A series of [24π] dithia meta-benzisapphyrins and [22π] dithia para-benzisapphyrins were synthesized by 3 + 2 condensation of appropriate benzitripyrrane with bithiophene diol under mild acid catalyzed conditions. The dithia m-benzisapphyrins and dithia p-benzisapphyrins were thoroughly characterized by HR-MS, 1D and 2D NMR, absorption, and electrochemical techniques. Our studies showed that dithia m-benzisapphyrins are nonaromatic, whereas the dithia p-benzisapphyrins are aromatic in nature. Thus, we demonstrated here that the dithiabenzisapphyrins can be made aromatic by replacing the m-phenylene moiety of the benzisapphyrin macrocycle with a p-phenylene unit. Furthermore, the studies also indicated that the aromaticity of the dithia p-benzisapphyrins was relatively more compared to the reported heterosapphyrins. The structural and spectral characteristics including aromaticity of the m-benzisapphyrins and p-benzisapphyrins were also discussed with the help of DFT, NICS, and TD-DFT studies.

In contrast to the nonaromatic meta-benziporphyrins, the para-benziporphyrins possess aromatic character depending on the type of five-membered ring present in the macrocyclic core. The effects of changing the para-benziporphyrinic core from C2N3 to C2NSN, C2NSeN, and C2NTeN by replacing the pyrrole with other five-membered heterocycles such as thiophene, selenophene, and tellurophene on aromatic properties of p-benziporphyrins are described here using spectral, electrochemical, X-ray, and density functional theory (DFT) studies. The missing core-modified p-benziporphyrins with C2NSeN and C2NTeN cores were synthesized by condensing 1 equiv of benzitripyrrane and 1,3-benzene-bis­((4-phenyl)­methanol with an appropriate diol such as 2,5-bis­[(p-tolyl)­hyroxymethyl]­selenophene and 2,5-bis­(hydroxymethyl)­tellurophene under mild acid-catalyzed conditions at room temperature and characterized in detail by high-resolution mass spectrometry (HR-MS), one- & two-dimensional NMR, and X-ray crystallography of the one of the macrocycles, Selena p-benziporphyrin. The X-ray structure of Selena p-benziporphyrin revealed that the macrocycle was almost planar apart from the p-phenylene ring, which was deviated by 49.71° from the mean plane of the macrocycle defined by four meso carbons, unlike Selena m-benziporphyrin, which is relatively more distorted. NMR studies revealed that, as the core changes from C2N3 to C2NSN, C2NSeN, and C2NTeN, the diatropic ring current decreases, indicating that the aromatic character also decreases in the same order. X-ray structure and DFT studies also revealed that the distortion in the macrocycle increases as the pyrrole ring of p-benziporphyrin was replaced with other heterocycles such as furan, thiophene, selenophene, and tellurophene and that the tellura p-benziporphyrin was the most distorted macrocycle among core-modified p-benziporphyrins. Absorption and electrochemical properties were in agreement with these observations. Our repeated attempts on metalation of these p-benziporphyrins resulted in the successful synthesis of a Pd­(II) complex of tellura p-benziporphyrin. The Pd­(II) complex was characterized by HR-MS and NMR techniques, and the structure was optimized by DFT. The studies indicated that the Pd­(II) ion was bonded to one of the pyrrolic nitrogens, tellurophene, tellurium, and two chloride ions in distorted square-planar geometry.

A series of first examples of dibenzofuran (DBF)/dibenzothiophene (DBT)-embedded dithia-bis(calix)-sapphyrins were synthesized by condensing 1 equiv of dibenzofuran/dibenzothiophene-based tripyrrane with 1 equiv of [2,2′-bithiophene]-5,5′diylbis(aryl)methanol under mild acid-catalyzed conditions in CH 2 Cl 2 followed by oxidation with DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone) and alumina column chromatographic purification afforded new dithia-bis(calix)-sapphyrins with two meso-sp 3 carbons in 5−7% yields. The DBF/DBT-embedded dithia-bis(calix)-sapphyrins were characterized by HRMS (high-resolution mass spectrometry), 1

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Three novel doubly fused unsymmetrical calixdicarbahexaphyrins were synthesized by mild acid-catalyzed (4+2) condensation of dicarbatetrapyrrane with dipyrroethene diol followed by oxidation. The condensation formed doubly fused calixdicarbahexaphyrins instead of π-conjugated dicarbahexaphyrins, due to the unusual fusion of the pyrrole N with the α-carbon of the adjacent pyrrole ring to form a tripentacyclic ring and one usual fusion of the pyrrole N with the adjacent phenylene C to form a fused moiety containing two pentacycles and one hexacycle ring. Both fusions occurred on one side of the macrocycle, making the macrocycles unsymmetric. The crystal structure obtained for one of the macrocycles exhibited a saddle-shaped structure with two benzene rings and four pyrrole rings connected via two ethylene and four methene meso-carbon atoms. The crystal structure also revealed unusual fusions in the macrocyclic framework and the presence of one sp3 carbon that disrupts the π-electron delocalization. 1H, 1H–1H COSY, NOESY, 13C, and HMBC NMR techniques were used to characterize the macrocycles. The absorption spectra of the macrocycles showed one intense sharp band at ∼485 nm along with a shoulder in the lower-energy region, suggesting its non-aromatic nature. Electrochemical studies indicated their electron rich nature, and DFT/TD-DFT studies corroborated the experimental observations.