Metal-Free Dehydrogenation of N-Heterocycles by Ternary h -BCN Nanosheets with Visible Light

Constructing Functional Radiation-Resistant Thorium Clusters for Catalytic Redox Reactions

When catalytic reactions are interfered with by radiation sources, thorium clusters are promising as potential catalysts due to their superior radiation resistance. However, there is currently very little research on the design synthesis and catalytic application of radiation-stable thorium clusters. In this work, we have elaborately engineered and fabricated three high-nuclear thorium cluster catalysts denoted as Th12L3-MA12, Th12L3-MA6-BF6, and Th12L3-Fcc12, which did not undergo any significant alterations in their molecular structures and compositions after irradiation with 690 kGy γ-rays. We systematically investigated the photocatalytic/thermocatalytic properties of these radiation-resistant thorium clusters for the first time and found that γ-rays could not alter their catalytic activities. In addition, it was found that ligand engineering could modulate the catalytic activity of thorium clusters, thus expanding the range of catalytic applications of thorium clusters, including reduction reactions (nitroarene reduction) and some oxidation reactions (N-heterocyclic oxidative dehydrogenation and diphenylmethane oxidation). Meanwhile, all of these organic transformation reactions achieved a >80% conversion and nearly 100% product selectivity. Radiation experiments combined with DFT calculations showed that the synergistic catalysis of thorium-oxo core and ligands led to the generation of specific active species (H+, O2•-, or tBuO/tBuOO•) and activation of substrate molecules, thus achieving superior catalytic performance. This work is not only the first to develop radiation-resistant thorium cluster catalysts to perform efficient redox reactions but also provides design ideas for the construction of high-nuclearity thorium clusters under mild conditions.

NBS-mediated bromination and dehydrogenation of tetrahydro-quinoline in one pot: scope and mechanistic study

A facile and general approach was developed for the efficient construction of functionalized bromoquinolines by the dehydrogenation of tetrahydroquinolines using NBS as the electrophile and as oxidant. The cascade transformation proceeded with good functional group tolerance under metal-free conditions with a short reaction duration. Various tetrahydroquinolines bearing either electron-rich or electron-deficient groups at different positions were successfully converted into the corresponding target products in moderate to high yields under mild conditions. It is worth noting that the obtained polybromoquinolines could further undergo classic metal-catalyzed cross-coupling reactions with good regioselectivity. The Sonagashira coupling reaction occurred regioselectively in the C-6 position of the obtained products followed by a Suzuki coupling reaction to give multifunctionalized quinolines. The mechanism indicated that electrophilic bromination/radical dehydrogenation sequences occurred in one pot.

Molecular Design of Porous Organic Polymer-Derived Carbonaceous Electrocatalysts for Pinpointing Active Sites in Oxygen Reduction Reaction

The widespread application of fuel cells is hampered by the sluggish kinetics of the oxygen reduction reaction (ORR), which traditionally necessitates the use of high-cost platinum group metal catalysts. The indispensability of these metal catalysts stems from their ability to overcome kinetic barriers, but their high cost and scarcity necessitate alternative strategies. In this context, porous organic polymers (POPs), which are built up from the molecular level, are emerging as promising precursors to produce carbonaceous catalysts owning to their cost-effectiveness, high electrical conductivity, abundant active sites and extensive surface area accessibility. To enhance the intrinsic ORR activity and optimize the performance of these electrocatalysts, recognizing, designing, and increasing the density of active sites are identified as three crucial steps. These steps, which form the core of our review, serve to elucidate the link between the material structure design and ORR performance evaluation, thereby providing valuable insights for ongoing research in the field. Leveraging the precision of polymer skeletons based on molecular units, POP-derived carbonaceous catalysts provide an excellent platform for in-depth exploration of the role and working mechanism for the specific active site during the ORR process. In this review, the recent advances pertaining to the synthesis techniques and electrochemical functions of various types of active sites, pinpointed from POPs, are systematically summarized, including heteroatoms, surficial substituents and edge/defects. Notably, the structure-property relationship, between these active sites and ORR performance, are discussed and emphasized, which creates guidelines to shed light on the design of high-performance ORR electrocatalysts.

Highly efficient metal-free borocarbonitride catalysts for electrochemical reduction of N2 to NH3

The electrocatalytic nitrogen reduction reaction (NRR) for ammonia (NH₃) under ambient conditions is emerging as a potentially sustainable alternative to the traditional, energy-intensive Haber-Bosch process for ammonia production. Currently, metal-based electrocatalysts constitute the majority of reported NRR catalysts. However, they often suffer from the shortcomings of competitive reactions of nitrogen adsorption/activation and hydrogen generation. Therefore, there is an urgent need to develop more environmentally friendly, low energy consumption, and non-polluting high-performance metal-free electrocatalysts. In this study, borocarbonitride (BCN) materials derived from boron imidazolate framework (BIF-20) were used to boost efficient electrochemical nitrogen conversion to ammonia under ambient conditions. The BCN catalyst demonstrated excellent performance in 0.1 M KOH, with an ammonia yield of 21.62 μg h^-1 mg_cat^-1 and a Faradaic efficiency of 9.88% at -0.3 V (Reversible Hydrogen Electrode, RHE). This performance is superior to most metal-free catalysts and even some metal catalysts for NRR. The ¹⁵N₂/¹⁴N₂ isotope labeling experiments and density functional theory (DFT) calculations showed that N₂ can be adsorbed and converted to NH₃ on the surface of BCN, and that the energy barrier can be significantly reduced by structural design for BCN. This work highlights the important role played by the presence of Lewis acid-base pairs in metal-free catalysts for enhancing electrochemical NRR performance.

Boosting Hydrogen Production via Selective Two-electron Mild Electrochemical Oxidation of Tetrahydroisoquinolines Completely to Dihydroisoquinolines

Different from the previous study that biomass derivatives replace water oxidation for enhancing hydrogen production, we found that mild oxidation was more conductive to cathodic hydrogen production. In this study, maximum Faradaic efficiency (>99 %) and lower energy consumption for hydrogen production was achieved by precisely controlling the two-electron mild electrochemical oxidation of tetrahydroisoquinolines (THIQs) to dihydroisoquinolines (DHIQs) in place of the four-electron deep oxidation to isoquinolines (IQs). Moreover, the high value-added DHIQs were prepared from THIQs with high selectivity (>99 %) at the low potential of 1.36 V. Operando electrochemical Raman and density functional theory proved that the high selectivity was attributed to the regulable active species of NiOOH induced by the interaction of Co and Fe for preferentially breaking C-H bond rather than N-H of THIQs. This novel method provides important insight into efficient biomass-assisted hydrogen production.

Light-driven redox deracemization of indolines and tetrahydroquinolines using a photocatalyst coupled with chiral phosphoric acid

The integration of oxidation and enantioselective reduction enables a redox deracemization to directly access enantioenriched products from their corresponding racemates. However, the solution of the kinetically microscopic reversibility of substrates used in this oxidation/reduction unidirectional event is a great challenge. To address this issue, we have developed a light-driven strategy to enable an efficient redox deracemization of cyclamines. The method combines a photocatalyst and a chiral phosphoric acid in a toluene/aqueous cyclodextrin emulsion biphasic co-solvent system to drive the cascade out-of-equilibrium. Systemic optimizations achieve a feasible oxidation/reduction cascade sequence, and mechanistic investigations demonstrate a unidirectional process. This single-operation cascade route, which involves initial photocatalyzed oxidation of achiral cyclamines to cyclimines and subsequent chiral phosphoric acid-catalyzed enantioselective reduction of cyclimines to chiral cyclamines, is suitable for constructing optically pure indolines and tetrahydroquinolines.

Continuous Room-Temperature Hydrogen Release from Liquid Organic Carriers in a Photocatalytic Packed-Bed Flow Reactor

Despite the potential of hydrogen (H₂ ) storage in liquid organic carriers to achieve carbon neutrality, the energy required for H₂ release and the cost of catalyst recycling have hindered its large-scale adoption. In response, a photo flow reactor packed with rhodium (Rh)/titania (TiO₂ ) photocatalyst was reported for the continuous and selective acceptorless dehydrogenation of 1,2,3,4-tetrahydroquinoline to H₂ gas and quinoline under visible light irradiation at room temperature. The tradeoff between the reactor pressure drop and its photocatalytic surface area was resolved by selective in-situ photodeposition of Rh in the photo flow reactor post-packing on the outer surface of the TiO₂ microparticles available to photon flux, thereby reducing the optimal Rh loading by 10 times compared to a batch reactor, while facilitating catalyst reuse and regeneration. An example of using quinoline as a hydrogen acceptor to lower the energy of the hydrogen production step was demonstrated via the water-gas shift reaction.

Sandwich-Structured Hybrid of NiCo Nanoparticles-Embedded Carbon Nanotubes Grafted on C3N4 Nanosheets for Efficient Photodehydrogenative Coupling Reactions

Exploring cheap and efficient hybrid catalysts offers exciting opportunities for enhancing the performance of photocatalysts in the green organic synthesis field. Herein, a facile and effective approach is designed for the synthesis of a sandwich-structured hybrid in which NiCo bimetallic nanoparticles are embedded in the tip of nitrogen-doped carbon nanotubes (N-CNTs) grafted on both sides of a nitrogen deficient C₃N₄ (N_v-C₃N₄) nanosheet for photodehydrogenative coupling reactions. Such a brand-new type of sandwich-structured hybrid comprises N_v-C₃N₄ nanosheets and surrounding N-CNTs embedded with NiCo nanoparticles at their tips. Remarkably, the resultant hybrid exhibits integrated functionalities, abundant active sites, enhanced visible light absorption, and excellent interfacial charge transfer ability. As a result, the optimized NiCo@N-CNTs@N_v-C₃N₄ photocatalyst shows significantly improved photodehydrogenative coupling performance of amines to imines compared to the control single-metal-based catalysts (Ni@N-CNTs@N_v-C₃N₄ and Co@N-CNTs@N_v-C₃N₄). The mechanistic investigation through experimental and computational study demonstrates that, compared with single-metal-based hybrids, the NiCo bimetallic hybrid exhibits stronger amine adsorption and weaker photogenerated hydrogen atom adsorption, thus promoting the dehydrogenative activation of primary amines and fast generation of imines. This work presents a promising insight for designing and preparing efficient photocatalysts to trigger organic synthesis in high yields.

Visible-Light-Promoted Iridium(III)-Catalyzed Acceptorless Dehydrogenation of N-Heterocycles at Room Temperature

An effective visible-light-promoted iridium(III)-catalyzed hydrogen production from N-heterocycles is described. A single iridium complex constitutes the photocatalytic system playing a dual task, harvesting visible-light and facilitating C–H cleavage and H₂ formation at room temperature and without additives. The presence of a chelating C–N ligand combining a mesoionic carbene ligand along with an amido functionality in the Ir^III complex is essential to attain the photocatalytic transformation. Furthermore, the Ir^III complex is also an efficient catalyst for the thermal reverse process under mild conditions, positioning itself as a proficient candidate for liquid organic hydrogen carrier technologies (LOHCs). Mechanistic studies support a light-induced formation of H₂ from the Ir–H intermediate as the operating mode of the iridium complex.

Highly Efficient and Selective Carbon-Doped BN Photocatalyst Derived from a Homogeneous Precursor Reconfiguration

The modification of inert boron nitride by carbon doping to make it an efficient photocatalyst has been considered as a promising strategy. Herein, a highly efficient porous BCN (p-BCN) photocatalyst was synthesized via precursor reconfiguration based on the recrystallization of a new homogeneous solution containing melamine diborate and glucose. Two crystal types of the p-BCN were obtained by regulating the recrystallization conditions of the homogeneous solution, which showed high photocatalytic activities and a completely different CO2 reduction selectivity. The CO generation rate and selectivity of the p-BCN-1 were 63.1 μmol·g−1·h−1 and 54.33%; the corresponding values of the p-BCN-2 were 42.6 μmol·g−1·h−1 and 80.86%. The photocatalytic activity of the p-BCN was significantly higher than those of equivalent materials or other noble metals-loaded nanohybrids reported in the literature. It was found that the differences in the interaction sites between the hydroxyl groups in the boric acid and the homolateral hydroxyl groups in the glucose were directly correlated with the structures and properties of the p-BCN photocatalyst. We expect that the developed approach is general and could be extended to incorporate various other raw materials containing hydroxyl groups into the melamine diborate solution and could modulate precursors to obtain porous BN-based materials with excellent performance.

Photocatalytic Aerobic Dehydrogenation of N-Heterocycles with Ir(III) Photosensitizers Bearing the 2(2'-Pyridyl)benzimidazole Scaffold

Photoredox catalysis constitutes a very powerful tool in organic synthesis, due to its versatility, efficiency, and the mild conditions required by photoinduced transformations. In this paper, we present an efficient and selective photocatalytic procedure for the aerobic oxidative dehydrogenation of partially saturated N-heterocycles to afford the respective N-heteroarenes (indoles, quinolines, acridines, and quinoxalines). The protocol involves the use of new Ir(III) biscyclometalated photocatalysts of the general formula [Ir(C^N)₂(N^N')]Cl, where the C^N ligand is 2-(2,4-difluorophenyl)pyridinate, and N^N' are different ligands based on the 2-(2'-pyridyl)benzimidazole scaffold. In-depth electrochemical and photophysical studies as well as DFT calculations have allowed us to establish structure-activity relationships, which provide insights for the rational design of efficient metal-based dyes in photocatalytic oxidation reactions. In addition, we have formulated a dual mechanism, mediated by the radical anion superoxide, for the above-mentioned transformations.

Fabrication of hexagonal boron carbonitride nanoplates using for in vitro photodynamic therapy and chemo therapy

Carbon nanomaterials and boron nitride nanomaterials have been proved to be very potential for biomedical applications. However, as an analog of them, boron carbonitride nanomaterials are rarely reported in biomedical field. In this study, the fabrication of visible light-responsive boron carbonitride nanoplates (BCNNPs) and their application in photodynamic therapy and chemo therapy were demonstrated. BCNNPs with an average size of 46 nm were fabricated via hydrogen peroxide treatment from bulk BCN. Cytotoxicity tests showed that the as-prepared BCNNPs are biocompatible and have no cytotoxicity to human breast cancer cells and human hepatocyte carcinoma cells. After conjunction with doxorubicin and folic acid, the BCNNPs were adopted as a targeted drug carrier, presenting pH-responsive release and tumor-targeting property for chemo therapy. Moreover, under certain intensity of visible light irradiation (45 mW/cm²), the BCNNPs can generate reactive oxygen species including superoxide radical, hydroxyl radical and singlet oxygen, so that synergistic photodynamic/chemo therapy effects were achieved. This work may be a groundbreaking discovery for utilizing BCNNPs as photosensitizer for photodynamic therapy and drug carrier for chemo therapy.

Camphorsulfonic Acid-Mediated One-Pot Tandem Consecutive via the Ugi Four-Component Reaction for the Synthesis of Functionalized Indole and 2-Quinolone Derivatives by Switching Solvents

A camphorsulfonic acid-mediated one-pot tandem consecutive approach was developed to synthesize functionalized indole and 2-quinolone derivatives from the Ugi four-component reaction by switching solvents. A reaction of the Ugi adduct in an aprotic solvent undergoes 5-exo-trig cyclization to form an indole ring. In a protic solvent, however, the Ugi adduct undergoes an alkyne-carbonyl metathesis reaction to form a 2-quinolone ring.

Metal-free carbocatalyst for room temperature acceptorless dehydrogenation of N-heterocycles

Catalytic dehydrogenation enables reversible hydrogen storage in liquid organics as a critical technology to achieve carbon neutrality. However, oxidant or base-free catalytic dehydrogenation at mild temperatures remains a challenge. Here, we demonstrate a metal-free carbocatalyst, nitrogen-assembly carbons (NCs), for acceptorless dehydrogenation of N-heterocycles even at ambient temperature, showing greater activity than transition metal-based catalysts. Mechanistic studies indicate that the observed catalytic activity of NCs is because of the unique closely placed graphitic nitrogens (CGNs), formed by the assembly of precursors during the carbonization process. The CGN site catalyzes the activation of C─H bonds in N-heterocycles to form labile C─H bonds on catalyst surface. The subsequent facile recombination of this surface hydrogen to desorb H₂ allows the NCs to work without any H-acceptor. With reverse transfer hydrogenation of various N-heterocycles demonstrated in this work, these NC catalysts, without precious metals, exhibit great potential for completing the cycle of hydrogen storage.

Non-metal-mediated N-oxyl radical (TEMPO)-induced acceptorless dehydrogenation of N-heterocycles via electrocatalysis

The development of protocols for direct catalytic acceptorless dehydrogenation of N-heterocycles with metal-free catalysts holds the key to difficulties in green and sustainable chemistry. Herein, an N-oxyl radical (TEMPO) acting as an oxidant in combination with electrochemistry is used as a synthesis system under neutral conditions to produce N-heterocycles such as benzimidazole and quinazolinone. The key feature of this protocol is the utilization of the TEMPO system as an inexpensive and easy to handle radical surrogate that can effectively promote the dehydrogenation reaction. Mechanistic studies also suggest that oxidative TEMPOs redox catalytic cycle participates in the dehydrogenation of 2,3-dihydro heteroarenes.

The development of protocols for direct catalytic acceptorless dehydrogenation of N-heterocycles with metal-free catalysts holds the key to difficulties in green and sustainable chemistry.

A biomass-derived N-doped porous carbon catalyst for the aerobic dehydrogenation of nitrogen heterocycles

N-doped porous carbon (NC) was synthesized from sugar cane bagasse, which is a sustainable and widely available biomass waste.

Recent advances in the synthesis of N-heteroarenes via catalytic dehydrogenation of N-heterocycles

Bio-active molecules having N-heteroarene core are widely used for numerous medicinal applications and as lifesaving drugs. In this direction, dehydrogenation of partially saturated aromatic N-heterocycles shows utmost importance for the synthesis of heterocycles. This feature article highlights the recent advances, from 2009 to April 2021, on the dehydrogenation of N-heteroaromatics. Notable features considering the development of newer catalysis for dehydrogenations are: (i) approaches based on precious metal catalysis, (ii) newer strategies and catalyst development technology using non-precious metal-catalysts for N-heterocycles having one or more heteroatoms, (iii) Synthesis of five or six-membered N-heterocycles using photocatalysis, electrocatalytic, and organo-catalytic approaches using different homogeneous and heterogeneous conditions' (iv) metal free (base and acid-promoted) dehydrogenation along with I₂, N-hydroxyphthalimide (NHPI) and bio catalyzed miscellaneous examples have also been discussed, (v) mechanistic studies for various dehydrogenation reactions and (vi) synthetic applications of various bio-active molecules including post-drug derivatization are discussed.

Photo-fluorination of nanodiamonds catalyzing oxidative dehydrogenation reaction of ethylbenzene

Styrene is one of the most important industrial monomers and is traditionally synthesized via the dehydrogenation of ethylbenzene. Here, we report a photo-induced fluorination technique to generate an oxidative dehydrogenation catalyst through the controlled grafting of fluorine atoms on nanodiamonds. The obtained catalyst has a fabulous performance with ethylbenzene conversion reaching 70% as well as styrene yields of 63% and selectivity over 90% on a stream of 400 °C, which outperforms other equivalent benchmarks as well as the industrial K-Fe catalysts (with a styrene yield of 50% even at a much higher temperature of ca. 600 °C). Moreover, the yield of styrene remains above 50% after a 500 h test. Experimental characterizations and density functional theory calculations reveal that the fluorine functionalization not only promotes the conversion of sp3 to sp2 carbon to generate graphitic layers but also stimulates and increases the active sites (ketonic C=O). This photo-induced surface fluorination strategy facilitates innovative breakthroughs on the carbocatalysis for the oxidative dehydrogenation of other arenes.

Syntheses of 1H-Indoles, Quinolines, and 6-Membered Aromatic N-Heterocycle-Fused Scaffolds via Palladium(II)-Catalyzed Aerobic Dehydrogenation under Alkoxide-Free Conditions

Aromatic N-heterocycle-fused scaffolds such as indoles and quinolines are important core structures found in various bioactive natural products and synthetic compounds. Recently, various dehydrogenation methods with the help of alkoxides, known to significantly promote dihydro- or tetrahydro-heterocycles to be oxidized, were developed for the heterocycle synthesis. However, these approaches are sometimes unsuitable due to resulting undesired side reactions such as reductive dehalogenation. Herein, expedient syntheses of 1H-indoles, quinolines, and 6-membered N-heterocycle-fused scaffolds from their hydrogenated forms through palladium(II)-catalyzed aerobic dehydrogenation under alkoxide-free conditions are reported. A total of 48 compounds were successfully synthesized with a wide range of functional groups including halogens (up to 99% yield). These methodologies provide facile routes for various privileged structures possessing aromatic N-heterocycles without the help of alkoxides, in highly efficient manners.

Cooperative Coupling of Oxidative Organic Synthesis and Hydrogen Production over Semiconductor-Based Photocatalysts

Merging hydrogen (H₂) evolution with oxidative organic synthesis in a semiconductor-mediated photoredox reaction is extremely attractive because the clean H₂ fuel and high-value chemicals can be coproduced under mild conditions using light as the sole energy input. Following this dual-functional photocatalytic strategy, a dreamlike reaction pathway for constructing C-C/C-X (X = C, N, O, S) bonds from abundant and readily available X-H bond-containing compounds with concomitant release of H₂ can be readily fulfilled without the need of external chemical reagents, thus offering a green and fascinating organic synthetic strategy. In this review, we begin by presenting a concise overview on the general background of traditional photocatalytic H₂ production and then focus on the fundamental principles of cooperative photoredox coupling of selective organic synthesis and H₂ production by simultaneous utilization of photoexcited electrons and holes over semiconductor-based catalysts to meet the economic and sustainability goal. Thereafter, we put dedicated emphasis on recent key progress of cooperative photoredox coupling of H₂ production and various selective organic transformations, including selective alcohol oxidation, selective methane conversion, amines oxidative coupling, oxidative cross-coupling, cyclic alkanes dehydrogenation, reforming of lignocellulosic biomass, and so on. Finally, the remaining challenges and future perspectives in this flourishing area have been critically discussed. It is anticipated that this review will provide enlightening guidance on the rational design of such dual-functional photoredox reaction system, thereby stimulating the development of economical and environmentally benign solar fuel generation and organic synthesis of value-added fine chemicals.

Ceramic boron carbonitrides for unlocking organic halides with visible light

Photochemistry provides a sustainable pathway for organic transformations by inducing radical intermediates from substrates through electron transfer process. However, progress is limited by heterogeneous photocatalysts that are required to be efficient, stable, and inexpensive for long-term operation with easy recyclability and product separation. Here, we report that boron carbonitride (BCN) ceramics are such a system and can reduce organic halides, including (het)aryl and alkyl halides, with visible light irradiation. Cross-coupling of halides to afford new C-H, C-C, and C-S bonds can proceed at ambient reaction conditions. Hydrogen, (het)aryl, and sulfonyl groups were introduced into the arenes and heteroarenes at the designed positions by means of mesolytic C-X (carbon-halogen) bond cleavage in the absence of any metal-based catalysts or ligands. BCN can be used not only for half reactions, like reduction reactions with a sacrificial agent, but also redox reactions through oxidative and reductive interfacial electron transfer. The BCN photocatalyst shows tolerance to different substituents and conserved activity after five recycles. The apparent metal-free system opens new opportunities for a wide range of organic catalysts using light energy and sustainable materials, which are metal-free, inexpensive and stable.

Metal-Free Photocatalysis: Two-Dimensional Nanomaterial Connection toward Advanced Organic Synthesis

Two-dimensional (2D) nanostructures are a frontier in materials chemistry as a result of their extraordinary properties. Metal-free 2D nanomaterials possess extra appeal due to their improved cost-effectiveness and lower toxicity with respect to many inorganic structures. The outstanding electronic characteristics of some metal-free 2D semiconductors have projected them into the world of organic synthesis, where they can function as high-performance photocatalysts to drive the sustainable synthesis of high-value organic molecules. Recent reports on this topic have inspired a stream of research and opened up a theme that we believe will become one of the most dominant trends in the forthcoming years.

Efficient acceptorless dehydrogenation of hydrogen-rich N-heterocycles photocatalyzed by Ni(OH)2@CdSe/CdS quantum dots

Ni(OH)₂@CdSe/CdS QDs exhibit excellent photocatalytic acceptorless dehydrogenation of hydrogen-rich N-heterocycles with the release of hydrogen at ambient temperature.

Visible-light-mediated synthesis of quinolines

Visible light promoted synthetic routes of quinolines using different strategies are hereby documented.

Synergistic Pd Single Atoms, Clusters, and Oxygen Vacancies on TiO2 for Photocatalytic Hydrogen Evolution Coupled with Selective Organic Oxidation

Developing efficient photocatalysts for synchronously producing H₂ and high value-added chemicals holds great promise to enhance solar energy conversion. Herein, a facile strategy of simultaneously engineering Pd cocatalyst and oxygen vacancies (V_O s) on TiO₂ to promote H₂ production coupled with selective oxidation of benzylamine is demonstrated. The optimized Pd_SA+C /TiO₂ -V_O photocatalyst containing Pd single atoms (SAs), clusters (C), and V_O s exhibits much superior performance to those of TiO₂ -V_O and Pd_SA /TiO₂ -V_O counterparts. The production rates of H₂ and N-benzylidenebenzylamine over Pd_SA+C /TiO₂ -V_O are 52.7 and 1.5 times those over TiO₂ -V_O , respectively. Both experimental and theoretical studies have elucidated the synergistic effect of Pd SAs, clusters, and V_O s on TiO₂ in boosting the photocatalytic reaction. The presence of Pd SAs facilitates the generation and stabilization of abundant V_O s by the formation of PdOTi³⁺ atomic interface, while Pd clusters promote the photogenerated charge separation and afford the optimum active sites for H₂ evolution. Surface V_O s of TiO₂ guarantee the efficient adsorption and dissociation/activation of reactant molecules. This study reveals the effect of active-site engineering on the photocatalysis and is expected to shed substantial light on future structure design and modulation of semiconductor photocatalysts.

One-pot photocatalytic transformation of indolines into 3-thiocyanate indoles with new Ir(iii) photosensitizers bearing β-carbolines

Herein, we harness the combination of two photocatalytic reactions, promoted by new Ir(iii) photosensitizers, for the direct access to 3-thiocyanato indoles from indolines in a one-pot process.

Synthesis of N-aryl amines enabled by photocatalytic dehydrogenation

Catalytic dehydrogenation (CD) via visible-light photoredox catalysis provides an efficient route for the synthesis of aromatic compounds. However, access to N-aryl amines, which are widely utilized synthetic moieties, via visible-light-induced CD remains a significant challenge, because of the difficulty in controlling the reactivity of amines under photocatalytic conditions. Here, the visible-light-induced photocatalytic synthesis of N-aryl amines was achieved by the CD of allylic amines. The unusual strategy using C₆F₅I as an hydrogen-atom acceptor enables the mild and controlled CD of amines bearing various functional groups and activated C–H bonds, suppressing side-reaction of the reactive N-aryl amine products. Thorough mechanistic studies suggest the involvement of single-electron and hydrogen-atom transfers in a well-defined order to provide a synergistic effect in the control of the reactivity. Notably, the back-electron transfer process prevents the desired product from further reacting under oxidative conditions.

The synergy of SET, HAT, and BET enables a visible-light induced catalytic dehydrogenation for the synthesis of N-aryl amines.

Boron Carbonitride Lithium-Ion Capacitors with an Electrostatically Expanded Operating Voltage Window

Lithium-ion capacitors (LICs) have emerged as attractive energy storage devices to bridge the gap between lithium-ion batteries and supercapacitors. While the distinct charge storage kinetics between the anode and the cathode is still a challenge to the widespread application of LICs, the key to improving the energy density of these devices is to widen the operating voltage window and balance the mismatch of the electrode kinetics. To this end, we propose a strategy based on electrostatic attraction by adjusting the B and N atom contents of boron carbonitride (BCN) electrode materials to alter their electronegativities and successfully prepared B-rich and N-rich BCN nanotubes (BCNNTs) via a facile solid-phase synthesis approach. The B-rich BCN (B-BCN) cathode and N-rich BCN (N-BCN) anode noticeably enhance the adsorption of anions and cations, promoting a matching degree between the anode and cathode. In particular, the rationally designed B-BCN//N-BCN LIC achieves a maximum voltage range of 4.8 V, setting a new record for LICs. Furthermore, the energy density reaches up to 200 Wh kg^-1 (based on the total mass of cathodic and anodic active materials). Density functional theory calculations provided insight into the mechanism underlying our strategy of widening the voltage range. Our philosophy provides new design guidelines and alternatives for identifying and optimizing high-performance electrodes for energy storage devices.

DMSO/t-BuONa/O2-Mediated Aerobic Dehydrogenation of Saturated N-Heterocycles

Aromatic N-heterocycles such as quinolines, isoquinolines, and indolines are synthesized via sodium tert-butoxide-promoted oxidative dehydrogenation of the saturated heterocycles in DMSO solution. This reaction proceeds under mild reaction conditions and has a good functional group tolerance. Mechanistic studies suggest a radical pathway involving hydrogen abstraction of dimsyl radicals from the N-H bond or α-C-H of the substrates and subsequent oxidation of the nitrogen or α-aminoalkyl radicals.

Mechanical exfoliation of boron carbide: A metal-free catalyst for aerobic oxidative desulfurization in fuel

Metal-free catalysts have been proved to be a low-cost and environmentally friendly species in aerobic oxidative desulfurization (ODS). In this work, exfoliated metal-free boron carbide with few-layered structure, small size, and abundant defects, was first employed in an aerobic ODS system for ultra-deep desulfurization. The exfoliation process was realized by employing a planetary ball mill strategy. Detailed characterizations showed that the ball milling process not only induces thinner layers and small sizes but also introduces numerous defects into the boron carbide catalysts, which is vital in metal-free catalysis. Furthermore, the exfoliated boron carbide catalyst was applied in aerobic ODS system, and 99.5 % of sulfur removal was obtained. Moreover, the catalyst can be recycled 17 times without a significant decrease in catalytic activity. In particular, it was found that ∼90 % of the sulfur compounds in real diesel oil could be removed by the current aerobic ODS system.

Methanol conversion on borocarbonitride catalysts: Identification and quantification of active sites

Borocarbonitrides (BCNs) have emerged as highly selective catalysts for the oxidative dehydrogenation (ODH) reaction. However, there is a lack of in-depth understanding of the catalytic mechanism over BCN catalysts due to the complexity of the surface oxygen functional groups. Here, BCN nanotubes with multiple active sites are synthesized for oxygen-assisted methanol conversion reaction. The catalyst shows a notable activity improvement for methanol conversion (29%) with excellent selectivity to formaldehyde (54%). Kinetic measurements indicate that carboxylic acid groups on BCN are responsible for the formation of dimethyl ether, while the redox catalysis to formaldehyde occurs on both ketonic carbonyl and boron hydroxyl (B─OH) sites. The ODH reaction pathway on the B─OH site is further revealed by in situ infrared, x-ray absorption spectra, and density functional theory. The present work provides physical-chemical insights into the functional mechanism of BCN catalysts, paving the way for further development of the underexplored nonmetallic catalytic systems.