Two Macrocycles in One Shot: Synthesis, Spectroscopy, Photophysics, and Tautomerism of 23‐Oxahemiporphycene and 21‐Oxacorrole‐5‐carbaldehyde. Issue 39 (25th June 2018)

• Record Type: Journal Article
• Authors: Ostapko, Jakub; Kelm, Anna; Kijak, Michał; Leśniewska, Barbara; Waluk, Jacek
• Is Part Of: Chemistry. Volume 24:Issue 39(2018)
• Page Start: 9884
• Page End: 9891
• Publication Date: 2018-06-25
• Subjects: corroles -- porphyrinoids -- reaction mechanisms -- structure elucidation -- tautomerism; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201801293
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The synthesis of 23‐oxahemiporphycene, the first monooxa analogue of hemiporphycene, a structural isomer of porphyrin, is reported. Its generation under McMurry reaction conditions is surprisingly accompanied by the appearance of a formyl derivative of oxacorrole, 21‐oxacorrole‐5‐carbaldehyde. A mechanism for the formation of the latter is proposed, relying on pinacol rearrangement of titanium pinacolate. The structures of the most stable tautomeric forms are established for both compounds based on IR and NMR spectra combined with DFT calculations. Spectral and photophysical characteristics are compared with those of structurally similar macrocycles. Replacement of one nitrogen by oxygen in hemiporphycene has only a minor impact. In contrast, for corrole it leads to the enhancement of stability and to strongly reduced rates of nonradiative deactivation of the lowest excited singlet state. This is explained by the planarity of oxacorroles, achieved by removing one of the inner hydrogen atoms from the inner cavity. Unusual crystal packing is observed for the protonated form of 23‐oxahemiporphycene, which exhibits a π–π stacked columnar alignment of positively charged macrocycle units. Abstract : Two‐for‐one : Two different porphyrinoids were obtained in one synthesis. Both 23‐oxahemiporphycene and 21‐oxacorrole‐5‐carbaldehyde were generated under McMurry reaction conditions (see scheme). A mechanism for the formation of the latter is proposed, relying on pinacol rearrangement of titanium pinacolate.