Increasing energy demand and environmental consequences associated with the combustion of fossil fuels have led a significant portion of the scientific community to focus on the development of renewable energy technologies. With the success demonstrated by the organometallic community in the catalytic transformation of C-H and C-C bonds, this sub-discipline attempts to expand the hydrocarbyl fundamental understanding to O-H and O-O bonds as a potential means of catalyst development for the water splitting reaction. While a number of catalysts have been realized to facilitate this reaction, they perform under highly oxidizing conditions preventing intermediate characterization and thus preclude detailed understanding of the mechanism of metal mediation. Iridium has shown remarkable potential for catalytic water oxidation in a variety of different coordination environments, despite its high price tag.
This thesis focussed on the design and development of an ancillary ligand framework, to support iridium in carrying out fundamental O-H bond transformation, namely, a highly electron donating “PCsp3P” or “PCcarbeneP” pincer ligand, which could encourage iridium to undergo oxidative addition of an O-H bond of water. The targeted ligand was bis-(2-(dialkylphosphino)phenyl)methane, which was synthesized and characterized with iso-propyl, cyclohexyl and tert-butyl examples. Complexation with iridium showed “benzylic” bound PCsp3P iridium (III) complexes in addition to “benzylidene” anchored PCcarbeneP iridium (I) species (double C-H activation), which interconvert with the addition or removal of hydrogen.
The stability of PCcarbeneP iridium (I) complexes imparted by the ortho-phenylene fused backbone was demonstrated through a variety of substitution reactions resulting in carbon, nitrogen and oxygen ligands bound trans to the anchoring carbene. This family of complexes was employed as precursors to PCsp3P iridium polyhydride complexes with ligand cooperation potential. Furthermore, PCcarbeneP iridium (I) anilido complexes proved to be precursors for 2-electron reductive coupling of acetonitrile and consequently the synthesis of iridium (I) cations, including an aqua-supported example.
Finally, the synthesis and examination of PCcarbeneP iridium (I) hydroxo and unusual μ-oxo complexes was performed to gain insight on the hydrolysis of the Ir-O linkage. Ultimately, Ir-O bond cleavage was evidenced to be initiated by protonation of the bridging oxygen atom.