title: [Rh(III)(dmbpy)2Cl2]+ as a highly efficient catalyst for visible-light-driven hydrogen production in pure water: comparison with other rhodium catalysts.
abstract: We report a very efficient homogeneous system for the visible-light-driven hydrogen production in pure aqueous solution at room temperature. This comprises [Rh(III) (dmbpy)(2)Cl(2)]Cl (1) as catalyst, [Ru(bpy)(3)]Cl(2) (PS1) as photosensitizer, and ascorbate as sacrificial electron donor. Comparative studies in aqueous solutions also performed with other known rhodium catalysts, or with an iridium photosensitizer, show that 1) the PS1/1/ascorbate/ascorbic acid system is by far the most active rhodium-based homogeneous photocatalytic system for hydrogen production in a purely aqueous medium when compared to the previously reported rhodium catalysts, Na(3)[Rh(I) (dpm)(3)Cl] and [Rh(III)(bpy)Cp*(H(2)O)]SO(4) and 2) the system is less efficient when [Ir(III) (ppy)(2)(bpy)]Cl(PS2) is used as photosensitizer. Because catalyst 1 is the most efficient rhodium-based H(2)-evolving catalyst in water, the performance limits of this complex were further investigated by varying the PS1/1 ratio at pH 4.0. Under optimal conditions, the system gives up to 1010 turnovers versus the catalyst with an initial turnover frequency as high as 857 TON h(-1). Nanosecond transient absorption spectroscopy measurements show that the initial step of the photocatalytic H(2)-evolution mechanism is a reductive quenching of the PS1 excited state by ascorbate, leading to the reduced form of PS1, which is then able to reduce [Rh(III)(dmbpy)(2)Cl(2)](+) to [Rh(I)(dmbpy)(2)](+). This reduced species can react with protons to yield the hydride [Rh(III)(H)(dmbpy)(2)(H(2)O)](2+), which is the key intermediate for the H(2) production.
authors.affiliation: Université Joseph Fourier Grenoble 1/CNRS, Département de Chimie Moléculaire, UMR 5250, Institut de Chimie Moléculaire de Grenoble, FR-CNRS-2607, Laboratoire de Chimie Inorganique Rédox, BP 53, 38041 Grenoble Cedex 9, France.
authors.forename: Thibaut
authors.initials: T
authors.lastname: Stoll
authors.forename: Marcello
authors.initials: M
authors.lastname: Gennari
authors.forename: Isabel
authors.initials: I
authors.lastname: Serrano
authors.forename: Jérôme
authors.initials: J
authors.lastname: Fortage
authors.forename: Jérôme
authors.initials: J
authors.lastname: Chauvin
authors.forename: Fabrice
authors.initials: F
authors.lastname: Odobel
authors.forename: Mateusz
authors.initials: M
authors.lastname: Rebarz
authors.forename: Olivier
authors.initials: O
authors.lastname: Poizat
authors.forename: Michel
authors.initials: M
authors.lastname: Sliwa
authors.forename: Alain
authors.initials: A
authors.lastname: Deronzier
authors.forename: Marie-Noëlle
authors.initials: MN
authors.lastname: Collomb