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Precise Monoselective Aromatic C–H Bond Activation by Chemisorption of Meta-Aryne on a Metal Surface
journal contribution
posted on 2018-05-11, 00:00 authored by Qitang Fan, Simon Werner, Jalmar Tschakert, Daniel Ebeling, André Schirmeisen, Gerhard Hilt, Wolfgang Hieringer, J. Michael GottfriedAromatic
C–H bond activation has attracted much attention
due to its versatile applications in the synthesis of aryl-containing
chemicals. The major challenge lies in the minimization of the activation
barrier and maximization of the regioselectivity. Here, we report
the highly selective activation of the central aromatic C–H
bond in meta-aryne species anchored to a copper surface,
which catalyzes the C–H bond dissociation. Two prototype molecules,
i.e., 4′,6′-dibromo-meta-terphenyl
and 3′,5′-dibromo-ortho-terphenyl,
have been employed to perform C–C coupling reactions on Cu(111).
The chemical structures of the resulting products have been clarified
by a combination of scanning tunneling microscopy and noncontact atomic
force microscopy. Both methods demonstrate a remarkable weakening
of the targeted C–H bond. Density functional theory calculations
reveal that this efficient C–H activation stems from the extraordinary
chemisorption of the meta-aryne on the Cu(111) surface,
resulting in the close proximity of the targeted C–H group
to the Cu(111) surface and the absence of planarity of the phenyl
ring. These effects lead to a lowering of the C–H dissociation
barrier from 1.80 to 1.12 eV, in agreement with the experimental data.