Beyond the Hawthorne Reaction: Li+Induced Thermal Dehydrocoupling of closo-10-vertex Carborane Anions

In the 1970s Hawthorne reported an electrochemical dehydrocoupling reaction of the closo-carborane anion [HCB9H91–] 1to form the biscarborane [C2B18H182–] 2. In this Communication we show that the said “Hawthorne Reaction” can be achieved thermally and that it tolerates C-butylation. The new compound 2butylwas fully characterized by 11B, 1H, and 13C NMR spectroscopies, high-resolution mass spectrometry, and single-crystal X-ray diffraction. One interesting caveat is that 2or 2butylonly form thermally when they are salts of Li+and not NEt4+, Na+, K+, or Cs+. This observation means that Li+in some way facilitates this process, introducing a new kind of Li+effect.