This PhD thesis reports computational investigations of SmI2-mediated radical reactions in order to develop a comprehensive understanding of these systems and thus further advance the synthetic capabilities of SmI2. The work has been performed using Density Functional Theory (DFT). The importance of using appropriate levels of theory has been highlighted across this work; in chapter 6, a better methodology was found with which to study our SmI2-mediated reactions, compared to what was previously in use. The use of different basis sets (and associated ECPs) from the previous work as well as including dispersion corrections throughout the geometry optimisations resulted in a superior methodology. In chapter 7, studies to determine the mechanism of a SmI2-mediated 1,4-ester migration were carried out to discern between two possible mechanisms â labelling and DFT studies highlighted the propensity for the substrates used in the SmI2-mediated 1,4-ester migration to cyclise via a ketyl radical at the acyclic ester rather than at the lactone carbonyl. In chapter 8, DFT studies were carried out to probe the feasibility of the proposed radical relay mechanism and rule out the possibility of a chain process in a SmI2-mediated alkene insertion into BCB ketones. Calculations confirmed that a radical relay mechanism was more likely than a chain process. However, calculations also revealed a high barrier to SET (32.5 kcal molâ1) which prompted more detailed investigation into the energy differences between different spin states in metal complexes (chapter 9). All-electron calculations were found to lower the entire quintet potential energy surface by approximately 15 kcal mol-1 compared to calculations where ECPs were used to treat scalar relativity. Since the all-electron calculations gave more realistic SET barriers, it was decided that all-electron calculations (with a scalar relativistic Hamiltonian) are a more appropriate methodology with which to study SmI2-mediated reactions. In chapter 10, the all-electron methodology was used in the investigation into hydrogen atom transfer as a potential mechanistic manifold for the invention of new SmI2-catalysed processes. This led to the perceived discovery of an unprecedented catalytic SmI2-mediate ketone reduction. Unfortunately, further experimental studies revealed that a less-interesting Lewis acid-mediated hydride transfer mechanism appeared to be involved.
Computational studies of SmI2-mediated radical reactions
Pye, E. (Author). 1 Aug 2024
Student thesis: Phd