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Updated: Aug 4, 2025
Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks MOFs
Published on: January 17, 2020
Brønsted Acid Catalysis-Controlling the Competition between Monomeric versus Dimeric Reaction Pathways Enhances
Maximilian Franta1, Johannes Gramüller1, Philipp Dullinger2
1Institute of Organic Chemistry, University of Regensburg, Universitätsstraße 31, 93053, Regensburg, Germany.
Abstract:
Chiral phosphoric acids (CPA) have become a privileged catalyst type in organocatalysis, but the selection of the optimum catalyst is still challenging. So far hidden competing reaction pathways may limit the maximum stereoselectivities and the potential of prediction models. In CPA-catalyzed transfer hydrogenation of imines, we identified for many systems two reaction pathways with inverse stereoselectivity, featuring as active catalyst either one CPA or a hydrogen bond bridged dimer. NMR measurements and DFT calculations revealed the dimeric intermediate and a stronger substrate activation via cooperativity. Both pathways are separable: Low temperatures and high catalysts loadings favor the dimeric pathway (ee up to -98 %), while low temperatures with reduced catalyst loading favor the monomeric pathway and give significantly enhanced ee (92-99 % ee; prior 68-86 % at higher temperatures). Thus, a broad impact is expected on CPA catalysis regarding reaction optimization and prediction.
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