Visible‐Light Unlocked Carbene Insertion and Radical Release in a Structurally Constrained Pincer Phosphorus Compound

Geometrically constrained phosphines have attracted significant attention for their ability to mediate reactions traditionally associated with transition metals. Here, we show that visible‐light excitation unlocks new transition‐metal‐like reactivity in a well‐studied ONO‐pincer phosphine. Photochemical generation of α‐siloxy carbenes enables rapid P─C bond formation, affording bicyclic phosphines with complete diastereocontrol. These phosphine intermediates readily engage with electrophiles to form air‐ and moisture‐stable phosphoranes, which, upon subsequent irradiation, undergo selective P─C bond homolysis, releasing carbon‐centered radicals while regenerating the initial phosphine framework. Time‐resolved EPR spectroscopy and DFT calculations reveal that geometric constraint is crucial for accessing both carbene‐insertion rearrangement and P─C bond homolysis pathways not observed with conventional phosphines. Together, these findings establish a rare light‐driven phosphine → phosphorane →phosphine (P(III) → P(V) → P(III)) reactivity loop and demonstrate how structural constraint enables main‐group centers to perform elementary steps analogous to transition metals.