A Mesoionic Carbene as Neutral Ligand for Phosphorescent Cationic Ir(III) Complexes

Two phosphorescent Ir­(III) complexes bearing a mesoionic carbene ligand based on 1,2,3-triazolylidene are obtained for the first time. A silver–iridium transmetalation of the in situ-generated mesoionic carbene affords the cationic dichloro complex [Ir­(trizpy)2Cl2]+ (3, trizpy = 1-benzyl-3-methyl-4-(pyridin-2-yl)-1H-1,2,3-triazolylidene) that reacts with a bis-tetrazolate (b-trz) dianionic ligand to give [Ir­(trizpy)2(b-trz)]+ (5). The new compounds are fully characterized by NMR spectroscopy and mass spectrometry, and the X-ray structure of 3 is determined. The electrochemical behavior is somewhat different compared to most standard cationic iridium complexes. The first oxidation process is shifted to substantially higher potential in both 3 and 5, due to peculiar and different ligand-induced effects in the two cases, which stabilize the highest occupied molecular orbital; reduction processes are centered on the mesoionic carbene ligands. Both compounds exhibit a mostly ligand-centered luminescence band in the blue-green spectral region, substantially stronger in the case of 5 versus 3, both in CH3CN solution and in poly­(methyl methacrylate) matrix at room temperature. Optimized geometries, orbital energies, spin densities, and electronic transitions are determined via density functional theory calculations, which support a full rationalization of the electrochemical and photophysical behavior. This work paves the way for the development of Ir-based emitters with neutral mesoionic carbene ligands and anionic ancillary ligands, a new concept in the area of cationic Ir­(III) complexes.