Efficient Regiospecific Conjugated Ring Fusion in N-Confused Porphyrin

Acid-catalyzed exocyclic ring formation in meso-tetrakis(3',5'-dimethoxyphenyl)-2-aza-21-carbaporphyrin takes place regioselectively between the external carbon atom of the confused pyrrole and the ortho-carbon atom of the adjacent meso-aryl group. The ring fusion strongly alters the spectroscopic properties of the macrocycle, but its aromaticity is preserved, as shown by NMR spectroscopy as well as DFT calculations. A tendency to self-associate is observed for partially protonated and nickel (II)-metalated systems. A novel silver(I)-bridged dimer is formed in the reaction of the fused carbaporphyrin with AgBF4. Cyclic voltammetry studies of this system indicate an interaction between the subunits. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)