Reversible Bergman cyclization by atomic manipulation

Journal name:
Nature Chemistry
Volume:
8,
Pages:
220–224
Year published:
DOI:
doi:10.1038/nchem.2438
Received
Accepted
Published online

Abstract

The Bergman cyclization is one of the most fascinating rearrangements in chemistry, with important implications in organic synthesis and pharmacology. Here we demonstrate a reversible Bergman cyclization for the first time. We induced the on-surface transformation of an individual aromatic diradical into a highly strained ten-membered diyne using atomic manipulation and verified the products by non-contact atomic force microscopy with atomic resolution. The diyne and diradical were stabilized by using an ultrathin NaCl film as the substrate, and the diyne could be transformed back into the diradical. Importantly, the diradical and the diyne exhibit different reactivity, electronic, magnetic and optical properties associated with the changes in the bond topology, and spin multiplicity. With this reversible, triggered Bergman cyclization we demonstrated switching on demand between the two reactive intermediates by means of selective C–C bond formation or cleavage, which opens up the field of radical chemistry for on-surface reactions by atomic manipulation.

At a glance

Figures

  1. Bergman cyclizations.
    Figure 1: Bergman cyclizations.

    a, The seminal experiment1 regarding the thermal isomerization of deuterated enediynes 1 and 3 through the formation of the diradical [2,3-D2]-1,4-didehydrobenzene (2). b, Bergman cyclization of the cyclic diyne 3,4-benzocyclodeca-3,7,9-triene-1,5-diyne (4) to generate the 9,10-didehydroanthracene diradical 5.

  2. Structures and AFM imaging of the starting material, reaction intermediates and product.
    Figure 2: Structures and AFM imaging of the starting material, reaction intermediates and product.

    ad, Chemical structures of the reaction products formed by successive STM-induced debromination of DBA (6) (a) and subsequent retro-Bergman cyclization: DBA, 9-dehydro-10-bromoanthracene (radical 7) (b), 9,10-didehydroanthracene (diradical 5) (c) and 3,4-benzocyclodeca-3,7,9-triene-1,5-diyne (diyne 4) (d). eh, Corresponding constant-height AFM images of the molecules in ad, respectively, on NaCl(2ML)/Cu(111) using a CO tip. Δf corresponds to the frequency shift of the oscillating cantilever.

  3. Diyne identification.
    Figure 3: Diyne identification.

    a, Constant-current STM image (I = 2 pA, V = 1.65 V) of diyne 4. bd, Constant-height AFM images of diyne 4 on NaCl(2ML)/Cu(111) at different heights z. e, Calculated LUMO orbital of diyne 4 with the molecular structure overlaid as a guide to the eye. fh, Calculated Δf maps of diyne 4 interacting with a CO tip at tip–molecule distances that correspond to the estimated experimental distances in bd.

  4. Reversible Bergman cyclization.
    Figure 4: Reversible Bergman cyclization.

    ac, Laplace-filtered AFM images of diyne 4R (a), diradical 5 (b) and diyne 4L (c) on NaCl(2ML)/Cu(111). The molecule is adsorbed at a step edge of an NaCl(3ML)/Cu(111) island, seen in the lower part of the images. d, Current trace during a voltage pulse of V = 1.64 V at the position indicated by the white circle in b. The different current levels correspond to the molecular structures of the same colour shown in the inset. e, Calculated energies of the Bergman cyclization using the distance between the carbons indicated by red circles (dC–C) as the reaction coordinate.

Compounds

7 compounds View all compounds
  1. [1,6-D2]-(Z)-hexa-3-en-1,5-diyne
    Compound 1 [1,6-D2]-(Z)-hexa-3-en-1,5-diyne
  2. [2,3-D2]-1,4-didehydrobenzene
    Compound 2 [2,3-D2]-1,4-didehydrobenzene
  3. [3,4-D2]-(Z)-hexa-3-en-1,5-diyne
    Compound 3 [3,4-D2]-(Z)-hexa-3-en-1,5-diyne
  4. 3,4-benzocyclodeca-3,7,9-triene-1,5-diyne
    Compound 4 3,4-benzocyclodeca-3,7,9-triene-1,5-diyne
  5. 9,10-didehydroanthracene
    Compound 5 9,10-didehydroanthracene
  6. 9,10-dibromoanthracene
    Compound 6 9,10-dibromoanthracene
  7. 9-bromo-10-dehydroanthracene
    Compound 7 9-bromo-10-dehydroanthracene

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Author information

  1. Present address: ABB Corporate Research, 5405 Baden-Dättwil, Switzerland

    • Fabian Mohn

Affiliations

  1. IBM Research – Zurich, 8803 Rüschlikon, Switzerland

    • Bruno Schuler,
    • Shadi Fatayer,
    • Fabian Mohn,
    • Nikolaj Moll,
    • Niko Pavliček,
    • Gerhard Meyer &
    • Leo Gross
  2. CIQUS, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain

    • Diego Peña

Contributions

B.S., S.F., F.M., N.P., G.M. and L.G. performed the STM/AFM experiments. N.M. performed the DFT calculations. D.P. identified the reaction. All the authors analysed the data and contributed to the manuscript.

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The authors declare no competing financial interests.

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