N‐Heterocyclic Vinylidene‐Stabilized Phosphorus Biradicaloid

Four‐membered biradicaloid compounds containing a N2E2 (E=main group element) framework have been thoroughly investigated; however, the synthesis of stable analogues with a C2P2 skeleton remains a challenge. Base‐mediated double C−H functionalization of IPr=CH2 (1) (IPr=C[N(2,6‐iPr2‐C6H3)CH]2) with PCl3 affords [{(IPr)CP}2Cl]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 C2P2 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. e‐Greening the blue: Two‐electron reduction of [(IPr)CP)2Cl]Cl (1) (IPr=C[N(2,6‐iPr2C6H3)CH]2) affords the N‐heterocyclic vinylidene‐stabilized singlet biradicaloid compound [(IPr)CP)]2 (2). Compound 2 is diamagnetic and exhibits temperature‐independent sharp NMR resonances.