ACS Catalysis 最新文献

Lithium–oxygen batteries (LOBs), despite high-energy densities, generally suffer from poor cycling performances, which put severe constraints on their commercialization. Herein, we demonstrate a cathode catalyst featuring a hollow structure with high-density, low-coordinated Ru active sites. The high-density low-coordinated Ru active sites could efficiently activate oxygen via bridge-adsorption configuration, and the hollow architecture could optimize the access of oxygen to the active sites and accommodate more Li₂O₂. These structural features could direct the Li₂O₂ to grow along the (010) faces into a unique highly dispersed fluff-like morphology, which could be readily decomposed in charge process, thereby conferring a long battery stability under high-rate current, the LOB capable of running stably for >700 cycles under the high-rate current density of 1 A·g^–1.

Tertiary alkylamines can coordinate palladium salts and direct C–H activation reactions. However, these tertiary alkylamines can suffer from decomposition through oxidative pathways. This report describes the DFT analysis of acyclic and cyclic tertiary alkylamines with respect to C–H bond cleavage through either γ-C(sp³)–H activation on the exo N-substituent or β-H elimination at the endocyclic position. The study assesses the role of an N-acetyl amino acid ligand in suppressing the β-H elimination pathway. Experiments using tertiary alkylamines with isotopically labeled α-C–D bonds demonstrate the small differences in energy barriers that discern both reaction pathways. Guided by the insights of computational studies on methyl and strained methylene γ-C–H activation in tertiary alkylamines, we report a successful methine γ-C–H activation to construct ring-strained quaternary centers through intermolecular C–H arylation.

Catalytic asymmetric construction of atropisomers with multiple stereogenic elements has recently become an emerging area. However, general methods that produced atropisomers bearing remote 1,5-axial and central chirality efficiently and stereoselectively are scarce yet highly challenging. We herein report a catalytic diastereo- and atroposelective remote desymmetrizing alkynylation of axially prochiral dialkynes with ortho-quinone methides (o-QMs), furnishing atropisomers bearing 1,5-remote centrally and axially stereogenic elements. The remote control of prochiral axis far from the reaction site could be simultaneously achieved during the stereoselective C(sp³)–C(sp) bond-forming process to generate a stereogenic center. In addition, a kinetic resolution of axially racemic alkynes via diastereo- and atroposelective remote alkynylation with o-QMs has been developed, further enriching structural diversity of atropisomers bearing 1,5-central and axial chirality. The present method expands the chemical space of atropisomeric molecules bearing multiple chiral elements by facile downstream diversification of C–C triple bonds. Finally, the alkynylation of o-QMs can also be applied for the construction of chiral motifs bearing 1,9- and 1,10-stereogenic centers.

Transition-metal-catalyzed cycloaddition reactions of strained small-ring compounds are powerful methods for constructing carbo- and heterocyclic structures of medicinal interest. However, the application of this strategy to bicyclo[1.1.0]butanes (BCBs), which are among the most strained carbocycles known, remains underdeveloped. Herein, we report vinylbicyclo[1.1.0]butane (VBCB) as a platform synthon for palladium-catalyzed formal [2σ+2π] cycloaddition reactions with various 2π-components, enabling the synthesis of BCHs, oxa-BCHs, and aza-BCHs under identical reaction conditions. The zwitterionic π-allyl-Pd species generated through the palladium-catalyzed activation of VBCBs is the key to circumventing potential carbene reactivity and serves as a common intermediate for cycloadditions with diverse 2π-systems, including alkenes, aldehydes, ketones, and imines. Notably, by utilizing Pd₂(dba)₃ and an anthracene-derived Trost ligand, a wide array of BCHs bearing two vicinal chiral centers has been prepared in a highly diastereo-, and enantioselective manner. The generality and practicality of this method have been demonstrated by a broad substrate scope, scale-up reactions, and the versatile transformation of multiple functional groups into BCH scaffolds. Preliminary mechanistic studies support the formation of the π-allyl-Pd species.

The hyperthermophile Thermotoga maritima possesses d-amino acid-metabolizing enzymes and multifunctional enzymes associated with l- and d-amino acid metabolism, although it does not have typical alanine and glutamate racemases. Intriguingly, in this study, we found that unexpectedly one PLP fold-type I enzyme from this organism, TM1270, has six different enzyme activities, namely amino acid racemase, cystathionine β-lyase, serine dehydratase, threonine aldolase, aspartate 4-decarboxylase, and amino acid aminotransferase activities. We characterized the properties of these six enzyme activities including their substrate specificities, pH and temperature dependences, and kinetic parameters. β-Lyase activity was the highest among the six activities based on kinetic parameters. Furthermore, we determined the crystal structure of TM1270 with the internal aldimine form of pyridoxal 5′-phosphate, which forms a Schiff base with Lys202. The possible reaction mechanisms of the six enzyme activities are proposed based on the crystal structure and the results of mutational analysis.

The transformation of carbon dioxide (CO₂) into formic acid (FA; HCOOH) in an aqueous phase is a promising method of realizing an environmentally friendly FA/CO₂-mediated chemical hydrogen storage/supply cycle. Despite progress in the design of catalysts that operate under basic conditions, the development of efficient catalysts that operate under additive-free conditions lags behind owing to the difficulty in activating CO₂ and the low solubility of CO₂ in pure water. In the present study, we present a heterogeneous tandem catalysis strategy in which Co₃O₄ is used as a CO₂ hydration cocatalyst to produce a HCO₃^– intermediate, in combination with our previously reported PdAg/TiO₂ as a catalyst for the hydrogenation of HCO₃^– to afford FA. The turnover number based on Pd improved by a factor of more than 8 in the presence of the Co₃O₄ cocatalyst with a cubic particle morphology enclosed by (100) facets. A series of morphology-controlled Co₃O₄ cocatalysts was investigated to elucidate the effect of the exposed crystal facets (i.e., (100), (111), or (112)) on their physicochemical properties and catalytic activity in FA synthesis. A systematic comparison based on experimental and density functional theory calculations demonstrated that the substantial enhancement effect of the Co₃O₄ cubes is attributable to the in situ generation of the largest amount of surface Co–OH groups with strong basicity originating from the exposed (100) facets. In addition, the present tandem catalytic system displayed high recyclability without exhibiting a structural change or a significant loss of activity. These findings will allow the rational design of an environmentally benign catalytic system for the hydrogenation of CO₂ to FA.