To study the catalytic activity of a chemically two-fold reduced catalyst, Rh III phenPer was dissolved in a sodium formate solution (50 mM) in water/acetonitrile mixtures (4:1, v:v) and was either heated in a water bath (to 40°C) or stored at room temperature. Reaction progress was tracked by absorption spectroscopy and quantified with the extinction coefficient of 1,4-NADH (6300 M -1 cm -1 at 340 nm).