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

Reactions of the activated tetraosmium hydrido cluster 1 with a series of bidentate phosphine ligands PPh2(CH2)nPPh2(n = 1, dppm; n = 3, dppp), PPh2(CH)2PPh2, (dppee) and (PPh2C5H4)2Fe, (dppf) gave several novel tetraosmium clusters [Os4( μ-H)4(CO)10( μ-dppm)] 2, [Os4( μ-H)4(CO)10( μ-dppee)] 3a, [Os4( μ-H)4(CO)10( η2-dppee)] 3b [Os4( μ-H)4(CO)10( μ-dppp)] 4 and [Os4( μ-H)4(CO)10( μ-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. (metric presented).