Activation of dihydrogen by group-14 substituted germylenes

We have investigated the structural and thermodynamic parameters of group-14 substituted germylenes and their reactivity toward the H₂ molecule using density functional theory (DFT). We conducted the detailed Kohn–Sham molecular orbital (KS-MO) analysis to quantify the effective factors behind the increased reactivity of germylenes in going from C to Sn as substituents. The quantum theory of atoms in molecules (QTAIM), non-covalent interaction (NCI), and natural bond orbital (NBO) analyses revealed the nature of bonds and interactions and demonstrated the reactivity trend of germylenes in the presence of H₂. The results showed that in going from C to Sn, the reactivity increased due to an improvement in $\sigma$-donation interaction between the filled lone-pair orbital of the germylene (LP_Ge) and the $\sigma$*-orbital of H₂, which decreased the reaction barrier ( $∆$E^‡). As the germylene substitution was varied from C to Sn, a significant reactivity was observed for the germylene toward the H₂. This observation was caused by a reduction in steric repulsion between the germylene and the H₂ and less activation energy due to the higher $\sigma$-donation and lower back-donation. We have presented the reactivity of new and rationally designed germylenes toward H₂ using various analyses that will serve as a guide for the activation of small molecules such as H₂, which is employed in many subsequent reactions.