The iron(III)-thiolate complex may be an intermediate of the iron reduction and/or an intermediate of the catalytic cycle. To probe the latter proposal, we tested the hydrogenation reaction with 10 mol% Fe II (acac)2(EtOH)2 and 5 mol% PhSSPh in the absence of acacH (Scheme 3a). After 8 h, we observed 8% product formation and incomplete consumption of starting material. In the absence of acacH, the formation of product may proceed through the [Fe III ]-SPh intermediate (Scheme 3b). Our results are consistent with [Fe III ]-SPh being on-cycle or in equilibrium with an on-cycle species.