The sodium salt of [B12H12](2-) dianion reacts with carboxylic acid ha
lides to give a mixture of B-acylated product [B12H11COR](2-) and an u
nstable intermediate, the latter undergoing hydrolysis to form [B12H11
OH](2-). The ratio of the products formed depends on the nature of the
radical R. The reaction mechanism was studied by NMR spectroscopy. A
number of novel [B12H11COR](2-) compounds were synthesized; their stru
ctures were confirmed by NMR and IR spectral data.