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.