Double Dehydrogenation of Primary Amines to Nitriles by a Ruthenium Complex Featuring Pyrazole Functionality

Electrocatalytic Anaerobic Oxidation of Benzylic Amines Enabled by Ferrocene-Based Redox Mediators

The generation and functionalization of carbon- or nitrogen-centered radicals are of great interest for their potential synthetic utility. Here, we report the anaerobic electrocatalytic oxidation of two primary benzylic amines, benzylamine and 2-picolylamine, in the presence of a catalytic quantity of an electron deficient ferrocene derivative as a single-electron redox mediator. The use of the appropriate redox mediator prevented fouling of the electrode surface and significantly decreased the potential at which the catalytic oxidation reaction occurred. Simulation of the electrochemical results revealed an ErCi' catalytic process between the redox mediator and both substrates and significant difference in the electron transfer rate between the two substrates and electrochemically oxidized mediator. Through anaerobic controlled-potential electrolysis, we demonstrated a method with a Faradaic efficiency of 90% forming the desired coupled imine product of benzylamine oxidation while avoiding an excess of problematic overoxidation, hydrolysis, and other side reactions. Based on the electrochemical data along with the product analyses using IR and 1H and 13C NMR spectroscopies, the proposed mechanistic steps for the redox mediated electrocatalytic process were laid out.

Unlocking Lattice Oxygen on Selenide-Derived NiCoOOH for Amine Electrooxidation and Efficient Hydrogen Production

In pursuit of advancing the electrooxidation of amines, which is typically encumbered by the inertness of C(sp3)-H/N(sp3)-H bonds, our study introduces a high-performance electrocatalyst that significantly enhances the production efficiency of vital chemicals and fuels. We propose a novel electrocatalytic strategy employing a uniquely designed (NixCo1-x)Se2-R electrocatalyst, which is activated through Se-O exchange and electron orbital spin manipulation. This catalyst efficiently generates M4+ species, thus enabling the activation of lattice oxygen and streamlining the electrooxidation of amines. Empirical evidence from isotope labeling, molecular probes, and computational analyses indicates that the electrocatalyst fosters the formation of energetically favorable peroxy radical intermediates, which substantially expedite the reaction kinetics. The refined electrocatalyst achieves an exceptional current density of 20 mA cm-2 at a potential of 1.315 V, with selectivity surpassing 99% for propionitrile, while demonstrating remarkable stability over 560 h. This work emphasizes the criticality of deciphering the fundamental mechanisms of amine electrooxidation and charts a more sustainable pathway for the nitrile and hydrogen production, marking a substantial advancement in the field of electrocatalysis.

Electrochemically Driven Denitrative Cyanation of Nitroarenes

A practical denitrative cyanation of feedstock nitroarenes under mild and transition metal-free reaction conditions has been developed. The key to success lies in the use of electrochemically driven, inexpensive ionic liquid N-methylimidazolium p-toluenesulfonate-promoted selective cathode reduction of nitroarenes to anilines, followed by diazoation, cathode reduction to form the aryl radical, and the essential radical cyanation process in one pot. Our protocol shows broad functional group tolerance and can be applied for the modification of bioactive targets.

Asymmetric synthesis of atropisomeric arylpyrazoles via direct arylation of 5-aminopyrazoles with naphthoquinones

Construction of axially chiral arylpyrazoles represents an attractive challenge due to the relatively low rotational barrier of biaryl structures containing five-membered heterocycles. This work describes the catalytic asymmetric construction of axially chiral arylpyrazoles using 5-aminopyrazoles and naphthoquinone derivatives. The chiral axis could be formed through a central-to-axial chirality relay step of the chiral phosphoric acid-catalyzed arylation reaction, which features excellent yields and enantioselectivities with a broad substrate scope under mild reaction conditions.

Computational design of cooperatively acting molecular catalyst systems: carbene based tungsten- or molybdenum-catalysts with rhodium- or iridium-complexes for the ionic hydrogenation of N2 to NH3

This density functional theory (DFT) study explores the efficacy of cooperative catalytic systems in enabling the ionic hydrogenation of N2 with H2, leading to NH3 formation. A set of N-heterocyclic carbene-based pincer tungsten/molybdenum metal complexes of the form [(PCP)M1(H)2] (M1 = W/Mo) were chosen to bind N2 at the respective metal centres. Simultaneously, cationic rhodium/iridium complexes of type [Cp*M2{2-(2-pyridyl)phenyl}(CH3CN)]+ (Cp* = C5(CH3)5 and M2 = Rh/Ir), are employed as cooperative coordination partners for heterolytic H2 splitting. The stepwise transfer of protons and hydrides to the bound N2 and intermediate NxHy units results in the formation of NH3. Interestingly, the calculated results reveal an encouraging low range of energy spans ranging from ∼30 to 42 kcal mol-1 depending on different combinations of ligands and metal complexes. The optimal combination of pincer ligand and metal center allowed for an energy span of unprecedented 29.7 kcal mol-1 demonstrating significant potential for molecular catalysts for the N2/H2 reaction system. While exploring obvious potential off-cycle reactions leading to catalyst deactivation, the computed results indicate that no increase in energy span would need to be expected.

Cobalt-Catalyzed Acceptorless Dehydrogenation of Primary Amines to Nitriles

The direct double dehydrogenation from primary amines to nitriles without an oxidant or hydrogen acceptor is both intriguing and challenging. In this paper, we describe a non-noble metal catalyst capable of realizing such a transformation with high efficiency. A cobalt-centered N,N-bidentate complex was designed and employed as a metal-ligand cooperative dehydrogenation catalyst. Detailed kinetic studies, control experiments, and DFT calculations revealed the crucial hydride transfer, proton transfer, and hydrogen evolution processes. Finally, a tandem outer-sphere/inner-sphere mechanism was proposed for the dehydrogenation of amines to nitriles through an imine intermediate.

Palladium-catalyzed dehydrogenation of α-cyclohexene-substituted nitriles to α-aryl nitriles

The development of a practical, inexpensive, and cyanide-free method for synthesizing α-aryl nitriles remains a challenging goal in synthetic chemistry. Here, we report an approach for synthesizing α-aryl nitriles toward achieving this goal, by which α-cyclohexenyl acetonitriles and α-cyclohexenyl alkenyl nitriles are dehydrogenated to α-aryl nitriles.

Thermodynamic evaluations of the acceptorless dehydrogenation and hydrogenation of pre-aromatic and aromatic N-heterocycles in acetonitrile

N-heterocycles are important chemical hydrogen-storage materials, and the acceptorless dehydrogenation and hydrogenation of N-heterocycles as organic hydrogen carriers have been widely studied, with the main focus on the catalyst synthesis and design, investigation of the redox mechanisms, and extension of substrate scope. In this work, the Gibbs free energies of the dehydrogenation of pre-aromatic N-heterocycles (YH2) and the hydrogenation of aromatic N-heterocycles (Y), i.e., ΔGH2R(YH2) and ΔGH2A(Y), were derived by constructing thermodynamic cycles using Hess' law. The thermodynamic abilities for the acceptorless dehydrogenation and hydrogenation of 78 pre-aromatic N-heterocycles (YH2) and related 78 aromatic N-heterocycles (Y) were well evaluated and discussed in acetonitrile. Moreover, the applications of the two thermodynamic parameters in identifying pre-aromatic N-heterocycles possessing reversible dehydrogenation and hydrogenation properties and the selection of the pre-aromatic N-heterocyclic hydrogen reductants in catalytic hydrogenation were considered and are discussed in detail. Undoubtedly, this work focuses on two new thermodynamic parameters of pre-aromatic and aromatic N-heterocycles, namely ΔGH2R(YH2) and ΔGH2A(Y), which are important supplements to our previous work to offer precise insights into the chemical hydrogen storage and hydrogenation reactions of pre-aromatic and aromatic N-heterocycles.

Recent advances in ring-opening of cyclobutanone oximes for capturing SO2, CO or O2via a radical process

Cyclobutanone oximes and their derivatives are pivotal core structural motifs in organic chemistry. Iminyl-radical-triggered C-C bond cleavage of cyclobutanone oximes delivers an efficient strategy to produce stable distal cyano-substituted alkyl radicals, which can capture SO2, CO or O2 to form cyanoalkylsulfonyl radicals, cyanoalkylcarbonyl radicals or cyanoalkoxyl radicals under mild conditions. In the past several years, cyanoalkylsulfonylation/cyanoalkylcarbonyaltion/cyanoalkoxylation has attracted a lot of interest. In this updated report, the strategies for trapping SO2, CO or O2via iminyl-radical-triggered ring-opening of cyclobutanone oximes are summarized.

Asymmetric Synthesis of Axially Chiral Arylpyrazole via an Organocatalytic Arylation Reaction

Herein, a highly enantioselective arylation reaction of 3-aryl-5-aminopyrazoles and quinone derivatives was realized using a chiral phosphoric acid catalyst under mild conditions. The reaction has a broad scope with respect to both arylation reaction partners and hence offers rapid access to an array of axially chiral arylpyrazoles with pretty outcomes (up to 95% yield and 99% ee). Notably, the reaction is very efficient, as the catalyst loadings for the model reaction can be reduced to 1 mol % and the enantioselectivity is still maintained. Besides, the synthetic utility of the protocol was proven by a gram-scale reaction and the transformation of the product.

Synchronous Proton-Hydride Transfer by a Pyrazole-Functionalized Protic Mn(I) Complex in Catalytic Alcohol Dehydrogenative Coupling

A series of Mn(I) complexes Mn(L1 )(CO)3 Br, Mn(L2 )(CO)3 Br, Mn(L1 )(CO)3 (OAc) and Mn(L3 )(CO)3 Br [L1 =2-(5-tert-butyl-1H-pyrazol-3-yl)-1,8-naphthyridine, L2 =2-(5-tert-butyl-1H-pyrazol-3-yl)pyridine, L3 =2-(5-tert-butyl-1-methyl-1H-pyrazol-3-yl)-1,8-naphthyridine] were synthesized and fully characterized. The acid-base equilibrium between the pyrazole and the pyrazolato forms of Mn(L1 )(CO)3 Br was studied by 1 H NMR and UV-vis spectra. These complexes are screened as catalysts for acceptorless dehydrogenative coupling (ADC) of primary alcohols and aromatic diamines for the synthesis of benzimidazole and quinoline derivatives with the release of H2 and H2 O as byproducts. The protic complex Mn(L1 )(CO)3 Br shows the highest catalytic activity for the synthesis of 2-substituted benzimidazole derivatives with broad substrate scope, whereas a related complex [Mn(L3 )(CO)3 Br], which is devoid of the proton responsive β-NH unit, shows significantly reduced catalytic efficiency validating the crucial role of the β-NH functionality for the alcohol dehydrogenation reactions. Control experiments, kinetic and deuterated studies, and density functional theory (DFT) calculations reveal a synchronous hydride-proton transfer by the metal-ligand construct in the alcohol dehydrogenation step.

Ammonolytic transfer dehydrogenation of amines and amides: a versatile method to valorize nitrogen compounds to nitriles

The dehydrogenation of amines has been identified as an efficient method for nitrile synthesis. At present, this approach is restricted to (oxidative) dehydrogenations of primary amines, most often with specialized homogeneous catalysts. In this work, amines were transfer dehydrogenated to nitriles using simple and cheap alkenes (e.g. ethylene or propene) as hydrogen scavengers. The scope was expanded to secondary amines, tertiary amines and even aldehydes. Additional nitrogen is built in from NH3. The versatility of the process was proven by coupling it to the ammonolysis of secondary amides. This enabled us to recycle long-chain polyamides (LCPA) into monomeric compounds, i.e. α,ω-amidonitriles and dinitriles. Reactions were performed with a recyclable heterogeneous Pt catalyst, at 200 °C and with limited addition of NH3 and ethylene. High yields of up to 94% were obtained for the corresponding nitriles.

Recent Developments in Reactions and Catalysis of Protic Pyrazole Complexes

Protic pyrazoles (N-unsubstituted pyrazoles) have been versatile ligands in various fields, such as materials chemistry and homogeneous catalysis, owing to their proton-responsive nature. This review provides an overview of the reactivities of protic pyrazole complexes. The coordination chemistry of pincer-type 2,6-bis(1H-pyrazol-3-yl)pyridines is first surveyed as a class of compounds for which significant advances have made in the last decade. The stoichiometric reactivities of protic pyrazole complexes with inorganic nitrogenous compounds are then described, which possibly relates to the inorganic nitrogen cycle in nature. The last part of this article is devoted to outlining the catalytic application of protic pyrazole complexes, emphasizing the mechanistic aspect. The role of the NH group in the protic pyrazole ligand and resulting metal-ligand cooperation in these transformations are discussed.

Catalyst Comparison for Additive-Free Acceptorless Dehydro­genation of Indoline Derivatives

A group of thirteen catalysts of type [Ru(Cp/Cp*)(P–P)(MeCN)]PF6, bearing cooperative or noncooperative bidentate phosphine ligands, were evaluated for the catalytic acceptorless dehydrogenation of indoline. The systematic comparison revealed that the optimal cooperative catalyst structure included a Cp ancillary ligand, and an N,N-disubstituted P,P-disubstituted 1,5-diaza-3,7-diphosphacyclooctane ligand, denoted as (PR 2NR′ 2). A cooperative complex bearing a PPh 2NPh 2 ligand exhibited about a twofold longer lifetime than a noncooperative analogue with (diphenylphosphino)ethane (dppe) as the supporting bisphosphine ligand. The cooperative catalyst effectively dehydrogenated a range of indoline substrates to give substituted indoles.

The stable "F-SO2 +" donor provides a mild and efficient approach to nitriles and amides

In this update, we developed a mild, efficient and practical method using fluorosulfuryl imidazolium salt A as an environment friendly promoter for conversion of oximes to nitriles or amides via β-elimination or Beckmann rearrangement in almost quantitative yield in 10 minutes. The target products were generated in gram-scale and could be collected through crystallization without silica gel column purification in excellent yield.

Acceptorless Dehydrogenation of Aliphatics, Amines, and Alcohols with Homogeneous Catalytic Systems

The dehydrogenation of saturated substrates is fundamentally essential for producing value-added unsaturated organic molecules both in academia and industry. In recent years, homogeneously catalyzed acceptorless C–C, C–N, and C–O bond desaturations have attracted increasing attention due to high atom economy, environmentally benign nature, and wide availability of the starting materials. This short review discusses the acceptorless dehydrogenation of aliphatics, alcohols, and amines by homogeneous catalytic systems based on two categories of reaction mechanisms: thermal transition-metal-catalyzed two-electron pathway and photoredox catalyzed or electrochemically driven one-electron pathway.

1 Introduction

2 Catalytic Acceptorless Dehydrogenation of Aliphatics

3 Catalytic Acceptorless Dehydrogenation of Amines

4 Catalytic Acceptorless Dehydrogenation of Alcohols

5 Conclusion

Facile Conversion of Aryl Amines Having No α-Methylene to Aryl Nitriles

Dimethyl carbonimidodithioates, 2 derived from various primary aryl amines (1) by reacting with carbon disulfide and methyl iodide in dimethyl formamide in the presence of concentrated sodium hydroxide, are converted to the diaziridine derivatives, 3 by reacting with hydrazine in ethanol. The diaziridines, 3 on oxidation with lead tetraacetate in refluxing xylene, extrudes nitrogen, and intramolecular stabilization, particularly 1,2-carbon migration, takes place to give the product, 5. The reaction may take place through the intermediates, diazirines, 4, which have not been isolated. This work provides a new approach for the conversion of aryl amines having no α-methylene to aryl nitriles.

In Situ Chalcogen Leaching Manipulates Reactant Interface toward Efficient Amine Electrooxidation

Engineering the reaction interface is necessary for advancing various electrocatalytic processes. However, most designed catalysts tend to be ineffective due to the inevitable structural reconstruction. Here we utilize that operando electrocatalysis variations (i.e., chalcogen leaching) manipulate the reactant interface toward amine electrooxidation. Taking chalcogen-doped Ni(OH)₂ as an example, operando techniques uncover that chalcogens leach from the matrix and then adsorb on the surface of NiOOH as chalcogenates during the electrooxidation process. The charged chalcogenates will induce the local electric field that pushes the polar amines through the inner Helmholtz plane to enrich on the catalyst surface. Meanwhile, the polarization effect of chalcogenates and amines boost amino C-N bond activation for dehydrogenation into nitrile C≡N bonds. Under the promotion effect of surface-adsorbed chalcogenate ions, our catalysts display over 99.5% propionitrile selectivity at the low potential of 1.317 V with an ultrahigh current density. This finding highlights the use of operando changes of catalysts to rationally design efficient catalysts and further clarifies the underlying role of chalcogen atoms in the electrooxidation process.

Metal-Free Boron-Mediated ortho-C-H Hydroxylation of N-Benzyl-3,4,5-tribromopyrazoles

A novel route has been reported for C-H hydroxylation of benzyl compounds directed by a 3,4,5-tribromopyrazole auxiliary via boronation/oxidation using BBr₃ and NaBO₃·4H₂O. The strategy exhibits outstanding site selectivity and affords the corresponding phenols in moderate to excellent yields under metal-free conditions. Besides, this protocol can be achieved in one pot, which is highly promising as a practical method for use in a multistep organic synthetic process.

NHC-BIAN-Cu(I)-Catalyzed Friedländer-Type Annulation of 2-Amino-3-(per)fluoroacetylpyridines with Alkynes on Water

The direct catalytic alkynylation/dehydrative cyclization of 2-amino-3-trifluoroacetyl-pyridines on water was developed for the efficient synthesis of a broad range of fluorinated 1,8-naphthyridines from terminal alkynes. A novel N-heterocyclic carbene (NHC) ligand system that combines a π-extended acenaphthylene backbone with sterically bulky pentiptycene pendant groups was successfully utilized in a copper- or silver-mediated cyclization. Computational analysis of the reaction pathway supports our explanation of the different experimental conversions and yields for the set of copper and silver catalysts. The impact of steric hindrance at the metal center and the flexibility of substituents on the imidazole ring of the NHC on catalytic performance are also discussed.

Efficient iron single-atom catalysts for selective ammoxidation of alcohols to nitriles

Zeolitic imidazolate frameworks derived Fe₁-N-C catalysts with isolated single iron atoms have been synthesized and applied for selective ammoxidation reactions. For the preparation of the different Fe-based materials, benzylamine as an additive proved to be essential to tune the morphology and size of ZIFs resulting in uniform and smaller particles, which allow stable atomically dispersed Fe-N₄ active sites. The optimal catalyst Fe₁-N-C achieves an efficient synthesis of various aryl, heterocyclic, allylic, and aliphatic nitriles from alcohols in water under very mild conditions. With its chemoselectivity, recyclability, high efficiency under mild conditions this new system complements the toolbox of catalysts for nitrile synthesis, which are important intermediates with many applications in life sciences and industry.

Nitrile Synthesis via Desulfonylative-Smiles Rearrangement

Herein, we designed a simple nitrile synthesis from N-[(2-nitrophenyl)sulfonyl]benzamides via base-promoted intramolecular nucleophilic aromatic substitution. The process features redox-neutral conditions as well as no requirement of toxic cyanide species and transition metals. Our process shows broad scope and various functional group compatibility, affording a variety of (hetero)aromatic nitriles in good to excellent yields.

Cyanation and cyanomethylation of trimethylammonium salts via electrochemical cleavage of C–N bonds

A practical and mild electrochemical protocol for cyanation and cyanomethylation of trimethylammonium salts has been developed.

A general and practical bifunctional cobalt catalytic system for N-heterocycle assembly via acceptorless dehydrogenation

A novel and highly-efficient N-heterocycle assembly methodology catalyzed by a cobalt-N,N-bidentate complex via acceptorless dehydrogenation coupling of alcohols and amines has been established.

Regioselective Synthesis of C3-Hydroxyarylated Pyrazoles

Pyrazoles are ubiquitous structures in medicinal chemistry. We report the first regioselective route to C3-hydroxyarylated pyrazoles obtained through reaction of pyrazole N-oxides with arynes using mild conditions. Importantly, this method does not require the C4 and C5 positions of the pyrazole to be functionalized to observe regioselectivity. Using this method, we completed the synthesis of a recently reported JAK 1/2 inhibitor. Our synthesis produces the desired product in 4 steps from commercially available starting materials.

Targeted Regulation of the Electronic States of Nickel Toward the Efficient Electrosynthesis of Benzonitrile and Hydrogen Production

Highly efficient electro-oxidation of benzylamine to generate value-added chemicals coupled with the hydrogen evolution reaction (HER) is crucial but challenging. Herein, targeted regulation of the electronic states of Ni sites was realized via simple yet precise nitridation engineering. Benefiting from the insertion of N atoms into the Ni lattice, the Ni₃N electrode exhibits superior activity, selectivity, and stability for the benzylamine oxidation reaction (BOR). Especially, under the industrially relevant current (∼250 mA), the Ni₃N catalyst remains ∼95% selective for benzonitrile production, reaching 1.43 mmol h^-1 cm^-2. Experimental and theoretical findings reveal that the formation of Ni-N bonds upshifts the Ni d-band center and optimizes the electrophilic properties of Ni sites, which contributes to the adsorption and dehydrogenations process of benzylamine. Furthermore, due to the work function difference between Ni and Ni₃N, a strong mutual interaction occurs at the heterogeneous interface for Ni-Ni₃N, which endows it with the appropriate H* adsorption energy and thus excellent HER performance. Impressively, the integrated solar-energy-driven BOR coupled with the HER electrolyzer affords 10 mA cm^-2 at an ultralow voltage of 1.4 V and exhibits a promising practical application (η_{solar-to-hydrogen} = 13.8%). This work offers a new perspective for the bifunctional design of nitrides in the field of electrosynthesis.

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.

Atomically Dispersed Co Clusters Anchored on N-doped Carbon Nanotubes for Efficient Dehydrogenation of Alcohols and Subsequent Conversion to Carboxylic Acids

The catalytic dehydrogenation of readily available alcohols to high value-added carbonyl compounds is a research hotspot with scientific significance. Most of the current research about this reaction is performed with noble metal-based homogeneous catalysts of high price and poor reusability. Herein, highly dispersed Co-cluster-decorated N-doped carbon nanotubes (Co/N-CNTs) were fabricated via a facile strategy and used for the dehydrogenation of alcohols with high efficiency. Various characterization techniques confirmed the presence of metallic Co clusters with almost atomic dispersion, and the N-doped carbon supports also enhanced the catalytic activity of Co clusters in the dehydrogenation reaction. Aldehydes as dehydrogenation products were further transformed in situ to carboxylic acids through a Cannizzaro-type pathway under alkaline conditions. The reaction pathway of the dehydrogenation of alcohols was clearly confirmed by theoretical calculations. This work should provide an effective and simple approach for the accurate design and synthesis of small Co-clusters catalysts for the efficient dehydrogenation-based transformation of alcohols to carboxylic acids under mild reaction conditions.

Ni-Catalyzed radical cyclization of vinyl azides with cyclobutanone oxime esters to access cyanoalkyl containing quinoxalin-2(1H)-ones

A nickel-catalyzed cascade addition/cyclization of 2-azido-N-arylacrylamides and cyclobutanone oxime esters for the construction of 3-cyanoalkylated quinoxalin-2(1H)-ones is developed. This reaction proceeds under mild conditions with good functional group tolerance and broad substrate scope. A preliminary mechanistic experiment indicated that the cyanoalkyl radical might be involved in this transformation.

Multiple N-H and C-H Hydrogen Atom Abstractions Through Coordination-Induced Bond Weakening at Fe-Amine Complexes

We report the use of the reported Fe-phthalocyanine complex, PcFe (1; Pc = 1,4,8,11,15,18,22,25-octaethoxy-phthalocyanine), to generate PcFe-amine complexes 1-(NH₃)₂, 1-(MeNH₂)₂, and 1-(Me₂NH)₂. Treatment of 1 or 1-(NH₃)₂ to an excess of the stable aryloxide radical, 2,4,6-tritert-butylphenoxyl radical (^tBuArO^•), under NH₃ resulted in catalytic H atom abstraction (HAA) and C-N coupling to generate the product 4-amino-2,4,6-tritert-butylcyclohexa-2,5-dien-1-one (2) and ^tBuArOH. Exposing 1-(NH₃)₂ to an excess of the trityl (CPh₃) variant, 2,6-di-tert-butyl-4-tritylphenoxyl radical (^TrArO^•), under NH₃ did not lead to catalytic ammonia oxidation as previously reported in a related Ru-porphyrin complex. However, pronounced coordination-induced bond weakening of both α N-H and β C-H in the alkylamine congeners, 1-(MeNH₂)₂ and 1-(Me₂NH)₂, led to multiple HAA events yielding the unsaturated cyanide complex, 1-(MeNH₂)(CN), and imine complex, 1-(MeN═CH₂)₂, respectively. Subsequent C-N bond formation was also observed in the latter upon addition of a coordinating ligand. Detailed computational studies support an alternating mechanism involving sequential N-H and C-H HAA to generate these unsaturated products.

Efficient photocatalytic hydrogen peroxide generation coupled with selective benzylamine oxidation over defective ZrS3 nanobelts

Photocatalytic hydrogen peroxide (H₂O₂) generation represents a promising approach for artificial photosynthesis. However, the sluggish half-reaction of water oxidation significantly limits the efficiency of H₂O₂ generation. Here, a benzylamine oxidation with more favorable thermodynamics is employed as the half-reaction to couple with H₂O₂ generation in water by using defective zirconium trisulfide (ZrS₃) nanobelts as a photocatalyst. The ZrS₃ nanobelts with disulfide (S₂^2-) and sulfide anion (S^2-) vacancies exhibit an excellent photocatalytic performance for H₂O₂ generation and simultaneous oxidation of benzylamine to benzonitrile with a high selectivity of >99%. More importantly, the S₂^2- and S^2- vacancies can be separately introduced into ZrS₃ nanobelts in a controlled manner. The S₂^2- vacancies are further revealed to facilitate the separation of photogenerated charge carriers. The S^2- vacancies can significantly improve the electron conduction, hole extraction, and kinetics of benzylamine oxidation. As a result, the use of defective ZrS₃ nanobelts yields a high production rate of 78.1 ± 1.5 and 32.0 ± 1.2 μmol h^-1 for H₂O₂ and benzonitrile, respectively, under a simulated sunlight irradiation.

Oxidize Amines to Nitrile Oxides: One Type of Amine Oxidation and Its Application to Directly Construct Isoxazoles and Isoxazolines

A facile oxidative heterocyclization of commercially available amines and tert-butyl nitrite with alkynes or alkenes leading to isoxazoles or isoxazolines is described. The unprecedented strategy of the oxidation of an amine directly to a nitrile oxide was used in this cyclization process. This reaction is highly efficient, regiospecific, operationally simple, mild, and tolerant of a variety of functional groups. Control experiments support a nitrile oxide intermediate mechanism for this novel class of oxidative cyclization reactions. Moreover, synthetic applications toward bioactive molecular skeletons and the late-stage modification of drugs were realized.

Selective Acceptorless Dehydrogenation of Primary Amines to Imines by Core-Shell Cobalt Nanoparticles

Core-shell nanocatalysts are attractive due to their versatility and stability. Here, we describe cobalt nanoparticles encapsulated within graphitic shells prepared via the pyrolysis of a cationic poly-ionic liquid (PIL) with a cobalt(II) chloride anion. The resulting material has a core-shell structure that displays excellent activity and selectivity in the self-dehydrogenation and hetero-dehydrogenation of primary amines to their corresponding imines. Furthermore, the catalyst exhibits excellent activity in the synthesis of secondary imines from substrates with various reducible functional groups (C=C, C≡C and C≡N) and amino acid derivatives.