Trapping Of Superoxide Cobalt And Peroxide Dicobalt Species: A Study Of Reversible Formation.pdf

This study investigates the trapping and oxygenation of superoxido cobalt ([CoII]^2+) and peroxido dicobalt ([CoIII]^3+) species derived from cobalt(II) chloride (CoCl2) and molecular oxygen (O2). The researchers synthesized two complexes: [CoII(Pytacn)(CH3CN)2](SbF6)2 (1SbF6) and [CoIII(Pytacn)(CH3CN)2](SbF6)3 (1+SbF6), where Pytacn is a pyridine-based ligand.

Key Findings:

1. Complex Synthesis:
- 1SbF6 was obtained by reacting CoCl2 with Pytacn in acetonitrile, followed by the addition of silver hexafluorosulfate (AgSbF6).
- 1+SbF6 was synthesized through a similar process but with a subsequent reaction between 1SbF6 and NOSbF6.

2. Characterization:
- 1SbF6 exhibits two sets of signals in its NMR spectra, confirming the presence of both [CoII]^2+ and [CoII(Pytacn)(CH3CN)2](SbF6)^2 species.
- X-ray crystallography reveals the structure of 1+SbF6, showcasing a unique coordination mode of the SbF6^- anion with the cobalt center.

3. Oxygenation and Reversibility:
- Exposure of 1SbF6 to O2 in acetone led to the formation of 1+SbF6, indicating reversible oxygenation between [CoII]^2+ and [CoIII]^3+.
- EPR spectroscopy confirmed the oxidation state change.

4. Reactivity:
- Both 1SbF6 and 1+SbF6 showed reactivity towards organic substrates, with 1+SbF6 demonstrating selective oxygenation.

5. Computational Studies:
- Density Functional Theory (DFT) calculations provided insights into the electronic structure and reactivity of the complexes, supporting experimental observations.