Angewandte Chemie最新文献

The reduction of carboxylic esters to aldehydes and alcohols is a fundamental functional group transformation in chemistry. However, the inertness of carbonyl group and the instability of ketyl radical anion intermediate impede the reduction of carboxylic esters via photochemical strategy. Herein, we described the reduction of aliphatic carboxylic esters with synergistic dual photocatalysis via phenolate-catalyzed single electron transfer process and thiol-catalyzed hydrogen atom transfer process. The competitive back electron transfer process was effectively inhibited by protonation of the ketyl-type radical anion. This protocol enabled the efficient reduction of carboxylic esters to alcohols under mild conditions. By interruption of the reduction with prolinol, the step-controlled reduction of carboxylic esters to aldehydes was accomplished. The developed process was also successfully applied to the preparation of deuterated alcohols and aldehydes from esters with D₂O as the deuterium source.

Iron-nitrogen-carbon (Fe−N−C) single-atom catalyst is the most promising alternative to platinum catalyst for proton-exchange membrane fuel cells (PEMFCs), however its high performance cannot be maintained for a long enough time in device operation. The construction of a new Fe coordination environment that is completely different from the square-planar Fe−N₄ configuration in classic Fe−N−C catalyst is expected to break the current stability limits of Pt-free catalysts, which however remains unexplored. Here, we report, for the first time, the conversion of Fe−N−C catalyst to a new FeN_xSe_y cluster catalyst, where the active Fe sites are three-dimensionally (3D) co-coordinated by N and Se atoms. Due to this unique Fe coordination configuration, the FeN_xSe_y catalyst exhibits much better 4e⁻ ORR activity and selectivity than the state-of-the-art Fe−N−C catalyst. Specifically, the yields of hydrogen peroxide (H₂O₂) and ⋅OH radicals on the FeN_xSe_y catalyst are only one-quarter and one-third of that on the Fe−N−C counterpart, respectively. Therefore, the FeN_xSe_y catalyst exhibits outstanding cyclic stability, losing only 10 mV in half-wave potential E_1/2 after 10,000 potential cycles, much smaller than that of the Fe−N−C catalyst (56 mV), representing the most stable Pt-free catalysts ever reported for PEMFCs. More significantly, the 3D co-coordination structure effectively inhibits the Fe demetallization of the FeN_xSe_y catalyst in the presence of H₂O₂. As a result, the FeN_xSe_y based PEMFC shows excellent durability, with the current density attenuation significantly lower than that of the Fe−N−C based device after accelerated durability testing. Our work provides guidance for the development of next-generation Pt-free catalysts for PEMFCs.

Conjugated coordination polymers (c-CPs), a novel class of organic–inorganic hybrid materials, are distinguished by their unique structural characteristics and exceptional charge transport properties. The electronic properties of these materials are critically determined by the constituting coordination atoms, with electron-rich selenol ligands emerging as promising candidates for constructing high-mobility semiconducting c-CPs. Despite their potential, c-CPs incorporating selenium-substituted ligands remain scarce due to the synthetic challenges associated with both the ligands and the coordination polymers. In this study, we successfully synthesized a new tetraselenol-hydroxyquinone (TSHQ) ligand using a “4+2” design strategy and developed a semiconducting three-dimensional Ag−Se coordination polymer, Ag₄TSHQ. Ag₄TSHQ exhibits room-temperature electrical conductivity of up to 1.6 S/m and shares the same structural topology as Ag₄TTHQ (TTHQ=tetrathiol-hydroxyquinone), enabling precise band gap modulation from 0.6 eV to 1.5 eV via a mixed-ligand approach. Time-resolved terahertz spectroscopy reveals that the charge mobility of Ag₄TSHQ in the dc limit is ~350 cm²/V ⋅ s, which is twice that of its sulfur counterpart, Ag₄TTHQ. Furthermore, our evaluations of their electrochemical energy storage capabilities demonstrate that Ag₄TSHQ effectively utilizes its redox potential, achieving a remarkable specific capacitance of up to 340 F/g-significantly outperforming Ag₄TTHQ, which has a capacitance of 294 F/g. These findings underscore the potential of selenium-ligand-based c-CPs for optoelectronic applications and energy storage technologies.

Transition-metal-catalyzed selective and efficient activation of an inert C−H bond in an organic substrate is of importance for the development of streamlined synthetic methodologies. An attractive approach is the design of a metal catalyst capable of recognizing an organic substrate through noncovalent interactions to control reactivity and selectivity. We report here a spirobipyridine ligand that bears a hydroxy group which recognizes pyridine and quinoline substrates through hydrogen bonding, and in combination with an iridium catalyst enables site-selective C−H borylation. The site selectivity can be switched by simply changing the position of the hydroxy group on the ligand. The catalyst also accelerates the reactions, overrides steric bias, and selectively recognizes a pyridine substrate in the presence of other hydrogen bond acceptors. These features are reminiscent of enzymatic catalysis and suggest that judicious design of the recognition group on the ligand can become a general strategy to selectively and efficiently functionalize organic substrates.

The development of chemically recyclable polymers for sustainable 3D printing is crucial to reducing plastic waste and advancing towards a circular polymer economy. Here, we introduce a new class of polythioenones (PCTE) synthesized via Michael addition-elimination ring-opening polymerization (MAEROP) of cyclic thioenone (CTE) monomers. The designed monomers are straightforward to synthesize, scalable and highly modular, and the resulting polymers display mechanical performance superior to commodity polyolefins such as polyethylene and polypropylene. The material was successfully employed in 3D printing using fused-filament fabrication (FFF), showcasing excellent printability and mechanical recyclability. Notably, PCTE−Ph retains its tensile strength and thermal stability after multiple mechanical recycling cycles. Furthermore, PCTE−Ph can be depolymerized back to its original monomer with a 90 % yield, allowing for repolymerization and establishing a successful closed-loop life cycle, making it a sustainable alternative for additive manufacturing applications.

Certain proteins and synthetic covalent polymers experience aqueous phase transitions, driving functional self-assembly. Herein, we unveil the ability of supramolecular polymers (SPs) formed by G₄.Cu⁺ to undergo heating-induced unexpected aqueous phase transitions. For the first time, guided by Cu⁺, guanosine (G) formed a highly stable G-quartet (G₄.Cu⁺)/G-quadruplex as a non-canonical DNA secondary structure with temperature tolerance, distinct from the well-known G₄.K⁺. The G₄.Cu⁺ self-assembled in water through π-π stacking, metallophilic and hydrophobic interactions, forming thermally robust SPs. This enhanced stability is attributed to the stronger coordination of Cu⁺ to four carbonyl oxygens of G-quartet and the presence of Cu⁺- - -Cu⁺ attractive metallophilic interactions in Cu⁺-induced G-quadruplex, exhibiting a significantly higher interaction energy than K⁺ as determined computationally. Remarkably, the aqueous SP solution exhibited heating-induced phase transitions—forming a hydrogel through dehydration-driven crosslinking of SPs below cloud temperature (T_cp) and a hydrophobic collapse-induced solid precipitate above T_cp, showcasing a lower critical solution temperature (LCST) behavior. Notably, this LCST behavior of G₄.Cu⁺ SP originates from biomolecular functionality rather than commonly exploited thermo-responsive oligoethylene glycols with supramolecular assemblies. Furthermore, exploiting the redox reversibility of Cu⁺/Cu²⁺, we demonstrated control over the assembly and disassembly of G-quartets/G-quadruplex and gelation reversibly.

Self-assembled bottlebrush block copolymers (BBCPs) offer a vibrant, eco-friendly alternative to traditional toxic pigments and dyes, providing vivid structural colors with significantly reduced environmental impact. Scaling up the synthesis of these polymers for practical applications has been challenging with conventional batch methods, which suffer from slow mass and heat transfer, inadequate mixing, and issues with reproducibility. Precise control over molecular weight and dispersity remains a significant challenge for achieving finely tuned color appearances. Here, we present an alternative strategy to overcome the challenges by integrating a rapid continuous flow technique with an in-line self-assembly procedure. This strategy enables the rapid, stable and large-scale synthesis of narrow-dispersed BBCPs, exceeding 2 kg/day, a significant improvement over conventional gram-scale methods. Furthermore, precise control over the degree of polymerization is achieved with an unprecedented interval accuracy of four repeat units. This level of precision enables refined color calibration in the resulting photonic pigments, effectively eliminating the need for labor-intensive and costly multiple batch syntheses.

Although metal–organic frameworks are coordination-driven assemblies, the structural prediction and design using metal-ligand interactions can be unreliable due to other competing interactions. Leveraging non-coordination interactions to develop porous assemblies could enable new materials and applications. Here, we use a multi-module MOF system to explore important and pervasive impact of ligand-ligand interactions on metal-ligand as well as ligand-ligand co-assembly process. It is found that ligand-ligand interactions play critical roles on the scope or breakdown of isoreticular chemistry. With cooperative di- and tri-topic ligands, a family of Ni-MOFs has been synthesized in various structure types including partitioned MIL-88-acs (pacs), interrupted pacs (i-pacs), and UMCM-1-muo. A new type of isoreticular chemistry on the muo platform is established between two drastically different chemical systems. The gas sorption and electrocatalytic studies were performed that reveal excellent performance such as high C₂H₂/CO₂ selectivity of 21.8 and high C₂H₂ uptake capacity of 114.5 cm³/g at 298 K and 1 bar.

Learning from nature has garnered significant attention in the scientific community for its potential to inspire creative solutions in material or catalyst design. The study highlights the design of a biomimetic single selenium (Se) site-modified carbon (C) moiety that retains the unique reactivity of selenoenzyme with peroxides, which plays crucial roles in selectively catalyzing the oxygen reduction reaction (ORR). The as-designed Se−C demonstrates nearly 100 % 4-electron selectivity, evidenced by 0.039 % of H₂O₂ yield at 0.5 V versus reversible hydrogen electrode, outperforming commercial platinum (Pt) by 65 times. In situ X-ray absorption spectroscopy and theoretical calculations attribute this exceptional selectivity to the enzyme-like behaviors of the Se site to steal an O atom from peroxide intermediates. The second achievement is the significantly increased consecutive 2+2 electron selectivity. Benefiting from the enzyme-like H₂O₂ reduction activity with a higher onset potential of 0.915 V compared to Pt at 0.875 V, the Se−C as a secondary catalytic site reduced the H₂O₂ yields of the Co−N−C, Fe−N−C, and N−C catalysts by 96 %, 67 %, and 98 %, respectively, via a consecutive 2+2 electron pathway. This also leads to more stable catalysts via protecting the active sites from oxidative attacks. This work establishes new pathways for precise tuning of reaction selectivity in ORR and beyond.