Sterically Stabilized End-On Superoxocopper(II) Complexes and Mechanistic Insights into Their Reactivity with O-H, N-H, and C-H Substrates

Quek, S.Y., Debnath, S., Laxmi, S. , Van Gastel, M., Krämer, T. 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

Full content URL: https://doi.org/10.1021/jacs.1c07837

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Sterically Stabilized End-On Superoxocopper(II) Complexes and Mechanistic Insights into Their Reactivity with O-H, N-H, and C-H Substrates
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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 ligand systems, 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 over which these complexes can be studied, 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 tuneling 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.

Keywords:Charge transfer, Copper compounds, Kinetics, Phenols, Rate constants, Bulky ligands, C-H bond, Dicopper, Dimerizations, Kinetic measurement, Mechanistics, Oxidation potentials, Second-order rate constants, Temperature window, Very low temperatures, Oxidation, 1,2 diphenylhydrazine, 4 methoxy 2,6 di tert butylphenol, carbon, copper complex, hydrazine derivative, hydrogen, ligand, nitrogen, oxygen, phenol derivative, superoxocopper complex, unclassified drug, Article, chemical binding, chemical bond, chemical reaction, chemical reaction kinetics, chemical structure, controlled study, correlation analysis, degradation, dimerization, Eyring plot, hydrogen atom transfer, kinetic isotope effect, mathematical analysis, molecular stability, oxidation reduction potential, oxygenation, second order rate constant, temperature
Subjects:F Physical Sciences > F120 Inorganic Chemistry
F Physical Sciences > F100 Chemistry
Divisions:College of Science > School of Chemistry
ID Code:51886
Deposited On:04 Oct 2022 09:23

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