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A class of non-aromatic 1,3-disilapyrroles acting as stable organosilicon-based triplet diradicals

Nature Synthesis volume 2, pages 678–687 (2023)Cite this article

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Abstract

Open-shell molecules with unpaired electrons and a high-spin S ≥ 1 configuration are of fundamental importance in chemistry, biology and molecular electronics. Among metal-free systems, carbon- and silicon-based triplet diradicals with two unpaired electrons and strong ferromagnetic coupling are proposed as key intermediates in many organic and organometallic transformations but their isolation remains challenging due to their very high reactivity. Here we report the facile synthesis of isolable 1,3-disilapyrroles which act as organosilicon-based delocalized triplet diradicals. The 1,3-disilapyrroles result from cycloaddition reactions of two divalent silicon atoms in a N,N-bis(silylenyl)aniline to the carbon–carbon triple bond of diphenylacetylenes. Remarkably, the spin-density distribution of these triplet diradicals exhibits an asymmetric delocalization due to steric congestion. The unpaired electrons in the 1,3-disilapyrroles show unprecedented reactivity, including cyclotetramerization and cleavage of the carbon–oxygen triple bond of CO at ambient temperature with subsequent C(sp3)–H bond activation to give a polycyclic product.

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Fig. 1: Examples of diradicals and biradicals, and the diradicals of this work.
Fig. 2: Syntheses of compounds 2H, 2F, t2H, t2F, (2H)4 and 3–6.
Fig. 3: Molecular structures of (2H)4, 2F, 2F+, 3 and 6.
Fig. 4: NAdO analysis of 2F, and the spin populations of 2F and 2F+.
Fig. 5: EPR spectra of 2H, t2H, 2F and t2F.

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Data availability

Crystallographic data for the structures reported in this Article have been deposited at the Cambridge Crystallographic Data Centre under deposition numbers CCDC 2211907 (3), 2211908 (4), 2211909 (2F), 2211910 (2H), 2211911 (t1), 2211912 (6), 2211913 (5), 2211914 (t2F), 2211915 (t2H) and 2211916 ((2H)4). Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/. Additional synthetic methods, NMR spectra, cyclic voltammetry data, single-crystal X-ray diffraction data, EPR spectra, magnetism data and computational details are available in the Supplementary Information.

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Acknowledgements

This work was funded by the DFG (German Research Foundation) under Germany´s Excellence Strategy–EXC 2008–390540038–UniSysCat for S.Y., C. Lorent, K.B.K., G.V., C. Limberg and M.D., and DR-226/21-1 for Y.X., S.Y., M.D., and the National Science Foundation of China (21873079) for S.D. and J.Z.

Author information

Authors and Affiliations

  1. Technische Universität Berlin, Department of Chemistry: Metalorganic and Inorganic Materials, Berlin, Germany

    Yun Xiong, Shenglai Yao, Gonela Vijaykumar & Matthias Driess

  2. Xiamen University, State Key Laboratory of Physical Chemistry of Solid Surface and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, and College of Chemistry and Chemical Engineering, Xiamen, People’s Republic of China

    Shicheng Dong & Jun Zhu

  3. Technische Universität Berlin, Department of Chemistry: Physical and Biophysical Chemistry, Berlin, Germany

    Christian Lorent

  4. Humboldt-Universität zu Berlin, Institut für Chemie, Berlin, Germany

    Konstantin B. Krause & Christian Limberg

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  1. Yun Xiong
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Contributions

Synthesis and X-ray diffraction analyses were performed by Y.X. and S.Y., and supervised by M.D. EPR experiments were performed and analysed by C. Lorent. Magnetic susceptibility measurements were performed and analysed by K.B.K. and C. Limberg. Cyclic voltammetry measurements were performed and analysed by G.V. DFT calculations and computational analysis were performed by S.D. and J.Z. The manuscript was written by Y.X., S.Y., M.D., and edited by all the authors.

Corresponding author

Correspondence to Matthias Driess.

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Nature Synthesis thanks Milan Gembicky, Dietmar Stalke and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary handling editor: Alison Stoddart, in collaboration with the Nature Synthesis team.

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Extended data

Extended Data Fig. 1 Spin population of 2H, t2H, t2F, 2-Ph, 2-Me, and 2-H.

a. Spin population of 2H, t2H, and t2F (red numbers, triplet) shows asymmetric spin density distribution. b. Spin population of 2-Ph, 2-Me, and 2-H shows nearly or completely symmetric spin density distribution. Hydrogen atoms in 3D structures are omitted for clarity. isovalue = 0.005 a.u.

Extended Data Fig. 2 NAdO analysis on the bonding modes of 2F2+.

a. NAdO analysis on the Si1-C3 bonding modes of 2F2+, b. NAdO analysis on the C3-C4 bonding modes of 2F2+, c. NAdO analysis on the C4-Si2 bonding modes of 2F2+, d. NAdO analysis on the Si2-N5 bonding modes of 2F2+, e. NAdO analysis on the Si1-N5 bonding modes of 2F2+. isovalue = 0.05 a.u.

Supplementary information

Supplementary Information

Synthetic methods, NMR spectra, cyclic voltammetry data, single-crystal X-ray diffraction data, EPR spectra, magnetism data and computational details including Supplementary Figs. 1–47 and Tables 1–26.

Supplementary Data 1

Crystal data for compound t1, CCDC 2211911

Supplementary Data 2

Crystal data for compound 2H, CCDC 2211910

Supplementary Data 3

Crystal data for compound 2F, CCDC 2211909

Supplementary Data 4

Crystal data for compound t2H, CCDC 2211915

Supplementary Data 5

Crystal data for compound t2F, CCDC 2211914

Supplementary Data 6

Crystal data for compound (2H)4, CCDC 2211916

Supplementary Data 7

Crystal data for compound 3, CCDC 2211907

Supplementary Data 8

Crystal data for compound 4, CCDC 2211908

Supplementary Data 9

Crystal data for compound 5, CCDC 2211913

Supplementary Data 10

Crystal data for compound 6, CCDC 2211912

Supplementary Data 11

Fig 1: Curie plot of the half-field transition from 2H, 2F, t2H and t2F; Fig 2: EPR spectra of 2F and 2F+; Fig 3: Magnetic susceptibility of 4; Fig 5: Cyclic voltammetry of 2F

Source data

Source Data Fig. 5

Source data of Figure 5

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Xiong, Y., Dong, S., Yao, S. et al. A class of non-aromatic 1,3-disilapyrroles acting as stable organosilicon-based triplet diradicals. Nat. Synth 2, 678–687 (2023). https://doi.org/10.1038/s44160-023-00279-6

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