38 results
Search Results
Now showing 1 - 10 of 38
- Item3,3-Difluoroallyl ammonium salts: highly versatile, stable and selective gem-difluoroallylation reagents([London] : Nature Publishing Group UK, 2021) Ye, Fei; Ge, Yao; Spannenberg, Anke; Neumann, Helfried; Xu, Li-Wen; Beller, MatthiasThe selective synthesis of fluorinated organic molecules continues to be of major importance for the development of bioactive compounds (agrochemicals and pharmaceuticals) as well as unique materials. Among the established synthetic toolbox for incorporation of fluorine-containing units, efficient and general reagents for introducing -CF2- groups have been largely neglected. Here, we present the synthesis of 3,3-difluoropropen-1-yl ammonium salts (DFPAs) as stable, and scalable gem-difluoromethylation reagents, which allow for the direct reaction with a wide range of fascinating nucleophiles. DFPAs smoothly react with N-, O-, S-, Se-, and C-nucleophiles under mild conditions without necessity of metal catalysts with exclusive regioselectivity. In this way, the presented reagents also permit the straightforward preparation of many analogues of existing pharmaceuticals.
- ItemGeneral and selective synthesis of primary amines using Ni-based homogeneous catalysts(Cambridge : RSC, 2020) Murugesan, Kathiravan; Wei, Zhihong; Chandrashekhar, Vishwas G.; Jiao, Haijun; Beller, Matthias; Jagadeesh, Rajenahally V.The development of base metal catalysts for industrially relevant amination and hydrogenation reactions by applying abundant and atom economical reagents continues to be important for the cost-effective and sustainable synthesis of amines which represent highly essential chemicals. In particular, the synthesis of primary amines is of central importance because these compounds serve as key precursors and central intermediates to produce value-added fine and bulk chemicals as well as pharmaceuticals, agrochemicals and materials. Here we report a Ni-triphos complex as the first Ni-based homogeneous catalyst for both reductive amination of carbonyl compounds with ammonia and hydrogenation of nitroarenes to prepare all kinds of primary amines. Remarkably, this Ni-complex enabled the synthesis of functionalized and structurally diverse benzylic, heterocyclic and aliphatic linear and branched primary amines as well as aromatic primary amines starting from inexpensive and easily accessible carbonyl compounds (aldehydes and ketones) and nitroarenes using ammonia and molecular hydrogen. This Ni-catalyzed reductive amination methodology has been applied for the amination of more complex pharmaceuticals and steroid derivatives. Detailed DFT computations have been performed for the Ni-triphos based reductive amination reaction, and they revealed that the overall reaction has an inner-sphere mechanism with H2metathesis as the rate-determining step. © The Royal Society of Chemistry 2020.
- ItemRuthenium-Catalyzed Site-Selective Trifluoromethylations and (Per)Fluoroalkylations of Anilines and Indoles(Weinheim : Wiley-VCH, 2020) Li, Yang; Neumann, Helfried; Beller, MatthiasIntroducing (per)fluoroalkyl groups into arenes continues to be an interesting, but challenging area in organofluorine chemistry. We herein report an ortho-selective C−H perfluoroalkylation including trifluoromethylations of anilines and indoles without the need of protecting groups using RfI and RfBr as commercially available reagents. The availability and price of the starting materials and the inherent selectivity make this novel methodology attractive for the synthesis of diverse (per)fluoroalkylated building blocks, for example, for bioactive compounds and materials. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemSynthesis of Molybdenum Pincer Complexes and Their Application in the Catalytic Hydrogenation of Nitriles(Weinheim : Wiley-VCH Verlag, 2020) Leischner, Thomas; Spannenberg, Anke; Junge, Kathrin; Beller, MatthiasA series of molybdenum(0), (I) and (II) complexes ligated by different PNP and NNN pincer ligands were synthesized and structurally characterized. Along with previously described Mo−PNP complexes Mo-1 and Mo-2, all prepared compounds were tested in the catalytic hydrogenation of aromatic nitriles to primary amines. Among the applied catalysts, Mo-1 is particularly well suited for the hydrogenation of electron-rich benzonitriles. Additionally, two aliphatic nitriles were transformed into the desired products in 80 and 86 %, respectively. Moreover, catalytic intermediate Mo-1a was isolated and its role in the catalytic cycle was subsequently demonstrated. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemTailored Palladium Catalysts for Selective Synthesis of Conjugated Enynes by Monocarbonylation of 1,3-Diynes(Weinheim : Wiley-VCH, 2020) Liu, Jiawang; Yang, Ji; Schneider, Carolin; Franke, Robert; Jackstell, Ralf; Beller, MatthiasFor the first time, the monoalkoxycarbonylation of easily available 1,3-diynes to give synthetically useful conjugated enynes has been realized. Key to success was the design and utilization of the new ligand 2,2′-bis(tert-butyl(pyridin-2-yl)phosphanyl)-1,1′-binaphthalene (Neolephos), which permits the palladium-catalyzed selective carbonylation under mild conditions, providing a general preparation of functionalized 1,3-enynes in good-to-high yields with excellent chemoselectivities. Synthetic applications that showcase the possibilities of this novel methodology include an efficient one-pot synthesis of 4-aryl-4H-pyrans as well as the rapid construction of various heterocyclic, bicyclic, and polycyclic compounds. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemActivation of perfluoroalkyl iodides by anions: extending the scope of halogen bond activation to C(sp3)-H amidation, C(sp2)-H iodination, and perfluoroalkylation reactions(Cambridge : RSC Publishing, 2023) Wang, Yaxin; Cao, Zehui; He, Qin; Huang, Xin; Liu, Jiaxi; Neumann, Helfried; Chen, Gong; Beller, MatthiasA simple, efficient, and convenient activation of perfluoroalkyl iodides by tBuONa or KOH, without expensive photo- or transition metal catalysts, allows the promotion of versatile a-sp3 C-H amidation reactions of alkyl ethers and benzylic hydrocarbons, C-H iodination of heteroaryl compounds, and perfluoroalkylations of electron-rich p bonds. Mechanistic studies show that these novel protocols are based on the halogen bond interaction between perfluoroalkyl iodides and tBuONa or KOH, which promote homolysis of perfluoroalkyl iodides under mild conditions.
- ItemManganese-catalyzed selective C–H activation and deuteration by means of a catalytic transient directing group strategy(London : Royal Society of Chemistry (RSC), 2021) Kopf, Sara; Neumann, Helfried; Beller, MatthiasA novel manganese-catalyzed C-H activation methodology for selective hydrogen isotope exchange of benzaldehydes is presented. Using D2O as a cheap and convenient source of deuterium, the reaction proceeds with excellent functional group tolerance. Highortho-selectivity is achieved in the presence of catalytic amounts of specific amines, whichin situform a transient directing group. © The Royal Society of Chemistry 2021.
- ItemAn amino acid based system for CO2 capture and catalytic utilization to produce formates(Cambridge : RSC, 2021) Wei, Duo; Junge, Henrik; Beller, MatthiasHerein, we report a novel amino acid based reaction system for CO2 capture and utilization (CCU) to produce formates in the presence of the naturally occurring amino acid l-lysine. Utilizing a specific ruthenium-based catalyst system, hydrogenation of absorbed carbon dioxide occurs with high activity and excellent productivity. Noteworthy, following the CCU concept, CO2 can be captured from ambient air in the form of carbamates and converted directly to formates in one-pot (TON > 50 000). This protocol opens new potential for transforming captured CO2 from ambient air to C1-related products. © 2021 The Royal Society of Chemistry.
- ItemEfficient methylation of anilines with methanol catalysed by cyclometalated ruthenium complexes(London : RSC Publ., 2021) Piehl, Patrick; Amuso, Roberta; Spannenberg, Anke; Gabriele, Bartolo; Neumann, Helfried; Beller, MatthiasCyclometalated ruthenium complexes4-10allow the effective methylation of anilines with methanol to selectively giveN-methylanilines. This hydrogen autotransfer procedure proceeds under mild conditions (60 °C) in a practical manner (NaOH as base). Mechanistic investigations suggest an active homogenous ruthenium complex and β-hydride elimination of methanol as the rate determining step. © The Royal Society of Chemistry 2021.
- ItemSite-Selective Real-Time Observation of Bimolecular Electron Transfer in a Photocatalytic System Using L-Edge X-Ray Absorption Spectroscopy(Weinheim : Wiley-VCH Verl., 2021) Britz, Alexander; Bokarev, Sergey I.; Assefa, Tadesse A.; Bajnóczi, Èva G.; Németh, Zoltán; Vankó, György; Rockstroh, Nils; Junge, Henrik; Beller, Matthias; Doumy, Gilles; March, Anne Marie; Southworth, Stephen H.; Lochbrunner, Stefan; Kühn, Oliver; Bressler, Christian; Gawelda, WojciechTime-resolved X-ray absorption spectroscopy has been utilized to monitor the bimolecular electron transfer in a photocatalytic water splitting system. This has been possible by uniting the local probe and element specific character of X-ray transitions with insights from high-level ab initio calculations. The specific target has been a heteroleptic [IrIII (ppy)2 (bpy)]+ photosensitizer, in combination with triethylamine as a sacrificial reductant and Fe3(CO)12 as a water reduction catalyst. The relevant molecular transitions have been characterized via high-resolution Ir L-edge X-ray absorption spectroscopy on the picosecond time scale and restricted active space self-consistent field calculations. The presented methods and results will enhance our understanding of functionally relevant bimolecular electron transfer reactions and thus will pave the road to rational optimization of photocatalytic performance.