An Intramolecular Cobalt-Peptoid Complex as an Effective Catalyst for Light-Driven Water Oxidation at pH 7.

Light-driven water splitting to produce hydrogen as an alternative clean renewable fuel for coping with the future energy crisis is one of the most important challenges of the 21st century. Water oxidation (WO), which is the first step in the water splitting process, is catalyzed in nature by a Mn4CaO5 cluster near pH 6. However, developing a synthetic catalyst for WO, which is based on nonprecious metal ions and can operate near neutral pH (e.g., pH 7.0), is still challenging. Herein, we demonstrate that the bioinspired intramolecular Co-(III)-peptoid complex CoTBE is a stable and efficient molecular catalyst for light-driven WO in phosphate buffer at pH 7 in the presence of a photosensitizer and a sacrificial electron acceptor under irradiation of blue LED light with an intensity of 1.5 mW/cm2, with a maximal turnover number of about 51 in 45 min. Co-(III) is coordinated and stabilized by terpyridine and bipyridine groups incorporated within the peptoid ligand, which also includes an ethanol group that acts as a proton shuttler and thus facilitates the activity at pH 7.