Mechanistic Role of Anion Basicity in Imidazolium Ionic Liquids for Amine–Borane Dehydrogenation: Experimental and Theoretical Insights

Hydrogen storage presents a significant challenge in the advancement of alternative energy systems. Amine−borane complexes, including ammonia borane (AB) and ethylenediamine bisborane (EDAB), are notable candidates owing to their high hydrogen content and stability. Ionic liquids (ILs) are increasingly recognized as effective reaction media for dehydrogenation due to their low vapor pressure, high thermal stability, and capacity to eliminate induction periods. This study presents an experimental and theoretical investigation into the mechanistic role of anion hydrogen bond basicity in imidazolium-based ILs on the thermal dehydrogenation of amine–borane complexes. Thermal experiments demonstrate that ILs containing methylsulfate anions ([Bmim][MeSO 4 ]) produce considerably greater hydrogen equivalents and shorter induction times than those with tetrafluoroborate ([Bmim][BF 4 ]) and hexafluorophosphate ([Bmim][PF 6 ]) anions. COSMO-SAC predictions indicate a linear relationship between the solubility of AB/EDAB and the hydrogen bond basicity (β) of the ILs. Complementary density functional theory (DFT) calculations and natural bond orbital (NBO) analyses indicate that the acidic protons of the hydrides engage in strong hydrogen bonds and electrostatic interactions with the IL anions, which act as the primary reactive sites for initiating dehydrogenation. Furthermore, advanced investigations employing the IGMH-IBSI approach and energy decomposition analysis through the SAPT methodology quantitatively elucidate the contributions of noncovalent interactions in the stabilization of IL-hydride complexes. These insights elucidate the mechanistic role of anion basicity and provide a framework for designing ILs to optimize dehydrogenation processes for hydrogen storage applications.