Network topology and cavity confinement-controlled diastereoselectivity in cyclopropanation reactions catalyzed by porphyrin-based MOFs

Epp, Konstantin, Bueken, Bart, Hofmann, Benjamin J., Cokoja, Mirza, Hemmer, Karina, De Vos, Dirk and Fischer, Roland A. (2019) Network topology and cavity confinement-controlled diastereoselectivity in cyclopropanation reactions catalyzed by porphyrin-based MOFs. Catalysis Science & Technology, 9 (22). pp. 6452-6459. ISSN 2044-4753

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Abstract

In this work, we show that the stereoselectivity of a reaction can be controlled by directing groups of substrates, by network topology and by local cavity confinement of metal-organic framework (MOF) catalysts. We applied the porphyrin-based PCN-224(Rh), which contains no stereocenters in the cyclopropanation reaction using ethyl diazoacetate (EDA) as carbene source. When styrene and other non-coordinating olefins are used as substrates, high activity, but no diastereoselectivity is observed. Interestingly, conversion of 4-amino- and 4-hydroxystyrene substrates occurs with high diastereomeric ratios (dr) of up to 23 : 1 (trans : cis). We attribute this to local pore confinement effects as a result of substrate coordination to neighboring Rh-centers, which position the olefin with respect to the active site, causing a break of local symmetry of the coordinated substrate. The effect of local pore confinement was improved by using PCN-222(Rh) as catalyst, which is a structural analog of PCN-224(Rh) with characteristic Kagomé topology featuring shorter Rh-Rh distances. A remarkable dr of 42 : 1 (trans : cis) was observed for 4-aminostyrene. In this case, the length of the substrate corresponds to the average distance between two neighboring Rh centers within the pores of PCN-222(Rh), which drastically boosts the diastereoselectivity. This work showcases how diastereomeric control can be achieved by favorable substrate-catalyst interactions and thoughtful adjustment of confined reaction space using porphyrin-based MOFs, in which stereocenters are inherently absent.

Item Type: Article
Uncontrolled Keywords: catalysis ,/dk/atira/pure/subjectarea/asjc/1500/1503
Faculty \ School: Faculty of Science > School of Chemistry
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Depositing User: LivePure Connector
Date Deposited: 17 Jul 2021 00:12
Last Modified: 10 Sep 2021 00:22
URI: https://ueaeprints.uea.ac.uk/id/eprint/80631
DOI: 10.1039/c9cy00893d

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