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- 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.
- ItemCyclometalated Ruthenium Pincer Complexes as Catalysts for the α-Alkylation of Ketones with Alcohols(Weinheim : Wiley-VCH, 2020) Piehl, Patrick; Amuso, Roberta; Alberico, Elisabetta; Junge, Henrik; Gabriele, Bartolo; Neumann, Helfried; Beller, MatthiasRuthenium PNP pincer complexes bearing supplementary cyclometalated C,N-bound ligands have been prepared and fully characterized for the first time. By replacing CO and H− as ancillary ligands in such complexes, additional electronic and steric modifications of this topical class of catalysts are possible. The advantages of the new catalysts are demonstrated in the general α-alkylation of ketones with alcohols following a hydrogen autotransfer protocol. Herein, various aliphatic and benzylic alcohols were applied as green alkylating agents for ketones bearing aromatic, heteroaromatic or aliphatic substituents as well as cyclic ones. Mechanistic investigations revealed that during catalysis, Ru carboxylate complexes are predominantly formed whereas neither the PNP nor the CN ligand are released from the catalyst in significant amounts. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- 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.
- 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.
- ItemA general strategy for the synthesis of α-trifluoromethyl- and α-perfluoroalkyl-β-lactams via palladium-catalyzed carbonylation(Cambridge : RSC, 2021) Li, Yang; Zhang, Cai-Lin; Huang, Wei-Heng; Sun, Ning; Hao, Meng; Neumann, Helfried; Beller, Matthiasβ-Lactam compounds play a key role in medicinal chemistry, specifically as the most important class of antibiotics. Here, we report a novel one-step approach for the synthesis of α-(trifluoromethyl)-β-lactams and related products from fluorinated olefins, anilines and CO. Utilization of an advanced palladium catalyst system with the Ruphos ligand allows for selective cycloaminocarbonylations to give diverse fluorinated β-lactams in high yields. © The Royal Society of Chemistry 2021.
- ItemEfficient Synthesis of Novel Plasticizers by Direct Palladium-Catalyzed Di- or Multi-carbonylations(Weinheim : Wiley-VCH, 2022) Hu, Yuya; Sang, Rui; Vroemans, Robby; Mollaert, Guillaume; Razzaq, Rauf; Neumann, Helfried; Junge, Henrik; Franke, Robert; Jackstell, Ralf; Maes, Bert U. W.; Beller, MatthiasDiesters are of fundamental importance in the chemical industry and are used for many applications, e.g. as plasticizers, surfactants, emulsifiers, and lubricants. Herein, we present a straightforward and efficient method for the selective synthesis of diesters via palladium-catalyzed direct carbonylation of di- or polyols with readily available alkenes. Key-to-success is the use of a specific palladium catalyst with the “built-in-base” ligand L16 providing esterification of all alcohols and a high n/iso ratio. The synthesized diesters were evaluated as potential plasticizers in PVC films by measuring the glass transition temperature (Tg) via differential scanning calorimetry (DSC).
- ItemRuthenium-Catalyzed Deuteration of Aromatic Carbonyl Compounds with a Catalytic Transient Directing Group(Weinheim : Wiley-VCH, 2021) Kopf, Sara; Ye, Fei; Neumann, Helfried; Beller, MatthiasA novel ruthenium-catalyzed C−H activation methodology for hydrogen isotope exchange of aromatic carbonyl compounds is presented. In the presence of catalytic amounts of specific amine additives, a transient directing group is formed in situ, which directs selective deuteration. A high degree of deuteration is achieved for α-carbonyl and aromatic ortho-positions. In addition, appropriate choice of conditions allows for exclusive labeling of the α-carbonyl position while a procedure for the preparation of merely ortho-deuterated compounds is also reported. This methodology proceeds with good functional group tolerance and can be also applied for deuteration of pharmaceutical drugs. Mechanistic studies reveal a kinetic isotope effect of 2.2, showing that the C−H activation is likely the rate-determining step of the catalytic cycle. Using deuterium oxide as a cheap and convenient source of deuterium, the methodology presents a cost-efficient alternative to state-of-the-art iridium-catalyzed procedures. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
- ItemEfficient palladium-catalyzed synthesis of 2-aryl propionic acids(Basel : MDPI, 2020) Neumann, Helfried; Sergeev, Alexey G.; Spannenberg, Anke; Beller, MatthiasA flexible two-step, one-pot procedure was developed to synthesize 2-aryl propionic acids including the anti-inflammatory drugs naproxen and flurbiprofen. Optimal results were obtained in the presence of the novel ligand neoisopinocampheyldiphenylphosphine (NISPCPP) (9) which enabled the efficient sequential palladium-catalyzed Heck coupling of aryl bromides with ethylene and hydroxycarbonylation of the resulting styrenes to 2-aryl propionic acids. This cascade transformation leads with high regioselectivity to the desired products in good yields and avoids the need for additional purification steps. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.