C–H Activation of Cp* Ligand Coordinated to Ruthenium Center: Synthesis and Reactivity of a Thiolate-Bridged Diruthenium Complex Featuring Fulvene-like Cp* Ligand

In the presence of weak base Et3N, the interaction of [Cp*Ru­(μ-η2:​η4-bdt)­RuCp*] (1, Cp* = η5-C5Me5; bdt = benzene-1,2-dithio­late) with 2 equiv of Fc·PF6 resulted in facile C–H activation of one methyl group in coordinated Cp* to give a diruthenium complex with a fulvene-like Cp* ligand, [(η5:​η1-C5Me4­CH2)­Ru­(μ-η2:​η4-bdt)­RuCp*]­[PF6] (2­[PF6]), in which the fulvene-like Cp* moiety is best described as an η5:η1-tetra­methyl­fulvene ligand based on 1H NMR and 13C NMR spectroscopic data. When complex 2­[PF6] was subjected to the electrophilic attack of HCl, an intact Cp* group was regenerated from the fulvene-like Cp* ligand along with the formation of the chloride bridged complex [Cp*Ru­(μ-η2:​η2-bdt)­(μ-Cl)­RuCp*]­[PF6] (3­[PF6]). While complex 2­[PF6] reacted with iodine, functionalization of a Cp* methyl group was realized to give a Cp* ring iodine-substituted complex [(η5-C5Me4­CH2I)­Ru­(t-I)­(μ-η2:​η4-bdt)­RuCp*]­[PF6] (4­[PF6]) in excellent yield. Importantly, reaction of 2­[PF6] with elemental sulfur led to the S–S bond fission of S8 following insertion of a disulfide fragment into the Ru–methylene bond to produce [(η5:​η1-C5Me4­CH2S2)­Ru­(μ-η2:​η4-bdt)­RuCp*]­[PF6] (5­[PF6]), which provides strong chemical evidence for structural description of the fulvene-like Cp* ligand in 2­[PF6]. Most strikingly, treatment of 2­[PF6] with CO and tBuNC resulted in the coordination mode switch of the fulvene-like Cp* ligand from η5:η1 on one ruthenium center to μ-η5:η1 between two ruthenium centers to afford [Ru­(μ-η5:​η1-C5Me4­CH2)­(t-CO)­(μ-η2:​η2-bdt)­RuCp*]­[PF6] (6­[PF6]) and [Ru­(μ-η5:​η1-C5Me4­CH2)­(t-tBuNC)­(μ-η2:​η2-bdt)­RuCp*]­[PF6] (7­[PF6]), respectively.