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 of 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.