Catalytic Water Oxidation by Ruthenium(II) Quaterpyridine (qpy) Complexes: Evidence for Ruthenium(III) qpy- N, N′′′-dioxide as the Real Catalysts.

Polypyridyl and related ligands have been widely used for the development of water oxidation catalysts. Supposedly these ligands are oxidation-resistant and can stabilize high-oxidation-state intermediates. In this work a series of ruthenium(II) complexes [Ru(qpy)(L)₂]²⁺ (qpy=2,2′:6′,2′′:6′′,2′′′-quaterpyridine; L=substituted pyridine) have been synthesized and found to catalyze Ce^IV-driven water oxidation, with turnover numbers of up to 2100. However, these ruthenium complexes are found to function only as precatalysts; first, they have to be oxidized to the qpy- N, N′′′-dioxide (ONNO) complexes [Ru(ONNO)(L)₂]³⁺ which are the real catalysts for water oxidation. [ABSTRACT FROM AUTHOR]