Comparative Study for the Cobalt(II)- and Iron(II)-Mediated Desulfurization of Disulfides Demonstrating That the C-S Bond Cleavage Step Precedes the S-S Bond Cleavage Step.

Abstract

A unique Co(II)- and Fe(II)-mediated complete desulfurization of disulfides of the type RS-SR and RC(O)S-SC(O)R to yield the corresponding alcohols (ROH) and carboxylic acids (RCOOH), respectively, along with the formation of a dicobalt(II)/diiron(II)-hydrosulfide complex, [M2(PhBIMP)(μ2-SH)(DMF)]2+ (M = Co, Fe), has been demonstrated. This new desulfurization reaction involves cleavage of both C-S and S-S bonds, where the cleavage of the S-S bond (presumably two-electron reduction of the S-S bond) may generate two-electron-oxidized dicobalt(III)/diiron(III) species, [MIII2(PhBIMP)(H2O)2(DMF)2]5+ (M = Co, Fe), in solution. While the generation of such a solvent- and/or H2O-coordinated dicobalt(III) species in the reaction solution could not be established beyond a doubt, formation of the diiron(III) species [FeIII2(PhBIMP)(H2O)2(DMF)2]5+ according to the proposed reaction mechanism has been confirmed by a combination of mass spectrometry and UV-vis spectroscopy in comparison with an authentic sample, synthesized directly by an independent procedure using Fe(ClO4)3·xH2O. Interestingly, a comparative study using different types of disulfides and the molecular structure determination of a key reaction intermediate, [Fe2(PhBIMP)(MeCOSS)]2+, generated via the cleavage of only one C-S bond of MeC(O)S-SC(O)Me, demonstrates that the C-S bond cleavage step precedes the S-S bond cleavage step during the Fe(II)-mediated desulfurization of disulfides.