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This thesis explores the reactivity of the {Rh(PONOP)}⁺ fragment with the tertiary amine-borane, H₃B·NMe₃, and the secondary amine-borane, H₃B·NMe₂H, with an overall aim of gaining mechanistic insight into the transition metal-catalysed dehydrocoupling of amine-boranes. Chapter One provides a thorough outline of the background that the work reported in this thesis follows on from. Chapter Two describes the synthesis of several {Rh(PONOP)}⁺–based complexes as potential pre-catalysts for amine-borane dehydrocoupling. Their stoichiometric reactivity with H₃B·NMe₃ and H₃B·NMe₂H is described and an amine-borane sigma complex is isolated and fully characterised. A neutral, monohydride complex, Rh(PONOP)H, is also synthesised and fully characterised. At the end of this chapter, adaptation of the PONOP ligand is preliminarily investigated. Chapter Three builds upon Chapter Two and describes an in-depth study of the catalytic dehydrocoupling of H₃B·NMe₂H with {Rh(PONOP)}+. Speciation studies, kinetic measurements and DFT calculations lead to a mechanistic proposal where neutral Rh(PONOP)H is a key intermediate. The roles of amine (NMe2H), boronium ([H₂B(NMe₂H)₂][BArF₄]), and ammonium ([NMe2H2][BArF₄]) in catalysis are also probed. Finally, in Chapter Four the general reactivity of Rh(PONOP)H is explored. In particular, the potential of Rh(PONOP)H as a catalyst for the reduction of CO₂ is probed and Rh(PONOP)H is found to catalytically react with H₃B·NMe₂H in the presence of CO₂.

N-Heterocyclic carbenes have been recognized for their ability to capture CO2 at standard temperature and pressure. This makes them a molecule that could be used for renewable energy synthetic methods. Synthesis and characterization of an IMesCO2 derivative based on bis-mesityl imidazolium chloride was performed, followed by one of four commonly used reduction methods. Methanol is a possible product from a successful reduction through hydrogenation. Efficient production of this species could establish CO2 as a viable renewable energy source. A high pressure hydrogen gas experiment as well as three possible hydride reduction pathways were investigated. Hydrogen gas was used to beak the C2-carbon dioxide bond. This technique explores the results of introducing the IMesCO2 to a neutral hydrogen, which resulted in the formation of formic acid. Hydride reductions were done with lithium aluminum hydride, lithium borohydride and sodium borohydride. They were introduced to the IMesCO2 to donate a hydride to the C2-carbon dioxide bond. The different hydrides varied in selectivity toward IMesCO2 reduction. IMesCO2, possessing a carbonyl group, was subjected to all the hydrides in appropriate solvents. Therefore, the reaction showed the formation of formate for several scenarios. The key to these reductions was the solvent: tetrahydrofuran in conjunction with lithium aluminum hydride; tetrahydrofuran, acetonitrile, and dimethyl sulfoxide used with lithium borohydride; and tetrahydrofuran, acetonitrile, and dimethyl sulfoxide with sodium borohydride. However, there seemed to be a need for a balance between reducing strength of the hydride and selectivity for the carbonyl. To further expand on the idea of using appropriate solvents, sodium tetraphenyl borate was included as an additive to promote reduction via increased solubility, but reactivity with the sodium borohydride did not generally increase. Furthermore, several reaction spectra show evidence of the imidazole ring opening to form unanticipated products. The ring opening may produce some of the reagents that were originally used to make the bis-mesityl imidazolium chloride.