Reactivity and mechanisms of hydridic hydrogen of B–H in ammonia borane towards acetic acids: the ammonia B-monoacyloxy boranes

Abstract

Non-classical acid–base neutralization reactions of ammonia borane (NH₃·BH₃, AB) with acetic acids are moderate, affected by strengths of acetic acid and its chloro derivatives, and concentrations and ratios of reactants. The experiment results indicate that only one hydridic hydrogen of B–H in AB is substituted and fortunately, four ammonia B-monoacyloxy boranes (NH₃·BH₂OOCR, R = CH_nCl_3−n, n = 0–3) are prepared. Two single crystals of 2NH₃BH₂OOCCH₂Cl·C₁₂H₂₄O₆ and 2NH₃BH₂OOCCHCl₂·C₁₂H₂₄O₆ were obtained and analyzed first. Theoretical calculations demonstrated that these reactions are two-step elimination-addition process that takes advantage of the formation of dihydrogen bonds (DHBs) and hydrogen bonds (HBs), and aminoborane (NH₂BH₂, AoB) is identified as the key intermediate.