title: Control of Reactivity and Regioselectivity for On-Surface Dehydrogenative Aryl-Aryl Bond Formation.
abstract: Regioselectivity is of fundamental importance in chemical synthesis. Although many concepts for site-selective reactions are well established for solution chemistry, it is not a priori clear whether they can easily be transferred to reactions taking place on a metal surface. A metal will fix the chemical potential of the electrons and perturb the electronic states of the reactants because of hybridization. Additionally, techniques to characterize chemical reactions in solution are generally not applicable to on-surface reactions. Only recent developments in resolving chemical structures by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) paved the way for identifying individual reaction products on surfaces. 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 (pap) molecule. Selective intermolecular aryl-aryl coupling via dehydrogenative C-H activation occurs on Au(111) upon thermal annealing under ultrahigh vacuum (UHV) conditions. A full atomistic description 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.
authors.affiliation: Institute of Experimental and Applied Physics, University of Regensburg , 93053 Regensburg, Germany.
authors.forename: Nemanja
authors.initials: N
authors.lastname: Kocić
authors.affiliation: Department of Chemistry and Biochemistry, University of Bern , 3012 Bern, Switzerland.
authors.forename: Xunshan
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Chemistry and Biochemistry, University of Bern , 3012 Bern, Switzerland.
authors.forename: Songjie
authors.initials: S
authors.lastname: Chen
authors.affiliation: Department of Chemistry and Biochemistry, University of Bern , 3012 Bern, Switzerland.
authors.forename: Silvio
authors.initials: S
authors.lastname: Decurtins
authors.affiliation: Institute of Physics of Czech Academy of Sciences , 16200 Prague, Czech Republic.|Charles University in Prague , Faculty of Mathematics and Physics, Department of Surface and Plasma Science, 18000 Prague, Czech Republic.
authors.forename: Ondřej
authors.initials: O
authors.lastname: Krejčí
authors.affiliation: Institute of Physics of Czech Academy of Sciences , 16200 Prague, Czech Republic.
authors.forename: Pavel
authors.initials: P
authors.lastname: Jelínek
authors.affiliation: Institute of Experimental and Applied Physics, University of Regensburg , 93053 Regensburg, Germany.
authors.forename: Jascha
authors.initials: J
authors.lastname: Repp
authors.affiliation: Department of Chemistry and Biochemistry, University of Bern , 3012 Bern, Switzerland.
authors.forename: Shi-Xia
authors.initials: SX
authors.lastname: Liu