Exploiting the twofold donor ability of carbodiphosphoranes: Theoretical Studies of [(PPh₃)₂C→EH₂]^q (E^q=Be, B⁺, C²⁺, N³⁺, O ⁴⁺) and synthesis of the dication [(Ph₃P) ₂C=CH₂]²⁺

Quantum chemical calculations at the BP86/TZVPP//BP86/SVP level of theory have been performed for the isoelectronic series of compounds [(PPh ₃)₂C→EH₂]^q (E^q=Be, B⁺, C²⁺, N³⁺, O⁴⁺). The equilibrium geometries and bond dissociation energies were calculated and the nature of the C→E bond was investigated with charge and energy decomposition methods. The dication [(PPh₃)₂C→CH₂]²⁺ could become isolated as a salt compound with two counter ions [AlBr ₄]^-. The X-ray structure analysis of [(PPh ₃)₂C→CH₂]²⁺ gave bond lengths and angles that are in good agreement with the calculated data. The geometry optimization of [(PPh₃)₂C→OH₂] ⁴⁺ gave [(PPh₃)₂C→OH]³⁺ as the equilibrium structure. Bonding analysis of [(PPh₃) ₂C→EH₂]^q shows that [(PPh ₃)₂C→BeH₂] and [(PPh₃) ₂C→BH₂]⁺ possess donor-acceptor bonds in which the σ and πlone-pair electrons of (PPh₃)₂C donate into the vacant orbitals of the acceptor fragment. The multiply charged compounds are better described as substituted olefins [(PPh₃) ₂C=CH₂]²⁺, [(PPh₃) ₂C=NH₂]³⁺, and [(PPh₃) ₂C=OH]³⁺, which possess electron-sharing σ and πbonds that arise from the interaction between the triplet states of [(PPh₃)₂C]²⁺ and the respective fragment CH₂, (NH₂)⁺, and (OH)⁺. The multiply charged cations [(PPh₃)₂C=CH₂]²⁺, [(PPh₃)₂C=NH₂]³⁺, and [(PPh ₃)₂C=OH]³⁺ are calculated to be stable toward dissociation.