The Synthesis Of Copper And Iron Complexes For Water Splitting

Direct decomposition of water into hydrogen chemical energy by solar energy is the frontier research for new energy, which is one of the top ten scientific problems of global concern. The efficient, stable, inexpensive and non-toxic water reduction system for hydrogen production is the core part of water splitting and the key question limiting the solar energy utilization efficiency. Based on copper-iron formatted water reduction system is a benign non-noble metal system, the design and synthesis of novel ligands, the photocatalytic properties and the mechanism of copper photosensitizers and iron catalysts are explored in this paper.Firstly 6,7-dihydro-benzophenanthroline derivatives（A-C） were synthesized by the Friedlander condensation reaction of o-aminobenzaldehyde or anthranilamide derivatives with 1,2-cyclohexanedione, then 5,8-diphenyl-6,7-benzo phenanthroline（D） was obtained by the Pd/C catalytic dehydrogenation aromatization of 5,8-diphenyl-6,7-dihydro-benzophen（C） as raw materials.Heteroleptic copper（I） photosensitizers were studied in a homogeneous photosensitive water splitting system by in situ method, using these phenanthroline derivatives A-D as nitrogen ligand, Xantphos（I） and Thixantphos（II） as phosphine ligand. Thixantphos（II） as P ligand and 5,8-diphenyl-6,7-dihydrodibenzo[b,j][1,10]phenanthroline（C） as N ligand constitutes the most efficient photosensitizer among the tested copper complexes. The highest turnover number of copper was up to 441 and the system achieved a stability of 15 h. Photophysical and electronic chemical charaction showed that the longer exited time of Cu complex is the reason for the higher photosensitive activity. By theoretical calculation it could be proven that ligand-to-ligand charge transfer is the main energy transition method. Noteworthy, for the first time it could be detected and explained why a C-C single bond at 6,7 positions of phenanthroline could significantly increase the light conversion efficiency. This is a result of the lower N ligand contribution in HOMO and the wider energy gap.Kn（?）lker’s irons as efficient reduction catalysts were confirmed at many organic reactions, so far the catalytic ability in water reduction is not explored. Using Cu（Xantphos）（BCP）（CuPS G I） as photosensitizer, in situ generated iron-based Kn（?）lker complexes were found to be efficient catalysts in a fully non-noble metal Cu-Fe photocatalytic water reduction system. These mono-nuclear iron catalysts resulted in up to fifteen times faster hydrogen generation compared to previously reported Fe₃（CO）₁₂. A reductive quenching mechanism was shown to operate by fluorescence experiments.In conclusion, the structure-activity relationship of novel N ligands in Cu photosensitisers were researched and new water reduction catalysts using Kn（?）lker’s irons were developed. All achievements will promote the further development of this non-noble metal water photocatalysis system.