title: Water oxidation with mononuclear ruthenium(II) polypyridine complexes involving a direct Ru(IV)═O pathway in neutral and alkaline media.
abstract: The catalytic water oxidation mechanism proposed for many single-site ruthenium complexes proceeds via the nucleophilic attack of a water molecule on the Ru(V)═O species. In contrast, Ru(II) complexes containing 4-t-butyl-2,6-di-1',8'-(naphthyrid-2'-yl)-pyridine (and its bisbenzo-derivative), an equatorial water, and two axial 4-picolines follow the thermodynamically more favorable "direct pathway" via [Ru(IV)═O](2+), which avoids the higher oxidation state [Ru(V)═O](3+) in neutral and basic media. Our experimental and theoretical results that focus on the pH-dependent onset catalytic potentials indicative of a PCET driven low-energy pathway for the formation of products with an O-O bond (such as [Ru(III)-OOH](2+) and [Ru(IV)-OO](2+)) at an applied potential below the Ru(V)═O/Ru(IV)═O couple clearly support such a mechanism. However, in the cases of [Ru(tpy)(bpy)(OH2)](2+) and [Ru(tpy)(bpm)(OH2)](2+), the formation of the Ru(V)═O species appears to be required before O-O bond formation. The complexes under discussion provide a unique functional model for water oxidation that proceeds by four consecutive PCET steps in neutral and alkaline media.
authors.affiliation: Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, United States.
authors.forename: Yosra M
authors.initials: YM
authors.lastname: Badiei
authors.forename: Dmitry E
authors.initials: DE
authors.lastname: Polyansky
authors.forename: James T
authors.initials: JT
authors.lastname: Muckerman
authors.forename: David J
authors.initials: DJ
authors.lastname: Szalda
authors.forename: Rubabe
authors.initials: R
authors.lastname: Haberdar
authors.forename: Ruifa
authors.initials: R
authors.lastname: Zong
authors.forename: Randolph P
authors.initials: RP
authors.lastname: Thummel
authors.forename: Etsuko
authors.initials: E
authors.lastname: Fujita