Experimental and Computational Study of the Formation Mechanism of the Diammoniate of Diborane: The Role of Dihydrogen Bonds

The mechanism of formation of ammonia borane (NH3BH3, AB) and the diammoniate of diborane ([H2B(NH3)2][BH4], DADB) in the reaction between NH3 and THF·BH3 was explored experimentally and computationally. Ammonia diborane (NH3BH2(μ-H)BH3, AaDB), a long-sought intermediate proposed for the formation of DADB, was directly observed in the reaction using 11B NMR spectroscopy. The results indicate that dihydrogen bonds between the initially formed AB and AaDB accelerate the formation of DADB in competition with the formation of AB.