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-1-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.