58th Annual Report on Research 2013 Under Sponsorship of the ACS Petroleum Research Fund

During this time period one postdoctoral scholar was funded. This second year of funding has allowed the postdoctoral scholar and the PI to develop new computational chemistry expertise in the area of ab initio direct dynamics simulations applied to main-group and transition-metal chemistry. Computational work during this second year focused on the electronic structure and reaction trajectories of divalent main-group activation of dihydrogen, which is a model σ-bond. Future studies will undertake trajectory calculations of C-H bond activation reactions.

Theory of Divalent Main Group H₂ Activation

The structure, barrier heights, thermodynamics, electronic properties, and dynamics of H₂ activation by singlet divalent main group compounds (ER₂; E = C, Si, Ge) were studied using density functional theory (DFT), absolutely localized molecular orbitals (ALMO), and quasiclassical trajectories (QCTs). ALMO energy and charge decomposition calculations revealed that in the transition state carbene-type compounds act as ambiphiles toward H₂ while heavier analogs (Si and Ge) act as nucleophiles. We also found that classic frontier molecular orbital (FMO) energy gaps do not provide a reasonable estimate of energy stabilization gained in the transition state or an accurate description of electronic character of the reaction. Examination of barrier heights and reaction energies showed a clear kinetic-thermodynamic relationship for ER₂ activation of H₂. QCTs show that dihydrogen approach and reaction with CR₂ may involve geometries that significantly deviate from those expected based on a static transition-state structure. In contrast, SiR₂ trajectories involve geometries close to the side-on approach that would be predicted by the static transition state. Trajectories also demonstrated that addition of H₂ to CR₂ and SiR₂ is dynamically concerted.