Methanol as the Hydrogen Source in the Selective Transfer Hydrogenation of Alkynes Enabled by a Manganese Pincer Complex
Jan Sklyaruk, Viktoriia Zubar, Jannik C. Borghs and Magnus Rueping*
*KAUST Catalysis Center (KCC), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia,
Email: magnus.rueping
kaust.edu.sa
J. Sklyaruk, V. Zubar, J. C. Borghs, M. Rueping, Org. Lett., 2020, 22, 6067-6071.
DOI: 10.1021/acs.orglett.0c02151
Abstract
An air and moisture stable manganese pincer complex catalyzes the semireduction of various alkynes to the corresponding (Z)-olefins in high yields. The reaction is stereo- and chemoselective and scalable.
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Details
The document describes the first base metal-catalyzed transfer hydrogenation of alkynes using methanol as a hydrogen source, facilitated by a manganese pincer complex. This method selectively reduces various alkynes to (Z)-olefins with high yields, offering a stereo- and chemoselective, scalable alternative to traditional noble metal catalysts and pressurized hydrogen gas. Methanol is highlighted as an attractive hydrogen donor due to its large-scale production and potential sustainability benefits. The study evaluates different manganese complexes, with Mn-1 showing the highest activity, achieving up to 97% yield with a Z/E ratio of 98/2. The reaction conditions were optimized, including the use of toluene as a cosolvent and adjusting methanol and catalyst amounts. The method tolerates various substituents and heterocycles, though terminal alkynes were inactive. Deuterium labeling experiments confirmed cis-selective hydrogen incorporation. The proposed catalytic cycle involves methanol coordination, deprotonation, and formaldehyde elimination, leading to the formation of the (Z)-olefin. This research demonstrates a sustainable and efficient approach to synthesizing (Z)-olefins, with potential applications in pharmaceuticals, polymers, and functional materials.
Key Words
semireduction of alkynes, methanol
ID: J54-Y2020
