Importance of Polar Effects in Halogen-Atom Transfer from Alkyl Iodides to α‑Aminoalkyl Radicals. A Kinetic and Computational Evaluation of the Role of Structural and Medium Effects.

α-Aminoalkyl radicals have emerged as practical halogen-atom transfer (XAT) agents, enabling the formation of carbon radicals from unactivated alkyl and aryl halides under mild conditions. A recent study correctly revised some of the XAT rate constants for these radicals downward, prompting broad mechanistic conclusions that contradict the key importance of polar effects and challenge the XAT reactivity for α-aminobenzyl radicals. Herein we report a comprehensive kinetic and computational analysis of XAT reactions of α-aminoalkyl and α-aminobenzyl radicals with alkyl iodides under both thermal and photochemical conditions. Laser flash photolysis experiments reveal a clear structure-reactivity relationship shaped by polar and steric effects, which is well supported by the computational results. These findings reaffirm the key importance of the nucleophilic character of α-aminoalkyl radicals in providing significant transition state stabilization to XAT processes. This confirms the prominent role played by polar effects in these reactions and the possibility for reactivity tuning using α-aminobenzyl radicals.