The Bis(ferrocenyl)phosphenium Ion Revisited.

The bis(ferrocenyl)phosphenium ion, [Fc2 P]+ , 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 [Fc2 P]+ possesses significant intramolecular Fe⋅⋅⋅P contacts, which are predominantly electrostatic and moderate the Lewis acidity. Nonetheless, [Fc2 P]+ undergoes complex formation with the Lewis bases PPh3 and IPr to give the donor-acceptor complexes [Fc2 P(PPh3 )]+ and [Fc2 P(IPr)]+ (IPr=1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene).