A Nonheme Thiolate-Ligated Cobalt Superoxo Complex

Synthesis and Spectroscopic Characterization, Computational Studies, and Hydrogen Atom Abstraction Reactivity

Jesse B. Gordon, Avery C. Vilbert, Maxime A. Siegler, Kyle M. Lancaster, Pierre Moenne-Loccoz, David P. Goldberg

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

The synthesis and characterization of a Co(II) dithiolato complex Co(Me 3 TACN)(S 2 SiMe 2 ) (1) are reported. Reaction of 1 with O 2 generates a rare thiolate-ligated cobalt-superoxo species Co(O 2 )(Me 3 TACN)(S 2 SiMe 2 ) (2) that was characterized spectroscopically and structurally by resonance Raman, EPR, and X-ray absorption spectroscopies as well as density functional theory. Metal-superoxo species are proposed to S-oxygenate metal-bound thiolate donors in nonheme thiol dioxygenases, but 2 does not lead to S-oxygenation of the intramolecular thiolate donors and does not react with exogenous sulfur donors. However, complex 2 is capable of oxidizing the O-H bonds of 2,2,6,6-tetramethylpiperidin-1-ol derivatives via H atom abstraction. Complementary proton-coupled electron-transfer reactivity is seen for 2 with separated proton/reductant pairs. The reactivity studies indicate that 2 can abstract H atoms from weak X-H bonds with bond dissociation free energy (BDFE) ≤ 70 kcal mol -1 . DFT calculations predict that the putative Co(OOH) product has an O-H BDFE = 67 kcal mol -1 , which matches the observed pattern of reactivity seen for 2. These data provide new information regarding the selectivity of S-oxygenation versus H atom abstraction in thiolate-ligated nonheme metalloenzymes that react with O 2 .

Original languageEnglish (US)
Pages (from-to)3641-3653
Number of pages13
JournalJournal of the American Chemical Society
Volume141
Issue number8
DOIs
StatePublished - Feb 27 2019

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Cobalt
Protons
Hydrogen
Oxygenation
X-Ray Absorption Spectroscopy
Metals
Dioxygenases
Atoms
Free energy
Reducing Agents
Sulfur
Sulfhydryl Compounds
X ray absorption spectroscopy
Electrons
Discrete Fourier transforms
Density functional theory
Paramagnetic resonance
Derivatives

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

A Nonheme Thiolate-Ligated Cobalt Superoxo Complex : Synthesis and Spectroscopic Characterization, Computational Studies, and Hydrogen Atom Abstraction Reactivity. / Gordon, Jesse B.; Vilbert, Avery C.; Siegler, Maxime A.; Lancaster, Kyle M.; Moenne-Loccoz, Pierre; Goldberg, David P.

In: Journal of the American Chemical Society, Vol. 141, No. 8, 27.02.2019, p. 3641-3653.

Research output: Contribution to journalArticle

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abstract = "The synthesis and characterization of a Co(II) dithiolato complex Co(Me 3 TACN)(S 2 SiMe 2 ) (1) are reported. Reaction of 1 with O 2 generates a rare thiolate-ligated cobalt-superoxo species Co(O 2 )(Me 3 TACN)(S 2 SiMe 2 ) (2) that was characterized spectroscopically and structurally by resonance Raman, EPR, and X-ray absorption spectroscopies as well as density functional theory. Metal-superoxo species are proposed to S-oxygenate metal-bound thiolate donors in nonheme thiol dioxygenases, but 2 does not lead to S-oxygenation of the intramolecular thiolate donors and does not react with exogenous sulfur donors. However, complex 2 is capable of oxidizing the O-H bonds of 2,2,6,6-tetramethylpiperidin-1-ol derivatives via H atom abstraction. Complementary proton-coupled electron-transfer reactivity is seen for 2 with separated proton/reductant pairs. The reactivity studies indicate that 2 can abstract H atoms from weak X-H bonds with bond dissociation free energy (BDFE) ≤ 70 kcal mol -1 . DFT calculations predict that the putative Co(OOH) product has an O-H BDFE = 67 kcal mol -1 , which matches the observed pattern of reactivity seen for 2. These data provide new information regarding the selectivity of S-oxygenation versus H atom abstraction in thiolate-ligated nonheme metalloenzymes that react with O 2 .",
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AB - The synthesis and characterization of a Co(II) dithiolato complex Co(Me 3 TACN)(S 2 SiMe 2 ) (1) are reported. Reaction of 1 with O 2 generates a rare thiolate-ligated cobalt-superoxo species Co(O 2 )(Me 3 TACN)(S 2 SiMe 2 ) (2) that was characterized spectroscopically and structurally by resonance Raman, EPR, and X-ray absorption spectroscopies as well as density functional theory. Metal-superoxo species are proposed to S-oxygenate metal-bound thiolate donors in nonheme thiol dioxygenases, but 2 does not lead to S-oxygenation of the intramolecular thiolate donors and does not react with exogenous sulfur donors. However, complex 2 is capable of oxidizing the O-H bonds of 2,2,6,6-tetramethylpiperidin-1-ol derivatives via H atom abstraction. Complementary proton-coupled electron-transfer reactivity is seen for 2 with separated proton/reductant pairs. The reactivity studies indicate that 2 can abstract H atoms from weak X-H bonds with bond dissociation free energy (BDFE) ≤ 70 kcal mol -1 . DFT calculations predict that the putative Co(OOH) product has an O-H BDFE = 67 kcal mol -1 , which matches the observed pattern of reactivity seen for 2. These data provide new information regarding the selectivity of S-oxygenation versus H atom abstraction in thiolate-ligated nonheme metalloenzymes that react with O 2 .

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