Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 141, Issue 8, Pages 3641-3653Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.8b13134
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Funding
- NIH [GM119374, R35GM124908]
- A. P. Sloan Research Fellowship
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-76SF00515]
- Department of Energy's Office of Biological and Environmental Research
- NIH/NIGMS [P41GM103393]
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The synthesis and characterization of a Co(II) dithiolato complex Co(Me(3)TACN)(S2SiMe2) (1) are reported. Reaction of 1 with O-2 generates a rare thiolate-ligated cobalt-superoxo species Co(O-2)(Me(3)TACN)(S2SiMe2) (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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