Lei Liu

• Boron is the fifth element of the periodic table, and it can covalently bind to itself forming a variety of atomic clusters in gas phase, with peculiar structures and unusual chemical bonding. On the other hand, many chemical compounds of boron are electron-deficient, and are considered as Lewis acids, displaying reactivity in solution. In the first part of this thesis, we investigate the electronic structures and fluxionality of boron clusters in gas phase. We employ first-principles calculations to study the structural transition from an icosahedral B12I122− to a planar B12 cluster, and the results show that the transition occurs between B12I7− and B12I5−, depending on the temperature. We also investigate the dimerization of two B12I9− anions and the unusual formation of a stable doubly charged B24I182− anion. Our DFT calculations and BO-MD simulations show that such dimerization is an exothermic process, and the formed B24I182− dimer is a stable species (up to 600 K). Finally, we address the issue of fluxionality in some planar boron clusters. We find that a variety of Bn clusters (n >10) contain fluxional units, and that fluxionality is promoted by certain structural patterns. In the second part of this thesis, we investigate the activation of molecular hydrogen by frustrated Lewis pairs (FLPs), in which substituted boranes act as Lewis acids. In FLPs, the Lewis acids and bases are sterically hindered by the presence of bulky organic substituents, and prevent the formation of classical Lewis adducts. Interestingly, such systems were demonstrated to work for H2 activation. First-principles calculations are performed to study a series of intermolecular FLPs towards H2 activation, and we successfully explain the factors that lead to reversible, irreversible and no H2 activation by such systems. We propose a new mechanism for H2 activation by intramolecular FLPs. By comparing this new mechanism with the one reported in the literature, we conclude that our new mechanism is more reasonable.