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)A, 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.