Ruthenium-, osmium- and cobalt-ion mediated selective activation of a C-Cl bond. Direct and spontaneous aromatic thiolation reaction via C-S bond cleavage

Abstract

The reactions of KSC(S)OEt and NaSC(S)NEt₂ with the complexes [RuL₂Cl₂] 1a, [OsL₂Br₂] 1b and [CoL₃][ClO₄]₂.H₂O 1c [L = 2-(o-chlorophenylazo)pyridine, 2-(o-ClC₆H₄N=N)C₅H₄ N] in boiling dimethylformamide solvent resulted in [Ru^IIL'₂] 3a, [Os^IIL'₂] 3b and [Co^IIIL'₂][ClO₄] 3c respectively [L' = 2-(o-SC₆H₄N N)C₅H₄N]. In complexes 3 the o-carbon-chlorine bond of the pendant phenyl ring of the parent ligand L has been selectively and directly thiolated via carbon-sulfur bond cleavage of the dithiocarbonate and dithiocarbamate molecules. Two such newly formed tridentate thiolated ligands (L') are bound to the metal ions in a meridional fashion. The reactions are spontaneous in the case of dithiocarbonate as thiolating agent, but relatively slow and incomplete for dithiocarbamate. During the thiolation reaction the metal ion in the cobalt complex is oxidised from the starting Co^II in 1c to Co^III in the final product 3c. The reactions are highly sensitive to the nature of the solvent used, taking place only in those having high boiling points and polarities. The meridional configuration (cis-trans-cis with respect to sulfur, azo and pyridine nitrogens respectively) of 3 has been established by ¹H and ¹³C NMR spectroscopy. The complexes exhibit two MLCT transitions in the visible region and intraligand (π-π, n-π) transitions in the UV region. In acetonitrile solution they display reversible M^III-M^II reduction potentials at 0.43 V for Ru (3a), 0.36 V for Os (3b) and -0.14 V for Co (3c) versus the saturated calomel electrode.