Preparation of [closo-CB11H12]- by Dichlorocarbene Insertion Into [nido-B11H14]-

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Abstract

In strongly basic media, the [ nido -B 11 H 14 ] - anion reacts with the haloforms. Dehydrogenation to [ closo -B 11 H 11 ] 2- is the only reaction observed with iodoform. With chloroform and bromoform, the cage is expanded by dihalocarbene insertion. The dominant products are the [ closo -CB 11 H 12 ] - and the [2-Br- closo -CB 11 H 12 ] - anion, respectively. The chief side product is the [ closo -B 11 H 11 ] 2- anion, which results from dehydrogenation of the starting material. It was identified by 11 B NMR spectroscopy and isolated after acidic aqueous workup in the form of the [ nido -7-OH-B 11 H 13 ] - anion. Since the starting [ nido -B 11 H 14 ] - anion is available from NaBH 4 and BF 3 ·Et 2 O in 50% yield, its conversion to [ closo -CB 11 H 12 ] - with chloroform and base in a 40% yield represents a useful laboratory route to the numerous known but previously very expensive derivatives of [ closo -CB 11 H 12 ] - , highly prized for their very low nucleophilicity.

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