Preparation of smaller nine- and ten-vertex monocarbaborane cages by the selective dismantling of twelve-vertex dicarbaboranes via the (nido7,9-C(sub 2)B(sub 10)H(sub 13))(super -)anion: synthesis of the monocarbaborane base adducts endo-9-Me-8-(NMe(sub 3))-arachno-6-CB9H12 (L = SMe2, NMe3, urotropine, pyridine, quinoline, MeCN, PPh3, MeNC)1a

Twelve-vertex (nido-7,9-C(2)B(10)H(13))(super -) anion undergoes cage degradation to produce compounds of smaller nine-and ten-vertex monocarboborane cages. This degradation involves the loss of one (CH) vertex. This technique avoids the use of hazardous sodium cyanide with dicarboborane. (II)B and (1)H NMR are used for characterization of these compounds.