Mechanistic study of photocatalytic CO reduction using a Ru(ii)-Re(i) supramolecular photocatalyst.

Supramolecular photocatalysts comprising [Ru(diimine)] photosensitiser and -[Re(diimine)(CO){OC(O)OCHNR}] catalyst units can be used to reduce CO to CO with high selectivity, durability and efficiency. In the presence of triethanolamine, the Re catalyst unit efficiently takes up CO to form a carbonate ester complex, and then direct photocatalytic reduction of a low concentration of CO, , 10% CO, can be achieved using this type of supramolecular photocatalyst. In this work, the mechanism of the photocatalytic reduction of CO was investigated applying such a supramolecular photocatalyst, with a carbonate ester ligand, using time-resolved visible and infrared spectroscopies and electrochemical methods. Using time-resolved spectroscopic measurements, the kinetics of the photochemical formation processes of the one-electron-reduced species , which is an essential intermediate in the photocatalytic reaction, were clarified in detail and its electronic structure was elucidated. These studies also showed that is stable for 10 ms in the reaction solution. Cyclic voltammograms measured at various scan rates besides temperature and kinetic analyses of produced by steady-state irradiation indicated that the subsequent reaction of proceeds with an observed first-order rate constant of approximately 1.8 s at 298 K and is a unimolecular reaction, independent of the concentrations of both CO and .