The Bis(ferrocenyl)phosphenium Ion Revisited

The bis(ferrocenyl)phosphenium ion, Fc₂P]⁺, reported by Cowley et al. (J. Am. Chem. Soc. 1981 , 103, 714–715), was the only claimed donor‐free divalent phosphenium ion. Our examination of the molecular and electronic structure reveals that Fc₂P]⁺ possesses significant intramolecular Fe???P contacts, which are predominantly electrostatic and moderate the Lewis acidity. Nonetheless, Fc₂P]⁺ undergoes complex formation with the Lewis bases PPh₃ and IPr to give the donor–acceptor complexes Fc₂P(PPh₃)]⁺ and Fc₂P(IPr)]⁺ (IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazole‐2‐ylidene).