Synthesis, structural characterisation and electrochemistry of ruthenium carbonyl clusters derived from ferrocenyl(formyl)acetylene

Two new ferrocenyl ruthenium carbonyl clusters, [Ru4(CO)12(μ4-η1,η1,η2,η2-{(C5H5)Fe(C5H4CCCHO)})] 1 (20%) and [Ru3(CO)8(μ3-η1,η2,η4-{(C5H5)Fe(C5H4CCCHO)}2)] 2 (10%), have been synthesised by reaction of (C5H5)Fe(C5H4C≡CCHO) with triruthenium dodecacarbonyl in cyclohexane under refluxing conditions. Thermolysis of 1 in refluxing toluene led to the formation of [Ru5(CO)13(μ-H)(μ5-C)(μ2-η1,η1-{(C5H5)Fe(C5H4C)})] 3 (10%). Reaction of [Ru3(CO)10(NCMe)2] with ferrocenyl(formyl)acetylene afforded the triruthenium cluster [Ru3(CO)9(μ-CO)(μ3-η1,η1,η2-{(C5H5)Fe(C5H4CCCHO)})] 4 (30%). All these new compounds have been characterised fully by conventional spectroscopic and X-ray diffraction methods. The structure of 1 consists of a ferrocenyl carboxaldehyde bound to the Ru4butterfly skeleton via a typical μ4-η1, η1, η2, η2coordination mode. Cluster 2 is based upon an Ru3closed triangle bearing a metallacyclopentadiene ring that arises from the coupling of two ligand molecules with the formation of O→Ru dative bond. Thermolysis of 1 afforded a rare pentanuclear ruthenium cluster containing a carboferrocenyl fragment with a μ2-η1,η1mode. Both fluxional and electrochemical behaviour of cluster 3 have been studied. Compound 4 consists of an alkyne ligand bound to the triruthenium cluster unit via a typical μ3-(η2-) coordination mode.