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 [HCB₉H₉^1-] 1 to form the biscarborane [C₂B₁₈H₁₈^2-] 2. In this Communication we show that the said "Hawthorne Reaction" can be achieved thermally and that it tolerates C-butylation. The new compound 2_butyl 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 2 or 2_butyl 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.