Incorporation of Hydrogen-Bonding Functionalities into the Second Coordination Sphere of Iron-Based Water-Oxidation Catalysts

Energy storage and conversion schemes based on environmentally benign chemical fuels will require the discovery of faster, cheaper, and more robust catalysts for the oxygen-evolution reaction (OER). Although the incorporation of pendant bases into molecular catalysts for hydrogen production and utilization has led to enhanced turnover frequencies, the analogous incorporation of pendant bases into molecular catalysts for water oxidation has received little attention. Herein, the syntheses, structures, and catalytic activities of new iron complexes with pendant bases are reported. Of these new complexes, [Fe(L-1)](2+) {L-1 = N,N-dimethyl-N,N-bis(pyridazin-3-ylmethyl)ethane-1,2-diamine} is the most active catalyst. Initial turnover frequencies of 141 and 24 h(-1) were measured by using ceric ammonium nitrate at pH 0.7 and sodium periodate at pH 4.7, respectively. These results suggest that the incorporation of pendant bases into molecular catalysts for water oxidation might be an effective strategy that can be considered in the development of new catalysts for the OER, but will require the careful balance of many factors.