Theoretical studies suggest that while heavy isocyanide analogs with Ge = P, Sn = P, and Pb = P groups are reactive toward CH₃I in an addition reaction, those with C = P or Si = P groups lack this reactivity.

Abstract

This study examines the reactivity of heavy isocyanide analogs G14 = P-Rea (cAAC→G14 = P–NHB; G14 = group 14 element) in addition reactions with methyl iodide through M06-2X-D3/def2-TZVP computational analysis. Theoretical insights suggest that the doubly bonded G14═P moiety in heavy isocyanide-like molecules (G14 = P-Rea) arises from an electron-sharing interaction between triplet cAAC→G14 and triplet P–NHB fragments. Our theoretical studies indicate that, except for carbon- and silicon-based isocyanides, the Ge = P, Sn = P, and Pb = P analogs readily undergo addition reactions with CH₃I via a back-side S_N2 mechanism. According to EDA-NOCV and FMO theory, the CH₃I addition to G14 = P-Rea is primarily governed by the filled p-π (G14 = P-Rea) → vacant σ* (H₃C–I) orbital interaction, with a minor contribution from the reverse empty p-π* (G14 = P-Rea) ← occupied σ (H₃C–I) interaction. The ASM analysis suggests that the activation barrier for CH₃I addition to G14 = P-Rea molecules is mainly dictated by the deformation energy of CH₃I. Shaik's VBSCD model indicates that the singlet-triplet energy difference in G14 = P-Rea can be a key factor in determining the reaction barrier for CH₃I addition.