Quek, Sebastian Y. and Debnath, Suman and Laxmi, Shoba and van Gastel, Maurice and Krämer, Tobias and England, Jason (2021) Sterically Stabilized End-On Superoxocopper(II) Complexes and Mechanistic Insights into Their Reactivity with O–H, N–H, and C–H Substrates. Journal of the American Chemical Society, 143 (47). pp. 19731-19747. ISSN 0002-7863

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Abstract

Instability of end-on superoxocopper(II) complexes, with respect to conversion to peroxo-bridged dicopper(II) complexes, has largely constrained their study to very low temperatures. This limits their kinetic capacity to oxidize substrates. In response, we have developed a series of bulky ligands, Ar3-TMPA (Ar = tpb, dpb, dtbpb), and used them to support copper(I) complexes that react with O2 to yield [CuII(η1-O2•–)(Ar3-TMPA)]+ species, which are stable against dimerization at all temperatures. Binding of O2 saturates at subambient temperatures and can be reversed by warming. The onset of oxygenation for the Ar = tpb and dpb systems is observed at 25 °C, and all three [CuII(η1-O2•–)(Ar3-TMPA)]+ complexes are stable against self-decay at temperatures of ≤−20 °C. This provides a wide temperature window for study of these complexes, which was exploited by performing extensive reaction kinetics measurements for [CuII(η1-O2•–)(tpb3-TMPA)]+ using a broad range of O–H, N–H, and C–H bond substrates. This includes correlation of second order rate constants (k2) versus oxidation potentials (Eox) for a range of phenols, construction of Eyring plots, and temperature-dependent kinetic isotope effect (KIE) measurements. The data obtained indicate that reaction with all substrates proceeds via H atom transfer (HAT), reaction with the phenols proceeds with significant charge transfer, and full tunneling of both H and D atoms occurs in the case of 1,2-diphenylhydrazine and 4-methoxy-2,6-di-tert-butylphenol. Oxidation of C–H bonds proved to be kinetically challenging, and whereas [CuII(η1-O2•–)(tpb3-TMPA)]+ can oxidize moderately strong O–H and N–H bonds, it is only able to oxidize very weak C–H bonds.

Item Type:	Article
Additional Information:	Cite as: Quek, S.Y., Debnath, S., Laxmi, S., van Gastel, M., Krämer, T. & England, J. 2021, "Sterically Stabilized End-On Superoxocopper(II) Complexes and Mechanistic Insights into Their Reactivity with O–H, N–H, and C–H Substrates", Journal of the American Chemical Society, vol. 143, no. 47, pp. 19731-19747.
Keywords:	Aromatic compounds; Ligands; Pyridines; Reactivity; Substituents;
Academic Unit:	Faculty of Science and Engineering > Chemistry Faculty of Science and Engineering > Research Institutes > Hamilton Institute
Item ID:	17440
Identification Number:	https://doi.org/10.1021/jacs.1c07837
Depositing User:	Tobias Kraemer
Date Deposited:	17 Aug 2023 11:28
Journal or Publication Title:	Journal of the American Chemical Society
Publisher:	American Chemical Society
Refereed:	Yes
URI:	Publisher
Use Licence:	This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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