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)<sub>2</sub> and PhNH<sub>2</sub> affording Ph2NH. The primary reaction products of PhB(OH)<sub>2 </sub>with NHC ligands such as BIMe, IMes, and IPr were obtained for the first time, showing that reducing steric hindrance improves the yield of Ph<sub>2</sub>NH and decreases side reactions. However, complete absence of steric shielding around copper prevents product formation.