Expanding the Landscape of Phosphorous‐Based Open Shell Species: Stable Mono‐, Di‐, and Trianionic Radicals Based on a Contorted Triphosphaalkene

The stepwise reduction of the highly contorted truxene‐based triphosphaalkene 1 using KC 8 led to the isolation of mono‐, di‐, and tri‐anionic species. The solid‐state molecular structures of mono‐ and diradical anionic species were elucidated by single crystal X‐ray diffractions, revealing elongated P−C bonds and a pronounced “indene” aromatization compared to the parent system. All three radical species displayed distinct Electron Paramagnetic Resonance (EPR) spectra, providing compelling evidence for the open‐shell electronic configuration of both the diradical and triradical species—an observation unprecedented in any previously reported phosphorous‐based anionic polyradicals. Mulliken spin density calculations revealed a dominant localization of radical spin on a single phosphorous atom in the monoanion. In the dianion, spin localization is observed on two phosphorous atoms (~34 % each), with a minor contribution from the third phosphorous (0.13 %), while the trianion demonstrates a uniform distribution of spin density (~30 %) across each phosphorous atom.