Detection of the site protected 7-coordinate RuV = O species and its chemical reactivity to enable catalytic water oxidation

Abstract Artificial photosynthesis could promise cheap and abundant energy but requires the discovery of new water oxidation catalysts. A Ru V  = O 7-coordinate intermediate is implicated in the reactivity of the fastest water oxidation catalysts. Previously we reported in situ characterization of the 7-coordinate [Ru V  = O(L) 2 (bda)] + stabilized on the electrode. Here we use ligand protection to stabilize [Ru V  = O(pic) 2 (dpp)] 3+ . We report the transformation of [Ru II (pic) 2 (dpp)] 2+ (dpp = 2,9-di-(pyrid-2′-yl)-1,10-phenanthroline, pic = 4-picoline) water oxidation catalyst using a combination of electron paramagnetic resonance (EPR), X-ray diffraction, resonance Raman (RR) and density functional theory (DFT). We observe the generation of [Ru V  = O(pic) 2 (dpp)] 3+ and its chemical reactivity in solution. Lag phase in the oxygen evolution by [Ru II (pic) 2 (dpp)] 2+ is due to catalyst activation via an oxygen atom transfer from [Ru V  = O(pic) 2 (dpp)] 3+ to the polypyridine dpp ligand and formation of [Ru III (pic) 2 (dpp-NO,NO)] 3+ . Detailed information regarding catalyst activation during the reaction will enable the design of more active and stable catalysts.