Stoichiometric and Catalytic C-H Activations

The primary focus of this Thesis is the study and development of photo-driven processes for the selective partial oxidation of methane. Light alkanes (i.e., methane, ethane, propane) are the primary components of natural gas, which is an abundant resource accounting for approximately a quarter of global energy production. Complications exist regarding the storage of natural gas at these reserve sites and its transportation to other locations for its use due to its gaseous state. Additionally, current methods available for the conversion of natural gas to liquid products are not economically viable for at-wellhead implementation. Natural gas is often flared to carbon dioxide at these “stranded” locations, contributing several hundred million tons of carbon dioxide into the atmosphere annually. Thus, the development of an economically viable process for at-wellhead direct gas-to- liquid conversion of natural gas, with a particular focus on methane-to-methanol, is highly desired.

C–H activation is a platform for the functionalization of organic compounds, including alkanes, to more valuable products. Methods for C–H functionalization include transition metal catalysis and radical-based processes. The synergistic process described in Chapter Two combines the photoredox properties of a photocatalyst with halogen radical chemistry for the C–H functionalization of methane. With this process, we were able to achieve the selective partial oxidation of methane to functionalized product that is stable against over-oxidation with > 350 turnovers and ~60% yield based on methane.

We probe for the extension of our photo-driven process to use of simple transition metal salts in place of a photocatalyst in Chapter Three. Copper salts were found to be unsuccessful as oxidants under the conditions explored for photo-driven methane functionalization. Manganese oxides were found to facilitate photo-driven methane functionalization, albeit stoichiometrically.

In Chapter Four, the functionalization of carbon dioxide to carboxylic acids is discussed. Molecular, homogeneous bifunctional catalysis is proposed as a strategy to activate the C–H bonds of arenes for carboxylation to produce aromatic carboxylic acids. Herein, the activation of dihydrogen is chosen first as a model study. The hydrogenation of carbon dioxide and carbonyl-containing substrates (i.e., aldehydes and ketones) is explored through a tandem approach using computational and experimental chemistry.