Konfigurations- und konformationsisomere antiaromatische [28]Tetraoxaporphyrinoide(4.2.4.2) und aromatische [26]Tetraoxaporphyrin(4.2.4.2)-dikationen. Eine neue Form molekularer Dynamik in makrocyclischen Systemen

Configurational and Conformational Isomeric Antiaromatic [28]Tetraoxaporphyrinoids(4.2.4.2) and Aromatic [26]Tetraoxaporphyrin(4.2.4.2) Dications. A New Type of Molecular Dynamics in Macrocyclic Systems The [28]tetraoxaporphyrinoids(4.2.4.2) 6 are synthesized by cyclizing Wittig reaction of (E, E)‐5, 5′‐(buta‐1, 3‐diene‐1, 4‐diyl)bis[furan‐2‐carbaldehyde] (8) with (E, E)‐{(buta‐1, 3‐diene‐diyl)bis[(furan‐5, 2‐diyl)methylene]}bis‐[triphenylphosphonium] dibromide (9) and 3, 3′‐{[(E)‐ethene‐1, 2‐diyl]bis(furan‐5, 2‐diyl)}bis[(E)‐prop‐2‐enal] (22) with (E)‐{(ethene‐1, 2‐diyl)bis[(furan‐5.2‐ diy)methylene]}bis[triphenylphosphonium] dibromide (23). An alternative path to get 6 is the McMurry condensation of 8. Four different configurational isomers of 6 could be isolated and characterized by 1H‐NMR spectroscopy. The (Z, EE, Z, EE)‐isomer 6a is the first macrocyclic system where the inner and outer protons of the (E, E)‐dienediyl bridges exchange by rotation around the adjacent single bonds. In the (Z, EE, E, EE)‐isomer 6b, the (E)‐ethenediyl bridge is rotationally active, while in the (E, ZE, E, EZ)‐isomer 6c and in the (E, EZ, E, EZ)‐isomer 6e, the rotation of both (E)‐ethenediyl bridges is observed. When in the dynamic systems the rotation of the active (E)‐double bonds at temperatures T < −90° is frozen, all configurational isomers of 6 appear to be antiaromatic and paratropic. The oxidation of the [28]tetraoxaporphyrinoids 6c and 6e with DDQ yields the aromatic, diatropic [26]tetraoxaporphyrin(4.2.4.2) dications 21e/21e′ both with (E, EZ, E, EZ)‐configuration but different fixed conformations. (Z, EE, Z, EE)‐Isomer 6a is oxidized to give the (Z, EE, Z, EE)‐dication 21a, while the oxidation of 6b yields a mixture of 21a and 21e/21e′. The standard formation enthalpies of the obtained and expected [28]tetraoxaporphyrinoids 6 and [26]tetraoxaporphyrin dications 21 have been calculated with the AM1 method, showing good accordance with the experimental results.