Proposed Catalytic Cycle. Based on the above experiments and analysis, a catalytic cycle for olefin hydrogenation by iron and thiol cHAT is proposed in Scheme 4. In a catalyst deactivation pathway, Fe III (acac)3 reacts with PhSH to form Fe II (acac)2 (Fe-2) and PhSSPh, proceeding through the iron(III)-thiolate intermediate Fe-1 (Steps A and B). This process is reversible; however, the poor solubility of Fe II (acac)2 limits the rate of oxidation of iron to re-enter the cycle.