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. 2023 May 16;29(28):e202300134.
doi: 10.1002/chem.202300134. Epub 2023 Mar 28.

Highly Stereospecific On-Surface Dimerization into Bishelicenes: Topochemical Ullmann Coupling of Bromohelicene on Au(111)

Jan Voigt  1 , Kévin Martin  2 , Egzona Neziri  1 , Miloš Baljozović  1 , Christian Wäckerlin  1 , Narcis Avarvari  2 , Karl-Heinz Ernst  1   3   4
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Highly Stereospecific On-Surface Dimerization into Bishelicenes: Topochemical Ullmann Coupling of Bromohelicene on Au(111)

Jan Voigt et al. Chemistry. .

Abstract

The on-surface dimerization into bis(hexahelicene) on a gold(111) surface has been studied by means of scanning tunneling microscopy and time-of-flight secondary mass spectrometry. C-C Ullmann coupling of (rac)-2-bromo-hexahelicene leads to formation of the (M,M)- and (P,P)-diastereomers of 2,2'-bis(hexahelicene), whilst formation of the (M,P)-diastereomer is not observed. Upon cooling, the bis(hexahelicene) aggregates into an ordered two-dimensional lattice with partly randomly distributed enantiomers. The highly specific diastereomeric coupling is explained by the surface alignment of educt in combination with the strong steric overcrowding in a possible surface-confined (M,P)-product.

Keywords: chirality; helicenes; on-surface chemistry; polyaromatic hydrocarbons; scanning tunneling microscopy.

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