Solution behaviour of some benzyne complexes of osmium and the X-ray crystal structure of µ3-benzyne-1,1,1,2,2,2,3,3,3-nonacarbonyl-µ-dimethylarsino-µ-hydrido-triosmium(2Os–Os)

Abstract

Variable-temperature ¹H and ¹³C n.m.r. analysis of [Os₃(C₆H₄)(AsMe₂)₂(CO)₇] and its C₆H₃Prⁱ analogue has confirmed that one CO ligand rapidly transfers between two Os atoms and that opposite faces of the µ₃-C₆H₄ ligand interchange during two distinct fast intramolecular processes. The X-ray crystal structure of [Os₃(C₆H₄)(AsMe₂)(CO)₉H] has been determined. The crystals are triclinic, space group P, with a= 9.302(3), b= 9.398(6), c= 15.063(7)Å, α= 101.87(4), β= 72.64(3), γ= 117.48(3)°, and Z= 2 and the structure has been refined to R= 0.0518 for 3 029 observed reflections. The compound contains a triangle of Os atoms joined by two Os–Os bonds with a AsMe₂ group bridging the two non-bonded metal atoms. The C₆H₄ ligand is triply bridging the metal atoms with two σ Os–C bonds and a η²-linkage. The hydride ligand was not located but its position inferred from the structure. Variable-temperature n.m.r. studies of this complex and its C₆H₃Prⁱ analogue show that the presence of only two Os–Os bonds does not interfere with the interchange of C₆H₄ ligand faces as indicated by the coalescence of the diastereotopic methyl signals of the Prⁱ group.