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

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 = 0(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. (C) 2019 Elsevier Inc. All rights reserved.