EPR study of phosphafulvene radical anions

Cyclic voltammetry of phosphafulvene and dibenzophosphafulvene shows that in DMF these compounds are reduced at -1.200 and -1.349 V, respectively. The EPR spectra of the corresponding radical anions, formed by electrochemical reduction or by reaction on a potassium mirror, are recorded between 110 K and room temperature. The g and P-31 hyperfine tensors are measured and compared to those previously obtained for a phosphaalkene radical anion. Ab initio investigations on model phosphaalkene and phosphafulvene radical anions show that, in accord with the experimental results, the electronic structure of these two species are quite different: whereas the unpaired electron is delocalized on the whole P=C(H)R moiety in the phosphaalkenic anion, it is markedly localized on the phosphorus atom in the phosphafulvene anion. Calculated spin densities and charge distributions for phosphafulvene and azafulvene anions are compared.