Carbenaporphyrins: No Longer Missing Ligands in N‐Heterocyclic Carbene Chemistry

The synthesis of an NHC‐containing porphyrinoid ligand is presented. The formally antiaromatic 20 πe− macrocyclic framework can be obtained via a 1,3‐dipolar cycloaddition (“click‐reaction”) to form two triazole moieties which were alkylated to the respective triazolium macrocycle. Deprotonation of the ligand precursor with lithium bases to the respective dilithio carbenaporphyrin complex and transmetallation to scandium lead to complexes that exhibit orange fluorescence. Optical property combined with TD‐DFT studies verify an aromatic character for each heterocyclic moiety rather than an antiaromatic macrocycle in the ligand precursor as well as in the complexes. While the geometric features of the carbenaporphyrin ligand strongly resemble those of porphyrin, DFT calculations reveal a stronger electron‐donating ability of the new ligand. The synthesis of a carbenaporphyrin ligand based on carbazole and triazolylidene is reported. Instead of a macrocyclic aromatic or antiaromatic character, the aromaticity of each heterocyclic moiety is preserved, which results in optical properties different from porphyrins, for example, fluorescence. In Li+ and Sc3+ complexes the ligand reveals striking geometric similarity to porphyrins, but is a stronger electron donor.