Twist it! The acid-dependent isomerization of homoleptic carbenic iridium(III) complexes

The first successful meridional to facial isomerization of homoleptic carbenic iridium(III) complexes is presented. The Bronsted-acid-mediated procedure allows the conversion of large amounts of material and additionally provides an in situ purification because of precipitation of the target material during the reaction. The pronounced acid-dependency of the reaction yield observed for tris(N-phenyl, N-methyl-benzimidazol-2-yl) iridium(III) and tris(N-phenyl,N-benzyl-benzimidazol-2-yl) iridium(III) was investigated by labelling experiments and quantum chemical calculations. The results reveal a subtle balance between the strength of the acid, the coordinating power of the corresponding base and steric effects of the ligand sphere. Based on these findings, general rules are given for a systematic and material-specific modification of the reaction conditions for the mer-fac isomerization of homoleptic carbenic Ir(III) complexes.