Acid-induced lsomerisations of osmium and ruthenium clusters involving hydroxide transfer from carbon to metal atoms. X-Ray crystal structure of nonacarbonyl-µ3-(3,3-diphenylallene- 1,1-diyl)-µ-hydrido-µ-hydroxo-triosmium(2 Os–Os)

Abstract

The complexes [M₃H(CO)₉(µ₃-CCCPh₂OH)](M = Ru or Os) were prepared by reaction of [M₃(CO)₁₂] with HOCPh₂CCCPh₂OH in saturated hydrocarbon at 130 °C for M = Os or in refluxing cyclohexane from M = Ru. In the latter case the yield of cluster is low and there is some 1,1,4,4-tetraphenylbutadiene formed. Treatment of the trinuclear clusters in chloroform with trifluoroacetic acid leads to isomerisation with migration of the OH group from carbon to metal atoms. This was confirmed by an X-ray structure determination for the osmium product [OS₃(µ-H)(µ-OH)(CO)₉(µ₃-CCCPh₂)]. The crystals are monoclinic, space group P2₁, a= 10.569(1), b= 20.259(3), c= 12.287(2)Å, β= 95.66(1)°, and Z= 4. The structure was refined to R= 0.0621 for 4 112 observed reflections. There are two independent molecules (A and B) in the unit cell with very closely similar structures. Spectroscopically, an OH group was identified and another hydrogen bound to osmium but neither hydrogen atom was located by X-ray diffraction. The OH group bridges two non-bonded osmium atoms separated by 3.374(5)Å in molecule A [3.372(5)Å in B], while the µ-H was deduced to be across the longer Os–Os bond [2.905(5)versus 2.861(5)Å for molecule A and 2.902(5)versus 2.869(5)Å for molecule B]. The 3,3-diphenylallene-1,1-diyl ligand is bonded through two Os–C σ bonds and a 1,2-η²-co-ordination to the other osmium atom and is bent about the central atom [145(3)° for molecule A and 144(3)° for B]. The orientation of the phenyl substituents at the non-co-ordinated allene carbon atom agrees with this interpretation of the bonding.