For electron donaQng subsQtuents (sp < 0), the data can be fieed with r of zero. However, for more electron poor subsQtuents (sp > 0) a negaQve slope with r = -1.4 is observed. The data are consistent with a change in the turnover-limiQng sequence as the electronics of the substrate are varied. Prior work has examined the role of substrate electronics in the formylaQon of aryl bromides with this catalyQc system. Based on compeQQon experiments, it has been suggested that more electrondeficient substrates react faster, with Hammee data fifng r = +1.0. 14 There are known issues using compeQQon experiments to extract kineQc informaQon. In this case, the Hammee data likely provide insight into a selecQvity event rather than turnover-limiQng event (vide infra). Based on our observaQons, further kineQc analysis was conducted with both 4-bromoanisole (sp = -0.27) and 4bromobenzotrifluoride (sp = +0.54) to ensure the behavior of both kineQc regimes was captured.