Organic azides are attractive not only for synthetic chemistry but also for their applicability in biosciences and materials chemistry. Copper(I)-catalysed azide-alkyne cycloaddition to give 1,2,3-triazoles is enormously popular constituting click chemistry. Organic azides are also widely employed in transition metal-catalysed nitrene transfer reactions.
Despite accomplishments in azide chemistry in solution or in a gas phase, transformations of azides and nitrenes on a solid surface under ultrahigh vacuum (UHV) have not so far been systematically studied. Teams headed by Ivo Starý from IOCB Prague and Pavel Jelínek from the Institute of Physics of the CAS studied the chemical transformation of 9-azidophenanthrene 1 on the Ag(111) surface by UHV nc-AFM and reported their results in Angewandte Chemie International Edition journal as a “hot paper”.
High-resolution imaging supported by first-principle calculations revealed the structure of the final products that originated from a common and elusive 9-phenanthryl nitrenoid intermediate chemisorbed on the Ag(111) surface. A formal "nitrene" insertion into the C-H bond (2,3) along with its dimerisation (4a,b) and hydrogenation (5) were identified as main reaction channels (Figure).
Thus, the ability of aryl azides to form covalent σ- and π-bonds between their transformation products on a solid surface was demonstrated at a single-molecule level. It is an important finding in the context of an emerging field of on-surface chemistry at the nanoscale where is an urgent need for developing a wider portfolio of building blocks and synthetic methodologies for the construction of complex molecular 2D architectures by connecting them through covalent bonds.
Paper:
- Hellerstedt, J., Cahlík, A., Stetsovych, O., Švec, M., Shimizu, T. K., Mutombo, P. , Klívar, J., Stará, I. G., Jelínek, P. and Starý, I. (2019) Aromatic Azide Transformation on the Ag(111) Surface Studied by Scanning Probe Microscopy. Angew. Chem. Int. Ed. doi:10.1002/anie.201812334
Fig. 1:
Transformation products of azide 1 on the surface of Ag(111)
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