Source: Dissertation Abstracts International, Volume: 78-11(E), Section: B.

Adviser: Robert H. Crabtree.

The selective and efficient oxidation of both water and organic molecules is important in biological systems and in industry. This dissertation describes the synthesis of a new IrI(CO)2(pyalc) (pyalc = (2-pyridyl)-2-propanoate) complex that was developed as an atom-efficient precursor for homogeneous oxidation catalysis. This compound gives cleaner catalyst activation and thus was chosen to simplify analysis of the oxidation catalyst species formed by the previously reported Cp*IrIII(pyalc)OH. This thesis presents a comparative study on the chemical and catalytic properties of these two precursors for both water and CH oxidation. Both the Cp*Ir and Jr bis-carbonyl precursors are shown to activate to a blue-colored diiridium IV-,mu-oxo dimer. This activation is concomitant with the loss of the placeholder ligands, Cp* or CO depending on the precursor; Cp* oxidatively degrades in the presence of periodate to form acetic acid, iodate, and other obligatory by-products while CO is lost. The species formed from oxidation of the Ir(CO)2(pyalc) precursor has fewer activation by-products, so the Ir(pyalc) active species can be examined in greater detail both catalytically and spectroscopically, although complete structural analysis is still elusive.

Additionally, this dissertation describes the characterization of a high-valent Cp*Iriv species potentially active for oxidation catalysis. This work demonstrates that the Cp*Ir(pyalc)Cl precursor has at least two distinct active species relevant for CH oxidation. In the presence of external CH substrate, the Cp* remains ligated to the Ir center during catalysis; the active species---believed to be a high-valent Cp*Ir(pyalc)-oxo species---preferentially oxidizes the substrate instead of its own Cp*. If there is no external CH substrate in the reaction mixture, the Cp* will be oxidized and lost, and the active species is then a diiridiumIV-mu-oxo dimer. This work also shows the IrI(CO)2(pyalc) precursor to be a highly active and stereoretentive CH oxidation precatalyst. As in the water oxidation case, the bis-carbonyl precursor is again found to have higher turnover frequency rates than the Cp*Ir analogue, which we attribute to the more efficient activation of the bis-carbonyl complex and the lack of obligatory degradation products from the placeholder ligands. The new bis-carbonyl precursor and active metal-oxo species described here may provide useful insights into oxidation mechanisms and help generate more efficient catalytic systems.