Haloaryl carbaboranes - 2. Synthesis and characterisation of haloaryl-closo-carbaboranes. Crystal structures of 1-(4-BrC6F4)-2-R-1,2-closo-C2B10H10 (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-C2B10H10 [R=Me(1), Ph (2), Bu-t (3)]. Compounds 1-3 were characterised by NMR spectroscopy and single crystal X-ray diffrac tion studies. A significant lengthening of the C-cage-C-cage connectivity i s seen as the steric demands of the cage bound substituents increase, from 1.712(7) Angstrom in 1 to 1.736(7) and 1.743(8) Angstrom in 2 and to 1.761( 6) Angstrom in 3, the last being the longest C-cage-C-cage distance recorde d for a carbaborane with alkyl or aryl substituents. (C) 1999 Elsevier Scie nce Ltd. All rights reserved.