Tetraphenyl-p-benziporphyrin: a carbaporphyrinoid with two linked carbon atoms in the coordination core

Carbazole-embedded p-benziporphyrinoid: synthesis, structure and a reversible chemodosimeter for mercury(II) ions

The first carbazole-embedded p-benziporphyrinoid is synthesized by a [3+1] acid-catalyzed condensation between appropriate coupling partners. The macrocycle 1 exhibited orange emission and showed a large Stokes shift of 5831 cm-1. Intriguingly, it shows a selective affinity towards Hg2+ ions over other metal-ions in a reversible manner. Job's plot confirmed the 1 : 1 stoichiometry with unambiguous confirmation of both 1 and 1-Hg by single crystal X-ray analysis.

Breaking Global Diatropic Current to Tame Diradicaloid Character: Thiele's Hydrocarbon Under Macrocyclic Constraints

A diradical/biradical character of organic derivatives is one of the key aspects of contemporary research focusing on the fundamental studies followed by potential applicability relying on the unique optical, electronic, or magnetic properties assigned to unpaired electrons. A precise involvement of two p-phenylenes into a cyclophane-like conjugated, diatropic system creates a flexible molecule with the two different characters of both subunits (benzene and quinone) imprinting into the structure a Kekulé delocalized system. A dynamic of both carbocyclic subunits, and their mutual interaction generates a singlet open-shell state (J=-1.25 kcal/mol) as documented spectroscopically (NMR and EPR). The extended theoretical analysis has proved a correlation between dihedral angle and the diradicaloid character that shifts from a closed-shell singlet to an open-shell state, eventually showing the y0=0.86 for 78 degrees and ΔEST=-0.34 kcal/mol.

Near-infrared absorbing nonaromatic core-modified meta-benzicalixhexaphyrin(1.1.1.1.1.1)s

Stable nonaromatic core-modified m-benzicalixhexaphyrins containing one m-phenylene ring, four pyrrole rings and one heterocyclic ring such as furan, thiophene, selenophene and telluorophene connected via four meso-sp2 carbons and two meso-sp3 carbons in a macrocyclic framework were synthesized. The m-benzitripyrrane dicarbinol was condensed with 16-heterocycle tripyrranes under mild acid-catalyzed and inert conditions followed by open-air oxidation with DDQ to obtain macrocycles in 2-5% yields. The presence of two -OH groups in the cis-orientation at two different meso-sp3 carbons, which are adjacent to the m-phenylene ring of the macrocycle, was confirmed through detailed 1D and 2D NMR studies. NMR studies indicated that the heterocyclic ring present across the m-phenylene ring prefers to be in the inverted conformation in these macrocycles. The macrocycles exhibited two intense absorption bands in the lower wavelength region of 320-580 nm and one broad absorption band that extended from the visible to NIR region, and the protonated derivatives of such macrocycles showed significant bathochromic shifts to the NIR region. Additionally, the electrochemical studies indicated that the macrocycles underwent easier oxidation due to their electron-rich nature. DFT studies revealed that the macrocycles adopted highly distorted conformation, which was consistent with experimental results.

Di(p-dibenzi)[40]decaphyrin(1.0.0.0.0.1.0.0.0.0) PdII Complex: A Weakly Hückel 38π-Aromatic Macrocycle

Di(p-benzi)[40]decaphyrin(1.0.0.0.0.1.0.0.0.0) BF2 complex and tris(p-benzi)[60]pentadecaphyrin(1.0.0.0.0.1.0.0.0.0.1.0.0.0.0) BF2 complex were synthesized by Suzuki-Miyaura coupling of α,α'-diborylated tetrapyrrole BF2 -complex with 1,4-diiodobenzene. Bis-BF2 complex was converted to bis-PdII complex via its free base. Macrocycles bis-BF2 and tris-BF2 complex take Möbius topology but are nonaromatic, since the macrocyclic conjugation is disrupted by the locally aromatic 1,4-phenylene units. In contrast, bis-PdII complex is a weakly Hückel 38π-aromatic macrocycle as evinced by its red-shifted, enhanced, and structured Q-like bands and a small electrochemical HOMO-LUMO gap. Interestingly, one 1,4-pheylene part of bis-PdII complex takes a quinonoidal distorted structure and the other takes a usual benzene structure in a figure-eight conformation with Hückel topology.

Structural isomers of di-p-benzidithiaoctaphyrins

The cis and trans structural isomers of di-p-benzidithiaoctaphyrins were synthesized by adopting two different synthetic routes using readily available precursors under acid-catalyzed conditions, and the isomers were separated using basic alumina column chromatography. 1D and 2D NMR spectroscopy were used to deduce the molecular structures of the macrocycles, which also helps to differentiate the cis isomer from the trans isomer. DFT studies revealed that both the cis and trans isomers adopt figure of eight conformations but exhibit clear differences in their structural features, and the trans isomer is more distorted than the cis isomer. Experimental and theoretical studies revealed that both the cis and trans isomers are nonaromatic stable macrocycles and show subtle differences in their structure, spectral and redox properties. The cis and trans isomers of di-p-benzidithiaoctaphyrin exhibit nonaromatic absorption features in the visible-NIR region, and electrochemical studies revealed their electron-rich nature. TD-DFT studies are in agreement with the experimental observations.

Synthesis and Properties of Nonaromatic meso-fused Heterobenzihomoporphyrin(2.1.1.1)s

Fluorene-based tripyrrane has been used as a fused precursor to synthesize three novel examples of nonaromatic meso-fused thia and selenabenzihomoporphyrin(2.1.1.1)s by condensing it with appropriate 2,5-bis(hydroxymethyl)aryl thiophene or selenophene under acid catalyzed conditions. The meso-fused heterobenzihomoporphyrins contain one fluorene unit, two pyrrole rings and one thiophene/selenophene ring connected via five meso-carbons in the macrocyclic framework. The macrocycles were thoroughly characterized by HR-MS, 1D and 2D NMR, absorption, cyclic voltammetry and DFT/TD-DFT studies. NMR, absorption, and DFT studies indicated the nonaromatic nature of meso-fused heterobenzihomoporphyrins. The macrocycles displayed one intense band at ∼380 nm along with a shoulder band at 450 nm and a broad band in the region of 590-850 nm which were bathochromically shifted in the monoprotonated derivatives and absorbed prominently in the NIR region with the peak maxima at ∼1035 nm. The electrochemical studies revealed that the macrocycles showed three well-defined oxidations and reductions, and TD-DFT studies corroborated experimental observations.

m-Benziporphyrin(1.1.0.0)s as a Rare Example of Ring-Contracted Carbaporphyrins with Metal-Coordination Ability: Distorted Coordination Structures and Small HOMO-LUMO Gaps

m-Benziporphyrin(1.1.0.0) and m-pyreniporphyrin(1.1.0.0) were prepared as ring-contracted carbaporphyrins. While m-Benziporphyrin(1.1.0.0) was unstable, m-pyreniporphyrin(1.1.0.0) was fairly stable. Both of their Pd^II complexes showed distorted coordination structures with extremely short Pd-C bonds. As compared with the reported m-benziporphyrin Pd^II complexes, these Pd^II complexes showed considerably small HOMO-LUMO gaps, despite their smaller molecular size. Pd^II metalation of the m-pyreniporphyrin(1.1.0.0) dimer gave the corresponding Pd^II complex, which showed similar distorted coordination and a smaller HOMO-LUMO gap. Finally, Pd^II metalation of a pyrene-sharing formal p-benziporphyrin(1.1.1.1) dimer gave a nonaromatic Pd^II dimer, which rearranged to an aromatic Pd^II complex upon treatment with alumina.

Organometallic Chemistry within the Structured Environment Provided by the Macrocyclic Cores of Carbaporphyrins and Related Systems

The unique environment within the core of carbaporphyrinoid systems provides a platform to explore unusual organometallic chemistry. The ability of these structures to form stable organometallic derivatives was first demonstrated for N-confused porphyrins but many other carbaporphyrin-type systems were subsequently shown to exhibit similar or complementary properties. Metalation commonly occurs with catalytically active transition metal cations and the resulting derivatives exhibit widely different physical, chemical and spectroscopic properties and range from strongly aromatic to nonaromatic and antiaromatic species. Metalation may trigger unusual, highly selective, oxidation reactions. Alkyl group migration has been observed within the cavity of metalated carbaporphyrins, and in some cases ring contraction of the carbocyclic subunit takes place. Over the past thirty years, studies in this area have led to multiple synthetic routes to carbaporphyrinoid ligands and remarkable organometallic chemistry has been reported. An overview of this important area is presented.

Synthesis of Dioxa-1,7-naphthicorrole and Its Oxidized Porphyrinoid as a Potential Built-In Linker for Biomolecules

The first aromatic benzicorrole termed naphthicorrole was synthesized with a carbon donor containing more than six members. Its oxidized (enedione-embedded) porphyrinoid was also obtained using different meso-aryl substitutions under sequential oxidation conditions. The resulting enedione motif of the nonaromatic porphyrinoid was regioselective to the C2 position for S or N nucleophiles. Thus, the oxidized porphyrinoid was tested as a built-in linker for biomolecules. The progress of the reaction was visually monitored due to their different conjugation pathways.

Synthesis and Studies of Fused Benzo-Benzisapphyrins

A series of rare examples of fused benzo-benzisapphyrins were synthesized readily by (3 + 2) condensation of benzodipyrrole-derived diol and para-benzitripyrrane in the presence of 0.5 equiv of TFA in CH₂Cl₂ under inert atmosphere conditions accompanied by DDQ oxidation in open air. The crude compounds were separated by basic alumina column chromatography and afforded pure fused benzo-benzisapphyrins in 20-22% yields. The fused sapphyrins were characterized in detail by high-resolution mass spectrometry (HRMS) and one-dimensional (1D) and two-dimensional (2D) NMR spectroscopy. The ¹H NMR spectra recorded at both 298 and at 233 K clearly exhibited the presence of a strong diatropic ring current in benzo-benzisapphyrins, and the macrocycles are of aromatic nature. The DFT-optimized structure of benzo-benzisapphyrin revealed that the macrocycle was planar to a great extent due to the rigid structure of the dibenzopyrrole moiety, and the NICS(0) value of -11.2 ppm supports the aromatic nature of macrocycles. The absorption spectra of benzo-benzisapphyrins showed three weak Q bands approximately in the region of 650-900 nm and a strong Soret band at 480 nm, along with a shoulder band at ∼510 nm. The diprotonated derivative generated by the addition of excess TFA to the benzo-benzisapphyrin macrocycle exhibited bathochromically shifted absorption bands compared to the free base macrocycle.

Synthesis and properties of p-benzithiahexaphyrin(1.1.1.1.1.1)s

Novel Mobius aromatic p-benzithiahexaphyrin(1.1.1.1.1.1)s having twisted topology were synthesized by [3 + 3] condensation of benzitripyrrane diol and appropriate 16-thiatripyrranes under TFA-catalysed conditions.

o-(2-Thienyl)vinylarene as an Alternative Synthetic Motif for Porphyrinoids: o-Arene-Connected Porphyrinoids

o-Arene-connected porphyrinoids were synthesized with o-(2-thienyl)vinylarene motif as a new building block for porphyrinoids. This motif can replace meso-aryl-substituted dipyrromethene and serve as a command key arranging o-connectivity of porphyrinoid. While 6a (benzene version) is very weak, 6b (pyridine version) shows a substantial amount of diatropic ring current due to reduced steric hindrance (without H23) and rigidified Pd-6a became more aromatic than 6b.

Synthesis and Properties of Nonaromatic Meta-Benziheptaphyrins and Aromatic Para-Benziheptaphyrins

Two examples of nonaromatic m -benziheptaphyrins and two examples of aromatic p -benziheptaphyrins were synthesized by [5+2] condensation of appropriate m -benzi pentapyrrane and p -benzi pentapyrrane respectively and bithiophene diol in CH 2 Cl 2 in the presence of one equivalent of TFA under inert conditions for 30 min followed by oxidation with DDQ in open air for 1 h. The 1 H NMR studies carried out at room temperature as well as at lower temperature indicated the nonaromatic nature of m -benziheptaphyrins with inversion of two thiophene rings and aromatic nature of p -benziheptaphyrins with inversion of one of the thiophene ring. The X-ray structure obtained for one of the p -benziheptaphyrins showed a planar conformation with alignment of one of the thiophene ring away from the macrocyclic inner core but maintained its coplanarity with the mean plane and supported the aromatic nature of the macrocycle. The absorption spectra of m -benziheptaphyrins resembled with the nonaromatic systems and showed two intense bands at 445 nm, 555 nm and a very broad band in the region of 600-1100 nm whereas the p -benziheptaphyrin showed three sharp intense bands at 534 nm, 585 nm and 832 nm due to their aromatic nature. The protonation of m -benziheptaphyrins and p -benziheptaphyrins resulted in significant bathochromic shifts in their absorption maxima and showed strong absorption in NIR region. The electrochemical studies indicated that m - & p -benziheptaphyrins undergo oxidations and reductions easily. DFT and TD-DFT studies were in agreement with the experimental observations.

Doubly Fused Unsymmetrical Calixdicarbahexaphyrins

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.

Reversible redox switching between local and global aromaticity for core-modified expanded carbaisophlorinoids

Two dithienothiophene based 28π antiaromatic macrocycles with benzene and azulene units and their effects on local and global (anti)aromaticity have been described. Experimental and computational studies confirmed the presence of weak paratropic and strong diatropic ring current effects in neutral and dicationic states, respectively.

Bis-(Fluorene)-Embedded Hexaphyrins

The polyaromatic hydrocarbon containing expanded porphyrins, bis-(fluorene)-embedded hexaphyrins, were synthesized by condensing fluorene-based tripyrrane with pentafluorobenzaldehyde in CH₂Cl₂ in the presence of 1 equiv of BF₃·OEt₂ under an inert atmosphere followed by oxidation with DDQ in open air at room temperature. The reaction worked only when 1 equiv of BF₃·OEt₂ was added to the reaction mixture under concentrated reaction conditions. The bis-(fluorene)-embedded macrocycles were characterized and studied by high-resolution mass spectrometry (HRMS), nuclear magnetic resonance (NMR), absorption, electrochemical, and density functional theory (DFT)/time-dependent (TD)-DFT techniques. In ¹H NMR, the hexaphyrins showed a few broad unresolved resonances at room temperature, but the NMR spectra were well-resolved at lower temperatures, indicating that the hexaphyrins were very flexible. The DFT-optimized structures indicated that the two fluorene units at the crossing point of the figure-eight loop makes an angle of ∼79.73° with each other, the fluorene moieties maintained their own planarity, and one of the fluorene moieties was not involved in conjugation with the rest of the macrocycle. The absorption spectra of hexaphyrins showed one intense sharp band in the higher energy region and a broad band in the lower energy region. The electrochemical studies indicated that expanded hexaphyrins are relatively electron-rich and showed three easier oxidations and one reduction. The DFT/TD-DFT studies are in agreement with the experimental observations.

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.

Synthesis and Studies of Stable Nonaromatic Dithia Pyribenzihexaphyrins

We report here one of the rare examples of expanded hexaphyrins named as dithia pyribenzihexaphyrin macrocycles containing six-membered rings such as pyridine and p-phenylene along with five-membered heterocycles such as pyrrole and thiophene as a part of a macrocyclic frame. Trifluoroacetic acid catalyzed [3 + 3] condensation of equimolar mixture of [10,10'-bis(p-tert-butyl phenyl)hydroxymethyl]-1,3-bis(2-thienyl)pyridine diol (2,6-pyri diol) and 1,4-bis(phenyl(1H-pyrrol-2-yl)methyl)benzene (p-benzidipyrrane) in CH₂Cl₂ followed by oxidation with DDQ afforded stable nonaromatic dithia 2,6-pyri-para-benzihexapyrins 1 and 2 in 6-8% yields. The macrocycles were characterized by high-resolution mass spectroscopy and 1D and 2D NMR spectroscopy. NMR studies revealed the nonaromatic nature of dithia 2,6-pyri-p-benzihexaphyrins and indicated that the para-phenylene ring prefers to be in quininoid form rather than in benzenoid form. The macrocycles displayed sharp absorption bands in the region of ∼380-500 nm and a broad band at ∼700 nm, reflecting their nonaromatic nature. Upon protonation, these macrocycles showed NIR absorption properties. The redox studies of macrocycles indicated their electron-deficient nature. The DFT/TD-DFT studies are in line with the experimental observations.

Carbaporphyrin Dimers That Bear a Rigid Naphthalene Motif as an Internal Strap

The first fully connected aromatic carbaporphyrin dimer (6) and its bis-Pd complex (6-Pd₂) that bear a rigid naphthalene motif as an internal strap were synthesized. These dimers consisted of two aromatic carbaporphyrins that shared a naphthalene motif. The π-electron conjugation of the obtained macrocycles was proposed to have two separated local 22 π-electron pathways and a 34 π-electron pathway. Their weak aromaticity was fully supported by ¹H NMR spectroscopy, NICS values, ACID calculations, and ICSS plots.

Synthesis and Structure of meso-Substituted Dibenzihomoporphyrins

Bench-stable meso-substituted di(p/m-benzi)homoporphyrins were synthesized through acid-catalyzed condensation of dipyrrole derivatives with aryl aldehydes. The insertion of a 1,1,2,2-tetraphenylethene (TPE) or but-2-ene-2,3-diyldibenzene unit in the porphyrin framework results in the formation of dibenzihomoporphyrins, merging the features of hydrocarbons and porphyrins. Single crystal X-ray analyses established the non-planar structure of these molecules, with the phenylene rings out of the mean plane, as defined by the dipyrromethene moiety and the two meso-carbon atoms. Spectroscopic and structural investigations show that the macrocycles exhibit characteristics of both TPE or but-2-ene-2,3-diyldibenzene and dipyrromethene units indicating the non-aromatic characteristics of the compounds synthesized. Additionally, the dibenzihomoporphyrins were found to generate singlet oxygen, potentially allowing their use as photosensitizers.

Expanded Carbaporphyrinoids

This Review outlines the progress in the field of synthetic expanded carbaporphyrinoids. The evolution of this topic is demonstrated with expanded porphyrin-inspired systems with a variety of incorporated entities that introduce one or more carbon atoms into the cavity. The discussion starts with platyrins-the macrocycles that were identified as parent molecules of not only the expanded carbaporphyrinoids, but the carbaporphyrinoid class in general. After historic considerations, the plethora of expanded porphyrin-like macrocycles containing N-confused or neo-confused pyrrole motifs and different carbocyclic subunits are presented. Special emphasis is given to applications of expanded carbaporphyrinoids in different areas, including organometallic chemistry, switching systems, or aromaticity, concluding with the demonstration of a covalent cage based on an expanded carbaporphyrinoid.

Synthesis, Structure, and Optical Properties of Di-m-benzihexaphyrins (1.1.0.0.0.0) and Di-m-benziheptaphyrins (1.0.1.0.0.0.0): Blackening of m-Phenylene-Linked Dicarbaporphyrinoids by Simple π-Expansion

Acid-catalyzed condensation of a newly prepared di-m-benzipentapyrrane with appropriate mono- and diheterocyclic dialcohols selectively produced stable di-m-benzihexaphyrins and di-m-benziheptaphyrins with only two meso-carbon bridges. Single-crystal X-ray diffraction analyses reveal planar conformation with slight distortion of bridged phenylene rings. Despite the presence of m-phenylene units interrupting the global delocalization, the presence of bithiophene units in di-m-benziheptaphyrins 3a-b exhibits altered optical features covering the entire visible region (ca. 250-720 nm), exhibiting a black dye property as a "metal-free" porphyrinoid.

Rational Synthesis of 5,5,5-Tricyclic Fused Thia-heptaphyrin (1.1.1.1.1.1.0) From a Helical Oligopyrrin Hybrid

Oxidation of a thiophene-hexapyrrane hybrid S-P₆ afforded a stable conjugated open-chain thiaheptapyrrolic helix 1 with the terminal thiophene and confused pyrrole units lying at a long distance that is adverse for further cyclization. Chelation of 1 with copper(II) ion afforded 1-Cu, which exhibits more distant terminal units. Interestingly, further oxidation of 1 triggered an intramolecular C-N fusion reaction to afford a unique 5,5,5-tricyclic fused linear thiaheptapyrrin 2, with the two terminals positioned in proximity, which favors the oxidative ring-closure reaction to give a unique 5,5,5-tricyclic fused thiaheptaphyrin (1.1.1.1.1.1.0) 3 under air. The inner-fusion strategy for positioning the reactive sites in proximity to promote oxidative cyclization offers a new approach for constructing large porphyrinoids through conjugated oligopyrrins without the assistance of metal ions.

Antiaromatic Carbaporphyrinoids: Fluorene as a Fused Motif toward the Synthesis of meso-Fused Heterobenziporphyrins

meso-Tetraphenyl meta-benziporphyrins are nonaromatic macrocycles which can be changed to antiaromatic by fusing the core benzene ring with one of the adjacent meso-phenyl groups, as demonstrated here by adopting a premodification method. We used a fluorene moiety in place of the m-phenylene ring as a premodified fused aromatic motif to synthesize fused heterobenziporphyrins. Spectral and X-ray data indicated that the macrocycles are antiaromatic, which was supported by DFT, ACID, and NICS calculations. These macrocycles formed organopalladium complexes.

Effects of Core Modification on Electronic Properties of para-Benziporphyrins

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.

28-Hetero-2,7-Naphthiporphyrins: Horizontal Expansion of the m-Benziporphyrin Macrocycle

Replacement of the m-phenylene moiety of m-benziporphyrins with the 2,7-naphthalenyl subunit yielded 28-hetero-2,7-naphthiporphyrins-macrocycles that can be considered as expanded carbaporphyrinoids. This group retains some features of parent m-benziporphyrins, but due to larger size and different shape of the macrocyclic cavity, their coordination properties are different. Upon reduction and conformational rearrangement the 28-thia- and 28-selena-2,7-naphthiporphyrin form organophosphorus(V) complexes.

Cyclobis(7,8-(para-quinodimethane)-4,4'-triphenylamine) and Its Cationic Species Showing Annulene-Like Global (Anti)Aromaticity

π-Conjugated macrocycles containing all-benzenoid rings usually show local aromaticity, but reported herein is the macrocycle CBQT, containing alternating para-quinodimethane and triphenylamine units displaying annulene-like anti-aromaticity at low temperatures as a result of structural rigidity and participation of the bridging nitrogen atoms in π-conjugation. It was easily synthesized by intermolecular Friedel-Crafts alkylation followed by oxidative dehydrogenation. X-ray crystallographic structures of CBQT, as well as those of its dication, trication, and tetracation were obtained. The dication and tetracation exhibited global aromaticity and antiaromaticity, respectively, as confirmed by NMR measurements and theoretical calculations. Both the dication and tetracation possess open-shell singlet ground states, with a small singlet-triplet gap.

Exploration of Li-Organic Batteries Using Hexaphyrin as an Active Cathode Material

Lithium-collaborating organic batteries (Li-[28]hexs) were investigated with [28]hexaphyrin(1.1.1.1.1.1) as an active electrode material. Each hexaphyrin of [28]Hex cathode ideally involved four electrons per unit cycle and performed a typical charge/discharge processes of Li-organic battery. Li-[28]Hex batteries set with fast charging rates showed reasonably stable charge and discharge performances over 200 cycles even though it caused incomplete (2~3 electrons) charge/discharge cycles due to failing the complete charging process. UV absorption changes of [28]hexaphyrin in CH2Cl2 were supplementary for the electrochemical oxidation, which performed a conversion from [28]hexaphyrin to [26]hexaphyrin.

Homocarbaporphyrinoids: The m-o-m and p-o-p Terphenyl Embedded Expanded Porphyrin Analogues and Their RhI Complexes

Stable homocarbaporphyrinoids were successfully synthesized by incorporating the m-o-m and p-o-p terphenyl units into the porphyrin core. The distinct bonding modes of terphenyl in the macrocycle generated two structural isomers with two and four carbon atoms in the macrocyclic environment. The core was utilized to stabilize the Rh^I ion. The spectral and structural analyses revealed that the restricted (m-o-m) and allowed (p-o-p) conjugation in the macrocyclic core provide overall non-aromatic characteristics both to the free bases and their complexes.

Organocopper(III) Phenanthriporphyrin-Exocyclic Transformations

5,6-Dimethoxyphenanthriporphyrin 1 and 5,6-dioxophenanthriporphyrin 2 act as suitable organometallic ligands for copper(III), adopting trianionic [CCNN] coordination cores. Under oxidizing conditions, in the presence of methanol, copper(III) phenanthriporphyrin 1-Cu undergoes transformation to copper(III) phenanthriporphodimethene with methoxy substituents attached to two trans meso positions. Addition of acids to 1-Cu yields two isomeric copper(III) isophenanthriporphyrins protonated on one of the meso carbon atoms. Protonation of copper(III) 5,6-dioxophenanthriporphyrin 2-Cu yields the aromatic diprotonated complex 2-Cu-H₂²⁺. In the presence of HBF₄ 2-Cu undergoes borylation at the carbonyl oxygen atoms, forming an aromatic exocyclic boron(III) complex.

Orthogonally arranged tripyrrin–BODIPY conjugates with an “edge to plane” mode

Molecular conjugates consisting of BODIPY and tripyrrin dyes in new “edge to plane” mode with modulated energy transfer.

Fully Conjugated [4]Chrysaorene. Redox-Coupled Anion Binding in a Tetraradicaloid Macrocycle

[4]Chrysaorene, a fully conjugated carbocyclic coronoid, is shown to be a low-bandgap π-conjugated system with a distinct open-shell character. The system shows good chemical stability and can be oxidized to well-defined radical cation and dication states. The cavity of [4]chrysaorene acts as an anion receptor toward halide ions with a particular selectivity toward iodides ( K_a = 207 ± 6 M^-1). The interplay between anion binding and redox chemistry is demonstrated using a ¹H NMR analysis in solution. In particular, a well-resolved, paramagnetically shifted spectrum of the [4]chrysaorene radical cation is observed, providing evidence for the inner binding of the iodide. The radical cation-iodide adduct can be generated in thin solid films of [4] chrysaorene by simple exposure to diiodine vapor.

Synthesis of Nonaromatic and Aromatic Dithia Benzisapphyrins

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.

Synthesis of Tellurabenziporphyrin and Its Pd(II) Complex

An unprecedented tellurabenziporphyrin containing C, N, and Te donor atoms was synthesized by condensing benzitripyrrane and tellurophene diol under acid catalyzed conditions. The tellurabenziporphyrin readily forms a Pd(II) complex when treated with PdCl₂ in CHCl₃/CH₃CN. The crystal structures of tellurabenziporphyrin and its Pd(II) complex revealed that the benzene ring hinders the π-electron delocalization. An unusual five-membered ring formed inside the macrocycle due to the strong interaction between "Te" and "N" in the Pd(II) complex.

Rhodium-Induced Reversible C-C Bond Cleavage: Transformations of Rhodium(III) 22-Alkyl-m-benziporphyrins

The structurally prearranged carbaporphyrins 22-methyl- and 22-ethyl-m-benziporphyrins provide the platform stabilizing aromatic rhodium(III) 22-(μ-methylene-m-benziporphyrin) and rhodium(III) 22-(μ-ethylidene-m-benziporphyrin). An intramolecular conversion facilitated by the m-phenylene reactivity and observed for both aromatic complexes efficiently leads to rhodium(III) 21-(μ-methylene)-21-carbaporphyrin and rhodium(III) 21-(μ-ethylidene)-21-carbaporphyrin. The distinctive macrocyclic environment of rhodium(III) 21-carbaporphyrin created an opportunity to trap unique organometallic transformations of inner core substituents affording the fulvene-like bond pattern or the rearrangement to 21-vinyl substituent. The one-electron reduction of the rhodium(III) carbaporphyrin anion π-radical with a (d_xy )² (d_xz )² (d_yz )² -(P^.- ) electronic configuration is demonstrated. The further process of reduction of paramagnetic species triggers the ethyl migration from carbon(22) to rhodium(III), affording the diamagnetic rhodium(III) meta-benziporphyrin containing the apically coordinated σ-ethyl ligand providing an example of reversible C(sp² )-C(sp³ ) bond cleavage.

The design of rigid cyclic tripyrrins: the importance of intermolecular interactions on aggregation and luminescence

Cyclic tripyrrin “locked” by a bridging benzyl moiety: enhancing the molecular rigidity and tuning aggregation and fluorescence via intermolecular halogen interactions.

Aromaticity control via modifications of a macrocyclic frame: 5,6-dimethoxyphenanthriporphyrin and 5,6-dioxophenanthriporphyrin

Antiaromatic phenanthriporphyrin and nonaromatic 5,6-dioxophenanthriporphyrin reveal specific reactivity toward protic and Lewis acids yielding respectively nonaromatic and aromatic macrocycles.

Synthesis of Stable [28π] m-Benzihexaphyrins (1.0.0.1.1.1)

Four new expanded [28π] m-benziporphyrins (1.0.0.1.1.1) were synthesized by [3+3] condensation of 10,10'-bis[(p-toly)hydroxymethyl]-1,3-bis(2-thienyl)benzenediol with various 16-tripyrranes such as 16-thiatripyrrane, 16-oxatripyrrane, 16-azatripyrrane, and 16-selenatripyrrane under mild trifluoroacetic acid-catalyzed reaction conditions. The macrocycles are freely soluble in common organic solvents, and their identities were confirmed by HRMS and detailed 1D and 2D NMR spectroscopy. The macrocycles showed one sharp Soret-type band at ∼500 nm and broad ill-defined Q-type band(s) in the region 600-950 nm, which supports their nonaromatic nature. Upon protonation, the macrocycles exhibited bathochromically shifted absorption bands with a distinct change in the color of the solutions. The preliminary studies carried out with one of the macrocycles indicated that the macrocycles have a weak tendency to form coordination complexes.