Pictet‐Spengler Synthesis of Fused‐Azepine‐ and 1 H ‐Azocine‐Bridged Ni II Porphyrin Dimers

ABSTRACT 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 ‐ tert buylphenyl‐fused dimer 5Ni in 43% yield but the similar oxidation of 4Ni led to the formation of singly meso ‐ tert buylphenyl‐fused dimer 6Ni in 94% yield. Fused 1 H ‐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.