Formation, preservation, and cleavage of the disulfide bond by vanadium

Reaction of the disulfide {HpicanS}(2) (HpicanS is the carboxamide based on picolinate (pic) and o-mercaptoaniline (anS); the {} brackets are used to denote disulfides) with [VOCl2(thf)(2)] leads to reductive scission of the disulfide bond and formation of the mixed-valence (V-IV/V-V) complex anion [(OV-picanS)(2)mu-O](-) (1), with the dianionic ligand coordinating through the pyridine-N atom, the deprotonated amide-N atom, and thiophenolate-S atom. Reductive cleavage of the S-S bond is also observed as [VCl2(tmeda)(2)] (tmeda = tetramethylethylenediamine) is treated with the disulfides {HsalanS}(2) or {HvananS}(2) (HsalanS and HvananS are the Schiff bases formed between o-mercaptoaniline and salicylaldehyde (Hsal) or vanillin (Hvan), respectively), yielding the V-III complexes [VCl(tmeda)-(salanS)] (2a), or [VCl(tmeda)-(vananS)] (2b). The disulfide bond remains intact in the aerial reaction between {HsalanS}(2) and [VCl3(thf)(3)] to yield the V-V complex [VOCl{salanS}(2)] (3), where (salanS)(2-) coordinates through the two phenolate and one of the imine functions. The S-S bond is also preserved as [VO(van)(2)] or [VO(nap)(2)] (Hnap = 2-hydroxynaphthalene-1-carbaldehyde) is treated with bis(2-aminophenyl)disulfide, {anS}(2), a reaction which is accompanied by condensation of the aldehyde and the diamine, and complexation of the resulting bis(Schiff bases) {HvananS}(2) or {HnapanS}(2) to form the complexes [VO{vananS}(2)] (4a) or [VO{napanS}(2)] (4b). In 4a and 4b, the phenolate and imine functions, and presumably also one of the disulfide-S atoms, coordinate to V-IV. 2-Mercaptophenyl-2'-pyridinecarboxamide (H(2)picanS) retains its identity in the presence of VIII; reaction between [VCl3(thf)(3)] and H(2)picanS yields [V{picanS}(2)](-) (5). The dithiophenolate 2,6-bis(mercaptophenylthio)dimethylpyridine (6a) is oxidized, mediated by VO2+, to the bis(disulfide) octathiadiaza-cyclo-hexaeicosane 6b. The relevance of these reactions for the speciation of vanadium under physiological conditions is addressed. [HNEt3]-1 (.) 0.5NEt(3), 3 (.) 3 CH2Cl2, {HsalanS}(2), [HNEt3]-5, and 6b (.) 4THF have been characterized by X-ray diffraction analysis.