[RuV(NCN-Me)(bpy)(O)]3+ mediated efficient photo-driven water oxidation

Abstract

The [Ru(NCN-Me)(bpy)H₂O](PF₆)₂ complex (1) (where NCN-Me is the neutral N-methyl-3,5-di(2-pyridyl)pyridinium iodide after deprotonation of the C–H bond) acts as an active catalyst for the visible light driven oxidation of water, when employed with [Ru(bpy)₃]²⁺ as the photosensitizer and Na₂S₂O₈ as the sacrificial electron acceptor in a phosphate buffer solution at pH 6.5, in the presence of a visible light emitting diode (LED; visible light 10.2 mW cm⁻²) at 20 °C. The system exhibits very high activity, achieving 130 turnovers with respect to catalyst and an initial turnover rate TOF of 0.10 s⁻¹. The controlled experiments conducted for the photo-oxidation of water indicate that the catalytic system is dependent upon the following: (i) a visible light source, (ii) photosensitizer, (iii) catalyst and, (iv) pH. During the photocatalysis of water oxidation for 2 h in a phosphate buffer solution at pH 6.5, there was no degradation of the catalyst 1, which indicates the good photo-stability of the complex. The NCN-Me coordinates as a neutral ligand after deprotonation of the central C–H bond; generating the negatively charged carbon center favors a reduction in the redox potential of the complex, which considerably lowers the overpotential to 100 mV at pH 6.5 for the oxidation of water.