Metal-organic frameworks invert molecular reactivity: Lewis acidic phosphonium zwitterions catalyze the Aldol-Tishchenko reaction.
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Published version
Date
2017-12-03
Authors
Bauer, Gerald
Ongari, Daniele
Xu, Xiaoying
Tiana, Davide
Smit, Berend
Ranocchiari, Marco
Journal Title
Journal ISSN
Volume Title
Publisher
American Chemical Society
Published Version
Abstract
The influence of metal–organic frameworks (MOFs) as additives is herein described for the reaction of n-alkyl aldehydes in the presence of methylvinylketone and triphenylphosphine. In the absence of a MOF, the expected Morita–Baylis–Hillman product, a β-hydroxy enone, is observed. In the presence of MOFs with UMCM-1 and MOF-5 topologies, the reaction is selective to Aldol-Tishchenko products, the 1 and 3 n-alkylesters of 2-alkyl-1,3-diols, which is unprecedented in organocatalysis. The (3-oxo-2-butenyl)triphenylphosphonium zwitterion, a commonly known nucleophile, is identified as the catalytic active species. This zwitterion favors nucleophilic character in solution, whereas once confined within the framework, it becomes an electrophile yielding Aldol-Tishchenko selectivity. Computational investigations reveal a structural change in the phosphonium moiety induced by the steric confinement of the framework that makes it accessible and an electrophile.
Description
Keywords
Metal–organic frameworks , Aldol-Tishchenko , MOFs , Phosphonium , Morita−Baylis−Hillman (MBH) reaction
Citation
Bauer, G., Ongari, D., Xu, X., Tiana, D., Smit, B. and Ranocchiari, M. (2017) 'Metal–Organic Frameworks Invert Molecular Reactivity: Lewis Acidic Phosphonium Zwitterions Catalyze the Aldol-Tishchenko Reaction', Journal of the American Chemical Society, 139(50), pp. 18166-18169. doi:10.1021/jacs.7b10928