An Experimental and Theoretical Elucidation : Does the Hydrogen Bond Basicity of Imidazolium-Based Ionic Liquids Affects the Thermolytic Dehydrogenation of Amine-Borane Complexes?

In the thermal dehydrogenation of ammonia borane (AB) or ethylenediamine bisborane (EDAB) within the Ionic Liquid(IL) medium, the hydrogen bond basicity (β) of the anions plays a prominent part. A comprehensive experimental study was conducted to demonstrate the catalytic effect of ILs on the thermolytic dehydrogenation of chemical hydrides. It was observed that methylsulfate-based anions AB/EDAB-[Bmim][MeSO 4 ] system produced 2.18 and 3.66 equivalents of hydrogen with a lower induction time when compared to other studied AB/EDAB-IL systems. This trend was also confirmed through COSMO-SAC predictions, where the infinite dilution activity coefficient values for the solubility of chemical hydrides on the examined IL systems were computed. The solubility of chemical hydrides (AB and EDAB) is shown to be linearly related to the hydrogen-bond basicity value (β). A quantum-chemical parameter, namely the most negative surface electrostatic potential (V s,min ), was used to explore the electrostatic properties of ILs' basicity at the microscopic level. It was observed that the ILs' basicity originates from their anionic moiety and that its value changes with the anion. Further DFT-based calculations were carried out to elucidate the interactions between the anionic moiety of the ILs and chemical hydrides, followed by an NBO charge analysis to further clarify the interaction within the complexes. Quantum mechanical calculations revealed the fact that the acidic protons of chemical hydrides form strong hydrogen bonds and electrostatic interactions with the highly basic anions of ILs. The electronic structure elucidation and charge analysis revealed that the anions of the ILs are the primary reactive sites that initiate the dehydrogenation reaction and result in the release of hydrogen equivalents