Structurally Isomerized Bis-Biphenyl Moieties Embedded in Hexaphyrin(3.1.1.3.1.1) and Octaphyrin(1.1.1.0.1.1.1.0)

Twists and Loops: Exploring Lemniscular Vinylogous Benzioctaphyrin(2.0.1.0.2.0.1.0)

Octaphyrins, offer unparalleled opportunities for designing complex molecular architectures with distinct physical and chemical properties. However, lemniscate-shaped benzioctaphyrins remain scantily explored, leaving a gap in understanding how this unconventional geometry/shape influences macrocyclic behaviour. In this study, we explore the design, synthesis, and structural properties of benzioctaphyrin by incorporating the bis-E-stilbene unit, where a vinylene π-bridge connects phenylene rings. The benzioctaphyrin(2.0.1.0.2.0.1.0) adopts a lemniscate topology to alleviate steric strain, with protonation inducing conformational desymmetrization. The presence of a meta-phenylene unit thwarts the global π-conjugation, rendering the macrocycle nonaromatic. Notably, this work represents the first exploration of the oligomeric vinylene group in benzioctaphyrin framework. It offers new insights into how structural modifications influence topology, π-electron delocalization, and macrocyclic flexibility, setting the stage for future advancements in topologically unique porphyrinoid systems.

Iso-dibenzo[g,p]chrysene-Fused Bis-dicarbaporphyrin: Pd Coordination-Induced Global Aromaticity and Stabilization of Double In-Plane Pd(IV) Cations

An iso-dibenzo[g,p]chrysene (DBC)-fused bis-dicarbaporphyrin (4) with two adj-CCNN cores was synthesized. This bis-dicarbaporphyrin can be regarded as an isomer of the previously reported DBC-fused bis-dicarbacorrole obtained by tuning the orientation of the DBC bridge. This subtle change has significant impacts on structure and properties. As prepared, 4 has a highly twisted figure-eight conformation, whereas DBC-fused bis-dicarbacorrole adopts roughly a planar conformation with slight distortion. The incorporation of two Pd(II) cations can induce a transformation in the molecular framework, resulting in a curved, arch-shaped π-system. Utilizing crystallographic data, along with the electron density of delocalized bonds (EDDB), electron localization function-π (ELF-π), harmonic oscillator model of aromaticity (HOMA), the anisotropy of the induced current density (ACID), and nucleus-independent chemical shift (NICS) calculations, a 34π-electron global aromatic pathway was elucidated for the bis-Pd(II) complex (5). The Pd coordination-induced global aromaticity is a distinctive feature that has not been observed in the previously reported bis-Pd complexes of DBC-fused bis-dicarbacorrole. Moreover, the treatment of 5 with CuCl2 leads to the formation of a rare in-plane bis-Pd(IV) complex 6 with two axial coordinated Cl anions. The bis-Pd(IV) complex retains the global aromatic feature and arch-shaped conformation. To our knowledge, this is the first well-defined in-plane bis-Pd(IV) organometallic complex using a porphyrinoid-type macrocyclic ligand.

Porphyrinoid framework embedded with polycyclic aromatic hydrocarbons: new synthetic marvels

The highly conjugated tetrapyrrolic porphyrin macrocycle and its contracted and expanded congeners have been extensively used for a wide range of applications across diverse research domains because of their captivating and intriguing features. Over the years, the porphyrin framework and electronic properties of porphyrinoids have been modified and tuned by replacing one or more pyrrole ring(s) with five- and six-membered heterocycles/carbacycles, and their resulting properties have been explored. In recent times, polycyclic aromatic hydrocarbons (PAHs), such as biphenyl, terphenyl, naphthalene, anthracene, phenanthrene, fluorene, pyrene and dibenzo[g,p]chrysene, have been used to replace one or more pyrrole rings of porphyrinoids, and resulting polycyclic-aromatic-embedded porphyrinoids show unique features that differ from those of other modified porphyrinoids. The polycyclic aromatic hydrocarbons in the porphyrinoid macrocyclic framework induce different π-conjugation pathways in macrocycles, exhibit variable degrees of aromaticity from nonaromatic to aromatic and antiaromatic and provide a unique ligand environment to form stable coordination and organometallic complexes in which metals show uncommon oxidation states and unusual reactivity. This review presents an overview of the synthesis, coordination chemistry, structure and properties of various porphyrinoids with an embedded PAH that have been reported to date.

Synthesis and Studies of Structural Isomers of meso-Fused Dicarbahexaphyrins

Two close structurally related isomers of nonaromatic meso -fused dicarbahexaphyrins were synthesized by condensing one equivalent of fluorene based tripyrrane with one equivalent of pentafluorobenzaldehyde in CH 2 Cl 2 under BF 3 .OEt 2 catalyzed conditions. The cis and trans isomers of meso -fused dicarbahexaphyrins were separated by preparative thin-layer chromatography and isolated pure macrocycles as green solids in 6-7% yields. NMR spectra of cis and trans isomers are quite distinct from each other and trans isomer was very symmetric and showed fewer resonances than cis isomer in NMR. The NMR study supported the nonaromatic nature of both cis and trans isomers of meso -fused dicarbahexaphyrins. DFT optimized structures revealed that the cis isomer adopted a singly twisted puckered conformation whereas the trans isomer displayed a saddle like conformation. Both cis and trans isomers almost showed similar nonaromatic absorption features with slight differences in their peak maxima. However, the protonated derivative of cis isomer showed absorption bands in visible-NIR region with bands extended upto 1000 nm whereas the trans isomer showed strong bands in the visible region. Both cis and trans macrocycles were easier to oxidize and reduce and TD-DFT studies corroborated with the experimental findings.

Kinetic trapping of a cobalt(ii) metallocage using a carbazole-containing expanded carbaporphyrinoid ligand

The meso-unsubstituted expanded porphyrinoid 3, incorporating two carbazole moieties, acts as an effective ligand for Co(ii) and permits the isolation and X-ray diffraction-based characterization of a 6 : 3 metal-to-ligand metallocage complex that converts spontaneously to the constituent 2 : 1 metal-to-ligand metalloring species in chloroform solution. The discrete metalloring is formed directly when the Co(ii) complex is crystallized from supersaturated solutions, whereas crystallization from more dilute solutions favors the metallocage. Studies with two other test cations, Pd(ii) and Zn(ii), revealed exclusive formation of the monomeric metalloring complexes with no evidence of higher order species being formed. Structural, electrochemical and UV-vis-NIR absorption spectral studies provide support for the conclusion that the Pd(ii) complex is less distorted and more effectively conjugated than its Co(ii) and Zn(ii) congeners, an inference further supported by TD-DFT calculations. The findings reported here underscore how expanded porphyrins can support coordination modes, including bimetallic complexes and self-assembled cage structures, that are not necessarily easy to access using more traditional ligand systems.

Carbazole containing expanded carbaporphyrinoid ligand supports the formation of 2 : 1 metal-to-ligand complexes with Pd, Co, and Zn. Solid-state studies also revealed formation of a 6 : 3 metal-to-ligand metallocage in the case of Co complexation.

Recent Advances in the Design and Syntheses of Porphyrinoids by Embedding Higher Analogues of Arene and Pyridine Units

Due to enthralling applications in various fields and augmenting fundamental wisdom, π-conjugated macrocycles in general and porphyrin systems in particular are constantly explored. Subtle modifications of porphyrin structure can amend the rudimentary properties. Pursuing innovative properties provides impetus to underpin arene or pyridine moiety embedded porphyrin derivatives. There have been several reviews related to arene incorporated carbaporphyrinoids; however, recent developments of porphyrin analogues by introducing higher analogues of arenes and pyridine units are not adequately inspected. This mini-review mainly focuses on biphenyl, bipyridine, terphenyl, and mixed arene pyridine embedded porphyrin analogues and their coordination chemistry.

Kinetic versus Thermodynamic Control Over Multiple Conformations of Di-2,7-naphthihexaphyrin(1.1.1.1.1.1)

Di-2,7-naphthihexaphyrin(1.1.1.1.1.1), a non-aromatic carba-analogue of the hexaphyrin(1.1.1.1.1.1), incorporating two built-in 2,7-naphthylene moieties was synthesized as two separate, conformationally locked stereoisomers. Both conformers followed complex protonation pathways involving structurally different species, which can be targeted under kinetic and thermodynamic control. The neutralization of the ultimate dicationic product, accessible from both stereoisomers of the free base, allowed to realize the complex conformational switching cycle involving six structurally different species.

PtCl2 mediated peripheral transformation of carbatriphyrin(3.1.1) into a meso-fused β-β' dimer and its monomer analogue

An unprecedented formation of a meso-fused β-β' carbaporphyrin dimer and its monomer with a keto group was described. These analogues were synthesized from carbatriphyrin(3.1.1.) by a metal assisted strategy using PtCl2 salt in a single step without any prefunctionalized precursors. Upon dimerization, the monomeric ligand with a dianionic core is transformed into a dimeric structure with unique trianionic cores.