$Os_5C(CO)_{11}$($\mu_3$-$\eta^2$,$\eta^2$,$\eta^2$-$C_{60}$)$PPh_3$ (1) and $Os_5C(CO)_{12}$(\mu-$\eta^2$,$\eta^2$-$C_{60}$)$PPh_3$ (2) have been prepared by the reaction of $Os_5C(CO)_{12}PPh_3(NCMe)_2$ with $C_{60}$ in refluxing chlorobenzene. The molecular structure of 2 reveals the first example of \mu-$\eta^2$,$\eta^2$-$C_{60}$ bonding mode of $C_{60}$-metal cluster derivative. Uncoordinated double bond in the $C_6$ ring is disposed away from the $Os_3$ triangle. Furthermore, it was demonstrated that \mu-$\eta^2$,$\eta^2$-$C_{60}$ and $\mu_3$-$\eta^2$,$\eta^2$,$\eta^2$-$C_{60}$ ligands of 1 and 2 are reversibly interconvertible.
Reaction of 1 with benzyl isocyanide at room temperature produces an addition product $Os_5C(CO)_{11}(CNCH_2C_6H_5)$ $(\mu_3-\eta^2,\eta^2,\eta^2-C_{60})$ $PPh_3$ (3). One $Os_{apical}-Os_{basal}$ bond in square pyramidal $Os_5C$ framework of 1 is cleaved by the addition of 2e- donor benzyl isocyanide ligand. Heating a chlorobenzene solution of the kinetic isomer 3 at 100℃ gave the thermodynamic product $Os_5C(CO)_{11}(CNCH_2C_6H_5)$ (\mu-$\eta^{2}$,$\eta^2$-$C_{60}$)$PPh_3$ (4). In contrast to 2, however, the $C_6$ ring of 4 positions centrally over the $Os_3$ triangle as observed in 1.
Substitution of a carbonyl ligand of 4 with MeCN and subsequent thermolysis compound gives $Os_5C(CO)_{10}(CNCH_2}C_6H_5)(C_{60})PPh_3$ (5), which is assumed to have the $\mu_3$-$\eta^2$,$\eta^2$,$\eta^2$-C$_{60}$ bonding mode and the ligand disposition similar to that of 4. Compound 5 is also produced by substitution of a carbonyl ligand of 4 with benzyl isocyanide. Compounds 4 and 5 are also reversibly interconvertible.
