meso-Trifluoromethyl-substituted expanded porphyrins

A series of meso-trifluoromethyl-substituted expanded porphyrins, including N-fused [24]pentaphyrin 3, [28]hexaphyrin 4, [32]heptaphyrin 5, [46]decaphyrin 6, and [56]dodecaphyrin 7, were synthesized by means of an acid-catalyzed one-pot condensation reaction of 2-(2,2,2-trifluoro-1-hydroxyethyl)pyrrole (1) as the first examples bearing meso-alkyl substituents. Besides these products, porphyrin 2 and two calix[5]phyrins 8 and 9 were also obtained. [28]Hexaphyrin 4 was quantitatively oxidized to [26]hexaphyrin 14 with MnO(2). These expanded porphyrins have been characterized by mass spectrometry, (1)H and (19)F NMR spectroscopy, and UV/Vis spectroscopy. The single-crystal structures have been determined for 3, 4, 6, 7, and 14. The N-fused [24]pentaphyrin 3 displays a distorted structure containing a tricyclic fused moiety that is similar to those of meso-aryl-substituted counterparts, whereas 8 and 9 are indicated to take roughly planar conformations with an inverted pyrrole opposite to the sp(3)-hybridized meso-carbon atom. Both [28]- and [26]hexaphyrins 4 and 14 have figure-of-eight structures. Solid-state structures of the decaphyrin 6 and dodecaphyrin 7 are remarkable, exhibiting a crescent conformation and an intramolecular two-pitch helical conformation, respectively.     

[32]π Fused Core‐Modified Heptaphyrin with Möbius Aromaticity

A new fused core‐modified 32π heptaphyrin with Möbius aromatic character is reported. The ¹H NMR data indicated a weak Möbius aromaticity at 298 K; however, at 213–183 K, the molecule predominates [4n]π Möbius conformation with strong diatropic ring current, which was further confirmed by X‐ray analysis. The protonation experiment led to preservation of the Möbius aromaticity at 298 K. Nevertheless, the experimental results were further supported by theoretical studies. Overall, this study represents the first example of Möbius aromatic fused core‐modified expanded porphyrin.     

A flexible porphyrin-annulene hybrid: a nonporphyrin conformation for meso-tetraaryldivacataporphyrin

An annulene–porphyrin hybrid, the diaaza‐deficient porphyrin 5,10,15,20‐tetraaryl‐21,23‐divacataporphyrin, has been synthesized by an extrusion of tellurium atom(s) from 5,10,15,20‐tetraaryl‐21,23‐ditelluraporphyrin under treatment with HCl. In addition, a monoaza‐deficient 5,10,15,20‐tetraaryl‐21‐tellura‐23‐vacataporphyrin was formed in the same reaction. The two new members of the vacataporphyrin family were characterized by X‐ray crystallography, as well as UV/Vis and NMR spectroscopy. These aromatic molecules preserve the fundamental structural and spectroscopic features of the parent tetraarylporphyrin. The X‐ray crystal structures of 21,23‐divacataporphyrin and 21‐tellura‐23‐vacataporphyrin show typical porphyrin patterns. The molecules are not strictly planar and show distortion of the annulene moieties. The N22???N24 distances (5.23 and 5.09 Å) are considerably longer than in regular porphyrins. For 21,23‐divacataporphyrin, variable‐temperature ¹H NMR spectroscopy data allowed the identification of divacataporphyrin stereoisomers differentiated by the geometry of the butadiene bridges. The forms remain in thermodynamic equilibrium.