An ab initio investigation of the molecular orbital and stabilization energy for substituted lithium carbene cations

Metal carbene cations, found in recent ten years, is a class of unstable intermediates with a high activity. In this paper, with CH2Li+ as a model compound, we first investigated the relative stabilization energies and molecular orbitals of substituted lithium carbene cations by ab initio method. The studies show that the substituents with pi donation have the biggest stabilization because they can form a two electron-multicentre conjugated orbital with carbene carbon and lithium in their planar configurations. In contrast, their stabilization energies are less in perpendicular one. The pi donation plays a leading role in the substituents with both pi donation and a induction. Then the substituents with only a inductive effets have destabilization. The most of LUMO of lithium carbene cations are conjugated molecular orbitals formed by empty p(z) of carbene carbon, lithium and substituents, and the carbene carbon is the major consistent. Their energy levels all are negative values, so they can be considered with a high electrophilic activity and the acting centre should be on the carbene carbon.