Controlled Core‐Modification of a Porphyrin into an Antiaromatic Isophlorin

Panchal, Santosh P.; Gadekar, Santosh C.; Anand, Venkataramanarao G.

doi:10.1002/anie.201511883

Cited by 35 publications

(47 citation statements)

References 32 publications

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“…The spectrum exhibited a sharp singlet signal for the β protons at δ =4.99 ppm (Figure c), which were, compared to 1 , considerably upfield shifted. Comparison of the chemical shifts of selected isophlorins with antiaromatic and nonaromatic characters, other relevant antiaromatic porphyrinoids, and quinoidal thiophene compounds is summarized in Table S16. The peak of [ 2 ] 2− is shifted downfield compared to those of the strong antiaromatic analogues (from 3 to −1 ppm), but shifted upfield compared to those of the distorted nonaromatic analogues and quinoidal thiophene compounds (from 8 to 6 ppm).…”

Section: Resultsmentioning

confidence: 99%

“…A tetrathia analogue had nonplanar conformation and therefore nonaromatic properties because of the steric repulsion of the bulky S atoms . Recently, antiaromatic trioxa analogues were reported and for the first time converted to aromatic porphyrins by 2 e − oxidation . Core modifications with heteroatoms inhibit π conjugation and result in destabilization of the oxidized 18 π aromatic state .…”

Section: Introductionmentioning

confidence: 99%

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Facile Redox‐Induced Aromatic–Antiaromatic Interconversion of a β‐Tetracyano‐21,23‐Dithiaporphyrin under Ambient Conditions

Yamashita

Nakajima

Honda

et al. 2020

Chemistry A European J

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Facile redox‐induced aromatic–antiaromatic interconversions were accomplished by using β‐tetracyano‐21,23‐dithiaporphyrin (CN4S2Por). Introduced cyano groups not only increased the reduction potential of the porphyrin core but also stabilized the antiaromatic isophlorin (CN4S2Iph) by π conjugation. The reduction of CN4S2Por with hydrazine in polar solvents quantitatively affords CN4S2Iph, even under ambient conditions. CN4S2Iph retains a nearly planar conformation and exhibits considerable antiaromaticity. Aerobic oxidation of CN4S2Iph to CN4S2Por occurs in nonpolar solvents. This study was conducted to contribute to the understanding of the structure–antiaromaticity relationship.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Facile Redox‐Induced Aromatic–Antiaromatic Interconversion of a β‐Tetracyano‐21,23‐Dithiaporphyrin under Ambient Conditions

Yamashita

Nakajima

Honda

et al. 2020

Chemistry A European J

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“…Compounds 4·PF 6 and 5·PF 6 exhibit porphyrin-like Soret and Q-bands, reflecting their 14π-electron aromatic nature. [39][40][41][42][43][44][45][46][47] However, to date, anti-aromatic ring-contracted porphyrins have scarcely been reported. Compounds 4·PF 6 and 5·PF 6 show fluorescence at 578 nm (fluorescence quantum yield, Φ f = 2.6 % and fluorescence life time, τ f = 1.1 ns) and 616 nm (Φ f = 9.0 %, τ f = 2.3 ns), respectively.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of [14]Oxatriphyrins(2.1.1) and Their Transformation into Ethane‐Bridged Oxatripyrrins by Boron Complexation

et al. 2018

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[14]Oxatriphyrins(2.1.1) incorporating a furan moiety in the macrocycle have been synthesized by intramolecular McMurry coupling of oxatripyrromethane followed by oxidation. The [14]oxatriphyrins(2.1.1) are highly planar structures with 14π‐electron aromaticity, inducing typical porphyrin‐like absorption and fluorescence features. Compared with [14]thiatriphyrin(2.1.1) and arene‐fused oxatriphyrins(2.1.1), arene‐unperturbed [14]oxatriphyrins(2.1.1) exhibit stronger aromatic characteristics and fluorescence properties. The borylation of [14]oxatriphyrins(2.1.1) with dichloro(phenyl)borane resulted in the formation of boron complexes with a reduced olefin bridge. As a result of the reduction, the macrocycles of these boron complexes lost their aromatic properties, although the targeted boron complexes were predicted to have distinct anti‐aromatic properties by DFT calculations. The resultant ethane‐bridged oxatripyrrins exhibit intense emission because of their rigid structures.

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“…In general, two‐electron‐ and one‐electron‐reduced porphyrins (20π and 19π porphyrins, respectively) are extremely unstable under atmospheric conditions because of their high‐energy highest occupied molecular orbital (HOMO) and singly occupied molecular orbital (SOMO), respectively . Several approaches have been proposed to isolate 20π and 19π porphyrins in neutral forms, which basically rely on the concept of lowering the HOMO or SOMO energy levels . However, most of the reported neutral 20π and 19π porphyrins are highly distorted and/or still air‐sensitive.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and properties of redox‐switchable zinc complexes of 10,15,20‐triaryl‐15‐aza‐5‐oxaporphyrin

Sudoh

Furukawa

Nakano

et al. 2018

Heteroatom Chemistry

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The synthesis, aromaticity, and optical and electrochemical properties of zinc(II) complexes of 10,15,20‐triaryl‐15‐aza‐5‐oxaporphyrin (TriAAOP) were investigated. Metal‐templated cyclization of a zinc(II) 1,19‐dichloro‐5,10,15‐triaryl‐10‐azatetrapyrrin complex with an oxygen source afforded 20π TriAAOP in the neutral form. Oxidation of 20π TriAAOP with silver (I) hexafluorophosphate generated the 19π radical cation or 18π dication depending on the content of oxidant used. The interconversion between the three oxidation states (18π, 19π, and 20π) resulted in distinct changes in the aromaticity and optical properties of the 15‐aza‐5‐oxaporphyrin π‐system. Nuclear magnetic resonance spectroscopy of 20π TriAAOP revealed its antiaromatic character, whereas that of the 18π TriAAOP dication showed its aromatic character. The combined effect of the two meso‐heteroatoms was directly reflected in the redox properties of the porphyrin ring; TriAAOP was reduced more easily and more difficult to oxidize than the zinc(II) complex of 5,10,15,20‐tetraaryl‐5,15‐diaz‐aporphyrin (TADAP). In the ultraviolet‐visible‐near–infrared spectra of the materials, the lowest‐energy electronic excitations of the 19π and 18π TriAAOP derivatives were considerably red‐shifted compared with those of the isoelectronic TADAP derivatives. Based on the results of density functional theory calculations, it was concluded that the observed differences between TriAAOP and TADAP would arise from the high electronegativity of oxygen; specific frontier orbitals of the TriAAOP π‐systems were energetically stabilized relative to those of the TADAP π‐system. The present findings corroborate that the meso‐modification of a porphyrin rings with different kinds of heteroatoms is a promising strategy to fine tune their light‐response properties that are switchable by reversible single electron transfer processes.

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Controlled Core‐Modification of a Porphyrin into an Antiaromatic Isophlorin

Cited by 35 publications

References 32 publications

Facile Redox‐Induced Aromatic–Antiaromatic Interconversion of a β‐Tetracyano‐21,23‐Dithiaporphyrin under Ambient Conditions

Facile Redox‐Induced Aromatic–Antiaromatic Interconversion of a β‐Tetracyano‐21,23‐Dithiaporphyrin under Ambient Conditions

Synthesis of [14]Oxatriphyrins(2.1.1) and Their Transformation into Ethane‐Bridged Oxatripyrrins by Boron Complexation

Synthesis and properties of redox‐switchable zinc complexes of 10,15,20‐triaryl‐15‐aza‐5‐oxaporphyrin

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