Exploiting the Twofold Donor Ability of Carbodiphosphoranes: Theoretical Studies of [(PPh ) C→EH ] (E =Be, B , C , N , O ) and Synthesis of the Dication [(Ph P) CCH ].

Quantum chemical calculations at the BP86/TZVPP//BP86/SVP level of theory have been performed for the isoelectronic series of compounds [(PPh ) C→EH ] (E =Be, B , C , N , O ). 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 [(PPh ) C→CH ] could become isolated as a salt compound with two counter ions [AlBr ] . The X-ray structure analysis of [(PPh ) C→CH ] gave bond lengths and angles that are in good agreement with the calculated data. The geometry optimization of [(PPh ) C→OH ] gave [(PPh ) C→OH] as the equilibrium structure. Bonding analysis of [(PPh ) C→EH ] shows that [(PPh ) C→BeH ] and [(PPh ) C→BH ] possess donor-acceptor bonds in which the σ and π lone-pair electrons of (PPh ) C donate into the vacant orbitals of the acceptor fragment. The multiply charged compounds are better described as substituted olefins [(PPh ) CCH ] , [(PPh ) CNH ] , and [(PPh ) COH] , which possess electron-sharing σ and π bonds that arise from the interaction between the triplet states of [(PPh ) C] and the respective fragment CH , (NH ) , and (OH) . The multiply charged cations [(PPh ) CCH ] , [(PPh ) CNH ] , and [(PPh ) COH] are calculated to be stable toward dissociation.