S-alkylation-induced redox reactions leading to reversible sulfur-sulfur coupling in a pentamethylcyclopentadienyl ruthenium(III) thiolate-thioether system

Alkylation of [Cp*Ru-III(tpdt)] (2) (Cp* = eta(5)-(CMe5)-Me-5, tpdt = eta(3)-S(CH2CH2S-)(2)) with MeI or Me3OBF4 resulted in the formation of a trans mu-eta(1)-eta(1)-S-2 coupled species, [{Cp*Ru-II}(2){mu-eta(6)(S(CH2)(2)S(CH2)(2)SMe)(2)}](2+) (3) as the predominant product. With MeI the reaction also gave a small amount of [Cp*Ru-II{eta(3)-S(CH2CH2SMe)(2)}]I, 4(I), but in the presence of acrylonitrile (AN), the products were 4(I) and [Cp*Ru-II{eta(3)-S((CH2)(2)S)(2)(CH2CHCN)}]I, 5(I), of which the latter was the sole product from the reaction of 2 with AN in the presence of iodine. 2 was electrochemically easily oxidized in a one-electron process; its chemical oxidation with 12 led to the isolation of [{Cp*Ru-II}(2){mu-eta(6)-(S(CH2CH2S)(2))(2)}](I-3)(2), 6(I-3)(2), containing a cyclic Ru-II(mu-S-2)(2)Ru-II core. A combination of electrochemical, EPR, UV-vis, and NMR experiments indicated that the solution phase chemistry of 3 is governed by its facile reversible dissociation into the mononuclear cation radical (3A). Based on this phenomenon were rationalized the pathways leading to the formation of the dinuclear species [{Cp*Ru-II}2{mu-eta(5)-MeS(CH2)(2)S(CH2)(2)SS(CH2)(2)S(CH2)(2)S}](+) (7) from the interaction of 3 and 2, or of a mixture of 4(1) and 5(I) in the presence of MeI and AN, and of [Cp*Ru-II{eta(3)-MeS(CH2)(2)S(CH2)(2)SSnBu3}](+) (9) from reaction with tri(n-butyl)tin hydride. Electrochemical measurements indicated that the sodium naphthalide reduction of 3 to generate the mono-S-methylated derivative, [Cp*Ru-II{eta(3)-S(CH2)(2)S(CH2)(2)SMe}] (8), occurred through 3A. It is proposed that some of the transformations also involved internal electron transfers and nucleophilic displacements. The X-ray crystal structures of the complexes 3-9 are reported.