Sterically stabilized end-on superoxocopper(II) complexes and mechanistic insights into their reactivity with O−H, N−H, and C−H substrates

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, A...

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Main Authors: Quek, Sebastian Y., Debnath, Suman, Laxmi, Shoba, van Gastel, Maurice, Krämer, Tobias, England, Jason
Other Authors: School of Physical and Mathematical Sciences
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Language:English
Published: 2022
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Online Access:https://hdl.handle.net/10356/163536
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spelling sg-ntu-dr.10356-1635362022-12-08T06:48:56Z Sterically stabilized end-on superoxocopper(II) complexes and mechanistic insights into their reactivity with O−H, N−H, and C−H substrates Quek, Sebastian Y. Debnath, Suman Laxmi, Shoba van Gastel, Maurice Krämer, Tobias England, Jason School of Physical and Mathematical Sciences Science::Chemistry Dopamine Beta-Monooxygenase Alpha-Hydroxylating Monooxygenase 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. Ministry of Education (MOE) Nanyang Technological University J.E. is grateful to NTU (M4081442, 000416-00001) and the Ministry of Education of Singapore (AcRF Tier 1 Grant RG8/19 (S), 002689-00001) for funding. 2022-12-08T06:48:56Z 2022-12-08T06:48:56Z 2021 Journal Article 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, 143(47), 19731-19747. https://dx.doi.org/10.1021/jacs.1c07837 0002-7863 https://hdl.handle.net/10356/163536 10.1021/jacs.1c07837 34783549 2-s2.0-85119908468 47 143 19731 19747 en M4081442 000416-00001 RG8/19 (S) 002689-00001 Journal of the American Chemical Society © 2021 American Chemical Society. All rights reserved.
institution Nanyang Technological University
building NTU Library
continent Asia
country Singapore
Singapore
content_provider NTU Library
collection DR-NTU
language English
topic Science::Chemistry
Dopamine Beta-Monooxygenase
Alpha-Hydroxylating Monooxygenase
spellingShingle Science::Chemistry
Dopamine Beta-Monooxygenase
Alpha-Hydroxylating Monooxygenase
Quek, Sebastian Y.
Debnath, Suman
Laxmi, Shoba
van Gastel, Maurice
Krämer, Tobias
England, Jason
Sterically stabilized end-on superoxocopper(II) complexes and mechanistic insights into their reactivity with O−H, N−H, and C−H substrates
description 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.
author2 School of Physical and Mathematical Sciences
author_facet School of Physical and Mathematical Sciences
Quek, Sebastian Y.
Debnath, Suman
Laxmi, Shoba
van Gastel, Maurice
Krämer, Tobias
England, Jason
format Article
author Quek, Sebastian Y.
Debnath, Suman
Laxmi, Shoba
van Gastel, Maurice
Krämer, Tobias
England, Jason
author_sort Quek, Sebastian Y.
title Sterically stabilized end-on superoxocopper(II) complexes and mechanistic insights into their reactivity with O−H, N−H, and C−H substrates
title_short Sterically stabilized end-on superoxocopper(II) complexes and mechanistic insights into their reactivity with O−H, N−H, and C−H substrates
title_full Sterically stabilized end-on superoxocopper(II) complexes and mechanistic insights into their reactivity with O−H, N−H, and C−H substrates
title_fullStr Sterically stabilized end-on superoxocopper(II) complexes and mechanistic insights into their reactivity with O−H, N−H, and C−H substrates
title_full_unstemmed Sterically stabilized end-on superoxocopper(II) complexes and mechanistic insights into their reactivity with O−H, N−H, and C−H substrates
title_sort sterically stabilized end-on superoxocopper(ii) complexes and mechanistic insights into their reactivity with o−h, n−h, and c−h substrates
publishDate 2022
url https://hdl.handle.net/10356/163536
_version_ 1753801136209395712