Polyhedral metallathiaborane chemistry: Synthesis and characterisation of metallathiaboranes based on the twelve-vertex icosahedral closo-{MSB10H10} unit, where M is Rh or Ir

The reaction of nido-7-SB₁₀H₁₂] with RhCl(PPh₃)₃] in the presence of N,N,N′N′-tetramethylnaphthalene-1,8-diamine (tmnd) in CH₂Cl₂ gives twelve-vertex 2,2-(PPh₃)₂-2-H-closo-2,1-RhSB₁₀H₁₀] (1) and eleven-vertex 8,8-(PPh₃)₂-nido-8,7-RhSB₉H₁₀] (2), as major products, plus the dimeric species {(PPh₃)-closo-RhSB₁₀H₁₀}₂] (3) as a minor product. Reaction of 1 with PMe₂Ph in CH₂Cl₂ results in phosphine exchange and hydride substitution, affording the chloro analogue of 1, 2,2-(PMe₂Ph)₂-2-Cl-closo-2,1-RhSB₁₀H₁₀] (4). By contrast, reaction between IrCl(PPh₃)₃] and nido-7-SB₁₀H₁₂] in CH₂Cl₂ with tmnd affords only one product, twelve-vertex 2,2-(PPh₃)₂-2-H-closo-2,1-IrSB₁₀H₁₀] (5). RhCl₂(η⁵-C₅Me₅)]₂ with nido-7-SB₁₀H₁₂] under the same conditions gives twelve-vertex 2-(η⁵-C₅Me₅)-closo-2,1-RhSB₁₀H₁₀] (6). All the compounds are characterised by NMR spectroscopy, and by mass spectrometry, and the molecular structure of 2,2-(PMe₂Ph)₂-2-Cl-closo-2,1-RhSB₁₀H₁₀] (4) was established by single-crystal X-ray diffraction analysis. This last rhodathiaborane 4 is fluxional in solution through a process that involves a reversible partial rotation of the {RhCl(PMe₂Ph)₂} unit above the {SB₄} pentagonal face of the {SB₁₀H₁₀} fragment.