The nature of the metal-silicon bond in [M(SiR3)H-3(PPh3)(3)] (M=Ru, Os) and the crystal structure of [Os{Si(N-pyrrolyl)(3)}H-3(PPh3)(3)]

The compounds [M(SiR3)H-3(PPh3)(3)] (1: M = Ru, R = 1 NC4H4 = pyr; 2a-c: M = Os, R = pyr, Et, Ph) are prepared through reaction of either [RuH2(PPh3)(4)] or [OsH4(PPh3)(3)] with the appropriate silane HSiR3, (3a-c: R = pyr, Et, Ph). The X-ray structure analysis of compound 2a and ab initio calculations on the model compounds [Os(SiR3)H-3(PH3)(3)] (4a-c: R = H, NH2, pyr) reveal a trigonal distortion along the Os-Si axis from an idealised tetrahedral geometry for the central OsSiP3, heavy-atom skeleton, The structure can be described as two face-shared octahedra, one based on osmium (OsH3P3) and the other based on silicon (SiH3N3). Studies of the bonding situation in 2a reveal that the N-pyrrolyl substituents have a marked shortening effect on the osmium-silicon distance (229.3(3)pm) and that each of the three hydride ligands participates in partial three-centre bonding involving osmium, silicon and hydrogen. H-1, C-13, Si-29 and P-31 NMR spectra were used to determine the solution structures of complexes 1 and 2a.