New synthetic routes to [M3(CO)9(µ3-η2:η2:η2-C6H6)](M = Ru or Os)

Abstract

A new, more convenient route to the benzene cluster [Ru₃(CO)₉(µ₃-η²:η²:η²-C₆H₆)] directly from [Ru₃(CO)₁₂] has been established. Triruthenium dodecacarbonyl, [Ru₃(CO)₁₂], undergoes reaction with Me₃NO–CH₂Cl₂ in the presence of cyclohexa-1,3-diene to give the clusters [Ru₃H(CO)₉(C₆H₇)] and [Ru₃(CO)₉(µ₃-η²:η²:η²-C₆H₆)] in moderate yield. Triosmium dodecacarbonyl does not react similarly, but from the reaction of [Os₃(CO)₁₀(MeCN)₂] with cyclohexa-1,3-diene a key intermediate compound [Os₃(CO)₁₀(η⁴-C₆H₈)] has been isolated and the solid-state structure of its acetonitrile solvate established by single crystal X-ray diffraction analysis at 150 K. The structure is monoclinic, space group P2₁/n, with a= 8.932(8), b= 17.387(13), c= 14.833(15)Å, β= 105.69(6)° and Z= 4. The three osmium atoms form a regular triangle with a mean Os–Os distance of 2.877(12)Å. Two osmium atoms, Os(1) and Os(2), are co-ordinated to four carbonyl ligands and one, Os(3), co-ordinates to two carbonyl ligands. All carbonyl ligands are terminal and approximately linear. The cyclohexadiene ligand is η⁴ co-ordinated to Os(3)via the 1,3-diene moiety, donating four electrons in total. On thermolysis, this compound is converted to [Os₃H(CO)₉(C₆H₇)] and then eventually to [Os₃(CO)₉(µ₃-η²:η²:η²-C₆H₆)] by established means.