Synthesis of peri-substituted acenaphthenes for carbon-heteroatom coupling

Abstract

The work presented in this thesis is an extension to the work started around peri¬-substituted acenaphthenes for carbon-heteroatom coupling, an expansion to dehydrocoupling and dealkacoupling (H–H and C–H bond formation). This thesis explores the synthesis of several classes of peri-substituted heteroatom species and investigates how the internal strain within the acenaphthene molecule is the catalyst for intermolecular coupling reaction tested under various conditions. The main focus of this thesis is the synthesis of peri-substituted acenaphthenes of phosphinous thioesters, using a range of alkyl, cyclic and dialkyl thiols. These underwent the coupling reaction under various reaction conditions; thermal, radical initiator with AIBN and under UV irradiation. Addition of a radical initiator indicates that the mechanism of the coupling reaction is indeed radical. This completed the sulfur series, allowing for comparison not only structurally but also with regards to the coupling reaction. These compounds demonstrate that C–S coupling is viable, although these compounds are sensitive to both air and moisture. This concept was extended to C–N heteroatom coupling, where a series of novel peri-substituted species were synthesised and where possible, structurally authenticated using single crystal X-ray diffraction. These were also subjected to the coupling reaction under both thermal and radical initiator conditions. However, unlike the sulfur series the nitrogen compounds do not couple under radical initiator conditions but do under thermal, indicating a higher activation barrier confirmed by computational calculations. Using one of the nitrogen compounds, the use of acenaphthene amines as a ligand for metal complexes was studied, allowing us to investigate the change in coupling constants between the two peri-atoms. Finally, additional bis(phosphino) monoxides were synthesised to extended the current class of compounds. These species were subjected to the coupling reaction under thermal, radial initiator and UV irradiation, with thermal conditions showing the most promise.