37 results
Search Results
Now showing 1 - 10 of 37
- 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.
- ItemHighly selective hydrogenation of amides catalysed by a molybdenum pincer complex : Scope and mechanism(Cambridge : RSC, 2019) Leischner, Thomas; Suarez, Lluis Artús; Spannenberg, Anke; Nova, Ainara; Junge, Kathrin; Nova, Ainara; Beller, MatthiasA series of molybdenum pincer complexes has been shown for the first time to be active in the catalytic hydrogenation of amides. Among the tested catalysts, Mo-1a proved to be particularly well suited for the selective C-N hydrogenolysis of N-methylated formanilides. Notably, high chemoselectivity was observed in the presence of certain reducible groups including even other amides. The general catalytic performance as well as selectivity issues could be rationalized taking an anionic Mo(0) as the active species. The interplay between the amide CO reduction and the catalyst poisoning by primary amides accounts for the selective hydrogenation of N-methylated formanilides. The catalyst resting state was found to be a Mo-alkoxo complex formed by reaction with the alcohol product. This species plays two opposed roles-it facilitates the protolytic cleavage of the C-N bond but it encumbers the activation of hydrogen. This journal is © The Royal Society of Chemistry.
- Item1-Diphenylphosphanyl-2-(diphenylphosphoryl)hydrazine(Chester : IUCr, 2018) Höhne, Martha; Aluri, Bhaskar; Spannenberg, Anke; Müller, Bernd H.; Peulecke, Normen; Rosenthal, UweThe title compound, C24H22N2OP2, is an asymmetrically substituted hydrazine derivative bearing a phosphoryl and a phosphanyl substituent. The PNNP backbone has a torsion angle of −131.01 (8)°. In the crystal, molecules form centrosymmetric dimers by intermolecular N—H...O hydrogen bonds, which are further linked into a three-dimensional network by weak C—H...O and C—H...π interactions.
- ItemCrystal structure of di-n-butylbis([eta]5-pentamethylcyclopentadienyl)hafnium(IV)(Chester : International Union of Crystallography, 2015) Arndt, Perdita; Schubert,Kathleen; Burlakov, Vladimir V.; Spannenberg, Anke; Rosenthal, UweThe crystal structure of the title compound, [Hf(C10H15)2(C4H9)2], reveals two independent molecules in the asymmetric unit. The diffraction experiment was performed with a racemically twinned crystal showing a 0.529 (5):0.471 (5) component ratio. Each HfIV atom is coordinated by two pentamethylcyclopentadienyl and two n-butyl ligands in a distorted tetrahedral geometry, with the cyclopentadienyl rings inclined to one another by 45.11 (15) and 45.37 (16)°. In contrast to the isostructural di(n-butyl)bis([eta]5-pentamethylcyclopentadienyl)zirconium(IV) complex with a noticeable difference in the Zr-butyl bonding, the Hf-Cbutyl bond lengths differ from each other by no more than 0.039 (3) Å.
- ItemTetracarbonyl[N-(diphenylphosphanyl-κP)-N,N′-diisopropyl-P-phenylphosphorus diamide-κP]molybdenum(0) with an unknown solvent(Chester : IUCr, 2018) Höhne, Martha; Gongoll, Marc; Spannenberg, Anke; Müller, Bernd H.; Peulecke, Normen; Rosenthal, UweThe title complex, [Mo(C24H30N2P2)(CO)4], contains a molybdenum centre bearing a P,P′-cis-chelating Ph2PN(iPr)P(Ph)NH(iPr) and four carbonyl ligands in a distorted octahedral coordination geometry. This results in a nearly planar four-membered metallacycle. In the crystal, molecules are linked by N—H...O and C—H...O hydrogen bonds to form layers parallel to the ac plane. For the final refinement, the contributions of disordered solvent molecules were removed from the diffraction data with SQUEEZE in PLATON [Spek (2015). Acta Cryst. C71, 9–18]. The given chemical formula and other crystal data do not take into account the unknown solvent molecule(s).
- ItemA Comparative Study on the Thermodynamics of Halogen Bonding of Group 10 Pincer Fluoride Complexes(Weinheim : Wiley-VCH, 2019) Joksch, Markus; Agarwala, Hemlata; Ferro, Monica; Michalik, Dirk; Spannenberg, Anke; Beweries, TorstenThe thermodynamics of halogen bonding of a series of isostructural Group 10 metal pincer fluoride complexes of the type [(3,5-R2-tBuPOCOPtBu)MF] (3,5-R2-tBuPOCOPtBu=κ3-C6HR2-2,6-(OPtBu2)2 with R=H, tBu, COOMe; M=Ni, Pd, Pt) and iodopentafluorobenzene was investigated. Based on NMR experiments at different temperatures, all complexes 1-tBu (R=tBu, M=Ni), 2-H (R=H, M=Pd), 2-tBu (R=tBu, M=Pd), 2-COOMe (R=COOMe, M=Pd) and 3-tBu (R=tBu, M=Pt) form strong halogen bonds with Pd complexes showing significantly stronger binding to iodopentafluorobenzene. Structural and computational analysis of a model adduct of complex 2-tBu with 1,4-diiodotetrafluorobenzene as well as of structures of iodopentafluorobenzene in toluene solution shows that formation of a type I contact occurs. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemSynthesis and molecular structures of the lowest melting odd- and even-numbered a,b-unsaturated carboxylic acids—(E)-hept-2-enoic acid and (E)-oct-2-enoic acid(Basel : MDPI, 2016) Sonneck, Marcel; Spannenberg, Anke; Wohlrab, Sebastian; Peppel, TimThe molecular structures of the two lowest melting odd- and even-numbered α,β-unsaturated carboxylic acids—(E)-hept-2-enoic acid (C7) and (E)-oct-2-enoic acid (C8)—are herein reported. The title compounds were crystallized by slow evaporation of ethanolic solutions at −30 °C. C7 crystallizes in the triclinic space group P1¯ with two molecules in the unit cell and C8 in the monoclinic space group C2/c with eight molecules in the unit cell. The unit cell parameters for C7 are: a = 5.3049(2) Å, b = 6.6322(3) Å, c = 11.1428(5) Å, α = 103.972(3)°, β = 97.542(3)°, γ = 90.104(3)°, and V = 376.92(3) Å3 (T = 150(2) K). The unit cell parameters for C8 are: a = 19.032(10) Å, b = 9.368(5) Å, c = 11.520(6) Å, β = 123.033(11)°, and V = 1721.80(16) Å3 (T = 200(2) K).
- ItemCrystal structure of (E)-hex-2-enoic acid(Chester : International Union of Crystallography, 2015) Peppel, Tim; Sonneck, Marcel; Spannenberg, Anke; Wohlrab, SebastianThe crystal structure of the title compound, C6H10O2, an [alpha],[beta]-unsaturated carboxylic acid, displays carboxylic acid inversion dimers linked by pairs of O-H...O hydrogen bonds. The packing is characterized by layers of acid dimers. All the non-H atoms of the (E)-hex-2-enoic acid molecule lie almost in the same plane (r.m.s. deviation for the non-H atoms = 0.018 Å).
- ItemCooperative catalytic methoxycarbonylation of alkenes: Uncovering the role of palladium complexes with hemilabile ligands(Cambridge : RSC, 2018) Dong, Kaiwu; Sang, Rui; Wei, Zhihong; Liu, Jie; Dühren, Ricarda; Spannenberg, Anke; Jiao, Haijun; Neumann, Helfried; Jackstell, Ralf; Franke, Robert; Beller, MatthiasMechanistic studies of the catalyst [Pd2(dba)3/1,1′-bis(tert-butyl(pyridin-2-yl)phosphanyl)ferrocene, L2] for olefin alkoxycarbonylation reactions are described. X-ray crystallography reveals the coordination of the pyridyl nitrogen atom in L2 to the palladium center of the catalytic intermediates. DFT calculations on the elementary steps of the industrially relevant carbonylation of ethylene (the Lucite α-process) indicate that the protonated pyridyl moiety is formed immediately, which facilitates the formation of the active palladium hydride complex. The insertion of ethylene and CO into this intermediate leads to the corresponding palladium acyl species, which is kinetically reversible. Notably, this key species is stabilized by the hemilabile coordination of the pyridyl nitrogen atom in L2. The rate-determining alcoholysis of the acyl palladium complex is substantially facilitated by metal-ligand cooperation. Specifically, the deprotonation of the alcohol by the built-in base of the ligand allows a facile intramolecular nucleophilic attack on the acyl palladium species concertedly. Kinetic measurements support this mechanistic proposal and show that the rate of the carbonylation step is zero-order dependent on ethylene and CO. Comparing CH3OD and CH3OH as nucleophiles suggests the involvement of (de)protonation in the rate-determining step.
- Item3,3′-Dimethyl-1,1′-methylenediimidazolium tetrabromidocobaltate(II)(Chester : IUCr, 2018) Peppel, Tim; Spannenberg, AnkeThe title compound, (C9H14N4)[CoBr4], was obtained as single crystals directly in very low yield as a side product in the reaction of 1,1′-bis(1-methylimidazolium)acetate bromide and CoBr2. The title compound consists of an imidazolium-based dication and a tetrabromidocobaltate(II) complex anion, which are connected via C—H...Br interactions in the crystal. The dihedral angle between the imidazolium rings in the cation is 72.89 (16)°. The CoII ion in the anion is coordinated tetrahedrally by four bromide ligands [Co—Br = 2.4025 (5)–2.4091 (5) Å and Br—Co—Br = 106.224 (17)–113.893 (17)°]. The compound exhibits a high melting point (>300°C) and is a light-blue solid under ambient conditions.