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Oxygen‐Dependent Photocatalytic Water Reduction with a Ruthenium(imidazolium) Chromophore and a Cobaloxime Catalyst
Author(s) -
Petermann Lydia,
Staehle Robert,
Pfeifer Maxim,
Reichardt Christian,
Sorsche Dieter,
Wächtler Maria,
Popp Jürgen,
Dietzek Benjamin,
Rau Sven
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201505113
Subject(s) - catalysis , chemistry , ruthenium , turnover number , photocatalysis , chromophore , medicinal chemistry , photochemistry , oxygen , ligand (biochemistry) , electron donor , imidazole , stereochemistry , organic chemistry , receptor , biochemistry
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)][PF 6 ] 3 (abbreviated as Ru(RR′ip)[PF 6 ] 3 ; tbbpy=4,4′‐di‐ tert ‐butyl‐2,2′‐bipyridine, RR′ip=1,3‐disubstituted‐1 H ‐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(1 H ‐imidazo[4,5‐ f ][1,10]phenanthrolinium)) and the catalytic activity of its Ru complex [{(tbbpy) 2 Ru} 2 (μ‐dd(ip) 2 )][PF 6 ] 6 (abbreviated as Ru 2 (dd(ip) 2 )[PF 6 ] 6 ) suggest an intermolecular catalytic cycle.