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

Abstract

Abstract Artificial photosynthesis could promise cheap and abundant energy but requires the discovery of new water oxidation catalysts. A RuV\u202f=\u202fO 7-coordinate intermediate is implicated in the reactivity of the fastest water oxidation catalysts. Previously we reported in situ characterization of the 7-coordinate [RuV\u202f=\u202fO(L)2(bda)]+ stabilized on the electrode. Here we use ligand protection to stabilize [RuV\u202f=\u202fO(pic)2(dpp)]3+. We report the transformation of [RuII(pic)2(dpp)]2+ (dpp\u202f=\u202f2,9-di-(pyrid-2′-yl)-1,10-phenanthroline, pic\u202f=\u202f4-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 [RuV\u202f=\u202fO(pic)2(dpp)]3+ and its chemical reactivity in solution. Lag phase in the oxygen evolution by [RuII(pic)2(dpp)]2+ is due to catalyst activation via an oxygen atom transfer from [RuV\u202f=\u202fO(pic)2(dpp)]3+ to the polypyridine dpp ligand and formation of [RuIII(pic)2(dpp-NO,NO)]3+. Detailed information regarding catalyst activation during the reaction will enable the design of more active and stable catalysts.