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- ItemSpecific Signal Enhancement on an RNA-Protein Interface by Dynamic Nuclear Polarization(Weinheim : Wiley-VCH, 2023) Aladin, Victoria; Sreemantula, Arun K.; Biedenbänder, Thomas; Marchanka, Alexander; Corzilius, BjörnSensitivity and specificity are both crucial for the efficient solid-state NMR structure determination of large biomolecules. We present an approach that features both advantages by site-specific enhancement of NMR spectroscopic signals from the protein-RNA binding site within a ribonucleoprotein (RNP) by dynamic nuclear polarization (DNP). This approach uses modern biochemical techniques for sparse isotope labeling and exploits the molecular dynamics of 13C-labeled methyl groups exclusively present in the protein. These dynamics drive heteronuclear cross relaxation and thus allow specific hyperpolarization transfer across the biomolecular complex's interface. For the example of the L7Ae protein in complex with a 26mer guide RNA minimal construct from the box C/D complex in archaea, we demonstrate that a single methyl-nucleotide contact is responsible for most of the polarization transfer to the RNA, and that this specific transfer can be used to boost both NMR spectral sensitivity and specificity by DNP.
- 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.
- ItemMetal/Metal Redox Isomerism Governed by Configuration(Weinheim : Wiley-VCH, 2020) Ludwig, Stephan; Helmdach, Kai; Hettenschmidt, Mareike; Oberem, Elisabeth; Rabeah, Jabor; Villinger, Alexander; Ludwig, Ralf; Seidel, Wolfram W.A pair of diastereomeric dinuclear complexes, [Tp′(CO)BrW{μ-η2-C,C′-κ2-S,P-C2(PPh2)S}Ru(η5-C5H5)(PPh3)], in which W and Ru are bridged by a phosphinyl(thiolato)alkyne in a side-on carbon P,S-chelate coordination mode, were synthesized, separated and fully characterized. Even though the isomers are similar in their spectroscopic properties and redox potentials, the like-isomer is oxidized at W while the unlike-isomer is oxidized at Ru, which is proven by IR, NIR and EPR-spectroscopy supported by spectro-electrochemistry and computational methods. The second oxidation of the complexes was shown to take place at the metal left unaffected in the first redox step. Finally, the tipping point could be realized in the unlike isomer of the electronically tuned thiophenolate congener [Tp′(CO)(PhS)W{μ-η2-C,C′-κ2-S,P-C2(PPh2)S}Ru(η5-C5H5)-(PPh3)], in which valence trapped WIII/RuII and WII/RuIII cationic species are at equilibrium. © 2020 The Authors. Published by Wiley-VCH GmbH
- ItemSupported CuII Single-Ion Catalyst for Total Carbon Utilization of C2 and C3 Biomass-Based Platform Molecules in the N-Formylation of Amines(Weinheim : Wiley-VCH, 2021) Dai, Xingchao; Wang, Xinzhi; Rabeah, Jabor; Kreyenschulte, Carsten; Brückner, Angelika; Shi, FengThe shift from fossil carbon sources to renewable ones is vital for developing sustainable chemical processes to produce valuable chemicals. In this work, value-added formamides were synthesized in good yields by the reaction of amines with C2 and C3 biomass-based platform molecules such as glycolic acid, 1,3-dihydroxyacetone and glyceraldehyde. These feedstocks were selectively converted by catalysts based on Cu-containing zeolite 5A through the in situ formation of carbonyl-containing intermediates. To the best of our knowledge, this is the first example in which all the carbon atoms in biomass-based feedstocks could be amidated to produce formamide. Combined catalyst characterization results revealed preferably single CuII sites on the surface of Cu/5A, some of which form small clusters, but without direct linking via oxygen bridges. By combining the results of electron paramagnetic resonance (EPR) spin-trapping, operando attenuated total reflection (ATR) IR spectroscopy and control experiments, it was found that the formation of formamides might involve a HCOOH-like intermediate and .NHPh radicals, in which the selective formation of .OOH radicals might play a key role. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
- ItemNickel-catalyzed carbonylative synthesis of dihydrobenzofurans(Amsterdam : Elsevier, 2021) Geng, H.-Q.; Wang, W.; Wu, X.-F.A nickel-catalyzed carbonylative synthesis of dihydrobenzofurans has been developed. With Mo(CO)6 as the CO source and manganese metal as the reductant, alkyl halides were reacted with aryl iodides to give the desired products in moderate to good yields. © 2020 Elsevier B.V.
- ItemCobalt-Catalyzed Aqueous Dehydrogenation of Formic Acid(Weinheim : Wiley-VCH, 2019) Zhou, Wei; Wei, Zhihong; Spannenberg, Anke; Jiao, Haijun; Junge, Kathrin; Junge, Henrik; Beller, MatthiasAmong the known liquid organic hydrogen carriers, formic acid attracts increasing interest in the context of safe and reversible storage of hydrogen. Here, the first molecularly defined cobalt pincer complex is disclosed for the dehydrogenation of formic acid in aqueous medium under mild conditions. Crucial for catalytic activity is the use of the specific complex 3. Compared to related ruthenium and manganese complexes 7 and 8, this optimal cobalt complex showed improved performance. DFT computations support an innocent non-classical bifunctional outer-sphere mechanism on the triplet state potential energy surface. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemAerobic iron-catalyzed site-selective C(sp3)–C(sp3) bond cleavage in N-heterocycles(Amsterdam : Elsevier, 2021) Leonard, David K.; Li, Wu; Rockstroh, Nils; Junge, Kathrin; Beller, MatthiasThe kinetic and thermodynamic stability of C(sp3)–C(sp3) bonds makes the site-selective activation of these motifs a real synthetic challenge. In view of this, herein a site-selective method of C(sp3)–C(sp3) bond scission of amines, specifically morpholine and piperazine derivatives, using a cheap iron catalyst and air as a sustainable oxidant is reported. Furthermore, a statistical design of experiments (DoE) is used to evaluate multiple reaction parameters thereby allowing for the rapid development of a catalytic process. © 2021
- ItemDehydropolymerisation of Methylamine Borane and an N-Substituted Primary Amine Borane Using a PNP Fe Catalyst(Weinheim : Wiley-VCH, 2020) Anke, Felix; Boye, Susanne; Spannenberg, Anke; Lederer, Albena; Heller, Detlef; Beweries, TorstenDehydropolymerisation of methylamine borane (H3B⋅NMeH2) using the well-known iron amido complex [(PNP)Fe(H)(CO)] (PNP=N(CH2CH2PiPr2)2) (1) gives poly(aminoborane)s by a chain-growth mechanism. In toluene, rapid dehydrogenation of H3B⋅NMeH2 following first-order behaviour as a limiting case of a more general underlying Michaelis–Menten kinetics is observed, forming aminoborane H2B=NMeH, which selectively couples to give high-molecular-weight poly(aminoborane)s (H2BNMeH)n and only traces of borazine (HBNMe)3 by depolymerisation after full conversion. Based on a series of comparative experiments using structurally related Fe catalysts and dimethylamine borane (H3B⋅NMe2H) polymer formation is proposed to occur by nucleophilic chain growth as reported earlier computationally and experimentally. A silyl functionalised primary borane H3B⋅N(CH2SiMe3)H2 was studied in homo- and co-dehydropolymerisation reactions to give the first examples for Si containing poly(aminoborane)s. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemCarbon Monoxide Coupling Reactions: A New Concept for the Formation of Hexahydroxybenzene(Weinheim : Wiley-VCH, 2020) Rosenthal, UweFor linear and cyclic coupling reactions of CO, among other products, the formation of the hexapotassium salt of hexahydroxybenzene is of particular interesting. The interaction of metallic potassium and CO offers, via the assumed K[OC≡CO]K as the result of several carbon monoxide coupling reactions, the formation of C6(OK)6 among other products. To date, only speculations exist about the reaction pathway for these products, which were first described by Liebig in 1834. A novel concept is suggested here, which consists of the single steps (i) reductive coupling of CO, (ii) formation of dihetero-metallacyclopentynes (cis-2,5-diheterobutatriene as formal ethylenedione O=C=C=O complexes), (iii) formation of its dinuclear 1-metalla-2,5-dioxo-cyclopentyne complexes by external coordination of the triple bond, (iv) insertion of CO into the M−C bond of the formed metallacyclopropene, and (v) the reductive elimination of C6(OK)6. The novel aspect of this concept is the formation of dihetero-metallacyclopentynes (in analogy to the well characterized all-C-metallacyclopentynes), which have not been considered in the mechanism of reductive CO coupling reactions. It is expected that the presence of transition-metal impurities would promote the reaction. © 2020 The Authors. Published by Wiley-VCH GmbH
- ItemPhotocatalytic nitrogen reduction to ammonia: Insights into the role of defect engineering in photocatalysts(New York, NY [u.a.] : Springer, 2021) Shen, Huidong; Yang, Mengmeng; Hao, Leiduan; Wang, Jinrui; Strunk, Jennifer; Sun, ZhenyuEngineering of defects in semiconductors provides an effective protocol for improving photocatalytic N2 conversion efficiency. This review focuses on the state-of-the-art progress in defect engineering of photocatalysts for the N2 reduction toward ammonia. The basic principles and mechanisms of thermal catalyzed and photon-induced N2 reduction are first concisely recapped, including relevant properties of the N2 molecule, reaction pathways, and NH3 quantification methods. Subsequently, defect classification, synthesis strategies, and identification techniques are compendiously summarized. Advances of in situ characterization techniques for monitoring defect state during the N2 reduction process are also described. Especially, various surface defect strategies and their critical roles in improving the N2 photoreduction performance are highlighted, including surface vacancies (i.e., anionic vacancies and cationic vacancies), heteroatom doping (i.e., metal element doping and nonmetal element doping), and atomically defined surface sites. Finally, future opportunities and challenges as well as perspectives on further development of defect-engineered photocatalysts for the nitrogen reduction to ammonia are presented. It is expected that this review can provide a profound guidance for more specialized design of defect-engineered catalysts with high activity and stability for nitrogen photochemical fixation.
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