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.