Understanding the influence of group 13 elements on the reactivity of G13-As-Ge imine analogues in 1,3-addition with methyl iodide

Using the M06-2X-D3/def2-TZVP level of theory, we investigated the 1,3-addition reactions of methyl iodide (CH₃I) with a series of heavy imine analogues, G13=As-Rea (where G13 = group 13 element), which feature a mixed G13-As-Ge backbone. Theoretical evidence reveals that the bonding character of the G13[double bond, length as m-dash]As moiety varies depending on the identity of the G13 center, exhibiting either donor-acceptor (singlet-singlet) or electron-sharing (triplet-triplet) interactions. According to our computational results, all G13=As-Rea compounds-except for the B[double bond, length as m-dash]As analogue-readily undergo 1,3-addition with CH₃I. Energy decomposition analysis combined with natural orbitals for chemical valence (EDA-NOCV), as well as frontier molecular orbital (FMO) theory, indicates that the dominant interaction in these 1,3-addition reactions is the donation from the lone pair on the Ge atom (G13=As-Rea) into the σ* orbital of the C-I bond in CH₃I. This contrasts with a less favorable interaction involving the filled σ(C-I) orbital donating into the vacant p-π* orbital on G13. The calculated activation barriers are largely governed by the deformation energy of the G13=As-Rea species, which, in turn, is significantly influenced by the relativistic effects associated with the heavy G13 central atom. Our computational findings reveal a clear correlation between the mass of the G13 atom and the reactivity of the corresponding G13=As-Rea species in 1,3-addition reactions. As the atomic weight of G13 increases, the relativistic effects become more pronounced, resulting in a contracted ∠G13-As-Ge angle. This geometric feature facilitates superior orbital overlap with CH₃I, thereby lowering the activation barrier and promoting reactivity.