Reversible interconversion between μ,η²:η²- and μ₃,η²:η²:η²- C₆₀ on a carbido pentaosmium cluster framework

Decarbonylation of Os₅(CO)₁₄(PPh₃) by 2 equiv of Me₃NO/CH₃CN at room temperature followed by reaction with C₆₀ in refluxing chlorobenzene produces Os₅C(CO)₁₁(PPh₃)(μ₃, η²:η²:η²-C₆₀) (1) in 44% yield. Thermal treatment of 1 at 80°C under 1 atm of carbon monoxide affords Os₅C(CO)₁₂(PPh₃)(μ,η²: η²-C₆₀) (2) in good yield (72%). Upon thermolysis of 2 at 132°C, 2 is cleanly reconverted to 1 (73%) by loss of a carbonyl ligand. Reaction of 1 with benzyl isocyanide at room temperature gives the addition product Os₅C(CO)₁₁(CNCH₂C₆H₅) (PPh₃)- (μ₃,η²:η²:η²- C₆₀) (3) in 85% yield. Thermolysis of 3 at 100°C forms the isomeric Os₅C(CO)₁₁(CNCH₂C₆H₅) (PPh₃) (μ,η²:η²-C₆₀) (4) in 64% yield. Treatment of 4 with 1 equiv of Me₃NO/CH₃CN at room temperature followed by heating at 132°C in chlorobenzene gives Os₅C(CO)₁₀(CNCH₂C₆H₅) (PPh₃) (μ₃,η²:η²:η²- C₆₀) (5) in 71% yield. Compound 5 can be alternatively prepared from the reaction of 1 with excess Ph₃P=NCH₂Ph at room temperature in 59% yield. Heating a chlorobenzene solution of 5 at 55°C under 3 atm carbon monoxide produces 4 as the only major product (16%). Treatment of Ru₅C(CO)₁₁(PPh₃)(μ₃, η²:η²:η²-C₆₀) (1′) with benzyl isocyanide at room temperature forms Ru₅C(CO)₁₁(CNCH₂C₆H₅) (PPh₃) (μ₃,η²:η²:η²- C₆₀) (3′) in 90% yield. Reaction of 1′ with benzyl isocyanide at a slightly elevated temperature of 40°C affords Ru₅C(CO)₁₀(CNCH₂C₆H₅) (PPh₃) (μ₃,η²:η²:η²- C₆₀) (5′) in an almost quantitative yield of 96%. Compounds 1-5, 3′, and 5′, isolated as crystalline solids, have been characterized by microanalytical and spectroscopic methods. Molecular structures of 1-4 and 5′ have been elucidated by X-ray crystallographic studies.