Certain ruthenium polypyridine complexes have been used as catalysts for water oxidation, with ceric ammonium nitrate (CAN) being a popular choice for the sacrificial oxidant (E<sub>ox</sub> = +1.71 V). However, such chemically driven systems may suffer from oxidative decay of the catalyst due to the harsh oxidizing conditions. Ligand design clearly plays a crucial role in determining the overall activity and stability of the catalyst. This work provides evidence for the oxidative transformation of the 2-(2'-hydroxyphenyl) derivative of 1,10-phenanthroline (phen) into a 2-carboxy-phen in the presence of CAN, while the ligand is still bound to the metal. Interestingly, the carboxy derivative was found to be highly active for O<sub>2</sub> evolution and resistant to further degradation. Incorporating a methyl substituent on the phenyl ring slows down this conversion. Exploration of an analogous series of 2,2'-bipyridine-based systems yielded much lower activity compared to the phen derivatives, underlining the importance of designing robust catalysts, as well as moving towards more benign oxidizing agents.

Oxidative transformation of a Ru-bound ligand during chemically driven water oxidation

254th National Meeting (2017)

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