Promotion effect of coordinated isocyanide on the oxidative addition of allyl bromide in triosmium clusters

Article abstract of DOI:10.1021/om00020a034

The unique linear triosmium clusters Os₃Br(CO)₁₀(CNR)(η³-C₃H ₅) (2) are prepared by reaction of Os₃(CO)₁₀(CNR)(NCMe) with allyl bromide. The reaction rate is faster in CH_2- Cl₂ than in cyclohexane. The oxidative addition of allyl bromide to the triosmium cluster is likely to involve a partial heterolytic metal-metal bond fission pathway, and the coordinated isocyanide ligand plays an important role in determining the regioselectivity and the transformation of allyl bromide in the coordination sphere of the cluster. In the absence of the coordinated isocyanide ligand, complex Os₃(CO)₁₁(NCMe) reacts with allyl bromide in CH₂Cl₂ to afford a similar linear complex Os₃Br(CO)₁₁(η³-C₃H₅) (4) with a slower rate. Complex Os₃Br(CO)₁₀(CNPr)(η³-C₃H ₅) (2a) crystallized in the triclinic space group P1 with a = 10.518(5) A?, b = 12.026(2) A?, c = 19.116(3) A?, α = 89.98(1)°, β = 90.13(3)°, γ= 93.23(3)°, V = 2414(1) A?³, Z = 4, R = 4.7%, and R_w = 5.1% for 3810 observed reflections. Both the bromide and the isocyanide ligands coordinate equatorially at the first Os atom, while the allyl group occupies an axial and an equatorial site on the third Os metal center in the linear triosmium cluster.