Palladium-Catalyzed O-Glycosylation through π-π Interactions.

A stereodivergent synthesis of ß- and α-O-glycosides using 3-O-quinaldoyl glucals was developed by palladium catalysis at 60 and 110 °C respectively. Various alcohols, monosaccharides, and amino acid were glycosylated to form ß- and α- products in good yields with high stereoselectivity. Mechanistic studies indicated no classic Pd-N (quinoline) coordination, but π-π stacking interactions promoted the anomeric stereodiversity. The practicality was demonstrated by glycosylating natural products/drugs and synthesizing a complex tetrasaccharide.

Hydrogen-Bond-Network Breakdown Boosts Selective CO2 Photoreduction by Suppressing H2 Evolution.

Conventional strategies for highly efficient and selective CO2 photoreduction focus on the design of catalysts and cocatalysts. In this study, we discover that hydrogen bond network breakdown in reaction system can suppress H2 evolution, thereby improving CO2 photoreduction performance. Photosensitive poly(ionic liquid)s are designed as photocatalysts owing to their strong hydrogen bonding with solvents. The hydrogen bond strength is tuned by solvent composition, thereby effectively regulating H2 evolution (from 0 to 12.6 mmol g-1 h-1). No H2 is detected after hydrogen bond network breakdown with trichloromethane or tetrachloromethane as additives. CO production rate and selectivity increase to 35.4 mmol g-1 h-1 and 98.9 % with trichloromethane, compared with 0.6 mmol g-1 h-1 and 26.2 %, respectively, without trichloromethane. Raman spectroscopy and theoretical calculations confirm that trichloromethane broke the systemic hydrogen bond network and subsequently suppressed H2 evolution. This hydrogen bond network breakdown strategy may be extended to other catalytic reactions involving H2 evolution.

Contact-Electro-Catalysis for Direct Oxidation of Methane under Ambient Conditions.

The conversion of methane under ambient conditions has attracted significant attention. Although advancements have been made using active oxygen species from photo- and electro- chemical processes, challenges such as complex catalyst design, costly oxidants, and unwanted byproducts remain. This study exploits the concept of contact-electro-catalysis, initiating chemical reactions through charge exchange at a solid-liquid interface, to report a novel process for directly converting methane under ambient conditions. Utilizing the electrification of commercially available Fluorinated Ethylene Propylene (FEP) with water under ultrasound, we demonstrate how this interaction promote the activation of methane and oxygen molecules. Our results show that the yield of HCHO and CH3OH can reach 467.5 and 151.2 µmol ⋅ gcat -1, respectively. We utilized electron paramagnetic resonance (EPR) to confirm the evolution of hydroxyl radicals (⋅OH) and superoxide radicals (⋅OOH). Isotope mass spectrometry (MS) was employed to analyze the elemental origin of CH3OH, which can be further oxidized to HCHO. Additionally, we conducted density functional theory (DFT) simulations to assess the reaction energies of FEP with H2O, O2, and CH4 under these conditions. The implications of this methodology, with its potential applicability to a wider array of gas-phase catalytic reactions, underscore a significant advance in catalysis.

Metal-Organic Frameworks: Direct Synthesis by Organic Acid-Etching and Reconstruction Disclosure as Oxygen Evolution Electrocatalysts.

Metal-organic frameworks (MOFs) have emerged as promising oxygen evolution reaction (OER) electrocatalysts. Chemically bonded MOFs on supports are desirable yet lacking in routine synthesis, as they may allow variable structural evolution and the underlying structure-activity relationship to be disclosed. Herein, direct MOF synthesis is achieved by an organic acid-etching strategy (AES). Using π-conjugated ferrocene (Fc) dicarboxylic acid as the etching agent and organic ligand, a series of MFc-MOF (M=Ni, Co, Fe, Zn) nanosheets are synthesized on the metal supports. The crystal structure is studied using X-ray diffraction and low-dose transmission electron microscopy, which is quasi-lattice-matched with that of the metal, enabling in situ MOF growth. Operando Raman and attenuated total reflectance Fourier transform infrared spectroscopy disclose that the NiFc-MOF features dynamic structural rebuilding during OER. The reconstructed one showing optimized electronic structures with an upshifted total d-band center, high M-O bonding state occupancy, and localized electrons on adsorbates indicated by density functional theory calculations, exhibits outstanding OER performance with a fairly low overpotential (130 mV at 10 mA cm-2 ) and good stability (144 h). The newly established approach for direct MOF synthesis and structural reconstruction disclosure stimulate the development of more prudent catalysts for advancing OER.

MXene-Derived Na+ -Pillared Vanadate Cathodes for Dendrite-Free Potassium Metal Batteries.

Cation-intercalated vanadates, which have considerable promise as the cathode for high-performance potassium metal batteries (PMBs), suffer from structural collapse upon K+ insertion and desertion. Exotic cations in the vanadate cathode may ease the collapse, yet their effect on the intrinsic cation remains speculative. Herein, a stable and dendrite-free PMB, composed of a Na+ and K+ co-intercalated vanadate (NKVO) cathode and a liquid NaK alloy anode, is presented. A series of NKVO with tuneable Na/K ratios are facilely prepared using MXene precursors, in which Na+ is testified to be immobilized upon cycling, functioning as a structural pillar. Due to stronger ionic bonding and lower Fermi level of Na+ compared to K+ , moderate Na+ intercalation could reduce K+ binding to the solvation sheath and favor K+ diffusion kinetics. As a result, the MXene-derived Na+ -pillared NKVO exhibits markedly improved specific capacities, rate performance, and cycle stability than the Na+ -free counterpart. Moreover, thermally-treated carbon paper, which imitates the microscopic structure of Chinese Xuan paper, allows high surface tension liquid NaK alloy to adhere readily, enabling dendrite-free metal anodes. By clarifying the role of foreign intercalating cations, this study may lead to a more rational design of stable and high-performance electrode materials.

Photocatalytic CO2 reduction to syngas using metallosalen covalent organic frameworks.

Metallosalen-covalent organic frameworks have recently gained attention in photocatalysis. However, their use in CO2 photoreduction is yet to be reported. Moreover, facile preparation of metallosalen-covalent organic frameworks with good crystallinity remains considerably challenging. Herein, we report a series of metallosalen-covalent organic frameworks produced via a one-step synthesis strategy that does not require vacuum evacuation. Metallosalen-covalent organic frameworks possessing controllable coordination environments of mononuclear and binuclear metal sites are obtained and act as photocatalysts for tunable syngas production from CO2. Metallosalen-covalent organic frameworks obtained via one-step synthesis exhibit higher crystallinity and catalytic activities than those obtained from two-step synthesis. The optimal framework material containing cobalt and triazine achieves a syngas production rate of 19.7 mmol g-1 h-1 (11:8 H2/CO), outperforming previously reported porous crystalline materials. This study provides a facile strategy for producing metallosalen-covalent organic frameworks of high quality and can accelerate their exploration in various applications.

Nb2 CTx MXene Derived Polymorphic Nb2 O5.

Previously, heat treatment was the only feasible route for tuning the crystal phases of niobium pentoxide (Nb2 O5 ). With the use of Nb2 CTx MXene precursors, the first case of phase tuning of Nb2 O5 in the low-temperature hydrothermal synthesis using sulfuric acid regulating agents is presented. By varying the amount of the agent, four pure-phase Nb2 O5 crystals and mixed phases in-between are obtained. The required amount is found to be related to the H-covered surface energy calculated based on density functional theory. Overall, MXene-derived B-phase Nb2 O5 is of particular interest due to its exceptionally high capacities as lithium-ion battery anodes, which are three times higher than the routine synthesized one. Oxygen vacancies induced by crystallographic shear would be responsible for the extraordinary performance. The proposed phase tuning strategy encourages the prudent synthesis of difficult-to-obtain crystal phases.

Poly(ionic liquid)s for Photo-Driven CO2 Cycloaddition: Electron Donor-Acceptor Segments Matter.

CO2 cycloaddition with epoxides is a key catalytic procedure for CO2 utilization. Several metal-based catalysts with cocatalysts are developed for photo-driven CO2 cycloaddition, while facing difficulties in product purification and continuous reaction. Here, poly(ionic liquid)s are proposed as metal-free catalysts for photo-driven CO2 cycloaddition without cocatalysts. A series of poly(ionic liquid)s with donor-acceptor segments are fabricated and their photo-driven catalytic performance (conversion rate of 83.5% for glycidyl phenyl ether) outstrips (≈4.9 times) their thermal-driven catalytic performance (17.2%) at the same temperature. Mechanism studies confirm that photo-induced charge separation is promoted by the donor-acceptor segments and can accelerate the CO2 cycloaddition reaction. This work paves the way for the further use of poly(ionic liquid)s as catalysts in photo-driven CO2 cycloaddition.

Heterogenization of Salen Metal Molecular Catalysts in Covalent Organic Frameworks for Photocatalytic Hydrogen Evolution.

Integrating a molecular catalyst with a light harvester into a photocatalyst is an effective strategy for solar light conversion. However, it is challenging to establish a crystallized framework with well-organized connections that favour charge separation and transfer. Herein, we report the heterogenization of a Salen metal complex molecular catalyst into a rigid covalent organic framework (COF) through covalent linkage with the light-harvesting unit of pyrene for photocatalytic hydrogen evolution. The chemically conjugated bonds between the two units contribute to fast photogenerated electron transfer and thereby promote the proton reduction reaction. The Salen cobalt-based COF showed the best hydrogen evolution activity (1378 µmol g-1 h-1 ), which is superior to the previously reported nonnoble metal based COF photocatalysts. This work provides a strategy to construct atom-efficient photocatalysts by the heterogenization of molecular catalysts into covalent organic frameworks.

MXene-Derived Metal-Organic Framework@MXene Heterostructures toward Electrochemical NO Sensing.

The electrochemical sensing of nitric oxide (NO) molecules by metal-organic framework (MOF) catalysts has been impeded, to a large extent, owing to their poor electrical conductivity and weak NO adsorption. In this work, incomplete in situ conversion of V2 CTx (T = terminal atoms) MXene to MOF is adopted, forming MOF@MXene heterostructures, which outperform MXene and MOF monocomponents toward electrochemical NO sensing. Density functional theory (DFT) calculation results indicate metal-like electronic characters for the heterostructure benefiting from the dominating contribution of the V 3d orbitals of the metallic MXene. Moreover, plane-averaged charge density difference shows substantial charge redistribution occurs at the heterointerfaces, producing a built-in field, which facilitates charge transfer. Besides, molecular mechanics-based simulated annealing calculation reveals greatly enhanced adsorption energies of NO molecules on the heterointerfaces than that on separate MOFs and MXenes. Hence, the facilitated charge transfer and preferential NO adsorption are responsible for the dramatically promoted performance toward NO sensing. The prudent design of MOF@MXene heterostructure may spur advanced electrocatalysts for electrochemical sensing.

Protocol for fabrication and characterization of Fe-SAC@COF for electrocatalytic oxygen evolution reaction.

Single-atom catalysts (SACs) have promising atomic utilization efficiency and catalytic activity, but their construction with a specific coordination mode remains challenging. This protocol describes the synthesis of a coordinated Fe-SAC@COF for boosted electrocatalytic oxygen evolution reaction (OER). We also detail the steps for single iron atoms confinement and characterization of the COF and Fe-SAC@COF with X-ray diffraction and transmission electron microscopy technique. For complete details on the use and execution of this protocol, please refer to Wang et al. (2022).

Rhodium-Catalyzed and Chiral Zinc Carboxylate-Assisted Allenylation of Benzamides via Kinetic Resolution.

Enantioenriched allenes are important building blocks. While they have been accessed by other coupling methodologies, enantioenriched allenes have been rarely obtained via C-H activation. In this work, kinetic resolution of tertiary propargyl alcohols as an allenylating reagent has been realized via rhodium(III)-catalyzed C-H allenylation of benzamides. The reaction proceeded efficiently under mild conditions, and both the allenylated products and the propargyl alcohols were obtained in high enantioselectivities with an s-factor of up to 139. The resolution results from bias of the two propargylic substituents and is assisted by a chiral zinc carboxylate additive.

Rhodium(iii)-catalyzed asymmetric [4+1] spiroannulations of O-pivaloyl oximes with α-diazo compounds.

Chiral RhIII catalysts can catalyze the asymmetric [4+1] spiroannulation of O-pivaloyl oximes with α-diazo homophthalimides under redox-neutral and acid/base-neutral conditions, leading to formation of chiral spirocyclic imines as a result of C-H activation and N-O cleavage. The reaction proceeded with high efficiency and features broad substrate scope, mild reaction conditions, and high to excellent enantioselectivities.

Rhodium-Catalyzed C-H Activation-Based Construction of Axially and Centrally Chiral Indenes through Two Discrete Insertions.

Reported herein is asymmetric [3+2] annulation of arylnitrones with different classes of alkynes catalyzed by chiral rhodium(III) complexes, with the nitrone acting as an electrophilic directing group. Three classes of chiral indenes/indenones have been effectively constructed, depending on the nature of the substrates. The coupling system features mild reaction conditions, excellent enantioselectivity, and high atom-economy. In particular, the coupling of N-benzylnitrones and different classes of sterically hindered alkynes afforded C-C or C-N atropochiral pentatomic biaryls with a C-centered point-chirality in excellent enantio- and diastereoselectivity (45 examples, average 95.6 % ee). These chiral center and axis are disposed in a distal fashion and they are constructed via two distinct migratory insertions that are stereo-determining and are under catalyst control.

Enhanced carbon dioxide conversion at ambient conditions via a pore enrichment effect.

Chemical fixation of carbon dioxide (CO2) may be a pathway to retard the current trend of rapid global warming. However, the current economic cost of chemical fixation remains high because the chemical fixation of CO2 usually requires high temperature or high pressure. The rational design of an efficient catalyst that works at ambient conditions might substantially reduce the economic cost of fixation. Here, we report the rational design of covalent organic frameworks (COFs) as efficient CO2 fixation catalysts under ambient conditions based on the finding of "pore enrichment", which is concluded by a detailed investigation of the 10994 COFs. The best predicted COF, Zn-Salen-COF-SDU113, is synthesized, and its efficient catalytic performance for CO2 cycloaddition to terminal epoxide is confirmed with a yield of 98.2% and turnover number (TON) of 3068.9 under ambient conditions, which is comparable to the reported leading catalysts. Moreover, this COF achieves the cycloaddition of CO2 to 2,3-epoxybutane under ambient conditions among all porous materials. This work provides a strategy for designing porous catalysts in the economic fixation of carbon dioxide.

Salen-Based Conjugated Microporous Polymers for Efficient Oxygen Evolution Reaction.

Exploring high-performance electrocatalysts, especially non-noble metal electrocatalysts, for the oxygen evolution reaction (OER) is critical to energy storage and conversion. Herein, we report for the first time that conjugated microporous polymers (CMPs) incorporating salen can be used as OER electrocatalysts with outstanding performances. The best OER electrocatalyst (salen-CMP-Fe-3) exhibits a low Tafel slope of 63 mV dec-1 and an overpotential of 238 mV at 10 mA cm-2 . DFT and Grand Canonical Monte Carlo calculations confirmed that the significantly improved electrocatalytic properties can be attributed to the intrinsic catalytic activity of the salen moiety and the enrichment effect of the pore structures. This work demonstrates that salen-based conjugated polymers are a type of metal-coordinated porous polymer that show excellent catalyst performance.

van der Waals Function for Molecular Mechanics.

van der Waals (vdW) interaction has been described with a Lennard-Jones potential for decades in molecular mechanics. Here, we report a new potential function Exp-PE from quantum mechanical derivation for vdW interactions for molecular mechanic simulation. High-order ab initio calculations and experimental atomic force microscopy measurements have been used to test its feasibility, and the results suggest that this formula is simple, accurate, and transferable. This new potential function is capable of upgrading the traditional force fields especially for the applications involving vdW interactions.

Combination Rules and Accurate van der Waals Force Field for Gas Uptakes in Porous Materials.

Morse function is suggested to be more suitable for studying the gas adsorption in porous frameworks than the Lennard-Jones and exponential-6 forms. However, there have not been some widely used Morse-based van der Waals force fields (vdW FFs) because of complicated parameterization. Combining rules is usually suggested to reduce the parameterization by calculating the unlike-pair parameters from the information of the like pair. A new set of combination rules (DRS) for Morse-based FF has been proposed in our prior work and shown good performance in the simulation of CH4 adsorption isotherms in covalent organic frameworks. Inspired by our prior work, we developed an accurate van der Waals FF using high-level ab initio calculations with the DRS combination rules. The validation was conducted by comparing the simulated gas uptakes with the experimental values for various known porous materials. The agreement between simulations and experiments is very good, showing the potential application of the FF and the DRS combination rules.

Chiral Hydroxytetraphenylene-Catalyzed Asymmetric Conjugate Addition of Boronic Acids to Enones.

( S)-2,15-Br2-DHTP-catalyzed asymmetric conjugate addition of boronic acids to ß-trifluoromethyl α,ß-unsaturated ketones and enones was studied. The reaction afforded the corresponding Michael addition products in moderate to high yields with excellent enantioselectivities (up to 99:1 er). This catalytic system features mild reaction conditions, high efficiency, and tolerance to heteroarylboronic acids.