Reaction Progress Kinetic Analysis as a Tool To Reveal Ligand Effects in Ce(IV)-Driven IrCp*-Catalyzed Water Oxidation

A series
of iridium-based complexes have been evaluated in Ce­(IV)-driven
water oxidation catalysis. Detailed kinetic data have been obtained
from UV–vis stopped-flow experiments, and these data have been
analyzed using reaction progress kinetic analysis. The graphical plots
show that there are three clear phases in the reaction: catalyst activation,
water oxidation catalysis, and cerium concentration controlled catalysis
at the end of the reaction. The ligand attached to the IrCp* complex
has a clear influence on both the activation as well as the catalysis.
Some bidentate ligands result in relatively slow catalysis, and the
first-order in iridium supports the presence of mononuclear active
species; however, other bidentates form the more active dinuclear
species. Monodentate ligands allow the formation of bis-μ-oxo bridged dimeric species, supported by kinetics displaying 1.6-order
in [Ir], leading to high reaction rates.