Understanding the Impact of Group 14 Elements on the Reactivity of [1 + 2] Cycloaddition Reaction between a Cyclic (Alkyl)(amino)carbene Analogue with a Group 14 Element and a Heavy Acetylene Molecule.

Computational exploration using the density functional theory framework (M06-2X-D3/def2-TZVP) was undertaken to investigate the [1 + 2] cycloaddition reaction between a five-membered-ring heterocyclic carbene analogue (; G14 = group 14 element) and a heavy acetylene molecule (). It was theoretically observed that exclusively , , and demonstrate the capacity to participate in the [1 + 2] cycloaddition reaction with the triply bonded . In addition, only three heavy acetylenes (, , and ) can catalyze the [1 + 2] cycloaddition reaction with . Our theoretical findings elucidated that the reactivity trend observed in these [1 + 2] cycloaddition reactions primarily arise from the deformation energies of the distorted . Also, our study reveals that the bonding characteristics of their respective transition states are controlled by the singlet-singlet interaction (donor-acceptor interaction), rather than the triplet-triplet interaction (electron-sharing interaction). Additionally, our work demonstrates that the bonding behavior between and is predominantly determined by the filled -π orbital of (HOMO) → the empty perpendicular -π orbital of (LUMO), rather than the vacant -π* orbital of LUMO) ← the filled sp orbital of (HOMO).