Synthesis and reactivity of cobalt complexes derived from tris(2-pyridylthio)methane ligand: Structural characterization of cobalt(III) complexes containing cobalt–carbon bond

The synthesis, characterization and reactivity of a cobalt(II) complex, [(HL)Co(PyS)](ClO4) (1) (where HL = tris(2-pyridylthio)methane and PyS = monoanionic pyridine-2-thiolate) are discussed. Complex (1) reacts with molecular oxygen to yield a mononuclear low-spin cobalt(III) complex, [(L)Co(PyS)](ClO4) (2). On the other hand, treatment of (1) with a protic acid (pyridinium perchlorate) followed by a base (triethylamine) and dioxygen forms an isomeric cobalt(III) complex, [(L)Co(PyS)](ClO4) (3) (L 2 = 1-[bis(2-pyridylthio)methyl]pyridine-2-thione). Ligand HL (in 1) rearranges to L (in 3) during the reaction as a result of C–S bond cleavage and subsequent C–N bond formation. X-ray crystal structures of both (2) and (3) reveal a distorted octahedral coordination geometry at cobalt(III) center with a strong cobalt–carbon bonding interaction. A four-coordinate distorted tetrahedral cobalt(II) complex, [Co(PySH)4](ClO4)2 (4) is formed via C–S bond cleavage of HL 1 in the reaction of (1) with an excess amount of pyridinium perchlorate. The electronic structure of (2) as established by DFT calculation suggests a delocalized LUMO with significant contribution from the metal ion. The organocobalt(III) complex converts to an air-stable organocobalt(II) complex (2) upon one-electron reduction.