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.