S-Alkylation-Induced Redox Reactions Leading to Reversible Sulfur−Sulfur Coupling in a Pentamethylcyclopentadienyl Ruthenium(III) Thiolate-Thioether System

Abstract

Alkylation of [Cp*RuIII(tpdt)] (2) (Cp* = η5-C5Me5, tpdt = η3-S(CH2CH2S-)2) with MeI or Me3OBF4 resulted in the formation of a trans μ-η1-η1-S2 coupled species, [{Cp*RuII}2{μ-η6-(S(CH2)2S(CH2)2SMe)2}]2+ (3) as the predominant product. With MeI the reaction also gave a small amount of [Cp*RuII{η3-S(CH2CH2SMe)2}]I, 4(I), but in the presence of acrylonitrile (AN), the products were 4(I) and [Cp*RuII{η3-S((CH2)2S)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 I2 led to the isolation of [{Cp*RuII}2{μ-η6-(S(CH2CH2S)2)2}](I3)2, 6(I3)2, containing a cyclic RuII(μ-S2)2RuII 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*RuII}2{μ-η5-MeS(CH2)2S(CH2)2SS(CH2)2S(CH2)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*RuII{η3-MeS(CH2)2S(CH2)2SSnBu3}]+ (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*RuII{η3-S(CH2)2S(CH2)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.

Singlet Diradical Character of an Oxidized Ruthenium Trithiolate: Electronic Structure and Reactivity

“…[19] The reaction is presumed to involve the enol tautomer; S-based reactivity Zuschriften of oxidized Ru thiolates with alkenes was reported by Goh, Webster, and co-workers. [22] As such, {Ru-(SR) 3 } 11 was oxidized in the presence of styrene by bulk electrolysis. The voltammogram after oxidation (1 e À ; Figure S2 in the Supporting Information) reveals a product with a single redox event at + 800 mV, assigned as Ru III …”

Sulfur-alkylation-initiated Cp∗Ru thiyl radicals

“…This dissociation is supported by evidence from a combination of electrochemical, EPR, UV-Vis and NMR experiments. Various aspects of the reactivity features of 11A have been reported previously [10] and are summarized in Scheme 6. Thus, it reacted as a radical initiator with n Bu 3 SnH, abstracting the radical n Bu 3 Sn Å to form the RuSSnBu 3 -containing complex 6 (route (a)).…”

“…It was established that in solution, the closely related compound 2A undergoes a monomerization reaction to form 2 mols of 11A (Scheme 5), so that cyclic voltammograms performed on solid samples of 2A dissolved in CH 2 Cl 2 , show only the presence of 11A [10]. The dashed lines in Fig.…”

“…An alternative mechanism to account for the electrochemistry of 2B is available based on the results of a previous study on compounds 1A, 2A and 7 [10]. It was established that in solution, the closely related compound 2A undergoes a monomerization reaction to form 2 mols of 11A (Scheme 5), so that cyclic voltammograms performed on solid samples of 2A dissolved in CH 2 Cl 2 , show only the presence of 11A [10].…”

“…Recently, Grapperhaus obtained spectroscopic, electrochemical and product evidence for Ru-coordinated thiyl radical intermediates in the oxidation reactions of [tris(phosphino)thiaphenolato)Ru(II)] monoanion [2d,9]. This paper reviews our previous results on Ru-thiyl radical formation, initiated by S-alkylation of the dithiolato-thioether ligand, S(CH 2 CH 2 S À ) 2 , coordinated to Cp * Ru(III) [10], and compares the results with those obtained for the analogous HN(CH 2 CH 2 S À ) 2 system.…”