CONVERSION OF [MOS4]2- TO [MO2S2(MU-S)2(S2)2]2- BY ORGANIC DISULFIDES - THE MECHANISM OF AN INDUCED REDOX REACTION

The kinetics of the reaction of tetrathiomolybdate, [MoS4]2−, with organic disulfides, RSSR, to produce the Mo(V) dimer [Mo2S2(μ-S)2(S2)2]2− have been investigated. The reaction involves an internal redox process and occurs in two stages. The overall rate of reaction is dependent on the electron-withdrawing properties of the disulfide such that diphenyl disulfide < bis(p-chlorophenyl) disulfide < bis(p-carboxyphenyl) disulfide. The first stage involves rapid equilibrium formation of an EPR-inactive, green intermediate. The reaction of [MoS4]2− with diphenyl disulfide or bis(p-chlorophenyl) disulfide is first order in tetrathiomolybdate and first order in organic disulfide. However, the reaction of [MoS4]2− with bis(p-carboxyphenyl) disulfide is more complex. Analysis of the molybdenum X-ray absorption spectrum of the green intermediate indicates the likelihood of a mononuclear species with two to three short Mo-S interactions at 2.16 Å and three to four longer Mo-S interactions at 2.41 Å. The rate-determining step of the second stage of the reaction involves first-order rearrangement or dissociation of the green intermediate. This is followed by rapid reaction of the resultant complex with another molybdenum species to produce [Mo2S2(μ-S)2(S2)2]2−. Mechanisms are proposed that are consistent with these findings and that provide potential insight into the use of oxidants to prepare new lower valent transition-metal sulfur-containing complexes from tetrathiometalate starting materials. © 1990, American Chemical Society. All rights reserved.