Archipelago Model Compound Synthesis by Rhodium-catalyzed Annulations of Island-tethered Alkynes with Aromatic Substrates
Creators: Guo, Yaowei
Publisher: name: University of Alberta Library
Year: 2022

<p>Asphaltenes are the most complex constituents in bitumen. They are distinguished from other components in bitumen by high density, high viscosity and a strong tendency to form aggregates in solutions. Asphaltene aggregates may precipitate as a result of small environmental changes, which is problematic for industrial production processes, thus restricting the bitumen resources as an alternative to conventional petroleum. To maximize bitumen resources, studies of asphaltene structures and aggregation behavior were conducted by many petroleum scientists.<br>
By applying several newly developed analytical techniques, different asphaltene structural models have been proposed, one of which is called “archipelago model”. This model describes asphaltenes as multiple polycyclic aromatic hydrocarbon islands linked together by alkyl chain bridges, and attributes asphaltene aggregation to different types of intramolecular and intermolecular associations. Results from many analytical techniques suggest the presence of archipelago structures in asphaltenes, but they have never been fully characterized from asphaltenes so far.<br>
Recent years, a new way to study asphaltenes has been developed, by using synthetic model compounds bearing archipelago structures to imitate asphaltenes. However, due to some factors such as low synthetic yields, low molecular weights, and lack of heteroatoms, these model compounds cannot imitate authentic asphaltenes well, which limits the scope of asphaltene studies.<br>
This dissertation describes an efficient approach to prepare a new library of archipelago model compounds that have high molecular weights, high structural complexity and variable heteroatom inclusion. At first, neutral model compounds were prepared by rhodium-catalyzed annulations of island-tethered alkynes with aryl-boron derivatives. The obtained model compounds all exhibit archipelago structures. Some of them incorporate sulfur, which has rarely been reported previously. These model compounds have compositions that differ from each other but are comparable to authentic asphaltenes, making them reasonable asphaltene models. The solution molecular and supramolecular structures of one model compound were determined by applying 1H-Diffusion ordered NMR spectroscopy (1H-DOSY). This is the first time that 1H-DOSY has been used to characterize a synthetic asphaltene model compound.<br>
Subsequently, nitrogen cation-embedded archipelago compounds were synthesized by rhodium-catalyzed annulations of island-tethered alkynes with nitrogen-containing arenes, which creates a new category of archipelago model compounds that have never been reported. These cationic nitrogen compounds have obviously different features than related neutral model compounds. They are good materials for studying the influence of supramolecular interactions in asphaltene aggregation.<br>
All synthesized archipelago model compounds were characterized by 1H and 13C{1H} NMR spectroscopies, high-resolution mass spectrometry and elemental analysis to confirm structures and purities. Overall, efficient methodologies were successfully developed to provide archipelago model compounds that can better represent native asphaltenes than previously reported.</p>