Pictet‐Spengler Synthesis of Fused‐Azepine‐ and 1 <i>H</i> ‐Azocine‐Bridged Ni ^II Porphyrin Dimers

Pictet-Spengler cyclization of meso-amino and meso, meso'-diamino β-β'-linked Ni^II porphyrin dimers 1Ni and 2Ni with paraformaldehyde gave fused azepine-bridged Ni^II porphyrin dimers 3Ni and 4Ni, respectively. Oxidation of 3Ni with FeCl3 and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) provided additionally meso-tertbuylphenyl-fused dimer 5Ni in 43% yield but the similar oxidation of 4Ni led to the formation of singly meso-tertbuylphenyl-fused dimer 6Ni in 94% yield. Fused 1H-azocine-bridged Ni^II porphyrin dimer 8Ni was synthesized by the similar Pictet-Spengler cyclization of meso-amino β-meso' linked Ni^II porphyrin dimer 7Ni. 3Ni and 4Ni were converted to the corresponding free bases and Zn^II complexes, which display fairly red-shifted absorption bands and fluorescence in the near infrared (NIR) region.