Effect of steric hindrance of N-heterocyclic carbene in a copper complex on the efficiency of the Chan–Evans–Lam reaction proceeding

This work investigates the effect of the steric hindrance of the NHC ligand in the NHC–CuCl complex on the Chan–Evans–Lam reaction between PhB(OH)₂ and PhNH₂ affording Ph2NH. The primary reaction products of PhB(OH)₂ with NHC ligands such as BIMe, IMes, and IPr were obtained for the first time, showing that reducing steric hindrance improves the yield of Ph₂NH and decreases side reactions. However, complete absence of steric shielding around copper prevents product formation.