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 → BH₂⁺ 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 15.1 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.