The Role of Elemental Factors in the Reactivity of Combination Reactions between Heavy Vinylidene-Like Molecules and Carbene Analogues

Utilizing the M06-2X-D3/def2-TZVP approach, we studied the capture reactions of carbene-like <b>G14Br</b>_<b>2</b> with NHC-supported vinylidene analogs, (NHC):→C═G14(Br)(Tbb) (<b>G14-Rea</b>; G14 = group 14 element). The findings indicate that the C═G14 double bond is formed through electron-sharing interactions between the triplet (NHC):→C and triplet G14(Br)(Tbb) fragments for G14 elements including C, Si, Ge, Sn, and Pb. Our computational study suggests that only vinylidene analogs bearing C═Si and C═Ge double bonds can effectively capture <b>GeBr</b>_<b>2</b> and proceed through a 1,2-migration reaction. In contrast, only <b>CBr</b>_<b>2</b>, <b>SiBr</b>_<b>2</b>, and <b>GeBr</b>_<b>2</b> exhibit successful addition to the (NHC):→C═Ge(Br)(Tbb) double bond. Computational analyses reveal that in the capture reaction of <b>G14Br</b>_<b>2</b> by <b>G14-Rea</b> vinylidene analogs, bonding is primarily governed by a forward interaction (<b>G14-Rea</b> → <b>G14Br</b>_<b>2</b>), while back-donation (<b>G14-Rea</b> ← <b>G14Br</b>_<b>2</b>) plays a minor role. Shaik's model effectively demonstrates that the reaction barrier for capturing carbene-like <b>G14Br</b>_<b>2</b> molecules by NHC-supported vinylidene-like <b>G14-Rea</b> compounds is significantly influenced by the singlet-triplet energy splitting in <b>G14-Rea</b> or carbenic <b>G14Br</b>_<b>2</b> species. The reactivity trend and mechanistic behavior of the vinylidene-like system are systematically examined through the activation strain model of reactivity and energy decomposition analysis.