Chemical Science最新文献

N-Heterocyclic carbenes (NHCs) have emerged as a privileged ligand family in organometallic chemistry, widely recognized for their unique steric and electronic properties. Among them, the 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene (IPr) ligand has become a cornerstone of NHC chemistry for its remarkable versatility, stability, and broad use. Since its discovery by the Nolan group in 1999, IPr has played a pivotal role in advancing catalytic transformations and facilitating the utilization of NHC ligands in various domains. This article highlights major contributions where IPr has helped shape modern organometallic chemistry, with a focus on its influence in transition metal catalysis and ligand design. Twenty five years after its discovery, the IPr ligand continues to be a benchmark ligand, inspiring and driving innovation.

Atomic-scale changes can significantly impact heterogeneous catalysis, yet their atomic mechanisms are challenging to establish using conventional analysis methods. By using identical location scanning transmission electron microscopy (IL-STEM), which provides quantitative information at the single-particle level, we investigated the mechanisms of atomic evolution of Ru nanoclusters during the ammonia decomposition reaction. Nanometre-sized disordered nanoclusters transform into truncated nano-pyramids with stepped edges, leading to increased hydrogen production from ammonia. IL-STEM imaging demonstrated coalescence and Ostwald ripening as mechanisms of nanocluster pyramidalization during the activation stage, with coalescence becoming the primary mechanism under the reaction conditions. Single Ru atoms, a co-product of the catalyst activation, become absorbed by the nano-pyramids, improving their atomic ordering. Ru nano-pyramids with a 2-3 nm² footprint consisting of 3-5 atomic layers, ensure the maximum concentration of active sites necessary for the rate-determining step. Importantly, the growth of truncated pyramids typically does not exceed a footprint of approximately 4 nm² even after 12 hours of the reaction, indicating their high stability and explaining ruthenium's superior activity on nanotextured graphitic carbon compared to other support materials. The structural evolution of nanometer-sized metal clusters with a large fraction of surface atoms is qualitatively different from traditional several-nm nanoparticles, where surface atoms are a minority, and it offers a blueprint for the design of active and sustainable catalysts necessary for hydrogen production from ammonia, which is becoming one of the critical reactions for net-zero technologies.

The elimination of the A' unit from -type Y6-derivatives has led to the development of a new class of ortho-benzodipyrrole (o-BDP)-based A-D_NB_ND-A-type NFAs. In this work, two new A-D_NB_ND-A-type NFAs, denoted as CFB and CMB, are designed and synthesized, where electron-withdrawing fluorine atoms and electron-donating methyl groups are substituted on the benzene ring of the o-BDP moiety, respectively. CFB exhibits a blue-shifted absorption spectrum, stronger intermolecular interactions, shorter π-π stacking distances, and more ordered 3D intermolecular packing in the neat and blend films, enabling it to effectively suppress charge recombination in the PM6:CFB device showing a higher PCE of 16.55% with an FF of 77.45%. CMB displays a higher HOMO/LUMO energy level, a smaller optical bandgap, and a less ordered 3D packing, which contributes to its superior ability to suppress energy loss in the PM6:CMB device with a high V _oc of 0.90 V and a PCE of 16.46%. To leverage the advantages of CFB and CMB, ternary PM6:Y6-16:CFB and PM6:Y6-16:CMB devices are fabricated. The PM6:Y6-16:CFB device exhibits the highest PCE of 17.83% with an increased V _oc of 0.86 V and a J _sc of 27.32 mA cm^-2, while the PM6:Y6-16:CMB device displayed an elevated V _oc of 0.87 V and an improved FF of 74.71%, leading to a PCE of 17.44%. The high PCE was achieved using the non-halogenated greener solvent o-xylene, highlighting their potential for facilitating more eco-friendly processing procedures. C-shaped disubstituted o-BDP-based A-D-A type acceptors open up new avenues for tailoring electronic properties and molecular self-assembly, achieving higher OPV performance with enhanced charge recombination suppression and reduced energy loss.

Developing a self-sensitized catalyst from earth-abundant elements, capable of efficient light harvesting and electron transfer, is crucial for enhancing the efficacy of CO₂ transformation, a critical step in environmental cleanup and advancing clean energy prospects. Traditional approaches relying on external photosensitizers, comprising 4d/5d metal complexes, involve intermolecular electron transfer, and attachment of photosensitizing arms to the catalyst necessitates intramolecular electron transfer, underscoring the need for a more integrated solution. We report a new Cu(ii) complex, K[CuNDPA] (1[K(18-crown-6)]), bearing a dipyrrin amide-based trianionic tetradentate ligand, NDPA (H₃L), which is capable of harnessing light energy, despite having a paramagnetic Cu(ii) centre, without any external photosensitizer and photocatalytically reducing CO₂ to CO in acetonitrile : water (19 : 1 v/v) with a TON as high as 1132, a TOF of 566 h^-1 and a selectivity of 99%. This complex also shows hemilability in the presence of water, which not only plays a role in the proton relay mechanism but also helps stabilize a crucial Cu(i)-NDPA intermediate. The hemilability was justified by the formation of N₃O (2) and N₂O₂ (3) coordinated congeners of the N₄ bound complex 1. The overall mechanism was further investigated via spectroscopic techniques such as EPR, UV-vis, and spectroelectrochemistry, culminating in the justification of a single electron-reduced Cu(i)NDPA species as a proposed intermediate. In the next step, the binding of CO₂ to the Cu(i) complex and subsequent electron transfer to form Cu(ii)-COO^·- was indirectly probed by a radical trapping experiment via the addition of p-methoxy-2,6-di-tert-butylphenol that led to the formation of a phenoxyl radical. This work provides new strategies for designing earth-abundant robust molecular catalysts that can function as photocatalysts without the aid of any external photosensitizers.