Bimetallic Zwitterionic Complexes with an Ambident Stanna-<i>c</i><i>loso</i>-dodecaborate Ligand: [1-{M(CO)<sub>5</sub>}-2,7,8-(μ-H)<sub>3</sub>-{Fe(triphos)}-SnB<sub>11</sub>H<sub>11</sub>] (M = Cr, Mo, W)
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Starting from FeBr2 the zwitterionic stannaborate complex [1-{Fe(MeCN)2(triphos)}-SnB11H11] (1) could be obtained in a straightforward one-pot synthesis. Via a facile η1(Sn) to η3(BH) rearrangement reaction 1 can be converted into [2,7,8-(μ-H)3-{Fe(triphos)}-SnB11H11] (2). The nucleophilicity of the tin atom in compound 2 is strongly reduced compared to the dianionic parent stannaborate cluster [SnB11H11]2-. Methylation at the tin atom using standard methods is not feasible. Transition metal fragments can be coordinated at the tin atom of 2 if reactive species such as M(CO)5(THF) (M = Cr, Mo, W) are employed. Reaction of these fragments with 2 yields the bimetallic zwitterions [1-{M(CO)5}-2,7,8-(μ-H)3-{Fe(triphos)}-SnB11H11] (M = Cr, Mo, W) (3, 4, 5), which contain an ambident stannaborate moiety. All new compounds have been characterized using 1H, 11B, 13C, 31P, and 119Sn NMR spectroscopy as well as 31P and 119Sn MAS NMR experiments. Single-crystal X-ray diffraction analyses have been carried out for all novel compounds.
