Haloaryl carbaboranes: 2. Synthesis and characterisation of haloaryl-closo-carbaboranes. Crystal structures of 1-(4-BrC₆F₄)-2-R-1,2-closo-C₂B ₁₀H₁₀ (R=Me, Ph, Bu^t)

Reaction of C₆F₅Br with Li[1-R-1,2-closo-C₂B₁₀H₁₀] readily gives compounds 1-(4-BrC₆F₄)-2-R-1,2-closo-C₂B ₁₀H₁₀ [R=Me (1), Ph (2), Bu^t (3)]. Compounds 1-3 were characterised by NMR spectroscopy and single crystal X-ray diffraction studies. A significant lengthening of the C_cage-C_cage connectivity is seen as the steric demands of the cage bound substituents increase, from 1.712(7) Å in 1 to 1.736(7) and 1.743(8) Å in 2 and to 1.761(6) Å in 3, the last being the longest C_cage-C_cage distance recorded for a carbaborane with alkyl or aryl substituents. © Elsevier Science Ltd.