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search.filters.applied.f.access: openAccess × Start date: 2021 × Subject: homogeneous catalysis × WGL Institute: LIKAT ×

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    Palladium-Catalyzed Cascade Carbonylation to α,β-Unsaturated Piperidones via Selective Cleavage of Carbon-Carbon Triple Bonds
    (Weinheim : Wiley-VCH, 2021) Ge, Yao; Ye, Fei; Yang, Ji; Spannenberg, Anke; Jiao, Haijun; Jackstell, Ralf; Beller, Matthias
    A direct and selective synthesis of α,β-unsaturated piperidones by a new palladium-catalyzed cascade carbonylation is described. In the presented protocol, easily available propargylic alcohols react with aliphatic amines to provide a broad variety of interesting heterocycles. Key to the success of this transformation is a remarkable catalytic cleavage of the present carbon–carbon triple bond by using a specific catalyst with 2-diphenylphosphinopyridine as ligand and appropriate reaction conditions. Mechanistic studies and control experiments revealed branched unsaturated acid 11 as crucial intermediate. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
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    Catalytic, Kinetic, and Mechanistic Insights into the Fixation of CO2 with Epoxides Catalyzed by Phenol-Functionalized Phosphonium Salts
    (Weinheim : Wiley-VCH, 2021) Hu, Yuya; Wei, Zhihong; Frey, Anna; Kubis, Christoph; Ren, Chang-Yue; Spannenberg, Anke; Jiao, Haijun; Werner, Thomas
    A series of hydroxy-functionalized phosphonium salts were studied as bifunctional catalysts for the conversion of CO2 with epoxides under mild and solvent-free conditions. The reaction in the presence of a phenol-based phosphonium iodide proceeded via a first order rection kinetic with respect to the substrate. Notably, in contrast to the aliphatic analogue, the phenol-based catalyst showed no product inhibition. The temperature dependence of the reaction rate was investigated, and the activation energy for the model reaction was determined from an Arrhenius-plot (Ea =39.6 kJ mol-1 ). The substrate scope was also evaluated. Under the optimized reaction conditions, 20 terminal epoxides were converted at room temperature to the corresponding cyclic carbonates, which were isolated in yields up to 99 %. The reaction is easily scalable and was performed on a scale up to 50 g substrate. Moreover, this method was applied in the synthesis of the antitussive agent dropropizine starting from epichlorohydrin and phenylpiperazine. Furthermore, DFT calculations were performed to rationalize the mechanism and the high efficiency of the phenol-based phosphonium iodide catalyst. The calculation confirmed the activation of the epoxide via hydrogen bonding for the iodide salt, which facilitates the ring-opening step. Notably, the effective Gibbs energy barrier regarding this step is 97 kJ mol-1 for the bromide and 72 kJ mol-1 for the iodide salt, which explains the difference in activity.
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    Site-Selective Real-Time Observation of Bimolecular Electron Transfer in a Photocatalytic System Using L-Edge X-Ray Absorption Spectroscopy
    (Weinheim : Wiley-VCH Verl., 2021) Britz, Alexander; Bokarev, Sergey I.; Assefa, Tadesse A.; Bajnóczi, Èva G.; Németh, Zoltán; Vankó, György; Rockstroh, Nils; Junge, Henrik; Beller, Matthias; Doumy, Gilles; March, Anne Marie; Southworth, Stephen H.; Lochbrunner, Stefan; Kühn, Oliver; Bressler, Christian; Gawelda, Wojciech
    Time-resolved X-ray absorption spectroscopy has been utilized to monitor the bimolecular electron transfer in a photocatalytic water splitting system. This has been possible by uniting the local probe and element specific character of X-ray transitions with insights from high-level ab initio calculations. The specific target has been a heteroleptic [IrIII (ppy)2 (bpy)]+ photosensitizer, in combination with triethylamine as a sacrificial reductant and Fe3(CO)12 as a water reduction catalyst. The relevant molecular transitions have been characterized via high-resolution Ir L-edge X-ray absorption spectroscopy on the picosecond time scale and restricted active space self-consistent field calculations. The presented methods and results will enhance our understanding of functionally relevant bimolecular electron transfer reactions and thus will pave the road to rational optimization of photocatalytic performance.