Bimetallic Zwitterionic Complexes with an Ambident Stanna-closo-dodecaborate Ligand:  [1-{M(CO)₅}-2,7,8-(μ-H)₃-{Fe(triphos)}-SnB₁₁H₁₁] (M = Cr, Mo, W)

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 eta(1)(Sn) to eta(3)(BH) rearrangement reaction 1 can be converted into [2,7,8-(mu-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-(mu-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 H-1, B-11, C-13, P-31, and Sn-119 NMR spectroscopy as well as P-31 and Sn-119 MAS NMR experiments. Single-crystal X-ray diffraction analyses have been carried out for all novel compounds.