Photocatalytic Water Reduction and Study of the Formation of FeIFe0 Species in Diiron Catalyst Sytems

• Published in: ChemSusChem 2012-05, Vol.5 (5), p.913-919
• Main Authors: Li, Xueqiang, Wang, Mei, Chen, Lin, Wang, Xiuna, Dong, Jingfeng, Sun, Licheng
• Format: Article
• Language: English
• Subjects: dyes; dyes/pigments; enzymes; hydrogen; iron; photocatalysis; pigments
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201100490

Noble‐metal‐free systems with bio‐inspired diiron dithiolate mimics of the [FeFe]‐hydrogenase active site, namely, [(μ‐pdt)Fe2(CO)5L] [pdt=propanedithiolate; L=P(CH2OH)3 (1), P(CH3)3 (2)], as water reduction catalysts with xanthene dyes as photosensitizers and triethylamine as a sacrificial electron donor were studied for visible‐light‐driven water reduction to hydrogen. These systems display good catalytic activities with the efficiencies in hydrogen evolution of up to 226 turnovers for 1, if Eosin Y was used as the photosensitizer in an environmentally benign solvent (EtOH/H2O) after 15 h of irradiation (λ>450 nm) under optimal conditions. Under all of the conditions adopted, 1 that has a water soluble phosphine ligand, P(CH2OH)3 displayed a higher efficiency than 2, which bears a PMe3 ligand. The photoinduced electron transfer in the systems was studied using fluorescence, transient absorption, time‐resolved UV/Vis, and in situ electron paramagnetic resonance (EPR) spectroscopy. A new electron‐transfer mechanism is proposed for hydrogen evolution by these iron‐based photocatalytic systems. Three gang up on hydrogen: Bioinspired diiron complexes, xanthene dyes, and triethylamine make up three‐component systems that display high turnover numbers for the photoinduced hydrogen production. The quantum yield is determined for this catalytic system. A plausible mechanism for the formation of the FeIFe0 species is proposed, which involves the reduction of the diiron catalyst by the neutral alkyl radical photogenerated from triethylamine.