The synthesis and molecular structure of 3-PPh₃- 4-SMe₂-3,1,2-closo-CuC₂B₉H₁₀: Relationship of its structure to those of 10,11-μ-H-9-SMe₂-7,8-nido- C₂B₉H₁₀ and 10,11-μ-(PPh₃Au)-9-SMe₂-7,8-nido-C₂B₉H₁₀

Stoichiometric reaction between Tl[9-SMe₂-7,8-nido-C₂B₉H₁₀] and [Ph₃PCuBr]₄ affords the title compound in good yield. Crystallographic analysis of this species shows that the copper atom is essentially symmetrically disposed above the five-atom ligand face, thus completing a closo 12 vertex polyhedron. In contrast, in the formally related species 10,11-μ-H-9-SMe₂-7,8-nido-C₂B₉H₁₀ and 10,11 -μ-(PPh₃Au)-9-SMe₂-7,8-nido-C₂B₉H₁₀ the hydrogen atom and {Ph₃PAu} fragment occupy bridging positions on an open face, whereas in anionic non-SMe₂-substituted analogues of the last two the hydrogen atom and {Ph₃PAu} fragment adopt endo-terminal sites. These differences in respect to the SMe₂- substituted compounds are traced to the form of the HOMO of the [9-SMe₂-7,8-nido- C₂B₉H₁₀]^t- ligand. Inspection of the three occupied π-MOs of this ligand additionally yields a semi-quantitative understanding of patterns visible in the facial BB, BC and CC distances of 3-PPh₃-4-SMe₂-3,1,2-closo-CuC₂B₉H₁₀ 10,11-μ-H-9-SMe₂-7,8-nido-C₂B₉H₁₀ and 10, 11-μ-(PPh₃Au)-9-SMe₂-7,8-nido-C₂B₉H₁₀.