Experimental and computational studies of unconventional main group compounds : stable radicals and reactive intermediates

Abstract

Ever since their discovery, radicals have intrigued the minds of experimental and theoretical chemists alike. While the vast majority of radicals are transient species, a large number of stable and persistent radicals are also known. This has enabled the use of radicals in different applications. For example, radicals are highly useful in chemical synthesis due to their selectivity and functional group tolerance. Detailed knowledge of the electronic structure of synthetic intermediates, both radical and non-radical, enables chemists to improve existing synthesis routes and to design completely new ones. This thesis is divided into two parts. The first part begins with an introduction to the chemistry of stable and persistent radicals and presents some seminal discoveries in the field. A brief review of the role of radicals in synthetic chemistry is then given. This is followed by an overview of reactive intermediates in main group chemistry. Some novel methods used in the characterisa- tion of such intermediates are presented along with selected examples of notable results. The second part outlines the most significant findings reported in the five research papers associated with this thesis. The discussion begins with a comprehensive analysis of structural effects induced by redox processes in a 2,2'- biquinoline complex of boron. A new synthetic route to neutral phenothiazinyl radicals via Smiles rearrangement is then presented. This is followed by a discussion of radical intermediates in homocoupling reactions of benzo[b]furans and benzo[b]thiophenes. The role of perfluoroarylboranes in the activation of silane Si–H bonds in hydrosilylation reactions is then presented. Finally, the importance of a thorough structural characterisation is illustrated by a complete scrutiny of a putative intermediate in the formation of tetra-n-butylammonium bicarbonate. Overall, the reported results advance our knowledge of stable main group radicals and provide new insight about reactive intermediates in quintessential chemical reactions.