Addition and elimination reactions of H<inf>2</inf> in ruthenaborane clusters: A computational study

Ruthenaborane clusters have been modelled by performing density functional theory calculations using the B3LYP functional. The calculations gain insights into hydrogen storage and the H-H bond activation by ruthenaboranes. To study the nature of the chemical bond of H2 molecules attached to ruthenaboranes, we carried out structural optimizations for different ruthenaborane clusters and determined transition state structures for their hydrogenation addition/elimination reactions. Calculations of the reaction pathways yielded different transition-state structures involving molecular hydrogen bonded to the cluster or formation of metal hydrides. The H-H bond of H2 seems to be activated by the ruthenaborane clusters as activation energies of 24-42 kcal/mol were calculated for the H2 addition reaction. The calculated Gibbs free energy for the H2 addition reaction is 14-27 kcal/mol. The calculated activation energies and the molecular structures of the [(C5Me5)Ru2B 10H16], [(C5Me5)Ru2B 8H14] and [(C5Me5)Ru 2B8H12] clusters with different degree of hydrogenation are compared. The mechanisms of the H2 addition and elimination reactions of the studied clusters suggest that they might be useful as hydrogen storage materials due to their ability to activate the H-H bond. They also serve as an example of the ability of hypoelectronic metallaboranes to reversibly or irreversibly bind hydrogen. © 2014 Elsevier B.V. All rights reserved.