Synthesis, characterization and base hydrolysis of cobalt(III) complexes coordinated by substituted phenylthioether ligands

A synthetic route to the preparation of cobalt(III) complexes coordinated by bidentate phenylthioether ligands is described. Complexes of the type ((2-(X-phenylthio)ethylamine)-N,S)bis(ethylenediamine)cobalt(III) perchlorate, [(en)₂Co(S(X-phenyl)CH₂CH₂NH₂)](ClO₄)₃, where X = 4-methoxy (2a), 4-methyl (2b), 3-methyl (2c), nothing (2d), 3-methoxy (2e), 4-bromo (2f) and 3-bromo (2g) were prepared. The synthetic route involves reaction of trans-dichloridobis(ethylenediamine)cobalt(III) chloride with NH₂CH₂CH₂SC₆H₄X to produce cis-[(en)₂CoCl(NH₂CH₂CH₂SC₆H₄X)]Cl₂ (1a–g). Formation of the Co–S bond, completing the ring closure, is then accomplished by removing the coordinated chlorido by addition of AgClO₄ in sulfolane. Complexes were characterized by ¹H and ¹³C NMR spectroscopy, UV-Vis spectroscopy and elemental analysis. In addition, the solid-state structure (X-ray) of the monohydrate of 2d confirms the coordination mode of the ligand. Preliminary kinetic investigations in basic solution show that the Co–S bond is broken resulting in the formation of [(en)₂Co(OH)(NH₂CH₂CH₂SC₆H₄X)]²⁺. At 15.0°C, a Hammett Plot is linear (r² = 0.981) with ρ = 2.24 ± 0.13.