Fate of the Molecular Ru-Phosphonate Water Oxidation Catalyst under Turnover Conditions

The present work uncovers the oxidative transformations of a recently reported polypyridyl phosphonate-phenoxo Ru-based water oxidation catalyst [Ru-III(tPaO-kappa-(NOpOc)-O-2) (py)(2)](2-), 2(2-) {tPaO(5-) is the 3-(hydroxo-[2,2':6',2 ''-terpyridine]-6,6 ''-diyl)bis-(phosphonate)}, under turnover conditions. We show how the catalyst 2(2-) suffers from oxidative degradation during water oxidation catalysis and generates the phosphonate-carboxylate Ru complex [Ru-II(Hbpc)(py)(2)], 3H, where bpc(3-) is 6'-phosphonato-[2,2'-bipyridine]-6-carboxylate. Complex 3H has been prepared by three different methods, and its oxidative transformations were also studied in detail. Under turnover conditions, complex 3H undergoes a series of transformations that can be monitored by electrochemical techniques including the generation of catalytically active molecular water oxidation catalyst intermediates and RuO2. In addition, catalytically inactive species such as [Ru-II(bpc-kappa-(NOp)-O-2)(2)] have also been detected.

Automated summary

The study reveals the oxidative degradation of a water oxidation catalyst under catalytic conditions, leading to the generation of a new complex with detailed analysis of its oxidative transformations. Under turnover conditions, the complex undergoes a series of transformations including the generation of catalytically active and inactive molecular water oxidation catalyst intermediates.