Synthesis and evaluation of indole-substituted N-heterocyclic carbene ligands

[Display omitted] •N-Heterocyclic carbenes with indole side chain synthesized.•Electronic and steric properties different from phenyl-substituted NHCs.•Excellent performance in Cu(I)-catalyzed carboxylation of organoboronic ester. Indole-substituted N-heterocyclic carbene ligands were synthesized and evaluated through both computational and experimental methods. The performances of medium-sized imidazolylidenes IIn3 and IIn4 were comparable to IPr in the Cu(I)-catalyzed carboxylation of organoboronic esters.