title: Oxygen-Dependent Photocatalytic Water Reduction with a Ruthenium(imidazolium) Chromophore and a Cobaloxime Catalyst.
abstract: Detailed investigations of a photocatalytic system capable of producing hydrogen under pre-catalytic aerobic conditions are reported. This system consists of the NHC precursor chromophore [Ru(tbbpy)2 (RR'ip)][PF6 ]3 (abbreviated as Ru(RR'ip)[PF6 ]3 ; tbbpy=4,4'-di-tert-butyl-2,2'-bipyridine, RR'ip=1,3-disubstituted-1H-imidazo[4,5-f][1,10]phenanthrolinium), the reduction catalyst Co(dmgH)2 (dmgH=dimethylglyoximato), and the electron donor ascorbic acid (AA). Screening studies with respect to solvent, cobaloxime catalyst, electron donor, pH, and concentrations of the individual components yielded optimized photocatalytic conditions. The system shows high activity based on Ru, with turnover numbers up to 2000 under oxygen-free and pre-catalytic aerobic conditions. The turnover frequency in the latter case was even higher than that for the oxygen-free catalyst system. The Ru complexes show high photostability and their first excited state is primarily located on the RR'ip ligand. X-ray crystallographic analysis of the rigid cyclophane-type ligand dd(ip)2 (Br)2 (dd(ip)2 =1,1',3,3'-bis(2,3,5,6-tetramethyl-1,4-phenylene)bis(methylene)bis(1H-imidazo[4,5-f][1,10]phenanthrolinium)) and the catalytic activity of its Ru complex [{(tbbpy)2 Ru}2 (μ-dd(ip)2 )][PF6 ]6 (abbreviated as Ru2 (dd(ip)2 )[PF6 ]6 ) suggest an intermolecular catalytic cycle.
authors.affiliation: Institute of Inorganic Chemistry, Materials and Catalysis, University of Ulm, Albert-Einstein-Allee 11, 89081, Ulm, Germany), Fax.
authors.forename: Lydia
authors.initials: L
authors.lastname: Petermann
authors.affiliation: Institute of Inorganic Chemistry, Materials and Catalysis, University of Ulm, Albert-Einstein-Allee 11, 89081, Ulm, Germany), Fax.
authors.forename: Robert
authors.initials: R
authors.lastname: Staehle
authors.affiliation: Solid State Chemistry, Helmholtz Institute Ulm (HIU), Helmholtzstraße 11, 89081, Ulm, Germany.
authors.forename: Maxim
authors.initials: M
authors.lastname: Pfeifer
authors.affiliation: Institute of Physical Chemistry and Abbe Center of Photonics, Friedrich Schiller University Jena, Helmholtzweg 4, 07743, Jena, Germany.|Leibniz Institute of Photonic Technology (IPHT), Albert-Einstein-Straße 9, 07745, Jena, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Reichardt
authors.affiliation: Institute of Inorganic Chemistry, Materials and Catalysis, University of Ulm, Albert-Einstein-Allee 11, 89081, Ulm, Germany), Fax.
authors.forename: Dieter
authors.initials: D
authors.lastname: Sorsche
authors.affiliation: Leibniz Institute of Photonic Technology (IPHT), Albert-Einstein-Straße 9, 07745, Jena, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Wächtler
authors.affiliation: Institute of Physical Chemistry and Abbe Center of Photonics, Friedrich Schiller University Jena, Helmholtzweg 4, 07743, Jena, Germany.|Leibniz Institute of Photonic Technology (IPHT), Albert-Einstein-Straße 9, 07745, Jena, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Popp
authors.affiliation: Institute of Physical Chemistry and Abbe Center of Photonics, Friedrich Schiller University Jena, Helmholtzweg 4, 07743, Jena, Germany.|Leibniz Institute of Photonic Technology (IPHT), Albert-Einstein-Straße 9, 07745, Jena, Germany.|Jena Center for Soft Matter (JCSM), Friedrich Schiller University Jena, Philosophenweg 7, 07743, Jena, Germany.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Dietzek
authors.affiliation: Institute of Inorganic Chemistry, Materials and Catalysis, University of Ulm, Albert-Einstein-Allee 11, 89081, Ulm, Germany), Fax. sven.rau@uni-ulm.de.
authors.forename: Sven
authors.initials: S
authors.lastname: Rau
keywords: N-heterocyclic carbene precursors; hydrogen; photocatalysis; pre-catalytic aerobic conditions; ruthenium