Activation and Transformation of C-F and C-H Bonds Through Late Transition Metal Binding
Mueller, Benjamin Richard Joseph
The activation and transformation of relatively inert bonds through transition metal mediated reactions is central to the field of organometallic chemistry. The ability of transition metal d orbitals to engage in backbonding interactions with ligands presents avenues of reactivity that are not accessible using traditional organic chemistry techniques. This work focuses on the activation of carbon-fluorine and carbon-hydrogen bonds through binding to ruthenium, iridium, and nickel. A mechanistic investigation of ruthenium-catalyzed nucleophilic aromatic substitution (SNAr) revealed key details about the thermodynamics of the system and the catalyst resting state, ultimately resulting in the development of a new precatalyst. The extent of product inhibition in this system, a parameter which has been the subject of speculation but not previously studied in detail, was quantified, revealing the magnitude of the energetic challenge to effective catalysis through this means of substrate activation. Additional experiments explored the scope of this transformation and the role of reported additives. The synthesis and reactivity of Lewis-base directed cationic iridium alkoxycarbenes are described. Cleavage of the alkoxycarbene carbon-oxygen bond results in an iridium benzylidene with azaquinone methide character based on X-ray parameters and calculations. This iridium benzylidene shows reactivity towards ethylene, and the formation of the corresponding ethylbenzylidene through an unusual carbon-carbon bond forming reaction. Efforts to develop catalytic reactions which make use of iridium alkoxycarbene ligands as intermediates are described. Finally, work towards the synthesis of model complexes of the metalloenzyme lactate racemase are described. The synthesis of three generations of ligands revealed interesting insights into the electronic properties of the cofactor, and lay groundwork for further synthesis of structural models of the enzyme active site.