Charge-Neutral Amidinate-Containing Iridium Complexes Capable of Efficient Photocatalytic Water Reduction

• Published in: Chemistry : a European journal 2013-01, Vol.19 (4), p.1303-1310
• Main Authors: Yu, Zhen-Tao, Yuan, Yong-Jun, Cai, Jian-Guang, Zou, Zhi-Gang
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Catalysts; Chemistry; Concerts; Emission analysis; Hydrogen; iridium; Iridium compounds; Photocatalysis; photochemistry; photosensitizer; Quenching; Reduction; water splitting
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201203029

Two new charge‐neutral iridium complexes, [Ir(tfm‐ppy)2(N,N′‐diisopropyl‐benzamidinate)] (1) and [Ir(tfm‐ppy)2(N,N′‐diisopropyl‐4‐diethylamino‐3,5‐dimethyl‐benzamidinate)] (2) (tfm‐ppy=4‐trifluoromethyl‐2‐phenylpyridine) containing an amidinate ligand and two phenylpyridine ligands were designed and characterised. The photophysical properties, electrochemical behaviours and emission quenching properties of these species were investigated. In concert with the cobalt catalyst [Co(bpy)3]2+, members of this new class of iridium complexes enable the photocatalytic generation of hydrogen from mixed aqueous solutions via an oxidative quenching pathway and display long‐term photostability under constant illumination over 72 h; one of these species achieved a relatively high turnover number of 1880 during this time period. In the case of complex 1, the three‐component homogeneous photocatalytic system proved to be more efficient than a related system containing a charged complex, [Ir(tfm‐ppy)2(dtb‐bpy)]+ (3, dtb‐bpy=4,4′‐di‐tert‐butyl‐2,2′‐dipyridyl). In combination with a rhodium complex as a water reduction catalyst, the performances of the systems using both complexes were also evaluated, and these systems exhibited a more efficient catalytic propensity for water splitting than did the cobalt‐based systems that have been studied previously. The photoreduction of water to hydrogen has been carried out using two charge‐neutral iridium complexes. The photophysical properties, electrochemical behaviours and emission quenching properties of these newly designed species have been investigated. In concert with the catalyst [Co(bpy)3]2+, members of this new class of complexes enable the photocatalytic generation of hydrogen from mixed aqueous solutions via an oxidative quenching pathway (see figure).