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. 2022 Sep 21;13(42):12533-12539.
doi: 10.1039/d2sc03937k. eCollection 2022 Nov 2.

A bis-NHC-CAAC dimer derived dicationic diradical

Mithilesh Kumar Nayak  1 , Pallavi Sarkar  2 , Benedict J Elvers  3 , Sakshi Mehta  4 , Fangyuan Zhang  5 , Nicolas Chrysochos  1 , Ivo Krummenacher  6 , Thangavel Vijayakanth  7 , Ramakirushnan Suriya Narayanan  1 , Ramapada Dolai  1 , Biswarup Roy  1 , Vishal Malik  1 , Hemant Rawat  1 , Abhishake Mondal  4 , Ramamoorthy Boomishankar  7 , Swapan K Pati  2 , Holger Braunschweig  6 , Carola Schulzke  3 , Prince Ravat  5 , Anukul Jana  1
Affiliations

A bis-NHC-CAAC dimer derived dicationic diradical

Mithilesh Kumar Nayak et al. Chem Sci. .

Abstract

The isolation of carbon-centered diradicals is always challenging due to synthetic difficulties and their limited stability. Herein we report the synthesis of a trans-1,4-cyclohexylene bridged bis-NHC-CAAC dimer derived thermally stable dicationic diradical. The diradical character of this compound was confirmed by EPR spectroscopy. The variable temperature EPR study suggests the singlet state to be marginally more stable than the triplet state (2J = -5.5 cm-1 (ΔE ST = 0.065 kJ mol-1)). The presence of the trans-1,4-cyclohexylene bridge is instrumental for the successful isolation of this dicationic diradical. Notably, in the case of ethylene or propylene bridged bis-NHC-CAAC dimers, the corresponding dicationic diradicals are transient and rearrange to hydrogen abstracted products.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Scheme 1
Scheme 1. Chemical structures of I–IX.
Scheme 2
Scheme 2. Synthesis of 3Cy, 4Cy, 5Cy, 6Cy, and 7Cy.
Fig. 1
Fig. 1. Molecular structure of 6Cy in the solid state with thermal ellipsoids at the 50% probability level. All hydrogen atoms except on C1 and C4 are omitted for clarity. Selected bond lengths (Å) and bond angles (°): N1–C2 1.380(6), C2–C3 1.439(7), N2–C5 1.366(6), C5–C6 1.431(7); N1–C2–C3 122.3(4), N2–C5–C6 122.5(4).
Fig. 2
Fig. 2. CW EPR spectrum of 6Cy in a 1 : 1 toluene/acetonitrile mixture at 40 K (left), temperature dependence of the half-field transitions between 10 and 140 K (middle), and experimental (black) and simulated (red) EPR spectra of 7Cy in acetonitrile (right). Best-fit simulation parameters: giso = 2.0029, a(14N) = 14.2 MHz (1N), 11.8 MHz (2N), and a(1H) = 3.2 MHz (6H).
Fig. 3
Fig. 3. Molecular structure of 7Cy in the solid state with thermal ellipsoids at the 50% probability level. All hydrogen atoms except on C1 and C4 and three triflate anions are omitted for clarity. Selected bond lengths (Å) and bond angles (°): N1–C2 1.361(4), C2–C3 1.459(4), N2–C5 1.277(3), C5–C6 1.488(4); N1–C2–C3 122.0(3), N2–C5–C6 125.2(2).
Scheme 3
Scheme 3. Synthesis of 5Et/5Pr, 8Et/8Pr, and 9Et/9Pr (Insert: Schematic Presentation of X).
Fig. 4
Fig. 4. Molecular structure of 8Et in the solid state with thermal ellipsoids at the 50% probability level. All hydrogen atoms except on C1, C1′, C2, and C2′ are omitted for clarity. Selected bond lengths (Å) and bond angles (°): N1–C2 1.457(2), C2–C3 1.505(3), C1–C1′ 1.324 (4); N1–C2–C3 111.82(15), N1–C1–C1′ 127.4(3).
Fig. 5
Fig. 5. Cyclic voltammetry plots for 5Cy at a scan rate of 100 mV s−1 and 1000 mV s−1 in acetonitrile (0.1 M [nBu4N][PF6]).
Fig. 6
Fig. 6. Molecular structure of 9Pr in the solid state with thermal ellipsoids at the 50% probability level. All hydrogen atoms except on C2, C1, and C5 are omitted for clarity. Selected bond lengths (Å) and bond angles (°):N1–C3 1.4200(18), C3–C4 1.352(2), C1–C2 1.330(2); N1–C3–C4 122.66(12), N1–C2–C1 129.63(14).
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References

    1. Abe M. Chem. Rev. 2013;113:7011–7088. doi: 10.1021/cr400056a. - DOI - PubMed
    2. Stuyver T. Chen B. Zeng T. Geerlings P. Proft F. D. Hoffmann R. Chem. Rev. 2019;119:11291–11351. doi: 10.1021/acs.chemrev.9b00260. - DOI - PubMed
    1. Zhang S. Pink M. Junghoefer T. Zhao W. Hsu S. N. Rajca S. Calzolari A. Boudouris B. W. Casu M. B. Rajca A. J. Am. Chem. Soc. 2022;144:6059–6070. doi: 10.1021/jacs.2c01141. - DOI - PMC - PubMed
    2. Gallagher N. Zhang H. Junghoefer T. Giangrisostomi E. Ovsyannikov R. Pink M. Rajca S. Casu M. B. Rajca A. J. Am. Chem. Soc. 2019;141:4764–4774. doi: 10.1021/jacs.9b00558. - DOI - PMC - PubMed
    3. Rajca A. Olankitwanit A. Rajca S. J. Am. Chem. Soc. 2011;133:4750–4753. doi: 10.1021/ja200708b. - DOI - PubMed
    4. Borden W. T. Hoffmann R. Stuyver T. Chen B. J. Am. Chem. Soc. 2017;139:9010–9018. doi: 10.1021/jacs.7b04232. - DOI - PubMed
    5. Han H. Zhang D. Zhu Z. Wei R. Xiao X. Wang X. Liu Y. Ma Y. Zhao D. J. Am. Chem. Soc. 2021;143:17690–17700. doi: 10.1021/jacs.1c08262. - DOI - PubMed
    6. Arikawa S. Shimizu A. Shiomi D. Sato K. Shintani R. J. Am. Chem. Soc. 2021;143:19599–19605. doi: 10.1021/jacs.1c10151. - DOI - PubMed
    1. Rajca A. Utamapanya S. Xu J. J. Am. Chem. Soc. 1991;113:9235–9241. doi: 10.1021/ja00024a032. - DOI
    2. Shu C. Zhang H. Olankitwanit A. Rajca S. Rajca A. J. Am. Chem. Soc. 2019;141:17287–17294. doi: 10.1021/jacs.9b08711. - DOI - PMC - PubMed
    3. Schmidt D. Son M. Lim J. M. Lin M. J. Krummenacher I. Braunschweig H. Kim D. Würthner F. Angew. Chem., Int. Ed. 2015;54:13980–13984. doi: 10.1002/anie.201507039. - DOI - PubMed
    4. Rajca A. Shiraishia K. Rajcaa S. Chem. Commun. 2009:4372–4374. doi: 10.1039/B909741D. - DOI - PubMed
    1. Jana A. Ishida M. Park J. S. Bähring S. Jeppesen J. O. Sessler J. L. Chem. Rev. 2017;117:2641–2710. doi: 10.1021/acs.chemrev.6b00375. - DOI - PubMed
    2. Schröder H. V. Schalley C. A. Beilstein J. Org. Chem. 2018;14:2163–2185. doi: 10.3762/bjoc.14.190. - DOI - PMC - PubMed
    3. Duvva N. Chilakamarthi U. Giribabu L. Sustainable Energy Fuels. 2017;1:678–688. doi: 10.1039/C7SE00068E. - DOI
    1. Striepe L. Baumgartner T. Chem.–Eur. J. 2017;23:16924–16940. doi: 10.1002/chem.201703348. - DOI - PubMed
    2. Berville M. Richard J. Stolar M. Choua S. Le Breton N. Gourlaouen C. Boudon C. Ruhlmann L. Baumgartner T. Wytko J. A. Weiss J. Org. Lett. 2018;20:8004–8008. doi: 10.1021/acs.orglett.8b03579. - DOI - PubMed
    3. Nakazato T. Takekoshi H. Sakurai T. Shinokubo H. Miyake Y. Angew. Chem., Int. Ed. 2021;60:13877–13881. doi: 10.1002/anie.202103667. - DOI - PubMed