Synthesis of Aminodiborane From Ammonia Borane Using Different Lewis Acids: A Competing Reaction for Diborane Formation with Boron Trihalides (BX₃, X=Cl, Br)

Abstract The dehydrogenation of ammonia borane in the presence of a variety of Lewis acids such as ICl, IBr, Br 2 , CuCl 2 , AlCl 3 , GaCl 3 , InCl 3 , and [Ph 3 C]BF 4 at a concentration of 7.5 mol % was effective in selectively producing aminodiborane (μ‐NH₂B₂H₅, ADB) at 80 °C. Compounds such as ICl, IBr, Br 2 , AlCl 3 , and GaCl 3 at the same concentration could also generate ADB at lower temperatures of 35 °C and 50 °C. In contrast, BX 3 (X=Cl, Br) at the same concentration of 7.5 mol % was found to give exclusively B 2 H 6 . Further, selective synthesis of diborane or ADB was achieved by adjusting the stoichiometry of the boron trihalides. A concentration of 7.5 mol % (upto 1 equivalent) of BBr 3 favored the formation of B 2 H 6 , while 1 mol % BBr 3 predominantly yielded ADB. Interestingly, both ADB and B 2 H 6 facilitated the reduction of acetanilides. A mechanism has been proposed for both diborane and ADB formation using these Lewis acids.