work provides a promising approach and facilitate the further advancement of TMDs in electronic and optoelectronic applications.

Fluorspar to fluorochemicals upon low-temperature activation in water.

The dangerous chemical hydrogen fluoride sits at the apex of the fluorochemical industry, but the substantial hazards linked to its production under harsh conditions (above 300 degrees Celsius) and transport are typically contracted to specialists. All fluorochemicals for applications, including refrigeration, electric transportation, agrochemicals and pharmaceuticals, are prepared from fluorspar (CaF2) through a procedure that generates highly dangerous hydrogen fluoride1-5. Here we report a mild method to obtain fluorochemicals directly from fluorspar, bypassing the necessity to manufacture hydrogen fluoride. Acid-grade fluorspar (more than 97 per cent CaF2) is treated with the fluorophilic Lewis acid boric acid (B(OH)3) or silicon dioxide (SiO2), in the presence of oxalic acid, a Brønsted acid that is highly effective for Ca2+ sequestration. This scalable process carried out in water at low temperature (below 50 degrees Celsius) enables access to widely used fluorochemicals, including tetrafluoroboric acid, alkali metal fluorides, tetraalkylammonium fluorides and fluoro(hetero)arenes. The replacement of oxalic acid with sulfuric acid gave comparable results for B(OH)3, but was not as effective when the fluorophilic Lewis acid was SiO2. A similar process also works with the lower-purity metspar. The production of fluorochemicals directly from fluorspar offers the possibility of decentralized manufacturing-an attractive model for the fluorochemical industry. With the renewed interest in innovative methods to synthesize oxalic acid via carbon dioxide capture and biomass6,7, and the challenges posed by our dependence on fossil fuels for sulfur and therefore sulfuric acid supply8,9, our technology may represent a departure towards a sustainable fluorochemical industry.

Breaking Activity‐Durability Inverse Relationship via Electrode Engineering by Utilizing β‐MnO2/RuO2 Heterostructures for Efficient Seawater Electrolysis

AbstractSignificant efforts are underway to enhance the efficiency of water electrolysis for sustainable hydrogen production. Approaches that were explored are the design of an efficient anode, engineering of electrolytes, and application of diffusion protective layer over the catalyst to protect it from corrosive reactions. Here we are exploring the engineering of electrode fabrication to enhance the efficacy of anode catalysts by ensuring that the materials are carefully selected. β‐MnO2 has been used to develop a cost‐effective method for electrode fabrication that establish a Schottky junction at heterostructure interface. This method transforms commercial RuO2, which is considered to be less active and stable, highly selective for chlorine oxidative reactions, into a highly active, stable, and OER‐selective in alkaline medium and surrogate seawater. With the help of thorough electrochemical techniques, we found that this engineering significantly improves the effective electrochemical surface area, and higher kinetics and conversion per unit site, profoundly affecting the charge transfer mechanism and optimizing the adsorption of OER intermediates, resulting in much‐increased mass activity. It is observed that the selectivity of the OER was enhanced due to the Lewis acid repercussions of β‐MnO2.

Host‐Guest Assemblies of Polyoxovanadate Clusters as Supramolecular Catalysts

Supramolecular functional materials can be used to overcome some of the most challenging tasks in materials science, where the dynamic nature of supramolecular interactions can be leveraged to fine‐tune the properties of the material. The Lindqvist hexavanadate family of polyoxometalates are interesting candidates for supramolecular materials due to their redox and Lewis acid properties that enable their application in energy conversion or catalysis. Despite their promising potential, hexavanadate clusters are underrepresented in supramolecular materials, mainly due to the synthetic challenges related to their inherent reactivity. In this work, pillar[5]arene was successfully grafted onto a Lindqvist hexavanadate and the resulting structure was confirmed by single crystal X‐ray diffraction, presenting the first example of a crystal structure of a polyoxometalate covalently functionalized with a pillar[5]arene. By introducing a ditopic guest molecule that could interlink pillar[5]arene moieties, host‐guest interactions were leveraged as the driving force for the formation of supramolecular assemblies incorporating hexavanadate clusters in a controlled manner. The enhanced catalytic performance of the resulting aggregates confirmed their potential application as functional catalytic materials. This novel approach for developing hexavanadate‐based catalysts reported here showcases the potential of using host‐guest interactions as a means to introduce catalytically active metal‐oxo clusters into supramolecular frameworks.

Production of Branched Alkanes by Upcycling of Waste Polyethylene over Controlled Acid Sites of SO4/ZrO2-Al2O3 Catalyst.

Branched alkanes, which enhance the octane number of gasoline, can be produced from waste polyethylene. However, achieving highly selective production of branched alkanes presents a significant challenge in the upcycling of waste polyethylene, and the maximum selectivity for branched alkanes reported up to date is about 70%. Here, we report a one-pot process to convert polyethylene into gasoline-range hydrocarbons (C4-C13) with yield of 73.3% over SO42-ZrO2-Al2O3 catalyst at 280 °C. The proportion of branched alkanes reaches 90.1% within the C4-C13 fraction. Incorporation of sulfate group endows the catalyst with strong Lewis acid sites and weak and moderate Brønsted acid sites. In situ X-ray absorption, in situ infrared spectroscopy, in situ small angle neutron scattering, and DFT calculations reveal that polyethylene activation occurs through the synergy between sulfate groups and strong Lewis acid sites (Zr sites). The weak and moderate Brønsted acid sites preferentially catalyze the isomerization and type A β-scission processes, which favors the formation of branched alkanes, while suppressing competing reactions that produce straight-chain alkanes.

Host-Guest Assemblies of Polyoxovanadate Clusters as Supramolecular Catalysts.

Supramolecular functional materials can be used to overcome some of the most challenging tasks in materials science, where the dynamic nature of supramolecular interactions can be leveraged to fine-tune the properties of the material. The Lindqvist hexavanadate family of polyoxometalates are interesting candidates for supramolecular materials due to their redox and Lewis acid properties that enable their application inenergy conversion or catalysis. Despite their promising potential, hexavanadate clusters are underrepresented in supramolecular materials, mainly due to the synthetic challenges related to their inherent reactivity. In this work, pillar[5]arene was successfully grafted onto a Lindqvist hexavanadate and the resulting structure was confirmed by single crystal X-ray diffraction, presenting the first example of a crystal structure of a polyoxometalate covalently functionalized with a pillar[5]arene. By introducing a ditopic guest molecule that could interlink pillar[5]arene moieties, host-guest interactions were leveraged as the driving force for the formation of supramolecular assemblies incorporating hexavanadate clusters in a controlled manner. The enhanced catalytic performance of the resulting aggregates confirmed their potential application as functional catalytic materials. This novel approach for developing hexavanadate-based catalysts reported here showcases the potential of using host-guest interactions as a means to introduce catalytically active metal-oxo clusters into supramolecular frameworks.

Production of Branched Alkanes by Upcycling of Waste Polyethylene over Controlled Acid Sites of SO4/ZrO2‐Al2O3 Catalyst

Branched alkanes, which enhance the octane number of gasoline, can be produced from waste polyethylene. However, achieving highly selective production of branched alkanes presents a significant challenge in the upcycling of waste polyethylene, and the maximum selectivity for branched alkanes reported up to date is about 70%. Here, we report a one‐pot process to convert polyethylene into gasoline‐range hydrocarbons (C4‐C13) with yield of 73.3% over SO42‐ZrO2‐Al2O3 catalyst at 280 °C. The proportion of branched alkanes reaches 90.1% within the C4‐C13 fraction. Incorporation of sulfate group endows the catalyst with strong Lewis acid sites and weak and moderate Brønsted acid sites. In situ X‐ray absorption, in situ infrared spectroscopy, in situ small angle neutron scattering, and DFT calculations reveal that polyethylene activation occurs through the synergy between sulfate groups and strong Lewis acid sites (Zr sites). The weak and moderate Brønsted acid sites preferentially catalyze the isomerization and type A β‐scission processes, which favors the formation of branched alkanes, while suppressing competing reactions that produce straight‐chain alkanes.

Ring Expansion toward Fused Diazabicyclo[3.1.1]heptanes through Lewis Acid Catalyzed Highly Selective C−C/C−N Bond Cross‐Exchange Reaction between Bicyclobutanes and Diaziridines

The synthesis of bicyclic scaffolds has garnered considerable interest in drug discovery because of their ability to mimic benzene bioisosteres. Herein, we introduce a new approach that utilizes a Lewis acid (Sc(OTf)3)‐catalyzed σ‐bond cross‐exchange reaction between the C−C bond of bicyclobutanes and the C−N bond of diaziridines to produce multifunctionalized and medicinally interesting azabicyclo[3.1.1]heptane derivatives. The reaction proceeds well with different bicyclobutanes and a broad range of aryl‐ as well as alkenyl‐, but also alkyl‐substituted diaziridines (up to 98% yield). Conducting a scale‐up experiment and exploring the synthetic transformations of the cycloadducts emphasized the practical application of the synthesis. Furthermore, a zinc‐based chiral Lewis acid catalytic system was developed for the enantioselective version of this reaction (up to 96% ee).

Ring Expansion toward Fused Diazabicyclo[3.1.1]heptanes through Lewis Acid Catalyzed Highly Selective C-C/C-N Bond Cross-Exchange Reaction between Bicyclobutanes and Diaziridines.

The synthesis of bicyclic scaffolds has garnered considerable interest in drug discovery because of their ability to mimic benzene bioisosteres. Herein, we introduce a new approach that utilizes a Lewis acid (Sc(OTf)3)-catalyzed σ-bond cross-exchange reaction between the C-C bond of bicyclobutanes and the C-N bond of diaziridines to produce multifunctionalized and medicinally interesting azabicyclo[3.1.1]heptane derivatives. The reaction proceeds well with different bicyclobutanes and a broad range of aryl- as well as alkenyl-, but also alkyl-substituted diaziridines (up to 98% yield). Conducting a scale-up experiment and exploring the synthetic transformations of the cycloadducts emphasized the practical application of the synthesis. Furthermore, a zinc-based chiral Lewis acid catalytic system was developed for the enantioselective version of this reaction (up to 96% ee).