LAUSR

Reaction pathways for H2 release mediated by H2X (X = O, S, Se) and HY (Y = F, Cl, Br) set of reagents from ammonia-borane (NH3BH3) have been explored in gas phase using density functional theory (DFT). The optimized geometries of reactant complexes, transition states and product complexes have been obtained using M06-2X functional in conjunction with 6-311+G(d,p) basis set. The study of catalytic effect of these cheap and easily available, yet highly effective, assisting reagents has farther been extended to analyze the thermochemistry involved in H2 departure from two other ammonia-borane-related compounds: aziridine-borane [C2H5N.BH3] and 3-methyl-1,2-BN-cyclopentane. The mechanism of H2 release channel is identical for all three compounds considered. The free energy barrier falls significantly from H2O to H2S to H2Se for the H2X set of reagents and from HF to HCl to HBr for the HY analogs. Our study endorses the fact that the HY set of reagents serves as better assisting reagents kinetically compared to H2X, with HBr being the best of the lot. HBr reduces the free energy barrier to 41.9 kJ mol−1 for ammonia-borane [NH3BH3], 42.7 kJ mol−1 for aziridine-borane [C2H5N·BH3] and 30.2 kJ mol−1 for 3-methyl-1,2-BN-cyclopentane in H2 release at 1 atm. pressure and 298 K temperature.