Precise Monoselective Aromatic C–H Bond Activation by Chemisorption of Meta-Aryne on a Metal Surface

Abstract

Aromatic 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.

Strain‐Induced Isomerization in One‐Dimensional Metal–Organic Chains

“…Thed issociation of this bond allows the system to reach the relaxed configuration by releasing the stress of the intermediate structure.I mportantly,o ur calculations also reveal av ertical movement of approximately 0.4 of the whole naphthalene unit as aconsequence of the activation of out-of-plane molecular vibration modes at elevated temperatures.T he temperature-induced vertical movement facilitates the reaction greatly by lowering the activation barrier.T his clearly illustrates the importance of performing free energy calculations at elevated temperatures when seeking to correctly describe on-surface reaction mechanisms and the associated entropic effects. C À Cu À Cb ond cleavage and C À Hb ond activation on catalytically active substrates typically require thermal treatment at over 400 K. [26][27][28][29] They are often followed by direct CÀCc oupling, leading to the formation of graphene-like nanostructures. [5,6] However, unlike the 2D MOC networks reported previously,t he 1D strained MOCs studied here undergo C À Cu À Cb ond cleavage at room temperature as part of acomplex reaction driven by the relief of substrate-induced strain.…”

Strain‐Induced Isomerization in One‐Dimensional Metal–Organic Chains

“…C−Cu−C bond cleavage and C−H bond activation on catalytically active substrates typically require thermal treatment at over 400 K . They are often followed by direct C−C coupling, leading to the formation of graphene‐like nanostructures .…”

Controlling a Chemical Coupling Reaction on a Surface: Tools and Strategies for On-Surface Synthesis

“…Selective C–H bond activation was obtained by making use of the steric hindering effect of phenyl groups. 166 The Ullmann coupling was blocked at one (DBMTP precursor) or both (DBOTP precursor) C–Br positions leading to monoselective dehydrogenative C–C coupling (see Figure 10a).…”