A Crystalline Phosphaalkene Radical Anion

Salts
containing phosphaalkene radical anions have been isolated
and characterized by electron paramagnetic resonance (EPR) spectroscopy,
UV–vis absorption spectroscopy, and single-crystal X-ray diffraction.
The radical anions feature
elongated P–C bonds and an aromatization of fulvene compared
to the neutral phosphaalkene. Their EPR spectra and theoretical calculations
indicate the spin density of the radicals mainly resides on phosphorus
atoms. This work provides the first example of a crystalline phosphaalkene
radical anion.