Catalytic water oxidation mediated by copper-triazolylpyridine complexes

Water oxidation reaction (WOR) is a rather sluggish process in the water splitting that hampers the extraction of hydrogen gas from water in a large scale. It is highly desirable to develop low-cost WOR catalysts to increase the efficacy. Herein two Cu(II) complexes [Cu (DTEL)(2)](n)(ClO4)(2n) (1) and [Cu(DTE)(2)(ClO4)(2)] (2) of two triazolylpyridines, 1-(2-hydroxy)-4-(2-pyridyl)1,2,3-triazole (DTEL) and 1-(2-acetoxymethyl)-4-(2-pyridyl)1,2,3-triazole (DTE), have been synthesized and characterized. The X-ray diffraction analysis revealed that the copper centers of 1 and 2 adopted the octahedral coordination geometry with four N atoms from two DTEL or DTE ligands in the equatorial plane. The two axial sites were weakly ligated by the hydroxyl group of DTEL or perchlorate. Both complexes 1 and 2 were homogenous molecular catalysts boosting the WOR in pH 9.0 phosphate buffer solution with the overpotentials being 568 and 478 mV, rate constants (k(cat)) of 0.1 and 0.39 s(-1), and Faradaic efficiencies of 90% and 93%, respectively. The pendant substituent on the two triazolylpyridine ligands DTEL and DTE apparently influenced the catalysis. A mechanism for the catalytic WOR mediated by 1 and 2 was suggested on the basis of the experimental data. This work illustrated that triazolylpyridines were promising scaffolds for forming metal complexes working as WOR catalysts.