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, [(HL1)Co-II(PyS)](ClO4) (1) (where HL1 = 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-1)Co-III(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-2)Co-III(PyS)](ClO4) (3) (L-2 = 1-[bis(2-pyridylthio)methyl]pyridine-2-thione). Ligand HL1 (in 1) rearranges to L-2 (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-II(PySH)(4)](ClO4)(2) (4) is formed via C-S bond cleavage of HL1 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(M) complex converts to an air-stable organocobalt(II) complex (2(red)) upon one-electron reduction.