Selective Formation of Helical Tetrapyrrin-Fused Porphyrins by Oxidation of β-to-β Linked meso-Aminoporphyrin Dimers

Oxidation of β-to-β directly linked and sulfur-bridged meso-amino Ni^II -porphyrin dimers with PbO₂ gave helical tetrapyrrin (biliverdin analogue)-fused Ni^II -porphyrins. These ring cleaving reactions differ markedly from the previously reported oxidation of a β-β linked Ni^II -porphyrin dimer carrying one amino group, which gave an azepine-fused porphyrin dimer. The tetrapyrrin-fused Ni^II -porphyrins display intense NIR absorption bands at 1200-1400 nm and reversible redox processes because of the highly π-conjugated networks and rigid structures. These tetrapyrrin-fused Ni^II -porphyrins were separated to stable enantiomers, which showed clear Cotton effects in their CD spectra with Δϵ of 10² order.