Regensburg 2016 – scientific programme
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O: Fachverband Oberflächenphysik
O 68: Nanostructures at Surfaces: 1D, 2D Structures and Networks
O 68.13: Poster
Wednesday, March 9, 2016, 18:15–20:30, Poster A
Pyrazine as a Directing Group in Control of Reactivity and Regioselectivity for On-Surface Dehydrogenative Aryl-Aryl Bond Formation — •Nemanja Kocić1, Xunshan Liu2, Songjie Chen2, Silvio Decurtins2, Jascha Repp1, and Shi-Xia Liu2 — 1Institute of Experimental and Applied Physics, University of Regensburg, 93053 Regensburg, Germany — 2Department of Chemistry and Biochemistry, University of Bern, 3012 Bern, Switzerland
Regioselectivity is of fundamental importance in chemical synthesis. While many concepts for site-selective reactions are well established for solution chemistry, for instance through introduction of electron donating or withdrawing directing groups, it is not a priori clear whether they can easily be transferred to reactions taking place on a metal surface. Here we exploit a combined STM/AFM technique to demonstrate the on-surface formation of complex molecular architectures built up from a heteroaromatic precursor, the tetracyclic pyrazino[2,3-f][4,7]phenanthroline molecule. Selective intermolecular aryl-aryl coupling via dehydrogenative C-H activation occurs on Au(111) upon thermal annealing under UHV conditions. A full atomistic analysis of the different reaction products based on an unambiguous discrimination between pyrazine and pyridine moieties is presented. Our work not only elucidates that ortho-hydrogen atoms of the pyrazine rings are preferentially activated over their pyridine equivalents, but also sheds new light onto the participation of substrate atoms in metal-organic coordination bonding during covalent C-C bond formation.