NHC (N-heterocyclic carbene) complexes are versatile in transition metal catalysis due to the stronger NHC-metal bond and the stability of the complex. In this work, we have prepared the NHC-iridium complexes (4-6) processing nitrile functional group on imidazolium ligand and investigated the ligand effect on the catalytic reactions. Herein, we used 1-aryl-3-cyanomethylimidazolium salts as the carbene ligands. The iridium complexes 4 were prepared via transmetalation from the corresponding silver carbene complexes 3. The cationic complexes 5 were prepared by abstraction of the chloride in the corresponding neutral complexes 4 by AgBF4. The coordinated COD (COD = 1,5-cyclooctadiene) of complexes 4 were replaced by carbon monoxide to yield the corresponding carbonyl complexes 6. The catalytic activities on N-alkylation of amines with alcohols of all complexes via hydrogen transfer reduction were examined. We also investigated the weak coordination effect of nitrile on the ligand of a series of iridium complexes in N-alkylation of amines. Furthermore, we studied the C-alkylation of indole with alcohol catalyzed by 4.