Interestingly, this reduction of iron(III) by thiol is reversible. We found that the reaction of Fe II (acac)2(EtOH)2, PhSSPh, and acetylacetone (acacH) produced Fe III (acac)3 as observed by 1 H NMR spectroscopy (Figure ). However, the efficiency of the iron oxidation pathway is impacted by the low solubility of Fe II (acac)2 in EtOH. To further probe the iron oxidation pathway, we tested the olefin hydrogenation reaction using 10 mol% Fe II (acac)2(EtOH)2, 5 mol% PhSSPh, and 10 mol% acacH (Figure ). After 8 h, we observed 29% yield of hydrogenated product with incomplete consumption of olefin starting material. The observation of very sluggish catalysis indicates that the catalyst may be rescued, but this is not kinetically competent on the timescale of the catalytic reaction. Thus, the reason for the apparent zero-order rate dependence on [Fe] may be that most of the iron in the reaction becomes reduced and inactive, and a small amount (relatively independent of the amount of added iron) is participating in the catalytic reaction.