The pentafluoroethyltrihydridoborate anion: from shock sensitive salts to stable room temperature ionic liquids.

The reaction of pentafluoroethyllithium with BH3·thf yields [C2F5BH3]- that is stable against H2O, OH- and air due to the electron withdrawing C2F5 group. M[C2F5BH3] (M = K, Cs) are shock sensitive solids whereas salts with organic cations such as the room temperature ionic liquid [EMIm][C2F5BH3] are stable for years. [C2F5BH3]- is a mild reducing agent, which is also reflected by its electrochemical properties. Oxidation with I2 or Br2 in the presence of Lewis bases yields the first stable adducts C2F5BH2·L.