Insertion of Acetylene and Nitriles into a Ru−C Bond of a Dicationic Triruthenium Complex Having a μ₃-η³-C₃ Ring: Formation of Six-Membered Ruthenacycles on a Triruthenium Core

A triruthenium complex having a μ3-ruthenacyclohexadienyl moiety, [(Cp*Ru)2{Cp*Ru(μ3-η2:η2-CHCMeCH−CHCH−)}(μ3-CH)]+ (9), was synthesized by the reaction of an equilibrating mixture of dicationic complexes having a μ3-η3-C3 ring, [(Cp*Ru)3(μ3-η3-C3H2Me)(μ3-CH)(μ-H)]2+ (2a and 2b), with acetylene. The protonation of 9 resulting in the formation of a dicationic μ3-ruthenacyclohexadienyl complex, [(Cp*Ru)2{Cp*Ru(μ3-η2:η2-CH−CMeCHCHCH−)}(μ3-CH)(μ-H)]2+ (10), strongly indicates that the hydrido ligand of 2 was removed as a proton after the six-membered metallacycle was formed by the insertion of an acetylene molecule into a Ru−C bond. The thermolysis of 9 resulted in an isomerization of the metallacycle moiety via the formation of a μ3-cyclopentadienyl intermediate and quantitatively afforded a μ3-4-methylruthenacyclohexadienyl complex, [(Cp*Ru)2{Cp*Ru(μ3-η3:η2-CHCHCMe−CHCH−)}(μ3-CH)]+ (13). Nitriles also inserted into a Ru−C bond of 2 and afforded a series of dicationic 2-azaruthenacyclohexadienyl complexes, [(Cp*Ru)2{Cp*Ru (μ3-η2:η3-NHCR−CHCMeCH−)}(μ3-CH)]2+ (18a: R = Me, 18b: R = Et, 18c: R = Ph).