Beyond the Hawthorne Reaction: Li<sup>+</sup> Induced\nThermal Dehydrocoupling of <i>closo</i>-10-vertex Carborane\nAnions

In the 1970s Hawthorne\nreported an electrochemical dehydrocoupling\nreaction of the <i>closo</i>-carborane anion [HCB<sub>9</sub>H<sub>9</sub><sup>1–</sup>] <b>1</b> to form the biscarborane\n[C<sub>2</sub>B<sub>18</sub>H<sub>18</sub><sup>2–</sup>] <b>2</b>. In this Communication we show that the said “Hawthorne\nReaction” can be achieved thermally and that it tolerates C-butylation.\nThe new compound <b>2</b><sub><b>butyl</b></sub> was fully\ncharacterized by <sup>11</sup>B, <sup>1</sup>H, and <sup>13</sup>C\nNMR spectroscopies, high-resolution mass spectrometry, and single-crystal\nX-ray diffraction. One interesting caveat is that <b>2</b> or <b>2</b><sub><b>butyl</b></sub> only form thermally when they\nare salts of Li<sup>+</sup> and not NEt<sub>4</sub><sup>+</sup>, Na<sup>+</sup>, K<sup>+</sup>, or Cs<sup>+</sup>. This observation means\nthat Li<sup>+</sup> in some way facilitates this process, introducing\na new kind of Li<sup>+</sup> effect.