1,720,965 research outputs found
Nickel‐Catalyzed Electrooxidative C−H Amination: Support for Nickel(IV)
No full textAbstract Nickel‐catalyzed electrochemical C−H aminations were accomplished by chemo‐ and position‐selective C−H activation with ample scope. Detailed mechanistic studies highlighted a facile C−H cleavage with unique chemo‐selectivity, while cyclovoltammetric analysis provided support for a nickel(II/III/IV) manifold.Distinguished International Students Scholarship https://doi.org/10.13039/501100010893Deutsche Forschungsgemeinschaft https://doi.org/10.13039/501100001659Alexander von Humboldt-Stiftung https://doi.org/10.13039/10000515
Remote C–H Functionalizations by Ruthenium Catalysis
No full textAbstract Synthetic transformations of otherwise inert C–H bonds have emerged as a powerful tool for molecular modifications during the last decades, with broad applications towards pharmaceuticals, material sciences, and crop protection. Consistently, a key challenge in C–H activation chemistry is the full control of site-selectivity. In addition to substrate control through steric hindrance or kinetic acidity of C–H bonds, one important approach for the site-selective C–H transformation of arenes is the use of chelation-assistance through directing groups, therefore leading to proximity-induced ortho-C–H metalation. In contrast, more challenging remote C–H activations at the meta- or para-positions continue to be scarce. Within this review, we demonstrate the distinct character of ruthenium catalysis for remote C–H activations until March 2021, highlighting among others late-stage modifications of bio-relevant molecules. Moreover, we discuss important mechanistic insights by experiments and computation, illustrating the key importance of carboxylate-assisted C–H activation with ruthenium(II) complexes. 1 Introduction 2 Stoichiometric Remote C–H Functionalizations 3 meta-C–H Functionalizations 4 para-C–H Functionalizations 5 meta-/ortho-C–H Difunctionalizations 6 Conclusion
Nickelaelektrokatalysierte, milde C‐H‐Alkylierungen bei Raumtemperatur
No full textDFG http://dx.doi.org/10.13039/501100001659Alexander von Humboldt-Stiftung http://dx.doi.org/10.13039/10000515
Nickela‐electrocatalyzed Mild C−H Alkylations at Room Temperature
No full textAbstract Direct alkylations of carboxylic acid derivatives are challenging and particularly nickel catalysis commonly requires high reaction temperatures and strong bases, translating into limited substrate scope. Herein, nickel‐catalyzed C−H alkylations of unactivated 8‐aminoquinoline amides have been realized under exceedingly mild conditions, namely at room temperature, with a mild base and a user‐friendly electrochemical setup. This electrocatalyzed C−H alkylation displays high functional group tolerance and is applicable to both the primary and secondary alkylation. Based on detailed mechanistic studies, a nickel(II/III/I) catalytic manifold has been proposed.Electrochemically enabled nickel‐catalyzed C−H alkylations with primary and secondary alkyl halides have been accomplished under exceedingly mild reaction conditions with Et3N at room temperature. Detailed mechanistic studies provided support for a nickel(II/III/I) manifold. imageDFG http://dx.doi.org/10.13039/501100001659Alexander von Humboldt-Stiftung http://dx.doi.org/10.13039/10000515
Mangana( iii / iv )electro-catalyzed C(sp 3 )–H azidation
No full textThe merger of manganese-catalyzed C–H functionalization with electrosynthesis enabled C(sp 3 )–H azidation devoid of chemical oxidants or photochemical irradiation. Detailed mechanistic studies are supportive of a manganese( iii/iv ) electrocatalysis.Manganaelectro-catalyzed azidation of otherwise inert C(sp 3 )–H bonds was accomplished using most user-friendly sodium azide as the nitrogen-source. The operationally simple, resource-economic C–H azidation strategy was characterized by mild reaction conditions, no directing group, traceless electrons as the sole redox-reagent, Earth-abundant manganese as the catalyst, high functional-group compatibility and high chemoselectivity, setting the stage for late-stage azidation of bioactive compounds. Detailed mechanistic studies by experiment, spectrophotometry and cyclic voltammetry provided strong support for metal-catalyzed aliphatic radical formation, along with subsequent azidyl radical transfer within a manganese( iii / iv ) manifold
)–H azidation without directing groups
No full textSelective up-cycling of polyolefins to C(sp 3 )–H azidated materials was achieved by electrocatalysis. The broad scope, ease of scale-up, and late-stage click-diversification are key features.The chemical up-cycling of polymers into value-added materials offers a unique opportunity to place plastic waste in a new value chain towards a circular economy. Herein, we report the selective up-cycling of polystyrenes and polyolefins to C(sp 3 )–H azidated materials under electrocatalytic conditions. The functionalized polymers were obtained with high retention of mass average molecular mass and high functionalization through chemo-selective mangana-electrocatalysis. Our strategy proved to be broadly applicable to a variety of homo- and copolymers. Polyethylene, polypropylene as well as post-consumer polystyrene materials were functionalized by this approach, thereby avoiding the use of hypervalent-iodine reagents in stoichiometric quantities by means of electrocatalysis. This study, hence, represents a chemical oxidant-free polymer functionalization by electro-oxidation. The electrocatalysis proved to be scalable, which highlights its unique feature for a green hydrogen economy by means of the hydrogen evolution reaction (HER).Alexander von Humboldt-Stiftung https://doi.org/10.13039/100005156Deutsche Forschungsgemeinschaft https://doi.org/10.13039/501100001659HORIZON EUROPE European Research Council https://doi.org/10.13039/10001918
Evolution of High‐Valent Nickela‐Electrocatalyzed C−H Activation: From Cross(‐Electrophile)‐Couplings to Electrooxidative C−H Transformations
No full textAbstract C−H activation has emerged as one of the most efficient tools for the formation of carbon–carbon and carbon–heteroatom bonds, avoiding the use of prefunctionalized materials. In spite of tremendous progress in the field, stoichiometric quantities of toxic and/or costly chemical redox reagents, such as silver(I) or copper(II) salts, are largely required for oxidative C−H activations. Recently, electrosynthesis has experienced a remarkable renaissance that enables the use of storable, safe and waste‐free electric current as a redox equivalent. While major recent momentum was gained in electrocatalyzed C−H activations by 4d and 5d metals, user‐friendly and inexpensive nickela‐electrocatalysis has until recently proven elusive for oxidative C−H activations. Herein, the early developments of nickela‐electrocatalyzed reductive cross‐electrophile couplings as well as net‐redox‐neutral cross‐couplings are first introduced. The focus of this Minireview is, however, the recent emergence of nickel‐catalyzed electrooxidative C−H activations until April 2020.Go electro! Nickela‐electrocatalyzed C−H activations have emerged as a sustainable platform in molecular sciences that avoid substrate prefunctionalizations and chemical oxidants by electricity. The robust nickela‐electrooxidations enabled C−C, C−O, and C−N formations with ample scope under exceedingly mild conditions. imageAlexander von Humboldt-Stiftung http://dx.doi.org/10.13039/100005156China Scholarship Council http://dx.doi.org/10.13039/501100004543DFG http://dx.doi.org/10.13039/50110000165
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