Catalytic dehydroaromatization of alkanes by pincer-ligated iridium complexes

Further understanding of the activation of small molecules by metal complexes is an ongoing goal in organometallic chemistry, and expansion on previously reported reactions is of particular interest. This thesis will discuss expansion of transfer dehydrogenation reactions, specifically multiple transfer dehydrogenation reactions of alkanes leading to aromatic products in one pot. The synthesis of the pincer catalyst used for dehydroaromatization reactions is presented along with full characterization of each step. Optimization of dehydroaromatization reactions was performed on a variety of n-alkane starting materials to maximize yield of alkylbenzene products. Kinetics and concentrations for each starting material are presented to highlight the complexity of these reactions. Despite a mechanism that would suggest otherwise, dehydroaromatization reactions surprisingly yield benzene regardless of the starting n-alkane. This interesting appearance of benzene is discussed along with yields of benzene for various n-alkanes. Mechanistic studies and DFT calculations were performed to elucidate the mechanism through which benzene is formed, and these studies show that benzene forms though a retro-ene mechanism. Attempts to limit or maximize benzene formation were performed by utilizing the information gained through the retro-ene mechanism. Expansion of dehydroaromatization reactions is discussed through multiple dehydroaromatization reactions on the same starting material. Of particular emphasis was the formation of 1,5-dimethylnaphthalene, which is a precursor to the desirable polymer polyethylene naphthalate. 1,5-dimethylnaphthalene was observed as a product from dehydroaromatization reactions, and mechanistic studies were performed to understand the mechanism for the second dehydroaromatization reaction. Attempts to maximize yield of 1,5-dimethylnaphthalene and o-pentyltoluene, which is a precursor to 1,5-dimethylnaphthalene, were performed. Further expansion of dehydroaromatization reactions is discussed through dehydroaromatization of branched alkanes to yield products not obtainable through dehydroaromatization of n-alkanes. Of particular focus is accessing p-xylene and m-xylene via dehydroaromatization. A new synthesis of p-xylene is presented using ethylene as a starting material and utilizing dehydroaromatization of 2-ethyl-1-hexene. Optimization of these reactions is also discussed.Ph.D.Includes bibliographical referencesby Andrew Murray Steffen