Our previous theoretical and experimental studies of water oxidation by the mononuclear ruthenium polypyridyl catalyst [RuII  ]2+ (RuII  = RuII(OH2)(NPM)(pic)2, NPM = 4-t-butyl-2,6-di-(1',8'-naphthyrid-2'-yl)-pyridine and pic = 4-picoline) and related species that contain an aqua ligand in an equatorial position, demonstrated that these catalysts exhibit the remarkable feature of promoting the formation of an O�O bond through the direct proton-coupled electron-transfer (PCET) oxidation of [RuIV  (O)]2+ and H2O to form [RuIII  (OOH)]2+, avoiding a well-known non-PCET RuV(O) pathway. This is important because at high pH the one-electron oxidation of [RuIV  (O)]2+ to [RuV  (O)]3+, as proposed for most other mononuclear ruthenium polypyridyl catalysts as a prerequisite for O�O bond formation, requires a very high potential.Recently, the mononuclear ruthenium(II) complex [RuII  ]2+ (RuII  = RuII(dpp)(pic)2, where dpp is the tetradentate 2,9-dipyrid-2'-yl-1,10-phenanthroline ligand and pic is 4-picoline) reported by Thummel's group in 2008 has been evaluated as a catalyst for water oxidation in artificial photosynthesis, despite the fact that it contains no water molecule in its primary coordination shell. A detailed theoretical characterization of the energetics, thermochemistry, and spectroscopic properties of intermediates allowed us to interpret new electrochemical and photochemical experimental data, and propose a mechanism for the water oxidation process that involves an unprecedented sequence of seven-coordinate ruthenium complexes as intermediates. This mechanism reveals an entirely �new chemistry� for water oxidation by polypyridyl ruthenium complexes of this type. The work at Brookhaven National Laboratory was carried out under contract DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Division of Chemical Sciences, Geosciences, & Biosciences, Office of Basic Energy Sciences.

New water oxidation chemistry of ruthenium complexes with polypyridyl ligands

248th National Meeting (2014)

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