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- ItemCrystal structure of (2S,4S,7S)-7,7-dichloro-4-(1-chloro-1-methylethyl)-1- (2,2,2-trichloroethyl)bicyclo[4.1.0]heptane, C12H16Cl 6(Berlin : de Gruyter, 2009) Boualy, B.; el Firdoussi, L.; Ali, M.A.; Karim, A.; Spannenberg, A.C12H16Cl6, orthorhombic, P2 12121 (no. 19), a = 6.0742(3) Å, b = 9.7189(6) Å, c = 26.700(1) Å, V = 1576.2 Å3, Z = 4, Rgt(F) = 0.019, wRref(F2) = 0.045, T= 200 K. © by Oldenbourg Wissenschaftsverlag.
- ItemCation-cation clusters in ionic liquids: Cooperative hydrogen bonding overcomes like-charge repulsion([London] : Macmillan Publishers Limited, part of Springer Nature, 2015) Knorr, Anne; Ludwig, RalfDirect spectroscopic evidence for H-bonding between like-charged ions is reported for the ionic liquid, 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate. New infrared bands in the OH frequency range appear at low temperatures indicating the formation of H-bonded cation-cation clusters similar to those known for water and alcohols. Supported by DFT calculations, these vibrational bands can be assigned to attractive interaction between the hydroxyl groups of the cations. The repulsive Coulomb interaction is overcome by cooperative hydrogen bonding between ions of like charge. The transition energy from purely cation-anion interacting configurations to those including cation-cation H-bonds is determined to be 3–4 kJmol−1. The experimental findings and DFT calculations strongly support the concept of anti-electrostatic hydrogen bonds (AEHBs) as recently suggested by Weinhold and Klein. The like-charge configurations are kinetically stabilized with decreasing temperatures.
- ItemNickel-Catalyzed Carbonylative Synthesis of Functionalized Alkyl Iodides(Amsterdam : Elsevier B.V., 2018) Peng, J.-B.; Wu, F.-P.; Xu, C.; Qi, X.; Ying, J.; Wu, X.-F.Chemistry; Catalysis; Organic Synthesis © 2018 The Author(s)Functionalized alkyl iodides are important compounds in organic chemistry and biology. In this communication, we developed an interesting nickel-catalyzed carbonylative synthesis of functionalized alkyl iodides from aryl iodides and ethers. With Mo(CO)6 as the solid CO source, both cyclic and acyclic ethers were activated, which is also a challenging topic in organic synthesis. Functionalized alkyl iodides were prepared in moderate to excellent yields with outstanding functional group tolerance. Besides the high value of the obtained products, all the atoms from the starting materials were incorporated in the final products and the reaction had high atom efficiency as well.
- ItemPhenazine Radical Cations as Efficient Homogeneous and Heterogeneous Catalysts for the Cross-Dehydrogenative Aza-Henry Reaction(New York, NY : Wiley-VCH, 2020) Unglaube, Felix; Hünemörder, Paul; Guo, Xuewen; Chen, Zixu; Wang, Dengxu; MejÃa, EstebanThe redox activity of molecular phenazine catalysts has been previously exploited for aerobic oxidative amine homo- and cross-coupling reactions. In this contribution, we have extended the reaction scope of this novel type of organocatalyst and used them in the cross-dehydrogenative aza-Henry coupling of isoquinolines with nitromethane under aerobic conditions. Additionally, we have designed and prepared a novel porous organic polymer by cross-linking of tetrakis(4-bromophenyl)silane and dihydrophenazine through Pd-catalyzed Buchwald-Hartwig cross-coupling. This new type of heterogeneous catalyst, apart from being robust and easily reusable, also showed outstanding catalytic activities and improved selectivity compared to its molecular counterpart. A plausible reaction mechanism was proposed based on spectroscopic and kinetic measurements. © 2020 The Authors. Helvetica Chimica Acta published by Wiley-VHCA AG, Zurich, Switzerland
- ItemA meta-analysis of catalytic literature data reveals property-performance correlations for the OCM reaction([London] : Nature Publishing Group UK, 2019) Schmack, Roman; Friedrich, Alexandra; Kondratenko, Evgenii V.; Polte, Jörg; Werwatz, Axel; Kraehnert, RalphDecades of catalysis research have created vast amounts of experimental data. Within these data, new insights into property-performance correlations are hidden. However, the incomplete nature and undefined structure of the data has so far prevented comprehensive knowledge extraction. We propose a meta-analysis method that identifies correlations between a catalyst’s physico-chemical properties and its performance in a particular reaction. The method unites literature data with textbook knowledge and statistical tools. Starting from a researcher’s chemical intuition, a hypothesis is formulated and tested against the data for statistical significance. Iterative hypothesis refinement yields simple, robust and interpretable chemical models. The derived insights can guide new fundamental research and the discovery of improved catalysts. We demonstrate and validate the method for the oxidative coupling of methane (OCM). The final model indicates that only well-performing catalysts provide under reaction conditions two independent functionalities, i.e. a thermodynamically stable carbonate and a thermally stable oxide support.
- ItemStability studies of ionic liquid [EMIm][NTf2] under short-term thermal exposure(London : RSC Publishing, 2016) Neise, Christin; Rautenberg, Christine; Bentrup, Ursula; Beck, Martin; Ahrenberg, Mathias; Schick, Christoph; Keßler, Olaf; Kragl, UdoIonic liquids (ILs) as new media for synthesis and as functional fluids in technical applications are still of high interest. Cooling a steel component from an annealing temperature of nearly 850 °C down to room temperature in a liquid bath is a technically important process. The use of ionic liquids offers advantages avoiding film boiling of the quenching medium. However, such a high immersion temperature exceeds the thermal stability of the IL, for example such as [EMIm][NTf2]. To obtain information about formation of potential toxic decomposition products, potential fragments at varied states of decomposition of [EMIm][NTf2] were studied by various spectroscopic and gravimetric methods. For the first time it was possible to quantify fluorine-containing products via mass spectrometry coupled directly with thermogravimetric (TG) measurements. While chemical and spectroscopic analysis of thermally stressed ILs revealed no hints concerning changes of composition after quenching hot steel for several times, the mass-spectrometer (MS) coupled TG analysis gives information by comparing the decomposition behaviour of fresh and used ILs. A number of fragments were detected in low amounts confirming the proposed decomposition mechanism.
- ItemPhotocatalytic Reduction of CO2 by Metal-Free-Based Materials: Recent Advances and Future Perspective(Weinheim : Wiley-VCH, 2020) Shen, Huidong; Peppel, Tim; Strunk, Jennifer; Sun, ZhenyuPhotocatalytic CO2 reduction to produce valuable chemicals and fuels using solar energy provides an appealing route to alleviate global energy and environmental problems. Searching for photocatalysts with high activity and selectivity for CO2 conversion is the key to achieving this goal. Among the various proposed photocatalysts, metal-free materials, such as graphene, nitrides, carbides, and conjugated organic polymers, have gained extensive research interest for photocatalytic CO2 reduction, due to their earth abundance, cost-effectiveness, good electrical conductivity, and environmental friendliness. They exhibit prominent catalytic activity, impressive selectivity, and long durability for the conversion of CO2 to solar fuels. Herein, the recent progress on metal-free photocatalysis of CO2 reduction is systematically reviewed. Opportunities and challenges on modification of nonmetallic catalysts to enhance CO2 transformation are presented. Theoretical calculations on possible reduction mechanisms and pathways as well as the potential in situ and operando techniques for mechanistic understanding are also summarized and discussed. Based on the aforementioned discussions, suitable future research directions and perspectives for the design and development of potential nonmetallic photocatalysts for efficient CO2 reduction are provided. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemHydrogen production from formic acid catalyzed by a phosphine free manganese complex: Investigation and mechanistic insights(Cambridge : RSC, 2020) Léval, Alexander; Agapova, Anastasiya; Steinlechner, Christoph; Alberico, Elisabetta; Junge, Henrik; Beller, MatthiasFormic acid dehydrogenation (FAD) is considered as a promising process in the context of hydrogen storage. Its low toxicity, availability and convenient handling make FA attractive as a potential hydrogen carrier. To date, most promising catalysts have been based on noble metals, such as ruthenium and iridium. Efficient non-noble metal systems like iron were designed but manganese remains relatively unexplored for this transformation. In this work, we present a panel of phosphine free manganese catalysts which showed activity and stability in formic acid dehydrogenation. The most promising results were obtained with Mn(pyridine-imidazoline)(CO)3Br yielding >14 l of the H2/CO2 mixture and proved to be stable for more than 3 days. Additionally, this study provides insights into the mechanism of formic acid dehydrogenation. Kinetic experiments, Kinetic Isotopic Effect (KIE), in situ observations, NMR labeling experiments and pH monitoring allow us to propose a catalytic cycle for this transformation.
- ItemA chemometric study in the area of feasible solution of an acid-base titration of N-methyl-6-oxyquinolone(London : RSC Publishing, 2018) Sawall, Mathias; Schmode, Stella; Schröder, Henning; Ludwig, Ralf; Neymeyr, KlausMultivariate curve resolution methods aim at recovering the underlying chemical components from spectroscopic data on chemical reaction systems. In most cases the spectra and concentration profiles of the pure components cannot be uniquely determined from the given spectral data. Instead continua of possible factors exist. This fact is known as rotational ambiguity. The sets of all possible pure component factors can be represented in the so-called area of feasible solutions (AFS). This paper presents an AFS study of the pure component reconstruction problem for a series of UV/Vis spectra taken from an acid-base titration of N-methyl-6-oxyquinolone. Additional information on the equilibrium concentration profiles for a varying acid concentration is taken from fluorescence measurements. On this basis chemometric duality arguments lead to the construction of a unique final solution.
- ItemSpectroscopic evidence of 'jumping and pecking' of cholinium and H-bond enhanced cation-cation interaction in ionic liquids(Cambridge : RSC Publ., 2015) Knorr, Anne; Fumino, Koichi; Bonsa, Anne-Marie; Ludwig, RalfThe subtle energy-balance between Coulomb-interaction, hydrogen bonding and dispersion forces governs the unique properties of ionic liquids. To measure weak interactions is still a challenge. This is in particular true in the condensed phase wherein a melange of different strong and directional types of interactions is present and cannot be detected separately. For the ionic liquids (2-hydroxyethyl)-trimethylammonium (cholinium) bis(trifluoro-methylsulfonyl)amide and N,N,N-trimethyl-N-propylammonium bis(trifluoromethylsulfonyl)amide which differ only in the 2-hydroxyethyl and the propyl groups of the cations, we could directly observe distinct vibrational signatures of hydrogen bonding between the cation and the anion indicated by ‘jumping and pecking’ motions of cholinium. The assignment could be confirmed by isotopic substitution H/D at the hydroxyl group of cholinium. For the first time we could also find direct spectroscopic evidence for H-bonding between like-charged ions. The repulsive Coulomb interaction between the cations is overcome by cooperative hydrogen bonding between the 2-hydroxyethyl functional groups of cholinium. This H-bond network is reflected in the properties of protic ionic liquids (PILs) such as viscosities and conductivities.