Preparation of [closo-CB11H12](-) by dichlorocarbene insertion into [nido-B11H14](-)

In strongly basic media, the [nido-B11H14](-) anion reacts with the halofor ms. Dehydrogenation to [closo-B11H11](2-) is the only reaction observed wit h iodoform. With chloroform and bromoform, the cage is expanded by dihaloca rbene insertion. The dominant products are the [closo-CB11H12](-) and the [ 2-Br-closo-CB11H12](-) anion, respectively. The chief side product is the [ closo-B11H11](2-) anion, which results from dehydrogenation of the starting material. It was identified by B-11 NMR spectroscopy and isolated after ac idic aqueous workup in the form of the [nido-7-OH-B11H13](-) anion. Since t he starting [nido-B11H14] anion is available from NaBH4 and BF3. Et2O in 50 % yield, its conversion to [closo-CB11H12](-) with chloroform and base in a 40% yield represents a useful laboratory route to the numerous known but p reviously very expensive derivatives of [closo-CB11H12](-), highly prized f or their very low nucleophilicity.