Dimerization of anilines and benzylamines with mercury(II) oxide-iodine reagent

Microwave Assisted Rapid and Sustainable Synthesis of Unsymmetrical Azo Dyes by Coupling of Nitroarenes with Aniline Derivatives

Aromatic azo dyes are of immense commercial importance, and the development of greener routes for their synthesis is imperative due to current environmental concerns. In the present study, a microwave-assisted route has been developed for rapid and convenient synthesis of unsymmetrical azo dyes in a single step. In a metal-catalyst-free approach, an aromatic amine was used as an in situ reductant to affect its direct cross-condensation with nitroarenes to afford a variety of dispersed and water-soluble azo dyes. The electronic and substituent effects were thoroughly understood by placing suitable substituents in both nitroarenes and aniline derivatives in competitive reactions. The microwave (MW) method worked better with aniline or electron-rich aromatic amines to prepare a range of unsymmetrical azo dyes in up to 97% yields within a few minutes. The method worked well in the gram-scale synthesis of commercial dye, solvent yellow 7.

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Microwave-based green synthesis of unsymmetrical azo dyes

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Catalyst-free, rapid synthesis

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Gram-scale synthesis of commercial dyes

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Efficient synthesis of water-soluble dyes

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.

Rhodocenium Functionalization Enabled by Half-Sandwich Capping, Zincke Reaction, Diazoniation and Sandmeyer Chemistry

In continuation of our exploration of metallocenium chemistry we report here on innovative ways toward monofunctionalized rhodocenium salts applying half-sandwich capping reactions of cyclopentadienyl rhodium(III) halide synthons with cyclopentadienyl ylides containing pyridine, phosphine or dinitrogen leaving groups, followed by Zincke and Sandmeyer reactions. Thereby amino, diazonio, bromo, azido and iodo rhodocenium salts containing valuable functional groups are accessible for the first time. Target compounds were characterized by spectroscopic (1H/13C/103Rh-NMR, IR, HR-MS), structural (single crystal XRD) and electrochemical (CV) methods and their properties were compared to those of isoelectronic cobaltocenium compounds. These new functionalized rhodocenium complexes significantly expand the so far extremely limited chemical space of rhodocenium salts with promising options for the future development in the area of rhodocenium chemistry.

Invisible Silver Guests Boost Order in a Framework That Cyclizes and Deposits Ag3Sb Nanodots

The infusion of metal guests into (i.e., metalating) the porous medium of metal-organic frameworks (MOFs) is a topical approach to wide-ranging functionalization purposes. We report the notable interactions of AgSbF₆ guests with the designer MOF host ZrL1 [Zr₆O₄(OH)₇(L1)_4.5(H₂O)₄]. (1) The heavy-atom guests of AgSbF₆ induce order in the MOF host to allow the movable alkyne side arm to be fully located by X-ray diffraction, but they themselves curiously remain highly disordered and absent in the strucutral model. The enhanced order of the framework can be generally ascribed to interaction of the silver guests with the host alkyne and thioether functions, while the invisible heavy-atom guest represents a new phenomenon in the metalation of open framework materials. (2) The AgSbF₆ guests also participate in the thermocyclization of the vicinal alkyne units of the L1 linker (at 450 °C) and form the rare nanoparticle of Ag₃Sb supported on the concomitantly formed nanographene network. The resulted composite exhibits high electrical conductivity (1.0 S/cm) as well as useful, mitigated catalytic activity for selectively converting nitroarenes into the industrially important azo compounds, i.e., without overshooting to form the amine side products. The heterogeneous/cyclable catalysis entails only the cheap reducing reagents of NaBH₄, ethanol, and water, with yields being generally close to 90%.

Azo synthesis meets molecular iodine catalysis

A metal-free synthetic protocol for azo compound formation by the direct oxidation of hydrazine HN-NH bonds to azo group functionality catalyzed by molecular iodine is disclosed. The strengths of this reactivity include rapid reaction times, low catalyst loadings, use of ambient dioxygen as a stoichiometric oxidant, and ease of experimental set-up and azo product isolation. Mechanistic studies and density functional theory computations offering insight into this reactivity, as well as the events leading to azo group formation are presented. Collectively, this study expands the potential of main-group element iodine as an inexpensive catalyst, while delivering a useful transformation for forming azo compounds.

Divergent synthesis of unsymmetrical azobenzenes via Cu-catalyzed C–N coupling

Efficient, one-pot, and low-cost metal-catalyzed tandem Chan–Lam coupling/deprotection and Ullmann/Chan–Lam/deprotection reactions to access unsymmetrical azobenzenes are disclosed.

Direct Oxidative Azo Coupling of Anilines Using a Self-Assembled Flower-like CuCo2O4 Material as a Catalyst under Aerobic Conditions

Herein, we report the synthesis of a self-assembled flower-like CuCo₂O₄ material by the oxalate decomposition method. The crystalline structure and morphology of the material have been analyzed by powder X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray measurement techniques. The self-assembled flower-like CuCo₂O₄ material showed remarkable catalytic activity in the direct aerobic oxidative azo coupling of anilines under oxidant and other additive-free reaction conditions. The mechanistic insight of CuCo₂O₄ in the oxidative azo coupling reaction has been established by density functional theory calculations, which disclosed that the absorption and dissociation of areal oxygen preferentially take place at the Cu site and dissociation of aniline takes place at the Co site. Thus, the Cu and Co sites of CuCo₂O₄ exert a cooperative effect on the direct oxidative azo coupling reactions through the selective activation of anilines and aerobic oxygen. The CuCo₂O₄ material was recovered from the reaction mixture and reused for at least eight runs without appreciable loss of catalytic activity.

Redox-Rich Metallocene Tetrazene Complexes: Synthesis, Structure, Electrochemistry, and Catalysis

Thermal or photochemical metal-centered cycloaddition reactions of azidocobaltocenium hexafluoridophosphate or azidoferrocene with (cyclooctadiene)(cyclopentadienyl)cobalt(I) afforded the first metallocenyl-substituted tetrazene cyclopentadienyl cobalt complexes together with azocobaltocenium or azoferrocene as side products. The trimetallic CpCo compounds are highly conjugated, colored, and redox-active metallo-aromatic compounds, as shown by their spectroscopic, structural, and electrochemical properties. The CpCo-tetrazenido complex with two terminally appended cobaltocene units catalyzes electrochemical proton reduction from acetic acid at a mild overpotential (0.35 V). Replacing cobaltocene with ferrocene moieties rendered the complex inactive toward catalysis.

Click Synthesis of Shape-Persistent Azodendrimers and their Orthogonal Self-Assembly to Nanofibres

The copper(i)-catalyzed azide–alkyne cycloaddition (CuAAC) reaction has been efficiently utilized to synthesize a series of dendrons with amino functionalities. The aminodendrons successfully underwent azodimerization to furnish a series of pyridyl- and phenyl-based azodendrimers with peripheral alkyl or ether side chain substituents. The molecular structures of the azodendrimers were fully assigned using different spectroscopic techniques, such as 1H NMR and 13C NMR, and the molecular weights were determined using MALDI-TOF mass spectrometry. The molecular self-assembly of the azodendrimers was investigated by scanning electron microscopy and transmission electron microscopy, which revealed the formation of highly ordered and uniform self-assembled nanofibres.

Stereoselective synthesis of N-ethyl-2-arylvinyl-5-methyl fulleropyrrolidines: reaction of [60]fullerene with aromatic aldehydes and triethylamine/diethylamine in the absence or presence of manganese(iii) acetate

Reaction of [60]fullerene with aromatic aldehydes and triethylamine/diethylamine afforded a series of novel fulleropyrrolidines.

Harnessing the Versatility of Continuous-Flow Processes: Selective and Efficient Reactions

There is a great need for effective transformations and a broad range of novel chemical entities. Continuous-flow (CF) approaches are of considerable current interest: highly efficient and selective reactions can be performed in CF reactors. The reaction setup of CF reactors offers a wide variety of possible points where versatility can be introduced. This article presents a number of selective and highly efficient gas-liquid-solid and liquid-solid reactions involving a range of reagents and immobilized catalysts. Enantioselective transformations through catalytic hydrogenation and organocatalytic reactions are included, and isotopically labelled compounds and pharmaceutically relevant 1,2,3-triazoles are synthesized in CF reactors. Importantly, the catalyst bed can be changed to a solid-phase peptide synthesis resin, with which peptide synthesis can be performed with the utilization of only 1.5 equivalents of the amino acid.

Rhodium-catalyzed synthesis of quinolines and imines under mild conditions

An efficient protocol for the synthesis of quinolines in aqueous medium using a Rh(ii)acetate/TPPTS recyclable catalytic system has been developed. Furthermore, imines were also synthesized from benzylamines in moderate to good yields under solvent free conditions.

Substituent effects in trans-p,p'-disubstituted azobenzenes: X-ray structures at 100 K and DFT-calculated structures

The crystal and molecular structures of two para-substituted azobenzenes with π-electron-donating -NEt2 and π-electron-withdrawing -COOEt groups are reported, along with the effects of the substituents on the aromaticity of the benzene ring. The deformation of the aromatic ring around the -NEt2 group in N,N,N',N'-tetraethyl-4,4'-(diazenediyl)dianiline, C20H28N4, (I), may be caused by steric hindrance and the π-electron-donating effects of the amine group. In this structure, one of the amine N atoms demonstrates clear sp(2)-hybridization and the other is slightly shifted from the plane of the surrounding atoms. The molecule of the second azobenzene, diethyl 4,4'-(diazenediyl)dibenzoate, C18H18N2O4, (II), lies on a crystallographic inversion centre. Its geometry is normal and comparable with homologous compounds. Density functional theory (DFT) calculations were performed to analyse the changes in the geometry of the studied compounds in the crystalline state and for the isolated molecules. The most significant changes are observed in the values of the N=N-C-C torsion angles, which for the isolated molecules are close to 0.0°. The HOMA (harmonic oscillator model of aromaticity) index, calculated for the benzene ring, demonstrates a slight decrease of the aromaticity in (I) and no substantial changes in (II).

Oxidative dimerization of (hetero)aromatic amines utilizing t-BuOI leading to (hetero)aromatic azo compounds: scope and mechanistic studies

A straightforward synthetic method of both symmetric and unsymmetric aromatic azo compounds through an efficient and cross-selective oxidative dimerization of aromatic amines using tert-butyl hypoiodite (t-BuOI) under metal-free and mild conditions has been developed. This method was also found applicable to the synthesis of heteroaromatic azo compounds. The spectroscopic study indicates the involvement of N,N-diiodoanilines in the oxidative reaction as the key intermediate.

Highly efficient iron phthalocyanine catalyzed oxidative synthesis of imines from alcohols and amines

An efficient iron phthalocyanine catalyzed method was developed for direct oxidative coupling of alcohols with amines to afford corresponding imines. The present protocol is applicable to various substituted aromatic and aliphatic alcohols and amines. The reaction is believed to proceed via activation of alcohols by iron phthalocyanines through Lewis acid–base interaction to form aldehydes, which by nucleophilic attack of amines are converted into the corresponding imines.

Facile Cu(I)-catalyzed oxidative coupling of anilines to azo compounds and hydrazines with diaziridinone under mild conditions

A mild and highly efficient Cu(I)-catalyzed oxidative coupling of anilines is described. Various primary and secondary anilines can be efficiently coupled under mild conditions to the corresponding azo compounds and hydrazines in high yields. This method provides a direct and practical access to these compounds and is also amenable to gram scale with no special precautions to exclude air or moisture.