Oxidative Coupling Of Primary Amines Research Articles

Unprecedented Selective Synthesis of Imines by Photocatalytic Oxidative Coupling of Primary Amines under N2O Atmosphere**

AbstractIn a climate change context, N2O contributes to global warming with CO2 and CH4. As an inert molecule, its upgrading as oxidant still constitutes a challenge in chemical synthesis. Here, the synthesis of imines was unprecedently performed using nitrous oxide (N2O) as a novel and highly selective oxidative agent for the photocatalytic homo‐coupling of amines. In a similar way, unsymmetric imines were produced through cross‐coupling of amines with alcohols. Promisingly, this greenhouse gas showed excellent performances towards the target reactions when photocatalytically activated at atmospheric pressure, with silver photodeposited on titanium dioxide as catalyst. Relevantly, reactions under N2O atmosphere exhibited high conversion rates and turn‐over frequencies, and higher selectivities than the ones carried out under a dioxygen atmosphere. Mechanisms for both reactions were detailed, showing the release of nitrogen and water as benign by‐products.

Porous nitrogen-doped carbon supported MoO2/Mo2C hybrid catalyst for efficient oxidative coupling of primary amines to imines

Porous nitrogen-doped carbon supported MoO2/Mo2C hybrid catalyst for efficient oxidative coupling of primary amines to imines

Controlled Assembly of Ru-Containing Polyoxometalates for Photocatalytic Activity of the Primary Amine Coupling Reaction.

Three Ru-induced structural interconversion polyoxometalates (POMs), Na13H5[Ru4(H2O)2(Cl)2(WO2)4(AsW9O33)4]·43H2O (1), K5Na9H8[Ru2(WO2)4(AsW9O33)4]·50H2O (2), and KNa13H14[(WO2)4(AsW9O33)4]·34H2O (3), were successfully synthesized and thoroughly characterized. Interconversion of structures was accomplished by changing the number of active sites for compounds 1-3. All three compounds contain one {As4W40O140} unit, showing similar structural characteristics except for the active center number (Ru). Interestingly, compound 1 [turnover number (TON)= 486; turnover frequency (TOF)= 20 h-1] showed highly efficient photocatalysis in achieving oxidative coupling of primary amines. Compound 2 (TON = 406, TOF = 17 h-1) was also found to promote the oxidative coupling with relatively poor efficiency; however, compound 3 (TON = 178; TOF = 7.4 h-1) had no obvious contribution to the coupling reaction system, and a chain of evidence indicates that the catalytic performances are strongly dependent on element contents of active sites. Furthermore, the Ru-containing POM-based photocatalysts are conveniently recyclable and reusable during the photocatalytic processes. This study demonstrates the possibility of tuning the catalytic efficiency and stability of POM-based photocatalysts by well designing and controlling their structures. The possible reaction mechanism for the photocatalysis synthesis of imine product is also proposed based on experimental studies.

Oxidative coupling of primary amines to imines catalyzed by CoCl2·6H2O

AbstractA high‐performance, readily available and eco‐friendly cobalt catalyst has been suggested for the first time for the additive‐free oxidative coupling of primary amines to imines. Different substituted benzylamine and heteroaryl methanamine compounds could be transformed into their corresponding imines in good to excellent yields over this catalyst. Meanwhile, it has been demonstrated that this catalyst can also afford the oxidative coupling of various benzylamines with o‐phenylenediamine to produce benzimidazole derivatives in medium to good yields.

Fabrication of Nitrogen-Doped Carbon Supported Moo2/Mo2c Hybrid Catalyst for Efficient Oxidative Coupling of Primary Amines to Imines

Fabrication of Nitrogen-Doped Carbon Supported Moo2/Mo2c Hybrid Catalyst for Efficient Oxidative Coupling of Primary Amines to Imines

Effect of exposed facets of bismuth vanadate, controlled by ethanolamine, on oxidative coupling of primary amines

This work firstly demonstrates the ethanolamine (ETA)-assisted hydrothermal synthesis of BiVO4, with different ratios of exposed {110}/{010} planes and relates this to performance in photocatalytic oxidative coupling of benzylamine under visible light. {110}-dominant BiVO4 exhibits outstanding photocatalytic activity at room temperature owing to synergistic effects of largely exposed {110}-oxidative facet along with excellent charge generation and migration abilities, as evidenced by X-ray diffraction patterns, electrochemical impedance spectra, and photocurrent responses. The catalyst can successfully transform benzylamine derivatives to corresponding imines with selectivities of >85%, indicating a wide scope of amine substrates that can be used with the developed catalyst. Based on radical scavenging, spin-trapping EPR, and Mott-Schottky results, a plausible oxidative coupling mechanism via a O2–-assisted route and band energy diagram of the catalyst are proposed. This work highlights the influence of ETA in controlling resultant exposed crystal facets of the final BiVO4, which is the main factor governing oxidative amine coupling activity. Importantly, the tunability of exposed {110}/{010} facet of BiVO4 controlled by ETA as well as a correlation between {110} facet and the coupling activity of benzylamine firstly disclosed in this work could be readily extended for designing functional catalysts with desired performances.

Bi2S3@NH2-UiO-66-S composites modulated by covalent interfacial reactions boost photodegradation and the oxidative coupling of primary amines

The Bi2S3@NH2-UiO-66-S heterostructures have been synthesized via covalent interfacial reactions, exhibiting excellent performance in the photodegradation of methylene and the oxidative coupling of primary amines compared to reported photocatalysts.

Advantages in Using Inexpensive CO2 To Favor Photocatalytic Oxidation of Benzylamines

In this work, we investigate using carbon dioxide (CO2) as an inexpensive reaction medium during the photocatalytic oxidative coupling of primary amines to the corresponding imines. As a model syst...

A Carbazolyl Porphyrin‐Based Conjugated Microporous Polymer for Metal‐Free Photocatalytic Aerobic Oxidation Reactions

AbstractHerein, a carbazolyl porphyrin‐based π‐conjugated microporous polymer was prepared via simple FeCl3‐catalyzed oxidative polymerization. The resulting polymer (TCPP‐CMP) exhibits high surface area, permanent pores, good stability, broad light absorption range and suitable redox potentials. As expected, TCPP‐CMP is a highly effective metal‐free and heterogeneous photocatalyst for a variety of aerobic oxidation reactions, including oxidative coupling of primary amines, oxidative dehydrogenation of secondary amines, and oxidation of sulfides into sulfoxides using molecular oxygen under visible light irradiation. Importantly, natural sunlight is able to promote the aerobic oxidation of benzylamine and thioanisole via TCPP‐CMP photocatalyst with high conversion and selectivity, which are comparable with reactions conducted under artificial light. In addition, heterogeneous TCPP‐CMP has good recyclability, which retained its activity even after four cycles. The current work lays the foundation for future applications of TCPP‐CMP as metal‐free heterogeneous photocatalyst for aerobic oxidation reactions.

A dual biomimetic process for the selective aerobic oxidative coupling of primary amines using pyrogallol as a precatalyst. Isolation of the [5 + 2] cycloaddition redox intermediates

Low-cost pyrogallol precatalyst undergoes an oxidative self-processing step for delivering the active organocatalystin situthrough a dual biomimetic process.

Synthesis, structure and catalytic activity of manganese(ii) complexes derived from bis(imidazole)methane-based ligands.

New mononuclear manganese(ii) complexes [Mn(κ2-L1)(OAc)2] ([Mn]-1), [Mn(κ2-L2)(OAc)2] ([Mn]-2) and [Mn(κ2-L3)(OAc)2] ([Mn]-3) with imidazole based ligands {4,4'-(phenylmethylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L1), {(4,4'-((2-methoxy phenyl)methylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L2) and {4,4'-((2-chlorophenyl) methylene)bis(2-ethyl-5-methyl-1H-imidazole)} (L3) are synthesized and fully characterized by a variety of techniques. Furthermore, the molecular structures of complexes [Mn]-1 and [Mn]-2 are established by single crystal X-ray structure analysis. The synthesized manganese(ii) complexes exhibited efficient catalytic oxidative coupling of primary amines in air under solvent-free conditions to the corresponding imines in moderate to good yields.

A Giant Mo/Ta/W Ternary Mixed-Addenda Polyoxometalate with Efficient Photocatalytic Activity for Primary Amine Coupling.

The reactivity and properties of polyoxometalates (POMs) vary remarkably as a function of the kind of addenda atoms, so the design and synthesis of new mixed-addenda POMs is a promising approach for the further development of the POM-related areas. In the present work, the first Mo/Ta/W ternary mixed-addenda POM (NH4)41H7[K3(H2O)3(P2W15Ta3O62)6(Mo2O4CH3CO2)3(MoO3)2]·85H2O (1), which is composed of 6 {P2W15Ta3O62} linked by 3 {MoV2O4(OOCCH3)+} and 2 {MoVIO3} via 18 novel Mo-O-Ta bridges has been synthesized. The precursor {P2W15Ta3}, which has lower redox potential, is crucial for the formation of 1. The red-brown solid sample of 1 shows strong absorption in the visible region. The visible-light responsive charge transfer from benzylamine to 1 was observed experimentally. 1 was proved to be an efficient photocatalyst under simulated sunlight (AM 1.5G) radiation for the oxidative coupling of primary amines to imines using atmospheric O2.

Transition Metal‐Free Oxidative Coupling of Primary Amines in Polyethylene Glycol at Room Temperature: Synthesis of Imines, Azobenzenes, Benzothiazoles, and Disulfides

A transition metal‐free protocol has been developed for the oxidative coupling of primary amines to imines and azobenzenes, thiols to disulfides, and 2‐aminothiophenols to benzothiazoles, offering excellent yields. The advantageous features of the present environmentally benign methodology include the usage of biocompatible and green reaction conditions such as, solvent, room temperature reactions and transition metal‐free approach. Moreover, it offers a broader substrate scope.

Aerobic Oxidation of Primary Amines to Imines in Water using a Cobalt Complex as Recyclable Catalyst under Mild Conditions.

Oxidative coupling of primary amines to imines has been achieved by using a water soluble cobalt complex as catalyst and air as the oxidant at near ambient conditions. Aromatic, heteroaromatic and aliphatic amines were successfully converted to the corresponding imines with yields of up to 96 %. A 20 gram scale reaction for the synthesis of imine from benzylamine in good yield is also demonstrated with this method. The catalyst has been found to be reusable with up to five cycles. It is highly efficient, gives a turnover number (TON) of up to 128, and shows chemoselectivity with the only byproducts being water and ammonia. Control experiments and mechanistic studies indicate that the CoII /CoIII catalytic cycle is responsible for these oxidative transformations. Some of the reactive intermediates of this reaction have also been isolated and structurally characterized.

Synthesis, characterization and Pd(ii)-coordination chemistry of the ligand tris(quinolin-8-yl)phosphite. Application in the catalytic aerobic oxidation of amines.

The synthesis and characterization of the ligand tris(quinolin-8-yl)phosphite, (P(Oquin)3), are described and its coordination chemistry toward the metal precursor [Pd(COD)Cl2] (COD = 1,5-cyclooctadiene, C8H12) is reported. A new Pd(ii)-P(Oquin)3 metal complex was isolated and fully characterized ([Pd{P(Oquin)3}Cl2]), and its X-ray diffraction analysis shows that the phosphite ligand coordinates as a bidentate P-N chelate. This complex is an efficient catalyst for the solvent-free mild oxidative coupling of primary amines to imines using air as an oxidant, obtaining moderate to good yields (up to 99%) and turnover numbers (TONs up to 230). This catalyst can be recovered from the reaction mixture and reused in a subsequent run without a significant loss of activity. Kinetic measurements of the oxidation of benzylamine suggest that the rate law is r = kapp[BnNH2][cat] ([BnNH2] = molar concentration of benzylamine, [cat] = molar concentration of [Pd{P(Oquin)3}Cl2], kapp = k[O2]c = 0.756 L mol-1 h-1 = apparent rate constant). In situ NMR tests were performed to gain some insight into the reactivity of the Pd(ii)-P(Oquin)3 complex toward benzylamine.

Recent Advances in the Synthesis of Benzimidazole Derivatives from the Oxidative Coupling of Primary Amines

Benzimidazole belongs to the top five most commonly used five-membered aromatic nitrogen heterocycles among U.S. FDA approved pharmaceuticals. Over the last few years, a large number of improved synthetic strategies have been developed to construct the benz­imidazole molecular framework under environmentally benign conditions. This review focuses on the use of primary amines as readily available substrates for the synthesis of benzimidazole derivatives through different types of oxidative cross-coupling reactions.1 Introduction2 Catalyst-Free Oxidative Coupling of Primary Amines3 Catalytic Oxidative Coupling of Primary Amines3.1 Metal-Catalyzed Reactions3.2 Metal-Free Catalyzed Reactions3.3 Bioinspired Catalyzed Reactions4 Conclusion

Metal-Free Organocatalytic Oxidative Ugi Reaction Promoted by Hypervalent Iodine.

We report here a novel IBX-promoted oxidative coupling of primary amines and its utilization to Ugi reaction. Advantageously, the reaction could be carried out in choline chloride urea as a natural deep eutectic solvent. A range of imines and bisamides from pseudo-four-component oxidative Ugi reaction could be synthesized under mild and metal-free conditions. Advantageously, the oxidant (IBX) and solvent could be recycled up to five times with only a slight loss in activity.

ChemInform Abstract: Novel Transition Bimetal—Organic Frameworks: Recyclable Catalyst for the Oxidative Coupling of Primary Amines to Imines at Mild Conditions.

AbstractA new and simple heterogeneous catalyst for promoting the oxidative coupling of benzylamines to the corresponding imines is developed.

ChemInform Abstract: Catalytic Oxidative Coupling of Primary Amines under Air: A Flexible Route to Benzimidazole Derivatives.

AbstractIn a bioinspired approach, the cooperative action of cupric bromide as electron‐transfer mediator and a topaquinone‐like co‐catalyst is studied.

Visible-Light Photocatalysis of Aerobic Oxidation Reactions Using Carbazolic Conjugated Microporous Polymers

Carbazolic conjugated microporous polymer (C-CMP) is obtained via straightforward carbazole-based oxidative coupling polymerization. C-CMP exhibits high porosity and a specific surface area of 1137 m2 g–1, and it is thermally stable to 600 °C in nitrogen. C-CMP is shown to be a highly effective heterogeneous photocatalyst for a wide range of reactions, including the oxidative coupling of primary amines, aerobic dehydrogenation of nonactive secondary amine substrates such as pharmaceutically relevant nitrogen heterocycles, and selective oxidation of sulfide using molecular oxygen and visible light. This work highlights the potential of developing photoactive N-containing CMPs as a highly stable, molecularly tunable, reusable, and metal-free visible light photocatalysts for a wide variety of organic transformations.