The Bergman cyclization is one of the most fascinating rearrangements in chemistry, with important implications in organic synthesis and pharmacology. Here we image a reversible Bergman cyclization for the first time. We induce the on-surface transformation of an individual aromatic diradical into a highly strained 10-membered diyne using atomic manipulation and verify the products by non-contact atomic force microscopy (AFM) with atomic resolution. The diyne and diradical were stabilized by using an ultrathin NaCl film as substrate and the diyne could be transformed back into the diradical. Importantly, diradical and diyne exhibit different reactivity, electronic, magnetic and optical properties associated to the changes in the bond topology and spin multiplicity. With the reversible, triggered Bergman cyclization, we demonstrated switching on demand between the two reactive intermediates by means of selective C-C bond formation or cleavage, opening up the entire field of radical chemistry for on-surface reactions by atomic manipulation.
By: Bruno Schuler, Shadi Fatayer, Fabian Mohn, Nikolaj Moll, Niko Pavlicek, Gerhard Meyer, Diego Pena, Leo Gross
Published in: RZ3902 in 2015
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