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 H-2 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 H-2 seems to be activated by the ruthenaborane clusters as activation energies of 24-42 kcal/mol were calculated for the H-2 addition reaction. The calculated Gibbs free energy for the H-2 addition reaction is 14-27 kcal/mol. The calculated activation energies and the molecular structures of the [(C5Me5) Ru2B10H16], [(C5Me5)Ru2B8H14] and [(C5Me5) Ru2B8H12] clusters with different degree of hydrogenation are compared. The mechanisms of the H-2 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.