Synthetic Leaves Based on Crystalline Olefin-Linked Covalent Organic Frameworks for Efficient CO2 Photoreduction with Water

We report, for the first time, a new synthetic strategy for the preparation of crystalline two-dimensional olefin-linked covalent organic frameworks (COFs) based on aldol condensation between benzodifurandione and aromatic aldehydes. Olefin-linked COFs can be facilely crystallized through either a pyridine-promoted solvothermal process or a benzoic anhydride-mediated organic flux synthesis. The resultant COF leaf with high in-plane π-conjugation exhibits efficient visible-light-driven photoreduction of carbon dioxide (CO2) with water (H2O) in the absence of any photosensitizer, sacrificial agents, or cocatalysts. The production rate of carbon monoxide (CO) reaches as high as 158.1 μmol g-1 h-1 with near 100% CO selectivity, which is accompanied by the oxidation of H2O to oxygen. Both theoretical and experimental results confirm that the key lies in achieving exceptional photoinduced charge separation and low exciton binding. We anticipate that our findings will facilitate new possibilities for the development of semiconducting COFs with structural diversity and functional variability.

Stabilization of Pd0 by Cu Alloying: Theory-Guided Design of Pd3Cu Electrocatalyst for Anodic Methanol Carbonylation

Electrocatalytic carbonylation of CO and CH3OH to dimethyl carbonate (DMC) on metallic palladium (Pd) electrode offers a promising strategy for C1 valorization at the anode. However, its broader application is limited by the high working potential and the low DMC selectivity accompanied with severe methanol self-oxidation. Herein, our theoretical analysis of the intermediate adsorption interactions on both Pd0 and Pd4+ surfaces revealed that inevitable reconstruction of Pd surface under strongly oxidative potential diminishes its CO adsorption capacity, thus damaging the DMC formation. Further theoretical modeling indicates that doping Pd with Cu not only stabilizes low-valence Pd in oxidative environments but also lowers the overall energy barrier for DMC formation. Guided by this insight, we developed a facile two-step thermal shock method to prepare PdCu alloy electrocatalysts for DMC. Remarkably, the predicted Pd3Cu demonstrated the highest DMC selectivity among existing Pd-based electrocatalysts, reaching a peaked DMC selectivity of 93 % at 1.0 V versus Ag/AgCl electrode. (Quasi) in situ spectra investigations further confirmed the predicted dual role of Cu dopant in promoting Pd-catalyzed DMC formation.

Influences of Ru and ZrO2 interaction on the hydroesterification of styrene

Interfacial Lewis acid-base pairs are commonly found in ZrO2-supported metal catalysts due to the facile generation of oxygen vacancies of ZrO2. These pairs have been reported to play a crucial role in olefin hydroesterification, especially in the absence of acid promoters and ligands. In this study, a series of ZrO2-supported Ru catalysts with ruthenium(iii) chloride and ruthenium(iii) acetylacetonate as precursors were prepared for the styrene hydroesterification. The catalysts were thoroughly characterized by TPR, TEM, EPR, XPS, and FTIR. The Ru precursors significantly influenced the size and electronic properties of Ru clusters, albeit having minimal impact on oxygen vacancies. Mechanistic studies of styrene hydroesterification over ZrO2-supported Ru catalysts revealed that the carbon monoxide insertion followed the hydrogen transfer step to activated styrene. Higher activity is exhibited over ZrO2-supported Ru catalysts prepared with ruthenium(iii) chloride as a precursor, attributed to the lower adsorption strength of CO over Ru clusters, as evidenced by FTIR and DFT calculations.

Aryl Chloride-Directed Enantioselective C(sp2)-H Borylation Enabled by Iridium Catalysis

We herein report the iridium-catalyzed enantioselective C-H borylation of aryl chlorides. A variety of prochiral biaryl compounds could be well-tolerated, affording a vast array of axially chiral biaryls with high enantioselectivities. The current method exhibits a high turnover number (TON) of 7000, which represents the highest in functional-group-directed asymmetric C-H activation. The high TON was attributed to a weak catalyst-substrate interaction that was caused by mismatched chirality between catalyst and substrate. We also demonstrated the synthetic application of the current method by C-B, ortho-C-H, and C-Cl bond functionalization, including programmed Suzuki-Miyaura coupling for the synthesis of axially chiral polyarenes.

Unveiling Optimal Synthesis and Structural Insights of Starch Ferulate via the Mechanoenzymatic Method

In this study, starch ferulate was synthesized employing a mechanoenzymatic method, specifically based on the twin screw extrusion technique and lipase catalysis. The research then primarily centered on optimizing process parameters and conducting structural analysis. Optimal conditions were determined to be 8.2% ferulic acid addition, 66 °C extrusion temperature, and 3.2% lipase (N435) addition. The enzyme-catalyzed time was 30 s. The degree of substitution for starch ferulate was quantified at 0.005581 under these specific conditions. The presence of C=O bonds in the synthesized starch ferulate proved that the synthesis process was efficient. Additionally, the crystal structure underwent reconstruction. Observations through Scanning Electron Microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM) demonstrated that the mechanoenzymatic method led to an augmentation in the specific surface area of starch molecules, thereby facilitating the exposure of active sites. This breakthrough underscores the vast potential of mechanoenzymatic techniques to revolutionize the rapid and sustainable synthesis of starch ferulate, marking a pioneering stride in ester synthesis. The insights garnered from this study transcend theory, offering a visionary roadmap for the development and real-world deployment of advanced modified starch esters.

Alkyl ferulic acid esters: Evaluating their structure and antibacterial properties

Ferulic acid (FA) is a natural antibacterial agent rich in plants, FA has excellent antioxidant and antibacterial properties. However, because of its short alkane chain and large polarity, FA is difficult to penetrate the soluble lipid bilayer in the biofilm to enter the cell to play an inhibitory role, limiting its biological activity. To improve the antibacterial activity of FA, with the catalytic condition of Novozym 435, four alkyl ferulic acid esters (FCs) with different alkyl chain lengths were obtained by fatty alcohols (including 1-propanol (C3), 1-hexanol (C6), nonanol (C9), and lauryl alcohol (C12)) modification. The effect of FCs on P. aeruginosa was determined by Minimum inhibitory concentrations (MIC), minimum bactericidal concentrations (MBC), Growth curves, alkaline phosphatase (AKP) activity, crystal violet method, scanning electron microscopy (SEM), membrane potential, PI, cell contents leakage. Results showed that the antibacterial activity of FCs increased after esterification, and the antibacterial activity significantly increased and then decreased with the extension of the alkyl chain of the FCs. Hexyl ferulate (FC6) showed the best antibacterial activities against E. coli and P. aeruginosa (MIC for E. coli was 0.5 mg/ml, MIC for P. aeruginosa was 0.4 mg/ml). And Propyl ferulate (FC3) and FC6 showed the best antibacterial activities S. aureus and B. subtilis (MIC for S. aureus was 0.4 mg/ml, The MIC of B. subtilis was 1.1 mg/ml). In addition, the growth, AKP activity, bacterial biofilm, bacterial cell morphology, membrane potential and cell contents leakage of P. aeruginosa after different FCs were investigated, which found that FCs could damage the cell wall of P. aeruginosa and showed different effects on the P. aeruginosa cell biofilm. FC6 showed the best inhibition on the biofilm formation of P. aeruginosa cells, which caused the surface of P. aeruginosa cells to be rough and wrinkled. Some P. aeruginosa cells showed aggregation and adhesion, even rupture. The membrane hyperpolarization was obvious, which appeared as holes, leading to cell contents leakage (protein and nucleic acid). All these results concluded that the antibacterial activities FCs against foodborne pathogens depended on different fatty alcohol esterification of FA. FC6 showed the best inhibition on P. aeruginosa due to its effect on P. aeruginosa cell walls and biofilms and the leak of the cell contents. This study provides more practical methods and a theoretical basis for giving full play to the bacteriostatic effect of plant FA.

Momentary Clicking Nitrile Synthesis Enabled by an Aminoazanium Reagent

Achieving fast and selective functional group interconversion is crucial for improving synthetic efficiency in nowadays chemical science. In this context, we report a momentary and selective Schmidt-type nitrile synthesis. The...

Manganese-Catalyzed [4 + 2] Annulation of N-H Amidines with Vinylene Carbonate via C-H Activation

Manganese-catalyzed C-H bond functionalization of aryl amidines for the synthesis of 1-aminoisoquinolines in the presence of vinylene carbonate has been developed. The reaction features a broad substrate scope and proceeds under mild reaction conditions with only the carbonate anion as the byproduct.

Iridium-Catalyzed Asymmetric Transfer Hydrogenation of Quinolines in Biphasic Systems or Water

An asymmetric transfer hydrogenation (ATH) of quinolines in water or biphasic systems was developed. This ATH reaction proceeds smoothly without the need for inert atmosphere protection in the presence of a water-soluble iridium catalyst, which bears an easily available aminobenzimidazole ligand. This ATH system can work at a catalyst loading of 0.001 mol % (S/C = 100 000, turnover number (TON) of up to 33 000) under mild reaction conditions. The turnover frequency (TOF) value can reach as high as 90 000 h-1. A variety of quinoline and N-heteroaryl compounds are transformed into the desired products in high yield and up to 99% enantiomeric excess (ee).

Electrochemical Approaches to Carbonylative Coupling Reactions

The carbonylation reaction is an effective way to introduce CO or other carbonyl groups into organic compounds, and widely used in the preparation of aldehydes, ketones, amides, and esters. The replacement of conventional reaction approaches by greener electrochemical methods is appealing with great synthetic potential as well as inherent safety, owing to the avoidance of external oxidants or reductants and a more facile control in product selectivity. In this minireview, we give a summary of the recent development of carbonylation reactions via the electrochemical approach.

Defective acidic 2D COF-based catalysts for boosting the performance of polyoxymethylene diethyl ether synthesis under mild conditions

Polyoxymethylene diethyl ethers (PODEEn) are oxygenated fuel additives with high performance due to their advantageous fuel properties. PODEEn can alleviate carbon debt as the production can utilize bioethanol and biomass syngas. Heterogeneous solid acid catalysts are desirable for an efficient PODEEn synthesis. In this study, well-defined sulfonated phthalocyanine-containing polymers were prepared, and the physicochemical properties were analyzed, exhibiting a 2D π-π stacking structure with crystalline-amorphous mixed phases. Owing to the tuning defects of the COF framework by mixing polymerization, the accessibility of the network and the capacity of strong acid were improved for the polymeric catalyst, showing an excellent activity with trioxane (TOX) conversion of 89% and PODEE2-8 selectivity of 87% at 80 °C under atmospheric pressure.

High Chemo-/Stereoselectivity for Synthesis of Polysubstituted Monofluorinated Pyrimidyl Enol Ether Derivatives

A novel intramolecular Smiles rearrangement of α-fluoro-β-keto-pyrimidylsulfones (usually used as a carbon nucleophile) was developed, providing a versatile avenue for synthesis of tri/tetra-substituted monofluorinated pyrimidyl enol ethers. Among these, diverse (Z)-monofluorovinylsulfones and sulfinates were efficiently assembled by adding extra electrophile and fine-tuning reaction conditions. The process is triggered by a keto-enol tautomerism from enol oxyanion to pyrimidine 2-carbon, completely different from the classical carbon nucleophilic addition reaction approach.

Enantioselective Construction of Quinoxaline-Based Heterobiaryls and P,N-Ligands via Chirality Transfer Strategy

Central-to-axial chirality transfer via C-N single bond oxidation was first achieved as a versatile and conceptually distinct strategy to prepare a new family of axially chiral heteroaromatic biaryl backbones and P,N-ligands (named as Quinoxalinaps) in gram scale. Two atropisomers of Quinoxalinaps (ee >99%) were readily accessed from the same precursor enantiomer by a simple dehydrogenative oxidation with MnO₂ and t-BuOOH under mild conditions. Phosphine could be introduced into the ligands before or after the chirality control process. Moreover, these Quinoxalinap P,N-ligands performed well for both asymmetric reactions of the CuBr-catalyzed alkyne conjugate addition with up to -94% ee and AgOAc-catalyzed glycinate imine [3 + 2] annulation with 90% ee, respectively.

Recent advances in the synthesis and transformation of gem-borylsilylalkanes

gem-Borylsilylalkanes have emerged as powerful reagents and attracted increasing attention in synthetic chemistry. This review summarizes the recent development in the synthesis of gem-borylsilylalkanes and their chemoselective transformation

Reductive amination of bio-based 2-hydroxytetrahydropyran to 5-Amino-1-pentanol over nano-Ni–Al2O3 catalysts

5-Amino-1-pentanol was efficiently synthesized by reductive amination of bio-based 2-hydroxytetrahydropyran with a high yield over stable nano-Ni–Al₂O₃ catalysts.

Visible-Light-Promoted Photoredox Dehydrogenative Coupling of Phosphines and Thiophenols

Herein, by applying visible-light photoredox catalysis, we have now achieved the first example of catalytic dehydrogenative coupling of phosphines and thiophenols that proceeds at room temperature. Key to our success is the use of benzaldehyde as a soft oxidant, which avoids the issue of phosphine oxidation. Furthermore, we observed the unexpected dealkylative coupling of secondary and tertiary alkylphosphine with thiophenols.

Proton Transfer Can Govern Regioselectivity Assisted by Iron Catalysis

Ortho-selective aromatic C-H functionalization is frequently used in organic synthesis and chemical/pharmaceutical industries. However, this reaction relies heavily on the use of directing groups suffering from limited substrate scope and extra steps to put on and remove the directing/protecting groups. Herein we present the previously neglected concept that enables good to nearly complete selective ortho position. Proton transfer was utilized to tune the electron density on the aryl ring and determine the positional selectivity of electrophilic substitution. Consistently with deuteration experiments and DFT studies, this work demonstrates that acid-promoted proton transfer directs accelerated ortho-selective halogenation of NH/OH contained aromatic amines/phenols with excellent selectivity (>40 examples; up to 98:2 ortho/para selectivity). The application potential of this Fe-catalyzed method is demonstrated by the convenient synthesis of three alkaloids and tizanidine. This report raises the possibility that proton transfer could serve as the basis of developing new selective C-H functionalization reactions.

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Highly ortho-selective halogenations of anilines and carbazoles

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Lewis acids being able to accelerate EAS reactions

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Proton shift found to be crucial for the regioselectivity

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Practical iron sulfonate catalysis being scaled up to 100 g

Chemodivergent transformations of amides using gem-diborylalkanes as pro-nucleophiles

Amides are versatile synthetic building blocks and their selective transformations into highly valuable functionalities are much desirable in the chemical world. However, the diverse structure and generally high stability of amides make their selective transformations challenging. Here we disclose a chemodivergent transformation of primary, secondary and tertiary amides by using 1,1-diborylalkanes as pro-nucleophiles. In general, selective B-O elimination occurs for primary, secondary amides and tertiary lactams to generate enamine intermediate, while tertiary amides undergo B-N elimination to generate enolate intermediate. Various in situ electrophilic trapping of those intermediates allows the chemoselective synthesis of α-functionalized ketones, β-aminoketones, enamides, β-ketoamides, γ-aminoketones, and cyclic amines from primary, secondary, tertiary amides and lactams. The key for these transformations is the enolization effect after the addition of α-boryl carbanion to amides.

Amides are versatile synthetic building blocks, however the general stability of the amide bond makes its selective transformation challenging. Here, the authors report a chemodivergent transformation of primary, secondary and tertiary amides by using 1,1-diborylalkanes as pro-nucleophiles.

Zirconium-Catalyzed Atom-Economical Synthesis of 1,1-Diborylalkanes from Terminal and Internal Alkenes

A general and atom‐economical synthesis of 1,1‐diborylalkanes from alkenes and a borane without the need for an additional H₂ acceptor is reported for the first time. The key to our success is the use of an earth‐abundant zirconium‐based catalyst, which allows a balance of self‐contradictory reactivities (dehydrogenative boration and hydroboration) to be achieved. Our method avoids using an excess amount of another alkene as an H₂ acceptor, which was required in other reported systems. Furthermore, substrates such as simple long‐chain aliphatic alkenes that did not react before also underwent 1,1‐diboration in our system. Significantly, the unprecedented 1,1‐diboration of internal alkenes enabled the preparation of 1,1‐diborylalkanes.

RhCl3·3H2O-Catalyzed C7-Selective C-H Carbonylation of Indolines with CO and Alcohols

An attractive method for the synthesis of indoline-7-carboxylates through RhCl₃-catalyzed C-H carbonylation of indolines with CO and alcohols was developed. The copper-based oxidant and removable pyrimidyl directing group played important roles in achieving high-level yields of the title products. Based on control experiments, a possible catalytic cycle was proposed.

How Does the Oxidation State of Palladium Surfaces Affect the Reactivity and Selectivity of Direct Synthesis of Hydrogen Peroxide from Hydrogen and Oxygen Gases? A Density Functional Study

Direct synthesis of H₂O₂ from H₂ and O₂ is an environmentally benign and atom economic process and as such is the ideal pathway in catalysis. However, currently no low-cost pathway of this kind of catalysis exists, although it would be an attractive alternative strategy to the common industrial anthraquinone method for H₂O₂ production. Metal-based catalysts are widely employed in such a direct synthesis process but often need to be oxidized, alloyed, or supplied with additives to make them selective. To understand the metal-oxidation state in heterogeneous catalysis, we studied the selective oxidation of hydrogen by molecular oxygen on Pd(111) and PdO(101) surfaces, leading to either H₂O₂ or H₂O products. Our results demonstrate, for the first time, that the oxidized PdO(101) surface clearly shows better performance and selectivity, as compared to the reduced Pd(111) one. The activation barrier on the oxidized Pd surface is ca. 0.2 eV lower than the one on the reduced Pd surface. On the oxidized surface, the H₂O₂ synthesis route is preferred, while, on the reduced surface, the H₂O route is predominant. The decomposition of H₂O₂ is also greatly inhibited on the oxidized surface. We analyzed the different pathways in detail through thermochemical cycles, which establishes that the oxidized surface shows weaker adsorption ability toward the reagents O₂ and H₂, the key intermediate OOH, and also the product H₂O₂ in comparison with the Pd(111) surface, which we believe affect the selectivity. The work presented here clearly shows that the oxidation state of metal surfaces is one of the most important factors that tunes the catalysis of a chemical reaction and can affect the selectivity and reaction patterns dramatically.

Recent advances in the borylative transformation of carbonyl and carboxyl compounds

The recent advances in the borylative transformation of carbonyl and carboxyl compounds are summarized.