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

Abstract

Alkylation of [Cp*Ru III(tpdt)] (2) (Cp* = η 5-C 5Me 5, tpdt = η 3-S (CH 2CH 2S -) 2) with MeI orMe 3OBF 4 resulted in the formation of a trans μ-η 1-η 1-S 2 coupled species, [{Cp*Ru II} 2{μ-η 6-(S(CH 2) 2S(CH 2) 2SMe) 2}] 2+ (3) as the predominant product. With MeI the reaction also gave a small amount of [Cp*Ru II{η 3-S(CH 2CH 2SMe) 2}]I, 4(I), but in the presence of acrylonitrile (AN), the products were 4(I) and [Cp*Ru II{η 3-S((CH 2) 2S) 2(CH 2CHCN)}] 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 I 2 led to the isolation of [{Cp*Ru II} 2{μ-η 6- (S(CH 2CH 2S) 2) 2}](I 3) 2,6(I 3) 2, containing a cyclic Ru II(μ-S 2) 2Ru 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{μ-η 5-MeS(CH 2) 2-S(CH 2) 2SS(CH 2) 2S(CH 2) 2S}] + (7) from the interaction of 3 and 2, or of a mixture of 4(I) and 5(I) in the presence of MeI and AN, and of [Cp*Ru II{η 3-MeS(CH 2) 2S(CH 2) 2SSnBu 3}] + (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-{η 3- S(CH 2) 2S(CH 2) 2SMe}] (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. © 2005 American Chemical Society.