Recent Advances on the Synthesis and Chemistry of Carbaporphyrins and Related Porphyrinoid Systems

One Pot Synthesis of Two Distinct Macrocycles: Aromatic p-Benzihexaphyrin and Nonaromatic Doubly Fused p-Benzihexaphyrin

Aromatic trithia p-benzihexaphyrins and nonaromatic doubly fused trithia p-benzihexaphyrins were synthesized in a one pot reaction by condensing a p-benzithiophene based tetrapyrrane with three different bithiophene diols under acid catalyzed conditions. The aromatic and nonaromatic macrocycles showed clear differences in colour, NMR, absorption, and electrochemical properties. Theoretical studies supported the observed aromatic and nonaromatic characteristics, respectively, of the p-benzihexaphyrins and their N-fused derivatives.

Aromatic Character and Relative Stability of Pyrazoloporphyrin Tautomers and Related Protonated Species: Insights into How Pyrazole Changes the Properties of Carbaporphyrinoid Systems

Pyrazoloporphyrins (PzPs), which are porphyrin analogues incorporating a pyrazole subunit, are examples of carbaporphyrin-type structures with a carbon atom within the macrocyclic cavity. DFT calculations were used to assess a series of 17 PzP tautomers, nine monoprotonated species and four related diprotonated PzP dications. The geometries of the structures were optimized using M06-2X/6-311++G(d,p), and the relative stabilities computed with the cc-PVTZ functional. Nucleus independent chemical shifts, both NICS(0) and NICS(1)_zz, were calculated, and the anisotropy of the induced current density (AICD) plots were generated for all of the species under investigation. The results for free base PzPs show that fully aromatic PzP tautomers are not significantly more stable than weakly aromatic cross-conjugated species. In addition, strongly aromatic structures with internal CH_2's are much less stable, a feature that is also seen for protonated PzPs. The degree of planarity for the individual macrocycles does not significantly correlate with the stability of these structures. The results allow significant aromatic conjugation pathways to be identified in many cases, and provide insights into the aromatic properties of this poorly studied system. These investigations also complement experimental results for PzPs and emphasize the need for further studies in this area.

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 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.

Two-photon absorption of 28-hetero-2,7-naphthiporphyrins: expanded carbaporphyrinoid macrocycles

The one- and two-photon absorption (1PA and 2PA) properties of three expanded aceneporphyrinoids, 28-thia-, 28-selena- and 28-tellura-2,7-naphthiporphyrin, have been studied. The open-aperture Z-scan technique was used to determine two-photon absorption cross-sections in the near infrared range using an amplified femtosecond laser system. The maximum values of the cross sections were found to be 99, 200 and 650 GM at 900 nm and 1, 13 and 31 GM at 1400 nm for the three investigated compounds, respectively. These results demonstrate enhanced 2PA properties compared with well-known porphyrin photosensitizers, such as Foscan®, showing the potential of porphyrin core modification for optimizing infrared nonlinear absorbers.

Metal Complexes of Porphyrinoids Containing Nonpyrrolic Heterocycles

The replacement of one or more pyrrolic building block(s) of a porphyrin by a nonpyrrolic heterocycle leads to the formation of so-called pyrrole-modified porphyrins (PMPs), porphyrinoids of broad structural variability. The wide range of coordination environments (type, number, charge, and architecture of the donor atoms) that the pyrrole-modified frameworks provide to the central metal ions, the frequent presence of donor atoms at their periphery, and their often observed nonplanarity or conformational flexibility distinguish the complexes of the PMPs clearly from those of the traditional square-planar, dianionic, N₄-coordinating (hydro)porphyrins. Their different coordination properties suggest their utilization in areas beyond which regular metalloporphyrins are suitable. Following a general introduction to the synthetic methodologies available to generate pyrrole-modified porphyrins, their general structure, history, coordination chemistry, and optical properties, this Review highlights the chemical, electronic (optical), and structural differences of specific classes of metalloporphyrinoids containing nonpyrrolic heterocycles. The focus is on macrocycles with similar "tetrapyrrolic" architectures as porphyrins, thusly excluding the majority of expanded porphyrins. We highlight the relevance and application of these metal complexes in biological and technical fields as chemosensors, catalysts, photochemotherapeutics, or imaging agents. This Review provides an introduction to the field of metallo-PMPs as well as a comprehensive snapshot of the current state of the art of their synthesis, structures, and properties. It also aims to provide encouragement for the further study of these intriguing and structurally versatile metalloporphyrinoids.

Synthesis, Characterization, and Spectroscopic Studies of Bis-(meso-4-methoxyphenyl)-Benziporphyrin and Its Pd-Metal Complex

Benziporphyrin systems are widely explored, yet alternative improved synthetic routes towards these systems are needed. Here, a fairly and efficient synthesis of the free base and its metal complex is well designed. Dimethoxybenzene dicarbinol intermediate was prepared in excellent yields by reacting 4-methoxyphenylmagnesium bromide with isophthaladehyde in diethyl ether. Reaction with equivalent pyrrole and pentafluorobenzaldehyde in the presence of trifluoroacetic acid (TFA), followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), provided good yields of bis-(meso-4-methoxyphenyl)-benziporphyrin. Metalation of the free base was performed using palladium(II) acetate salt in acetonitrile. All intermediates and the final products are fully characterized using NMR, HMRS, and UV-Vis spectroscopies and briefly discussed.

Magnetically induced ring currents in naphthalene-fused heteroporphyrinoids

The magnetically induced current density of an intriguing naphthalene-fused heteroporphyrin has been studied, using the quantum-chemical, gauge-including magnetically induced currents (GIMIC) method. The ring-current strengths and current-density pathways for the heteroporphyrin, its Pd complex, and the analogous quinoline-fused heteroporphyrin provide detailed information about their aromatic properties. The three porphyrinoids have similar current-density pathways and are almost as aromatic as free-base porphyrin. Notably, we show that the global ring current makes a branch at three specific points. Thus, the global current is composed of a total of eight pathways that include 22 π-electrons, with no contributions from 18-electron pathways.

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.

Classic highlights in porphyrin and porphyrinoid total synthesis and biosynthesis

Porphyrins feature prominently in nature, be it as enzymatic cofactors, electron and exciton shuffles, as photoactive dyes, or as signaling substances. Their involvement in the generation, storage and use of oxygen is pivotal to life, while their photochemical properties are central to the biochemical functioning of plants. When complexed to metals, porphyrins can engage in a multitude of contemporary applications ranging from solar energy generation to serving as catalysts for important chemical reactions. They are also able to function as useful theranostic agents, and as novel materials for a wide range of applications. As such, they are widely considered to be highly valuable molecules, and it almost goes without saying that synthetic organic chemistry has dramatically underpinned all the key advances made, by providing reliable access to them. In fact, strategies for the synthesis of functionalized porphyrins have now reached a state of refinement where pretty well any desired porphyrin can successfully be synthesized with the approaches that are available, including a cornucopia of related macrocycle-modified porphyrinoids. In this review, we are going to illustrate the development of this exciting field by discussing a number of classic syntheses of porphyrins. Our coverage will encompass the natural protoporphyrins and chlorophylls, while also covering general strategies for the synthesis of unsymmetrical porphyrins and chlorins. Various industrial syntheses of porphyrins will also be discussed, as will other routes of great practical importance, and avenues to key porphyrinoids with modified macrocycles. A range of selected examples of contemporary functionalization reactions will be highlighted. The various key syntheses will be described and analyzed from a traditional mechanistic organic chemistry perspective to help student readers, and those who are new to this area. The aim will be to allow readers to mechanistically appreciate and understand how many of these fascinating ring-systems are built and further functionalized.

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.

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.

Redox-Associated Variation of Hückel Aromaticity from Lactam-Embedded Smallest Antiaromatic trans-Doubly N-Confused Porphyrins: Synthesis and Characterization

High-yield synthesis, spectroscopic and solid-state structural proof of the lactam-embedded smallest ever metal-free stable Hückel antiaromatic trans-doubly N-confused [16] porphyrins are reported. These new facets of trans-doubly N-confused porphyrins have been anticipated to exhibit the redox-associated variation of Hückel aromaticity as a mere consequence of the amido-like structures of the N-confused N-methyl pyrrole rings of the macrocycles. Strong aromaticity upon NaBH₄ reduction leading to a resonance dipolar structure of the [18]π-conjugated system as the reduced congener with concomitant Hückel topology are the important highlights. Excellent agreement between experimental spectroscopic measurements and the theoretically determined properties elucidate aromaticity switching upon chemical reduction. Recent years have witnessed an upsurge of demand for the experimental realization of stable antiaromatic systems because of their versatile applications in material science. The conformational rigidity and the enriched stability of these novel 16π antiaromatic doubly N-confused porphyrins might entitle these macrocycles toward such applications.

Tropylium cation-fused aromatic [26]dicarbaporphyrinoids with NIR absorptions: Synthesis, spectroscopic and theoretical characterization

An easy and efficient synthetic methodology for two hitherto unknown tropylium-cation-fused Hückel aromatic [26] dicarbaporphyrinoids has been developed by acid-catalyzed Lindsey type condensation of bithiophene/biselenophene diol with azulene using BF3 · Et2O followed by oxidation with chloranil and/or DDQ. Both the macrocycles have been achieved in moderately good yields. Their structures, aromaticity and optical properties have been elucidated by NMR, UV-vis-NIR spectroscopic analyses and in-depth theoretical calculations. Both the macrocycles exhibited strongly diatropic characteristics with the UV-vis spectra closely resembling the spectra for true porphyrins. Detailed structural analyses using 1H–1H COSY, ROESY and DFT level theoretical investigations indicated fully conjugated [26][Formula: see text] main conjugation pathway being benefitted by the tropylium character of the seven membered rings.

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.

Ruthenium N-Confused Porphyrins: Selective Reactivity for Ambident 2-Heteroatom-Substituted Pyridines Serving as Axial Ligands

Three types of ruthenium(II) N-confused porphyrin (NCP) complexes bearing an axial 2-thiopyridine, 2-pyridone, and 2-iminopyridine moiety at the inner carbon atom, respectively, were synthesized. The unique reactivity of the 2-substituted pyridine derivatives (2-X-pyridine; X=SH, OH, NH₂ ) toward the inner carbon atom of the NCP allows the formation of two types of coordinated products (i. e., pyridine donor versus 2-heteroatom donors), as inferred from single-crystal X-ray structures. The selective reactivity was investigated by using density functional theory (DFT) calculations. Finally, the catalytic activity of these ruthenium complexes was demonstrated through the styrene oxidation reactions. As a result, the ruthenium(II) NCP complex bearing a 2-thiopyridine moiety, together with aqueous H₂ O₂ as an oxidant showed the highest selectivity for benzaldehyde (benzaldehyde/styrene oxide=20 : 1).

meso-Alkylidenyl dibenzihexaphyrins: synthesis and protonation studies

The synthesis and characterization of the alkylidenyl-dibenzihexaphyrins bearing four indanedionyl groups at themeso-positions linkedviafourmeso-exocyclic double bonds is reported.

Stable Core-Modified Doubly N-Fused Expanded Dibenziporphyrinoids

We describe one-pot synthesis of stable doubly N-fused expanded dibenziporphyrinoids using readily available precursors under acid-catalyzed conditions. The doubly N-fused expanded dibenziporphyrinoids have been synthesized by adopting an inversion followed by fusion strategy. The studies showed that the dibenziporphyrinoids undergo mono fusion initially, but due to the high stability of doubly fused dibenziporphyrinoids, the monofused macrocycles undergo further fusion to form doubly fused dibenziporphyrinoids. The mono fusion and double fusion in these dibenziporphyrinoids were established by X-ray crystallography.

Thiophene-fused dithiaoctaphyrins: π-system switching between cross-conjugated and macrocyclic π-networks

We synthesized for the first time octaphyrins with a dithieno[3,4-b:3′,4′-d]thiophene core as thiophene-fused dithiaoctaphyrins with a cross-conjugated structure.

Optical and magnetic properties of antiaromatic porphyrinoids

Magnetic and spectroscopic properties of a number of formally antiaromatic carbaporphyrins, carbathiaporphyrins and isophlorins with 4n π electrons have been investigated at density functional theory and ab initio levels of theory.

What’s in a name? The MacDonald condensation

In 1960, MacDonald and coworkers introduced a new method for porphyrin synthesis that involved the acid-catalyzed condensation of dipyrrylmethane dialdehydes with [Formula: see text],[Formula: see text]-diunsubstituted dipyrrylmethanes or the related dicarboxylic acids, followed by an air oxidation. The key bond forming steps entail electrophilic substitution at two pyrrole units with the aldehyde moieties to generate, following elimination of water, a 5,15-dihydroporphyrin or porphodimethene intermediate. Following addition of sodium acetate, or in later procedures zinc acetate, the dihydroporphyrins readily air oxidize to the fully aromatic porphyrin system. This strategy, which parallels chemistry contemporaneously developed by R. B. Woodward at Harvard for the total synthesis of chlorophyll [Formula: see text], demonstrated that dipyrrylmethanes were sufficiently stable to be utilized as intermediates in porphyrin syntheses and that porphodimethene formation circumvented acidolytic scrambling reactions that might lead to isomeric porphyrin products. This type of chemistry was later adapted by Johnson, Woodward and others to prepare porphyrin-type systems by a “3 + 1” strategy, or expanded porphyrins by “3 + 2” or other combinations of oligopyrrolic precursors. In recent years, the term “MacDonald condensation” has been increasingly used to describe other types of chemistry involving oligopyrrolic intermediates. Following on from a historical review of this area, guidelines for the identification of MacDonald-type reactions are proposed.

Regioselective oxidation and metalation of meso-unsubstituted azuliporphyrins

Azuliporphyrins are intriguing porphyrin analogues that incorporate an azulene ring in place of a pyrrolic unit. This system undergoes regioselective oxidation reactions and favors the formation of stable organometallic derivatives. Reaction of meso-unsubstituted azuliporphyrins with Co₂(CO)₈ or CoCl₂·6H₂O gave 21-oxyazuliporphyrins, while Cu(OAc)₂ produced the corresponding copper(ii) complexes. Treatment of an oxyazuliporphyrin with Ni(OAc)₂ or Pd(OAc)₂ afforded analogous nickel(ii) and palladium(ii) derivatives. Silver(i) acetate in pyridine reacted with azuliporphyrins to give moderate yields of silver(iii) benzocarbaporphyrins, and the prevalence of structures with a formyl moiety at the sterically crowded 2¹-position suggested that the ring contraction reactions were triggered in part by intramolecular attack from an axial peroxide ligand. Related thiaazuliporphyrins reacted with palladium(ii) acetate to give palladium(ii) benzothiacarbaporphyrins but this chemistry did not give rise to structures with 2¹-formyl groups, suggesting that the ring contraction reactions occurred by a different mechanistic pathway. These results demonstrate the existence of a rich tapestry of oxidation and metalation reactions for azuliporphyrin systems.

Rhodium(i), rhodium(iii) and iridium(iii) carbaporphyrins

Treatment of a benzocarbaporphyrin with [Rh(CO)2Cl]2 in refluxing dichloromethane gave a rhodium(i) dicarbonyl complex, and further reaction in refluxing pyridine afforded an organometallic rhodium(iii) derivative. The carbaporphyrin also reacted with [Ir(COD)Cl]2 and pyridine in refluxing p-xylene to generate a related iridium(iii) compound. These novel metalated porphyrinoids retained strongly diatropic characteristics and were fully characterized by XRD.

Out of the Blue! Azuliporphyrins and Related Carbaporphyrinoid Systems

First reported in 1997, azuliporphyrins have proven to be a truly remarkable family of porphyrin analogues. In this system, although the porphyrin framework is retained, one of the pyrrolic moieties has been replaced by an azulene unit. Azulene favors electrophilic substitution at the 1,3-positions, which are structurally analogous to the α-positions in pyrrole, and this property facilitates the construction of azulene-containing porphyrinoid systems. Azuliporphyrins were first prepared from tripyrranes and 1,3-azulenedicarbaldehyde using a "3 + 1" variant on the MacDonald reaction. Subsequently, azulenes were shown to react with acetoxymethylpyrroles under acidic conditions to generate azulitripyrranes that could be utilized in a back-to-front "3 + 1" methodology to form azuliporphyrins and related heteroporphyrinoids. In addition, the favorability of azulenes toward 1,3-substitution was applied to one-pot syntheses of tetraarylazuliporphyrins and calix[4]azulenes. Azuliporphyrins have significant diatropic character that is greatly enhanced upon protonation. They have been shown to form organometallic complexes with Ni(II), Pd(II), Pt(II), Ir(III), Rh(III), and Ru(II) and undergo selective oxidations at the internal carbon with copper(II) or silver(I) salts to afford 21-oxyazuliporphyrins. In addition, oxidative ring contractions readily occur under basic conditions in the presence of peroxides to give benzocarbaporphyrins, and this reactivity provides access to tetraarylbenzocarbaporphyrins and their organometallic derivatives. A diazulenylmethane dialdehyde has been shown to react with dipyrrylmethanes in the presence of HCl or HBr to give diazuliporphyrins that were isolated in a monoprotonated form, and metalation with palladium(II) acetate afforded a stable zwitterionic palladium(II) complex. Equally intriguing dicarbaporphyrinoids incorporating indene and azulene rings have been reported, and these systems exhibit significant aromatic character. Recent studies have demonstrated that calixazulenes form supramolecular complexes with quaternary ammonium salts and afford a 1:1 complex with C60. In addition, conjugated structures have been prepared from calixazulenes that are structurally related to quatyrin, the theoretically important hydrocarbon analogue of the porphyrins. Examples of expanded azuliporphyrinoids have also been described. These azulene-containing porphyrinoids exhibit unique and complex reactivity that compares favorably with better studied porphyrin analogue systems such as the N-confused porphyrins, and azuliporphyrin derivatives show promise in the development of new catalytic systems.

Porphyrin Macrocycle Modification: Pyrrole Ring-Contracted or -Expanded Porphyrinoids

In recent years, several synthetic strategies aiming at the peripheral functionalization of porphyrins were developed. Particularly interesting are those involving the modification of β-pyrrolic positions leading to pyrrole-modified porphyrins containing four-, five-, six- or seven-membered heterocycles. Azeteoporphyrins, porpholactones and morpholinoporphyrins are representative examples of such porphyrinoids. These porphyrin derivatives have recently gained an increasing interest due to their potential application in PDT, as multimodal imaging contrast agents, NIR-absorbing dyes, optical sensors for oxygen, cyanide, hypochlorite and pH, and in catalysis.

Synthesis and spectroscopic behaviour of metal complexes of meso-alkylidenyl carbaporphyrinoids and their expanded analogues

Metal complexes of meso-diethyl malonylidene carbaporphyrinoids have been synthesized and fully characterized.

New insights into aromatic pathways of carbachlorins and carbaporphyrins based on calculations of magnetically induced current densities

The aromatic pathways of carbaporphyrins and carbachlorins that are based on magnetically induced current density DFT-GIMIC calculations are presented and discussed.

Core chemistry and skeletal rearrangements of porphyrinoids and metalloporphyrinoids

Porphyrin core alteration allows for the exploration of porphyrin-like or porphyrin-unlike coordination chemistry and provides an insight into reactions inside particularly shaped macrocyclic architecture including metal-mediated structural transformations.

adj-Dicarbachlorin, the first free base carbaporphyrinoid system with an internal methylene unit

Base-catalyzed condensation of dicyclopentadienylmethane with a dipyrrylmethane dialdehyde gave a dicarbachlorin with an internal CH₂ group.

Predicting the degree of aromaticity of novel carbaporphyrinoids

Magnetically induced current densities have been calculated for dioxaporphyrin, dithiaporphyrin, true carbaporphyrins, and N-confused porphyrins using the gauge-including magnetically induced current (GIMIC) method.

Effects of cyano, ethynyl and ethylenedioxy groups on the photophysical properties of carbazole-based porphyrins

The synthesis and photophysical properties of cyano and ethynyl substituted carbazole-based porphyrins were investigated.

Benziporphyrins, a unique platform for exploring the aromatic characteristics of porphyrinoid systems

Benziporphyrins and related systems exhibit a wide range of properties and may possess nonaromatic, strongly aromatic or even antiaromatic characteristics.

Tropone-fused carbaporphyrins

Previous attempts to prepare tropone-fused carbaporphyrins by reacting peroxides with azuliporphyrins under basic conditions afforded benzocarbaporphyrins instead. In this study, a methoxyazulitripyrrane condensed with a pyrrole dialdehyde in the presence of TFA, followed by oxidation with ferric chloride, to give a tropone-fused carbaporphyrin following a spontaneous demethylation. The porphyrinoid gave a modified UV-vis spectrum showing multiple bands in the Soret region, and the proton NMR spectrum showed that it has a reduced diamagnetic ring current in comparison to other carbaporphyrins. The tropone-fused derivative failed to react with tert-butyl hydroperoxide and potassium hydroxide, demonstrating that this type of structure is not an intermediate in the formation of benzocarbaporphyrins. However, the reaction with silver(I) acetate gave the corresponding silver(III) complex. Condensation of the methoxyazulitripyrrane with 2,5-thiophenedicarbaldehyde gave a related tropone-fused thiacarbaporphyrin together with a methoxythiaazuliporphyrin. Treatment of the carbaporphyrins with DBU resulted in the formation of anionic species, while addition of acid afforded dicationic structures. DFT studies were performed on a series of tautomers, protonated species, and anionic structures related to these tropone-fused carbaporphyrins, and NICS calculations were carried out. These results allowed favorable conjugation pathways to be identified. In addition, these studies predicted that protonation initially occurs on the carbonyl moiety rather than on the expected interior pyrrolenine nitrogen atom.