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 [RuIII(tPaO-κ-N2OPOC)­(py)2]2–, 22– {tPaO5– is the
3-(hydroxo-[2,2′:6′,2″-terpyridine]-6,6″-diyl)­bis­(phosphonate)},
under turnover conditions. We show how the catalyst 22– suffers from oxidative degradation
during water oxidation catalysis and generates the phosphonate–carboxylate
Ru complex [RuII(Hbpc)­(py)2], 3H, where bpc3– 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 [RuII(bpc-κ-N2OP)2] have also been detected.