The Winding Road towards an Atropo‐enantioselective ‘ARYNE Coupling’

Par / 4 mars 2021 / Non classé
The Winding Road towards an Atropo‐enantioselective ‘ARYNE Coupling’

The enantioselective addition of aryllithiums onto arynes, leading to axially chiral biaryls in the absence of transition metals, was investigated by means of chiral ligands of lithium. Biaryls with a high degree of steric congestion around the aryl–aryl bond could be obtained.

Abstract

For the first time, the challenging atropo‐enantioselective coupling of in‐situ generated arynes and aryllithiums in the presence of a chiral ligand of lithium was investigated. This preliminary study demonstrates the feasibility of this concept, by affording enantioenriched axially chiral biaryls even in the case of products showing a high degree of steric congestion around the newly created aryl−aryl bond.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: David Augros, Corinne Comoy, Yves Fort, Frédéric R. Leroux, Armen Panossian
doi.org/10.1002/ejoc.202100087

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Do Sulfonamides Interact with Aromatic Rings?

Par / 3 mars 2021 / Non classé
Do Sulfonamides Interact with Aromatic Rings?

Through space! It is demonstrated, by using experimental and quantum chemical techniques, that aromatic rings can stabilize sulfonamides via through‐space NH–π interactions. These findings have implications in the rational drug design targeting electron‐rich aromatic rings in proteins.

Abstract

Aromatic rings form energetically favorable interactions with many polar groups in chemical and biological systems. Recent molecular studies have shown that sulfonamides can chelate metal ions and form hydrogen bonds, however, it is presently not established whether the polar sulfonamide functionality also interacts with aromatic rings. Here, synthetic, spectroscopic, structural, and quantum chemical analyses on 2,6‐diarylbenzenesulfonamides are reported, in which two flanking aromatic rings are positioned close to the central sulfonamide moiety. Fine‐tuning the aromatic character by substituents on the flanking rings leads to linear trends in acidity and proton affinity of sulfonamides. This physical‐organic chemistry study demonstrates that aromatic rings have a capacity to stabilize sulfonamides via through‐space NH–π interactions. These results have implications in rational drug design targeting electron‐rich aromatic rings in proteins.

Wiley: Chemistry – A European Journal: Table of Contents
Authors: Jie Jian, Roel Hammink, Christine J. McKenzie, F. Matthias Bickelhaupt, Jordi Poater, Jasmin Mecinović
chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/chem.202004732

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Efficient n‐Doping of Polymeric Semiconductors through Controlling the Dynamics of Solution‐State Polymer Aggregates

Par / 3 mars 2021 / Non classé
Efficient n‐Doping of Polymeric Semiconductors through Controlling the Dynamics of Solution‐State Polymer Aggregates

The dynamic behaviors of conjugated polymer aggregates in solution are correlated with the solid‐state doping efficiency of polymer films. The n‐type electrical conductivity of the polymer P(PzDPP‐CT2) can be significantly enhanced by controlling the dynamics of solution‐state aggregates. The method is general and can be used for other polymer systems with different aggregation tendencies and dynamic behaviors.

Abstract

Doping of polymeric semiconductors limits the miscibility between polymers and dopants. Although significant efforts have been devoted to enhancing miscibility through chemical modification, the electrical conductivities of n‐doped polymeric semiconductors are usually below 10 S cm−1. We report a different approach to overcome the miscibility issue by modulating the solution‐state aggregates of conjugated polymers. We found that the solution‐state aggregates of conjugated polymers not only changed with solvent and temperature but also changed with solution aging time. Modulating the solution‐state polymer aggregates can directly influence their solid‐state microstructures and miscibility with dopants. As a result, both high doping efficiency and high charge‐carrier mobility were simultaneously obtained. The n‐doped electrical conductivity of P(PzDPP‐CT2) can be tuned up to 32.1 S cm−1. This method can also be used to improve the doping efficiency of other polymer systems (e.g. N2200) with different aggregation tendencies and behaviors.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Miao Xiong, Xinwen Yan, Jia‐Tong Li, Song Zhang, Zhiqiang Cao, Nathaniel Prine, Yang Lu, Jie‐Yu Wang, Xiaodan Gu, Ting Lei
doi.org/10.1002/anie.202015216

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Minimization of Back‐Electron Transfer Enables the Elusive sp3 C−H Functionalization of Secondary Anilines

Par / 3 mars 2021 / Non classé
Minimization of Back‐Electron Transfer Enables the Elusive sp3 C−H Functionalization of Secondary Anilines

Divergent radical sp3 C−H functionalization of N‐alkyl anilines has been achieved using a photoredox strategy. This approach enables to overcome back‐electron transfer and therefore allows direct access to previously elusive α‐anilinoalkyl radicals.

Abstract

Anilines are some of the most used class of substrates for application in photoinduced electron transfer. N,N‐Dialkyl‐derivatives enable radical generation α to the N‐atom by oxidation followed by deprotonation. This approach is however elusive to monosubstituted anilines owing to fast back‐electron transfer (BET). Here we demonstrate that BET can be minimised by using photoredox catalysis in the presence of an exogenous alkylamine. This approach synergistically aids aniline SET oxidation and then accelerates the following deprotonation. In this way, the generation of α‐anilinoalkyl radicals is now possible and these species can be used in a general sense to achieve divergent sp3 C−H functionalization.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Huaibo Zhao, Daniele Leonori
doi.org/10.1002/anie.202100051

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Oxalohydrazide Ligands for Copper‐Catalyzed C−O Coupling Reactions with High Turnover Numbers

Par / 3 mars 2021 / Non classé
Oxalohydrazide Ligands for Copper‐Catalyzed C−O Coupling Reactions with High Turnover Numbers

A copper‐catalyzed coupling of (hetero)aryl halides with phenols and aliphatic alcohols to form biaryl ethers and alkyl aryl ethers, with loadings down to 125 ppm of the combination of CuBr and oxalohydrazide ligands with broad scope, is reported. Experiments on reaction rates show that the copper catalysts ligated by oxalohydrazide ligands are long lived with measurably higher initial rates than those of the state‐of‐the‐art copper catalysts.

Abstract

Here, we report a class of ligands based on oxalohydrazide cores and N‐amino pyrrole and N‐amino indole units that generates long‐lived copper catalysts for couplings that form the C−O bonds in biaryl ethers. These Cu‐catalyzed coupling of phenols with aryl bromides occurred with turnovers up to 8000, a value which is nearly two orders of magnitude higher than those of prior couplings to form biaryl ethers and nearly an order of magnitude higher than those of any prior copper‐catalyzed coupling of aryl bromides and chlorides. This ligand also led to copper systems that catalyze the coupling of aryl chlorides with phenols and the coupling of aryl bromides and iodides with primary benzylic and aliphatic alcohols. A wide variety of functional groups including nitriles, halides, ethers, ketones, amines, esters, amides, vinylarenes, alcohols and boronic acid esters were tolerated, and reactions occurred with aryl bromides in pharmaceutically related structures.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Ritwika Ray, John F. Hartwig
doi.org/10.1002/anie.202015654

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Red to Near‐Infrared Mechanochromism from Metal‐free Polycrystals: Noncovalent Conformational Locks Facilitating Wide‐Range Redshift

Par / 3 mars 2021 / Non classé
Red to Near‐Infrared Mechanochromism from Metal‐free Polycrystals: Noncovalent Conformational Locks Facilitating Wide‐Range Redshift

Noncovalent conformational locks are shown to be an effective strategy to endow the highly coplanar luminophore with good stability and high fluorescence efficiency. The high degree of conformational coplanarity is responsible for red to near‐infrared mechanochromism of metal‐free crystals.

Abstract

Piezochromic organic materials that present a large difference in fluorescence wavelength in the near‐infrared region have important potential applications; however, few such metal‐free luminophores have been reported. In this study, we design and prepare π‐conjugated electron acceptors whose planar conformation can be locked by the noncovalent interactions. The planar fused‐ring geometry can narrow the optical band gap, enhance the molecular stability and rigidity, as well as increase the radiative rate. As expected, the polymorphs Re‐phase and Ni‐phase emit the high‐brightness fluorescence with wavelength maxima (λem,max) at 615 and 727 nm, respectively. Upon full grinding, the λem,max of Re‐phase is bathochromically shifted to 775 nm. The ground powder of Re‐phase becomes metastable as a consequence of noncovalent conformational locking and that the red to near‐infrared (large colour difference) mechanochromism arises from the high degree of conformational coplanarity. This strategy is both conceptually and synthetically simple and offers a promising approach to the development of organic piezochromic materials with wide‐range redshift and excellent penetrability.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Chenfei Zhu, Qing Luo, Yunxia Shen, Chunyan Lv, Sanhu Zhao, Xiaojing Lv, Feng Cao, Kunyan Wang, Qingbao Song, Cheng Zhang, Yujian Zhang
doi.org/10.1002/anie.202100301

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Highly Efficient Near‐Infrared Electrofluorescence from a Thermally Activated Delayed Fluorescence Molecule

Par / 3 mars 2021 / Non classé
Highly Efficient Near‐Infrared Electrofluorescence from a Thermally Activated Delayed Fluorescence Molecule

A highly efficient NIR‐TADF emitter with high kRISC is developed for NIR‐OLEDs. The NIR‐TADF‐OLED showed a significantly high EQE of 13.4 % with an EL peak at 734 nm. Notably, the NIR‐TADF molecule can sensitize a deeper‐NIR‐fluorophore, resulting in an EQE of 1.1 % at over 900 nm in the TADF‐sensitized NIR‐OLED.

Abstract

Near‐IR organic light‐emitting diodes (NIR‐OLEDs) are potential light‐sources for various sensing applications as OLEDs have unique features such as ultra‐flexibility and low‐cost fabrication. However, the low external electroluminescence (EL) quantum efficiency (EQE) of NIR‐OLEDs is a critical obstacle for potential applications. Here, we demonstrate a highly efficient NIR emitter with thermally activated delayed fluorescence (TADF) and its application to NIR‐OLEDs. The NIR‐TADF emitter, TPA‐PZTCN, has a high photoluminescence quantum yield of over 40 % with a peak wavelength at 729 nm even in a highly doped co‐deposited film. The EL peak wavelength of the NIR‐OLED is 734 nm with an EQE of 13.4 %, unprecedented among rare‐metal‐free NIR‐OLEDs in this spectral range. TPA‐PZTCN can sensitize a deeper NIR fluorophore to achieve a peak wavelength of approximately 900 nm, resulting in an EQE of over 1 % in a TADF‐sensitized NIR‐OLED with high operational device durability (LT95>600 h.).

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Umamahesh Balijapalli, Ryo Nagata, Nishiki Yamada, Hajime Nakanotani, Masaki Tanaka, Anthony D’Aléo, Virginie Placide, Masashi Mamada, Youichi Tsuchiya, Chihaya Adachi
doi.org/10.1002/anie.202016089

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Current Trends in Metal–Organic and Covalent Organic Framework Membrane Materials

Par / 3 mars 2021 / Non classé
Current Trends in Metal–Organic and Covalent Organic Framework Membrane Materials

Metal–organic frameworks, covalent organic frameworks, polymers, and composites are disruptive key technologies for gas separation membranes. This Minireview highlights the state of the art in materials and material development and their utilization in membrane applications in highly relevant processes such as carbon capture, energy‐ and resource‐efficient separations of basic chemicals, and quantum sieving.

Abstract

Metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) have been thoroughly investigated with regards to applications in gas separation membranes in the past years. More recently, new preparation methods for MOFs and COFs as particles and thin‐film membranes, as well as for mixed‐matrix membranes (MMMs) have been developed. We will highlight novel processes and highly functional materials: Zeolitic imidazolate frameworks (ZIFs) can be transformed into glasses and we will give an insight into their use for membranes. In addition, liquids with permanent porosity offer solution processability for the manufacture of extremely potent MMMs. Also, MOF materials influenced by external stimuli give new directions for the enhancement of performance by in situ techniques. Presently, COFs with their large pores are useful in quantum sieving applications, and by exploiting the stacking behavior also molecular sieving COF membranes are possible. Similarly, porous polymers can be constructed using MOF templates, which then find use in gas separation membranes.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Bahram Hosseini Monjezi, Ksenia Kutonova, Manuel Tsotsalas, Sebastian Henke, Alexander Knebel
doi.org/10.1002/anie.202015790

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In Situ Stable Generation of Reactive Intermediates by Open Microfluidic Probe for Subcellular Free Radical Attack and Membrane Labeling

Par / 3 mars 2021 / Non classé
In Situ Stable Generation of Reactive Intermediates by Open Microfluidic Probe for Subcellular Free Radical Attack and Membrane Labeling

An open space microfluidic probe has been developed to stably synthesize reactive intermediates in situ for subcellular chemistry. Reactant systems (A, B) mix and react with each other within a chemical reaction microregion (several μm). The continuously produced free radicals can attack cellular compounds within the microregion before quenching, realizing subcellular radical stimulation.

Abstract

Subcellular stimulation by free radicals is crucial for deeper insight of cell behaviors. However, it remains a tough challenge due to the high spatial precision requirement and short life of radicals. Herein, we report a versatile open microfluidic probe for stable generation of free radical and subcellular stimulation. By optimizing parameters, the chemical reaction can be confined in a microregion with a diameter of several μm, and the real‐time produced reactive radicals can attack the desired subcellular region of a single cell. In order to reveal the attacked region, fluorescent cyanine 3 labeled tyramide free radicals are synthesized, and the target microregion on a single cell is successfully stained by the covalent linking reaction between radicals and membrane proteins, which proves the feasibility of our method. We believe this method will open new avenues for short‐lived reactive intermediates stimulation at the single‐cell/sub‐cell level and selective membrane labeling.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Qiang Zhang, Shuo Feng, Weiwei Li, Tianze Xie, Wanling Zhang, Jin‐Ming Lin
doi.org/10.1002/anie.202016171

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Bright and Robust Phosphorescence Achieved by Non‐Covalent Clipping

Par / 3 mars 2021 / Non classé
Bright and Robust Phosphorescence Achieved by Non‐Covalent Clipping

A pre‐organized tweezer receptor has been constructed to encapsulate triplet emitters. The emitters displayed bright and robust phosphorescence in versatile media upon non‐covalent clipping, regardless of emitter concentration, oxygen content, and environmental polarity variations.

Abstract

Phosphorescent materials with bright emission in versatile media are important for their practical applications, which require to lower the susceptibility of triplet excitons to surroundings. Herein a non‐covalent clipping strategy has been developed to attain this objective, by designing a tweezer receptor to encapsulate PtII‐based triplet emitters through two‐fold π‐stacking interactions. The PtII emitters display robust phosphorescence by virtue of synergistic rigidifying and shielding effects, which are hardly influenced by emitter concentration, oxygen content, and solvent polarity changes. The phosphorescent colors are elaborately modulated by varying ligand substitutes on PtII emitters. Circularly polarized phosphorescence is further amplified for chiral PtII emitters, by taking advantage of dual phosphorescence and chirality enhancement upon non‐covalent tweezer complexation. Overall, the clipping approach paves the way for the development of high‐performance phosphorescent materials with bright emission, environmental robustness, and facile color tunability.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Zijian Li, Yifei Han, Fude Nie, Mingyang Liu, Hua Zhong, Feng Wang
doi.org/10.1002/anie.202015846

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Fe‐Catalyzed Anaerobic Mukaiyama‐Type Hydration of Alkenes using Nitroarenes

Par / 3 mars 2021 / Non classé
Fe‐Catalyzed Anaerobic Mukaiyama‐Type Hydration of Alkenes using Nitroarenes

The highly diastereoselective Fe‐catalyzed anaerobic Markovnikov‐selective hydration of alkenes using nitroarenes as oxygenation reagents is reported.

Abstract

Hydration of alkenes using first row transition metals (Fe, Co, Mn) under oxygen atmosphere (Mukaiyama‐type hydration) is highly practical for alkene functionalization in complex synthesis. Different hydration protocols have been developed, however, control of the stereoselectivity remains a challenge. Herein, highly diastereoselective Fe‐catalyzed anaerobic Markovnikov‐selective hydration of alkenes using nitroarenes as oxygenation reagents is reported. The nitro moiety is not well explored in radical chemistry and nitroarenes are known to suppress free radical processes. Our findings show the potential of cheap nitroarenes as oxygen donors in radical transformations. Secondary and tertiary alcohols were prepared with excellent Markovnikov‐selectivity. The method features large functional group tolerance and is also applicable for late‐stage chemical functionalization. The anaerobic protocol outperforms existing hydration methodology in terms of reaction efficiency and selectivity.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Anup Bhunia, Klaus Bergander, Constantin Gabriel Daniliuc, Armido Studer
doi.org/10.1002/anie.202015740

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Metal–Organic‐Framework‐Supported Molecular Electrocatalysis for the Oxygen Reduction Reaction

Par / 3 mars 2021 / Non classé
Metal–Organic‐Framework‐Supported Molecular Electrocatalysis for the Oxygen Reduction Reaction

A variety of porphyrin@MOF hybrids were synthesized by grafting porphyrins on MOFs through ligand exchange. These hybrids showed boosted activity and significantly improved selectivity for the four‐electron reduction of oxygen. Zn‐air batteries assembled with these hybrids exhibited comparable performance to that with Pt‐based materials. Combining various molecular catalysts and MOFs is appealing to develop materials with diverse applications.

Abstract

Synthesizing molecule@support hybrids is appealing to improve molecular electrocatalysis. We report herein metal–organic framework (MOF)‐supported Co porphyrins for the oxygen reduction reaction (ORR) with improved activity and selectivity. Co porphyrins can be grafted on MOF surfaces through ligand exchange. A variety of porphyrin@MOF hybrids were made using this method. Grafted Co porphyrins showed boosted ORR activity with large (>70 mV) anodic shift of the half‐wave potential compared to ungrafted porphyrins. By using active MOFs for peroxide reduction, the number of electrons transferred per O2 increased from 2.65 to 3.70, showing significantly improved selectivity for the 4e ORR. It is demonstrated that H2O2 generated from O2 reduction at Co porphyrins is further reduced at MOF surfaces, leading to improved 4e ORR. As a practical demonstration, these hybrids were used as air electrode catalysts in Zn‐air batteries, which exhibited equal performance to that with Pt‐based materials.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Zuozhong Liang, Hongbo Guo, Guojun Zhou, Kai Guo, Bin Wang, Haitao Lei, Wei Zhang, Haoquan Zheng, Ulf‐Peter Apfel, Rui Cao
doi.org/10.1002/anie.202016024

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Scalable De Novo Synthesis of Aldgarose and Total Synthesis of Aldgamycin N

Par / 3 mars 2021 / Non classé
Scalable De Novo Synthesis of Aldgarose and Total Synthesis of Aldgamycin N

One sugar has to be attached before the transannular ketone is revealed from an alkyne precursor to render the first successful total synthesis ever of a member of the aldgamycin family of antibiotics. Although this phasing of events implies that the precious branched monosaccharide must be carried through several steps, a practical and scalable synthesis of the required aldgarose fragment greatly mitigates the “cost” of this strategy.

Abstract

Since the accompanying study had shown that the introduction of the eponymous aldgarose sugar to the C5‐OH group of the macrocyclic aglycone of aldgamycin N is most difficult, if not even impossible, the synthesis route was revised and the glycosidation performed at an earlier stage. To mitigate the “cost” of this strategic amendment, a practical and scalable de novo synthesis of this branched octose was developed. The glycoside formation required mild conditions; it commenced with the reaction of the aglycone with the trichloroacetimidate donor to give a transient orthoester, which slowly rearranged to the desired aldgaropyranoside. The presence of the polar peripheral groups in the product did not impede the selective late‐stage functionalization of the macrolide ring itself: the contained propargylic alcohol entity was readily transformed into the characteristic acyloin motif of the target by a ruthenium‐catalyzed trans‐hydrostannation followed by a modified Chan‐Lam‐type coupling.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Georg Späth, Alois Fürstner
doi.org/10.1002/anie.202016477

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Metal–Organic Framework Decorated Cuprous Oxide Nanowires for Long‐lived Charges Applied in Selective Photocatalytic CO2 Reduction to CH4

Par / 3 mars 2021 / Non classé
Metal–Organic Framework Decorated Cuprous Oxide Nanowires for Long‐lived Charges Applied in Selective Photocatalytic CO2 Reduction to CH4

Cu2O nanowires are decorated with Cu3(BTC)2 by a surfactant‐free method. The Cu2O@Cu3(BTC)2 core–shell structure offers enlarged active surfaces and prolonged lifetime of separated electrons for CO2 reduction into CH4, exhibiting enhanced photocatalytic activity and stability compared to the bare Cu2O.

Abstract

Improving the stability of cuprous oxide (Cu2O) is imperative to its practical applications in artificial photosynthesis. In this work, Cu2O nanowires are encapsulated by metal–organic frameworks (MOFs) of Cu3(BTC)2 (BTC=1,3,5‐benzene tricarboxylate) using a surfactant‐free method. Such MOFs not only suppress the water vapor‐induced corrosion of Cu2O but also facilitate charge separation and CO2 uptake, thus resulting in a nanocomposite representing 1.9 times improved activity and stability for selective photocatalytic CO2 reduction into CH4 under mild reaction conditions. Furthermore, direct transfer of photogenerated electrons from the conduction band of Cu2O to the LUMO level of non‐excited Cu3(BTC)2 has been evidenced by time‐resolved photoluminescence. This work proposes an effective strategy for CO2 conversion by a synergy of charge separation and CO2 adsorption, leading to the enhanced photocatalytic reaction when MOFs are integrated with metal oxide photocatalyst.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Hao Wu, Xin Ying Kong, Xiaoming Wen, Siang‐Piao Chai, Emma C. Lovell, Junwang Tang, Yun Hau Ng
doi.org/10.1002/anie.202015735

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On‐Surface Synthesis of Nitrogen‐Doped Kagome Graphene

Par / 3 mars 2021 / Non classé
On‐Surface Synthesis of Nitrogen‐Doped Kagome Graphene

Nitrogen‐doped Kagome graphene is predicted to display a topological band gap and unconventional superconductivity. Two‐dimensional graphene sheets possessing a long‐range honeycomb Kagome lattice have now been synthesized by a substrate‐assisted Ullmann reaction on Ag(111). Scanning probe microscopy supported by density functional theory proves the appearance of Kagome flat bands, opening the design of graphene‐based topological materials.

Abstract

Nitrogen‐doped Kagome graphene (N‐KG) has been theoretically predicted as a candidate for the emergence of a topological band gap as well as unconventional superconductivity. However, its physical realization still remains very elusive. Here, we report on a substrate‐assisted reaction on Ag(111) for the synthesis of two‐dimensional graphene sheets possessing a long‐range honeycomb Kagome lattice. Low‐temperature scanning tunneling microscopy (STM) and atomic force microscopy (AFM) with a CO‐terminated tip supported by density functional theory (DFT) are employed to scrutinize the structural and electronic properties of the N‐KG down to the atomic scale. We demonstrate its semiconducting character due to the nitrogen doping as well as the emergence of Kagome flat bands near the Fermi level which would open new routes towards the design of graphene‐based topological materials.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Rémy Pawlak, Xunshan Liu, Silviya Ninova, Philipp D’Astolfo, Carl Drechsel, Jung‐Ching Liu, Robert Häner, Silvio Decurtins, Ulrich Aschauer, Shi‐Xia Liu, Ernst Meyer
doi.org/10.1002/anie.202016469

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Challenges and Opportunities in the Post‐Synthetic Modification of Interlocked Molecules

Par / 3 mars 2021 / Non classé
Challenges and Opportunities in the Post‐Synthetic Modification of Interlocked Molecules

This Review highlights the challenges in covalently modifying interlocked molecules, whereby the chemical bond plays a fundamental role in the strategy employed. Such routes can involve cleavage of the axle’s main chain, but always with conservation of the mechanical bond, and allow access to more sophisticated interlocked molecules.

Abstract

Several strategies have been successfully utilised to obtain a wide range of interlocked molecules. However, some interlocked compounds are still not obtained directly and/or efficiently from non‐interlocked components because the requisites for self‐assembly cannot always be enforced. To circumvent such a synthetic problem, a strategy that consists of synthesizing an isolable and storable interlocked building block in a step that precedes its modification is an appealing chemical route to more sophisticated interlocked molecules. Synthetic opportunities and challenges are closely linked to the fact that the mechanical bond might greatly affect the reactivity of a functionality of the encircled axle, but that the interlocked architecture needs to be preserved during the synthesis. Hence, the mechanical bond plays a fundamental role in the strategy employed. This Review focuses on the challenging post‐synthetic modifications of interlocked molecules, sometimes through cleavage of the axle’s main chain, but always with conservation of the mechanical bond.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Philip Waelès, Maxime Gauthier, Frédéric Coutrot
doi.org/10.1002/anie.202007496

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Exclusive Strain Effect Boosts Overall Water Splitting in PdCu/Ir Core/Shell Nanocrystals

Par / 3 mars 2021 / Non classé
Exclusive Strain Effect Boosts Overall Water Splitting in PdCu/Ir Core/Shell Nanocrystals

By precisely controlling the thickness of the shell layer, an exclusive strain effect and the complete elimination of the ligand effect can be achieved on the PdCu/Ir core/shell nanocrystals to optimize the d‐band center and boost electrocatalytic overall water splitting performance.

Abstract

Core/shell nanocatalysts are a class of promising materials, which achieve the enhanced catalytic activities through the synergy between ligand effect and strain effect. However, it has been challenging to disentangle the contributions from the two effects, which hinders the rational design of superior core/shell nanocatalysts. Herein, we report precise synthesis of PdCu/Ir core/shell nanocrystals, which can significantly boost oxygen evolution reaction (OER) via the exclusive strain effect. The heteroepitaxial coating of four Ir atomic layers onto PdCu nanoparticle gives a relatively thick Ir shell eliminating the ligand effect, but creates a compressive strain of ca. 3.60%. The strained PdCu/Ir catalysts can deliver a low OER overpotential and a high mass activity. Density functional theory (DFT) calculations reveal that the compressive strain in Ir shell downshifts the d‐band center and weakens the binding of the intermediates, causing the enhanced OER activity. The compressive strain also boosts hydrogen evolution reaction (HER) activity and the strained nanocrystals can be served as excellent catalysts for both anode and cathode in overall water‐splitting electrocatalysis.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Menggang Li, Zhonglong Zhao, Zhonghong Xia, Mingchuan Luo, Qinghua Zhang, Yingnan Qin, Lu Tao, Kun Yin, Yuguang Chao, Lin Gu, Weiwei Yang, Yongsheng Yu, Gang Lu, Shaojun Guo
doi.org/10.1002/anie.202016199

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Consecutive β,β′‐Selective C(sp3)−H Silylation of Tertiary Amines with Dihydrosilanes Catalyzed by B(C6F5)3

Par / 3 mars 2021 / Non classé
Consecutive β,β′‐Selective C(sp3)−H Silylation of Tertiary Amines with Dihydrosilanes Catalyzed by B(C6F5)3

Acyclic tertiary amines with alkyl substitution undergo two consecutive C(sp3)−H silylation reactions with dihydrosilanes to form 4‐silapiperidines. Bond formation occurs β to the nitrogen atom at two of the alkyl residues. The reaction is catalyzed by the strong boron Lewis acid B(C6F5)3 and involves enamine intermediates generated by dehydrogenation.

Abstract

Tris(pentafluorophenyl)borane has been found to catalyze the two‐fold C(sp3)−H silylation of various trialkylamine derivatives with dihydrosilanes, furnishing the corresponding 4‐silapiperidines in decent yields. The multi‐step reaction cascade involves amine‐to‐enamine dehydrogenation at two alkyl residues and two electrophilic silylation reactions of those enamines, one inter‐ and one intramolecular.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Huaquan Fang, Kaixue Xie, Sebastian Kemper, Martin Oestreich
doi.org/10.1002/anie.202016664

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Efficient Palladium‐Catalyzed Carbonylation of 1,3‐Dienes: Selective Synthesis of Adipates and Other Aliphatic Diesters

Par / 3 mars 2021 / Non classé
Efficient Palladium‐Catalyzed Carbonylation of 1,3‐Dienes: Selective Synthesis of Adipates and Other Aliphatic Diesters

High value‐added conversion: From gas to nylon precursor. This 100 % atom economic and industrially relevant process is strongly influenced by the system polarity.

Abstract

The dicarbonylation of 1,3‐butadiene to adipic acid derivatives offers the potential for a more cost‐efficient and environmentally benign industrial process. However, the complex reaction network of regioisomeric carbonylation and isomerization pathways, make a selective and direct transformation particularly difficult. Here, we report surprising solvent effects on this palladium‐catalysed process in the presence of 1,2‐bis‐di‐tert‐butylphosphin‐oxylene (dtbpx) ligands, which allow adipate diester formation from 1,3‐butadiene, carbon monoxide, and methanol with 97 % selectivity and 100 % atom‐economy under scalable conditions. Under optimal conditions a variety of di‐ and triesters from 1,2‐ and 1,3‐dienes can be obtained in good to excellent yields.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Ji Yang, Jiawang Liu, Yao Ge, Weiheng Huang, Francesco Ferretti, Helfried Neumann, Haijun Jiao, Robert Franke, Ralf Jackstell, Matthias Beller
doi.org/10.1002/anie.202015329

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M(NH2SO3)2 (M=Sr, Ba): Two Deep‐Ultraviolet Transparent Sulfamates Exhibiting Strong Second Harmonic Generation Responses and Moderate Birefringence

Par / 3 mars 2021 / Non classé
M(NH2SO3)2 (M=Sr, Ba): Two Deep‐Ultraviolet Transparent Sulfamates Exhibiting Strong Second Harmonic Generation Responses and Moderate Birefringence

A new non‐π‐conjugated group, (NH2SO3)−, was discovered by the first‐principles calculation. By combining alkaline‐earth metals with (NH2SO3)− group, two deep‐UV transparent NLO sulfamates, M(NH2SO3)2 (M=Sr, Ba) with excellent optical properties have been successfully synthesized and grown. BNSO shows the largest powder SHG efficiency among the known DUV NLO sulfates and sulfamates.

Abstract

Over the last few decades, the development of each new nonlinear optical (NLO)‐active functional unit has led to the discoveries of a series of excellent NLO materials. In the present work, based on first‐principles studies, we identified a novel deep‐UV (DUV) NLO‐active functional unit, a non‐π‐conjugated group viz. (NH2SO3)−. By combining alkaline‐earth metals with (NH2SO3)− group, two DUV transparent NLO sulfamates, M(NH2SO3)2 (M=Sr, Ba) with superior optical properties including strong SHG responses (1.2 and 2.7 × KH2PO4 (KDP)), short UV cut‐off edge (<190 nm) and moderate birefringence (0.056@589.3 nm for Sr(NH2SO3)2) were successfully synthesized. Our work has provided not only two promising DUV transparent NLO crystals, but also an innovative non‐π‐conjugated unit for developing more DUV transparent NLO materials.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Xia Hao, Min Luo, Chensheng Lin, Guang Peng, Feng Xu, Ning Ye
doi.org/10.1002/anie.202016372

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Visible‐Light Promoted C–O Bond Formation with an Integrated Carbon Nitride–Nickel Heterogeneous Photocatalyst

Par / 3 mars 2021 / Non classé
Visible‐Light Promoted C–O Bond Formation with an Integrated Carbon Nitride–Nickel Heterogeneous Photocatalyst

A Ni‐deposited carbon nitride material was developed as a fully heterogeneous dual photocatalyst. Visible light‐driven C–O cross‐coupling is demonstrated free of organic ligands and additives. This dual catalytic system operates with very low nickel loadings and the heterogeneous photocatalyst can be easily recycled.

Abstract

Ni‐deposited mesoporous graphitic carbon nitride (Ni‐mpg‐CNx) is introduced as an inexpensive, robust, easily synthesizable and recyclable material that functions as an integrated dual photocatalytic system. This material overcomes the need of expensive photosensitizers, organic ligands and additives as well as limitations of catalyst deactivation in the existing photo/Ni dual catalytic cross‐coupling reactions. The dual catalytic Ni‐mpg‐CNx is demonstrated for C–O coupling between aryl halides and aliphatic alcohols under mild condition. The reaction affords the ether product in good‐to‐excellent yields (60–92 %) with broad substrate scope, including heteroaryl and aryl halides bearing electron‐withdrawing, ‐donating and neutral groups. The heterogeneous Ni‐mpg‐CNx can be easily recovered from the reaction mixture and reused over multiple cycles without loss of activity. The findings highlight exciting opportunities for dual catalysis promoted by a fully heterogeneous system.

Wiley: Angewandte Chemie International Edition: Table of Contents
Authors: Arjun Vijeta, Carla Casadevall, Souvik Roy, Erwin Reisner
doi.org/10.1002/anie.202016511

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Stereoselective Organocatalytic Construction of Spiro Oxindole Pyrrolidines Using Unsaturated α‐Ketoesters and α‐Ketoamides

Par / 3 mars 2021 / Non classé
Stereoselective Organocatalytic Construction of Spiro Oxindole Pyrrolidines Using Unsaturated α‐Ketoesters and α‐Ketoamides

Spiro‐oxindole pyrrolidines are formed by formal [3+2] cycloaddition between oxindole imines and unsaturated keto esters and keto amide. Keto amides also afford alternative products via enolate protonation and addition of nitrogen on the carbonyl group. Quinine‐based squaramide organocatalyst was able to provide keto ester pyrrolidines in enantiomeric purity of up to e.r. 86 : 14.

Abstract

We have investigated the stereoselective formation of spiro oxindole pyrrolidines via formal [3+2] cycloaddition of oxindole imines with ketoesters and ketoamides. Bifunctional squaramide organocatalyst was able to induce enantioselectivity of up to 60 % ee, increased to 72 % ee after re‐crystallization, in the formation of spiro pyrrolidines with ketoesters. Interestingly, ketoamides provided alternative spiro oxindole pyrrole products in addition to the main product, which was formed via a different reaction pathway. Structures of spiro oxindole pyrrolidine as well as pyrrole products were confirmed by X‐ray crystallographic analysis. Two new squaramide based catalysts were synthesized and tested. DFT calculation helped elucidate the reaction course.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Tibor Peňaška, Vitalii Palchykov, Erik Rakovský, Gabriela Addová, Radovan Šebesta
doi.org/10.1002/ejoc.202100022

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Excited‐State 2,3‐Dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ*) Initiated Organic Synthetic Transformations under Visible‐Light Irradiation

Par / 3 mars 2021 / Non classé
Excited‐State 2,3‐Dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ*) Initiated Organic Synthetic Transformations under Visible‐Light Irradiation

2,3‐Dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) is a classic oxidation reagent in organic synthesis. Upon visible light excitation its oxidation potential is boosted beyond+3 V vs SCE. This property has been used for oxidative organic transformations and catalyst regeneration is achieved by air oxygen or electrochemically.

Abstract

The one‐electron oxidizing capacity of 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) improves significantly by visible‐light excitation. The exited‐state DDQ (DDQ*) even converts benzene, fluoroarenes, heteroarenes, benzyls, and olefins into their corresponding radical cations as well as chloride and other anions into their radicals. These reactive intermediates have been utilized for the generation of C−C and C−X (N, O, or Cl) bonds in the synthesis of valuable organic compounds and natural products. This mini review provides an overview of such DDQ*‐initiated organic transformations with their scope and limitations and discusses the proposed reactions mechanisms.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Palani Natarajan, Burkhard König
doi.org/10.1002/ejoc.202100011

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Catalytic Synthesis of Dibenzazepines and Dibenzazocines by 7‐Exo‐ and 8‐Endo‐Dig‐Selective Cycloisomerization

Par / 3 mars 2021 / Non classé
Catalytic Synthesis of Dibenzazepines and Dibenzazocines by 7‐Exo‐ and 8‐Endo‐Dig‐Selective Cycloisomerization

The cationic Au(I)‐catalyzed reaction achieved 7‐exo‐dig‐selective cycloisomerization of 2‐propargylamino‐N‐tosylbiphenyls with terminal alkyne along with the construction of a dibezazepine skeleton. In addition, the reaction of internal alkynes gave 8‐endo‐dig‐selective products. This strategy could be used for the ynamide substrate and the intramolecular reaction provided 7‐exo‐dig‐selctive cycloadducts by use of a Ag salt.

Abstract

The 7‐exo‐ and 8‐endo‐dig‐selective gold‐catalyzed cycloisomerizations of 2‐propargylamino biphenyl derivatives were developed. The reaction of terminal alkynes gave dibenzo[b,d]azepines by 7‐exo‐dig cycloisomerization. In contrast, when internal alkynes were subjected to the reaction, 8‐endo‐dig cycloisomerization proceeded to provide dibenzo[b,d]azocines. The nucleophilicity at the reaction site and the electron‐withdrawing effect of a tosyl group were important for the present selective transformation. This protocol could be used for ynamide substrates and a silver‐catalyzed reaction gave 7‐exo‐dig products selectively.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Mamoru Ito, Asahi Takaki, Moeka Okamura, Kyalo Stephen Kanyiva, Takanori Shibata
doi.org/10.1002/ejoc.202001643

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Synthesis, Structures, and Electrochemical Properties of Bis‐ and Tetrakis(diphenylphosphino)tetrathiafulvalenes Extended with an Anthraquinoid Spacer

Par / 3 mars 2021 / Non classé
Synthesis, Structures, and Electrochemical Properties of Bis‐ and Tetrakis(diphenylphosphino)tetrathiafulvalenes Extended with an Anthraquinoid Spacer

Tetrathiafulvalenes extended with an anthraquinoid spacer (TTFAQ) functionalized diphenylphosphino groups were successfully synthesized. X‐ray structure analysis revealed that the phosphorus atoms adopt the typical distorted tetrahedral geometry. The cyclic voltammetry suggested the coexistence of two different reduction processes depending on the scan rate. It is the first observation in TTFAQs without TTF moieties.

Abstract

Bis‐ and tetrakis(diphenylphosphino)tetrathiafulvalenes extended with an anthraquinoid spacer were successfully synthesized. X‐ray structure analysis revealed that the phosphorus atoms adopt the typical distorted tetrahedral geometry. Their average C−P−C angles and phosphorus−carbon distances resemble those of diphenylphosphino‐substituted TTF derivatives. The cyclic voltammograms consisted of one pair of irreversible, simultaneous two‐electron transfer waves. A combination of cyclic voltammetry experiments and DFT calculations suggested the coexistence of two different reduction processes depending on the scan rate.

Wiley: European Journal of Organic Chemistry: Table of Contents
Authors: Aya Yoshimura, Keisuke Henmi, Ayaka Handa, Kohei Kagawa, Takashi Shirahata, Yohji Misaki
doi.org/10.1002/ejoc.202100039

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