NH Tautomerism of a Quadruply Fused Porphyrin

Rigid Fused Structure Delays the Proton Transfer

Yuta Saegusa, Tomoya Ishizuka, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

研究成果: ジャーナルへの寄稿記事

抄録

We report herein NH tautomerism of a freebase derivative of a quadruply fused porphyrin (H2QFP-Mes, 3), which has one mesityl group at one of the β-positions of the nonfused pyrroles to lower the structural symmetry, allowing us to observe the NH tautomerism with 1H NMR spectroscopy. Compound 3 was revealed to have the two inner NH protons on the two nonfused pyrroles, and the NH tautomerism of 3 was evidenced by variable-temperature (VT) 1H NMR experiments in various deuterated solvents. The VT-NMR studies revealed that the activation barrier for the NH tautomerism of 3 was larger than that of tetraphenylporphyrin. The positive activation entropy (ΔS = 89 J mol-1 K-1), determined for the NH tautomerism, can be explained by dissociation of the π-π stacked dimer structure of 3 in the ground state, as evidenced by the crystal structure and NMR measurements. On the basis of the kinetic studies and density functional theory calculations, the stability of intermediates in the NH tautomerism of 3 and the transition states have been discussed in detail.

元の言語英語
ページ(範囲)316-327
ページ数12
ジャーナルJournal of Physical Chemistry B
122
発行部数1
DOI
出版物ステータス出版済み - 1 11 2018

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Pyrroles
Proton transfer
Porphyrins
rigid structures
porphyrins
Protons
Nuclear magnetic resonance
nuclear magnetic resonance
Temperature
protons
Entropy
pyrroles
Chemical activation
Magnetic Resonance Spectroscopy
activation
Dimers
Ground state
Nuclear magnetic resonance spectroscopy
Density functional theory
Crystal structure

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

これを引用

NH Tautomerism of a Quadruply Fused Porphyrin : Rigid Fused Structure Delays the Proton Transfer. / Saegusa, Yuta; Ishizuka, Tomoya; Shiota, Yoshihito; Yoshizawa, Kazunari; Kojima, Takahiko.

:: Journal of Physical Chemistry B, 巻 122, 番号 1, 11.01.2018, p. 316-327.

研究成果: ジャーナルへの寄稿記事

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AU - Yoshizawa, Kazunari

AU - Kojima, Takahiko

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N2 - We report herein NH tautomerism of a freebase derivative of a quadruply fused porphyrin (H2QFP-Mes, 3), which has one mesityl group at one of the β-positions of the nonfused pyrroles to lower the structural symmetry, allowing us to observe the NH tautomerism with 1H NMR spectroscopy. Compound 3 was revealed to have the two inner NH protons on the two nonfused pyrroles, and the NH tautomerism of 3 was evidenced by variable-temperature (VT) 1H NMR experiments in various deuterated solvents. The VT-NMR studies revealed that the activation barrier for the NH tautomerism of 3 was larger than that of tetraphenylporphyrin. The positive activation entropy (ΔS‡ = 89 J mol-1 K-1), determined for the NH tautomerism, can be explained by dissociation of the π-π stacked dimer structure of 3 in the ground state, as evidenced by the crystal structure and NMR measurements. On the basis of the kinetic studies and density functional theory calculations, the stability of intermediates in the NH tautomerism of 3 and the transition states have been discussed in detail.

AB - We report herein NH tautomerism of a freebase derivative of a quadruply fused porphyrin (H2QFP-Mes, 3), which has one mesityl group at one of the β-positions of the nonfused pyrroles to lower the structural symmetry, allowing us to observe the NH tautomerism with 1H NMR spectroscopy. Compound 3 was revealed to have the two inner NH protons on the two nonfused pyrroles, and the NH tautomerism of 3 was evidenced by variable-temperature (VT) 1H NMR experiments in various deuterated solvents. The VT-NMR studies revealed that the activation barrier for the NH tautomerism of 3 was larger than that of tetraphenylporphyrin. The positive activation entropy (ΔS‡ = 89 J mol-1 K-1), determined for the NH tautomerism, can be explained by dissociation of the π-π stacked dimer structure of 3 in the ground state, as evidenced by the crystal structure and NMR measurements. On the basis of the kinetic studies and density functional theory calculations, the stability of intermediates in the NH tautomerism of 3 and the transition states have been discussed in detail.

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