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DDC: 660 × Type: Text × Publisher: Weinheim : Wiley-VCH × Subject: hydrogenation ×

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    A Highly Active Cobalt Catalyst for the General and Selective Hydrogenation of Aromatic Heterocycles
    (Weinheim : Wiley-VCH, 2023) Bauer, Christof; Müller, Felix; Keskin, Sercan; Zobel, Mirijam; Kempe, Rhett
    Nanostructured earth abundant metal catalysts that mediate important chemical reactions with high efficiency and selectivity are of great interest. This study introduces a synthesis protocol for nanostructured earth abundant metal catalysts. Three components, an inexpensive metal precursor, an easy to synthesize N/C precursor, and a porous support material undergo pyrolysis to give the catalyst material in a simple, single synthesis step. By applying this catalyst synthesis, a highly active cobalt catalyst for the general and selective hydrogenation of aromatic heterocycles could be generated. The reaction is important with regard to organic synthesis and hydrogen storage. The mild reaction conditions observed for quinolines permit the selective hydrogenation of numerous classes of N-, O- and S-heterocyclic compounds such as: quinoxalines, pyridines, pyrroles, indoles, isoquinoline, aciridine amine, phenanthroline, benzofuranes, and benzothiophenes.
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    Synthesis of 3,4-Dihydro-2H-Pyrroles from Ketones, Aldehydes, and Nitro Alkanes via Hydrogenative Cyclization
    (Weinheim : Wiley-VCH, 2022) Klausfelder, Barbara; Blach, Patricia; de Jonge, Niels; Kempe, Rhett
    Syntheses of N-heterocyclic compounds that permit a flexible introduction of various substitution patterns by using inexpensive and diversely available starting materials are highly desirable. Easy to handle and reusable catalysts based on earth-abundant metals are especially attractive for these syntheses. We report here on the synthesis of 3,4-dihydro-2H-pyrroles via the hydrogenation and cyclization of nitro ketones. The latter are easily accessible from three components: a ketone, an aldehyde and a nitroalkane. Our reaction has a broad scope and 23 of the 33 products synthesized are compounds which have not yet been reported. The key to the general hydrogenation/cyclization reaction is a highly active, selective and reusable nickel catalyst, which was identified from a library of 24 earth-abundant metal catalysts.
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    Preparation of a Series of Supported Nonsymmetrical PNP-Pincer Ligands and the Application in Ester Hydrogenation
    (Weinheim : Wiley-VCH, 2019) Konrath, Robert; Spannenberg, Anke; Kamer, Paul C.J.
    In contrast to their symmetrical analogues, nonsymmetrical PNP-type ligand motifs have been less investigated despite the modular pincer structure. However, the introduction of mixed phosphorus donor moieties provides access to a larger variety of PNP ligands. Herein, a facile solid-phase synthesis approach towards a diverse PNP-pincer ligand library of 14 members is reported. Contrary to often challenging workup procedures in solution-phase, only simple workup steps are required. The corresponding supported ruthenium-PNP catalysts are screened in ester hydrogenation. Usually, industrially applied heterogeneous catalysts require harsh conditions in this reaction (250–350 °C at 100–200 bar) often leading to reduced selectivities. Heterogenized reusable Ru-PNP catalysts are capable of reducing esters and lactones selectively under mild conditions. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.