Synthesis, Spectroscopic Properties, and Metalation of 3-Alkoxybenziporphyrins

A series of 5-alkoxy-1,3-benzenedicarbaldehydes and related dimers were prepared in three steps from dimethyl 5-hydroxyisophthalate. Acid catalyzed condensation of the dialdehydes with a tripyrrane dicarboxylic acid, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, afforded good yields of 3-alkoxybenziporphyrins, although dimeric tetraaldehydes failed to give isolatable porphyrinoid products. Proton NMR spectroscopy gave no indication of an aromatic ring current, but addition of trifluoroacetic acid resulted in the formation of dications that exhibited weakly diatropic characteristics. Spectroscopic titration with TFA demonstrated that stepwise protonation took place, generating monocationic and dicationic species. 3-Alkoxybenziporphyrins reacted with nickel(II) or palladium(II) acetate to give the related nickel(II) or palladium(II) complexes. These stable organometallic derivatives showed increased diatropic properties that were most pronounced for the palladium(II) complexes. These unique porphyrinoids provide further insights into the properties of benziporphyrins.

Mono- and bis-Pd(ii) complexes of N-confused dithiahexaphyrin(1.1.1.1.1.0) with the absorption and aromaticity modulated by Pd(ii) coordination, macrocycle contraction and ancillary ligands

To further enrich the coordination chemistry of hexaphyrins and probe the underlying property-structural correlations, N-confused dithiahexaphyrin(1.1.1.1.1.0) (1) with 26 π-electron Hückel aromaticity was synthesized. Based on its unprecedented two unsymmetrical cavities, five palladium complexes 2, 3, 4-Ph, 4-Cl and 5 have been successfully synthesized under various coordinations. Thus, two mono-Pd(ii) complexes 2 and 3 with the Pd(ii) atom coordinated in the two different cavities were obtained by treating 1 with palladium reagents PdCl2, and (PPh3)2PdCl2 respectively. On this basis, bis-Pd(ii) complexes 4-Ph and 4-Cl were synthesized by treating 2 and 3 with (PPh3)2PdCl2 and PdCl2, respectively. As a result, both 4-Ph and 4-Cl contain two Pd(ii) atoms coordinated within the two cavities, with one of the Pd(ii) atoms further coordinated to a triphenylphosphine ligand in addition to an anionic ancillary ligand of Ph- and Cl-, respectively. Notably, a further contracted mono-Pd(ii) complex 5 was synthesized by treating 1 with Pd(PPh3)4 by eliminating one of the meso-carbon atoms together with the corresponding C6F5 moiety. These complexes present tunable 26 π aromaticity and NIR absorption up to 1060 nm. This work provides an effective approach for developing distinctive porphyrinoid Pd(ii) complexes from a single porphyrinoid, without resorting to tedious syntheses of a series of porphyrinoid ligands.

Dibenzi Heteroheptaphyrin(2.0.1.1.1.1.0)s: Synthesis, Spectral, Redox and Theoretical Studies

Three examples of dibenzi heteroheptaphyrin(2.0.1.1.1.1.0)s were synthesized by condensing bis(phenylene ethene) based hexapyrrane with appropriate diol, 2,5-bis(α-hydroxy-α-arylmethyl) thiophene or selenophene in CH2 Cl2 under BF3  ⋅ OEt2 catalyzed inert atmosphere conditions followed by DDQ oxidation in open air. HR-MS analyses confirmed the identities of dibenzi heteroheptaphyrins. The DFT optimized structures revealed that dibenzi heteroheptaphyrins were highly distorted nonplanar macrocycles with two thiophene rings preferred to be in an inverted conformation. 1D & 2D NMR helped in deducing the molecular structures of dibenzi heteroheptaphyrins and supported their nonaromatic nature. The theoretical NMR calculations were carried which matched closely with the experimental NMR data. NMR studies also revealed that the π-delocaliztion was significantly altered in dibenzi heteroheptaphyrins compared to previously reported dibenzi hexaphyrins. The dibenzi heptaphyrins showed one sharp absorption band in 400-500 nm region and a broad band in the region of 600-800 nm which were bathochromically shifted in their diprotonated derivatives. The theoretical absorption calculations corroborate the slight hypsochromic shift of the broad absorption band in the lower energy region of dibenzi heptaphyrins compared to dibenzi hexaphyrins. The electrochemical studies revealed that the dibenzi heptaphyrins were easier to reduce but difficult to oxidize compared to dibenzi hexaphyrins.

Cross-Coupling Reactions Enabled by Well-Defined Ag(III) Compounds: Main Focus on Aromatic Fluorination and Trifluoromethylation

AgIII compounds are considered strong oxidizers of difficult handling. Accordingly, the involvement of Ag catalysts in cross-coupling via 2e- redox sequences is frequently discarded. Nevertheless, organosilver(III) compounds have been authenticated using tetradentate macrocycles or perfluorinated groups as supporting ligands, and since 2014, first examples of cross-coupling enabled by AgI /AgIII redox cycles saw light. This review collects the most relevant contributions to this field, with main focus on aromatic fluorination/perfluoroalkylation and the identification of AgIII key intermediates. Pertinent comparison between the activity of AgIII RF compounds in aryl-F and aryl-CF3 couplings vs. the one shown by its CuIII RF and AuIII RF congeners is herein disclosed, thus providing a more profound picture on the scope of these transformations and the pathways commonly associated to C-RF bond formations enabled by coinage metals.

Magnetic Circular Dichroism of Porphyrinoid Silver Complexes: Evidence of the Electronic Structure Inversion upon Protonation of the N-Confused Core

We report a systematic investigation of a series of Ag(II) and Ag(III) complexes of porphyrins and their analogues using UV-vis magnetic circular dichroism (MCD) spectroscopies and theoretical calculations. Ag(II) and Ag(III) octaethyl- and tetraarylporphyrins show the usual sign sequence in the Q-band region (i.e., negative to positive intensities with increasing energy) of their MCD spectra, indicative of the ΔHOMO > ΔLUMO relationship (ΔHOMO is the energy difference between Michl's a and s orbitals, and ΔLUMO is the energy difference between Michl's -a and -s pair of MOs). In contrast, Ag(II) complexes of β,β'-pyrrole-modified porphyrins (with an effective chlorin-type π-system) and Ag(III) corroles have sign reverse features in the MCD spectra of their Q-band region (ΔHOMO < ΔLUMO relationships). The Ag(III) complex of N-confused porphyrin shows the ΔHOMO > ΔLUMO relationship in the neutral state and the ΔHOMO < ΔLUMO relationship in the protonated form.

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.

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.

Electrophilicity of neutral square-planar organosilver(III) compounds

Neutral Ag(III) complexes stabilised with just monodentate ligands are here unambiguously established. In a series of square-planar (CF₃)₃Ag(L) compounds with hard and soft Group 15 donor ligands, L, the metal center has been found to exhibit substantial acidity favouring apical coordination of an additional ligand under no coordination constraints.

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.

Rh(I) and Organo-Rh(III) Complexes of meso-Triarylbiphenylcorrole

Rhodium complexes of biphenylcorrole are reported, and the molecular structures of the complexes are unambiguously confirmed by single-crystal X-ray analysis. The adj-CCNN core of the dicarbacorrole efficiently stabilizes a rhodium metal ion in its two different oxidation states. It is pertinent to point out that the Rh(I) metal complex attains square-planar geometry while organo-Rh(III) forms an octahedral complex. Furthermore, density functional theory studies corroborate the experimental findings.

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.

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.

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.

Creation from Confusion and Fusion in the Porphyrin World─The Last Three Decades of N-Confused Porphyrinoid Chemistry

Confusion is a novel concept of isomerism in porphyrin chemistry, delivering a steady stream of new chemistry since the discovery of N-confused porphyrin, a porphyrin mutant, in 1994. These days, the number of confused porphyrinoids is increasing, and confusion and associated fusion are found in various fields such as supramolecular chemistry, materials chemistry, biological chemistry, and catalysts. In this review, the birth and growth of confused porphyrinoids in the last three decades are described.

Synthesis of Non- or Antiaromatic Dicarbaamethyrin: [24]Diazulihexaphyrin(0.1.0.0.1.0)

A "3+3" condensation reaction of 1,3-di(2-pyrrolyl)azulene with aryl aldehyde followed by an oxidative aromatization afforded diazuliamethyrin, [24]diazulihexaphyrin(0.1.0.0.1.0). X-ray diffraction analysis revealed a relatively planar structure of diprotonated diazuliamethyrin with a mean plane deviation of 0.37 Å. A 24π non- or antiaromatic character was confirmed by ¹H NMR, absorption, MCD spectra, and TD-DFT calculations that included the NICS values and ACID plots.

A Five-Coordinate Compound with Inverted Ligand Field: An Unprecedented Geometry for Silver(III)

By using suitable synthetic procedures, we have first isolated the square-planar organosilver(III) compounds [PPh₄ ][trans-(CF₃ )₂ AgX₂ ] [X=Cl (1 a), Br (2 a)]. The geometry and stereochemistry of the chloro-derivative 1 a have been unambiguously established by single-crystal X-ray diffraction (SC-XRD) methods. Following our calculations on the relative stability of the cis-/trans-[(CF₃ )₂ AgX₂ ]^- couples (X=F, Cl, Br, I), the experimentally obtained compounds 1 a and 2 a appear to be kinetically favored stereoisomers. They display some tendency to associate an additional X^- ligand affording rare five-coordinate Ag^III species [(CF₃ )₂ AgX₃ ]^2- . Interestingly, compound [PPh₄ ]₂ [(CF₃ )₂ AgBr₃ ] (3) has been identified by SC-XRD methods as the first Ag^III derivative with trigonal symmetry in general and trigonal bipyramidal geometry in particular. This unusual five-coordinate species also exhibits inverted ligand field.

Inverted and fused expanded heteroporphyrins

Expanded heteroporphyrins are a class of porphyrin macrocycles containing pyrrole, thiophene, furan, selenophene and other heterocyclic rings that are connected to form an internal ring pathway containing a minimum of 17 atoms and more than 18 delocalized π electrons in their conjugated macrocyclic framework. Considering that expanded heteroporphyrins are large in size, these macrocycles are structurally flexible and prefer to adopt various conformations in which one or more pyrrole(s)/heterocycle(s) tend to be in an inverted conformation and pointed outward from the centre of the macrocyclic core. The inverted expanded heteroporphyrins are divided into two classes as follows: (1) N-inverted expanded heteroporphyrins and (2) hetero-atom inverted expanded heteroporphyrins. Both inverted expanded heteroporphyrins show quite unique features in terms of their structure, aromaticity, and electronic and coordination properties. Sometimes, inverted expanded heteroporphyrins lead to the formation of fused expanded heteroporphyrins because of the intramolecular fusion of the pyrrole "N" with the "C" of the inverted heterocycle ring, which also exhibit unique features compared to inverted expanded heteroporphyrins. In this review, we attempt to describe the synthesis, structure, and aromatic, electronic and coordination properties of inverted and fused expanded heteroporphyrins. This review covers the synthesis, structure and properties of inverted and fused expanded heteroporphyrins containing a combination of pyrrole/heterocycle rings starting with five pyrrole/heterocycle-containing pentaphyrins, and then expanded heteroporphyrins containing six, seven, eight and more pyrrole/heterocyclic rings in their porphyrin macrocyclic framework.

Synthesis and Structural Properties of NIR-Absorbing Pyridine-Containing Heptaphyrins

Four examples of stable nonaromatic pyridine containing heteroheptaphyrins (pyrithiaheptaphyrins) 2-5 were synthesized in 8-13% yields by [5+2] condensation of newly synthesized pyridine-based pentapyrrane 8 and bithiophene diol 9 a-d. The X-ray crystallographic analysis of macrocycle 2 proved that the macrocycle assumes a highly planar structure with two inverted thiophene rings. The heteroheptaphyrins 2-5 are asymmetric and showed a greater number of resonances in ¹ H NMR spectra compared to our previously reported symmetric heterohexaphyrin (pyrithiahexaphyrin) 1 c. Most of the macrocyclic core protons in pyrithiahepaphyrins 2-5 experienced upfield/downfield shifts compared to pyrithiahexaphyrin 1 c indicating the alteration of π-conjugation in the macrocycles. The absorption bands were significantly red-shifted and located in the NIR region in macrocycles 2-5 compared to 1 c supporting the increase of π-delocalization. The theoretical studies support the experimental findings and NICS(0) value supports the non-aromaticity of the macrocycles.

Benzene- and pyridine-incorporated octaphyrins with different coordination modes toward two PdII centers

Expanded porphyrins have received considerable attention due to their unique optical, electrochemical and coordination properties. Here, we report benzene- and pyridine-incorporated octaphyrins(1.1.0.0.1.1.0.0), which are synthesized through Suzuki-Miyaura coupling of α,α'-diboryltripyrrane with m-dibromobenzene and 2,6-dibromopyridine, respectively, and subsequent oxidation with 2,3-dicyano-5,6-dichlorobenzoquinone. Both octaphyrins are nonaromatic and take on dumbbell structures. Upon treatment with Pd(OOCCH₃)₂, the benzene-incorporated one gives a C_i symmetric NNNC coordinated bis-Pd^II complex but the pyridine incorporated one gives C_i and C_s symmetric NNNC coordinated bis-Pd^II complexes along with an NNNN coordinated bis-Pd^II complex bearing a transannular C-C bond between the pyrrole α-positions. In addition, these two pyridine-containing NNNC Pd^II complexes undergo trifluoroacetic acid-induced clean interconversion.

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.

Synthesis of internally alkylated azuliporphyrins

Examples of internally alkylated azuliporphyrins were prepared by MacDonald-type “3 + 1” condensations. 2-Methyl- and 2-ethylazulene reacted with an acetoxymethylpyrrole in the presence of an acid catalyst to give azulitripyrranes. Following cleavage of the terminal protective groups, condensation with a diformylpyrrole in the presence of hydrochloric acid and oxidation with ferric chloride afforded 21-alkylazuliporphyrins. An azulene dialdehyde similarly reacted with an [Formula: see text]-methyltripyrrane to generate a 23-methylazuliporphyrin. The products could only be isolated in protonated form and the free-base internally alkylated azuliporphyrins proved to be unstable. Nevertheless, the dications are highly diatropic and the internal alkyl group resonances were shifted upfield to beyond -3 ppm. Reaction of a 23-methylazuliporphyrin with palladium(II) acetate primarily afforded a palladium(II) complex with loss of the internal methyl substituent. However, two palladium(II) benzocarbaporphyrins were also identified that were formed by sequential oxidative ring contraction and methyl group migration. Internally alkylated azuliporphyrins provide new insights into the reactivity of the system and the results show that the introduction of alkyl substituents within porphyrinoid cavities greatly modifies the properties of these structures.

Alkylation, metalation and ring contraction of tropiporphyrin

Tropiporphyrins are an intriguing class of carbaporphyrinoids that incorporate a cycloheptatriene subunit. Previous investigations have shown that this system acts as a trianionic ligand that can form stable silver(III) complexes. In this work, tropiporphyrin was reacted with excess methyl iodide and potassium carbonate in refluxing acetone to give an internally alkylated derivative. The reaction occurred regioselectively to introduce a methyl group onto the 24-position. Reaction with palladium(II) acetate afforded a palladium(II) complex that retained the [Formula: see text]-methyl substituent. In contrast, reaction of [Formula: see text]-unsubstituted tropiporphyrin with palladium(II) acetate gave two palladium(II) benziporphyrins, one of which possessed a formyl substituent. Although these organometallic derivatives were obtained in relatively low yields, the observation of unexpected ring contraction products demonstrates that the reactivity of the tropiporphyrin system deserves to be further investigated.

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.

Azulichlorins and Benzocarbachlorins Derived Therefrom

Acid-catalyzed condensation of azulidipyrrane aldehydes with a dihydrodipyrrin carbaldehyde afforded the first examples of azulichlorins. These macrocyclic products were isolated in a monoprotonated form, and the free bases proved to be somewhat unstable. The monocations were strongly diatropic, and proton NMR spectroscopy showed the internal C-H at ca. -2 ppm. Addition of TFA gave the related dications, but these exhibited significantly reduced aromatic ring currents. Reaction of an azulichlorin with tert-butyl hydroperoxide and KOH in dichloromethane/methanol gave a benzocarbachlorin and two related aldehydes. The UV-vis spectrum for the benzocarbachlorin showed a split Soret band at 414 and 430 nm, together with a strong chlorin-like absorption at 684 nm. The proton NMR spectrum indicated that the carbachlorin is strongly aromatic and the internal C-H was observed at -4.64 ppm. Addition of TFA afforded a C-protonated dication with a significantly increased diatropic ring current. The proton NMR spectrum, NICS calculations, and AICD plots indicated that the system favors a 22π electron delocalization pathway that runs through the fused benzo unit. Addition of TFA to the benzocarbachlorin aldehydes primarily led to the formation of monocations, and the generation of C-protonated dications was no longer favored due to the presence of electron-withdrawing formyl moieties.

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.

Incorporation of a p-Phenylene Unit into the Azuliporphyrinogens Frame-Oxidation and Ruthenium Cluster Coordination

A porphyrinogen macrocycle incorporating two azulenes, phenylene and thiophene into the framework, joined by four C(sp³ ) atoms has been obtained as a mixture of six isomers. They were successfully separated and characterized spectroscopically. The identity of two of them was confirmed by X-ray crystallography. One isomer was tested in reaction with [Ru₃ (CO)₁₂ ] yielding exclusively π-complex with two clusters attached to azulenes. The partial oxidation of porphyrinogens yielded dication with two unmodified meso bridges. The stepwise oxidation followed by reaction with water as nucleophile afforded the dicationic species with two hydroxyl groups and a trication with one OH group. The hydroxy-dication can be reversibly transformed into hydroxy-trication by addition of HBF₄ etherate.

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.

Alphabet soup within a porphyrinoid cavity: synthesis of heterocarbaporphyrins with CNNO, CNOO, CNSO and CNSeO Cores from an oxacarbatripyrrin

The first examples of porphyrin analogues with four different core atoms have been synthesized from an oxacarbatripyrrin intermediate.

Oxidative Transformation of a Tetrathia S-Confused Isophlorin into Porphyrin Cation

The synthesis and redox properties of first generation S-confused isophlorins are described. Despite structural resemblance to a confused porphyrin, spectroscopic and computational studies reveal weak paratropic ring current effects in these 20π macrocycles. They display redox properties atypical of parent tetrathia isophlorins. Experimental evidence supports the oxidation of an unstable 19π neutral radical, as a transient intermediate, for the formation of a unique 18π aromatic monocationic species. Spectroscopic and structural characterization revealed the substituent dependent macrocycle oxidation unfamiliar to the chemistry of antiaromatic isophlorinoids.

Late transition metal complexes of oxypyriporphyrin and the platinum(II) complex of oxybenziporphyrin

Even though oxypyriporphyrin, a pyridone-containing porphyrinoid system, has the equivalent coordination core to true porphyrins, its coordination chemistry has been little explored. In this study, the first examples of palladium(II), platinum(II) and silver(II) oxypyriporphyrins have been synthesized. Conventional conditions failed to result in the formation of a platinum(II) complex, but moderate yields were obtained when oxypyriporphyrin was reacted with platinum(II) chloride in refluxing mixtures of DMF and acetic acid containing potassium acetate. The palladium(II) and platinum(II) derivatives were characterized by X-ray crystallography. The structurally analogous carbaporphyrinoid system oxybenziporphyrin was also shown to react with platinum(II) chloride under the same conditions to give a platinum(II) hydroxybenziporphyrin complex. Unlike oxybenziporphyrin, this complex is only weakly diatropic. In the presence of base, the diatropic character was reasserted to afford an aromatic anionic species.

An alternative synthesis of benziporphyrins starting from isophthaloyl chloride

An alternative route to benziporphyrins has been developed. Reaction of an [Formula: see text]-unsubstituted pyrrole ethyl ester with isophthaloyl chloride in the presence of aluminum chloride afforded a diketone that underwent selective reduction with diborane to give a benzitripyrrane. Cleavage of the ethyl esters with sodium hydroxide in refluxing ethylene glycol, followed by acid catalyzed condensation with a pyrrole dialdehyde and oxidation with DDQ, generated the targeted benziporphyrin product. Spectrophotometric titration of the benziporphyrin with trifluoroacetic acid (TFA) demonstrated the sequential formation of mono- and dicationic species. At lower dilutions, the free base benziporphyrin showed unusually strong [Formula: see text] coupling between two adjacent methyl substituents, indicating that the connecting unit has substantial olefinic characteristics.

Ruthenium(II) and Ruthenium(III) Complexes of p-Benziporphyrin: Merging Equatorial and Axial Organometallic Coordination

A diamagnetic ruthenium(II) complex of 5,10,15,20-tetraphenyl-p-benziporphyrin [Ru^II(p-BzP)(CO)Cl] was obtained via the insertion of ruthenium into p-benziporphyrin using triruthenium(0) dodecacarbonyl [Ru₃(CO)₁₂] as the metal source. The procedure applying dichloro(cycloocta-1,5-diene)ruthenium(II) (polymer, [Ru(COD)Cl₂]_n) afforded the paramagnetic six-coordinate ruthenium(III) p-benziporphyrin [Ru^III(p-BzP)Cl₂]. As shown by X-ray crystallography, the p-phenylene ring in both complexes is sharply tilted out of the N₃ plane, as reflected by the respective N₃ (pyrrole)-C₆ (p-phenylene) dihedral angle [Ru^II(p-BzP)(CO)Cl, 52.5°; Ru^III(p-BzP)Cl₂, 53.7°]. p-Phenylene is bound to the ruthenium cation in an η² fashion, revealing the shortest ever Ru-C distance in the series of p-benziporphyrin complexes [Ru^II(p-BzP)(CO)Cl, 2.275(2) Å; Ru^III(p-BzP)Cl₂, 2.324(5) Å]. The reaction of Ru^II(p-BzP)(CO)Cl with ArMgCl or AlkMgCl results in the formation of diamagnetic six-coordinate ruthenium(II) p-benziporphyrin complexes containing the apically coordinated σ-alkyl or σ-aryl ligands, where the metal ion simultaneously coordinates to three carbon centers respectively accommodating η² (phenylene) and σ (aryl and alkyl) modes. Reactions of σ-aryl (alkyl) carbanions with paramagnetic Ru^III(p-BzP)Cl₂ have been followed by ¹H NMR spectroscopy. The procedure afforded the six-coordinate paramagnetic ruthenium(III) p-benziporphyrin [Ru^III(p-BzP)(Ph)Cl], which binds one σ-aryl ligand, as reflected by the characteristic ¹H NMR spectra spread within the +120 to -120 ppm range. Both paramagnetic complexes Ru^III(p-BzP)(Ph)Cl and Ru^III(p-BzP)(p-Tol)Cl are formed as a mixture of two stereoisomers differentiated by two nonequivalent locations of σ-aryl with respect to the puckered macrocyclic ring. The paramagnetic shifts of σ-aryls are indicative of π-spin delocalization patterns. Analysis of the contact shifts and parallel density functional theory calculations of the spin density distribution in Ru^III(p-BzP)Cl₂, Ru^III(p-BzP)(Ar)Cl, and Ru^III(p-BzP)(Alk)Cl reflect the features of the d_xy²(d_xzd_yz)³ electronic ground state.

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.

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.