N-Heterocyclic Vinylidene-Stabilized Phosphorus Biradicaloid

Four-membered biradicaloid compounds containing a N₂ E₂ (E=main group element) framework have been thoroughly investigated; however, the synthesis of stable analogues with a C₂ P₂ skeleton remains a challenge. Base-mediated double C-H functionalization of IPr=CH₂ (1) (IPr=C[N(2,6-iPr₂ -C₆ H₃ )CH]₂ ) with PCl₃ affords [{(IPr)CP}₂ Cl]Cl (2) as a royal blue solid. Treatment of 2 with KC₈ yields the stable phosphorus biradicaloid [(IPr)CP]₂ (3) featuring a four-membered C₂ P₂ ring. Compound 3 is diamagnetic and shows sharp and temperature-independent NMR resonances, revealing its singlet biradicaloid nature. The stability of 3 is attributed to the σ- and π-electron-donating property of the N-heterocyclic vinylidene [(IPr)C] group.