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 .
ASJC Scopus subject areas
- Colloid and Surface Chemistry