Dehydrogenation of ethylene diamine monoborane adducts and their cyclic products (monomers, dimers, and trimers): Potential liquid organic hydrogen carriers.

The dehydrogenation mechanisms of ethylene diamine monoborane (EDMB) adducts and its derivatives having CH 3 , Cl, F, NH 2 , OCH 3 , CN, and H substituents at two sites on the ethylene backbone were investigated to explore their potential as liquid organic hydrogen carriers (LOHCs). Using density functional theory calculations, the thermodynamic parameters of the EDMB adducts and dehydrogenation reactions to form cyclic monomers, dimers, and trimers were calculated. In particular, we focused on the free energy barriers of EDMB adducts substituted with Cl/CN, Cl/OCH 3 , F/CN, F/OCH 3 , F/F, and NH 2 /H for cyclic monomer formation, H/CH 3 , H/CN, Cl/H, and NH 2 /H for cyclic dimer formation, and H/Cl, H/F, and NH 2 /H for cyclic trimer formation, which are promising candidates for chemical hydrogen storage. We also explored the formation of cyclic trimers from the selected cyclic monomers with CH 3 /CH 3 , H/CH 3 , and NH 2 /H substituents. As a result, the dehydrogenation pathways and transition states of the various adducts for the formation for the various cycles were identified, and electrostatic potential surfaces and frontier molecular orbitals calculations were calculated to understand the reaction further. The results obtained indicate the potential of these materials for hydrogen storage, and we hope that this work will encourage the experimental investigation of these materials. Image 1 • Amine–boranes studied as potential liquid organic hydrogen carriers. • Amine–borane adducts undergo dehydrogenation via cyclization. • Substituent electronic and steric effects alter reaction energetics. • Electronegative substituents (Cl, CN, and F) result in favorable dehydrogenation. [ABSTRACT FROM AUTHOR]