Fluxional processes and structural characterization of mu(3)-eta(2),eta(2),eta(2)-C-60 triosmium cluster complexes, Os-3(CO)(9-n)(PMe3)(n)(mu(3)-eta(2),eta(2),eta(2)-C-60) (n=1, 2, 3)

The title complex, Os-3(CO)(6)(PMe3)(3)(mu(3)-eta(2),eta(2),eta(2)-C-60) (3 ), has been prepared by decarbonylation of Os-3(CO)(9)(mu(3)-eta(2),eta(2), eta(2)-C-60) with three equivalents of Me3NO in the presence of excess PMe3 ligand. The solid-state structures of Os-3(CO)(7)(PMe3)(2)(mu(3)-eta(2),et a(2),eta(2)-C-60) (2) and 3 have been determined by single-crystal X-ray di ffraction studies. Compound 2 has two inequivalent equatorial phosphine lig ands on adjacent osmium atoms and compound 3, with a distorted C-3 symmetry , has one equivalent equatorial phosphine ligand on each osmium center. The fluxional processes of Os-3(CO)(8)(PMe3)(mu(3)-eta(2),eta(2),eta(2)-C-60) (1), 2 and 3 have been examined by variable-temperature C-13- and P-31-NMR studies. Only one isomer exists in solution and a restricted ligand rotatio n on each phosphine-substituted osmium center appears to occur for all thre e compounds, 1-3. Activation barriers for the carbonyl exchange process inc rease with increasing phosphine substitution, presumably, due to the steric effect of the phosphine ligands. (C) 2000 Elsevier Science S.A. All rights reserved.