LAUSR

The first comparative study of group I elements in hydrophosphination catalysis is presented, which identifies hydrophosphination catalyzed by rubidium and cesium compounds for the first time. Catalytic activity increases down the group with a step up in reactivity past the third period. Despite the differences in activity, the trends in reactivity are consistent with nucleophilicity, as evidenced by a Hammett analysis. Radical reactivity was eliminated through EPR monitoring under catalytic conditions. Information from deuterium labeling experiments was limited due to the basicity of the precatalysts and an apparent sigmatropic shift. Overall, enhanced hydrophosphination activity from group I metals is observed that is competitive with transition‐metal catalysts for even modestly activated unsaturated substrates. Optimization through a few key factors may be exportable for further development, even if the substrate scope for group I elements is not yet as broad as it is for transition‐metal catalysts.