Control and prediction of eliminative cyclisation.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Eliminative cyclisation is a class of intramolecular reactions that provide a versatile synthetic route to functionalised and substituted polyaromatic and heteroaromatic compounds, which form the building blocks of molecular electronic devices such as organic photovoltaics and organic light-emitting diodes.
These reactions may be either thermally or photochemically driven, and proceed via two steps: 1) planarisation to form a stable proto-aromatic intermediate, and 2) elimination of the groups or atoms adjacent to the forming bond to yield the final fully aromatic product. Although experimental studies have been performed on a wide range of starting materials to characterise reaction mechanisms and product distributions, there remains no predictive model for determining whether or not any given reactant will yield a product under specified reaction conditions.
This thesis investigated the factors that control both the thermodynamics and kinetics of these reactions by explicitly mapping out reaction coordinate profiles and analysing induced atomic forces upon photo-excitation for a diverse range of molecules. Results showed that the kinetics and thermodynamics of both planarisation and elimination in thermal cyclisation are highly sensitive to the reaction conditions, which include the presence and position of the heteroatoms as well as the oxidation potential of the reactants. In photocyclisation, the planarisation step is a photo-activated excited-state process that is in contrast less sensitive to reaction condition; elimination is proposed to proceed in the ground state. The magnitude of the projected force along the bond vectors of the putative forming ring is shown to be a good predictor for the outcome of the photoplanarisation step.