The original report of olefin hydrogenation by cHAT suggested a mechanism with two intersecting cycles (Scheme 2). In the iron cycle (left/red intermediates), the iron(III) catalyst reacts with PhSiH3 to generate the iron(III) hydride complex, which undergoes mHAT to the unactivated olefin I to generate the alkyl radical II. Then, a thiol HAT cycle (right/blue intermediates) provides the radical trap to generate hydrogenated product III. The thiyl radical then intercepts the iron(II) intermediate to regenerate the iron(III) and thiol. One striking feature of the system is the overall compatibility of intersecting cycles predicated on the mutual roles for Febased catalyst and thiols. A number of experiments supported this mechanistic model: TEMPO inhibition suggests the presence of radical intermediates; deuterium labeling studies support that the EtOH/thiol exchange is the source of the second H•, which is delivered to the alkyl radical through the thiol catalytic cycle. However, important mechanistic questions remained, particularly about the intersection of the two cycles. For example, how does the system avoid the plausible inhibition of the iron catalyst by thiol/thiolate donors? What is the speciation of the iron catalyst? Is the radical trap the free thiol or an Fe-thiol complex? Additionally, can chiral information be introduced into the thiol to influence the stereochemistry of the second C-H bond forming event? These questions were the motivating force behind the study described herein.