AB-INITIO CALCULATIONS ON FORMAMIDINE-X(+) (X=H, LI, NA, MG, AND AL) COMPLEXES

High-level ab initio calculations have been performed to investigate the structures and relative stabilities of complexes between formamidine and different metal monocations. For the sake of completeness protonation was also considered. The relative stabilities of both conformers of formamidine, E and Z, and the interconversion barrier between them have been investigated. The harmonic vibrational frequencies of both isomers and those of the most stable protonated species are reported. Formamidine is predicted to be a very strong base in the gas phase when protonation takes place at the imino nitrogen. This is also the most basic center as far as metal monocation association is concerned. However, the global minima of the potential energy surfaces correspond to association to the less stable conformer of the neutral, Z. Although the structures in which the metal cation bridges both basic centers are minima on the potential energy surface, they lie about 5 kcal/mol above the global minima. Quite interestingly, formamidine presents enhanced binding energies with Mg+ and Al+ which are about 4 kcal/mol greater than those with Li+. The H2NCNH2 carbene isomer is significantly stabilized by cation association in the gas phase.