Sequential Activation of Aromatic C─H Bonds on Cu(111)

Abstract

avenue to prepare carbon-based nanomaterials. The emerging on-surface synthesis offers an unprecedented opportunity to achieve aromatic C−H activation on metal surfaces. Previous works mostly focus on the activation of either C−H bonds of phenyl rings or C−H bonds of functionalized aromatic rings. The research on the activation priority of two aromatic C−H bonds within a molecule has remained unreported. In this work, starting from a building block comprising both phenyl and phenol rings, we achieve the sequential activation of ortho C−H bonds of the phenol ring and meta C−H bonds of the phenyl ring on Cu(111) via stepwise annealing. During annealing, the hydrogen bond-and coordination interactionstabilized chiral nanostructures are observed successively below 450 K. At 450 K, covalent dimers and trimers originating from the activation of ortho C−H bonds of phenol ring are generated. Annealing to 500 K gives birth to the complex covalent polymers formed by the further activation of meta C−H bonds of phenyl ring. The morphologies of these nanostructures are resolved by scanning tunneling microscopy (STM). The synchrotron radiation photoemission spectroscopy (SRPES) is utilized to follow the chemical states of surface species during the reaction process. This work determines the activation priority of two aromatic C−H bonds. The attained principle could be potentially used to guide the hierarchical C−C coupling on metal surfaces.

Selective Activation of Aromatic C–H Bonds Catalyzed by Single Gold Atoms at Room Temperature

“…We claim that this significant difference between positions A and B explains the experimentally observed regioselectivity of the C−H dissociation. The 19 kcal/mol barrier represents a significant reduction relative to comparable C−H activation reactions with barriers of 30−40 kcal/mol (1.3−1.8 eV), experimentally occurring in a temperature window of 400−700 K. 60,68,69,72 Furthermore, other onsurface reactions with barriers of ∼20 kcal/mol (∼0.87 eV) have been observed at RT, 71,73 supporting the interpretation of our experimental results as RT C−H activation.…”

Hierarchical Activation of C–Br and Cyano ortho C–H to Form Chiral Organometallics on Ag(111)

“…By comparison, it is revealed that cyano functionalization effectively reduces the activation barrier for its ortho C−H, just as in the cases of hydroxyl-functionalized precursors. 26,65 The absence of the second step of Ullmann coupling is different from the case of conventional aryl halides, where annealing OM intermediates formed after dehalogenation typically triggers the second step of Ullmann coupling (C−C coupling). Scheme 1 shows the reactions of 4-bromobiphenyl molecules Cu(110).…”

“…The activation of C–H on pristine aromatic rings usually occurs at the meta positions and entails the assistance of certain substrates, − proper temperatures, , atomic hydrogen, or bromine . In contrast, on directing group-functionalized (e.g., hydroxyl, , pyridine, − and bromine , ) aromatic rings, the C–H activation takes place at the ortho position at moderate temperatures.…”

Real-space visualization of sequential debromination of polybrominated benzenes on Ag(111)

“…The influence of substituents at different sites, 18 closely related to the precursor design, has also been extensively investigated in previous reports, where substituents could affect the dehalogenation sequence 19 as well as the reactivity of adjacent sites. 20 Moreover, distinct interaction with the substrate can greatly affect the activation sequence of symmetric sites through manipulation and thermal activation on surfaces. 6,21 Recently, debromination reactions of typical linear molecules with para-substitution 22,23 have been explored, showing dissymmetric debromination processes on surfaces.…”