Doherty, S, Knight, JG, Backhouse, T et al. (13 more authors) (2019) Highly Selective and Solvent-Dependent Reduction of Nitrobenzene to N-Phenylhydroxylamine, Azoxybenzene and Aniline Catalyzed by Phosphino-Modified Polymer Immobilized Ionic Liquid-Stabilized AuNPs. ACS Catalysis, 9 (6). pp. 4777-4791. ISSN 2155-5435
Abstract
Gold nanoparticles stabilized by phosphine-decorated polymer immobilized ionic liquids (AuNP@PPh2-PIILP) is an extremely efficient multi-product selective catalyst for the sodium borohydride-mediated reduction of nitrobenzene giving either N-phenylhydroxylamine, azoxybenzene or aniline as the sole product under mild conditions and a very low catalyst loading. The use of a single nanoparticle-based catalyst for the partial and complete reduction of nitroarenes to afford three different products with exceptionally high selectivities is unprecedented. Under optimum conditions, thermodynamically unfavorable N-phenylhydroxylamine can be obtained as the sole product in near quantitative yield in water whereas a change in reaction solvent to ethanol results in a dramatic switch in selectivity to afford azoxybenzene. The key to obtaining such a high selectivity for N-phenylhydroxylamine is the use of a nitrogen atmosphere as reactions conducted under an inert atmosphere occur via the direct pathway and are essentially irreversible while reactions in air afford significant amounts of azoxy-based products by virtue of competing condensation due to reversible formation of N-phenylhydroxylamine. Ultimately, aniline can also be obtained quantitatively and selectively by adjusting the reaction temperature and time accordingly. Introduction of PEG onto to the polyionic liquid resulted in a dramatic improvement in catalyst efficiency such that N-phenylhydroxylamine could be obtained with a TON of 100,000 (TOF of 73,000 h-1, with >99% selectivity), azoxybenzene with a TON of 55,000 (TOF of 37,000 h-1 with 100% selectivity) and aniline with a TON of 500,000 (TOF of 62,500 h-1, with 100% selectivity). As the combination of ionic liquid and phosphine are required to achieve high activity and selectivity further studies are currently underway to explore whether interfacial electronic effects influence adsorption and thereby selectivity and whether channelling of the substrate by the electrostatic potential around the AuNPs is responsible for the high activity. This is the first report of a AuNP-based system that can selectively reduce nitroarenes to either of two synthetically important intermediates as well as aniline and, in this regard, is an exciting discovery that will form the basis to develop new catalyst technology for implementation in a continuous flow process for scale-up.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | Copyright © 2019 American Chemical Society. This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in ACS Catalysis, after peer review. To access the final edited and published work see https://doi.org/10.1021/acscatal.9b00347 |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Chemical & Process Engineering (Leeds) The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Chemistry (Leeds) > Inorganic Chemistry (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 26 Apr 2019 09:58 |
Last Modified: | 15 Apr 2020 00:38 |
Status: | Published |
Publisher: | American Chemical Society |
Identification Number: | 10.1021/acscatal.9b00347 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:145350 |