Chiral Arene Ruthenium Complexes : Synthesis and Molecular Structure of the Enantiopure Cluster Cation (<i>S</i>)-[H₃Ru₃{C₆H₅[CH(CH₃)CH₂OH]}(C₆Me₆)₂(O)]⁺

The reaction of enantiopure (<i>R</i>)-(2-cyclohexa-1,4-dienyl)propan-1-ol with ruthenium chloride hydrate yields, without racemisation of the chiral ligand, the chloro-bridged dinuclear complex (<i>S,S</i>)-[RuCl₂{C₆H₅[CH(CH₃)CH₂OH]}]₂ (<b>1</b>). The dimer <b>1</b> reacts with triphenylphosphane to give the mononuclear complex (<i>S</i>)-[RuCl₂{C₆H₅[CH(CH₃)CH₂OH]}(PPh₃)] (<b>2</b>). A single-crystal X-ray structure analysis of <b>2</b> reveals the absolute configuration of the asymmetric carbon atom to have remained, the change from (<i>R</i>) to (<i>S</i>) being due to the priority change caused by coordination; in the solid state, onedimensional hydrogen-bonded chains are formed between the hydroxy functions and chloro ligands of neighbouring molecules. The mononuclear cationic complex (<i>S</i>)-[Ru{C₆H₅[CH(CH₃)CH₂OH]}(H₂O)₃]²⁺, formed in situ from <b>1</b> in aqueous solution, reacts with the dinuclear complex [H₃Ru₂(C₆Me₆)₂]⁺ to give a chiral trinuclear arene-ruthenium cluster, the cation (<i>S</i>)-[H₃Ru₃{C₆H₅[CH(CH₃)CH₂OH]} (C₆Me₆)₂(O)]⁺ (<b>3</b>). This enantiopure cation has been isolated and characterised as its tetrafluoroborate salt. The single-crystal X-ray structure analysis of (<i>S</i>)^-[<b>3</b>][BF₄] shows a strong intramolecular hydrogen bond between the μ₃-oxo cap and the hydroxy function, which also persists in acetone solvent, as demonstrated by NMR spectroscopy.