2-Acetylpyridine thiosemicarbazones cause rapid substitution of amine and pyridyl ligands coordinated to cobalt(III)

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The reaction of 2-acetylpyridine 4-phenyl-3-thiosemicarbazone, 2-acetylpyridine 4-methyl-3-thiosemicarbazone and 2-acetylpyridine 4-allyl-3-thiosemicarbazone with [(en)2Co(OSO2CF3)2]CF3SO3, (dien)Co(OSO2CF3)3 and [(picen)Co(OSO2CF3)2]CF3SO3 results in the rapid substitution of coordinated amine and pyridyl ligands to form cobalt(III) complexes coordinated by two deprotonated 2-acetylpyridine thiosemicarbazone ligands, each bound tridentate through the sulfur atom and two nitrogen atoms (N2S). While the mechanism of this reaction remains unclear, it is suspected that an electron transfer reaction occurs between the thiosemicarbazone and the metal complex resulting in reduction to cobalt(II). Rapid ligand loss from cobalt(II) followed by chelation of the tridentate ligands and subsequent re-oxidation to cobalt(III) results in formation of the final product. The resulting complexes were characterized by NMR. In addition, the solid-state structure (X-ray) of the methyl derivative confirms the coordination mode of the ligand.