Unexpected Enhanced acidity of Diborane-Nitrogen Base complexes

• The interaction of borane, BH 3 , with N-bases is stronger than that of the same bases with BeH 2 . • The interaction of diborane, B 2 H 6 , with N-bases is much weaker than that of the same bases with borane or BeH 2 dimer. • The interaction of diborane with deprotonated N-bases is about ten times larger than with the neutral base. • Despite diborane’s weaker interaction with nitrogen bases, it produces a greater acidity enhancement than that caused by borane. The effect that borane and diborane have on the structure and acidity of various N-bases was analyzed using G4 ab-initio calculations. Although diborane is expected to be a stronger Lewis acid than borane, its interaction with N-bases is weaker due to the loss of one of its (3c,2e) bonds. Surprisingly, however, diborane has a significantly greater effect on the intrinsic acidity of these bases than borane. Upon deprotonation of the base, the interaction strength increases by a factor of 10 with diborane and only 3 with borane, as both the B–N and BH 3 ···BH 3 interactions are reinforced in diborane.