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)CH2CH2 N H2)](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(N H2CH2CH2SC6H4X)]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)(N H2CH2CH2SC6H4X)]2+. At 15.0°C, a Hammett Plot is linear (r 2 = 0.981) with ρ = 2.24 ± 0.13. We have prepared a series of cobalt(III) complexes coordinated in a κ 2N,S manner by substituted phenylthioether ligands. The preparation is a two-step process starting with trans- dichloridobis(ethylenediamine)cobalt(III) chloride. NMR spectroscopy was used to characterize the complexes. In addition, the presence of an intense ligand-to-metal charge-transfer transition in the UV region confirms that a sulfur atom is bonded to the cobalt(III) center. In basic solution, the Co–S bond is broken, presumably by the classical SN1CB mechanism. The rate of the cleavage reaction increases as the electron-withdrawing ability of the phenyl substituent increases. (Image credit: Lee Roecker.) [ABSTRACT FROM AUTHOR]