Dimethylfumarate triosmium clusters, $Os_3(CO)_{10}$(dmf)L [L = CO (1), NCMe (2), $PPh_3$ (3)] have been prepared as model compounds for $C_{60}$ triosmium derivatives, and studied by variable temperature NMR spectroscopy. Fluxionality of 1 reveals a typical rotation of the fumarate ligand. Six isomers are present for 2 which are in a rapid equilibrium. Two molecular structures of the six isomers have been solved by single crystal X-ray diffraction studies. The dmf and MeCN ligands are coordinated to the metal center, and the dmf ligand occupies an equatorial site, whereas the MeCN ligand either an equatorial or axial site. Three isomers exist for 3, and the phosphine and the dmf ligands occupy equatorial sites bonded to the different metal centers. The structures of the $C_{60}$ triosmium derivatives are considered to be similar to those of the dmf triosmium derivatives.
Bisphosphine triosmium complexes of $C_{60}$, $Os_3(CO)_9(PMe_3)_2(\eta^2-C_{60})$ [R = Me (4), Et (5)] have been synthesized. These are soluble enough to obtain $^{13}C$ NMR spectrum. VT NMR studies for 4 and 5 reveal a restricted in-plane cyclic motion of equatorial carbonyl and $C_{60}$ ligands via a triply bridged intermediate. The bis adduct $\{Os_3(CO)_9(PMe_3)_2\}_2(\eta^2-C_{60})$ has also been prepared and characterized.
