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Mechanistic insights into selective oxidation of polyaromatic compounds using RICO chemistry

Nowicka, Ewa, Hickey, Niamh, Sankar, Meenakshisundaram, Jenkins, Robert, Knight, David W., Willock, David J., Hutchings, Graham J., Francisco, Manuel and Taylor, Stuart H. 2018. Mechanistic insights into selective oxidation of polyaromatic compounds using RICO chemistry. Chemistry - A European Journal 24 (47) , pp. 12359-12369. 10.1002/chem.201800423

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Abstract

Ruthenium‐ion‐catalyzed oxidation (RICO) of polyaromatic hydrocarbons (PAHs) has been studied in detail using experimental and computational approaches to explore the reaction mechanism. DFT calculations show that regioselectivity in these reactions can be understood in terms of the preservation of aromaticity in the initial formation of a [3+2] metallocycle intermediate at the most‐isolated double bond. We identify two competing pathways: C−C bond cleavage leading to a dialdehyde and C‐H activation followed by H migration to the RuOx complex to give diketones. Experimentally, the oxidation of pyrene and phenanthrene has been carried out in monophasic and biphasic solvent systems. Our results show that diketones are the major product for both phenanthrene and pyrene substrates. These diketone products are shown to be stable under our reaction conditions so that higher oxidation products (acids and their derivatives) are assigned to the competing pathway through the dialdehyde. Experiments using 18O‐labelled water do show incorporation of oxygen from the solvents into products, but this may take place during the formation of the reactive RuO4 species rather than directly during PAH oxidation. When the oxidation of pyrene is carried out using D2O, a kinetic isotope effect (KIE) is observed implying that water is involved in the rate‐determining step leading to the diketone products.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Advanced Research Computing @ Cardiff (ARCCA)
Cardiff Catalysis Institute (CCI)
Subjects: Q Science > QD Chemistry
Publisher: Wiley
ISSN: 0947-6539
Funders: EPSRC
Date of First Compliant Deposit: 24 May 2018
Date of Acceptance: 15 May 2018
Last Modified: 17 Oct 2019 19:59
URI: http://orca-mwe.cf.ac.uk/id/eprint/111722

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