Flash Communication: Microwave-Assisted Synthesis of 2-Alkylphenyl-Substituted (NHC)CuCl Complexes

A base-free, microwave-assisted protocol using Cu2O and NHC·HCl salts is reported, which allows the synthesis of sterically less hindered 2-alkylphenyl-substituted (NHC)CuCl complexes, (SIMeortho)CuCl, (SIPrortho)CuCl, (IMeortho)CuCl and (IPrortho)CuCl; the use of dichloromethane in place of conventionally used tetrahydrofuran as a solvent is the key to success. Structural and NMR analyses show that 2-alkylphenyl substitution efficiently modulates the steric properties of the (NHC)CuCl complexes while largely preserving the electronic properties of the NHC ligands. This work offers a useful strategy for designing diverse NHC ligands, providing a straightforward approach to sterically tunable (NHC)CuCl complexes.