Electronic Structure and Energy of the Complexes: Methyllithium—Unsaturated Polar Monomer

Abstract

The electronic structure and the energy of CH3Li and its dimer have been calculated using a CNDO/2-method. The geometry of a planar rhombus was adopted for (LiCH3)2. Variation of the rhombus dimensions led to equilibrium distances of Li—Li=1.65 Å and C—C=3.85 Å. The dimerization energy was equal to 430 kcal/ mol. Dimerization decreased the energy of all molecular orbitals including the frontier ones, i.e., it increased the acidity. The calculations for the complexes of LiCH3 with formaldehyde and acrylonitrile were carried out for various relative positions of the components. Sometimes the energy minimum was found when LiCH3 was located out of the plane of the Lewis base near to C atom which is adjacent to the heteroatom. The complexation energies of LiCH3 with acrolein, vinyl formate and methyl acrylate were also calculated and found to be 120, 80 and 140 kcal/mol respectively. It corroborates the assumption that conjugated bases should form with organometallics complexes of higher stability than the unconjugated ones (the complexation energy with formaldehyde was equal to 100 kcal/mol). The complexation energy with acrylonitrile was found to be 180 kcal/mol. This correlates with the higher activity of this monomer when compared to methyl acrylate in anionic systems and correlates with the lower activity of acrylonitrile compared to methyl acrylate if they are in the same system but in the presence of a small amount of strong Lewis base competing for the complexing center.