Turnover Frequency Research Articles

Illuminating light on D-π-A Zn porphyrin dyes for efficient solar to chemical fuel generation

In this study, we design tunable D-π-A porphyrin dyes, 2,1,3-benzo thiadiazole (BTD)-phenyl (LG-6) and 4-ethynyl thiophene (LG-5) as photosensitizers of Pt/TiO2 (PCT) for solar to chemical fuel generation. The PCT-LG5 and PCT-LG6 photocatalysts are evaluated for photoinduced hydrogen evolution and CO2 reduction to methanol. The PCT-LG6 at optimum (pH 1, 3, 7, and 10) reaction conditions produced hydrogen generation rate of 5.70 mmol.g−1.h−1 with a turnover number (TON) of 1140 and apparent quantum yield (AQY) of 13.8% under visible-light and remarkably high CO2 reduction reaction to methanol with a rate of 1.99, 1.38 mmol.g−1.h−1 for PCT-LG5, PCT-LG6 systems, respectively. The extended light absorptions (400–900 nm) of the photocatalysts is due to the correct pairing of functionalization between porphyrin and the anchoring group cyanoacrylic acid in LG-5 and carboxylic acid in LG-6. The cyanoacrylic group acts as an anchoring group in LG-5, inducing a red (bathochromic) shift in the Soret band and Q-bands, indicating effective intramolecular electronic charge transfer behavior alongside the implementation of strategies to enhance light harvesting properties which further substantiated by the density functional theory (DFT) studies.

Laser-induced graphene nano-anchored WS2/WO3 heterostructures for electrocatalytic oxygen evolution reaction

Tailoring surface components and nanostructures via integration of dual transition metal heteroatoms is a highly effective technique for the design and synthesis of electrocatalysts with superior performance. In this study, we report WS₂/WO₃ nanostructure enriched with sulphur and oxygen vacancies, embedded within laser-induced graphene (LIG) as carbon support, to improve alkaline and seawater splitting applications for the oxygen evolution reaction (OER). The LIG-WS₂/WO₃ nanohybrid demonstrates high OER activity and improved stability due to the synergistic interaction between LIG, WS₂, WO₃, and optimized proportion of sulphur and oxygen vacancies, which facilitates efficient charge transfer, reduces recombination losses and allows significant tuning of various electrocatalytic parameters as a function of annealing temperature. The optimized sample, LWSO@450, exhibits excellent electrocatalytic activity with a low overpotential of 350 mV at a current density of 50 mA/cm2 and an exceptionally low Tafel slope of 33 mV/decade in an alkaline medium. Moreover, the high electrochemically active surface area of 134 cm2, mass activity of 60 A/g, and turnover frequency of 0.012 s⁻1 indicate a substantial number of active sites. These findings highlight the considerable potential of this catalyst in various electrochemical domains, particularly in energy conversion, and other renewable energy systems, due to its cost-effectiveness, availability, and scalability.

Ultrastable monolithic electrodes with single-atom platinum-oxygen sites for efficient hydrogen evolution in acidic conditions

PtNC single-atom catalysts (SACs) single-atom catalysts (SACs) are promising for acidic hydrogen evolution reaction (HER) but suffer from instability at high current densities, limiting their large-scale application. Herein, PtO bonds are constructed to securely anchor atomically dispersed Pt for single-atom (SA) catalysis, utilizing etched vertical graphene (EVG) nanosheets as monolithic supports (Pt-SAs/EVG). Compared to PtNC, the resultant PtO4 coordination demonstrates improved stability while maintaining significant catalytic activity. When applying this catalyst in the acidic HER, a high turnover frequency (34.6 s−1) is achieved at 70 mV, accompanied by exceptional durability exceeding 100 h at −100 mA cm−2. Theoretical analyses indicate that the PtO bonds confer stability to the Pt atoms, facilitating the efficient adsorption of protons and the subsequent desorption of hydrogen. The prepared Pt-SAs/EVG can also be directly employed as the cathode to afford stable operation at 0.5 A cm−2 in a proton exchange membrane electrolyzer cell. This study offers novel insights into enhancing the performance of SACs for industrial applications in electrocatalysis.

DLKcat cannot predict meaningful k cat values for mutants and unfamiliar enzymes.

The recently published DLKcat model, a deep learning approach for predicting enzyme turnover numbers (k cat), claims to enable high-throughput k cat predictions for metabolic enzymes from any organism and to capture k cat changes for mutated enzymes. Here, we critically evaluate these claims. We show that for enzymes with <60% sequence identity to the training data DLKcat predictions become worse than simply assuming a constant average k cat value for all reactions. Furthermore, DLKcat's ability to predict mutation effects is much weaker than implied, capturing none of the experimentally observed variation across mutants not included in the training data. These findings highlight significant limitations in DLKcat's generalizability and its practical utility for predicting k cat values for novel enzyme families or mutants, which are crucial applications in fields such as metabolic modeling.

Selective hydrogenation of nitro compounds to amines by coupled redox reactions over a heterogeneous biocatalyst

Cleaner synthesis of amines remains a key challenge in organic chemistry because of their prevalence in pharmaceuticals, agrochemicals and synthetic building blocks. Here, we report a different paradigm for chemoselective hydrogenation of nitro compounds to amines, under mild, aqueous conditions. The hydrogenase enzyme releases electrons from H2 to a carbon black support which facilitates nitro-group reduction. For 30 nitroarenes we demonstrate full conversion (isolated yields 78 – 96%), with products including pharmaceuticals benzocaine, procainamide and mesalazine, and 4-aminophenol – precursor to paracetamol (acetaminophen). We also showcase gram-scale synthesis of procainamide with 90% isolated yield. We demonstrate potential for extension to aliphatic substrates. The catalyst is highly selective for reduction of the nitro group over other unsaturated bonds, tolerant to a wide range of functional groups, and exhibits excellent stability in reactions lasting up to 72 hours and full reusability over 5 cycles with a total turnover number over 1 million, indicating scope for direct translation to fine chemical manufacturing.

Unveiling the mechanistic synergy in Mn-doped NiO catalysts with atomic-burry structure: Enhanced CO oxidation via Ni-OH and Mn bifunctionality

The development of non-noble metal catalysts for low-temperature CO oxidation is a pivotal subject in various disciplines. In this study, an optimized Mn-doped NiO catalyst (Mn-NiO-0.5), prepared via aerosol pyrolysis with an equal molar ratio of Ni to Mn, demonstrates remarkable performance. It achieves an 82 % CO conversion at -20 °C and a 100 % conversion between 10 °C and 800 °C. The catalyst’s turnover frequency (TOF) for CO oxidation significantly surpasses that of previously reported noble-metal-based catalysts, underscoring its superior efficiency. Dynamic analyses suggest that the enhanced catalytic activity is a result of the unique atom burr structure, which presents an extensive surface area replete with abundant active sites. This structural feature is instrumental in maximizing the catalyst’s interaction with CO molecules. Experimental findings, corroborated by density functional theory (DFT) calculations, elucidate the mechanism of CO oxidation on the Mn-NiO-0.5 catalyst. The process is facilitated by the synergistic action of bimetallic sites, where the Ni–OH site acts as the primary adsorption point for CO. Subsequently, the CO is oxidized to bicarbonate through the interaction with the oxygen (O or O2) at adjacent Mn sites. This pioneering study introduces a paradigm-shifting insight: the effectiveness of non-noble metal oxide catalysts can now compete with, and in some cases, outperform their noble metal counterparts. This breakthrough is set to transform the industry, presenting a compelling alternative to conventional noble metal catalysts and propelling the evolution of state-of-the-art environmental conservation technologies.

N, N’-bidentate ligand anchored palladium catalysts on MOFs for efficient Heck reaction

Metal-organic frameworks (MOFs), recognized as advanced catalyst carriers due to their adjustable porous, diverse structure and highly exposed active sites, have earned increasing attention for their potential to address the longevity of catalytic centers. In this manuscript, we have devised and synthesized a multifunctional amino-pyridine benzoic acid (APBA) ligand to replace the modulator ligand of the MOF-808 and disperse the palladium catalytic centers atomically on the MOF-APBA. The resulting single-site catalytic system, Pd@MOF-APBA, demonstrates preeminent efficiency and stability, as evidenced by a high average turnover number (95000) and a low metal residue (4.8 ppm) in the Heck reaction. This catalyst has exhibited recyclability for multiple runs without significant loss of reactivity for gram-scale reactions. The catalyst’s high activity and efficiency can be attributed to the suitable electrical properties and structures of the N, N’-bidentate ligand for the catalytic palladium ions, postponing their deactivations, including leaching and agglomeration.

High-Efficiency Solar Transformation of Sugars via a Heterogenous Gallium(III) Catalyst.

Extremely limited research exploring the photocatalytic potential of main group metals, such as aluminum, gallium, and tin, has been undertaken due to their weak light harvesting properties. This study reports the efficient transformation of sugars to 5-hydroxymethylfurfural (HMF) with high yield employing an original heterogeneous photocatalyst comprising a gallium(III) complex immobilized on an alumina support. Under visible light irradiation, the reaction rate of HMF formation is ~143 times higher than the equivalent thermal reaction performed in the absence of light. The turnover number (TON) of the heterogeneous gallium(III) photocatalyst was as high as 1500, which was ca. two orders of magnitude higher than the TON of the homogeneous gallium(III) system. It is proposed that photoirradiation significantly enhances the Lewis acidity of the catalyst by forming a semi-coordination state between gallium(III) and N-donor ligands, enabling the increased interaction of reactant sugar molecules with gallium(III) active sites. Consistent with this, the photoresponsive coordination of the gallium(III) complex and the abstraction of the hydroxy group by the metal under irradiation with visible light is observed by NMR spectroscopy for the first time. These findings demonstrate that efficient photocatalysts derived from the main group elements can facilitate biomass conversion using visible light.

High‐Efficiency Solar Transformation of Sugars via a Heterogenous Gallium(III) Catalyst

AbstractExtremely limited research exploring the photocatalytic potential of main group metals, such as aluminum, gallium, and tin, has been undertaken due to their weak light harvesting properties. This study reports the efficient transformation of sugars to 5‐hydroxymethylfurfural (HMF) with high yield employing an original heterogeneous photocatalyst comprising a gallium(III) complex immobilized on an alumina support. Under visible light irradiation, the reaction rate of HMF formation is ~143 times higher than the equivalent thermal reaction performed in the absence of light. The turnover number (TON) of the heterogeneous gallium(III) photocatalyst was as high as 1500, which was ca. two orders of magnitude higher than the TON of the homogeneous gallium(III) system. It is proposed that photoirradiation significantly enhances the Lewis acidity of the catalyst by forming a semi‐coordination state between gallium(III) and N‐donor ligands, enabling the increased interaction of reactant sugar molecules with gallium(III) active sites. Consistent with this, the photoresponsive coordination of the gallium(III) complex and the abstraction of the hydroxy group by the metal under irradiation with visible light is observed by NMR spectroscopy for the first time. These findings demonstrate that efficient photocatalysts derived from the main group elements can facilitate biomass conversion using visible light.

Architecture of bimodal porous CuO/Al2O3-controlled continuous and low-temperature production of biomass-derived γ-butyrolactone

Biomedical activities of gamma butyrolactone (GBL) play an important role in the development of novel physiological and therapeutic agents. Maleic anhydride catalytic liquid phase hydrogenation allows for selective synthesis of GBL. However, this process is hampered by high cost noble metals and high reaction pressure conditions. Here, we demonstrate cyclic dehydrogenation of biomass-derived 1,4-butanediol (1,4-BDO) under atmospheric pressure and low-temperature conditions using highly dispersed and chemically stabilized Cu species on bimodal porous Al2O3. The bimodal porous Al2O3 exhibited both Lewis and Brønsted acidic properties along with high specific surface area and large pore volume. Among prepared catalysts, 15 wt% Cu/Al2O3 catalyst has shown an optimal crystallite size, bimodal porous nature, and high diffusion properties. Hence, high catalytic activity and remarkable GBL yields with very high 1,4-BDO conversion for 50 h of continuous time-on-stream. The unique bimodal textural properties help to enhance the dehydrogenation activity with a high turnover frequency (TOF) of about 5.0118 x 10-3 s-1via efficient chemical interaction between metallic Cu and 1,4-BDO molecules.

Construction of N-Fe-S bridge in atomic iron catalyst for boosting Fenton-like reactions

Constructing the coordination environment of single-atom catalysts (SACs) can be an attractive technical strategy to regulate the generation of reactive oxygen species for Fenton-like reactions. Herein, we have constructed an asymmetric coordination of Fe single-atom catalyst (FeSA-NS-PCNS) with abundant N-Fe-S bridge (FeSA-N3S1) for robust Fenton-like reactions. 82.5 % of singlet oxygen (1O2) selectivity and high turnover frequency of bisphenol A degradation (0.568 min−1) were achieved at mild conditions. Experimental works and theoretical analyses illustrated that S doping breaks the inert environment of the original N-Fe-N symmetric coordination equilibrium and modulates the electron density of the atomic Fe center, which is beneficial for boosting PMS adsorption and reducing the energy barriers of vital *OH and *O intermediates. The coupling between the FeSA-N3S1 interface and peroxymonosulfate molecule boosts in-situ electron transfer through the N-Fe-S bridge, which induces more electron flow from the low valence Fe to OH* on the surface of Fe-*O-H, forming a high yield of 1O2. Moreover, we designed the Fenton-like reactions by FeSA-NS-PCNS membrane reactor for an efficient contaminant removal rate of over 90 % even after 11 cycles. This work provides a novel perspective on developing SACs with asymmetric coordination to regulate reactive oxygen species for the treatment of organic contaminants in water bodies.

A self‐powered system to electrochemically generate ammonia driven by palladium single atom electrocatalyst

AbstractThe utilization of single atoms (SAs) as trifunctional electrocatalyst for nitrogen reduction, oxygen reduction, and oxygen evolution reactions (NRR, ORR, and OER) is still a formidable challenge. Herein, we devise one‐pot synthesized palladium SAs stabilized on nitrogen‐doped carbon palladium SA electrocatalyst (Pd‐SA/NC) as efficient trifunctional electrocatalyst for NRR, ORR, and OER. Pd‐SA/NC performs a robust catalytic activity toward NRR with faradaic efficiency of 22.5% at −0.25 V versus reversible hydrogen electrode (RHE), and the relative Pd utilization efficiency is enhanced by 17‐fold than Pd‐NP/NC. In addition, the half‐wave potential reaches 0.876 V versus RHE, amounting to a 58‐time higher mass activity than commercial Pt/C. Moreover, the overpotential at 10 mA cm−2 is as low as 287 mV for Pd‐SA/NC, outperforming the commercial IrO2 by 360 times in turnover frequency at 1.6 V versus RHE. Accordingly, the assembled rechargeable zinc‐air battery (ZAB) achieves a maximum power density of 170 mW cm−2, boosted by 2.3 times than Pt/C–IrO2. Two constructed ZABs efficiently power the NRR‐OER system to electrochemically generate ammonia implying its superior trifunctionality.

Green Syngas Production from Natural Lignin, Sunlight, and Water over Pt‐Decorated InGaN Nanowires

AbstractTransformation of lignin to syngas can turn waste into treasure yet remains a tremendous challenge because of its naturally evolved stubborn structure. In this work, light‐driven reforming of natural lignin in water for green syngas production is explored using Pt‐decorated InGaN nanowires. The spectroscopic characterizations, isotope, and model compound experiments, as well as density function theory calculation, disclose that among a variety of groups including aromatic ring, −OH, −OCH3, −C3H7 with complex chemical bonds of O−H, C−H, C−C, C−O, etc., InGaN nanowires are cooperative with Pt for preferably breaking the C−O bond of the rich O−CH3 group in lignin to liberating ⋅CH3 by photogenerated holes with a minimum dissociation energy of 2.33 eV. Syngas are subsequently yielded from the continuous evolution of ⋅CH3 and ⋅OH from photocatalytic reforming of lignin in water. Together with the superior optoelectronic attributes of Pt‐decorated InGaN nanowires, the evolution rate of syngas approaches 43.4 mol ⋅ g−1 ⋅ h−1 with tunable H2/CO ratios and a remarkable turnover number (TON) of 150, 543 mol syngas per mol Pt. Notably, the architecture demonstrates a high light efficiency of 12.1 % for syngas generation under focused light without any extra thermal input. Outdoor test ascertains the viability of producing syngas with the only inputs of natural lignin, water, and sunlight, thus presenting a low‐carbon route for synthesizing transportation fuels and value‐added chemicals.

Tailoring Single‐Atom Coordination Environments in Carbon Nanofibers via Flash Heating for Highly Efficient Bifunctional Oxygen Electrocatalysis

The rational design of carbon‐supported transition metal single‐atom catalysts necessitates precise atomic positioning within the precursor. However, structural collapse during pyrolysis can occlude single atoms, posing significant challenges in controlling both their utilization and coordination environment. Herein, we present a surface atom adsorption‐flash heating (FH) strategy, which ensures that the pre‐designed carbon nanofiber structure remains intact during heating, preventing unforeseen collapse effects and enabling the formation of metal atoms in nano‐environments with either tetra‐nitrogen or penta‐nitrogen coordination at different flash heating temperatures. Theoretical calculations and in situ Raman spectroscopy reveal that penta‐nitrogen coordinated cobalt atoms (Co‐N5) promote a lower energy pathway for oxygen reduction and oxygen evolution reactions compared to the commonly formed Co‐N4 sites. This strategy ensures that Co‐N5 sites are fully exposed on the surface, achieving exceptionally high atomic utilization. The turnover frequency (65.33 s‐1) is 47.4 times higher than that of 20% Pt/C under alkaline conditions. The porous, flexible carbon nanofibers significantly enhance zinc‐air battery performance, with a high peak power density (273.8 mW cm‐2), large specific capacity (784.2 mA h g‐1), and long‐term cycling stability over 600 h. Additionally, the flexible fiber‐shaped zinc‐air battery can power wearable devices, demonstrating significant potential in flexible electronics applications.

Ni-Pt nanoparticle decorated, C, N-doped titania microparticles with low band gap energy as an efficient catalyst for hydrogen generation from hydrous hydrazine

The recent studies demonstrated superior catalytic activity and higher selectivity of carbon doped defect-rich catalysts in hydrogen production via dehydrogenation of hydrazine hydrate (HH). The synthesis of a new defect-rich catalyst capable of providing high hydrogen evolution rate in either catalytic or photocatalytic dehydrogenation of HH was aimed. For this purpose, “polymerization-induced colloid aggregation” (PICA) was proposed for the synthesis of carbon and nitrogen doped-mesoporous, gravel-like TiO2 microparticles (m-CN/TiO2 MPs) with a reduced band-gap energy of 2.3 eV. The Ti(III) content and oxygen vacancy concentration of pristine m-CN/TiO2 MPs were 6.06 % and 22.57 %, respectively. A defect-rich catalyst with high Ti(III) content (40.25 %) and high oxygen vacancy concentration (39.14 %) was obtained by the decoration of m-CN/TiO2 MPs with nickel-platinum nanoparticles (Ni-Pt NPs) via NaBH4 reduction (Ni-Pt/m-CN/TiO2 MPs) for the first time. The charge unbalance stimulated by Ti(III) species supported the formation of oxygen vacancies on m-CN/TiO2 MPs. The unique approach based on the synthesis of a C, N doped-mesoporous TiO2 based support by PICA and the deposition of Ni-Pt NPs by NaBH4 reduction in the presence of m-CN/TiO2 MPs allowed to obtain a heterogeneous catalyst with a low band energy of 1.7 eV for hydrogen production. The turnover frequency (TOF) values up to 1140.7 h−1 were achieved with 100 % H2 selectivity using the catalyst containing an active metallic site composed of 78.3 % mol Ni and 21.7 % mol Pt on m-CN/TiO2 MPs in the catalytic dehydrogenations performed at 323 K. The TOF values up to 530 h−1 with 100 % H2 selectivity were obtained by using Ni-Pt/m-CN/TiO2 MPs as a photocatalyst in the visible light driven photocatalytic dehydrogenation of HH at room temperature.

Tailoring Single-Atom Coordination Environments in Carbon Nanofibers via Flash Heating for Highly Efficient Bifunctional Oxygen Electrocatalysis.

The rational design of carbon-supported transition metal single-atom catalysts necessitates precise atomic positioning within the precursor. However, structural collapse during pyrolysis can occlude single atoms, posing significant challenges in controlling both their utilization and coordination environment. Herein, we present a surface atom adsorption-flash heating (FH) strategy, which ensures that the pre-designed carbon nanofiber structure remains intact during heating, preventing unforeseen collapse effects and enabling the formation of metal atoms in nano-environments with either tetra-nitrogen or penta-nitrogen coordination at different flash heating temperatures. Theoretical calculations and in situ Raman spectroscopy reveal that penta-nitrogen coordinated cobalt atoms (Co-N5) promote a lower energy pathway for oxygen reduction and oxygen evolution reactions compared to the commonly formed Co-N4 sites. This strategy ensures that Co-N5 sites are fully exposed on the surface, achieving exceptionally high atomic utilization. The turnover frequency (65.33 s-1) is 47.4 times higher than that of 20 % Pt/C under alkaline conditions. The porous, flexible carbon nanofibers significantly enhance zinc-air battery performance, with a high peak power density (273.8 mW cm-2), large specific capacity (784.2 mAh g-1), and long-term cycling stability over 600 h. Additionally, the flexible fiber-shaped zinc-air battery can power wearable devices, demonstrating significant potential in flexible electronics applications.

One-Pot Preparation of Nitro-Functionalized Bimetallic UiO-66(Zr-Hf) with Hierarchical Porosity for Oxidative Desulfurization Performance.

Preparation of multifunctional metal-organic frameworks (MOFs) offers new opportunities to obtain ultrahigh synergistic catalytic performance for heterogeneous reactions; however, the application of a one-pot method for preparing multifunctional MOFs remains challenging. Herein, we develop a one-pot green route for synthesizing bimetallic nitro-functionalized UiO-66(Zr-Hf)-NO2 with hierarchical porosity under solvent-free conditions. The optimal UiO-66(Zr-Hf0.6)-NO2 shows an ultrahigh enhancement of oxidative desulfurization (ODS) efficiency to oxidize sulfur compounds (1000 ppm sulfur) in a model fuel at 40 °C within 12 min due to the introduction of more active Hf sites in the nodes, the increased Lewis acidity of Zr/Hf-O nodes by the electron-withdrawing NO2 group, and the enhanced diffusion rates by the mesopores. The turnover frequency (TOF) over UiO-66(Zr-Hf0.6)-NO2 at 40 or 50 °C reaches 145.3 or 217.0 h-1 that surpasses the TOF of most reported MOF-based catalysts in the ODS reaction. Quenching and electron paramagnetic resonance experiments confirm that the formed Hf-OH on the Zr/Hf-O nodes can easily decompose the oxidant (H2O2) for generating a Hf-OOH-active intermediate and dominate the ODS efficiency. This contribution provides a one-pot solvent-free avenue to synthesize multifunctional MOFs for enhancing their catalytic activities for targeted applications.

Catalytic efficiency and kinetic analysis of manganese Polyoxometalate Heterogenized in MIL-100-Fe for selective Olefin oxidation using H2O2

In our previous study, we introduced a heterogeneous catalyst, denoted as H5[PMo11MnO39(H2O)]0.30@ [Fe3O(OH)(H2O)2[C6H3(CO2)3]2·8H2O (C1), through the encapsulation of a homogeneous polyoxometalate, H5[PMo11Mn(H2O)O39] (MnP), within a metal–organic framework [Fe3O(OH)(H2O)2[C6H3(CO2)3]2·14H2O (MIL-100-Fe). In the present study, we utilized the same catalyst for the oxidation of cyclohexene (CyH), cis-cyclooctene (CyO), styrene (Sty), and geraniol (Ger) in acetonitrile, employing H2O2 as a green oxidant. Kinetic studies were carried out to investigate the influence of substrate, H2O2, catalyst concentration, reaction time, temperature, and total H2O2 decompositions on oxidation and selectivity. C1 exhibited significantly higher efficiency in catalyzing the allylic oxidation of all substrates compared to individual components MnP and MIL-100-Fe, in terms of conversion percentage, rate constants, turnover numbers (TONs), H2O2 efficiencies, and product selectivity. Under optimized conditions, C1 achieved overall conversions of 85 %, 96 %, 98 %, and 100 % for CyH, CyO, Sty, and Ger, respectively. The harmonious catalytic function of polyoxometalates (POM) and metal-organic frameworks (MOF) in C1 also reduced the auto-decomposition of H₂O₂ which resulted into higher H2O2 efficiencies. Notably, the catalyst exhibited complete recoverability and reusability without any structural changes or loss of activity.

Iron Corrole-Catalyzed Intramolecular Amination Reactions of Alkyl Azides. Spectroscopic Characterization and Reactivity of [FeV(Cor)(NAd)

As nitrogen analogues of iron-oxo species, high-valent iron-imido species have attracted great interest in the past decades. FeV-alkylimido species are generally considered to be key reaction intermediates in Fe(III)-catalyzed C(sp3)─H bond aminations of alkyl azides but remain underexplored. Here, it is reported that iron-corrole (Cor) complexes can catalyze a wide range of intramolecular C─H amination reactions of alkyl azides to afford a variety of 5-, 6- and 7-membered N-heterocycles, including alkaloids and natural product derivatives, with up to 3880 turnover numbers (TONs) and excellent diastereoselectivity (>99:1d.r.). Mechanistic studies including density functional theory (DFT) calculations and intermolecular hydrogen atom abstraction (HAA) reactions reveal key reactive FeV-alkylimido intermediates. The [FeV(Cor)(NAd)] (Ad = adamantyl) complex is independently prepared and characterized through electron paramagnetic resonance (EPR), resonance Raman (rR) measurement, and X-ray photoelectron spectroscopy (XPS). This complex is reactive toward HAA reactions with kinetic isotope effects (KIEs) similar to [Fe(Cor)]-catalyzed intramolecular C─H amination of alkyl azides.

Highly Efficient and Robust Platinum Nanocluster Catalyst Mediated by Polyamine Amidine‐Decorated Mesoporous Polymer Beads

AbstractPlatinum nanoclusters (PtNCs) are promising in catalysis due to their large specific surface area and unique physicochemical properties. Here, ultrasmall and uniform PtNCs are facilely synthesized with the mediation of amidine‐functionalized polyamines patched on mesoporous poly(divinylbenzene‐4‐vinylbenzyl chloride) beads. When each ligand patch has 14 amidines, ultrafine PtNCs (with the size as low as 1.1±0.1 nm) are formed as a result of several factors: deprotonated amidines (carbenes) strongly passivate on Pt atoms, amidines act as co‐stabilizers along with weak polyamine ligands, and PtNCs are confined to discrete ligand patches. When one ligand patch contains 9.3 amidines, the resulting PtNCs (1.7±0.3 nm) reach the highest turnover frequency of 536 h−1 for the catalytic reduction of 4‐nitrophenol in a batch reaction. This catalyst remains rather stable in a continuous flow test as a 4‐nitrophenol conversion of over 95 % is still achieved after running consecutively for 10 h.