Within both the industrial and academic laboratory, the coupling of two aryl moieties is a process of significant synthetic use. To achieve such transformations typically requires the use of expensive transition metal catalysts that cannot always be recovered from the reaction mixtures. Consequently, the investigation of biaryl coupling reactions without the requirement for any such catalysts has been of key interest amongst chemists.Throughout the literature, a variety of simple organic molecules have been incorrectly termed as "ligands" or "catalysts" with respect to their role in transition metal-free biaryl coupling reactions. We have discovered that these molecules in fact undergo reaction with a strong base to form an organic electron donor in situ, capable of reducing aryl iodides to their respective radical anions. This reduction can then initiate a cyclic radical reaction mechanism, furnishing the desired biaryl product.A number of key structures, identified through experimental studies, have helped to guide the early theoretical investigations. These allowed the feasibility of the formation of organic electron donors in situ, based on their free energy profiles, to be investigated. The mechanistic understanding gained from these calculations was then applied to rationalise the reactivity of other molecules shown to effectively promote this chemistry. To fully understand the reactivity in this chemistry, the computational application of Marcus Theory was called upon to predict the relative reducing ability of the proposed donor species.Shortcomings of the present protocol for the computational application of Marcus Theory prompted the development of a novel reaction model utilising electron transfer complexes. These complexes more accurately capture the internal reorganisation energy associated with the electron transfer reaction, affording calculated reaction energetics in stronger agreement with experiment. The foundations for the predictive application of this model to identify novel electron donors have been laid. Synthetic routes towards novel electron donor precursors have been identified for future work on this research.
|Date of Award||3 Oct 2016|
- University Of Strathclyde
|Sponsors||EPSRC (Engineering and Physical Sciences Research Council)|
|Supervisor||Tell Tuttle (Supervisor) & John Murphy (Supervisor)|