Competitive and trapping experiments demonstrated that the reductive cyclization of o-nitrobiphenyl to carbazole using CO as the reductant and a palladium/phenanthroline catalyst proceeds through the formation of free o-nitrosobiphenyl. A kinetic study of its cyclization reaction to N-hydroxycarbazole indicated that the reaction does not require a metal catalyst, but is accelerated by bases, as also observed in the catalytic reaction starting from the nitro compound. Theoretical calculations provided details on the mechanism, including the involvement of DMF (solvent), when no additional base is added. The cyclization reaction is similar in the case of the synthesis of indoles from o-nitrostyrenes, but the two reactions show different sensitivities to air. This was attributed to different rate-determining steps, involving a Pd(II) complex as the resting state for the synthesis of carbazoles and a Pd(0) one for that of indoles. A palladacyclic complex was isolated from a reaction of o-nitrobiphenyl under conditions close to those employed in the catalytic reaction and shown to afford carbazole when reacted with pressurized CO. For the synthesis of indoles, a Pd(0) olefin complex, Pd(Phen)(η2-(E)-3-(5-fluoro-2-nitrophenyl)-1-phenylprop-2-en-1-one), was isolated directly from a catalytic reaction and characterized by single crystal XRD. An analogous complex, Pd(Phen)(η2-methyl (E)-2-nitrocinnamate), was also independently synthesized and structurally characterized, affording 2-carboxymethyl-indole when treated with CO. Some previously reported pieces of evidence apparently in favor of the involvement of metal-imido species as intermediates in cyclization reactions of nitroarenes when CO is employed as a reductant were dismissed. In particular, a compound previously identified as an aziridine was proven to be an allylic amine, whose formation does not require a metal-imido intermediate. Overall, the results strongly indicate that the cyclization occurs outside the metal coordination sphere at the nitrosoarene stage, excluding the involvement of imido (nitrene) complexes.
Catalytic ozonation offers a promising approach for removing perfluorinated compounds, yet developing catalysts with both high activity and stability remains a great challenge due to severe metal ions leaching. Herein, we design a Mn single atom decorated γ-AlOOH catalyst (denoted as Mnx/γ-AlOOH), which displays efficient catalytic ozonation towards perfluorooctanoic acid (PFOA) removal. Under optimal conditions, Mn2.2/γ-AlOOH achieves a defluorination ratio of 99.39% after 15 h of catalytic ozonation process, with a distinctive low leaching percentage (0.52% for Mn and 0.21% for Al, compared to 10.44% for Mn leaching from MnO2 and 0.95% for Al leaching from γ-AlOOH). Comprehensive analysis indicates that the introduction of Mn single atom optimizes the electronic structure and provides an additional indirect electron transfer pathway, which not only facilitates O3 activation, but also reduces Mn ion leaching by decreasing electron loss, and simultaneously enhances the activity and stability of the catalyst. This work provides new insights into enhancing the activity and stability of catalysts during the catalytic ozonation process via the rational design of atomically dispersed sites.
A deoxygenative enyne-aldehyde coupling for the regioselective 1,4-hydroalkylation of 1,3-enynes with readily available aldehydes under Pd/NHC catalysis is developed. Given the synthetic versatility of the carbonyl functionality and its prevalence in organic molecules, the use of aldehydes as latent carbanion equivalents is highly appealing. This method exhibits a broad substrate scope, good functional group tolerance, excellent scalability, and the ability to modify complex molecules, thereby providing a reliable catalytic platform for accessing structurally significant allenes of medicinal and biological interest. Mechanistic studies and density functional theory calculations elucidate that hydrazine monohydrate contributes not only to the carbonyl deoxygenation but also to the crucial regioselective protonation process.
Covalent organic frameworks (COFs) have emerged as a versatile class of crystalline porous materials for photocatalysis, owing to their structural programmability, high stability, and tailorable electronic properties. In this work, we report a flexible three-dimensional COF (CTP-TFPy) constructed from D3h-symmetric hexa(4-formylphenoxy)cyclotriphosphazene (CTP) and D2h-symmetric pyrene-based tetraaniline (TFPy), forming an extended donor–acceptor heteromotif architecture. The incorporation of a redox-active phosphazene core together with a π-conjugated pyrene unit establishes an efficient intraframework charge-transfer network, which promotes charge separation, suppresses recombination, and enhances the accessibility of catalytically active sites within the open 3D structure. The crystalline nature and structural robustness of the framework are confirmed by powder X-ray diffraction and high-resolution transmission electron microscopy. Density functional theory (DFT) calculations, supported by experimental investigations, elucidate a synergistic charge-transfer pathway and identify the key active sites governing photocatalytic hydrogen peroxide formation. In particular, the heteromotif molecular junction plays a crucial role in modulating electron flow and facilitating interfacial redox reactions.Under visible-light irradiation, the CTP-TFPy COF exhibits excellent photocatalytic performance for H2O2 production, achieving rates of 50.2μmol h−1 in pure water (AQE = 7.9 %) and 61.8μmol h−1 in ethanol-assisted systems (AQE = 9.8 %). These results highlight the effectiveness of rational donor–acceptor engineering in 3D COF and demonstrate a promising strategy for constructing metal-free photocatalysts for efficient and sustainable solar-driven H2O2 generation.
Hydrogenation of phenolic compounds is of practical importance for the synthesis of cyclohexanol and its derivatives. In this work, we report that a series of Ru catalysts supported on N-doped TiO2 were prepared for the hydrogenation of phenolic compounds. The experimental results indicated that the doping amount of N had a great influence on the catalytic performance of Ru catalysts. A catalyst with N dopant amount of 20% named as 0.8 wt%Ru/N0.2-TiO2 showed high conversion (99.9%) and selectivity (99.1%) of 4-tert-butylcyclohexanol in the hydrogenation of 4-tert-butylphenol at 130 °C and 1.5 MPa H2 pressure, which gave a TOF of 1152.2 h−1. The results from XPS and EPR characterization suggested that the structure with high concentration of both substitutional N and oxygen vacancies had a close relationship with the catalytic performance. The calculation results from density functional theory revealed that N-doping could strengthen the strong interaction between Ru metal and TiO2 support and generate small Ru nanoparticles with an average size of 1.1 nm, which are helpful for enhancing the catalytic hydrogenation performance of Ru-supported catalyst. Moreover, it is demonstrated that 0.8 wt%Ru/N0.2-TiO2 is also highly efficient for the hydrogenation of diverse phenolic compounds.
The telomerization of 1,3-butadiene with methanol represents an atom-economical route to the production of high-value 1-octene derivatives, yet current catalytic systems are still constrained by difficult catalyst separation and limited long-term stability. Herein, we report the construction of a structurally well-defined Pd single-site heterogeneous catalyst for efficient telomerization of 1,3-butadiene, in which an N-heterocyclic carbene Pd (NHC-Pd) complex is incorporated into a hierarchical hypercrosslinked porous polymer (HCP) framework via a direct knitting strategy. Comprehensive characterizations reveal that the NHC-Pd complex is uniformly distributed throughout the polymer network as isolated single sites while retaining its molecular coordination environment. The optimized catalyst HCP-NHC-Pd-10 exhibits outstanding catalytic performance, delivering a turnover number (TON) of 200,000 with up to 98.4% selectivity toward the target product 1-methoxy-2,7-octadiene (1-MOD) under mild reaction conditions. Remarkably, the catalyst is readily applicable to scale-up reaction and can be successively recycled at least 10 times without appreciable loss in catalytic activity or selectivity, accompanied by negligible Pd leaching, highlighting its exceptional stability and potential in practice. This study provides a general and feasible strategy for the construction of structurally well-defined and robust heterogeneous single-site catalysts for efficient telomerization and other organic transformations.
The 2-aminobenzothiazole scaffold is a privileged heterocycle with broad relevance in pharmaceuticals and materials science. Herein, we report a novel highly efficient transition metal-catalyzed room-temperature tandem protocol for its direct synthesis from a wide range of readily available phenyl isothiocyanates and amines. This cobalt-catalyzed transformation proceeds rapidly under a room-temperature open-air conditions without the need for any base (except substrates bearing electron-withdrawing groups on phenylisothiocyanates) or additives, delivering the desired products within 5 min. The method exhibits broad substrate scope, tolerating diverse phenyl isothiocyanates and both primary and secondary amines to afford the corresponding 2-aminobenzothiazoles in moderate to excellent yields. Notably, the protocol features low catalyst loading, short reaction time, operational simplicity, scalability, broad substrate scope and excellent functional group tolerance, collectively offering a robust, sustainable, and efficient synthetic platform for accessing this valuable scaffold.
