The first structurally characterized $metal-C_{60}$ \sigma-complex, $Os_3(CO)_8(RNC)_2(\mu_3-\eta^1\eta^2\eta^1-C_{60})$ ($R = CH_2C_6H_5$) (2), has shown very interesting reactivities with various 2-electron donor ligands. The hydrogen-substituted compound $Os_3(CO)_7(RNC)_2(\mu-H)_2(\mu_3-\eta^1\eta^2\eta^1-C_{60})$ (3) has been prepared by decarbonylation of 2 with $Me_3NO$ followed by reaction under $H_2$ pressure in 65% yield. An axial CO ligand on Os2 is abstracted and the Os1-Os2 and Os2-Os3 bonds are bridged by two hydride ligands. A new \sigma-type $Os_3(CO)_7(RNC)_2(PPh_3)(\mu_3-\eta^1\eta^1\eta^2-C_{60})$ (4) has been generated from 2 upon substitution of CO with $PPh_3$ in 70% yield, and 4 is reconverted to 2 quantitatively under CO pressure. A similar reaction of 2 with $PMe_3$ produces $Os_3(CO)_7(RNC)_2(PMe_3)(\mu_3-\eta^1\eta^2\eta^1-C_{60})$ (5) in 49% yield. The bulky $PPh_3$ ligand substitutes an equatorial carbonyl ligand of the Os1 atom, and the carbon atoms of the $C_60$ ligand bonded to the metal centers have undergone orbital rearrangement from $\mu_3-\eta^1\eta^2\eta^1-C_{60}$ in 2 to $\mu_3-\eta^1\eta^1\eta^2-C_{60}$ in 4 upon coordination of $PPh_3$. However, the smaller $PMe_3$ ligand merely substitutes an axial CO of Os2 atom without changing the $C_{60}$ bonding mode.
