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Azolium/Hydroquinone Organo‐Radical Co‐Catalysis: Aerobic C−C‐Bond Cleavage in Ketones

Par / 18 janvier 2021 / Non classé
Azolium/Hydroquinone Organo‐Radical Co‐Catalysis: Aerobic C−C‐Bond Cleavage in Ketones

Combine and conquer: A new method for the generation of radical species that does not require photoirradiation, radical initiators, or preactivated substrates is reported. The combined use of an azolium salt and hydroquinone generated an efficient catalytic system for the aerobic C−C‐bond cleavage of 2‐substituted ketones. A reaction mechanism is proposed based on the results of diffusion‐ordered spectroscopy and cyclic voltammetry measurements, as well as computational studies.

Abstract

Organo‐radical catalysts have recently attracted great interest, and the development of this field can be expected to broaden the applications of organocatalysis. Herein, the first example of a radical‐generating system is reported that does not require any photoirradiation, radical initiators, or preactivated substrates. The oxidative C−C‐bond cleavage of 2‐substituted cyclohexanones was achieved using an azolium salt and a hydroquinone as co‐catalysts. A catalytic mechanism was proposed based on the results of diffusion‐ordered spectroscopy and cyclic voltammetry measurements, as well as computational studies.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Yuya Nakatsuji, Yusuke Kobayashi, Sakyo Masuda, Yoshiji Takemoto
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004943

Direct Synthesis of Unsymmetrical Dithioacetals

Par / 18 janvier 2021 / Non classé
Direct Synthesis of Unsymmetrical Dithioacetals

No symmetry: A general protocol for the direct synthesis of unsymmetrical dithioacetals is reported. A variety of unsymmetrical S,S‐acetals consisting of one (hetero)aromatic and one aliphatic thiol bearing diverse functional groups is synthesized in excellent yields. A high selectivity towards the mixed product is achieved through a kinetically controlled reaction and renders this protocol attractive for the generation of compound libraries.

Abstract

Dithioacetals are a frequently used motif in synthetic organic chemistry and have recently seen increasing attention as structural motif in promising antiviral agents against plant pathogens. Most existing reports, however, only discuss symmetrical dithioacetals. Examples of mixed dithioacetals are scarce and no general method for the selective synthesis of these compounds exists. Herein, a synthetically simple general one‐step protocol was developed for the synthesis of a broad range of unsymmetrical dithioacetals consisting of one aromatic and one aliphatic thiol moiety from the corresponding aldehyde/thiol mixture. The mixed S,S‐acetals were obtained in high yields, and a great variety of functional groups was tolerated. Kinetic control enabled an excellent selectivity in regard to the unsymmetrical dithioacetal.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Sabine Bognar, Manuel Gemmeren
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004835

Urea‐Substituted Tetramethylcyclopentadienyl Ligands for Supramolecularly Accelerated RhIII‐Catalyzed ortho‐C−H Olefination of Benzoic Acid Derivatives

Par / 18 janvier 2021 / Non classé
Urea‐Substituted Tetramethylcyclopentadienyl Ligands for Supramolecularly Accelerated RhIII‐Catalyzed ortho‐C−H Olefination of Benzoic Acid Derivatives

Supramolecular chemistry: The design and synthesis of urea‐substituted RhIII‐cyclopentadienyl catalysts, which accelerate the C−H olefination of benzoic acid derivatives, is reported. The catalysts’ substrate recognition ability mediated by H‐bonding is identified to be the reason for this effect. Its application to a variety of substrates proves the catalyst system’s advantages compared to the results obtained with widely used [RhCp*Cl2]2.

Abstract

The design and synthesis of air‐stable and conveniently crystallizable RhIII‐cyclopentadienyl catalysts substituted with a urea moiety, which are able to accelerate the C−H olefination of benzoic acid derivatives, is reported. Through kinetic studies and NMR titration experiments, the catalysts’ substrate recognition ability mediated by hydrogen bonding was identified to be the reason for this effect. Introduction of pyridone‐phosphine ligands capable of forming additional H‐bond interactions increased the catalytic performance even further. By unveiling a proportionality between reaction rate and relative complex formation enthalpy the hypothesis of a supramolecular catalyst preformation was supported. Its application to a variety of substrates proved the catalyst system’s advantages, generally increasing the yields when compared to the results obtained with widely used [RhCp*Cl2]2.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: David Maurer, Bernhard Breit
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202005130

Intramolecular Halo Stabilization of Silyl Cations—Silylated Halonium‐ and Bis‐Halo‐Substituted Siliconium Borates

Par / 18 janvier 2021 / Non classé
Intramolecular Halo Stabilization of Silyl Cations—Silylated Halonium‐ and Bis‐Halo‐Substituted Siliconium Borates

Silyl cation or halonium ion? That′s the question: The Corey reaction of acenaphthyl‐ and naphthyl‐based silanes allows the synthesis of silyl halonium ions, the nature of which was confirmed by NMR spectroscopy, X‐ray diffraction analysis, and DFT calculations. Moreover, the chloro‐ and bromonium ion can react with the starting silane to form penta‐coordinated siliconium ions, which are intramolecularly stabilized by electron donation from both halogen atoms.

Abstract

The stabilizing neighboring effect of halo substituents on silyl cations was tested for a series of peri‐halo substituted acenaphthyl‐based silyl cations 3. The chloro‐ (3 b), bromo‐ (3 c), and iodo‐ (3 d) stabilized cations were synthesized by the Corey protocol. Structural and NMR spectroscopic investigations for cations 3 b–d supported by the results of density functional calculations, which indicate their halonium ion nature. According to the fluorobenzonitrile (FBN) method, the silyl Lewis acidity decreases along the series of halonium ions 3, the fluoronium ion 3 a being a very strong and the iodonium ion 3 d a moderate Lewis acid. Halonium ions 3 b and 3 c react with starting silanes in a substituent redistribution reaction and form siliconium ions 4 b and 4 c. The structure of siliconium borate 4 c2[B12Br12] reveals the trigonal bipyramidal coordination environment of the silicon atom with the two bromo substituents in the apical positions.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Anastasia Merk, Lukas Bührmann, Natalie Kordts, Katharina Görtemaker, Marc Schmidtmann, Thomas Müller
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004838

Gas Storage in Porous Molecular Materials

Par / 18 janvier 2021 / Non classé
Gas Storage in Porous Molecular Materials

Poring over intriguing materials: Advanced porous materials have seen rapid development for diverse applications, including gas storage; however, efforts have largely focused on 3D porous materials. In this minireview, we highlight examples where molecular porous materials such as POCs, PCCs, macrocycles, and extrinsically porous molecules have been explored for gas storage applications.

Abstract

Molecules with permanent porosity in the solid state have been studied for decades. Porosity in these systems is governed by intrinsic pore space, as in cages or macrocycles, and extrinsic void space, created through loose, intermolecular solid‐state packing. The development of permanently porous molecular materials, especially cages with organic or metal–organic composition, has seen increased interest over the past decade, and as such, incredibly high surface areas have been reported for these solids. Despite this, examples of these materials being explored for gas storage applications are relatively limited. This minireview outlines existing molecular systems that have been investigated for gas storage and highlights strategies that have been used to understand adsorption mechanisms in porous molecular materials.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Meaghan M. Deegan, Michael R. Dworzak, Aeri J. Gosselin, Kyle J. Korman, Eric D. Bloch
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202003864

BIAN‐NHC Ligands in Transition‐Metal‐Catalysis: A Perfect Union of Sterically Encumbered, Electronically Tunable N‐Heterocyclic Carbenes?

Par / 18 janvier 2021 / Non classé
BIAN‐NHC Ligands in Transition‐Metal‐Catalysis: A Perfect Union of Sterically Encumbered, Electronically Tunable N‐Heterocyclic Carbenes?

A comprehensive overview of BIAN‐NHC (BIAN = bis(imino)acenaphthene), NHC = N‐heterocyclic carbene) ligands in transition‐metal‐catalysis with a focus on both the catalyst structure and the scaffold’s role in catalysis is presented.

Abstract

The discovery of NHCs (NHC = N‐heterocyclic carbenes) as ancillary ligands in transition‐metal‐catalysis ranks as one of the most important developments in synthesis and catalysis. It is now well‐recognized that the strong σ‐donating properties of NHCs along with the ease of scaffold modification and a steric shielding of the N‐wingtip substituents around the metal center enable dramatic improvements in catalytic processes, including the discovery of reactions that are not possible using other ancillary ligands. In this context, although the classical NHCs based on imidazolylidene and imidazolinylidene ring systems are now well‐established, recently tremendous progress has been made in the development and catalytic applications of BIAN‐NHC (BIAN = bis(imino)acenaphthene) class of ligands. The enhanced reactivity of BIAN‐NHCs is a direct result of the combination of electronic and steric properties that collectively allow for a major expansion of the scope of catalytic processes that can be accomplished using NHCs. BIAN‐NHC ligands take advantage of (1) the stronger σ‐donation, (2) lower lying LUMO orbitals, (3) the presence of an extended π‐system, (4) the rigid backbone that pushes the N‐wingtip substituents closer to the metal center by buttressing effect, thus resulting in a significantly improved control of the catalytic center and enhanced air‐stability of BIAN‐NHC‐metal complexes at low oxidation state. Acenaphthoquinone as a precursor enables facile scaffold modification, including for the first time the high yielding synthesis of unsymmetrical NHCs with unique catalytic properties. Overall, this results in a highly attractive, easily accessible class of ligands that bring major advances and emerge as a leading practical alternative to classical NHCs in various aspects of catalysis, cross‐coupling and C−H activation endeavors.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Changpeng Chen, Feng‐Shou Liu, Michal Szostak
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202003923

Base‐Free Pd‐Catalyzed C−Cl Borylation of Fluorinated Aryl Chlorides

Par / 18 janvier 2021 / Non classé
Base‐Free Pd‐Catalyzed C−Cl Borylation of Fluorinated Aryl Chlorides

The best base is no base! We report an efficient method for the palladium‐catalyzed C−Cl borylation of aryl chlorides containing two ortho‐fluorines. The reactions are conducted under base‐free conditions to avoid decomposition of the products which are sensitive to base.

Abstract

Catalytic C−X borylation of aryl halides containing two ortho‐fluorines has been found to be challenging, as most previous methods require stoichiometric amounts of base and the polyfluorinated aryl boronates suffer from protodeboronation, which is accelerated by ortho‐fluorine substituents. Herein, we report that a combination of Pd(dba)2 (dba=dibenzylideneacetone) with SPhos (2‐dicyclohexylphosphino‐2’,6’‐dimethoxybiphenyl) as a ligand is efficient to catalyze the C‐Cl borylation of aryl chlorides containing two ortho‐fluorine substituents. This method, conducted under base‐free conditions, is compatible with the resulting di‐ortho‐fluorinated aryl boronate products which are sensitive to base.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Yudha P. Budiman, Sabine Lorenzen, Zhiqiang Liu, Udo Radius, Todd B. Marder
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004648

Easy Access to Enantiomerically Pure Heterocyclic Silicon‐Chiral Phosphonium Cations and the Matched/Mismatched Case of Dihydrogen Release

Par / 18 janvier 2021 / Non classé
Easy Access to Enantiomerically Pure Heterocyclic Silicon‐Chiral Phosphonium Cations and the Matched/Mismatched Case of Dihydrogen Release

Chiral silyl phosphonium ions are a synthetically valuable class of compounds from a stereochemical and preparative point of view. Convenient routes towards small and configurationally stable, silicon‐chiral four‐membered heterocyclic cations are disclosed (see scheme). By combining experimental, spectroscopic, stereochemical, and computational methods, a matched/mismatched case was identified for both dehydrogenation and protodesilylation and the intermolecularity of these reactions proven.

Abstract

Phosphonium ions are widely used in preparative organic synthesis and catalysis. The provision of new types of cations that contain both functional and chiral information is a major synthetic challenge and can open up new horizons in asymmetric cation‐directed and Lewis acid catalysis. We discovered an efficient methodology towards new Si‐chiral four‐membered CPSSi* heterocyclic cations. Three synthetic approaches are presented. The stereochemical sequence of anchimerically assisted cation formation with B(C6F5)3 and subsequent hydride addition was fully elucidated and proceeds with excellent preservation of the chiral information at the stereogenic silicon atom. Also the mechanism of dihydrogen release from a protonated hydrosilane was studied in detail by the help of Si‐centered chirality as stereochemical probe. Chemoselectivity switch (dihydrogen release vs. protodesilylation) can easily be achieved through slight modifications of the solvent. A matched/mismatched case was identified and the intermolecularity of this reaction supported by spectroscopic, kinetic, deuterium‐labeling experiments, and quantum chemical calculations.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Nicolò Fontana, Noel Angel Espinosa‐Jalapa, Michael Seidl, Jonathan O. Bauer
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202005171

Selective Formation of Polyaniline Confined in the Nanopores of a Metal–Organic Framework for Supercapacitors

Par / 18 janvier 2021 / Non classé
Selective Formation of Polyaniline Confined in the Nanopores of a Metal–Organic Framework for Supercapacitors

Polymer power: Polyaniline (PANI) solely confined within the nanopores of a water‐stable metal–organic framework (MOF) without forming obvious bulk PANI between MOF crystals is synthesized. The PANI/UiO‐66‐NH2 thin films exhibit a pseudocapacitive electrochemical characteristic, and their resulting electrochemical activity is remarkably higher than those of the bulk PANI thin films.

Abstract

In this study, a strategy that can result in the polyaniline (PANI) solely confined within the nanopores of a metal–organic framework (MOF) without forming obvious bulk PANI between MOF crystals is developed. A water‐stable zirconium‐based MOF, UiO‐66‐NH2, is selected as the MOF material. The polymerization of aniline is initiated in the acidic suspension of UiO‐66‐NH2 nanocrystals in the presence of excess poly(sodium 4‐styrenesulfonate) (PSS). Since the pore size of UiO‐66‐NH2 is too small to enable the insertion of the bulky PSS, the quick formation of pore‐confined solid PANI and the slower formation of well dispersed PANI:PSS occur within the MOF crystals and in the bulk solution, respectively. By taking advantage of the resulting homogeneous PANI:PSS polymer solution, the bulk PANI:PSS can be removed from the PANI/UiO‐66‐NH2 solid by successive washing the sample with fresh acidic solutions through centrifugation. As this is the first time reporting the PANI solely confined in the pores of a MOF, as a demonstration, the obtained PANI/UiO‐66‐NH2 composite material is applied as the electrode material for supercapacitors. The PANI/UiO‐66‐NH2 thin films exhibit a pseudocapacitive electrochemical characteristic, and their resulting electrochemical activity and charge‐storage capacities are remarkably higher than those of the bulk PANI thin films.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Yi‐Da Song, Wei Huan Ho, Yu‐Chuan Chen, Jun‐Hong Li, Yi‐Sen Wang, Yu‐Juan Gu, Cheng‐Hsun Chuang, Chung‐Wei Kung
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004516

Light‐Triggered Nitric Oxide Release by a Photosensitizer to Combat Bacterial Biofilm Infections

Par / 18 janvier 2021 / Non classé
Light‐Triggered Nitric Oxide Release by a Photosensitizer to Combat Bacterial Biofilm Infections

Exposing films: A boronic acid‐decorated ruthenium compound, RBNO, functions as both a photosensitizer (PS) and a nitric oxide (NO) releasing agent. RBNO is capable of binding to the bacterial cell envelope and the biofilm matrix. Upon photoirradiation, released NO from the compound can induce bacterial biofilm dispersal. The exposed bacteria are eradicated by the reactive oxygen species (ROS) generated from the PS.

Abstract

Bacterial biofilms are a serious global health concern, often responsible for persistent infections. New strategies to prevent and treat bacterial infections by eradication of the biofilms are urgently needed. A novel ruthenium‐based compound is reported in this study that functions as both a boronic acid‐decorated photosensitizer (PS) and a light‐triggered nitric oxide (NO) releasing agent. The compound can selectively attach to the bacterial membrane and biofilms and it is highly potent at eradicating Pseudomonas aeruginosa biofilms through the simultaneous release of NO and reactive oxygen species (ROS). The compound, which is more effective than clinical antibiotic tobramycin, also has excellent bacterial specificity and shows no significant cytotoxicity to human cells. The results reveal potential applications of this innovative dual‐functional photoactivated ruthenium compound to combat bacterial biofilm infections.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Zhennan Zhao, Huinan Li, Xuan Tao, Yanxuan Xie, Liang Yang, Zong‐Wan Mao, Wei Xia
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004698

Not‐So‐Innocent Anions Determine the Mechanism of Cationic Alkylators

Par / 18 janvier 2021 / Non classé
Not‐So‐Innocent Anions Determine the Mechanism of Cationic Alkylators

Alkylating reagents based on thioimidazolium ionic liquids were synthesized and the influence of the anion on the alkylation reaction mechanism explored in detail using both experimental and computational methods.

Abstract

Alkylating reagents based on thioimidazolium ionic liquids were synthesized and the influence of the anion on the alkylation reaction mechanism explored in detail using both experimental and computational methods. Thioimidazolium cations transfer alkyl substituents to nucleophiles, however the reaction rate was highly dependent on anion identity, demonstrating that the anion is not innocent in the mechanism. Detailed analysis of the computationally‐derived potential energy surfaces associated with possible mechanisms indicated that this dependence arises from a combination of anion induced electronic, steric and coordinating effects, with highly nucleophilic anions catalyzing a 2‐step process while highly non‐nucleophilic, delocalized anions favor a 1‐step reaction. This work also confirms the presence of ion‐pairs and aggregates in solution thus supporting anion‐induced control over the reaction rate and mechanism. These findings provide new insight into an old reaction allowing for better design of cationic alkylators in synthesis, gene expression, polymer science, and protein chemistry applications.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: S. Maryamdokht Taimoory, Vincenzo Alessandro Cataldo, Andreas Schäfer, John F. Trant, Ryan Guterman
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004208

Proton‐Functionalized Graphitic Carbon Nitride for Efficient Metal‐Free Destruction of Escherichia coli under Low‐Power Light Irradiation

Par / 18 janvier 2021 / Non classé
Proton‐Functionalized Graphitic Carbon Nitride for Efficient Metal‐Free Destruction of Escherichia coli under Low‐Power Light Irradiation

Water, water everywhere: The efficiency of graphitic carbon nitride (g‐C3N4) in photocatalytic water disinfection is plagued by its rapid charge recombination and sluggish electron‐transfer kinetics. Protonation of g‐C3N4 can enhance its conductivity and provide a “highway” for the delocalization of electrons. Consequently, protonated g‐C3N4 demonstrated 100 % destruction of E. coli within 4 h under low‐power household light irradiation.

Abstract

Universal access to clean water has been a global ambition over the years. Photocatalytic water disinfection through advanced oxidation processes has been regarded as one of the promising methods for breaking down microbials. The forefront of this research focuses on the application of metal‐free photocatalysts for disinfection to prevent secondary pollution. Graphitic carbon nitride (g‐C3N4) has achieved instant attention as a metal‐free and visible‐light‐responsive photocatalyst for various energy and environmental applications. However, the photocatalytic efficiency of g‐C3N4 is still affected by its rapid charge recombination and sluggish electron‐transfer kinetics. In this contribution, two‐dimensionally protonated g‐C3N4 was employed as metal‐free photocatalyst for water treatment and demonstrated 100 % of Escherichia coli within 4 h under irradiation with a 23 W light bulb. The introduction of protonation can modulate the surface charge of g‐C3N4; this enhances its conductivity and provides a “highway” for the delocalization of electrons. This work highlights the potential of conjugated polymers in antibacterial application.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Boon‐Junn Ng, Muhammad Khosyi Musyaffa, Chen‐Chen Er, Kulandai Arockia Rajesh Packiam, W. P. Cathie Lee, Lling‐Lling Tan, Hing Wah Lee, Chien Wei Ooi, Siang‐Piao Chai
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004238

Dynamic Ion Speciation during the Hydrolysis of Aryltrifluoroborates**

Par / 18 janvier 2021 / Non classé
Dynamic Ion Speciation during the Hydrolysis of Aryltrifluoroborates**

It′s complicated: ESI‐MS analysis of aryltrifluoroborate hydrolysis reveals a complex soup of partially hydrolyzed, dehydrated and aggregate products that eventually settles into a complex equilibrium in which a wide array of species is present. Therefore, when aryltrifluoroborates are used as a “single‐component” aryl source in Suzuki–Miyaura reactions, an equally complex system might in fact exist.

Abstract

Organotrifluoroborates serve as coupling partners during transmetalation in the Suzuki–Miyaura reaction but require hydrolysis prior to the coupling reaction. Their anionic nature allows study of their hydrolysis by electrospray ionization mass spectrometry (ESI‐MS) through real‐time monitoring, complemented by pH analysis. The induction period varied according to the borates employed, and a dynamic series of equilibria for numerous ions was observed during hydrolysis. We found that the induction periods and reaction rates were sensitive to the R group of the borates, the shape of the reaction vessel, and stir rate.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Isaac Omari, Lars P. E. Yunker, Johanne Penafiel, Darlene Gitaari, Atzin San Roman, J. Scott McIndoe
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004726

A Switchable Catalyst Duo for Acyl Transfer Proximity Catalysis and Regulation of Substrate Selectivity

Par / 18 janvier 2021 / Non classé
A Switchable Catalyst Duo for Acyl Transfer Proximity Catalysis and Regulation of Substrate Selectivity

Two switchable catalysts with differently sized cavities and allosteric control are reported that allow complementary size‐selective acyl transfer in an on/off manner by modulating the effective local concentration of the substrates. Selective activation of one of the two catalysts in a mixture of reactants of similar reactivity enabled upregulation of the desired product.

Abstract

Enzymes are encoded with a gamut of information to catalyze a highly selective transformation by selecting the proper reactants from an intricate mixture of constituents. Mimicking biological machinery, two switchable catalysts with differently sized cavities and allosteric control are conceived that allow complementary size‐selective acyl transfer in an on/off manner by modulating the effective local concentration of the substrates. Selective activation of one of two catalysts in a mixture of reactants of similar reactivity enabled upregulation of the desired product.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Abir Goswami, Sudhakar Gaikwad, Michael Schmittel
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004416

A Synthetic Strategy for Cofacial Porphyrin‐Based Homo‐ and Heterobimetallic Complexes

Par / 18 janvier 2021 / Non classé
A Synthetic Strategy for Cofacial Porphyrin‐Based Homo‐ and Heterobimetallic Complexes

Simple route to dimeric complexes: Three different types of covalently linked metalloporphyrin dimers were synthesized. The monomers were synthesized sequentially and can be filled with metals before linking. As a result, different heterobimetallic systems can be made. Depending on the metals M1 and M2 used (M=Mn, Fe, Ni, Cu, Zn, Pd), a wide range of potentially catalytically active species can be prepared, such as analogues of carbon monoxide dehydrogenase.

Abstract

We present a straightforward and generally applicable synthesis route for cofacially linked homo‐ and heterobimetallic porphyrin complexes. The protocol allows the synthesis of unsymmetrical aryl‐based meso‐meso as well as β‐meso‐linked porphyrins. Our method significantly increases the overall yield for the published compound known as o‐phenylene‐bisporphyrin (OBBP) by a factor of 6.8. Besides the synthesis of 16 novel homobimetallic complexes containing MnIII, FeIII, NiII, CuII, ZnII, and PdII, we achieved the first single‐crystal X‐ray structure of an unsymmetrical cofacial benzene‐linked porphyrin dimer containing both planar‐chiral enantiomers of a NiII2 complex. Additionally, this new methodology allows access to heterobimetallic complexes such as the FeIII‐NiII containing carbon monoxide dehydrogenase active site analogue. The isolated species were investigated by various techniques, including ion mobility spectrometry, DFT calculations, and UV/Vis spectroscopy. This allowed us to probe the influence of interplane distance on Soret band splitting.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Christoph Schissler, Erik K. Schneider, Benjamin Felker, Patrick Weis, Martin Nieger, Manfred M. Kappes, Stefan Bräse
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202002394

Bio‐Coreactant‐Enhanced Electrochemiluminescence Microscopy of Intracellular Structure and Transport

Par / 18 janvier 2021 / Non classé
Bio‐Coreactant‐Enhanced Electrochemiluminescence Microscopy of Intracellular Structure and Transport

Amine‐rich biomolecules as consumed coreactants drive electrochemiluminescence with Ru(bpy)32+, enabling bio‐coreactant‐enhanced single‐cell electrochemiluminescence microscopy. This allows the imaging of intracellular hierarchical structures without the use of multiple labels. Dynamic signals disclose the universal edge effect of cellular electroporation and enable the visualization of heterogeneous molecular transport.

Abstract

A bio‐coreactant‐enhanced electrochemiluminescence (ECL) microscopy realizes the ECL imaging of intracellular structure and dynamic transport. This microscopy uses Ru(bpy)32+ as the electrochemical molecular antenna connecting extracellular and intracellular environments, and uses intracellular biomolecules as the coreactants of ECL reactions via a “catalytic route”. Accordingly, intracellular structures are identified without using multiple labels, and autophagy involving DNA oxidative damage is detected using nuclear ECL signals. A time‐resolved image sequence discloses the universal edge effect of cellular electroporation due to the influence of the geometric properties of cell membranes on the induced transmembrane voltage. The dynamic transport of Ru(bpy)33+ in the different cellular compartments unveils the heterogeneous intracellular diffusivity correlating with the actin cytoskeleton. In addition to single‐cell studies, the bio‐coreactant‐enhanced ECL microscopy is used to image a slice of a mouse liver and a colony of Shewanella oneidensis MR‐1.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Cheng Ma, Shaojun Wu, Yang Zhou, Hui‐Fang Wei, Jianrong Zhang, Zixuan Chen, Jun‐Jie Zhu, Yuehe Lin, Wenlei Zhu
doi.org/10.1002/anie.202012171

Energy Efficient Ultrahigh Flux Separation of Oily Pollutants from Water with Superhydrophilic Nanoscale Metal–Organic Framework Architectures

Par / 18 janvier 2021 / Non classé
Energy Efficient Ultrahigh Flux Separation of Oily Pollutants from Water with Superhydrophilic Nanoscale Metal–Organic Framework Architectures

In this work we introduce the synthesis of a pillar‐like Co‐CAT‐1 MOF nanoarchitecture on gold‐coated woven stainless steel meshes. These nanostructured mesh surfaces feature extreme superhydrophilic and underwater superoleophobic wetting properties, allowing for gravity‐driven, highly efficient oil–water separation with ultra‐high flux of up to nearly one million L m−2 h−1.

Abstract

The rising demand for clean water for a growing and increasingly urban global population is one of the most urgent issues of our time. Here, we introduce the synthesis of a unique nanoscale architecture of pillar‐like Co‐CAT‐1 metal–organic framework (MOF) crystallites on gold‐coated woven stainless steel meshes with large, 50 μm apertures. These nanostructured mesh surfaces feature superhydrophilic and underwater superoleophobic wetting properties, allowing for gravity‐driven, highly efficient oil–water separation featuring water fluxes of up to nearly one million L m−2 h−1. Water physisorption experiments reveal the hydrophilic nature of Co‐CAT‐1 with a total water vapor uptake at room temperature of 470 cm3 g−1. Semiempirical molecular orbital calculations shed light on water affinity of the inner and outer pore surfaces. The MOF‐based membranes enable high separation efficiencies for a number of liquids tested, including the notorious water pollutant, crude oil, affording chemical oxygen demand (COD) concentrations below 25 mg L−1 of the effluent. Our results demonstrate the great impact of suitable nanoscale surface architectures as a means of encoding on‐surface extreme wetting properties, yielding energy‐efficient water‐selective large‐aperture membranes.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Andre Mähringer, Matthias Hennemann, Timothy Clark, Thomas Bein, Dana D. Medina
doi.org/10.1002/anie.202012428

Enantioselective Three‐Component Coupling of Heteroarenes, Cycloalkenes and Propargylic Acetates

Par / 18 janvier 2021 / Non classé
Enantioselective Three‐Component Coupling of Heteroarenes, Cycloalkenes and Propargylic Acetates

Wacker‐type reaction of cyclic alkenes, propargylic acetates and nucleophilic heteroarenes and arenes, including indoles, pyrroles, activated thiophenes, furans and anilines, proceeds to give trans isomers of 2,3‐disubstituted pyrrolidines and tetrahydrofurans.

Abstract

Asymmetric coupling proceeds efficiently between propargylic acetates, cycloalkenes and electron‐rich heteroarenes including indoles, pyrroles, activated furans and thiophenes. 2,3‐Disubstituted tetrahydrofurans and pyrrolidines are produced in trans configuration and excellent enantiomeric ratios. The reaction proceeds via Wacker‐type attack of nucleophilic heteroarenes on alkenes activated by allenyl PdII species.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Shenghan Teng, Yonggui Robin Chi, Jianrong Steve Zhou
doi.org/10.1002/anie.202014781

A Stable Triplet‐Ground‐State Conjugated Diradical Based on a Diindenopyrazine Skeleton

Par / 18 janvier 2021 / Non classé
A Stable Triplet‐Ground‐State Conjugated Diradical Based on a Diindenopyrazine Skeleton

A stable triplet‐ground‐state conjugated diradical with pyrazine as a linker group was synthesized with a half‐life time of about 22 days under ambient conditions. The electron‐deficient pyrazine unit impedes spin delocalization to the peripheral phenyl rings, which increases the spin density distribution on the central meta‐pyrazine unit, leading to a large ΔES‐T.

Abstract

High‐spin conjugated radicals have great potential in magnetic materials and organic spintronics. However, to obtain high‐spin conjugated radicals is still quite challenging due to their poor stability. We report the successful synthesis and isolation of a stable triplet conjugated diradical, 10,12‐diaryldiindeno[1,2‐b:2′,1′‐e]pyrazine ( m‐DIP). With the m‐xylylene analogue skeleton containing electron‐deficient sp2‐nitrogen atoms, m‐DIP displays significant aromatic character within its pyrazine ring and its spin density mainly delocalizes on the meta‐pyrazine unit, making it a triplet ground state conjugated diradical. Our work provides an effective “spin density tuning” strategy for stable high‐spin conjugated radicals.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Zi‐Yuan Wang, Ya‐Zhong Dai, Li Ding, Bo‐Wei Dong, Shang‐Da Jiang, Jie‐Yu Wang, Jian Pei
doi.org/10.1002/anie.202012989

Synthesis of Indanones and Spiroindanones by Diastereoselective Annulation Based on a Hydrogen Autotransfer Strategy

Par / 18 janvier 2021 / Non classé
Synthesis of Indanones and Spiroindanones by Diastereoselective Annulation Based on a Hydrogen Autotransfer Strategy

A nickel‐catalyzed domino reductive cyclization of alkynes and o‐bromoaryl aldehydes provided straightforward access to biologically significant indanones and spiroindanone pyrrolidine derivatives (see scheme). The reaction was found to be tolerant of a variety of functional groups and proceeded in good yields with excellent regio‐ and diastereoselectivity.

Abstract

An unprecedented nickel‐catalyzed domino reductive cyclization of alkynes and o‐bromoaryl aldehydes is described. The reaction features broad substrate scope and is tolerant of a variety of functional groups, providing straightforward access to biologically significant indanones and spiroindanone pyrrolidine derivatives in good yields with excellent regio‐ and diastereoselectivity. Preliminary mechanistic studies have shown that indanones are formed by the cyclization of o‐bromoaryl aldehydes and alkynes to form indenol intermediates, followed by hydrogen autotransfer.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Yate Chen, Zhengtian Ding, Yiming Wang, Wenfeng Liu, Wangqing Kong
doi.org/10.1002/anie.202013792

Dimer Organization of Membrane‐Associated NS5A of Hepatitis C Virus as Determined by Highly Sensitive 1H‐Detected Solid‐State NMR

Par / 18 janvier 2021 / Non classé
Dimer Organization of Membrane‐Associated NS5A of Hepatitis C Virus as Determined by Highly Sensitive 1H‐Detected Solid‐State NMR

The membrane orientation of the hepatitis C virus NS5A protein was assessed by combining a cell‐free protein synthesis approach with highly sensitive 1H‐detected solid‐state NMR. Insertion of lipids chelated with a paramagnetic Gd3+ ion allowed to orient the protein with respect to its membrane anchor using PRE. This information allowed to propose a model for the interaction of NS5A with a direct acting antiviral.

Abstract

The Hepatitis C virus nonstructural protein 5A (NS5A) is a membrane‐associated protein involved in multiple steps of the viral life cycle. Direct‐acting antivirals (DAAs) targeting NS5A are a cornerstone of antiviral therapy, but the mode‐of‐action of these drugs is poorly understood. This is due to the lack of information on the membrane‐bound NS5A structure. Herein, we present the structural model of an NS5A AH‐linker‐D1 protein reconstituted as proteoliposomes. We use highly sensitive proton‐detected solid‐state NMR methods suitable to study samples generated through synthetic biology approaches. Spectra analyses disclose that both the AH membrane anchor and the linker are highly flexible. Paramagnetic relaxation enhancements (PRE) reveal that the dimer organization in lipids requires a new type of NS5A self‐interaction not reflected in previous crystal structures. In conclusion, we provide the first characterization of NS5A AH‐linker‐D1 in a lipidic environment shedding light onto the mode‐of‐action of clinically used NS5A inhibitors.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Vlastimil Jirasko, Alons Lends, Nils‐Alexander Lakomek, Marie‐Laure Fogeron, Marco E. Weber, Alexander A. Malär, Susanne Penzel, Ralf Bartenschlager, Beat H. Meier, Anja Böckmann
doi.org/10.1002/anie.202013296

Designable Al32‐Oxo Clusters with Hydrotalcite‐like Structures: Snapshots of Boundary Hydrolysis and Optical Limiting

Par / 18 janvier 2021 / Non classé
Designable Al32‐Oxo Clusters with Hydrotalcite‐like Structures: Snapshots of Boundary Hydrolysis and Optical Limiting

A series of Al32‐oxo clusters with hydrotalcite‐like cores and π‐conjugated shells were isolated, which are unique models of two‐dimensional or layered materials and may be used to study boundary activity and optical limiting properties.

Abstract

The hydrolysis of earth‐abundant AlIII has implications in mineral mimicry, geochemistry and environmental chemistry. Third‐order nonlinear optical (NLO) materials are important in modern chemistry due to their extensive optical applications. The assembly of AlIII ions with π‐conjugated carboxylate ligands is carried out and the hydrolysis and NLO properties of the resultant material are studied. A series of Al32‐oxo clusters with hydrotalcite‐like cores and π‐conjugated shells are isolated. X‐ray diffraction revealed boundary hydrolysis occurs at the equatorially unsaturated coordination sites of AlIII ions. Charge distribution analysis and DFT calculations support the proposed boundary substitution. The Al32‐oxo clusters possess a significant reverse saturable absorption (RSA) response with a minimal normalized transmittance up to 29 %, indicating they are suitable candidates for optical limiting (OL) materials. This work elucidates the hydrolysis of AlIII and provides insight into layered materials that also have strong boundary activity at the edges or corners.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Ya‐Jie Liu, Qiao‐Hong Li, De‐Jing Li, Xue‐Zhen Zhang, Wei‐Hui Fang, Jian Zhang
doi.org/10.1002/anie.202012919

S‐Adenosyl‐l‐ethionine is a Catalytically Competent Analog of S‐Adenosyl‐l‐methione (SAM) in the Radical SAM Enzyme HydG

Par / 18 janvier 2021 / Non classé
S‐Adenosyl‐l‐ethionine is a Catalytically Competent Analog of S‐Adenosyl‐l‐methione (SAM) in the Radical SAM Enzyme HydG

The radical S‐adenosyl‐l‐methione (SAM) enzyme HydG can use S‐adenosyl‐l‐ethionine (SAE) in place of SAM during catalysis. HydG reacts with SAE and tyrosine to form the organometallic intermediate Ω, similar to reaction with SAM. The SAE‐bound [4Fe‐4S]+ cluster of HydG undergoes cryogenic blue light photolysis to generate an ethyl radical. Upon annealing the radical forms an organometallic species in which an ethyl is bound to the unique iron of a [4Fe‐4S]3+ cluster.

Abstract

Radical S‐adenosyl‐l‐methionine (SAM) enzymes initiate biological radical reactions with the 5′‐deoxyadenosyl radical (5′‐dAdo.). A [4Fe‐4S]+ cluster reductively cleaves SAM to form the Ω organometallic intermediate in which the 5′‐deoxyadenosyl moiety is directly bound to the unique iron of the [4Fe‐4S] cluster, with subsequent liberation of 5′‐dAdo.. We present synthesis of the SAM analog S‐adenosyl‐l‐ethionine (SAE) and show SAE is a mechanistically equivalent SAM‐alternative for HydG, both supporting enzymatic turnover of substrate tyrosine and forming the organometallic intermediate Ω. Photolysis of SAE‐bound HydG forms an ethyl radical trapped in the active site. The ethyl radical withstands prolonged storage at 77 K and its EPR signal is only partially lost upon annealing at 100 K, making it significantly less reactive than the methyl radical formed by SAM photolysis. Upon annealing above 77 K, the ethyl radical adds to the [4Fe‐4S]2+ cluster, generating an ethyl‐[4Fe‐4S]3+ organometallic species termed ΩE.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Stella Impano, Hao Yang, Eric M. Shepard, Ryan Swimley, Adrien Pagnier, William E. Broderick, Brian M. Hoffman, Joan B. Broderick
doi.org/10.1002/anie.202014337

Light‐Promoted C–N Coupling of Aryl Halides with Nitroarenes

Par / 18 janvier 2021 / Non classé
Light‐Promoted C–N Coupling of Aryl Halides with Nitroarenes

C–N coupling of aryl halides with nitroarenes is achieved by nickel catalysis under light irradiation and mild basic conditions, with no need for any external photosensitizers, offering a nitro version for the Buchwald–Hartwig C–N coupling reaction.

Abstract

A photochemical C–N coupling of aryl halides with nitroarenes is demonstrated for the first time. Catalyzed by a NiII complex in the absence of any external photosensitizer, readily available nitroarenes undergo coupling with a variety of aryl halides, providing a step‐economic extension to the widely used Buchwald–Hartwig C–N coupling reaction. The method tolerates coupling partners with steric‐congestion and functional groups sensitive to bases and nucleophiles. Mechanistic studies suggest that the reaction proceeds via the addition of an aryl radical, generated from a NiI/NiIII cycle, to a nitrosoarene intermediate.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Gang Li, Liu Yang, Jian‐Jun Liu, Wei Zhang, Rui Cao, Chao Wang, Zunting Zhang, Jianliang Xiao, Dong Xue
doi.org/10.1002/anie.202012877

Behavior of Smart Surfactants in Stabilizing pH‐Responsive Emulsions

Par / 18 janvier 2021 / Non classé
Behavior of Smart Surfactants in Stabilizing pH‐Responsive Emulsions

Newly structured smart surfactants, N+‐(n)‐N, were synthesized with a tertiary amine group at the end of the hydrophobic chain. At neutral and alkaline pH they behave as a cationic surfactant and can stabilize oil‐in‐water emulsions alone or, together with charged nanoparticles, conventional Pickering, or oil‐in‐dispersion emulsions. In acidic media they turn to the Bola form, resulting in demulsification, returning into the aqueous phase which is then recycled when triggered by pH change.

Abstract

Newly structured pH‐responsive smart surfactants (N+‐(n)‐N, n=14, 16) from alkyl trimethylammonium bromides are reported. In neutral and alkaline media N+‐(n)‐N behaves as a normal cationic surfactant and stabilizes conventional emulsions alone, as well as Pickering emulsions and oil‐in‐dispersion emulsions together with oppositely and similarly charged nanoparticles, respectively. In acidic media N+‐(n)‐N becomes a hydrophilic Bola‐type surfactant, N+‐(n)‐NH+, and is an inferior emulsifier either when used alone or together with charged nanoparticles, resulting in demulsification. N+‐(n)‐NH+ returns to the aqueous phase alone or together with nanoparticles after demulsification without contaminating the oil phase, and the aqueous phase can be recycled when triggered by pH change. This protocol is a green process and leads to preparation of various temporarily stable emulsions which are often used in emulsion polymerization, heterogeneous catalysis, and oil transportation.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Xiaomei Pei, Sheng Zhang, Wanqing Zhang, Pei Liu, Binglei Song, Jianzhong Jiang, Zhenggang Cui, Bernard P. Binks
doi.org/10.1002/anie.202013443