Fluxional processes and structural characterization of μ3-η2,η2,η2-C60 triosmium cluster complexes, Os3(CO)9−n(PMe3)n(μ3-η2,η2,η2-C60) (n=1, 2, 3)

The title complex, Os3(CO)6(PMe3)3(μ3-η2,η2,η2-C60) (3), has been prepared by decarbonylation of Os3(CO)9(μ3-η2,η2,η2-C60) with three equivalents of Me3NO in the presence of excess PMe3 ligand. The solid-state structures of Os3(CO)7(PMe3)2(μ3-η2,η2,η2-C60) (2) and 3 have been determined by single-crystal X-ray diffraction studies. Compound 2 has two inequivalent equatorial phosphine ligands on adjacent osmium atoms and compound 3, with a distorted C3 symmetry, has one equivalent equatorial phosphine ligand on each osmium center. The fluxional processes of Os3(CO)8(PMe3)(μ3-η2,η2,η2-C60) (1), 2, and 3 have been examined by variable-temperature 13C- and 31P-NMR studies. Only one isomer exists in solution and a restricted ligand rotation on each phosphine-substituted osmium center appears to occur for all three compounds, 1–3. Activation barriers for the carbonyl exchange process increase with increasing phosphine substitution, presumably, due to the steric effect of the phosphine ligands.