An Amphoteric Switch to Aromatic and Antiaromatic States of a Neutral Air‐Stable 25π Radical

Gopalakrishna, Tullimilli Y.; Reddy, J. Sreedhar; Anand, Venkataramanarao G.

doi:10.1002/ange.201406893

Cited by 31 publications

(5 citation statements)

References 30 publications

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“…Under similar reaction conditions, thiophene and pentafluoro benzaldehyde were catalyzed by BF 3 •OEt 2 followed by oxidation with FeCl 3 (Scheme 33). 71 The MALDI TOF/TOF mass spectrum of this reaction mixture confirmed the formation of different macrocycles whose constitution varied from four to ten thiophene units. Among these, the pentathiophene, 69, was found to form in 35% yields.…”

Section: Aromatic Expanded Isophlorinsmentioning

confidence: 87%

Isophlorinoids: The Antiaromatic Congeners of Porphyrinoids

et al. 2016

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Ever since the discovery of the porphyrin ring in "pigments of life", such as chlorophyll and hemoglobin, it has become a prime synthetic target for optoelectronic properties and in the design of metal complexes. During one such early expedition on the synthesis of porphyrin, Woodward proposed that condensing pyrrole with an aldehyde under acidic conditions yields the "precursor" porphyrinogen macrocycle. Its four-electron oxidation leads to the "transitory" 20π isophlorin, which undergoes subsequent two-electron oxidation to form the 18π "porphyrin". Due to its fleeting lifetime, it has been a synthetic challenge to stabilize the tetrapyrrolic isophlorin. This macrocycle symbolizes the antiaromatic character of a porphyrin-like macrocycle. In addition, the pyrrole NH also plays a key role in the proton-coupled, two-electron oxidation of isophlorin to the aromatic porphyrin. However, a major aspect of its unstable nature was attributed to its antiaromatic character, which is understood to destabilize the macrocycle upon conjugation. Antiaromaticity in general has not gained significant attention mainly due to the lack of stable 4nπ systems. In this regard, a stable isophlorin and its derivatives provide a glimmering hope to peek into the world of antiaromatic systems. This review will focus on the attempted synthesis of antiaromatic isophlorin ever since its conception. Based on recent synthetic advances, the chemistry of isophlorins can be expected to blossom into expanded derivatives of this antiaromatic macrocycle. Along with the synthetic details, the structural, electronic, and redox properties of isophlorin and its expanded derivatives will be elaborated.

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Section: Aromatic Expanded Isophlorinsmentioning

confidence: 87%

Isophlorinoids: The Antiaromatic Congeners of Porphyrinoids

et al. 2016

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“…Upon oxidation of KL S into L S• a weak band at 455 nm is seen, similar in shape to that of KL S , and due to combined α/β singly occupied molecular orbital (SOMO)−LUMO transitions. As in the related thiophene compounds, 38,47 the oxidation of the anion to the radical is accompanied by a hypsochromic shift that is indicative of a larger orbital gap in the radical of 5.50 eV (α-spin) and 5.31 eV (β-spin) against 4.24 eV for the anion. The electronic absorption spectra of the furan-containing compounds are different, in which the HOMO−LUMO transition observed at 284 nm for HL NO (Figure S11) is modified to multiple bands on deprotonation to KL NO , with the low-energy band at 630 nm associated with the HOMO−LUMO transition (Figure 7).…”

Section: Inorganic Chemistrymentioning

confidence: 75%

Radical Relatives: Facile Oxidation of Hetero-Diarylmethene Anions to Neutral Radicals

et al. 2018

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Furan and thiophene diarylmethenes are potential redox-active ligands for metal centers that could be exploited in the development of nontraditional, stoichiometric, and catalytic redox reactions. As such, we describe here the selective meso-deprotonations of dithiophene, difuran, and diimine-difuran diarylmethanes to form the π-conjugated anions, for which only the diimino-difuryl anion is truly isolable and studied by X-ray crystallography. In all cases, facile one-electron oxidation of these anions occurs, which allows the isolation of the neutral dithienyl and diimino-difuryl radicals. UV-Visible and time-dependent density functional theory studies reveal that the oxidation of the dithienyl anion to its radical is associated with an increase in the highest (singly) occupied molecular orbital-lowest unoccupied molecular orbital gap, evident through a hypsochromic shift of the main absorption band in the electronic spectrum, whereas oxidation of the diimino-difuryl anion causes only minor spectroscopic changes. Electrochemical studies support the stability of the radicals with respect to the anion, showing strongly negative oxidation potentials. The control of the redox activity of these diarylmethene carbanions through variation of the nature of the substituents, donor-atom, and the conjugated π-system and their potential as ligands for redox-inert metal centers makes them intriguing candidates as noninnocent partners for redox reactions.

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“…The oxidative conversion of 11 into 12 could be accelerated by treatment with single electron oxidants. For example, treatment of a CH 2 Cl 2 solution of 11 with [(Et 3 O) + (SbCl 6 ) À ] [20] afforded compound 12 (as its chloride salt) in essentially quantitative yield (Figure S14, Supporting Information). On the other hand, quantitative single-electron reduction of complex 12 to the corresponding radical 11 could be achieved by treating with an electron donor such as cobaltocene.…”

Section: Results and Discissionmentioning

confidence: 99%

One Carbon Ring Expansion of Bipyrrole to Bipyridine Enables Access to a π‐Extended, Non‐innocent, Corrole‐like Ligand

Samala

Lee

Park

et al. 2023

Chemistry A European J

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A π-extended, diaza-triphenylene embedded, mono-anionic corrole analogue and its Ni II complex were synthesized from a diaza-triphenylene precursor, which was obtained from a double one-carbon insertion into a naphthobipyrrole diester. Following conversion to the corresponding activated diol and acid-catalyzed condensation with pyrrole, subsequent reaction with pentafluorobenzaldehyde afforded mono-anionic, π-extended bipyricorrole-like macrocycle. Attempted Ni II insertion with Ni(OAc) 2 • 4H 2 O resulted an ESR active, Ni II bipyricorrole radical complex, which was converted to a stable cationic Ni II complex upon treatment with [(Et 3 O) + (SbCl 6 ) À ]. Both complexes were characterized by 1 H and 13 C NMR, UV/Vis spectroscopy and single crystal X-ray diffraction analysis. The Ni II bipyricorrole radical complex is converted to a cationic Ni II complex by single-electron reduction using cobaltocene. Both the cationic Ni II complex and the radical Ni II complex exhibited ligand-centered redox behavior, whereas the Ni II remains in the + 2 oxidation state.

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An Amphoteric Switch to Aromatic and Antiaromatic States of a Neutral Air‐Stable 25π Radical

Cited by 31 publications

References 30 publications

Isophlorinoids: The Antiaromatic Congeners of Porphyrinoids

Isophlorinoids: The Antiaromatic Congeners of Porphyrinoids

Radical Relatives: Facile Oxidation of Hetero-Diarylmethene Anions to Neutral Radicals

One Carbon Ring Expansion of Bipyrrole to Bipyridine Enables Access to a π‐Extended, Non‐innocent, Corrole‐like Ligand

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