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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.

The topic of this thesis is aromatic oligoamide foldamers. The literary review of the thesis discusses the general features of foldamers and their design and then focuses on the specific examples of aromatic oligoamide foldamers. The experimental part of the thesis discusses the design and preparation of a family of aromatic oligoamide foldamers that can adopt a helical conformation. The folding is directed by intramolecular hydrogen bonding and stabilized by intramolecular aromatic interactions. The focus of the thesis is the analysis of the solid state conformations of ten foldamer analogues. The analysis is based on forty different crystal structures which are determined using single crystal X-ray diffraction. In selected cases the solution behavior of the compounds is analyzed using NMR spectroscopy, and the conformations are compared to DFT calculations. Three types of aromatic oligoamide foldamers were synthesized: a benzene foldamer and its sulfonamide analogue, where two of the amide bonds were replaced by a sulfonamide bond, and a series of pyridine foldamers. The benzene foldamer, while able to fold in a fairly open helical conformation, was found to have high flexibility that hinders the design of consistently folding molecules. DFT calculations showed that the sulfonamide foldamer could fold in a highly folded helical conformation, but the folding was not observed experimentally. Pyridine foldamers have a central 2,6-pyridine core unit that is planar and directs the adjacent amide N-H groups towards the inner face of the folded conformation. The first pyridine foldamer, the analogue of the benzene foldamer, showed improved folding predictability and solubility. The other pyridine foldamers are asymmetric analogues designed to study the effect of the different electron density donating properties, as well as, the presence, size and bulkiness of the substituent to the folding properties of the compounds.

Chelating polydentate ligands play a key role in several areas of modern coordination chemistry. They can be exploited, for example, in catalysis, bioinorganic chemistry, heavy metal abstraction and molecular magnetism. Furthermore, compounds of this type can be found in natural chemicals, commercial products and industrial applications. In this dissertation, several 3d, 4d and 5d transition metal complexes with polydentate amino- and amidophenolate ligands were prepared and their structure, reactivity and magnetic properties were studied with experimental and computational techniques. In the first part of the dissertation, the solid-state structure, reactivity and magnetic properties of 12 novel 3d transition metal complexes were examined. The magnetic behavior of a polynuclear metal complex can be linked to its solid-state structural features to constitute so-called magnetostructural correlations. A clear connection between the M-O-M angles and exchange coupling constants was found in the studied dinuclear Fe(III) complexes. Similar magnetostructural correlations were not equally strong in dinuclear ferromagnetically coupled mixed-valence Mn(II)/Mn(III) system. However, the distortion of the Mn(II) polyhedron from ideal square pyramidal geometry was shown to be related to the strength of the exchange coupling, and together with the M-O-M angle, the nature and strength of the coupling could be estimated. The second part of this work describes the synthesis and behavior of four novel complexes with heavier 4d and 5d transition metals. Two high-valent molybdenum(VI) complexes with non-innocent tetradentate amidophenolate ligand were prepared and thoroughly characterized using a variety of experimental and computational methods. One of the complexes is the first stable molybdenum(VI) amidophenoxide radical. In addition, the versatility of the bidentate aminophenolate ligands was observed in the synthesis of tungsten(VI) complexes which showed unexpected ligand reactivity upon coordination to a metal cation.