Conversion of tetrathioxomolybdate(2-) to bis(disulfido)di-.mu.-thioxodithioxodimolybdate(2-) by organic disulfides: the mechanism of an induced redox reaction

The kinetics of the reaction of tetrathiomolybdate, (MoS{sub 4}){sup 2{minus}}, with organic disulfides, RSSR, to produce the Mo(V) dimer (Mo{sub 2}S{sub 2}({mu}-S){sub 2}(S{sub 2}){sub 2}){sup 2{minus}} 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 (MoS{sub 4}){sup 2{minus}} with diphenyl disulfide or bis(p-chlorophenyl) disulfide is first order in tetrathiomolybdate and first order in organic disulfide. However, the reaction of (MoS{sub 4}){sup 2{minus}} with bis(p-carboxyphenyl) dsulfide 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 {angstrom} and three to four longer Mo-S interactions at 2.41 {angstrom}. 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 (Mo{sub 2}S{sub 2}({mu}-S){sub 2}(S{sub 2}){sub 2}){sup 2{minus}}. Mechanisms are proposed that are consistent withmore » 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. 22 refs., 9 figs., 2 tabs.« less