Selective aldehyde reductions in neutral water catalysed by encapsulation in a supramolecular cage

Paul, A., Shipman, M. A., Onabule, D. Y., Sproules, S. and Symes, M. D. (2021) Selective aldehyde reductions in neutral water catalysed by encapsulation in a supramolecular cage. Chemical Science, 12(14), pp. 5082-5090. (doi: 10.1039/D1SC00896J)

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Abstract

The enhancement of reactivity inside supramolecular coordination cages has many analogies to the mode of action of enzymes, and continues to inspire the design of new catalysts for a range of reactions. However, despite being a near-ubiquitous class of reactions in organic chemistry, enhancement of the reduction of carbonyls to their corresponding alcohols remains very much underexplored in supramolecular coordination cages. Herein, we show that encapsulation of small aromatic aldehydes inside a supramolecular coordination cage allows the reduction of these aldehydes with the mild reducing agent sodium cyanoborohydride to proceed with high selectivity (ketones and esters are not reduced) and in good yields. In the absence of cage, low pH conditions are essential for any appreciable conversion of the aldehydes to the alcohols. In contrast, the specific microenvironment inside the cage allows this reaction to proceed in bulk solution that is pH-neutral, or even basic. We propose that the cage acts to stabilise the protonated oxocarbenium ion reaction intermediates (enhancing aldehyde reactivity) whilst simultaneously favouring the encapsulation and reduction of smaller aldehydes (which fit more easily inside the cage). Such dual action (enhancement of reactivity and size-selectivity) is reminiscent of the mode of operation of natural enzymes and highlights the tremendous promise of cage architectures as selective catalysts.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Sproules, Dr Stephen and Paul, Dr Avishek and Symes, Dr Mark and Onabule, Dolapo and Shipman, Mr Michael
Authors: Paul, A., Shipman, M. A., Onabule, D. Y., Sproules, S., and Symes, M. D.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Chemical Science
Publisher:Royal Society of Chemistry
ISSN:2041-6520
ISSN (Online):2041-6539
Published Online:12 March 2021
Copyright Holders:Copyright © 2021 The Authors
First Published:First published in Chemical Science 12(14): 5082-5090
Publisher Policy:Reproduced under a Creative Commons licence
Data DOI:10.5525/gla.researchdata.1124

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
301241Ultra-Reduced Polyoxometalates as Electron-Coupled-Proton-Systems for Energy StorageLeroy CroninEngineering and Physical Sciences Research Council (EPSRC)EP/R020914/1Chemistry
173495Driving energetically uphill processes using metal-ligand coordination complexesMark SymesThe Royal Society (ROYSOC)UF150104Chemistry