Synthesis and characterisation of {Mo(η-L)(CO)₃}⁺ (η-L = C₅H₅ or C₅Me₅) fragments ligated with [CB₁₁H₁₂]^- and derivatives. Isolation and structural characterisation of an intermediate in a silver salt metathesis reaction

The synthesis of {Mo(η-L)(CO)₃}⁺ (η-L = C₅H₅ or C₅Me₅) fragments, ligated to the mono-anionic, weakly co-ordinating, carboranes [closo-l-CB₁₁H₁₂]^- and [closo-CB₁₁Br₆H₆]^-, has been investigated. Treatment of [MoCp(CO)₃X] (X = Cl or I) with Ag[CB₁₁H₁₂] eventually affords the zwitterionic complex [MoCp(CO)₃(x-μ-H-1-CB₁₁H₁₂)] (x = 12 or 7), via an intermediate dimeric species [MoCp(CO)₃X·Ag(CB₁₁H₁₂)]₂ . For X = I this intermediate has been characterised by ¹H, ¹¹B NMR spectroscopy and X-ray crystallography and represents the first structurally characterised intermediate in a silver salt metathesis reaction. When the less nucleophilic carborane [CB₁₁Br₆H₆]^- (as its silver salt) is used metathesis is halted at the intermediate stage, affording the complex [MoCp(CO)₃I·Ag(CB₁₁Br₆H₆ )]₂. Silver salt metathesis does not proceed using the sterically more demanding [Mo(Cp*)(CO)₃I], with only intractable products isolated. The carborane anion can be introduced into the co-ordination sphere of this complex by reaction of [H(OEt₂)_x[CB₁₁H₁₂] with [Mo(Cp*)(CO)₃Me] affording [Mo(Cp*)(CO)₃(x-μ-H-1-CB₁₁H₁₂) ] (x = 12 or 7). All new compounds have been characterised by multinuclear NMR spectroscopy and X-ray crystallography.