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

In the 1970s Hawthorne reported an electrochemical dehydrocoupling reaction of the <i>closo</i>-carborane anion [HCB₉H₉^1-] <b>1</b> to form the biscarborane [C₂B₁₈H₁₈^2-] <b>2</b>. In this Communication we show that the said "Hawthorne Reaction" can be achieved thermally and that it tolerates C-butylation. The new compound <b>2</b>_<b>butyl</b> was fully characterized by ¹¹B, ¹H, and ¹³C NMR spectroscopies, high-resolution mass spectrometry, and single-crystal X-ray diffraction. One interesting caveat is that <b>2</b> or <b>2</b>_<b>butyl</b> only 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.