COBALT-MEDIATED DIRECT AND SELECTIVE AROMATIC THIOLATION IN THE COMPLEX [CO-III(O-SC6H4N=NC5H4N)(2)]CLO4 - SYNTHESIS, SPECTROSCOPIC CHARACTERIZATION AND ELECTRON-TRANSFER PROPERTIES

The reaction of K[SC(S)OR] (R = Me, Et, Pr-n, Pr-i, Bu-n, Bu-i or CH2P h) with the complex [(CoL3)-L-II][ClO4](2) . H2O 1 [L = phenyl(2-pyrid yl)diazene, C6H5N=NC5H4N] in boiling dimethylformamide resulted in [(C oL)-L-III'(2)]ClO4 2 (L' = o-SC6H4N=NC5H4N). In complex 2 the o-carbon -hydrogen bond of the pendant phenyl ring of both the parent ligands L has been selectively and directly thiolated via carbon-sulfur bond cl eavage of the dithiocarbonate. During the thiolation the metal ion is oxidised from the starting Co-II in 1 to Co-III in the final product 2 . The reaction is highly sensitive to the nature of the solvent used, taking place only in those having high boiling points and relative per mittivities. Its rate is dependent,n the: nature of the R group presen t in the thiolating agent, following the order Me approximate to Et > Pr-n > Bu-n > Pr-i > Bu-i much greater than benzyl. A meridional confi guration (cis-trans-cis with respect to the sulfur, azo and pyridine n itrogens respectively) has been established by H-1 and C-13 NMR spectr oscopy. The complex exhibits reversible Co-III reversible arrow Co-II reduction at -0.135 V and four ligand-based azo (N=N) reductions at -0 .51 (one electron) and at -1.175 V (simultaneous three-electron reduct ion) respectively versus saturated calomel electrode. The oxidation of the co-ordinated thiol group occurs at 0.90 V.