The structure of a new isomer of dicarba-nido-undecaborane(13)

The intramolecular rearrangement involved in the electrophilic methylation of 7,8-B₉C₂H₁₁^2? leads after protonation to the methyl derivative of a new isomer of dicarba-nido-undecaborane(13). By an X-ray structure analysis the latter compound is shown to be 11-methyl-2,7-dicarba-nido-undecaborane(12). It has the structure of an icosahedron with one missing vertex, with the carbon atoms adjacent, one in the open face of the polyhedron and the other in its closed part. The methyl group is attached to the boron atom of the open face bonded to both carbon atoms. The open face has two BHB-bridges which are symmetric relative to its carbon atom. The main interatomic distances are: av. BB 1.794(8), av. BC 1.685(7), CC 1.606(6), BMe 1.551(8), av. BH (terminal) 1.08(3), av. BH (bridging) 1.26(4), av. CH 0.92(4) Å.