Photocatalytic H2 Production with a Rhenium/Cobalt System in Water under Acidic Conditions

In photocatalytic H-2 formation, tertiary amines are commonly used as sacrificial electron donors, thereby limiting the pH range for studies in water and the concentration of free protons. We found that ascorbate rapidly reductively quenches the excited state of [Re(CO)(3)(bipy)(py)](+) (bpy = 2,2'- bipyridyl; py = pyridine). In combination with the water reduction catalyst (WRC) [Co{(DO)(DOH)pn}Br-2] [(DO)(DOH)pn =N-2,N-2'-propanediylbis(2,3-butanedione 2-imine 3-oxime)], this system produces H-2 upon irradiation with light under acidic conditions (pH range 2-6) and with significantly enhanced turnover numbers. Furthermore, we observed that, in contrast to similar systems with tertiary amines, oxidized ascorbate (dehydroascorbic acid) is slowly re-reduced during the course of photocatalysis.