Rapid one-pot synthesis of pyrrole-appended isocorroles

Abstract

Free-base meso-triarylcorroles have been found to undergo oxidative coupling with an excess of pyrrole in dichloromethane in the presence of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) affording 5/10-pyrrole-appended isocorroles in reasonable yields (35–60%) and in a matter of seconds. The free-base isocorrole ligands could all be complexed to copper with Cu(OAc)₂·H₂O in chloroform/methanol in 55–80% yields. Single-crystal X-ray structures of two of the new compounds (H₂[5-pyr-TpOMePiC] and Cu[10-pyr-TpOMePiC]) revealed planar macrocycles with rms atomic displacements of only 0.02 and 0.06 Å relative to their respective best-fit C₁₉N₄ planes. Both free-base and Cu(II)-complexed isocorroles exhibit richly featured UV-vis-NIR spectra with red/NIR absorption maxima at ∼650 nm and ∼725 nm for the free-bases and ∼800–850 nm for the copper complexes, suggesting potential applications in photodynamic therapy. Cyclic voltammetric analyses of five of the Cu complexes revealed fully reversible redox cycles with multiple oxidation and reduction features.