Ruthenium Complexes as Molecular Water Oxidation Catalysts

Over the last four decades, the field of molecular water oxidation catalysis has received a prodigious progress. However, there are still a few challenges ahead in order to see molecular catalysts in working artificial photosynthetic devices. Among them, it is still necessary to reach optimum catalytic rates on (photo)electrode surfaces and this is directly related to the mechanistic pathways followed by a specific catalyst. To reach this goal, the different steps and multiple intermediates involved in the whole catalytic process must be investigated.

This thesis focuses on the synthesis of ruthenium complexes and the study of their structural, spectroscopic, chemical and electrochemical properties as well as their capacity to catalyse the oxidation of water to dioxygen reaction. In particular, a series of compounds has been prepared which are included in two main families.

1) Ruthenium complexes containing a key equatorial tetradentate dianionic ligand that coordinates through two pyridinic groups and two carboxylate groups providing high electronic density to the metallic centre. Second coordination sphere effects and reaction mechanism have been thoroughly explored.

 2) Ruthenium complexes containing an equatorial neutral ligand of the bis(phenantroline) family. This complex converts to a Ru-aquo complex being active for the water oxidation reaction. The latter evolves to a dimeric complex, which contains an oxo bridge, blocking the catalysis. Detailed kinetic studies of all the transformations are presented.

 Overall, this thesis highlights the complexity of ruthenium chemistry and its implications in the water oxidation reaction.