Synthesis, characterization and crystal structures of a series of tetraosmium carbonyl clusters containing bidentate phosphine ligands

Reactions of the activated tetraosmium hydride cluster 1 with a series of bidentate phosphine ligands PPh2(CH2)(n)PPh2 (n = 1, dppm; n = 3, dppp), PPh2(CH)(2)PPh2, (dppee) and (PPh2C5H4)(2)Fe, (dppf) gave several novel tetraosmium dusters [Os-4(mu-H)(4)(CO)(10)(mu-dppm)] 2, [Os-4(mu-H)(4)(CO)(10)(mu-dppee)] 3a, [Os-4(mu-H)(4)(CO)(10) (eta(2)-dppee)] 3b [Os-4(mu-H)(4)(CO)(10)(mu-dppp)] 4 and [Os-4(mu-H)(4)(CO)(10)(mu-dppf)] 5 in moderate to good yields. All the complexes were fully characterized by both spectroscopic and crystallographic methods. Each of the structures of 2, 3a, 4 and 5 contains a tetraosmium metal core with a bridging diphosphine ligand. Compound 3a and 3b are geometrical isomers and they differ in the bonding modes of the diphosphine ligand dppee exhibits. A chelating dppee ligand bonded to a single osmium atom is observed in complex 3b. (C) 1997 Elsevier Science S.A.