Photoredox-catalyzed C(sp2)–N coupling reactions

Photoredox-catalyzed radical reactions have attracted intense interest from synthetic chemists over the past several years. The photoredox-catalyzed C(sp²)–N coupling reactions, including Ullmann type C–N coupling (C–X/N–H type coupling), redox neutral C–N coupling (C–H/N–X type coupling) and oxidative C–N coupling (C–H/N–H type coupling), have been summarized in this digest.     

Cu(I)-anchored polyvinyl alcohol coated-magnetic nanoparticles as heterogeneous nanocatalyst in Ullmann-type C–N coupling reactions

In this paper, the preparation of a novel magnetic nanocatalyst (Fe₃O₄@PVA/CuCl) is described, which involves coating of polyvinyl alcohol (PVA) onto the surface of Fe₃O₄ nanoparticles and its subsequent coordination with CuCl catalyst. The nanocatalyst was characterized by various analytical methods, including Fourier-transform infrared, X-ray diffraction, inductively coupled plasma spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy, vibrating-sample magnetometry, and EDX elemental mapping. Moreover, the nanocatalyst was efficiently used in the N-arylation of amines via the formation of a carbon–nitrogen bond between the aryl halides and amines by Ullmann-type coupling reactions. The catalyst was sufficiently stable and can be reused for at least seven times in a model Ullmann reaction without remarkable alteration in its catalytic behavior. Heterogeneity of the catalyst was investigated by a hot filtration test.     

Copper-doped sulfonic acid-functionalized MIL-101(Cr) metal–organic framework for efficient aerobic oxidation reactions

A series of Cr-based metal–organic framework MIL-101-SO₃H bearing sulfonic acid functional groups were utilized for the immobilization of catalytically active copper species via a post-synthetic metalation method. The novel materials were fully characterized by scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), the Brunauer–Emmett–Teller method, and thermogravimetric analysis. XPS and the EDX element map both suggested that Cu²⁺ is coordinately bonded to the MIL-101-SO₃H, which forms the MIL-101-SO₃@Cu structure. The obtained copper-doped MIL-101-SO₃@Cu-1, MIL-101-SO₃@Cu-2, and MIL-101-SO₃@Cu-3 catalysts were utilized in the selective oxidation of alcohols and epoxidation of olefins using molecular oxygen as an oxidant. Catalytic aerobic oxidation optimization showed that MIL-101-SO₃@Cu-1 is the optimal catalyst and it can be reused ten times without compromising the yield and selectivity.     

Heterogeneous oxidation of alcohols with hydrogen peroxide catalyzed by polyoxometalate metal–organic framework

HSiW-MOF, PMo-MOF, HPMo-MOF and PW-MOF were synthesized and characterized by elemental analysis, UV–Vis, FT-IR, cyclic voltammetry and XRD. These compounds were used as catalyst for the selective oxidation of alcohols by hydrogen peroxide. Within them, PW-MOF showed a higher catalytic activity compared to other catalysts in a similar reaction condition. Therefore, PW-MOF catalyst system was successfully used for the selective oxidation of the benzylic, linear and secondary alcohols to the corresponding aldehydes and ketones. Also, allylic alcohols were converted to the corresponding aldehydes with high conversion and significant selectivity. Moreover, PW-MOF was stable to leaching, behaved as true heterogeneous catalysts, easily recovered by filtration, and reused four times with the preserve of the catalytic performance.     

Structural variability of Ag(I) metal–organic networks: C–H⋯π and metal⋯π interactions

The synthesis and X-ray structural characterization of two silver(I) coordination polymers, [Ag₂(bpp)₂(Phdac)]·5H₂O (1) and [Ag₂(bpp)(HSSal)] (2), are reported, where bpp = 4,4′-trimethylene dipyridine, H₂Phdac = 1,4-phenylenediacetic acid, and H₃SSal = 5-sulfosalicylic acid. X-ray crystallography reveals that the structures are stabilized through hydrogen bonding interactions. The C–H?π and metal?π interactions of aromatic molecules play a crucial role in building a layered framework. Intricate combinations of the weak non-covalent interactions have been analyzed to explore cooperativity and competitiveness in the solid-state structures.     

Ullmann-type C–N coupling reaction catalyzed by CuI/metformin

A facile and efficient method for Ullmann-type C–N coupling reaction of amine and aryl halide catalyzed by CuI/metformin in EtOH is described. The advantages of this method are the use of an inexpensive and readily available catalyst and ligand, easy workup, shorter reaction time, improved yields, and the use of green solvent. Furthermore, this procedure is applied successfully for the modification of natural products, such as Vindoline and Tabersonin.     

Development and outlook of chiral carbene–gold(I) complexes catalyzed asymmetric reactions

Great progress has been made in developing of homogeneous Au-catalyzed reactions in the past decade. The unique versatility and efficiency of gold complexes have been obtained including carbene ligated gold complexes. Due to the special linear coordination mode of gold(I) complex, Au catalyzed asymmetric reactions have become a huge challenge. Chiral carbene–gold complexes also have been applied in asymmetric reactions. Major breakthrough in this field has been obtained by the Toste group recently and more are expected in the future. This digest, by highlighting recent works, aims to make further progress in this fascinating research field.     

Bridging nitrile groups in a metal–organic framework

This article describes two coordination polymers based on sodium and nickel triflates, respectively, and the linker adiponitrile (1,4-butanedinitrile). Sodium triflate forms a coordination network with adiponitrile, where the nitriles bridge the sodium ions, a rare coordination mode for a nitrile. Crystal structures of alkali metal complexes of linear aliphatic dinitriles have not been reported previously. With nickel triflate, a cationic 1-D coordination polymer results upon coordination of adiponitrile.     

Electrochemical dehydrogenative N–H/N–H coupling reactions

The N–N bond is present in many important organic compounds, such as hydrazines, pyrazoles, azos, etc. Many methods based on transition metal catalyzed N–N coupling or functionalization of hydrazine have been reported for the synthesis of N–N containing organic compounds. In recent years, electrochemical dehydrogenative N–H/N–H coupling has become a powerful tool for the construction of N–N bearing organic compounds. The electrochemical methods employ electrons as traceless redox reagents instead of chemicals and produce hydrogen as the only byproduct. In this review, we summarize the recent advances in the electrochemical dehydrogenative N–H/N–H coupling reactions with focus on the mechanistic insights and synthetic applications of these transformations.     

Pd(0)-Schiff-base@MCM-41 as high-efficient and reusable catalyst for C–C coupling reactions

A Pd-Schiff-base grafted on functionalized mesoporous MCM-41 (Pd(0)-Schiff-base@MCM-41) was prepared using a post-grafting procedure and used as a highly efficient and reusable nanostructural catalyst for the carbon–carbon cross-coupling reactions of various aryl halides (including aryl iodide, bromide and chloride) with sodium tetraphenyl borate, phenylboronic acid and butyl acrylate. This catalyst exhibits interesting reactivity through Heck and Suzuki reactions.     

Transition metal catalyzed Fe–C coupling reactions in synthesis of dicarbonyl(2-thienylethynyl)(η5-cyclopentadienyl)iron complex: Spectroscopic,structure and electrochemical study

Transition Metal Chemistry - The new σ-alkynyl iron(II) complex Cp(CO)2Fe-C≡C-(2-C4H3S) was synthesized with application of several known approaches based on the transition metal...     

New ligands for copper-catalyzed C–N coupling reactions with aryl halides

2-Carbomethoxy-3-hydroxyquinoxaline-di-N-oxide was identified as an efficient novel ligand for the copper-catalyzed coupling reactions of aryl iodides, bromides, and chlorides with aliphatic amines and N-containing heterocycles under mild conditions. The catalytic system showed great functional-group tolerance and excellent chemoselectivity.     

Silver catalyzed C–C and C–S coupling of aryl halides and thiols with boronic acids

An efficient Ag(I) catalyzed carbon–carbon and carbon–sulfur bond formation reaction of aryl halides and thiols with boronic acids has been demonstrated. Using this protocol, substrates with a wide range of functional group including electron-rich, and electron deficient substituents have been explored. These reactions are particularly useful to prepare symmetrical and unsymmetrical biphenyls and thioethers. These products were isolated in high yield.     

Exceptional thermal stability and thermodynamic properties of lithium based metal–organic framework

A three-dimensional lithium-based metal–organic framework Li₂(2,6-NDC) (2,6-NDC = 2,6-naphthalene dicarboxylate) has been synthesized solvothermally and characterized by X-ray powder diffraction, elemental analysis, FT-IR spectroscopy, thermogravimetry and mass spectrometer analysis (TG–MS). The framework has exceptional stability and is stable to 863 K. The thermal decomposition characteristic of this compound was investigated through the TG–MS from 293 to 1250 K. The molar heat capacity of the compound was measured by temperature modulated differential scanning calorimetry (TMDSC) over the temperature range from 195 to 670 K for the first time. The thermodynamic parameters such as entropy and enthalpy versus 298.15 K based on the above molar heat capacity were calculated.     

A tandem and tunable Pd catalyzed C–N coupling of heteroarenols with ureas via C–OH bond activation

At this circumstance for the first time, a facile and convenient method for heteroaryl ureas has been developed via a two-step process involving in situ C–OH activation followed by palladium catalyzed C–N coupling of heteroarenols with ureas, which show excellent functional group tolerance and give out rapid coupling in good to excellent yield.     

Asymmetric Diels–Alder reactions of N-allenoyloxazolidinones catalyzed by Cu(II)–bis(oxazoline) complexes

Catalytic asymmetric Diels–Alder reactions of N-allenoyloxazolidinones were investigated. Various chiral metal–bis(oxazoline) and metal–pyridinebis(oxazoline) complexes were screened. Cu(SbF₆)₂(H₂O)₂(t-BuBox) was found to be the most effective catalyst, giving the product in high yield, enantioselectivity, and endo:exo selectivity. The relative reactivity between N-allenoyloxazolidinones and N-alkenoyloxazolidinones was also investigated. A model for stereoinduction was proposed to account for the enantioselectivity and endo:exo selectivity.     

Polymer-supported palladium (II) containing N2O2: An efficient and robust heterogeneous catalyst for C–C coupling reactions

A new polymer was prepared from 1,3,5-triformylphloroglucinol (noted as TDTB) and o-phenylenediamine through Schiff base condensation reaction, and palladium (II) was immobilized on the polymer (noted as TbPo-Pd(II)). This process was easy to work-up and cost-effective. The structure and composition of TbPo-Pd(II) were fully characterized by FTIR, TGA, XPS, AAS, SEM, and TEM analyses. Meanwhile, this catalyst showed desired thermal stability and excellent performance in water/methanol system for Suzuki and Sonogashira coupling reactions. In addition, this heterogeneous catalyst can be readily recovered by simple filtration with no appreciable Pd leaching in the reaction. This work provides a powerful protocol for rapid access to asymmetrical biphenyls and aryl alkynes. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2344–2353     

Construction of visible-light-responsive metal–organic framework with pillared structure for dye degradation and Cr(VI) reduction

A water-stable mixed-linker metal–organic framework (MOF) was rationally synthesized using a controllable pillared-layer method. The prepared Co(II)–MOF shows wide-range absorption in the visible light region due to the incorporation of highly conjugated anthracene-based bipyridine ligand. Experiments suggest that the MOF is highly efficient for the photoreduction of toxic Cr(VI) ions in water under visible light. Important issues affecting photocatalytic performance, such as the influence of pH and the control of electron–hole separation by scavenger, were carefully examined. Beyond Cr(VI) ions, we also explored the photocatalytic degradation performance of the MOF using a persistent azo dye as a model substrate, where H₂O₂-involved advanced oxidation process was applied. Control experiments suggest that the introduction of environmentally benign H₂O₂ significantly enhances the degradation performance due to the generation of reactive hydroxyl radicals. The study not only demonstrates the great feasibility of the preparation of a new MOF photocatalyst through a controllable pillared-layer method, but also reveals that rational functionalization of ligand in the MOF is convenient for achieving desirable applications.