Selective synthesis of the B 11 H 14 − and B 12 H 12 2− borane derivatives and the general mechanisms of the B-H bond condensation

Polyhedral boranes are a class of well-known boron molecular clusters with unique physical and chemical properties, and great efforts have been made in the past decades to find more effective synthetic methods. However, the established synthetic methods suffer from low efficiency and low selectivity because the mechanism of the B–H bond condensation reaction, critical for the synthesis of the polyhedral boranes, is not well understood. Here we report highly selective and efficient synthetic methods of the salts of the tetradecahydridoundecaborate (1–) (B 11 H 14 − ) and dodecahydrido-dodecaborates (2–) (B 12 H 12 2− ) anions by employing commercially available and inexpensive starting materials. Both theoretical and experimental investigations are carried out to elucidate the reaction mechanisms. We have found that the nature of the B–H bond condensation is the dihydrogen bonding interaction in which the positively charged hydrogens (bridged hydrogens) play a crucial role. The current study has not only led to more effective and selective synthetic methods for B 11 H 14 − and B 12 H 12 2− but also unveiled the nature of the B–H bond condensation and the general formation mechanisms of polyhedral boranes. This finding will facilitate the development of more effective synthetic methods for polyhedral boranes and spur their wide application.