Bonding Situation in Stannocene and Plumbocene N-Heterocyclic Carbene Complexes

A detailed experimental and computational study of a series of stannocene and plumbocene N-heterocyclic carbene complexes is presented. This unique class of group 14 Lewis acid–base adducts was obtained from reactions of the corresponding metallocenes and N-heterocyclic carbenes (NHC) and was structurally characterized by single-crystal X-ray diffraction. The obtained structures show a perpendicular pose of the NHC with respect to the metallocene, hence precluding the maximum interaction between the moieties. The nature of the Sn–CNHC and Pb–CNHC bonds has been investigated by applying natural bond orbital (NBO) analysis and energy decomposition analysis (EDA-NOCV). For the sake of comparison, known stannocene and plumbocene Lewis base complexes have been included in the series. The attractive chemical bonding interactions are around 50% electrostatic, 30% covalent, and 20% dispersion. Indeed, dispersion interactions play a determining role the larger the substituents become. The covalent interactions der...