The carbon compounds called “carbones”, L→C←L, have only recently been discovered. These compounds possess two lone-pair orbitals at a dicoordinated carbon atom, thus making them double donors. This new bonding mode has inspired the synthesis of several new compounds. For example, carbodiphosphorane (PPh₃)₂C has been shown to stabilize the previously elusive borenium cation, BH²⁺, in the complex [(PPh₃₎₂C→BH₂]⁺.

Gernot Frenking and co-workers, Philipps-Universität, Marburg, Germany, explored carbones in a joint theoretical and experimental study to gain a better understanding of these compounds.  The theoretical calculations predict that carbodiphosphorane (PPh₃)₂C can stabilize cations other than BH²⁺ by the formation of complexes such as dication [(PPh₃)₂C→CH₂]²⁺ and even trication [(PPh₃)₂C→NH₂]³⁺. This approach can not be extended to the tetracation [(PPh₃)₂C→OH₂]⁴⁺ as this species dissociates to the trication [(PPh₃)₂C→OH]³⁺.

The prediction that [(PPh₃)₂C→CH₂]²⁺(pictured) could be formed was verified by the synthesis and isolation of this dication. However, analysis of the bonding suggests that the compound is better described as the substituted olefin [(PPh₃)₂C=CH₂]²⁺.

• Exploiting the Twofold Donor Ability of Carbodiphosphoranes: Theoretical Studies of [(PPh₃)₂C→EH₂]^q (E^q=Be, B⁺, C²⁺, N³⁺, O⁴⁺) and Synthesis of the Dication [(Ph₃P)₂C=CH₂]²⁺,
  Mehmet Ali Celik, Gernot Frenking, Bernhard Neumüller, Wolfgang Petz,
  ChemPlusChem 2013.
  DOI: 10.1002/cplu.201300169