UC Irvine

Catecholate-type ligands on transition metals have demonstrated the ability to act as proton and electron reservoirs, enabling diverse chemical transformations. This dissertation investigates how redox-active amidophenolate ligands control the electronic structure, reactivity and physical properties of transition metal complexes, spanning five-coordinate ruthenium complexes as well as group IV charge-transfer dyes.Chapter 2 examines the synthesis of a new series of five-coordinate ruthenium (II) amidophenolate complexes, LnRu(Phap)(PR3)m (L = N2, MeCN, CO, C2H4, Phap = 3,5-di-tert-butyl-(6-phenylamidophenolate), PR3 = PPh3, PMe3, diphenylphosphinoethane). The geometry of these complexes is controlled by the rich electron density donated by the amidophenolate ligand as well as the ancillary phosphines’ steric bulk. X-ray diffraction analysis supported by DFT calculations reveal a high level of covalency between the metal and amidophenolate which leads to intermediate ligand oxidation states. The apical L ligand is readily replaced, allowing these complexes to be a good platform for exploring reactivity. Chapter 3 explores the reactivity of the ruthenium (II) amidophenolate platform. Electrochemical analysis and chemical oxidation showcase the stability of the doubly oxidized state of the complex, suggesting multielectron chemistry. H2 activation is observed across the RuN bond through metal-ligand cooperation. However, exposure to excess H2 leads to the hydrogenation of the ligand and decomposition of the complex. Addition of organic azide produces a stable tetrazene complex which halts productive nitrene transfer, though kinetic studies suggest an imido intermediate. Reaction with phenylacetylene generates a metal vinylidene complex which enables catalytic alkyne homocoupling with moderate selectivity towards the Z-enyne. Chapter 4 probes the effect of the d electrons of the metal and the angle of the donor and acceptor ligands in a series of group IV ligand-to-ligand charge-transfer (LL'CT) complexes. The zirconium complexes display a single low-intensity absorption band observed through UV-Vis spectroscopy, while the titanium analogues exhibit a stronger, broader absorption due to the increased level of metal and ligand orbital mixing. Modifying the bipyridine acceptor tunes the energy of the LL'CT band by up to 0.15 eV. Structural analysis through X-ray diffraction revealed the dihedral angle between the donor and acceptor ligand was near 80 °, which modulated the orbital overlap and subsequently the intensity of the transition.