Ir-Catalyzed Reversible Acceptorless Dehydrogenation/Hydrogenation of N-Substituted and Unsubstituted Heterocycles Enabled by a Polymer-Cross-Linking Bisphosphine
Deliang Zhang, Tomohiro Iwai* and Masaya Sawamura*
*Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan,
Email: iwai-tsci.hokudai.ac.jp, sawamura
sci.hokudai.ac.jp
D. Zhang, T. Iwai, M. Sawamura, Org. Lett., 2020, 22, 5240-5245.
DOI: 10.1021/acs.orglett.0c01874
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Abstract
The polystyrene-cross-linking bisphosphine ligand PS-DPPBz was effective for the Ir-catalyzed reversible acceptorless dehydrogenation/hydrogenation of N-heterocycles. Notably, this protocol is applicable to the dehydrogenation of a broad range of indoline derivatives.
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PS-DPPBz
Details
The document details a study on the Ir-catalyzed reversible acceptorless dehydrogenation/hydrogenation of N-substituted and unsubstituted heterocycles using a polystyrene-cross-linking bisphosphine ligand (PS-DPPBz). This method is notable for its efficiency in dehydrogenating N-substituted indoline derivatives with various N-substituents, producing only molecular hydrogen as a byproduct, making it a cleaner and more atom-economical process compared to traditional methods using strong oxidants. The (PS-DPPBz)-Ir catalyst system also facilitates the backward hydrogenation of N-heteroarenes with molecular hydrogen, demonstrating the process's reversibility.
The study highlights the catalyst's high activity and selectivity, even in the presence of electron-withdrawing groups on the N atom, which typically inhibit such reactions. The catalyst's reusability is noted, although with a decrease in yield over successive runs. The proposed reaction pathway involves the oxidative addition of an N-adjacent C(sp3)−H bond to the bisphosphine-coordinated Ir(I) center.
The document also explores the scope of the reaction, demonstrating its applicability to various N-substituted indolines and NH-heterocycles, and its utility in synthesizing pharmacologically active molecules. The study concludes that this catalytic system offers significant potential for organic synthesis and hydrogen storage applications.
Key Words
ID: J54-Y2020