Reversible Carbon–Carbon Bond Breaking and Spin Equilibria in Bis(pyrimidinenorcorrole)

Liu, Bin; Yoshida, Takuya; Li, Xiaofang; Stępień, Marcin; Shinokubo, Hiroshi; Chmielewski, Piotr J.

doi:10.1002/anie.201607237

Cited by 75 publications

(46 citation statements)

References 77 publications

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“…[2f] Recently Wu andc o-workersr eported that, in the case of benzannulatedTs chitschibabin hydrocarbon 3,t he closed-shell quinonoid state 3-CS was destabilizedb yi ntramolecular steric repulsion between the two anthracene units (Scheme 1). [4] Then it occurred to us that the similarc ontrolo fo pen-shell structure mightb ep ossible for 2 by replacing the central metals.G enerally,N i II -porphyrins tend to take non-planar structuress uch as ruffled and saddle-like conformationso wing to the relatively short NÀNi II distances, whereasZ n II -porphyrins prefer planars tructures. In addition,Li, Chmielewski, and co-workers also observed as imilare quilibrium in a pyrimidinenorcorrole dimer.…”

Section: Introductionmentioning

confidence: 99%

Metalation Control of Open‐Shell Character in meso‐meso Linked Porphyrin meso‐Oxy Radical Dimers

Jun-i

Fukui

Furukawa

et al. 2018

Chemistry A European J

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Control of open-shell character of meso-meso linked porphyrin meso-oxy radical dimers has been demonstrated by core metalation. Namely, Ni -porphyrin dimer 6Ni exhibits a clear H NMR spectrum and a distorted but rather coplanar quinonoidal structure consisting of two ruffled porphyrin rings, in accordance with the previous report. Freebase dimer 6H shows a similar quinonoidal structure in the solid state but displays slightly broader and temperature-dependent H NMR spectra, indicating a partial diradical character in solution that increases at high temperature. In sharp contrast, bis-imidazole-coordinated Zn -porphyrin dimer 6ZnIm exhibits a perpendicular structure consisting of two planar Zn -porphyrins and has been characterized as a distinct open-shell diradical on the basis of its non-observable H NMR signals, a clear ESR signal, and a characteristic absorption spectrum reaching about 1700 nm. Despite the distinct diradical character, 6ZnIm is an extremely stable molecule.

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Section: Introductionmentioning

confidence: 99%

Metalation Control of Open‐Shell Character in meso‐meso Linked Porphyrin meso‐Oxy Radical Dimers

Jun-i

Fukui

Furukawa

et al. 2018

Chemistry A European J

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“…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. [51,52] In accord with previous research, we also considered the creation of the anti-aromatic boron complexes 6 and 7 from 4·PF 6 and 5·PF 6 . [36][37][38] In contrast, the highly planar and rigid structures of 4·PF 6 and 5·PF 6 with hydrogen bonding in the cavity induce higher fluorescence intensities, similarly to the thiophene-fused oxatriphyrins.…”

Section: Resultsmentioning

confidence: 84%

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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“…Ther adical was shown to be fairly planar with the two inner NH protons involved in the hydrogen-bond network. Norcorroles are [16]porphyrins-(1.0.1.0), and are remarkably stable,w hen suitably substituted, despite their strong antiaromatic characters.Aring expansion of norcorrole afforded the radical 36, [56] which existed in equilibrium with its C 2 -symmetric s-dimer with aC3 ÀC3' linkage.V ariable-temperature spectroscopic studies in toluene revealed the dissociation enthalpy to be 20.2 kcal mol À1 and the monomer content to be 12 and 90 %a t3 00 K and 373 K, respectively.The spectral changes were reversible under inert conditions.I np olar solvents,t his s-dimer underwent dehydrogenation to form the dimer 37,p robably by reaction with atmospheric oxygen. In 2018, Matanosg roup reported that 19p neutral radicals (38R)b ased on 5,10,20triaryl-5,15-diazaporphyrins were quite stable.…”

Section: Porphyrinoid-based and Other Macrocycle-based Radicalsmentioning

confidence: 99%

Platforms for Stable Carbon‐Centered Radicals

2019

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Organic radicals can potentially play important roles in functional materials owing to an unpaired electron, but they are usually highly reactive and difficult to use. Therefore, stabilization of organic radicals is important. Among organic radicals, carbon‐centered radicals are promising because of their trivalent nature, which enables structural diversity and elaborate designs, but they are also less stable because of the reactivities towards carbon–carbon bond formation and atmospheric oxygen. Recently, stable carbon‐centered radicals across diverse molecular platforms have been increasingly explored. This Minireview highlights these newly explored, stable carbon‐centered radicals, with a focus on porphyrinoid‐stabilized radicals because of their remarkable spin delocalization abilities.

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Reversible Carbon–Carbon Bond Breaking and Spin Equilibria in Bis(pyrimidinenorcorrole)

Cited by 75 publications

References 77 publications

Metalation Control of Open‐Shell Character in meso‐meso Linked Porphyrin meso‐Oxy Radical Dimers

Metalation Control of Open‐Shell Character in meso‐meso Linked Porphyrin meso‐Oxy Radical Dimers

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

Platforms for Stable Carbon‐Centered Radicals

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