Pyrrolyl‐Appended Zinc Porphodimethenes: Branched Oligopyrrole Products From the Templated One‐Pot Isoporphyrin Synthesis

Abstract

AbstractThe one‐pot synthesis of zinc isoporphyrins from pyrrole, an aryl aldehyde and zinc acetate was investigated with regard to the formation of by‐products. The optical spectra of the product mixtures differ strongly from each other depending on the aldehyde used and the water content in the solvent mixture of the condensation step. The compounds belonging to the two most prominent bands at approx. 500 nm and at approx. 640 nm could be isolated and structurally characterised. These are the homoleptic complexes (dipy)2Zn with a dipyrrolic ligand, and unexpected zinc‐tripyrrin species (trpy)ZnCl, respectively. The tripyrrin species further react under the conditions of chromatography to green intermediates and yellow end products, whose mass spectroscopic investigations indicate dimers and loss of one ZnCl2 equivalent. The final products could be crystallographically identified as zinc‐porphodimethene complexes and analysed with respect to the stereochemical situation and optical behaviour. In one case, the green intermediate form could be enriched. The investigations indicate a helical pentapyrrolic zinc complex with a non‐coordinated pyrrolyl side arm and give clues to the stereochemical course of the stepwise dimerisation.