Synthesis and structural studies of group 16 peri-substituted naphthalenes and related compounds

Abstract

Understanding how atoms interact is a fundamental aspect of chemistry, biology and materials science. There have been great advances in the knowledge of covalent and ionic bonding over the past twenty years but one of the major challenges for chemistry is to develop full understanding of weak interatomic/intermolecular forces. This thesis describes fundamental studies that develop the basic understanding of weak interactions between heavier polarisable elements. The chosen methodology is to constrain heavy atoms using a rigid naphthalene backbone.

When substituents larger than hydrogen, are positioned at close proximity at the peri-positions of a naphthalene molecule they experience steric strain; the extent of which is dictated by intramolecular interactions. These interactions can be repulsive due to steric hindrance or attractive due to weak or strong bonding.

In efforts to understand the factors which influence distortion in sterically crowded naphthalenes and study possible weak intramolecular interactions between peri-atoms, investigations focussed on previously unknown mixed 1,8-disubstituted naphthalene systems. Mixed phosphorus-chalcogenide species were initially studied; three mixed phosphine compounds of the type Nap[ER][PPh2] were prepared along with their chalcogenides and a series of metal complexes.

The study of interactions between heavy atoms was progressed by investigations into a series of mixed chalcogenide compounds of the type Nap[EPh][E’Ph] (E = S, Se, Te). Subsequent reaction of the chalcogenide systems with the di-halogens, dibromine and diiodine, afforded a mixture of charge transfer and insertion adducts displaying an array of different geometries around the chalcogen atom.

From molecular structural studies, a collection of intramolecular peri-interactions were found, extending from no interaction due to repulsive effects, weak attractive 3c-4e type interactions and one example containing a strong covalent peri-bond. Further weak intramolecular interactions observed include CH-π and E•••E’ type interactions plus π-π stacking between adjacent phenyl rings. It was discovered that the bulk of the peri-atoms is influential on the distance between them, but this is not the only factor determining the naphthalene geometry. Inter- and intramolecular interactions can also have an impact and furthermore the number, size and electronic properties of substituents attached to the peri-atoms can determine molecular distortion.