Advantages in Using Inexpensive CO2 To Favor Photocatalytic Oxidation of Benzylamines

The oxidative coupling of primary amines with internal alkynes catalyzed by Ru complexes is presented as a general atom-economy methodology with a broad scope of applications in the synthesis of N-heterocycles. Reactions proceed through regioselective C-H bond activation in 15 minutes under microwave irradiation or in 24 hours with conventional heating. The synthesis of 2,3,5-substituted pyridines, benzo[h]isoquinolines, benzo[g]isoquinolines, 8,9-dihydro-benzo[de]quinoline, 5,6,7,8-tetrahydroisoquinolines, pyrido[3,4g]isoquinolines, and pyrido[4,3g]isoquinolines is achievable depending on the starting primary amine used. DFT calculations on a benzylamine substrate support a reaction mechanism that consists of acetate-assisted C-H bond activation, migratory-insertion, and C-N bond formation steps that involve 28-30 kcal mol(-1) . The computational study is extended to additional substrates, namely, 1-naphthylmethyl-, 2-methylallyl-, and 2-thiophenemethylamines.

A novel nanohybrid structure was synthesized by assembling gold nanoparticles on polymerized polydiacetylene nanotubes. Combination of the nanohybrid with gallacetophenone afforded an efficient cooperative co-catalytic system for the oxidative coupling of primary amines into imines. The system is highly efficient and sustainable as it operates in high yields using minimal amounts of the metal and the quinone, under ambient atmosphere, at room temperature, in water, and is easily recycled.

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.

A 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.

Herein, a highly active Cu‐UiO‐66 catalyst was constructed by precisely anchoring monodisperse Cu sites through Zr 6 ‐oxo cluster nodes, which enabled efficient oxidative coupling of primary amines under mild conditions with 98% imine yield. The catalytic system used oxygen in air as the oxidant, and no noble metal or strong chemical oxidant was required. The high selectivity of imine was achieved by inhibiting further oxidation of the C═N bond through the pore‐limited domains of metal‐organic frameworks (MOFs) and Cu site synergy. As a result of experimental and characterization results, Cu doping was found to significantly increase the oxygen vacancy concentration, enhance the electron transfer efficiency, and promote the generation of the key active species O 2 ·− . In addition, Cu‐UiO‐66 exhibits excellent cycling stability (≥ 5 cycles) and maintains superior catalytic activity. Cu‐UiO‐66 solves the problems of low selectivity and harsh conditions in imine synthesis through its unique structural properties.

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.

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

Flower-like TiO₂Nanostructures Coated with Fe₃O₄ Nanoparticles as Magnetic Ohmic Heterojunctions for the Photocatalytic Selective Oxidative Coupling of Primary Amines and Degradation of Tetracycline

Oxidative coupling of primary amines to imines is achieved with high to moderate yields by refluxing suspensions of amines and water under one atmosphere dioxygen without any additives. Tandem acid-free aza Diels-Alder reactions for synthesis of N-alkyl-4-pyridones are also accomplished.

New phenothiazine based organic dyes were prepared for visible-light-driven organic transformations. The 3,7-disubstituted phenothiazine derivatives showed visible light absorption and reversible one-electron oxidation behavior. In the presence of 0.5 mol % of 3,7-disubstituted phenothiazines, primary benzylamines showed oxidative coupling under visible light irradiation from a blue LED. The electronic effect of substituents in phenothiazine dyes was observed in catalytic activities. The mechanistic pathway of oxidative coupling was discussed based on the detection of H(2)O(2) after the reaction.

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.

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.

Porous graphene oxide can be used as a metal-free catalyst in the presence of air for oxidative coupling of primary amines. Herein, we explore a GO-catalyzed carbon-carbon or/and carbon-heteroatom bond formation strategy to functionalize primary amines in tandem to produce a series of valuable products, i.e., α-aminophosphonates, α-aminonitriles, and polycyclic heterocompounds. Furthermore, when decorated with nano-Pd, the Pd-coated porous graphene oxide can be used as a bifunctional catalyst for tandem oxidation and hydrogenation reactions in the N-alkylation of primary amines, achieving good to excellent yields under mild conditions.

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.

Benzimidazoles are of fundamental importance in chemistry and biology, and the development of efficient, environmentally benign methods for their preparation remains a key challenge for organic chemists. In a biomimetic approach inspired by copper amine oxidases, we disclose herein the scope and factors influencing the success of the cooperative action of CuBr2 as electron‐transfer mediator and a topaquinone‐like substrate‐selective catalyst in the oxidative cyclocondensation of primary amines with o‐aminoanilines. This one‐pot atom‐economic multistep process, which works under green conditions with ambient air as the terminal oxidant, low loadings of catalyst, and equimolar amounts of commercially available amine substrates, is particularly suitable for the preparation of 1,2‐disubstituted benzimidazoles. Furthermore, it allows the functionalization of nonactivated primary aliphatic amines, which are known to be challenging substrates for non‐enzymatic catalytic aerobic systems.