Synthesis and Structure of Cationic Triruthenium Complexes Containing an Oxametallacycle: Reversible Carbon−Oxygen Bond Formation and Scission on an Electron-Deficient Triruthenium Plane

A trimetallic μ-hydroxo complex, [(Cp*Ru)3(μ-OH)(μ3-CH)(μ3-η1:η3:η1-CHCMeCH)]2+ (6), was obtained by the reaction of an equilibrating mixture of the dicationic tris(μ-carbene) complexes [(Cp*Ru)3(μ3-CH)(μ-H)(μ3-η3-C3MeH2)]2+ (4a and 4b) with water. Treatment of the μ-hydroxo complex with a base affords a novel μ3-2-oxa-4-methylruthenacyclopentenyl complex, [(Cp*Ru)3(μ3-CH){μ3-OC(H)C(Me)CH−}]2+ (8), as a result of reductive C−O bond coupling. Complex 8 underwent unprecedented isomerization to a μ3-2-oxa-3-methylruthenacyclopentenyl complex, [(Cp*Ru)3(μ3-CH){μ3-O-C(Me)C(H)CH−}]2+ (8), containing a methyl group at the 3-position of the oxaruthenacycle moiety upon heating, which involves sequential C−O bond cleavage and re-formation via the formation of a transient μ-oxo complex having a μ3-η3-C3 ring on the triruthenium plane.