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Aromaticity Switching In Porphyrinoids And Heterorphyrinoids
Lechosław Latos-Grażyński
University of Wrocław, Wrocław, POLAND, llg@wchuwr.pl
One of the ways to study the phenomenon of aromaticity is through the synthesis of new
molecules, which are often specifically designed to test various aspects of the theory or
to pose new problems. 1 Aromaticity of porphyrinoids can be influenced by a variety of
structural modifications, such
as peripheral substitution,
covalent linking of multiple
macrocycles, ring expansion
or contraction, and
introduction of non pyrrolic
subunits. The latter approach
is most readily realized by
replacing one of the pyrrole
rings of the porphyrin with a
different hetero- or carbocyclic fragment. Such a modification can have a profound
influence on the aromaticity of the macrocycle, as demonstrated by the investigated
family of porphyrinoids (1 – 7). The studies have been focused on the physical
manifestations of aromaticity, with a special emphasis on NMR spectroscopy. The aim
of the presentation is to provide a description of porphyrinoid aromaticity and its
connection with linking mode of arene moieties, tautomeric equilibria, intramolecular
rearrangements, reversible peripheral modifications, oxidation state or coordination. The
selected processes act as peculiar reversible switches of aromaticity. For instance a
figure-eight expanded porphyrinoid 5 exhibits an unprecedented controlled switching
between several Möbius and Hückel π-delocalization modes. 2 Similarly the palladium
complexes of vacataporphyrin 2 reveal Hückel aromaticity or Möbius antiaromaticity of
[18]annulene applying a butadiene fragment of vacataporphyrin as a topology selector. 3
(1) Stępień, M., Sprutta, N., Latos-Grażyński, L., Angew. Chem. Int. Ed. 2011, 50, 4288-4340.
(2) Stępień, M.; Latos-Grażyński, L.; Sprutta, N.; Chwalisz, P.; Szterenberg, L. Angew. Chem. Int. Ed.
2007, 46, 7869-7874.
(3) Pacholska-Dudziak, E.; Skonieczny, J.; Pawlicki, M.; Szterenberg, L.; Ciunik, Z.; Latos-
Grażyński, L. J. Am. Chem. Soc. 2008, 130, 6182-6195.