Access Type

Open Access Dissertation

Date of Award

January 2015

Degree Type


Degree Name




First Advisor

Claudio N. Verani


We designed several redox-active ligand architectures to optimize and understand the redox, electronic, and catalytic properties of their respective cobalt complexes. Ligand design was varied from pentadentate donor phenolate to tetradentate acceptor oxime in order to reduce the overpotential of hydrogen generation in organic solvents. We altered the substitution, axial ligands and axial ligand substitutions to vary electronic and catalytic properties for such tetra- or pentadentate ligand systems. Knowledge of the nature of the active species for catalysis enabled us to design the pentadentate oxime ligand which exhibited rich reaction chemistry along with suitable catalytic property in organic solvent. Presence of several polar groups like -OH and -NH and the absence of any aromatic rings make this complex water soluble which is an added advantage. Additionally, this complex exhibited excellent catalytic properties in water with low onset overpotential and high turnover number. We developed similar redox-active π-acceptor pentadentate phenylene-bridged pyridine-rich ligand which provided extremely versatile reaction chemistry after complexation with cobalt. These complexes displayed catalytic properties at moderate to low-overpotential in acetonitrile with good turnover numbers. Furthermore, the water solubility and tunability of such complexes make them suitable candidates for water reduction. Therefore, water reduction was carried out with these complexes showing low onset overpotentials and high turnover numbers.

Finally, we incorporated [Ru(bpy)2]2+-based photosensitized with one of the catalytic module (cobalt tetradentate oxime) to generate heterobimetallic [RuIICoIII] species which displayed quenching of CoIII upon electron transfer from RuII* excited state.

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