Theoretical Insight: Dual Roles of Electron-Pair Donors and Acceptors in Activating and Mediating Iodine Atom Transfer

Abstract

Lewis bases (Lbs) act as electron-pair donors and react with BH₃ to form Lbs→BH₃ complexes. In catalytic systems, these precursors generate two key reactive species: the Lbs→ BH₂ • radical species, which directly activates the C(sp³)-I bonds in alkyl iodides (R-I) via iodine atom transfer (IAT) , leading to the generation of alkyl radicals; and the Lb→BH ₂ ⁺ cationic species, which facilitates XAT by enhancing C-I bond polarization. The energy barrier for the IAT process mediated solely by Lbs → BH₂• is 19.7 kcal•mol⁻¹, whereas in the presence of the Lb → BH₂⁺ cationic complex, the barrier decreases to 15.9 kcal•mol⁻¹, significantly reducing the kinetic barrier.This work provides a new mechanism for generating alkyl radicals from a theoretical computational perspective. By systematically evaluating 28 distinct Lbs → BH₃ complexes and computationally analyzing key elementary steps and competing reactions, we establish preliminary structure-activity relationships that elucidate the influence of Lewis bases on the XAT mechanism. The synergistic cooperation between engineered Lbs→BH₃ complexes and copper catalysts not only promotes efficient C-N coupling but also provides a robust theoretical foundation and innovative design principles for the development of related catalytic transformations.