Generation and Characterization of a Tetraradical Embedded in a Curved Cyclic Paraphenylene Unit

Miyazawa, Y.; Wang, Zhe; Hatano, Sayaka; Takagi, Ryukichi; Matsuoka, Hideto; Amamizu, Naoka; Kitagawa, Yasutaka; Kayahara, Eiichi; Yamago, Shigeru; Abe, Manabu

doi:10.1002/chem.202301009

Cited by 8 publications

(5 citation statements)

References 80 publications

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“…As mentioned in the Introduction section, σ- 2 was computed to be energetically more stable than π- 2 by 63.7 kJ mol –1 at the same level of theory. This switch in the energy relationship between the σ- and π-bonded compounds was rationalized by the strain energy (SE) induced by the macrocyclic structure − of σ- 3b . The SE of σ-bonded σ- 3b was computed to be 75.6 kJ mol –1 higher than that of π- 3b (Table S2).…”

Section: Results and Discussionmentioning

confidence: 99%

Energetically More Stable Singlet Cyclopentane-1,3-diyl Diradical with π-Single Bonding Character than the Corresponding σ-Single Bonded Compound

Liu,

Onishi,

Miyazawa

et al. 2023

J. Am. Chem. Soc.

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Carbon–carbon σ-single bonds are crucial for constructing molecules like ethane derivatives (R3C–CR3), which are composed of tetrahedral four-coordinate carbons. Molecular functions, such as light absorption or emission, originate from the π-bonds existing in ethylene derivatives (R2CCR2). In this study, a relatively stable cyclopentane-1,3-diyl species with π-single bonding system (C−π–C) with planar four-coordinate carbons is constructed. This diradicaloid is energetically more stable than the corresponding σ-single bonding system. The π-electron single bonding system provides deeper insights into the chemical bonding and the physical properties derived from the small energy gaps between the bonding and antibonding molecular orbitals.

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Section: Results and Discussionmentioning

confidence: 99%

Energetically More Stable Singlet Cyclopentane-1,3-diyl Diradical with π-Single Bonding Character than the Corresponding σ-Single Bonded Compound

Liu,

Onishi,

Miyazawa

et al. 2023

J. Am. Chem. Soc.

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“…Thus, it is suggested that the quantum interference effect of the π-conjugated molecular parallel circuit can be designed with an open-shell nature, which is chemically controlled by the substituent groups. The open-shell systems with spin polarization due to the strong electron correlation have been a focus because of their applicability to functional materials [ 67 , 68 ]. However, a relationship between their open-shell nature and conductivity has not been clarified.…”

Section: Discussionmentioning

confidence: 99%

Theoretical Study on the Open-Shell Electronic Structure and Electron Conductivity of [18]Annulene as a Molecular Parallel Circuit Model

Amamizu,

Nishida,

Sasaki

et al. 2023

Nanomaterials

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Herein, the electron conductivities of [18]annulene and its derivatives are theoretically examined as a molecular parallel circuit model consisting of two linear polyenes. Their electron conductivities are estimated by elastic scattering Green’s function (ESGF) theory and density functional theory (DFT) methods. The calculated conductivity of the [18]annulene does not follow the classical conductivity, i.e., Ohm’s law, suggesting the importance of a quantum interference effect in single molecules. By introducing electron-withdrawing groups into the annulene framework, on the other hand, a spin-polarized electronic structure appears, and the quantum interference effect is significantly suppressed. In addition, the total current is affected by the spin polarization because of the asymmetry in the coupling constant between the molecule and electrodes. From these results, it is suggested that the electron conductivity as well as the quantum interference effect of π-conjugated molecular systems can be designed using their open-shell nature, which is chemically controlled by the substituents.

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“…The interaction in meta -D is smaller than in para -D , which was given as a possible reason for the exclusive observation of the closed-shell species meta -D . Besides main-group-element-centered tetraradicals B and para -D , some furtherhowever less relatedcompounds like cluster- or organic aminoxyl- − and aminyl-based as well as C-centered ,− tetraradicals are known.…”

Section: Introductionmentioning

confidence: 99%

Rational Design of Persistent Phosphorus-Centered Singlet Tetraradicals and Their Use in Small-Molecule Activation

et al. 2023

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Biradicals are important intermediates in the process of bond formation and breaking. While main-group-element-centered biradicals have been thoroughly studied, much less is known about tetraradicals, as their very low stability has hampered their isolation and use in small-molecule activation. Herein, we describe the search for persistent phosphorus-centered tetraradicals. Starting from an shydrindacenyl skeleton, we investigated the introduction of four phosphorus-based radical sites linked by an N−R unit and bridged by a benzene moiety. By varying the size of the substituent R, we finally succeeded in isolating a persistent P-centered singlet tetraradical, 2,6diaza-1,3,5,7-tetraphospha-s-hydrindacene-1,3,5,7-tetrayl (1), in good yields. Furthermore, it was demonstrated that tetraradical 1 can be utilized for the activation of small molecules such as molecular hydrogen or alkynes. In addition to the synthesis of P-centered tetraradicals, the comparison with other known tetraradicals as well as biradicals is described on the basis of quantum mechanical calculations with respect to its multireference character, coupling of radical electrons, and aromaticity. The strong coupling of radical electrons enables selective discrimination between the first and the second activations of small molecules, which is shown by the example of H 2 addition. The mechanism of hydrogen addition is investigated with parahydrogen-induced hyperpolarization NMR studies and DFT calculations.

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Generation and Characterization of a Tetraradical Embedded in a Curved Cyclic Paraphenylene Unit

Cited by 8 publications

References 80 publications

Energetically More Stable Singlet Cyclopentane-1,3-diyl Diradical with π-Single Bonding Character than the Corresponding σ-Single Bonded Compound

Energetically More Stable Singlet Cyclopentane-1,3-diyl Diradical with π-Single Bonding Character than the Corresponding σ-Single Bonded Compound

Theoretical Study on the Open-Shell Electronic Structure and Electron Conductivity of [18]Annulene as a Molecular Parallel Circuit Model

Rational Design of Persistent Phosphorus-Centered Singlet Tetraradicals and Their Use in Small-Molecule Activation

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