The mononuclear ruthenium(II) complex [Ru]2+ (Ru = Ru(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 (Inorg. Chem. 2008, 47, 1835-1848) that contains no water molecule in its primary coordination shell is evaluated as a catalyst for water oxidation in artificial photosynthesis. A detailed theoretical characterization of the energetics, thermochemistry, and spectroscopic properties of intermediates allowed us to interpret new electrochemical and spectroscopic experimental data, and propose a mechanism for the water oxidation process that involves an unprecedented sequence of seven-coordinate ruthenium complexes as intermediates. This analysis provides insights into a mechanism that generates four electrons and four protons in the solution and a gas-phase oxygen molecule at different pH values. On the basis of the calculations and corroborated substantially by experiments, the catalytic cycle goes through [2Ru III]3+ and [2RuV(O)]3+ to [1RuIV(OOH)]3+ then [2Ru III(···3O2)]3+ at pH 0, and through [3RuIV(O)]2+, [ 2RuV(O)]3+, and [1Ru IV(OO)]2+ at pH 9 before reaching the same [ 2RuIII(···3O 2)]3+ species, from which the liberation of the weakly bound O2 might require an additional oxidation to form [ 3RuIV(O)]2+ to initiate further cycles involving all seven-coordinate species.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry