Items 1-20 of 595

    • Journal Article

      Electrochemical Access to Aza-Polycyclic Aromatic Hydrocarbons: Rhoda-Electrocatalyzed Domino Alkyne Annulations 

      Kong, Wei-Jun; Shen, Zhigao; Finger, Lars H.; Ackermann, Lutz
      Angewandte Chemie International Edition(59) p.1-7
      Nitrogen-doped polycyclic aromatic hydrocarbons (aza-PAHs) have found broad applications in material sciences. Herein, a modular electrochemical synthesis of aza-PAHs was developed via a rhodium-catalyzed cascade C-H activation and alkyne annulation. A multifunctional O-methylamidoxime enabled the high chemo- and regioselectivity. The isolation of two key rhodacyclic intermediates made it possible to delineate the exact order of three C-H activation steps. In addition, the metalla-electrocatalyzed multiple C-H transformation is characterized by unique functional group tolerance, including highly reactive iodo and azido groups.
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    • Journal Article

      An Unprecedented Fully H - Substituted Phosphate Hydride Sr5(PO4)3H Expanding the Apatite Family 

      Mutschke, Alexander; Wylezich, Thomas; Ritter, Clemens; Karttunen, Antti J.; Kunkel, Nathalie
      European Journal of Inorganic Chemistry 2019; 2019(48) p.5073-5076
      The apatite family is a mineral class that also contains the biologically very important hydroxyapatite. Here, we are reporting on the synthesis and characterization of a fully hydride‐substituted strontium apatite, which could be obtained via mechanochemical synthesis and subsequent annealing treatment. The full substitution by hydride anions is proven by various methods, such as neutron powder diffraction of a deuterated sample Sr5(PO4)3D, as well 1H MAS solid state NMR combined with quantum chemical calculations, vibrational spectroscopy and elemental analysis. The present work expands the apatite family from the known halide and hydroxide apatites to the fully hydride‐anion‐substituted variant and is expected to open up a new field of materials containing coexistent phosphate and hydride anions.
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    • Journal Article

      Sequential Double Dearomatization of the Pyrazolate-Based “Two-in-One” Pincer Ligand in a Dinuclear Rhodium(I) Complex 

      Gers-Barlag, Alexander; Goursot, Pierre; Li, Ming; Dechert, Sebastian; Meyer, Franc
      European Journal of Inorganic Chemistry 2019; 2019(28) p.3329-3334
      A binucleating pyrazolate‐based ligand providing two tridentate PNN compartments is shown to form a dinuclear rhodium(I) complex [L{Rh(CO)}2](PF6) (1) that can be deprotonated at both side arm methylene groups between pyridine and phosphino donors to give K[L**{Rh(CO)}2] (3). Sequential twofold deprotonation has been monitored by NMR and UV/Vis spectroscopy and proceeds via the neutral intermediate L*{Rh(CO)}2 (2). X‐ray crystallographic characterization of 1 and the K[2,2,2]+ salt 3′ ([2,2,2] is a cryptand) evidences pyridine dearomatization upon deprotonation, and all spectroscopic and structural signatures are in good agreement with those of related mononuclear rhodium complexes based on a common PNN pincer ligand, which corroborates that pyrazolate‐bridged L– is best described as a scaffold with two pincer‐type subunits.
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    • Journal Article

      Oxidative Coupling of Terminal Rhenium Pnictide Complexes 

      Abbenseth, Josh; Diefenbach, Martin; Hinz, Alexander; Alig, Lukas; Würtele, Christian; Goicoechea, Jose M.; Holthausen, Max C.; Schneider, Sven
      Angewandte Chemie International Edition 2019; 58(32) p.10966-10970
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    • Journal Article

      A Terminal Iridium Oxo Complex with a Triplet Ground State 

      Delony, Daniel; Kinauer, Markus; Diefenbach, Martin; Demeshko, Serhiy; Würtele, Christian; Holthausen, Max C.; Schneider, Sven
      Angewandte Chemie International Edition 2019; 58(32) p.10971-10974
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    • Journal Article

      First-Row Transition Metal (De)Hydrogenation Catalysis Based On Functional Pincer Ligands 

      Alig, Lukas; Fritz, Maximilian; Schneider, Sven
      Chemical Reviews 2018; 119(4) p.2681-2751
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    • Journal Article

      Metal-Ligand Cooperative Synthesis of Benzonitrile by Electrochemical Reduction and Photolytic Splitting of Dinitrogen 

      Schendzielorz, Florian; Finger, Markus; Abbenseth, Josh; Würtele, Christian; Krewald, Vera; Schneider, Sven
      Angewandte Chemie International Edition 2018; 58(3) p.830-834
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    • Journal Article

      Iron‐Electrocatalyzed C−H Arylations: Mechanistic Insights into Oxidation‐Induced Reductive Elimination for Ferraelectrocatalysis 

      Zhu, Cuiju; Stangier, Maximilian; Oliveira, João C. A.; Massignan, Leonardo; Ackermann, Lutz
      Chemistry – A European Journal 2019; 25(71) p.16382-16389
      Despite major advances, organometallic C-H transformations are dominated by precious 5d and 4d transition metals, such as iridium, palladium and rhodium. In contrast, the unique potential of less toxic Earth-abundant 3d metals has been underexplored. While iron is the most naturally abundant transition metal, its use in oxidative, organometallic C-H activation has faced major limitations due to the need for superstoichiometric amounts of corrosive, cost-intensive DCIB as the sacrificial oxidant. To fully address these restrictions, we describe herein the unprecedented merger of electrosynthesis with iron-catalyzed C-H activation through oxidation-induced reductive elimination. Thus, ferra- and manganaelectro-catalyzed C-H arylations were accomplished at mild reaction temperatures with ample scope by the action of sustainable iron catalysts, employing electricity as a benign oxidant.
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    • Journal Article

      Hydrosilane Synthesis by Catalytic Hydrogenolysis of Chlorosilanes and Silyl Triflates 

      Glüer, Arne; Schweizer, Julia I.; Karaca, Uhut S.; Würtele, Christian; Diefenbach, Martin; Holthausen, Max C.; Schneider, Sven
      Inorganic Chemistry 2018; 57(21) p.13822-13828
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    • Journal Article

      Iron catalyzed hydrogenation and electrochemical reduction of CO 2 : The role of functional ligands 

      Glüer, Arne; Schneider, Sven
      Journal of Organometallic Chemistry 2018; 861 p.159-173
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    • Journal Article

      Synthesis of Benzonitrile from Dinitrogen 

      Klopsch, Isabel; Schendzielorz, Florian; Volkmann, Christian; Würtele, Christian; Schneider, Sven
      Zeitschrift für anorganische und allgemeine Chemie 2018; 644(17) p.916-919
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    • Journal Article

      π‐Extended Polyaromatic Hydrocarbons by Sustainable Alkyne Annulations through Double C−H/N−H Activation 

      Gońka, Elżbieta; Yang, Long; Steinbock, Ralf; Pesciaioli, Fabio; Kuniyil, Rositha; Ackermann, Lutz
      Chemistry – A European Journal 2019; 25(71) p.16246-16250
      The widespread applications of substituted diketopyrrolopyrroles (DPPs) call for the development of efficient methods for their modular assembly. Herein, we present a π-expansion strategy for polyaromatic hydrocarbons (PAHs) by C-H activation in a sustainable fashion. Thus, twofold C-H/N-H activations were accomplished by versatile ruthenium(II)carboxylate catalysis, providing step-economical access to diversely decorated fluorogenic DPPs that was merged with late-stage palladium-catalyzed C-H arylation on the thus-assembled DPP motif.
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    • Journal Article

      Nonlinear Loading-Rate-Dependent Force Response of Individual Vimentin Intermediate Filaments to Applied Strain 

      Block, Johanna; Witt, Hannes; Candelli, Andrea; Peterman, Erwin J. G.; Wuite, Gijs J. L.; Janshoff, Andreas; Köster, Sarah
      Physical Review Letters 2017; 118(4): Art. 048101
      The mechanical properties of eukaryotic cells are to a great extent determined by the cytoskeleton, a composite network of different filamentous proteins. Among these, intermediate filaments (IFs) are exceptional in their molecular architecture and mechanical properties. Here we directly record stress-strain curves of individual vimentin IFs using optical traps and atomic force microscopy. We find a strong loading rate dependence of the mechanical response, supporting the hypothesis that IFs could serve to protect eukaryotic cells from fast, large deformations. Our experimental results show different unfolding regimes, which we can quantitatively reproduce by an elastically coupled system of multiple two-state elements.
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    • Journal Article

      Ruthenium(II)‐Catalyzed Hydrogen Isotope Exchange of Pharmaceutical Drugs by C−H Deuteration and C−H Tritiation 

      Müller, Valentin; Weck, Remo; Derdau, Volker; Ackermann, Lutz
      ChemCatChem(11) p.1-6
      Well-defined ruthenium(II) biscarboxylate complexes enabled selective ortho-deuteration with weakly-coordinating, synthetically useful carboxylic acid with outstanding levels of isotopic labeling. The robust nature of the catalytic system was reflected by a broad functional group tolerance in an operationallysimple manner, allowing the isotope labeling of challenging pharmaceuticals and bioactive heterocyclic motifs. The synthetic power of our method was highlighted by the selective tritium-labeling of repaglinide, an antidiabetic drug, providing access to defined tritium labeled therapeutics.
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    • Journal Article

      Non-merohedral twinning: from minerals to proteins 

      Sevvana, Madhumati; Ruf, Michael; Usón, Isabel; Sheldrick, George M.; Herbst-Irmer, Regine
      Acta Crystallographica Section D Structural Biology 2019; 75(12) p.1040-1050
      In contrast to twinning by merohedry, the reciprocal lattices of the different domains of non-merohedral twins do not overlap exactly. This leads to three kinds of reflections: reflections with no overlap, reflections with an exact overlap and reflections with a partial overlap of a reflection from a second domain. This complicates the unit-cell determination, indexing, data integration and scaling of X-ray diffraction data. However, with hindsight it is possible to detwin the data because there are reflections that are not affected by the twinning. In this article, the successful solution and refinement of one mineral, one organometallic and two protein non-merohedral twins using a common strategy are described. The unit-cell constants and the orientation matrices were determined by the program CELL_NOW. The data were then integrated with SAINT. TWINABS was used for scaling, empirical absorption corrections and the generation of two different data files, one with detwinned data for structure solution and refinement and a second one for (usually more accurate) structure refinement against total integrated intensities. The structures were solved by experimental phasing using SHELXT for the first two structures and SHELXC/D/E for the two protein structures; all models were refined with SHELXL.
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    • Journal Article

      Visible‐Light‐Mediated Dearomatisation of Indoles and Pyrroles to Pharmaceuticals and Pesticides 

      Schilling, Waldemar; Zhang, Yu; Riemer, Daniel; Das, Shoubhik
      Chemistry – A European Journal(25) p.1-7
      Dearomatisation of indole derivatives to the corresponding isatin derivatives has been achieved with the aid of visible light and oxygen. It should be noted that isatin derivatives are highly important for the synthesis of pharmaceuticals and bioactive compounds. Notably, this chemistry works excellently with N-protected and protection-free indoles. Additionally, this methodology can also be applied to dearomatise pyrrole derivatives to generate cyclic imides in a single step. Later this methodology was applied for the synthesis of four pharmaceuticals and a pesticide called dianthalexin B. Detailed mechanistic studies revealed the actual role of oxygen and photocatalyst.
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    • Journal Article

      Synthesis of benzannelated sultams by intramolecular Pd-catalyzed arylation of tertiary sulfonamides 

      Rassadin, Valentin A; Scholz, Mirko; Klochkova, Anastasiia A; de Meijere, Armin; Sokolov, Victor V
      Beilstein Journal of Organic Chemistry 2017; 13 p.1932-1939
      A new and efficient approach to five- and six-membered benzannelated sultams by intramolecular C-arylation of tertiary 1-(methoxycarbonyl)methanesulfonamides under palladium catalysis is described. In case of the α-toluenesulfonamide derivative, an unexpected formation of a 2,3-diarylindole was observed under the same conditions.
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    • Journal Article

      Expanding the Scope of Cu(I) Catalyzed “Click Chemistry” with Abnormal NHCs: Three-Fold Click to Tris-Triazoles 

      Ho, Nga Kim T.; Reichmann, Sven O.; Rottschäfer, Dennis; Herbst-Irmer, Regine; Ghadwal, Rajendra S.
      Catalysts 2017; 7(9)
      Cationic copper(I) complexes [Cu(aIPrPh)(IPr)]I (3) and [Cu(aIPrPh)2]I (4) featuring an abnormal N-heterocyclic carbene (aNHC) (aIPrPh = 1,3-bis(2,6-diisopropylphenyl)-2-phenylimidazol- 4-ylidene) and/or an NHC (IPr = 1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene) ligand(s) are reported. Treatment of Cu(aIPrPh)I (2) with IPr affords complex 3. Reaction of (IPrPh)I (1) (IPrPh = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl-imidazolium) with CuI in the presence of K{N(SiMe3)2} leads to the formation of 4. Complexes 3 and 4 represent rare examples of mixed aNHC-NHC and bis-aNHC metal complexes, respectively. They are characterized by elemental analysis, NMR spectroscopic, and mass spectrometric studies. The solid-state molecular structures of 3 and 4 have been determined by single crystal X-ray diffraction analyses. The catalytic activity of 2, 3, and 4 has been investigated in the [3+2] cycloaddition of alkynes and organic azides, affording triazole derivatives in an almost quantitative yield. Notably, complexes 2, 3, and 4 are excellent catalysts for the three-fold cycloaddition of a tris-azide with various alkynes. This catalytic protocol offers a high yield access to tris-triazoles in a shorter reaction time and considerably reduces the experimental work-up compared to the classical synthetic method.
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    • Journal Article

      Yeast Prp2 liberates the 5′ splice site and the branch site adenosine for catalysis of pre-mRNA splicing 

      Bao, Penghui; Höbartner, Claudia; Hartmuth, Klaus; Lührmann, Reinhard
      RNA 2017; 23(12) p.1770-1779
      The RNA helicase Prp2 facilitates the remodeling of the spliceosomal Bact complex to the catalytically activated B* complex just before step one of splicing. As a high-resolution cryo-EM structure of the B* complex is currently lacking, the precise spliceosome remodeling events mediated by Prp2 remain poorly understood. To investigate the latter, we used chemical structure probing to compare the RNA structure of purified yeast Bact and B* complexes. Our studies reveal deviations from conventional RNA helices in the functionally important U6 snRNA internal stem-loop and U2/U6 helix Ib in the activated Bact complex, and to a lesser extent in B*. Interestingly, the N7 of U6-G60 of the catalytic triad becomes accessible to DMS modification in the B* complex, suggesting that the Hoogsteen interaction with U6-A52 is destabilized in B*. Our data show that Prp2 action does not unwind double-stranded RNA, but enhances the flexibility of the first step reactants, the pre-mRNA's 5' splice site and branch site adenosine. Prp2 therefore appears to act primarily as an RNPase to achieve catalytic activation by liberating the first step reactants in preparation for catalysis of the first step of splicing.
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    • Journal Article

      Selectivity of tungsten mediated dinitrogen splitting vs. proton reduction 

      Schluschaß, Bastian; Abbenseth, Josh; Demeshko, Serhiy; Finger, Markus; Franke, Alicja; Herwig, Christian; Würtele, Christian; Ivanovic-Burmazovic, Ivana; Limberg, Christian; Telser, Joshua; et al.
      Schneider, Sven
      Chemical Science 2019; 10(44) p.10275-10282
      Mo complexes are currently the most active catalysts for nitrogen fixation under ambient conditions. In comparison, tungsten platforms are scarcely examined. For active catalysts, the control of N2vs. proton reduction selectivities remains a difficult task. We here present N2 splitting using a tungsten pincer platform, which has been proposed as the key reaction for catalytic nitrogen fixation. Starting from [WCl3(PNP)] (PNP = N(CH2CH2PtBu2)2), the activation of N2 enabled the isolation of the dinitrogen bridged redox series [(N2){WCl(PNP)}2]0/+/2+. Protonation of the neutral complex results either in the formation of a nitride [W(N)Cl(HPNP)]+ or H2 evolution and oxidation of the W2N2 core, respectively, depending on the acid and reaction conditions. Examination of the nitrogen splitting vs. proton reduction selectivity emphasizes the role of hydrogen bonding of the conjugate base with the protonated intermediates and provides guidelines for nitrogen fixation.
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