Formation and Structure of a Stable Monoradical Cation by Reduction of a Diphosphafulvenium Salt

One-electron reduction of a diphosphafulvenium dication gives the first stable diphosphafulvenium monoradical cation (see scheme). An X-ray crystal structure analysis, EPR measurements, and DFT calculations clearly show that reduction takes place at the exocyclic double bond and that the excess of electron density is stabilized by the two electron-withdrawing phosphonium groups (see SOMO; P orange, C dark gray, H light gray).