Addition and elimination reactions of H2 in ruthenaborane clusters: A computational study

• Calculations of hydrogen storage and activation of H–H bond by ruthenaborane were performed.
• Mechanisms of the H2 addition–elimination reactions in ruthenaborane clusters were studied.
• Calculated activation energies of the ruthenaborane upon hydrogenation are compared.
• H2 addition to metallaborane clusters with high hydride content is predicted.

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)Ru2B10H16], [(C5Me5)Ru2B8H14] and [(C5Me5)Ru2B8H12] 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.

Hydrogenation and dehydrogenation processes of ruthenaborane clusters ([Cp2Ru2B10H14]) A and ([Cp2Ru2B10H14]) D have been studied computationally at the DFT/B3LYP level. Calculations show different bonding modes of the added H2 molecule to the investigated clusters: (TS1, TS2, TS3 and TS4). Activation pathways of the H-H bond by ruthenaboranes were also analyzed.Figure optionsDownload as PowerPoint slide