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, Br2, CuCl2, AlCl3, GaCl3, InCl3, and [Ph3C]BF4 at a concentration of 7.5 mol% was effective in selectively producing aminodiborane (µ‐NH2B2H5, ADB) at 80°C. Compounds such as ICl, IBr, Br2, AlCl3, and GaCl3 at the same concentration could also generate ADB at lower temperatures of 35°C and 50°C. In contrast, BX3 (X=Cl, Br) at the same concentration of 7.5 mol% was found to give exclusively B2H6. 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 BBr3 favored the formation of B2H6, while 1 mol% BBr3 predominantly yielded ADB. Interestingly, both ADB and B2H6 facilitated the reduction of acetanilides. A mechanism has been proposed for both diborane and ADB formation using these Lewis acids.