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Lookup NU author(s): Dr Simon DohertyORCiD,
Dr Julian Knight,
This is the authors' accepted manuscript of an article that has been published in its final definitive form by American Chemical Society, 2019.
For re-use rights please refer to the publisher's terms and conditions.
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 at room temperature 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 channeling 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 a continuous flow process enabling facile scale-up.
Author(s): Doherty S, Knight JG, Backhouse T, Abood E, Simpson W, Paget W, Bourne RA, Chamberlain TW, Stones R, Lovelock KRJ, Seymour JM, Isaacs MA, Hardacre C, Daly H, Rees NH
Publication type: Article
Publication status: Published
Journal: ACS Catalysis
Print publication date: 07/06/2019
Online publication date: 15/04/2019
Acceptance date: 12/04/2019
Date deposited: 13/04/2019
ISSN (electronic): 2155-5435
Publisher: American Chemical Society
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