A simple, straightforward [2+1] condensation of 5,6-diaryldipyrroethene dicarbinols with pyrrole under mild acid-catalyzed conditions resulted in the formation of highly desirable aromatic β-free meso-tetraaryl [14]triphyrins(2.1.1) in 15-18% yields. The triphyrins(2.1.1) are very novel monoanionic tridentate ligands that form metal complexes readily as demonstrated here by preparing Re(I) complexes.

Functionalized meso-tetraaryl triphyrins(2.1.1) containing two meso-iodophenyl groups or a bromo group at the β-pyrrole carbon were synthesized over a sequence of steps.

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.

Various core-modified tellurophene-containing pentaphyrin(2.1.1.1.1)­s were synthesized via (3 + 2) condensation of 16-telluratripyrrane with different heterodiols under mild acid catalyzed conditions in 5–12% yields. The formation of pentaphyrin (2.1.1.1.1) with a N2O2Te core was not successful due to its inherent instability. The new pentaphyrins were characterized and studied by HR-MS, 1D and 2D NMR, X-ray crystallography for one of the pentaphyrins, absorption and DFT/TD-DFT techniques. The NMR studies indicated their nonaromatic nature. The X-ray structure obtained for pentaphyrin(2.1.1.1.1) with N4Te core revealed that the macrocycle exists in a highly distorted nonplanar structure. The DFT studies showed that the macrocycles are nonaromatic and exists in highly distorted nonplanar geometry. Furthermore, as the core heterocyclic groups at ethene moiety were changed from pyrrole to furan to thiophene to benzene, the macrocycles tended toward more planar structures. The absorption spectra of pentaphyrins showed one strong sharp band in the region of 450–540 nm along with a broad band in the region of 700–800 nm. The pentaphyrin(2.1.1.1.1) with N4Te core upon protonation showed distinct color change in solution and large bathochromic shifts in absorption bands with an absorption in the NIR region.

A series of hetero analogues of pentaphyrins(2.1.1.1.1) such as oxapentaphyrins(2.1.1.1.1) and thiapentaphyrins(2.1.1.1.1) were synthesized by 3 + 2 condensation of dipyrroethenedicarbinol with 16-oxatripyrrane/16-thiatripyrrane under mild acid-catalyzed reaction conditions. The stable macrocycles are freely soluble in organic solvents, and their identities were confirmed by a corresponding molecular-ion peak in highresolution mass spectrometry, 1D and 2D NMR spectroscopy, and X-ray structure obtained for one of the oxapentaphyrin(2.1.1.1.1) macrocycles. The crystal structure and NMR studies indicated that the heterocyclic ring, such as furan in oxapentaphyrins(2.1.1.1.1) and thiophene in thiapentaphyrins(2.1.1.1.1), was inverted. In absorption spectra, the macrocycles showed one sharp band at ∼516 nm and one broad band at ∼744 nm. The spectral and X-ray studies supported the nonaromatic nature of these macrocycles. This is in contrast to the recently reported aza analogue of pentaphyrins(2.1.1.1.1), which showed antiaromatic behavior. Upon protonation, the core-modified pentaphyrins(2.1.1.1.1) macrocycles exhibited bathochromically shifted absorption bands with a distinct change in the color of the solution. The 1 H NMR, nucleus-independent chemical shift, and anisotropy-induced current density studies indicated the presence of Mobius aromaticity in the protonated macrocycles. The core-modified pentaphyrins(2.1.1.1.1) can act as good coordinating ligands, as shown here by synthesizing a bis(difluoroborane) complex of one of the thiapentaphyrins(2.1.1.1.1).