ABSTRACT 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.
Ghosh et al. (Thu,) studied this question.