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

Abstract

The synthesis, characterization and reactivity of a cobalt(II) complex, [(HL¹)Co^II(PyS)](ClO₄) (<b style="">1)</b> (where HL¹ = tris(2-pyridylthio)methane and PyS = monoanionic pyridine-2-thiolate) are discussed. Complex (<b style="">1</b>) reacts with molecular oxygen to yield a mononuclear low-spin cobalt(III) complex, [(L¹)Co^III(PyS)](ClO₄) (<b style="">2</b>). On the other hand, treatment of (<b style="">1</b>) with a protic acid (pyridinium perchlorate) followed by a base (triethylamine) and dioxygen forms an isomeric cobalt(III) complex, [(L²)Co^III(PyS)](ClO₄) (<b style="">3</b>) (L² = 1-[bis(2-pyridylthio)methyl]pyridine-2-thione). Ligand HL¹ (in <b style="">1</b>) rearranges to L² (in <b style="">3</b>) during the reaction as a result of C–S bond cleavage and subsequent C–N bond formation. X-ray crystal structures of both (<b style="">2</b>) and (<b style="">3</b>) 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 (<b style="">4</b>) is formed via C–S bond cleavage of HL¹ in the reaction of (<b style="">1</b>) with an excess amount of pyridinium perchlorate. The electronic structure of (<b style="">2</b>) 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 (<b style="">2^red</b>) upon one-electron reduction.