1,720,979 research outputs found
Allenes for Versatile Iron-Catalyzed C–H Activation by Weak O-Coordination: Mechanistic Insights by Kinetics, Intermediate Isolation, and Computation
No full textRoom temperature photo-promoted iron-catalysed arene C–H alkenylation without Grignard reagents
No full textDeutsche Forschungsgemeinschaft https://doi.org/10.13039/501100001659EC | Horizon 2020 Framework Programme https://doi.org/10.13039/100010661Verband der Chemischen Industrie https://doi.org/10.13039/10000721
C7‐Indole Amidations and Alkenylations by Ruthenium(II) Catalysis
No full textAbstract C7−H‐functionalized indoles are ubiquitous structural units of biological and pharmaceutical compounds for numerous antiviral agents against SARS‐CoV or HIV‐1. Thus, achieving site‐selective functionalizations of the C7−H position of indoles, while discriminating among other bonds, is in high demand. Herein, we disclose site‐selective C7−H activations of indoles by ruthenium(II) biscarboxylate catalysis under mild conditions. Base‐assisted internal electrophilic‐type substitution C−H ruthenation by weak O‐coordination enabled the C7−H functionalization of indoles and offered a broad scope, including C−N and C−C bond formation. The versatile ruthenium‐catalyzed C7−H activations were characterized by gram‐scale syntheses and the traceless removal of the directing group, thus providing easy access to pharmaceutically relevant scaffolds. Detailed mechanistic studies through spectroscopic and spectrometric analyses shed light on the unique nature of the robust ruthenium catalysis for the functionalization of the C7−H position of indoles.Lucky seven: The challenging C7−H activation of indoles has been accomplished by ruthenium(II) catalysis. The versatile ruthenium catalysis allowed C−N andC−C bond formation, scalable reactions, and the traceless removal of the directing group. Detailed mechanistic investigations based on diverse analysis tools shed light on a novel mode of action. imageDFG http://dx.doi.org/10.13039/501100001659Kwanjeong Educational Foundation http://dx.doi.org/10.13039/50110000409
A Strategy for Site‐ and Chemoselective C−H Alkenylation through Osmaelectrooxidative Catalysis
No full textA Strategy for Site‐ and Chemoselective C−H Alkenylation through Osmaelectrooxidative Catalysis
No full textHerein, we disclose osmaelectrocatalyzed C−H activations that set the stage for electrooxidative alkyne annulations by benzoic acids. The osmium electrocatalysis enables site‐ and chemoselective electrooxidative C−H activations with unique levels of selectivity. The isolation of unprecedented osmium(0) and osmium(II) intermediates, along with crystallographic characterization and analyses by spectrometric and spectroscopic in operando techniques delineate a synergistic osmium redox catalyst regime. Detailed mechanistic studies revealed a facile C−H cleavage, which allows for an ample substrate scope, providing provide robust and user‐friendly access to annulated heterocycles
Cyclometallated Iron(II) Alkoxides in Iron-Catalyzed C–H Activations by Weak O-Carbonyl Chelation
No full textIron catalysts represent an economically attractive tool for C–H activations because of their low costs and low toxicities. Despite an exponential increase of interest in this area, detailed mechanistic understanding remains at a nascent stage. Herein, a detailed investigation of the C–H activation mechanism with [Fe(PMe3)4] unraveled an unexpected iron(II) alkoxide intermediate that was fully characterized and was found to be a more active catalyst in phenone-assisted C–H activations with respect to the previously reported mer-iron hydride cyclometallated counterpart. Mechanistic studies by stoichiometric experimentation, reaction profiling through electron paramagnetic resonance (EPR) and in operando NMR spectroscopy, deuterium labeling, crystallographic analyses, and density functional theory (DFT) calculations provided strong evidence for an oxidative addition of the pivalophenone to a low-valent iron intermediate toward the formation of a transient fac-hydride complex, which very quickly rearranges to an iron alkoxide complex. According to detailed DFT studies, it is proposed that the isolated iron(II) alkoxide is a highly reactive precatalyst, which can easily access the on-cycle fac-hydride complex, thereby translating into highly efficient catalysis. These mechanistic insights form the basis for further developments in iron-catalyzed C–H activation with prospects for stereoselective transformations
Air‐Stable Bis‐Cyclometallated Iridium Catalysts for Ortho‐Directed C( sp 2 )−H Borylation
No full textAbstract
We report a class of isolable bis‐cyclometallated iridium precatalysts (ImIr) and their use in regioselective
ortho
−C−H borylation of aromatic, heteroaromatic, acrylic, and aliphatic systems. The catalysts consist of two imine ligands and an acetate coordinated to an iridium (III) center. The isolable character of ImIr warrants its compatibility with high‐throughput experimentation, a prerequisite for applications in late‐stage functionalization (LSF) of complex substrates. Initial mechanistic studies point towards an inner‐sphere mechanism involving bis‐cyclometallated species shedding light on the general mechanistic understanding of
ortho
‐selective C−H borylations.Syngenta International https://doi.org/10.13039/50110001076
Nitrogen Activation and Transformation on Monometallic Niobium Boron Oxide Cluster Anions at Room Temperature: A Dual-Site Mechanism
No full text- …
